Search

Today, the transition to renewable energy from conventional energy practices is more important than ever to establish energy security and mitigate climate change. The wastewater treatment plants (WWTP) consume a remarkable amount of energy and cause significant greenhouse gas emissions. The energy balance of WWTP can be improved by implementing energy-efficient applications such as anaerobic digestion. However, most of the existing WWTPs utilize only sewage sludge in conventional anaerobic digesters (CAD) which results in low biogas generation. Generally, co-digestion is indicated as an effective solution for the low biogas generation faced in mono-digestion. Moreover, recently, anaerobic membrane bioreactors (AnMBR) have been promoted as a prominent alternative to CADs. This paper overviews the current situation of co-digestion applications by AnMBRs for municipal WWTPs. Furthermore, the environmental and economic aspects of these applications were reviewed. Lastly, challenges and future perspectives related to the co-digestion applications by AnMBR were thoroughly discussed. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion is an effective method for addressing the issue of a single substrate not being able to achieve optimal conditions for anaerobic digestion. By adjusting the mixture ratio of sewage sludge and food waste to achieve the optimal carbon to nitrogen ratio, the effectiveness of thermophilic–mesophilic temperature phase anaerobic co-digestion (TPAcD) was evaluated in comparison to single phase mesophilic anaerobic co-digestion (MAcD) and thermophilic anaerobic co-digestion (TAcD). The results indicated that TPAcD increased methane yield by 50.3% and 32.7% compared to MAcD and TAcD, respectively. The variation in VFA, pH, and ammonia nitrogen levels demonstrated that TPAcD combines the advantages of both MAcD and TAcD, with a higher hydrolysis rate in the early stage under thermophilic conditions (55 °C) and a suitable environment in the later stage under mesophilic conditions (35 °C). The kinetic parameters of anaerobic co-digestions also demonstrated that TPAcD performs better. Therefore, further research on TPAcD of sewage sludge and food waste is warranted due to its significant improvements in methane production rate, total methane yield, and system stability. Additionally, TPAcD contributes to reducing carbon emissions and supports the realization of "carbon neutrality". [ABSTRACT FROM AUTHOR]

Conventional pretreatment technologies have been assessed to resolve the slow hydrolysis of sewage sludge, but high operating costs have prevented their wide use. This study investigated non-thermal plasma (NTP) technologies as an alternative to promote anaerobic digestion (AD). Various contact time (CT) and temperature (T) conditions were used to assess how NTP pretreatment improves the methane conversion of organics in sewage sludge. A multi-response surface model (RSM) using a central composite design (CCD) identified the optimal CT (4.6 h) and T (45 °C). This statistical optimization of NTP pretreatment led to an enhanced biochemical methane potential of 297 ± 46 mL CH4 g–1 COD by reducing operating cost as power consumption as low as 0.08 USD L–1. The result was comparable to those of other advanced oxidation processes (0.14 – 0.60 USD L–1) demonstrating that accelerated hydrolysis of sewage sludge using NTP pretreatment show potential for improving renewable energy recovery from sewage sludge. [ABSTRACT FROM AUTHOR]

This manuscript presents a scientometric review of recent advances in microwave pretreatment processes for sewage sludge, systematically identifying existing gaps and prospects. For this purpose, 1763 papers on the application of microwave technology to sludge pretreatment were retrieved from the Web of Science (WoS) using relevant keywords. These publications were then analyzed using diverse scientometric indices. The results show that research in this field encompasses applications based on the non-thermal effects of microwaves, enhanced effectiveness of anaerobic digestion (AD), and the energy balance of this pretreatment system. Overcoming existing technical challenges, such as the cleavage of extracellular polymers, reducing microwave energy consumption, understanding the non-thermal effects of microwaves, promoting AD of sludge in combination with other chemical and physical methods, and expanding the application of the technology, are the main scientific focuses. Additionally, this paper thoroughly examines both the constraints and potential of microwave pretreatment technology for wastewater treatment. [ABSTRACT FROM AUTHOR]

