Search

[Display omitted] • Strong magnetization promotes the fertilizing potential of sewage sludge digestate. • Magnetization enriched the digestate of slow-release nutrient-based precipitates. • Nutrient precipitation in the digestate increases with increasing magnetic exposure. • In-line oxygenation during digestion promoted precipitation more than pre-oxygenation. • The best treatment conditions for struvite formation were identified. Anaerobic digestion (AD) is a sustainable and well-established option to handle sewage sludge (SS), as it generates a methane-rich biogas and a digestate with potential fertilizing properties. In the past, different strategies have been proposed to enhance the valorization of SS. Among these, the application of a static magnetic field (SMF) has been poorly evaluated. This study aims to determine the effects of a high-intensity SMF (1.5 and 2 T) on the chemical composition of SS anaerobic digestate. Several strategies (i.e., number of magnetization cycles, addition of different sources and quantities of magnesium, and digestate aeration) have been applied to evaluate the possible formation of compounds with valuable fertilizing properties in the digestate. Experimental results showed that by combining different strategies promoting digestate exposure to the magnetic field it is possible to favour the reduction in the liquid phase of NH 4 +, NO 3 −, PO 4 3−, SO 4 2− and Mg2+ concentrations up to 28%, 38%, 34%, 39% and 31%, respectively. The XRD analyses conducted on the solid phase of the same magnetized digestate samples showed an increase in crystalline and amorphous phases of nitrogen and phosphorus compounds with fertilizing value, such as struvite. These results highlight that SMF application can increase the fertilizing potential of sewage sludge digestate and promote its valorization in a sustainable and circular perspective. [ABSTRACT FROM AUTHOR]

• Sludge-derived humic acid is converted into carbon materials. • Low-cost energy storage materials can be prepared. • The purified humic acid-based carbon material has better performance. • Optimized material exhibits high performance in supercapacitors. As one of the main methods for sludge treatment, recovery of renewable biogas energy by anaerobic digestion (AD) is a promising strategy to deal with the conflict between carbon neutralization and sharply increase of sewage sludge. Humic acid (HA) in sludge is a major inhibitor of biogas yields and needs to be removed or pretreated. However, as the graphene oxide-like material, HA is an ideal precursor for the preparation of energy storage materials with high performance. Based on that, this study i) proposes the extraction and utilization of HA in sludge, ii) discusses the feasibility of HA-based materials after thermal reduction as electrodes for supercapacitor, and iii) investigates the factors with positive influences on the structure and electrochemical performance. It reveals that, with a synergistic effect of purification and activation at a low mass ratio, the HA-based material exhibits superior capacitive performance with the highest specific capacitance of 186.7 F/g (at 0.05 A/g), as well as excellent rate capability and cycling stability. Sludge is verified a cheaper and more abundant precursor resource of HA for energy storage application. The results of this study are expected to provide a new green, energy-efficiency and sustainability way for sludge treatment, which has the double benefits: efficient conversion and capture of bio-energy during AD process, and high value-added utilization of HA for supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aerobic SS had the lowest energy with the lowest Ea to start pyrolysis reaction. • The bio-oil yield of aerobic SS was higher than that of raw and anaerobic SS. • Digested SSs required higher temperatures for higher bio-oil yields than raw SS. • Biochar from aerobic SS was most suitable for soil amendment. Studies on the evaluation of sewage sludge (SS) as a feedstock through thermochemical processes have gained momentum. Due to the complex structure of SS, it is necessary to determine SS treatment stage to which thermochemical processes will be added to the wastewater treatment plants and to configure the optimum process scheme. The pyrolysis process is an important process for resource recovery as bio-oil and biochar. While bio-oil is important source of the value-added products, biochar is widely evaluated as soil improver. With the aim of the designation of the optimum process scheme for pyrolysis of three different sewage sludges (SSs): raw SS (RSS), anaerobically digested SS (ANSS), and aerobically digested SS (AESS); after the investigation of thermal behaviors by thermogravimetric analysis (TGA), the optimum process conditions were investigated to obtain maximum possible bio-oil yield from fast pyrolysis of SSs. By applying the central composite design in the response surface methodology, optimum fast pyrolysis operating conditions were determined for each SS type and the fast pyrolysis products obtained under optimum conditions were characterized. While the highest HHV was achieved for RSS, lowest activation energy (Ea) and maximum bio-oil yield was achieved for AESS. The optimum fast pyrolysis operating conditions for obtaining maximum bio-oil yield as 35.75 % were determined as 485 °C and 100 mL min−1 carrier gas flowrate for AESS. While the bio-oil produced from ANSS was determined as a resource for oleic acid production, the toxicity test results revealed that biochar produced from fast pyrolysis of AESS is suitable for soil amendment. [ABSTRACT FROM AUTHOR]

• Inventory data of biological treatment of sludge address all inputs and outputs. • Biogas production varies considerably in the 64 datasets on anaerobic digestion. • Very few data are available on digestate or energy in anaerobic digestion of sludge. • VS degradation in composting is hard to estimate due to the added bulking materials. • Data on emissions into the air are currently scarce for sludge composting processes. The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions. [ABSTRACT FROM AUTHOR]

• AWOEx pretreated DSS tested at various temperatures, residence times and O 2 dosages. • Methane yield of DSS is improved by 98% using AWOEx and Anaerobic digestion. • Oxygen addition during pretreatment resulted in significant improvement in methane yield. • First-time demonstration of 84% organics conversion in sewage sludge using AWOEx pretreatment. Anaerobic digestion (AD) of sewage sludge shows low carbon conversion efficiency (CCE) due to the poor biodegradability of sewage sludge. The lack of digestibility is specifically linked to the waste-activated sludge (WAS) making up the majority of sewage sludge along with a smaller portion of primary sludge, depending on the wastewater treatment plant configuration. In this study, we examine the Advanced Wet Oxidation & Steam Explosion process (AWOEx) for improving the CCE of digested sewage sludge (DSS) by thermophilic AD. The effect of the pretreatment temperature in the range between 160 and 185 °C at a fixed residence time of 20 min with and without oxygen added at a dosage of 5 % of the organics present was tested. Methane yield improved by 97.92 % to 183.91 ± 4.93 mL/g vS over the untreated DSS (control), whose methane yield was 92.92 ± 9.07 mL/g vS We have demonstrated for the first time that 84 % of the organics in sewage sludge can successfully be transformed into biogas following AWOEx pretreatment, which can contribute significantly to the circular economy instead of greenhouse gas emissions from landfilling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Removal of antibiotics and ARGs was highly improved at 30 mg/gSS cellulase or papain. • Combination of biological enzymes further enhanced the removal of qnr S and erm X. • Enzymes integrated with ZVI had synergistic effects on removing antibiotics and ARGs. • Enzymes and ZVI changed removal-related bacteria and archaea community structure. • ARGs removal during in situ ADD was mainly due to partial changes of host bacteria. Antibiotics and antibiotic resistance genes (ARGs) in sewage sludge can cause high ecotoxicological risks in the environment and public health concerns. The aims of this study were to establish enzymatic integrated in-situ advanced anaerobic digestion (AAD) by adding cellulase and papain as well as the two enzymes combined with zero valent iron (ZVI) directly into the anaerobic digesters to explore the removal of antibiotics and ARGs under the mesophilic condition (35 °C). The methane production potential during in-situ AAD was effectively improved. Papain and cellulase at 30 mg/gTSS were most effective in improving antibiotic removal. The removal of sulfamerazine (SMZ) and sulfadiazine (SMR) could reach 89.10 % and 71.75 %. Combined enzymes with ZVI also enhanced the removal of all target antibiotics, especially roxithromycin (ROX), SMZ and SMR most significantly. Except for sul 1, tet A and tet B, the removal of ARGs by papain reached 6.33 %-82.15 %. The addition of cellulase effectively improved tet A removal. The combination of biological enzymes further enhanced the removal of qnr S and erm X. The tet G, tet B, sul 3, erm X, erm T, qnr S, and aac (6′)-IB-CR by combined enzymes with ZVI could even not be detected after digestion. Addition of papain, cellulase, and ZVI caused variations in the dominant bacteria. All target antibiotics presented significant positive correlations with the genera norank_f__ Bacteroidetes _ vadinHA17 , norank_f__norank_o__ SJA-15 , norank_f__norank_o__ Aminicenantales. Redundancy analysis showed archaea Methanosaeta and Candidatus_ Methanoacidiosum genera greatly contributed to antibiotics removal with the combination of enzymes and ZVI. Co-occurrence network analysis indicated the removal of ARGs was mainly based on the changes of existence of host bacteria. [ABSTRACT FROM AUTHOR]