The widespread use of bisphenol A (BPA) has resulted in the emergence of new pollutants in various environments, particularly concentrated in sewage sludge. This study investigated the effects of BPA on sludge anaerobic digestion, focusing specifically on the interaction of microbial communities and their metabolic responses. While the influence of BPA on methane accumulation is not significant, BPA still enhanced the conversion of soluble COD, protein, and polysaccharides. BPA also positively influenced the hydrolysis-acidogenesis process, leading to 17% higher concentrations of volatile fatty acids (VFAs). Lower BPA levels (0.2–0.5 mg/kg dw) led to decreased hydrolysis and acidogenesis gene abundance, indicating metabolic inhibition; conversely, higher concentrations (1–5 mg/kg dw) increased gene abundance, signifying metabolic enhancement. Diverse methane metabolism was observed and exhibited alterations under BPA exposure. The presence of BPA impacted both the diversity and composition of microbial populations. Bacteroidetes, Proteobacteria, Firmicutes, and Chloroflexi dominated in BPA-treated groups and varied in abundance among different treatments. Changes of specific genera Sedimentibacter, Fervikobacterium, Blvii28, and Coprothermobacter in response to BPA, affecting hydrolysis and acetogenesis. Archaeal diversity declined while the hydrogenotrophic methanogen Methanospirillum thrived under BPA exposure. BPA exposure enabled microorganisms to form structured community interaction networks and boost their metabolic activities during anaerobic digestion. The study also observed the enrichment of BPA biodegradation pathways at high BPA concentrations, which could interact and overlap to ensure efficient BPA degradation. The study provides insights into the digestion performance and interactions of microbial communities to BPA stress and sheds light on the potential effect of BPA during anaerobic digestion. [ABSTRACT FROM AUTHOR]

Dewatered sludges from twenty-two sewage treatment facilities were characterized to develop the quality control indices in India. This study used fertilizer index (FI) and clean index (CI) as a tool for categorizing sludge utilization into different classes (A, B, C and limited use classes LU-1, LU-2, LU-3) by their fertilizing potential, toxicity level, pathogen presence, and vector attraction reduction criteria. The findings revealed that total P (as P2O5), total N, and K (as K2O) in the sludge samples ranged from 0.9 to 5.7%, 1.2 to 3.8%, and 0.1 to 1.5%, respectively. Moreover, all sludges belong to Class C and lower category due to the presence of toxic metals and pathogens. The helminth eggs were found in the range of 25–1450 Numbers/4gTS in sludge samples. The highest number of helminth eggs of 1450/4 g of TS was found in the fecal sludge. The specific oxygen uptake rate (SOUR) values in the sludge samples varied from 0.3 to 4.9, with a median value of 1.3 and an RSD of 86% is way too high. It indicates that the sludge samples need further treatment to be less attractive as a food source for vectors and rodents. However, sludge samples have fertilizing potential and FI values ranges from 4.1 to 4.9, and CI value ranges from 2.5 to 5.0. It indicates that compost is best in quality and has high-fertilizer potential and low heavy-metal content, which is suitable for high-value crops such as organic farming. Further sludge treatment using typical composting, aerobic or anaerobic digestion, and solar or thermal drying could bring the sludges into the Class A and B categories. [ABSTRACT FROM AUTHOR]

This study investigated the effect of ultrasonic (US) pretreatment at three different contact times (30, 45, and 60 min) with a power of 240 W and frequency of 40 kHz on the fate of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and enteric pathogens during anaerobic digestion (AD) of sludge. By using real time-qPCR, three MGEs (int1, int2, and tnpA) and seven ARGs (sul1, sul2, tetW, tetA, tetO, ermF, and aac(6')-lb) were quantified that have serious human health impacts and represent the most widely used antibiotics (tetracycline, sulfonamide, macrolide, and aminoglycoside). Results indicated that US pretreatment under different contact times improved the removal of ARGs and MGEs. Compared to 30 and 45 min of US pretreatment, 60 min of US pretreatment resulted in a higher reduction of ARGs with total ARG reduction of 41.70 ± 1.13%. Furthermore, the relative abundance of ARGs and MGEs after US pretreatment was reduced more effectively in anaerobic reactors than in a control AD without US pretreatment. The total ARGs and MGEs removal efficiency of control AD was 44.07 ± 0.72% and 63.69 ± 1.43%, and if US pretreatment at different times were applied, the total ARGs and MGEs removal efficiency of the whole pretreatment AD process improved to 59.71 ± 2.76–68.54 ± 1.58% and 69.82 ± 2.15–76.84 ± 0.22%. The highest removal of total ARGs (68.54 ± 1.58%) and MGEs (76.84 ± 0.22%) was achieved after AD with US pretreatment at 45 min. However, US pretreatment and AD with US pretreatment were not effective in inactivation of enteric pathogens (total coliforms and E. coli), suggesting that posttreatment is needed prior to land application of sludge to reduce the level of enteric pathogens. There was no detection of the studied ARGs and MGEs in the enteric pathogens after US pretreatment in subsequent AD. According to this study, long contact times of US pretreatment can mitigate ARGs and MGEs in AD processes, offering valuable insight into improving environmental safety and sustainable waste management. Additionally, the study highlights the need to investigate posttreatment techniques for reducing enteric pathogens in AD effluent, a crucial consideration for agricultural use and environmental protection. [ABSTRACT FROM AUTHOR]