• Environmental impacts of sewage sludge treatment were quantified. • Nitrogen recovery from thermal drying condensate requires improvements. • Combustion showed lower impacts compared to composting and pyrolysis. • More data on pyrolysis of sewage sludge digestate would be required. Due to the global trend of urbanization, the amount of sewage water is increasing in cities. This calls for efficient treatment of the resulting sewage sludge. To date, in the 27 European Union member countries (EU-27), the prevailing treatment method is application on arable land. Anaerobic digestion is one of the treatment methods being increasingly used nowadays. However, the resulting digestate requires further utilization. Therefore, in this study, the environmental performance of composting, combustion, and pyrolysis options for dewatered sewage sludge digestate is evaluated based on a life cycle assessment. The results show that digestate combustion and composting performed better than pyrolysis for most of the selected impact categories. However, pyrolysis of sewage sludge is still under development, and there are, to some degree, uncertainties in the data related to this technology; thus, more information for the performance assessment of pyrolysis is still required. [ABSTRACT FROM AUTHOR]

• First detailed linking of metabolic with community transitions in ammonia adaptation. • Simultaneous acetoclastic and hydrogenotrophic methanogenesis by Methanosarcinaceae. • 14C assay provides semi-quantitative indication of metabolic pathway. • HRT and OLR affect dominant pathway and community in real organic feedstock digestion. Transitions in microbial community structure in response to increasing ammonia concentrations were determined by monitoring mesophilic anaerobic digesters seeded with a predominantly acetoclastic methanogenic community from a sewage sludge digester. Ammonia concentration was raised by switching the feed to source segregated domestic food waste and applying two organic loading rates (OLR) and hydraulic retention times (HRT) in paired digesters. One of each pair was dosed with trace elements (TE) known to be essential to the transition, with the other unsupplemented digester acting as a control. Samples taken during the trial were used to determine the metabolic pathway to methanogenesis using 14C labelled acetate. Partitioning of 14C between the product gases was interpreted via an equation to indicate the proportion produced by acetoclastic and hydrogenotrophic routes. Archaeal and selected bacterial groups were identified by 16S rRNA sequencing, to determine relative abundance and diversity. Acclimatisation for digesters with TE was relatively smooth, but OLR and HRT influenced both metabolic route and community structure. The 14C ratio could be used quantitatively and, when interpreted alongside archaeal community structure, showed that at longer HRT and lower loading Methanobacteriaceae were dominant and hydrogenotrophic activity accounted for 77% of methane production. At the higher OLR and shorter HRT, Methanosarcinaceae were dominant with the 14C ratio indicating simultaneous production of methane by acetoclastic and hydrogenotrophic pathways: the first reported observation of this in digestion under mesophilic conditions. Digesters without TE supplementation showed similar initial changes but, as expected failed to complete the transition to stable operation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two cavitated mixtures of BSG suspended in MPW or MLL were co-digested with SS. • In the presence of cavitated BSG and MPW, the biogas yields increased significantly. • The energy profits were enhanced in both co-substrates presence. • Co-digestion of cavitated BSG and MPW with SS is a profitable solution. • Co-digestion of cavitated BSG and MLL with SS was not efficient enough. In the present study, a combined technology for energetic brewery spent grain (BSG) use in co-digestion with sewage sludge (SS) was presented. A holistic approach that includes the impact of co-substrates and their carriers on the anaerobic digestion (AD) process, and the energetic aspects, was involved. Prior to AD, BSG was pretreated involving the hydrodynamic cavitation (HC); two different carriers were applied: MPW (municipal pre-settled wastewater) and mature landfill leachate (MLL). An orifice plate with a conical concentric hole of 3/10 mm (inlet/outlet diameter) was applied as cavitation device. The initial pressure was 7 bar and the number of recirculation passes through the cavitation zone was 30. The AD experiments were performed in semi-flow reactors, under mesophilic conditions at HRT of 20 and 21 d. In both co-digestion series, the constant co-substrate dose of 6% v/v was adopted. In the presence of cavitated BSG and MPW, a significant increase in biogas/methane production was provided as compared to SS mono-digestion, with the related improvement in kinetic constant by 3.5%. The average biogas yield was 0.48 ± 0.03 m3 kg−1 VS added, while in the control run 0.41 ± 0.03 m3 kg−1 VS added. Using cavitated BSG and MLL, such a beneficial effect was not observed. In both co-digestion series, slightly lower VS removal (as for the control) and stable process performance occurred. Moreover, the improved energy balance was provided. Due to the technological aspects, only co-digestion of cavitated BSG and MPW with SS is recommended for implementation into a full-scale. [ABSTRACT FROM AUTHOR]

• 71 OCs mass balances were performed in full-scale sludge treatment facilities. • Screw decanter was selected as reference as its action is only physical. • Several OCs mass balances are frequently not correct in screw decanter. • The frequency of correct mass balances is significantly correlated to logKow. • Removal of the 71 OCs are reported in full-scale sludge digestion process. This paper analyzes the fate of 71 priority and emerging organic contaminants all along the treatment trains of sewage sludge treatment facilities in Paris including dewatering by centrifugation, thermal drying and anaerobic digestion. It aimed at proposing and applying a mass balances calculation methodology to each process and pollutant. This data validation strategy demonstrated the complexity to perform representative inlet/outlet sampling and analysis campaigns at industrial scales regarding organic compounds and to propose options to overcome this issue. Centrifugation and drying processes only implied physical mechanisms as phase separation and water elimination. Hence, correct mass balance were expected observed for organic contaminants if sampling and analysis campaigns were representative. This was the case for hydrophobic and neutral compounds. For the other more hydrophilic and charged compounds, the mass balances were scarcely correct. Thus, the conventional sampling and analytical practices used with sludge should be questioned and adapted to better take into account the high heterogeneity of sludge and the evolution of matrix effect within sludge treatment processes on micropollutant determination. For the biological anaerobic digestion process where degradations can occur and removals can be observed, the mass balances were deeply interpreted for 60 contaminants. This process contributed to the elimination above 70% of 21 detected compounds including 16 pharmaceuticals, 2 phthalates, 2 hormones and 1 perfluorinated compound. Removals of domperidone, propranolol, escitalopram, lidocaine, verapamil and cefoperazone under this condition were reported for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sewage sludge is used as infeed for anaerobic digestion in a full-scale plant. • The plant produces a soil improver (digestate) and a fertilizer (ammonium sulphate). • Ammonium sulphate has high ammonium concentration, i.e. 74 ± 2 g kg−1 wet weight. • The digestate produced has both high carbon content and biological stability. • Digestate and ammonium sulphate present low pollutant and pathogen contents. This work reports a full-scale study in which organic wastes were transformed by high-solid thermophilic anaerobic digestion (HSAD), into N fertilizers and organic fertilizers, i.e. digestate. The produced fertilizers were characterized over 42 months and their properties were discussed in comparisons with literature data. HSAD coupled with N stripping technology led to ammonia sulphate production having high N concentration (74 ± 2 g kg−1 wet weight), neutral pH (6.8 ± 1.3) and low traces of other elements. Digestate showed both higher carbon (C) content (314 ± 30 g kg−1 on dry matter (DM) and biological stability than green composts, indicating good amendment properties. Digestate was also interesting for its N (77 ± 3.7 g kg−1 dry matter – DM) content, half of it in the ammonia form, and P content (28 ± 4.1 g kg−1 DM) that was 43% readily available as soluble P-orthophosphate. K content was low (6.5 ± 1.3 g kg−1 DM), indicating poor fertilizing ability of digestate for this element. All organic pollutants investigated were much lower than the limits required for agricultural use and levels of some of them were lower than the content revealed for other organic matrices such as agricultural and energy crop digestates and compost. Emerging pollutants (i.e., pharmaceuticals) were tested as markers and they were found to be below the detection limit (<0.01 mg kg−1 DM) indicating very low content. The results obtained showed that HSAD coupled with N stripping allowed transforming sewage sludge into fertilizers and soil improvers exploitable in agriculture. [ABSTRACT FROM AUTHOR]

[Display omitted] • GAC and GBC addition enhanced the biogas yield over control. • Shorter lag phase reported in GAC and GBC amended digesters. • GAC and GBC amendments improved buffering and maintained pH in optimum range. • High concentration of GAC is inhibitory to AD possibly due to carbon-toxicity. Management of agro-waste is a major challenge globally due to inefficient disposal techniques, which concominantly leads pollution and loss of renewable bioenergy. Anaerobic digestion of agro-waste is one of the ways to tackle this problem but hindered by the recalcitrant nature of agro-waste. This study investigated the effect of granular activated carbon (GAC) and granular biochar (GBC) addition to enhance the thermophilic anaerobic co-digestion of wheat husk and sewage sludge. The conductive materials (particle size: 2–5 mm) were added separately at five different concentrations: 10, 20, 30, 40, 50 g/L inoculum. The findings revealed that samples amended with GAC and GBC at 20 g/L dosage had the highest biogas yield of 263 and 273 mL/gVS added , respectively, corresponding to 22 and 27% higher yield than the control. Additionally, a shorter lag phase was observed in both cases compared to the Control. However, the GBC amended samples showed relatively stable biogas production compared to GAC and consistent results regarding pH, alkalinity, total volatile fatty acids, and soluble chemical oxygen demand. The preliminary techno-economic analysis indicates that addition of GAC or GBC may not be feasible and require other innovative engineered solutions for the addition of conductive materials. This study confirms that GAC and GBC amendments enhance the biogas productivity and process stability in anaerobic digestion of recalcitrant agro-waste under the high-temperature regime and calls for further research in this direction. [ABSTRACT FROM AUTHOR]