Wind, solar, biomass, tidal, etc. are renewable energy sources obtained from natural sources. Among these resources, biomass can be characterized as a significant energy source. Today, the process of producing biogas from waste and turning it into electrical energy has become more popular. So, clean, sustainable, and eco-friendly energy is generated as the waste is managed and converted into electrical energy. The estimation of the electrical energy that will be produced by wastewater recovery using machine learning (ML) algorithms is vital and has not yet been investigated. Thus, this study fills this gap. In this study, it is aimed to predict the electrical energy recovery potential of the sewage sludge of Kahramanmaraş Advanced Biological Wastewater Treatment Plant (KABWWTP) (Turkey), through incineration and anaerobic digestion. For this aim, 6 distinct ML algorithms including linear regression (LR), extreme gradient boosting (XGB), Gaussian process regression (GPR), ridge regression (RR), Lasso regression (LASReg), and Bayesian ridge regression (BR) have been used. Another novelty in this study is the restricted number of input parameters. That is, the electrical energy (output parameter) is predicted using only 3 distinct input parameters (gas flow, conductivity, and TSS). With a MAPE value of 1.032, the XGB method has been determined as the most successful model. Heat mapping and correlation analyses are used to evaluate the relationship between these parameters. Performance results are presented in tables and graphs. [ABSTRACT FROM AUTHOR]

This study investigated the anaerobic co-digestion (AcoD) of brewery by-products for biomethane and bioenergy recovery, focusing on operational performance evaluation, kinetic analysis, microbial metataxonomic, and metabolic function prediction. The biochemical methane potential was conducted under mesophilic (35 °C) and methanogenic conditions (pH 7.5) by mixing brewery wastewater and sludge from the brewery wastewater treatment plant (1:1, v/v), following the addition (2.5 – 12.5 %, w/v) of brewer's spent grains (BSG). The results demonstrate that the highest methane yield (88.02 mL CH4/g TVS) was obtained with 12.5 % BSG, which was 20.66-fold higher than the control reactor operated with wastewater and sludge (4.26 mL CH4/g TVS). The bioenergy recovery from biomethane could generate electricity (0.348 kWh/kg TVS) and heat (1556 MJ/kg TVS), avoiding greenhouse gas emissions (0.114 kg CO2-eq/kg TVS). The microbial community dynamics revealed a predominance of Halobacterota, Chloroflexi, and Euryarchaeota phylum. The genera Methanosaeta and Methanobacterium, and the Anaerolineaceae family predominated in the AcoD process. The metabolic function prediction showed the presence of genes (K01895, K00193, K00625, and K00925) associated with the direct activation of acetate in the acetoclastic pathway and methane production. Finally, the data obtained provide a perspective on using brewery by-products for bioenergy production in a biorefinery concept, reducing the environmental impacts and contributing to the circular bioeconomy transition of the beer industry. [ABSTRACT FROM AUTHOR]

Diverse feedstocks utilized in anaerobic digestion (AD) pose challenges to enzymatic disintegration because of their nature and complex physical structures and thereby limiting biogas generation. To overcome this, the AD process is often combined with pretreatment techniques, which facilitate the breaking of organic feedstock into smaller molecules and eventually result in enhanced biogas production. Among several techniques, ultrasound-assisted pretreatment of AD feedstock remains promising because it is simple to implement, requires no chemicals, and combines physical (or cavitation) and biological phenomena for degrading AD feed. This review is primarily centered on the applications of ultrasound pretreatment for disintegrating various feedstocks and increasing biogas production during AD. Biogas generation is described in relation to the ultrasound-assisted disintegration of dairy industry waste, hybrid food and municipal wastes, olive mill wastewater, rice straw, tannery wastewater, meat processing sludge, hybrid industrial waste municipal sewage sludge, and lignocellulosic biomass. The disintegration schemes of feedstocks under ultrasound are proposed. COD is solubilized, and suspended solids (SS) are reduced upon ultrasonication. The impact of ultrasonic treatment on biogas production might be amplified if paired with alkali. Furthermore, the techno-economic commercial scopes of ultrasound pretreatment-based biogas production are discussed, and recommendations for future studies are suggested. [ABSTRACT FROM AUTHOR]

Sewage sludge is regarded by wastewater treatment plants as problematic, from a financial and managerial point of view. Thus, a variety of disposal routes are used, but the most popular is methane fermentation. The proportion of macromolecular compounds in sewage sludges varies, and substrates treated in methane fermentation provide different amounts of biogas with various quality and quantity. Depending on the equipment and financial capabilities for methane fermentation, different methods of sewage sludge pretreatment are available. This review presents the challenges associated with the recalcitrant structure of sewage sludge and the presence of process inhibitors. We also examined the diverse methods of sewage sludge pretreatment that increase methane yield. Moreover, in the field of biological sewage sludge treatment, three future study propositions are proposed: improved pretreatment of sewage sludge using biological methods, assess the changes in microbial consortia caused with pretreatment methods, and verification of microbial impact on biomass degradation. [ABSTRACT FROM AUTHOR]

The increasing production of sewage sludge at global level has addressed the search for technical solutions to take advantage from it, reducing the environmental burden originating from its disposal. Anaerobic digestion is a suitable option to handle sewage sludge in accordance with circular economy principles, as it generates a methane-rich biogas and a digestate with potential fertilizing properties. Several techniques have been proposed to enhance anaerobic digestion performances and, among these, the application of static magnetic field (SMF) has recently gained attention. Nonetheless, the effects of high-intensity SMF on the sewage sludge destined to anaerobic digestion and its impact on the anaerobic digestion process have not been evaluated yet. This study aims to determine the effects of a 1.5 T SMF on the chemical composition of sewage sludge as well as on methane generation during anaerobic digestion. The main parameters influencing the SMF (i.e., flow rate, mixing ratio of magnetized to non-magnetized sludge, number of pumping cycles, and total solid content) were varied to evaluate the impact of different exposure conditions on the chemical characteristics and methane potential of sewage sludge. An extensive exposure to the high-intensity SMF applied resulted in a 24% decrease of methane production, reduced the concentration of the monitored ionic species (i.e., NH4+, NO3−, PO43−, SO42− and Mg2+) in the liquid phase of sewage sludge, and promoted the precipitation of compounds with valuable fertilizing properties, e.g., struvite. These outcomes suggest that high-intensity SMF, although negatively influencing methane generation, can promote the precipitation, and possibly the recovery/recycle of valuable compounds from sewage sludge, enhancing its proper management in a circular economy perspective. [ABSTRACT FROM AUTHOR]

In the context of the COVID-19 pandemic, antiviral drugs (AVDs) were heavily excreted into wastewater and subsequently enriched in sewage sludge due to their widespread use. The potential ecological risks of AVDs have attracted increasing attention, but information on the effects of AVDs on sludge anaerobic digestion (AD) is limited. In this study, two typical AVDs (lamivudine and ritonavir) were selected to investigate the responses of AD to AVDs by biochemical methane potential tests. The results indicated that the effects of AVDs on methane production from sludge AD were dose- and type-dependent. The increased ritonavir concentration (0.05–50 mg/kg TS) contributed to an 11.27–49.43% increase in methane production compared with the control. However, methane production was significantly decreased at high lamivudine doses (50 mg/kg TS). Correspondingly, bacteria related to acidification were affected when exposed to lamivudine and ritonavir. Acetoclastic and hydrotropic methanogens were inhibited at a high lamivudine dose, while ritonavir enriched methylotrophic and hydrotropic methanogens. Based on the analysis of intermediate metabolites, the inhibition of lamivudine and the promotion of ritonavir on acidification and methanation were confirmed. In addition, the existence of AVDs could affect sludge properties. Sludge solubilization was inhibited when exposed to lamivudine and enhanced by ritonavir, perhaps caused by their different structures and physicochemical properties. Moreover, lamivudine and ritonavir could be partially degraded by AD, but 50.2–68.8% of AVDs remained in digested sludge, implying environmental risks. [ABSTRACT FROM AUTHOR]