• 10 UK biogas plant methane emission rates were estimated. • Total methane emissions were in range of 0.1 to 58.7 kg hr -1. • The percentage of losses relative to the calculated production rate ranged from 0.02 to 8.1%. • Biogas plants may averagely account for up to 1.9% of total methane emissions in the UK. The rising number of operational biogas plants in the UK brings a new emissions category to consider for methane monitoring, quantification and reduction. Minimising methane losses from biogas plants to the atmosphere is critical not only because of their contribution of methane to global warming but also with respect to the sustainability of renewable energy production. Mobile greenhouse gas surveys were conducted to detect plumes of methane emissions from the biogas plants in southern England that varied in their size, waste feed input materials and biogas utilization. Gaussian plume modelling was used to estimate total emissions of methane from ten biogas plants based on repeat passes through the plumes. Methane emission rates ranged from 0.1 to 58.7 kg CH 4 hr-1, and the percentage of losses relative to the calculated production rate varied between 0.02 and 8.1%. The average emission rate was 15.9 kg CH 4 hr-1, and the average loss was 3.7%. In general, methane emission rates from smaller farm biogas plants were higher than from larger food waste biogas plants. We also suggest that biogas methane emissions may account for between 0.4 and 3.8%, with an average being 1.9% of the total methane emissions in the UK excluding the sewage sludge biogas plants. [ABSTRACT FROM AUTHOR]

• ALK-2-CSTRs enhanced methane yield from co-digesting WCO and sewage sludge. • Stage-1 of the ALK-2-CSTRs protected methanogens from exposure to high LCFAs. • Alkaline conditioning masked the effects of thermophilic operation on hydrolysis. • Thermophilic operation stimulated the bioconversion of unsaturated fatty acids. • Economic evaluation demonstrated the economic advantages of ALK-2-CSTR. Anaerobic digestion is a promising way for resource recovery from waste cooking oil (WCO) due to its high bio-methanation potential. In-situ mild alkaline (pH 8) enhanced two-stage continuous stirred tank reactors (ALK-2-CSTRs) were implemented to explore its efficiency in co-digesting WCO and sewage sludge with stepwise increase of WCO in the co-substrates. Results demonstrate that the ALK-2-CSTRs effectively promoted methane yield from the co-substrates via promoting hydrolysis, long chain fatty acids (LCFAs) degradation and protecting methanogens from exposure to high concentration of LCFAs directly. The maximum methane yield of the ALK-2-CSTRs is 39.2% higher than that of a single stage CSTR system at the optimal feed mixture of 45:55 (WCO:SS [VS]). The thermophilic operation applied to the stage-1 of the ALK-2-CSTRs failed to improve the methane yield when the methanogenic performance was stable; while upon WCO overloaded, the elevated temperature mitigated the deterioration of methanogenesis by stimulating the bioconversion of the toxic LCFAs, especially the unsaturated oleic acid. Microbial community analysis reveals the ALK-2-CSTRs stimulated the growth of lipolytic bacteria and hydrogenotrophic methanogens, which suggests the hydrogenotrophic methanogenic pathway was promoted. Cost evaluation demonstrates the economical superiority of the ALK-2-CSTR over the prevailing strategies developed for enhancing methane yield from the co-substrates. [ABSTRACT FROM AUTHOR]

• Highest CH 4 yield was achieved when biopulp shared 80% VS and sludge shared 20% VS. • Co-digestion process sufficiently succeeded in continuous mode. • IC 50 of potassium for co-digestion (80% biopulp/20% sludge) was 8 g/L. • The continuous co-digestion process was validated using BioModel accurately. • Simulations confirmed the strong inhibition of potassium to the co-digestion. Process instability with consecutive low methane production are common challenges of the anaerobic digestion (AD) of municipal wastes. In the present study, the co-digestion of sewage sludge and municipal biopulp was investigated at batch and continuously fed digesters. At batch tests, the highest methane yield for co-digestion (467 ± 17 mLCH 4 /gVS) was achieved when biopulp contributed to 80% of organic matter content and sludge the remaining 20%. At continuous mode operation, co-digestion achieved 0.91 ± 0.11 L/(L·d) methane productivity, while mono-digestion of sludge achieved 0.62 ± 0.05 L/(L·d). Potassium inhibition was investigated at the most efficient co-digestion scenario and was found that the half maximal inhibitory concentration (IC 50) occurred at 8 g-K+/L. Subsequently, the effect of K+ was investigated at different scenarios at continuous operation. Simulations based on BioModel described the inhibitory effect of K+ by introducing non-competitive inhibition of methanogens. Simulation results confirmed the strongly inhibitory effect of potassium to the AD process. [ABSTRACT FROM AUTHOR]

• Chemical composition of OFMSW and biomass ashes is presented. • Biomass ashes deliver complementary trace elements to OFMSW. • Biomass ashes show positive effects on AD. • CO 2 precipitation via metal oxides elevates CH 4 concentration in biogas to 98%. The purpose of this study is to test alternative additives for trace element (TE) supplementation and process stabilization during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and sewage sludge. Process instabilities due to acidification are a typical problem in waste fermentation. Provision with minerals and TE is crucial for microorganisms in AD to work effectively, allowing higher organic loading rates within the digester without risking acid accumulation. In batch-fermentation tests, different mixture configurations of OFMSW, digested sewage sludge and biomass ashes were evaluated. Based on an extensive characterization of the TE contained in wood ashes, suitable combinations of digested sewage sludge and OFMSW as a baseline substrate together with ash additives were derived. While high dosages of ash reduced biogas production, 1:1 mix of ash and OFMSW facilitated higher CH 4 yields (6%). The supplementation of ashes increased the pH-value within AD and CO 2 precipitation through metal oxides in situ elevated the CH 4 concentration in biogas up to 98%. Therefore, ashes may increase the efficiency of AD and serve as a basis for a new gas purification method, minimizing technical effort. Additional investigations are needed to examine long-term effects as well as financial and legal aspects such as possible ways of digestate usage. As a further area of research, the transferability of batch-test results into practical applications is identified. [ABSTRACT FROM AUTHOR]

• Valorization of macroalgal residues by anaerobic digestion. • Knife milling and alkaline pretreatment enhanced methane production. • In semi-continuous reactors, alkaline pretreatment enhanced methane by 20%. • Digestates did not exhibit phytotoxicity. • Digestate from codigestion with sludge led to the highest tomato plant growth. The aim of this paper is to investigate the impact of pretreating macroalgal residue (MAR) from agar-agar extraction and its co-digestion with sewage sludge on methane production and the agronomic quality of the digestates produced. First, different pretreatments were assessed on BMP tests. Among milling technologies used, knife milling with a 4 mm-screen improved methane production by 25%. The MAR was then knife milled before alkaline, acid and thermal pretreatment. KOH pretreatment (5% TS basis, 25 °C for 2 days) led to the highest methane improvement. It was applied to semi-continuous anaerobic digestion and methane production achieved 237 Nml/gVS which was 20% higher than the control (198 Nml/gVS). In comparison to MAR mono-digestion, co-digestion with thickened activated sludge produced less methane (184 Nml/gVS) but reduced H 2 S emission by 91%. None of the digestates was toxic for the germination or growth of wheat and tomato plants. Particularly, co-digestion had the highest impact on tomato plant dry weight (+94% compared to soil alone) mainly due to the phosphorous brought by sludge. However, the impact of alkaline pretreatment on plant growth was not significant. [ABSTRACT FROM AUTHOR]

• OFMSW co-digestion with sewage sludge digestate an effective strategy for low OLR. • Energy analysis shows 48% increase in electricity for export, 22% in heat. • Mesophilic digestion at low OLR unstable due to low N concentration. • Digestate addition limited by N input in thermophilic conditions. • Process integration offers a promising route for contaminated feedstocks. Changing waste management practice, introduction of new technologies, and population demographics and behaviour will impact on both quantity and composition of future waste streams. Laboratory-scale anaerobic digestion of the mechanically-separated organic fraction of municipal solid waste (ms-OFMSW) was carried out at relatively low organic loading rates (OLR), and results analysed using an energy modelling tool. Thermophilic operation with water addition and liquor recycle was compared to co-digestion with dilution water replaced by sewage sludge digestate (SSD); thermophilic and mesophilic mono-digestion were also tested at low OLR. All thermophilic conditions showed stable operation, with specific methane production (SMP) from 0.203 to 0.296 m3 CH 4 kg−1 volatile solids (VS). SSD addition increased biogas production by ~20% and there was evidence of further hydrolysis and degradation of the SSD. Long-term operation at 1 kg VS m−3 day−1 had no adverse effect except in mesophilic conditions where SMP was lower at 0.256 m3 CH 4 kg−1 VS and stability was reduced, especially during OLR increases. This was probably due to low total ammonia nitrogen, which stabilised at ~0.2 g N kg−1 and limited the buffering capacity. Energy analysis showed thermophilic operation at OLR 2 g VS L−1 day−1 gave 42% of the theoretical methane potential and 38% of the higher heating value, reducing to 37% and 34% respectively in mesophilic conditions. Scenario modelling indicated that under low ms-OFMSW load even an energy-depleted co-substrate such as SSD could contribute to the energy balance, and would be a better diluent than water due to its nutrient and buffering capacity. [ABSTRACT FROM AUTHOR]