Soil amendments, such as pyrochar (PC) and hydrochar (HC), have the potential to enhance soil properties and crop yields. The objective was to investigate the effects of HC from anaerobic digestion effluent (ADE) of sewage sludge (SS), ADE of manure (M), and PC, as soil amendments. Lettuce seeds were sown and grown in soil amended with chars at rates of 1 to 15 g char/kg soil. Soil properties and plant responses were compared to soil without amendment (control). Soil amended with HC-ADE-SS and HC-ADE-M had higher pH, phosphorus content, and cation exchange capacity than the control. All treatments and the control resulted in 80% + emergence rates. Root dry mass of plants grown on soil with 10 and 15 g/kg was higher than the control. No negative effects were observed in emergence and whole-plant dry biomass, indicating that HC-ADE-SS and HC-ADE-M could be amended without negative impacts on soil properties and plant responses. [ABSTRACT FROM AUTHOR]

The hydrothermal pretreatment (HTP) characteristics and the fate of phosphorus (P) and anaerobic digestion (AD) performance of dewatered sewage sludge (DSS) were investigated at different hydrothermal conditions. The maximum methane yield reached 241 mL CH4/g COD when the hydrothermal conditions were 200 °C-2 h-10% (A4), and the yield was 78.28% higher than that without pretreatment (A0) and 29.62% higher than that of the initial hydrothermal conditions (A1, 140 °C-1 h-5%). Proteins, polysaccharides, and volatile fatty acids (VFAs) were the main hydrothermal products of DSS. 3D-EEM analysis revealed that tyrosine, tryptophan proteins, and fulvic acids decreased after HTP, but the content of humic acid-like substances increased, and this phenomenon was more noticeable after AD. Solid-organic P was converted into liquid-P during the hydrothermal process, and nonapatite inorganic P was converted into organic P during AD. All samples achieved positive energy balance, and the energy balance of A4 was 10.50 kJ/g VS. Microbial analysis showed that the composition of the anaerobic microbial degradation community changed as the sludge organic composition was altered. Results showed that the HTP improved the anaerobic digestion of DSS. [ABSTRACT FROM AUTHOR]

The design of this study was to investigate the solid-aqueous migration and chemical speciation transformation of heavy metals (HMs) in the sewage sludge during the combined process of thermal hydrolysis, anaerobic digestion and heat-drying. The results showed that most of the HMs were still accumulated in the solid phase of various sludge samples after treatment. After thermal hydrolysis, the concentrations of Cr, Cu and Cd increased slightly. All the HMs measured after anaerobic digestion were concentrated obviously. While the concentrations of all HMs decreased slightly after heat-drying. The stability of HMs in the sludge samples was enhanced after treatment. The environmental risks of various HMs were also relieved in the final dried sludge samples. [ABSTRACT FROM AUTHOR]

The aim of the research work was to explain the possibilities of application of waste activated sludge (WAS) pretreatment processes prior to anaerobic digestion (mesophilic fermentation). Hydrodynamic disintegration and freezing/thawing disintegration methods were used. Based on the microbiological and parasitological analyses, a significant decrease in pathogenic bacteria, coliphages, and parasite eggs was observed. The number of bacteria analyzed (Salmonella sp., Escherichia coli, Clostridium perfringens) and coliphages were reduced from 19.3to 42.3% after hydrodynamic cavitation. A similar effect was achieved for destruction by freezing/thawing with dry ice between 7.8 and 14.9%. The effectiveness of parasite eggs reduction (Ascaris sp., Trichuris sp., Toxocara sp.) for these disintegration methods ranged from 10.7 to 29.3%. The highest results were observed for the hybrid disintegration method (hydrodynamic cavitation + dry ice disintegration) caused by a synergistic effect. Salmonella sp. in 1 gd.w. decrease about 69.7%, E. coli by 70.0%, Clostridium perfringens by 38.4%, and coliphages by 48.2%. Disruption of WAS by a hybrid method led to a reduction in the number of helminth eggs Ascaris sp. (63.8%), Trichuris sp. (64.3%), and Toxocara sp. (66.4%). After anaerobic digestion under mesophilic conditions, an additional reduction of analyzed bacterial pathogens and helminth eggs were observed. The introduction of hybrid disintegrated WAS to the fermentation chamber resulted in higher efficiency in decrease (from 1 to 23%) in comparison to the control sample (70%WAS + 30%DS (inoculum-digested sludge)). [ABSTRACT FROM AUTHOR]

The rising occurrence of emerging contaminants in sludges both inhibits the anaerobic digestion of sludges and induces health issues when sludges are recycled in agriculture, calling for methods to remove contaminants. Here we review emerging pollutants in wastewater treatment plants, before and after anaerobic digestion. We present their inhibitory effects and remediation methods to alleviate inhibition. Pharmaceuticals have been detected in about 50% of the sludge samples. Sewage sludge contaminants include 19% of diuretics, 16–21% of lipid-modifying agents, hydrochlorothiazide, diclofenac, furosemide, clarithromycin, atorvastatin, and carbamazepine. Levels of antibiotics, azithromycin, ciprofloxacin, and estrone range from 500 to 600 ng/g in sludges from wastewater treatment plants. Remediation methods comprise electrooxidation, ultrasonication, thermal hydrolysis, ozonation, and bioaugmentation. Fermenting the sludges with acidogenic bacteria reduces the level of emerging pollutants in the supernatant. Nonetheless, liquid digestates still contains emerging pollutants such as sunscreen octocrylene at 147 ug/L and acetaminophen at 58.6 ug/L. As a result, pretreatment of sludge containing emerging pollutants is required. [ABSTRACT FROM AUTHOR]

To tap the organic waste generated onboard cruise ships is a very promising approach to reduce their adverse impact on the maritime environment. Biogas produced by means of onboard anaerobic digestion offers a complementary energy source for ships' operation. This report comprises a detailed presentation of the results gained from comprehensive investigations on the gas yield from onboard substrates such as food waste, sewage sludge and screening solids. Each person onboard generates a total average of about 9 kg of organic waste per day. The performed analyses of substrates and anaerobic digestion tests revealed an accumulated methane yield of around 159 L per person per day. The anaerobic co-digestion of sewage sludge and food waste (50:50 VS) emerged as particularly effective and led to an increased biogas yield by 24%, compared to the mono-fermentation. In the best case, onboard biogas production can provide an energetic output of 82 W/P, on average covering 3.3 to 4.1% of the total energy demand of a cruise ship. [ABSTRACT FROM AUTHOR]

This study aimed at investigating the influence of anaerobic digestion (AD) on the humification of sludge–leachate matrix and the risk of heavy metals (HMs). The characteristics of humic acid (HA) and HM in different digestate (D1–D4) were examined after AD of sewage sludge (SS) with fresh leachate (FL) at varying ratios (i.e., 0, 5%, 15%, 30%). The results showed that C and O constituted the major elements of HA, with the content of 51.73–52.35% and 28.34–28.73%, respectively. Further analysis of the ultraviolet–visible and Fourier transform infrared spectra indicated that AD of co-substrates containing 5% and 15% of FL presented increased humification degree compared to the mono-digestion, whereas co-digestion with 30% of FL showed the opposite results. Moreover, the HM risk assessment suggested that co-digestion decreased the risk level of Cr, Cu, Zn, and Mn in D2 and D3 but increased that of Cr, Ni, Cu, and Mn in D4. From these findings, AD of SS with FL at relatively low proportions (i.e., 5%, 15%) was conducive to enhancing the humification degree and reducing the HM risk. [ABSTRACT FROM AUTHOR]