• Thermal treatment improves digestate P-leachability. • Acid leaching led to lignite-like upgraded hydrochars with HHV. • Leachate neutralisation with CaO enabled the precipitation of P-rich brown solids. • High energy recovery was obtained (hydrochars and methane from AD of PW). This work evaluates the potential of hydrothermal carbonization (HTC) to valorize the digestate derived from the anaerobic digestion of sewage sludge into useful materials for P and energy recovery. The hydrothermal treatment of digestate at 180–240 °C did not lead to high-rank hydrochars. On the other hand, inorganic P concentration did not change with the temperature, while as the carbonization temperature increased, the organic P retention yield in hydrochar became lower, increasing the total P in the process water obtained at the highest temperature, up to 25.3%. P recovery from acid leaching of the hydrochar obtained at 180 °C, via precipitation with CaO at pH up to 9, led to a brown solid precipitate with total P content close to 42 mg g−1, in the range of low grade phosphorus ores. Moreover, acid leaching reduced by 50% the ash content, yielding lignite-like upgraded hydrochars with higher heating values in the range of 20.5–23.1 MJ kg−1, fairly interesting as solid fuels. Anaerobic digestion of the process water enabled additional energy recovery in form of biogas (325 and 279 mL CH 4 g−1 VS -at standard temperature and pressure; STP- from the process water resulting at 180 and 210 °C, respectively). [ABSTRACT FROM AUTHOR]

• Sixteen sludge treatment plants in China were investigated and analyzed. • Complexity index and humic-like substances were proposed to evaluate the stabilization level. • The humic-like substance contents in the end-products were 157.8–461.1 mg/gVS. • Complexity index can predict the humification degree. The treatment, disposal and resource recovery of sewage sludge is a major bottleneck for the water and environmental remediation efforts in China. In this paper, sixteen sludge treatment plants using anaerobic digestion and aerobic composting as stabilization procedures were investigated and analysed. The organic degradation rates varied from 0.5% to 80.2% of different plants, showing the close relationship with raw sludge property and treatment process. The increment rate of humic-like substances ranged from 19% to 81% in different cases. It has been aware of that stabilization procedures coupled the degradation of simple organics (proteins, polysaccharides, lipids) with the synthesis of complex organics (humic-like substances). Therefore, an alternative methodology, considering the content of humic-like substances (no less than 150 mg/gVS) and the fluorescence complexity index (up to 5.0) in the end-products, was proposed to evaluate the stabilization level. Humic-like substances indicate the ecological value of the end-products. Fluorescence complexity index, combining the reduction of protein-like substances with the increment of humic-like substances, can predict the humification degree. The new criterion can be the supplementary of the current ones. [ABSTRACT FROM AUTHOR]

• A new anaerobic digestate valorization pathway was investigated. • Humic-like substances extracted from two digestates were used for biostimulation. • First paper screening doses of biostimulants extracted from different digestates. • Digestate extracts presented better biostimulation than the commercial reference. Digestate valorization is a key challenge for the feasibility of Anaerobic Digestion plants. In this study, humic-like substances (HLS) extracted from two digestates (sewage sludge and manure) were used for the biostimulation of hydroponic cultures of Lactuca sativa (lettuce) at different doses and compared to a commercial reference of leonardite HLS. Aerial biomass increase averages ranged from 7 to 30 %, but the results presented a high coefficient of variation (around 20 %). The commercial reference did not present statistically significant biomass yield improvement. The application of manure digestate extract at the higher fulvic-like acids dose (4.6 mg/L of dissolved organic carbon) presented the best and most significant results compared to the blank (Hoagland's solution only). However, this result cannot be strictly dissociated from the supplementary amounts of nutrients brought by the extracts. Additionally, all the products presented low heavy metal content compared to the recent EU regulation for biostimulants (2019/1009). This preliminary study confirmed the interest of extracting HLS from two digestates for application as biostimulants, shedding light on a new perspective for digestate valorization. [ABSTRACT FROM AUTHOR]

• Fluorescence maxima >Ex: 400 unique to anaerobically digested (AD) leachates. • Peak picking/ratio analysis more targeted than Fluorescence Regional Integration. • Similar N releases for AD solids with variable pretreatments during soil incubation. • Fluorescence >Ex: 400 of leachable organic matter decayed during incubations. • Targeted organic matter characterization informs biosolids management programs. Thermal hydrolysis pretreatments (THP) coupled to anaerobic digestion (AD) are implemented to treat municipal solids, but limited study indicates whether THP-AD materials merit different land application rates than AD biosolids without THP. Three AD biosolids types with either no pretreatment, THP, or two-hour fermentation were evaluated for differences in leachable dissolved organic matter (DOM), DOM decomposition, and nitrogen (N) releases in biosolids incubated in sandy loam soil. DOM characterizations of size exclusion chromatography, FTIR, and fluorescence maxima > Ex: 400 nm indicated similarities in among AD-DOM that contrasted waste activated sludge Milorganite and Suwannee River Organic Matter (SRNOM). Fluorescence peak picking was a more adaptable analysis for shifted leachate spectra than fluorescence regional integration (FRI). Peak ratio analysis is recommended over FRI for biosolids-DOM. The 3-month net inorganic N produced in biosolids-soil incubations was 155 ± 12.1, 149 ± 18.2, 140 ± 17.4, and 354 ± 15.1 mg N/kg for AD biosolids with no pretreatment, fermentation-AD, THP-AD, and Milorganite respectively. Overall, there was limited evidence of differences in leachable organic matter quality or net mineral N release after 105 days for AD solids with or without THP. Red-shifted fluorescence of leachates decayed by day 45 in aerobic biosolids-soil incubations, suggesting that larger, complex carbon sources liberated during solids stabilization may decompose readily in soils. Overall, other variables (source material, AD operation) may have a greater influence on final nutrient releases and organic matter quality than full-scale pretreatments to AD alone. Critical and targeted application of DOM spectroscopy specific to biosolid-leachates will improve use in advanced stabilization studies. [ABSTRACT FROM AUTHOR]

• 240 TWh.year−1 could be generated from food outlets' FOG in the London area. • FOG collected further away from source were richer in water and other contaminants. • FOG demonstrated high biomethane potentials. • Lipids accounted for most of the organic in FOG. • A shift from unsaturated to saturated fats was noticed from source to end point. Several of the waste materials that have a negative impact on the sewer system are produced by fats, oils and greases (FOG) discharged from commercial and domestic kitchens. These materials accumulate at different points in the sewer catchment, from kitchens to pumping stations, sewers and sewage treatment works (STWs), and comprise oily wastewater, floating agglomerates and hard deposits. Despite their detrimental effects, these waste materials have a high calorific content and are an ideal feedstock for energy recovery processes. So far, the overall volume of each type of waste and their physical-chemical properties in relation to their collection point are unknown. However, from a management point of view, knowledge on each feedstock quality and volumes is necessary to develop an economic viable solution for their collection and for energy recovery purposes. In this study, FOG wastes collected from households, food service establishments (FSEs), sewage pumping stations, sewers and STWs, were compared to sewage sludge in terms of organic contents and energy potentials. As expected, FOG recovered at source (households and FSEs) were 'cleaner' and had a higher energy content. Once mixed with wastewater the materials changed in composition and lost some of their energy per unit mass. Our results showed that around 94,730 tonnes.year−1 of these materials could be recovered from the Thames Water Utilities' catchment, one of the most populated in the UK. These materials could produce up to 222 GWh.year−1 as biogas, close to double of what is produced with sewage sludge digestion and around 19% of the company energy needs. Finally, even with over six million households in the catchment, the results showed that most of the FOG waste was produced by FSEs (over 48,000 premises) with an estimated average of 79,810 tonnes.year−1 compared to 14,920 tonnes.year−1 from private households. This is an important outcome as recovery from FSEs will be cheaper and easier if the company decides to implement a collection system for energy recovery. [ABSTRACT FROM AUTHOR]

• The stability of the AcoD of sewage sludge and industrial waste was assessed. • In batch mode, a positive synergistic effect of 15% in the R m was observed with BW. • Instability was observed at 10% BW with an OLR of 2.4 in semi-continuous mode. • In semi-continuous, the kinetic parameters were 20–60% of those obtained in batch. • Clostridiales abundance was significantly greater in stable AcoD digesters. In this study, beverage wastewater (BW) and extended aeration sewage sludge were assessed as co-substrates with both mixed sludge and thermally hydrolyzed sludge as substrates in an anaerobic codigestion (AcoD) process. The methodology is an integrated methodology that comprises a batch test (BMP) and semicontinuous reactor along with microbial diversity analysis. The results showed that in batch conditions, neither significant synergistic nor antagonistic effects were observed on the maximum potential (P) due to the cosubstrates presence. However, synergistic effects on a kinetic parameter (R m) were observed when BW was used as cosubstrate. Process instability was observed in semi-continuous mode with cosubstrate BW, which was not predicted by the BMP test. As demonstrated in this study, the BMP approach is also not suitable for predicting continuous performance in real systems; however, it can be used to screen an array of substrates. In semi-continuous mode, one can expect to reach values between 50 and 60% of the biogas potential and 20–40% of the maximum production rate achieved in batch tests. The agreement between batch and semi-continuous results is also dependent on the type of inoculum used. The microbial diversity of the system was more influenced by the reactor stability than the presence of cosubstrates. To predict the performance (and stability) of real anaerobic digesters, dynamic models should be employed. [ABSTRACT FROM AUTHOR]

• Anaerobic digestates from sewage sludge (SSADs) were characterised. • SSADs revealed an appreciable nutrients content. • No phytotoxic effects were observed at low digestate concentrations. • Plant growth significantly improved after amendment with SSADs. • SSADs fertilizing effect was more consistent on a nutrient poor soil. Sewage sludge production in European countries has widely raised in the last decade and its fate is currently landfilling, incinerators, composting or land application. To explore its agronomic potential, the main target of this work is to understand the effects of anaerobic digestates from sewage sludge (SSAD). To this aim, four different SSADs (two liquids and two dewatered) were characterized. On the liquid ones, Germination Index was evaluated through a plate bioassay with Lepidium sativum L. seeds; low concentrations of SSAD (2.5%) improved GI in one case, while at higher concentrations phytotoxic effects occurred in both. Then, pot experiments were set in climate chamber with Cucumis sativus L. grown for 30 days on two different substrates: a sandy, alkaline and poor soil, and peat substrate. All SSADs and a mineral fertilizer were used at three increasing dosages: 85, 170, 255 kg of nitrogen per hectare (kg N/ha). Results in terms of germination, dry biomass, chlorophyll content, net photosynthesis, stomatal conductance, CO 2 concentration in substomatal cavity and root development were compared to a not treated control. All treatments gave results significantly higher or similar to control on all the parameters evaluated. Moreover, the intermediate nitrogen dosage (170 kg N/ha) generally showed the highest results compared to other dosages, especially for dewatered SSADs. All these results were much more evident for cucumber plants grown on an the alkaline, sandy and poor soil than on peat substrate, such demonstrating that SSADs have a fertilizing effect for plants growing on this kind of soil. [ABSTRACT FROM AUTHOR]

• Increased loading was possible both with and without thermal hydrolysis treatment. • The pre-treatment had more pronounced effect on sewage sludge than on food waste. • Dewatering and pre-treatment were effective ways to increase retention time. • Pre-treatment increased the proportion of Clostridia in industrial-scale digesters. • Firmicutes:Bacteriodetes ratio positively correlated with methane yield. This study examined the impact of thermal hydrolysis process (THP) pre-treatment on anaerobic co-digestion of wastewater sludge and household waste and assessed whether THP was vital to achieve higher process capacity. Performance data were collected for both industrial- and laboratory-scale digesters and response in microbial community structure was evaluated by Illumina sequencing. Implementation of THP at the industrial-scale plant increased methane yield by 15% and enhanced substrate degradability. Possibility to extend the sludge retention time due to a higher solid content of the substrate, sanitisation of the digestate and improved fertiliser quality of the digestate were other industrial-scale benefits of THP installation. Continuously-fed laboratory-scale digesters were fed THP-treated or untreated substrate at an organic loading rate (OLR) of 5 g volatile solid (VS)/L/day, a feeding rate necessary at the corresponding industrial-scale plant to meet the estimated population increase within the municipality. The results indicated that the plant could have increased the capacity with unimpaired stability independently of THP installation, even though the retention time was significantly shortened during operation with untreated substrate. Microbial community analyses revealed increased contribution of the Clostridia class after THP installation in industrial-scale digesters and positive correlation between Firmicutes:Bacteriodetes and methane yield in all digesters. Differentiated profiles in laboratory-scale digesters indicated that a temperature increase from 37 to 42 °C in association with THP installation and altered substrate composition were strong determining factors shaping the microbial community. Overall, these findings can assist industrial-scale plants in choosing management strategies aimed at improving the efficiency of anaerobic digestion processes. [ABSTRACT FROM AUTHOR]

• Thermal alkaline pretreatment promoted methane yield of sludge. • Protein-like organics mainly located in SPOM and REOM fractions. • Biodegradability is well correlated with the ratio of I RB to I PB. • Bioaccessibility of readily degradable organic matters was enhanced by LAT. Thermal hydrolysis has proven to be a successful approach to make sewage sludge more amenable to anaerobic digestion. Three heat pretreatment scenarios were compared in this study, i.e. thermal alkaline treatment (LAT, 0.1 M NaOH, 80 °C), low temperature thermal treatment (LT, 80 °C) and high temperature thermal treatment (HT, 170 °C). The biodegradability of pretreated sludge was testified by using biochemical methane potential (BMP) test, meanwhile, the repartition and complexities of organic matters in sludge subjected to various pretreatments were characterized by a revised chemical extraction protocol combined with 3D fluorescence spectroscopy. The cumulative methane yield of sewage sludge was significantly increased by LAT (+135%), LT (+95%) and HT (+112%) as compared to the control. Nevertheless, results show that the solubilization degree of sludge was insignificantly correlated to BMP values, meanwhile high correlation values were observed for the soluble polysaccharide concentration in hydrolysate. The degradation rates of bioaccessible fraction of soluble particulate organic matter (SPOM) and readily extractible organic matter (REOM) were improved after thermal pretreatments at varied levels, which indicates that the chemical accessibility is positively correlated with the bioaccessibility. Furthermore, the biodegradable index F digestion was proposed to evaluate the biodegradability of organic matter, which is helpful for the optimization of various pretreatment strategies. [ABSTRACT FROM AUTHOR]

• An improved AD configuration with THP post-treatment was developed. • High concentration of SCOD could be dissolved during THP post-treatment. • AD-THP performed much better than the THP pretreatment system. • The dewatering of post-THP sludge was excellent without addition of polymer. • The pH changed in opposite directions during pre- and post-THP treatment. Thermal hydrolysis process (THP) is widely used as the pretreatment for sludge anaerobic digestion (AD), but with limited improvement of biogas production, dewaterability, and high energy consumption. In this study, an improved AD configuration based on post-THP treatment (AD-THP) was developed to overcome these limitations. The digested sludge was thermally hydrolyzed and then dewatered directly, the centrate was recirculated for re-digestion with raw sludge. Batch and semi-continuous experiments were conducted to investigate the differences between pre- and post-THP treatment and compare the process performances of three configurations, including conventional anaerobic digestion (CAD), thermal hydrolysis pretreatment (THP-AD), and post-treatment (AD-THP). Results showed that post-THP could further dissolve much SCOD from the digested sludge by disintegrating the recalcitrant organic matter of raw sludge and EPS generated during digestion, resulting in further improvement of methane production. The SCOD solubilization during THP post-treatment was depended on the degradation extent of digested sludge. The main difference between pre- and post-treatment was that the pH changed towards the opposite directions due to the different properties of raw and digested sludge. The maximum specific methane production and volatile solid reduction of the AD-THP system were 344.25 mL CH 4 /g VS add and 62% during the CSTR experiments, respectively, significantly higher than those of THP-AD and CAD configurations. In addition, the dewaterability of THP treated sludge was always significantly better than the digested sludge, whether for THP pretreatment or post-treatment. The improved AD-THP configuration could be a promising alternative for the upgrading of sludge treatment. [ABSTRACT FROM AUTHOR]

• Amino acids were decomposed evidently by THP at 120 °C (8.9%) and 160 °C (26.7%). • Amino acids degradation in AD was promoted largely via decomposition during THP. • Varied THP temperature changed dominating bacteria utilizing amino acids in AD. • 120 °C played little role in promoting amino acids metabolic pathways during AD. • 160 °C effectively enhanced amino acids metabolism via Stickland pathway during AD. Three semi-continuous anaerobic digesters with raw sludge (R1) or thermally hydrolyzed sludge (120 °C (R2) or 160 °C (R3)) were operated to investigate the effects of thermal hydrolysis on the metabolism of amino acids during high solid anaerobic digestion with sewage sludge. Thermal hydrolysis pretreatment (THP) decomposed protein in terms of hydrolytic amino acid in raw sludge by 8.90% and 26.69% under 120 °C and 160 °C, respectively. The decomposition of amino acids during THP was the main contributor to the final enhanced amino acids degradation in sewage sludge with THP after anaerobic digestion. The dominating bacterial genera related to amino acids degradation in R2 and R3 shifted to Fastidiosipila and Proteiniphilum / Tissierella , respectively, from Gelria in R1, influencing the utilization of amino acids, especially glutamic acid, glycine and proline. Different from 120 °C, THP at 160 °C played an important role in promoting amino acid metabolism during AD through the Stickland pathway by the bacteria belonged to order Clostridiales. [ABSTRACT FROM AUTHOR]