The positive impact of the thermal hydrolysis process (THP) of sewage sludge on antibiotic resistance genes (ARGs) removal during anaerobic digestion (AD) has been reported in the literature. However, little information is available on how changes in different extracellular polymeric substances (EPS) due to THP can influence ARG propagation during AD. This study focused on systematically correlating EPS components and ARG abundance in AD of sewage sludge pretreated with THP (80 °C, 110 °C, 140 °C, 170 °C). THP under different conditions improved sludge solubilization followed by improved methane yields in the biochemical methane potential (BMP) test. The highest methane yield of 275 ± 11.5 ml CH4/g COD was observed for THP-140 °C, which was 40.5 ± 2.5% higher than the control. Increasing THP operating temperatures showed a non-linear response of ARG propagation in AD due to the rebound effect. The highest ARGs removal in AD was achieved with THP at 140 °C. The multivariate analysis showed that EPS polysaccharides positively correlated with most ARGs and integrons, except for macrolides resistance genes. In contrast, EPS protein was only strongly correlated with β-lactam resistance genes. These results suggest that manipulating THP operating conditions targeting specific EPS components will be critical to effectively mitigating the dissemination of particular ARG types in AD. [ABSTRACT FROM AUTHOR]

This study intends to examine the effects of NiO, CoO and Fe3O4 nanoparticles (NPs) (experiment A) and their combinations (experiment B) on the anaerobic digestion (AD) of mixture of primary sludge and waste activated sludge of municipal wastewater treatment plant. The effects of NPs addition, each at three different concentrations (1, 10 and 100 mg/l) and their combinations were evaluated by running laboratory-scale batch reactors and measuring biogas production, methane and hydrogen sulfide (H2S) content of biogas and organic matter reduction. The results indicated that the efficiency of anaerobic digesters exposed to the NPs was dosage-dependent. In experiment A, Addition of 1 mg/l NiO, 1 mg/l CoO, 10 and 100 mg/l Fe3O4 NPs increased biogas yield by 26.94%, 21.12%, 23.41% and 14.29% and methane yield by 39.04%, 30.37%, 35.59% and 22.65% in comparison with the control respectively. While 100 mg/l NiO and CoO NPs decreased biogas and methane yield significantly compared to the control. Furthermore 10 mg/l NiO and CoO and 1 mg/l Fe3O4 NPs didn't affect AD process significantly. In experiment B all the combinations led to enhancement of biogas and methane production except combination of 100 mg/l of the three NPs and the highest increase including 43.90% for biogas and 62.85% for methane belonged to the combination of the optimum dosages of NPs in experiment A. H2S concentration in biogas was not affected by low dosages of NPs (1 and 10 mg/l), while high dosages (100 mg/l) could reduce it 13.36–52.57% compared to the control. [ABSTRACT FROM AUTHOR]

In anaerobic digestion (AD) system, the C/N ratio can affect utilization efficiency of organic matter and microbial community structure, thereby influencing methane production. This study investigated that the C/N ratio in AD of sewage sludge (SS) suitably enhanced by adding food waste (FW) to improve methane production efficiency. The effects of different C/N ratios (9, 11, 13, and 15) on dry thermophilic anaerobic co-digestion of SS and FW and the microbial community structure were researched. The cumulative methane production at C/N ratio of 11 reached 165.68 ± 11.88 mL/g VSadded which increased by 1.23 times compared with the mono-digestion of SS; and the cumulative methane production increased by 8.15 – 63.55% at C/N ratios of 9, 13, and 15. The methanogenic pathway changed from acetoclastic methanogenesis process to hydrogenotrophic methanogenesis process with the increasing of C/N ratio. Redundancy analysis explained that the C/N ratio had obvious effects on the variation of the microbial phylum and genus, which contributed 21.63% and 29.27%, respectively. The C/N ratio of 11 enriched the dominant bacterial phyla (Firmicutes and Thermotogae) and increased the methanogens diversity at genus level. This research found an approach that could improve methane production in the lower C/N range. [ABSTRACT FROM AUTHOR]