• Co-digestion performances improved since 25% of fish or beyond 50% of grass added. • Optimal Digestion Indicator was built to assess the optimal methane production. • Mono-Digestion Indicator was built to assess the expected methane production. • 75% (gCOD) of fish in co-digestion increased final methane production by 1.9 times. • 75% (gCOD) of grass in co-digestion increased final methane production by 1.7 times. Anaerobic co-digestion (AcoD) is a promising strategy to increase the methane production of anaerobic digestion plants treating wastewater sludge (WAS). In this work the degradability of six different mixtures of WAS with fish waste (FW) or garden-grass (GG) was evaluated and compared to the three mono-digestions. Degradation performances and methanogenic pathways, determined with the isotopic signatures of biogas, were compared across time. Fish and grass mono-digestion provided a higher final methane production than WAS mono-digestion. In co-digestion the addition of 25% of fish was enough to increase the final methane production from WAS while 50% of grass was necessary. To determine the optimal blend of WAS co-digestion two indicators were specifically designed, representing the maximum potential production (ODI) and the expected production in mono-digestion conditions (MDI). The comparison between these indicators and the experimental results showed that the most productive blend was composed of 75% of co-substrate, fish or grass, with WAS. Indeed, the final methane production was increased by 1.9 times with fish and by 1.7 times with grass associated to an increase of the methane production rate by 1.5 times. Even if the same succession of methanogenic pathways across time was observed for the different mixtures, their relative proportions were different. Sewage sludge degradation was mostly achieved through hydrogenotrophic pathway while acetoclastic pathway was dominant for fish and grass degradation. These results were confirmed by the identification of Archaea with 16S sequencing. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Effects of THP on sludge properties and anaerobic biodegradability were evaluated. • THP affected sludge viscosity, sludge solubilization, and biogas production. • Optimal biomethane production was achieved at a THP temperature of 180 °C. • At > 180 °C, THP negatively affected anaerobic biodegradability and CH 4 production. Abstract The influence of thermal hydrolysis pretreatment (THP) on physicochemical properties (pH, total solids, volatile solids, chemical oxygen demand, total nitrogen, ammonium nitrogen, volatile fatty acids, viscosity, and cell morphology) and anaerobic biodegradability of highly concentrated waste activated sludge (WAS) with TS content ranging from 1 to 7% was evaluated at different temperatures ranging from 100 to 220 °C. The biomethane potential (BMP) of the WAS was systematically analyzed and evaluated. Images of its cellular structure were also analyzed. The results indicated that THP is a useful method for solubilizing volatile solids and enhancing CH 4 production regardless of the TS content of the WAS feed. The ultimate CH 4 production determined from the BMP analysis was 313–348 L CH 4 /kg VS (72.6–74.1% CH 4) at the optimum THP temperature of 180 °C. The results showed that THP could improve both the capacity and efficiency of anaerobic digestion, even at a high TS content, and could achieve the dual purpose of sludge reduction and higher energy recovery. [ABSTRACT FROM AUTHOR]

Highlights • One tonne of raw material produces 8.01 m3 of waste water (60 kg of sludge). • Agri-food sludge are more adequate as organic amendment than urban sludge. • Agri-sludge composting is one of the best solution if agriculture sites are around. • Sludge composting can be improved by incorporating beneficial microorganisms. Abstract Agri-food sludge is both an environmental and economic problem, since companies must bear the costs of proper management as required by current disposal regulations. The aim of this work was to quantify the sludges in a typical Mediterranean area like the Segura River basin in Spain, which has a high concentration of agri-food businesses and intensive farming operations. Ultimately, we wanted to offer options for converting this "waste" into a "resource." The agri-food companies studied were classified according to their final product: juices, frozen vegetables or canned products. The total volume of sludge ranged between 12,895 and 22,520 tonnes per year, with an average cost of around 350,000 euros. In characterising the agri-food sludges, we identified a high organic load and nutrient content. Besides, the heavy metal levels were well below those legally permitted in sewage sludge, fertilisers or similar products for agricultural use. Furthermore, we only detected pesticide residues occasionally, and we did not detect Salmonella spp. or Listeria monocytogenes in the samples analysed. E. coli was only found in about 20% of the samples. This paper identifies the most suitable technologies for the specific agri-food industries in the area, which are surrounded by intensive agriculture operations. We have analysed direct soil application, sludge drying, composting and the use of anaerobic digestion to produce energy and have shown the main advantages and disadvantages of each. We found that composting and its advanced modifications for making tailored composts are among the most adequate strategies for obtaining organic amendments. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion has made a greater impact on the biogas production from mixing different type of waste. In this research, sewage sludge (SS) and cow manure (CM), was used as a primary waste along with kitchen waste (KW), yard waste (YW), floral waste (FW) and dairy wastewater (DWW) as co-substrate for anaerobic digestion. Mixtures with a ratio of 1:2 ratio is fed into a single stage up-flow anaerobic sludge blanket (UASB) reactor. Digestion was carried out in a mesophilic temperature range for 20 days. pH and VFA were measured and ranged from 5 to 7.5 and 3500–500 mg/L, respectively, for all the mixtures throughout the digestion period. Percentage of COD removal efficiency after 20 days was found to be in the range of 76–86%. The maximum biogas production rate was found to be 4500 mL/day. Characterization of the final residue from each of the digesters was carried out by Scanning Electron microscope, Energy dispersive, thermogravimetric, FTIR Spectra, and Atomic microscope. Thermal analysis reveals that spent sludge can be potential waste energy sources. [ABSTRACT FROM AUTHOR]

In the present study, the influence of substrate pre-treatment (grinding and sieving) on batch anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was first assessed, then followed by co-digestion experiments with the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered sewage sludge (DSS). The methane yield of batch anaerobic digestion after grinding and sieving (20 mm diameter) the OFMSW was considerably higher (453 mL CH 4 STP g −1 VS added ) than that of untreated OFMSW (285 mL CH 4 STP g −1 VS added ). The modified Gompertz model adequately predicted process performance. The maximum methane production rate, R m , for ground and sieved OFMSW was 2.4 times higher than that of untreated OFMSW. The anaerobic co-digestion of different mixtures of OFMSW and LFHTC of DSS did not increase the methane yield above that of the anaerobic digestion of OFMSW alone, and no synergistic effects were observed. However, the co-digestion of both wastes at a ratio of 75% OFMSW-25% LFHTC provides a practical waste management option. The experimental results were adequately fitted to a first-order kinetic model showing a kinetic constant virtually independent of the percentage of LFHTC (0.52–0.56 d −1 ) and decreasing slightly for 100% LFHTC (0.44 d −1 ). [ABSTRACT FROM AUTHOR]

The main goal of this study was to investigate the co-digestion of sewage sludge and mature landfill leachate pretreated through hydrodynamic cavitation. The process efficiency was analyzed from the aspects of organics removal, biogas production, kinetics and digestate quality. Energy efficiency of the overall treatment was evaluated as well. A dose of hydrodynamically cavitated leachate of 5% v/v was used as a substrate for co-digestion with sewage sludge at a hydraulic retention time of 20 days. This improved the kinetics, biogas production and corresponding yields, as well as digestate quality. Fourier transform infrared photoacoustic spectroscopy analysis seemed to indicate that no new toxic compounds were formed with co-digestion. The investigated two-stage treatment is recommended as a safe and cost-effective method of utilizing mature leachate. [ABSTRACT FROM AUTHOR]

In this study, hydrogen and methane production from co-digestion of food waste (FW), sewage sludge (SS) and raw glycerol (GL) was evaluated in a two-stage acidogenesis-methanogenesis anaerobic system under mesophilic conditions (35 °C). The effect of glycerol addition (1 and 3% v/v) as co-substrate was assessed in ternary mixtures (FW + SS + GL), with the concentration of all substrates kept at 10 g VS/L. Besides contributing to reduce the lag phase of the acidogenic bacterial culture, the presence of GL increased the hydrogen production in all tested conditions and the maximum hydrogen yield was obtained for the FW + SS + 3%GL mixture (179.3 mL H 2 /g VS). On the other hand, the highest methane production (342 mL CH 4 /g VS) was achieved in the test supplemented with 1% GL. At 3% GL, abrupt reductions in the biogas CH 4 content and pH values resulting from instability in methanogenesis process were noticed over the experiment. By taking into account the hydrogen and methane production stages, the highest energy yield (i.e., 15.5 kJ/g VS) was obtained with the ternary mixture containing 1% GL. Overall, the results of this study demonstrate the feasibility of using glycerol as co-substrate to increase the H 2 and CH 4 production efficiency in a two-stage anaerobic co-digestion process, allowing simultaneous treatment of three residues (FW, SS and GL) and energy production. [ABSTRACT FROM AUTHOR]

In this study, the anaerobic mesophilic co-digestion of food waste (FW) with municipal sewage sludge (MSS) and slaughterhouse waste (SHW) was undertaken in 3-dm 3 laboratory reactors as well as in 50-dm 3 reactors operated in semi-continuous conditions. The highest methane yield of around 0.63 m 3 CH 4 /kgVS fed was achieved for the mixture of FW and SHW treated in the laboratory digester operated at solids retention time (SRT) of 30 days, whereas the co-digestion of FW with MSS under similar operating conditions produced 0.46 m 3 of methane from 1 kgVS fed . No significant differences between methane yields from laboratory digesters and large-scale reactors were reported. The conditioning tests with the digestates from reactor experiments revealed the highest efficiency of inorganic coagulants among all investigated chemicals, which applied in a dose of 10 g/kg allowed to reduce capiliary suction time (CST) of the digestate below 20 s. The combined conditioning with coagulants and bentonite did not further reduce the CST value but improved the quality of the digestate supernatant. In particular, the concentrations of suspended solids, COD as well as metals in the supernatant were considerably lowered. [ABSTRACT FROM AUTHOR]

The aim of this research is to enhance the mesophilic anaerobic digestion of municipal sludge from Cadiz-San Fernando (Spain) wastewater treatment plant at 20 days hydraulic retention time (HRT). Two different strategies were tested to improve the process: co-digestion with the addition of soluble organic matter (1% v/v); and alkali sludge pre-treatment (NaOH) prior to co-digestion with glycerine (1% v/v). Methane production (MP) was substantially enhanced (from 0.36 ± 0.09 L CH 4 l/d to 0.85 ± 0.16 L CH 4 l/d), as was specific methane production (SMP) (from 0.20 ± 0.05 L CH 4 /g VS to 0.49 ± 0.09 L CH 4 /g VS) when glycerine was added. The addition of glycerine does not seem to affect sludge stability, the quality of the effluent in terms of pH and organic matter content, i.e. volatile fatty acids (VFA), soluble organic matter and total volatile solid, or process stability (VFA/Alkalinity ratio < 0.4). Alkali pre-treatment prior to co-digestion resulted in a high increase in soluble organic loading rates (more than 20%) and acidification yield (more than 50%). At 20 days HRT, however, it led to overload of the system and total destabilization of the mesophilic anaerobic co-digestion of sewage sludge and glycerine. [ABSTRACT FROM AUTHOR]

The modelling of the effect of trace elements on anaerobic digestion, and specifically the effect of fly ash, has been scarcely studied. Thus, the present work was aimed at the development of a new function that allows accumulated methane models to predict the effect of FA on the volume of methane accumulation. For this, purpose five fly ash concentrations (10, 25, 50, 250 and 500 mg/L) using raw and pre-treated sewage sludge were used to calibrate the new function, while three fly ash concentrations were used (40, 150 and 350 mg/L) for validation. Three models for accumulated methane volume (the modified Gompertz equation, the logistic function, and the transfer function) were evaluated. The results showed that methane production increased in the presence of FA when the sewage sludge was not pre-treated, while with pretreated sludge there is inhibition of methane production at FA concentrations higher than 50 mg/L. In the calibration of the proposed function, it fits well with the experimental data under all the conditions, including the inhibition and stimulating zones, with the values of the parameters of the methane production models falling in the range of those reported in the literature. For validation experiments, the model succeeded in representing the behavior of new experiments in both the stimulating and inhibiting zones, with NRMSE and R 2 ranging from 0.3577 to 0.03714 and 0.2209 to 0.9911, respectively. Thus, the proposed model is robust and valid for the studied conditions. [ABSTRACT FROM AUTHOR]

Five semi-continuous flow anaerobic digesters treating a mixture of food waste (FW) and municipal biosolids (primary sludge and thickened wasted activated sludge) at an solids retention time (SRT) of 20 days and different blend ratios i.e. 0, 10%, 20%, 40% by volume with the fifth digester treating only biosolids at the same COD/N ratio as the 40% FW digester were operated to investigate co-digestion performance. Sixty days of steady-state operation at organic loading rates (OLR) of 2.2–3.85 kgCOD/m 3 /d showed that COD removals were higher for the three co-digesters than for the two municipal biosolids digesters i.e. 61–69% versus 47–52%. Specific methane production per influent CODs were 1.3–1.8 folds higher in co-digestion than mono-digestion. The first-order COD degradation kinetic constants for co-digestion were more than double the mono-digestion. Additional methane production through synergism accounted for a minimum of 18–20% of the overall methane production. The estimated non-biodegradable fraction of the FW particulate COD was 7.3%. However, the co-digesters discharged 1.23–1.64 times higher soluble nitrogen than the control. [ABSTRACT FROM AUTHOR]

Citrus crops are among the most abundant crops in the world, which processing is mainly based on juice extraction, generating large amounts of effluents with properties that turn them into potential pollution sources if they are improperly discarded. This study evaluated the potential for bioconversion of effluents from citrus-processing industry (wastewater and vinasse) into hydrogen through the dark fermentation process, by applying anaerobic sewage sludge as inoculum. The inoculum was previously heat treated to eliminate H2-consumers microorganisms and improve its activity. Anaerobic batch reactors were operated in triplicate with increasing proportions (50, 80 and 100%) of each effluent as substrate at 37 °C, pH 5.5. Citrus effluents had different effects on inoculum growth and H2 yields, demonstrated by profiles of acetic acid, butyric acid, propionic acid and ethanol, the main by-products generated. It was verified that there was an increase in the production of biogas with the additions of either wastewater (7.3, 33.4 and 85.3 mmol L-1) or vinasse (8.8, 12.7 and 13.4 mmol L-1) in substrate. These effluents demonstrated remarkable energetic reuse perspectives: 24.0 MJ m-3 and 4.0 MJ m-3, respectively. Besides promoting the integrated management and mitigation of anaerobic sludge and effluents from citrus industry, the biohydrogen production may be an alternative for the local energy supply, reducing the operational costs in their own facilities, while enabling a better utilization of the biological potential contained in sewage sludges. [ABSTRACT FROM AUTHOR]

The management and valorization of residual organic matter, such as sewage sludge and manure, is gaining interest because of the increasing volume of these residues, their localized generation and the related problems. The anaerobic digestion of mixtures of sewage sludge and manure could be performed due to the similarities between both residues. The purpose of this study is to evaluate the feasibility of the copyrolysis of sewage sludge (SS) and digested manure (DM) as a potential management technology for these residues. Pyrolysis of a sewage sludge/manure blend (50:50%) was performed at 525 °C in a stirred batch reactor under N2 atmosphere. The product yields and some characteristics of the product were analyzed and compared to the results obtained in the pyrolysis of pure residues. Potential synergetic and antagonist effects during the co-pyrolysis process were evaluated. Although sewage sludge and manure seem similar in nature, there are differences in their pyrolysis product properties and distribution due to their distinct ash and organic matter composition. For the co-pyrolysis of SS and DM, the product yields did not show noticeable synergistic effects with the exception of the yields of organic compounds, being slightly higher than the predicted average, and the H2 yield, being lower than expected. Co-pyrolysis of SS and DM could be a feasible management alternative for these residues in locations where both residues are generated, since the benefits and the drawbacks of the co-pyrolysis are similar to those of the pyrolysis of each residue. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is one of the most widely used processes to stabilize waste sewage sludge and produce biogas as renewable energy. The relatively low organic matter content and high heavy metal concentrations in sewage sludge have severely restricted the application and development of AD technology in China. In this study, the effect of energy grass ( Pennisetum alopecuroides ) addition on methane production and heavy metal fractionation during the AD of sewage sludge was evaluated. Methane production was enhanced by 11.2% by the addition of P. alopecuroides . The addition of P. alopecuroides significantly reduced the percentages of the water-soluble and exchangeable fractions of the target heavy metals in the sewage sludge after AD, and the dominant species were concentrated in Fe-Mn oxide-bound and organic- and sulfide-bound fractions of the digested sludge. The addition of P. alopecuroides at a dosage of 0.3 kg significantly ( P < 0.05) decreased the mobility factors (MFs) of the target heavy metals after AD. In particular, the MFs of Cr and Ni were 61% and 32% lower, respectively, relative to the control. The increase in the added dose did not necessarily lead to further decreases in the MFs of the heavy metals. These results demonstrate that an appropriate addition of energy grass could enhance AD, decrease the mobility of heavy metals and promote heavy metal stabilization in sewage sludge during AD, which is beneficial for the subsequent land application of sewage sludge. [ABSTRACT FROM AUTHOR]

Organic wastes, such as the organic fractions of municipal solid waste (OFMSW) or sewage sludge (SS), have become a serious environmental problem in Russia as well as in other countries. The use of these wastes as soil amendments allows their negative impact on the environment to be minimized. However, before these wastes can be used, they need to be treated appropriately in order to decrease their level of hazard. In this study, composting of raw SS, OFMSW, a mixture of these two wastes (OFMSW + SS) at a ratio 1:2 as well as the anaerobically digested variants of these wastes (SSd, OFMSWd and OFMSWd + SSd) mixed with oiled sawdust was performed. Composting was conducted in the containers containing 20 kg of the wastes. The results of three elutriate bioassays (with water flea Daphnia magna , infusoria Paramecium caudatum and radish plant, Raphanus sativus ) and one contact bioassay (with oat plant Avena sativa ) were used to indirectly estimate changes in the hazardous properties of the biological treatments. Besides, C org , N tot content and pH were analyzed in the process of composting. Within the study stability tests to determine maturation process completion were not carried out. It was revealed, that in the process of anaerobic pretreatment for 15 days, the toxicity increased by a mean of 1.3-, 1.9- and 1.1-fold for OFMSW, SS and OFMSW + SS, respectively. During composting, the toxicity level of these pretreated samples decreased more rapidly as compared with those which were not pretreated. As a result, the toxicity levels of the elutriates from the final composts made of pretreated wastes OFMSW, SS and OFMSW + SS were three-, two- and 17-fold lower for D. magna and 15-, 21- and 12-fold lower for P. caudatum . As follows from phytotoxicity estimations, composts from digested substrates became mature on the 60th day and had a stimulation effect on the plants after the 90th day of incubation. For the composts prepared from raw substrates, a significantly longer period was needed for maturation. On the basis of ecotoxicity changes of the wastes treated, it can be concluded that anaerobic pretreatment of the municipal solid wastes is an effective acceleration tool for further composting and that waste mixtures can be treated more efficient as compared with raw wastes. [ABSTRACT FROM AUTHOR]

In a previous work co-digestion of food waste and sewage sludge was performed in a pilot apparatus reproducing operating conditions of an existing full scale digester and processing waste mixed sludge (WMS) and fruit and vegetable waste (FVW) at different organic loading rates. An analysis of the relationship among bio-methane generation, process stability and digestate phytotoxicity was conducted. In this paper we considered humification parameters and spectroscopic analysis. Humification parameters indicated a higher not humified fraction (NH) and a lower degree of humification (DH) of FVW with respect to WMS (NH = 19.22 and 5.10%; DH = 36.65 and 61.94% for FVW and WMS, respectively) associated with their different chemical compositions and with the stabilization process previously undergone by sludge. FVW additions seemed to be favourable from an agronomical point of view since a lower percentage of organic carbon was lost. Fourier transform infrared spectra suggested consumption of aliphatics associated with rising in bio-methane generation followed by accumulation of aliphatics and carboxylic acids when the biogas production dropped. The trend of peaks ratios can be used as an indicator of the process efficiency. Fluorescence intensity of peak B associated with tryptophan-like substances and peak D associated with humic-like substances observed on tridimensional Excitation Emission Matrix maps increased up to sample corresponding to the highest rate of biogas production. Overall spectroscopic results provided evidence of different chemical pathways of anaerobic digestion associated with increasing amount of FVW which led to different levels of biogas production. [ABSTRACT FROM AUTHOR]

Sewage sludge (SWS) is inevitably produced in urban wastewater treatment plants (WWTPs). The treatment of SWS on site at small WWTPs is not economical; therefore, the SWS is typically transported to an alternative SWS treatment center. There is increased interest in the use of anaerobic digestion (AnD) with co-digestion as an SWS treatment alternative. Although the availability of different co-substrates has been ignored in most of the previous studies, it is an essential issue for the optimization of AnD co-digestion. In a pioneering approach, this paper applies an Ant-Colony-Optimization (ACO) algorithm that maximizes the generation of biogas through AnD co-digestion in order to optimize the discharge of organic waste from different waste sources in real-time. An empirical application is developed based on a virtual case study that involves organic waste from urban WWTPs and agrifood activities. The results illustrate the dominate role of toxicity levels in selecting contributions to the AnD input. The methodology and case study proposed in this paper demonstrate the usefulness of the ACO approach in supporting a decision process that contributes to improving the sustainability of organic waste and SWS management. [ABSTRACT FROM AUTHOR]

Anaerobic codigestion of source selected organic fraction of municipal solid waste (SS-OFMSW) and sewage sludge may be one of the most viable solutions to optimize oversized digesters efficiency in wastewater treatment plants. Based on results of BMP tests obtained for sewage sludge and SS-OFMSW, pilot plant tests were carried out by 3.4 m 3 CSTR reactor at mesophilic temperature. A mix of fruit and vegetable waste from wholesale market and canteen waste was used as SS-OFMSW substrate. Tests were conducted applying an OLR (organic loading rate) ramp with 6 different phases until a value of 3.2 kgVS/m 3 d. Feedstock and digestate characteristics, efficiency and process parameters were monitored. The anaerobic codigestion development was stable in each phase: early indicators like VFA (volatile fatty acids) and FOS/TAC ratio were always below instability threshold values. The maximum OLR tested determined a GPR (gas production rate) of 0.95 N m 3 /m 3 d and SGP (specific gas production) of 0.49 N m 3 /kgVS with a VS abatement of 67.3%. [ABSTRACT FROM AUTHOR]

This study attempted to enhance anaerobic conversion of lignocellulosic materials in excess sludge by bioaugmentation and pretreatment. The results reveal that highly active lignocellulolytic microorganisms ( Clostridium stercorarium and Bacteroides cellulosolvens ) could be enriched from anaerobic sludge in ordinarily operated anaerobic digester (AD). Inoculating these microorganisms into AD could substantially enhance the degradation of cellulose and hemicellulose. However, this effect of bioaugmentation was shielded for raw excess sludge due to lignin incrustation in native biosolids. For this problem, pretreatments including acid, alkali, thermal and ultrasonic methods were effectively used to deconstruct the lignin incrustation, in which thermal pretreatment was demonstrated to be the most effective one. Then, pretreatment associated with bioaugmentation was successfully used to enhance the energy conversion of lignocellulosic materials, which resulted in the degradation of cellulose, hemicellulose and lignin to 68.8–78.2%, 77.4–89% and 15.4–33.7% respectively and thus increased the CH 4 production by 210–246%, compared with ordinary AD. [ABSTRACT FROM AUTHOR]

Cognisant of the negative debate and public sentiment about the land application of treated sewage sludges (‘biosolids’), it is important to characterise such wastes beyond current regulated parameters. Concerns may be warranted, as many priority metal pollutants may be present in biosolids. This study represents the first time that extensive use was made of a handheld X-ray fluorescence (XRF) analyser to characterise metals in sludges, having undergone treatment by thermal drying, lime stabilisation, or anaerobic digestion, in 16 wastewater treatment plants (WWTPs) in Ireland. The concentrations of metals, expressed as mg kg −1 dry solids (DS), which are currently regulated in the European Union, ranged from 11 (cadmium, anaerobically digested (AD) biosolids) to 1273 mg kg −1 (zinc, AD biosolids), and with the exception of lead in one WWTP (which had a concentration of 3696 mg kg −1 ), all metals were within EU regulatory limits. Two potentially hazardous metals, antimony (Sb) and tin (Sn), for which no legislation currently exists, were much higher than their baseline concentrations in soils (17–20 mg Sb kg −1 and 23–55 mg Sn kg −1 ), meaning that potentially large amounts of these elements may be applied to the soil without regulation. This study recommends that the regulations governing the values for metal concentrations in sludges for reuse in agriculture are extended to include Sb and Sn. [ABSTRACT FROM AUTHOR]

The fate of organic matter during anaerobic digestion of sewage sludge was studied in batch systems thanks to a sequential chemical fractionation of the particulate phase coupled to fluorescence spectroscopy. Polycyclic Aromatic Hydrocarbons (PAHs) distribution within the organic pools was characterized from their analysis in the residual fraction after each extraction. Both methods were combined to understand the link between PAHs presence in organic pools and their spectral characterization after extraction. Two batch systems (sludge and inoculum mixture) were set up to study the impact of PAHs spiking on their fate and distribution. The sequential fractionation allowed us to extract and characterize about 50% of total Chemical Oxygen Demand. Moreover, fluorescence spectroscopy helped us to understand the organic pools evolution: the most easily extracted pools composed of protein-like molecules were highly degraded meaning that chemical accessibility mimics the bioaccessibility to degrading microorganisms. PAHs were present in all pools of organic matter but native PAHs were mainly present in low accessible (hardly extractable) fractions and during anaerobic digestion, they accumulated in the non-accessible (non extractable) fraction. Spiked PAHs were more dissipated during anaerobic digestion since spiking made them present in more accessible fractions. During the anaerobic digestion, contrary to native PAHs, spiked ones relocated toward less accessible organic fractions confirming the ageing phenomenon. PCA analysis showed that, in spiked mixture, PAHs presence in organic pools is linked to both PAHs physical–chemical properties and quality/quantity of the associated organic pools. [ABSTRACT FROM AUTHOR]