The purpose of this research is to experimentally evaluate the anaerobic co-digestion in the city of Guaranda of slaughterhouse residues (RM) with straw residues from agriculture, such as amaranth residues (AM), quinoa residues (QU) and residues of wheat (TR), to reduce slaughterhouse discharges and prevent contamination of the city. The study was carried out on a laboratory scale in 311-ml biodigesters under mesophilic conditions of 37 °C. In addition, sewage sludge was used as inoculum with two relationships between substrate and inoculum (SIR 1:1 and SIR 1:2). The design was completed using three relationships between substrate (RM) and co-substrate (AM, QU and TR): 25:75, 50:50 and 75:25. Anaerobic co-digestion resulted in methane yields of 407 ml CH4/g VS, with a methane content in the biogas of 77% for the mixture of RM and QU (RM-QU (25:75)). The increase in inoculum in the mixtures composed of RM and QU increased the biodegradability between 17 and 22%. However, in the mixtures of slaughterhouse waste and amaranth (RM-AM (25:75)), a further increase in inoculum reduced biodegradability by 5%. The results revealed that there is a greater synergy between the RM and QU as the percentage of QU in the mixture is increased. This meant that the co-digestion of the RM with the QU accelerates the biodegradability of the mixture, increasing the production of biogas. [ABSTRACT FROM AUTHOR]

As the transition to renewable energy systems is accelerating, anaerobic digestion, which is one of the methods of energy recovery from organic substrates, continues to be studied with great interest by scientists. Anaerobic digestion research and applications are mostly carried out with biochemical methane potential (BMP) tests to decide the methane potency of sewage sludge, energy crops, and organic wastes. Unlike long and costly continually reactor experiments, actually, BMP tests are cumulative and can be performed with a relatively low investment of materials, technical labor, and also time. For the BMP to give accurate results, the effect of all the tools and technical parameters used in the implementation of the BMP should be well understood. In such situations, it is very useful to apply fuzzy logic methods in multi-criteria decision-making stages when more than one parameter changes at the same time. Therefore, in this study, fifteen parameters were determined and analyzed with the fuzzy DEMATEL (decision-making trial and evaluation laboratory) method to understand the cause-effect mechanism of the technical parameters of BMP. As a result of these analyses, it was seen that the material of the reactor (ri-cj value of 0.55), the particle size (ri-cj value of 0.43), the effect of mixing (ri-cj value of 0.32), and the amount of the total solids (TSA) (ri-cj value of 0.25) had a high effect in the causal sense. It was observed that the first-order parameter (material of reactor) was 27% stronger than the second-order (the particle size) parameter in terms of causality. Likewise, the second-order parameter is 34% stronger than the third-order parameter (the effect of mixing) in terms of cause effect. In addition, it was understood that the most effective parameters in the mechanism of effect were pH (ri + cj value of 3.41), C/N ratio (ri + cj value of 3.26), and temperature (ri + cj value of 3.07), respectively. Besides, high methane yield is seen in mesophilic conditions. The average cumulative biogas yield of the reactor is 282.1 NmL/g VS. The highest percentage of methane formed in the biogas occurred on the 21st day. Briefly, this study is important to provide a facilitating way for researchers working on BMP to understand the cause-effect mechanism of system technical requirements. [ABSTRACT FROM AUTHOR]

This study is aimed at evaluating through Life Cycle Assessment (LCA) the environmental performances of an integrated system of an existing Water Resources Recovery Facility (WRRF) and a hypothetical hydrothermal carbonization (HTC) plant applied to the generated sewage sludge (SS). Beside the valorisation of the solid product (hydrochar, HC) as a fuel substituting lignite, the possibility to valorize also the liquid fraction (process water, PW) derived by the HTC, by anaerobic digestion to produce biogas, is here proposed and analysed. Additionally, phosphorus recovery from HC, prior its use, by acid leaching with nitric acid is also suggested and evaluated. Thus, four integrated scenarios, based on SS carbonization, are proposed and compared with the current SS treatment, based on composting outside of the WRRF (Benchmark scenario). The proposed scenarios, based on HTC, show improved performances with respect to the benchmark one, for thirteen of sixteen considered impact indicators. For the Climate Change (CC) indicator, the two HTC scenarios are able to reduce the impacts up to – 98%, with respect to the Benchmark. Further, the introduction of anaerobic digestion of PW proves to reduce impacts more than other configurations in eleven on sixteen impact categories. On the contrary, the introduction of phosphorus recovery process negatively affects the values for most of indicators. Thus, possible solutions to improve the integration of this process are outlined (e.g., the use of sulfuric acid instead of nitric one, or the application of a different ratio between solid and acidified solution during acid leaching of HC to recover phosphorus). [ABSTRACT FROM AUTHOR]

This study assessed the biogas and methane production potential of wastewater sludge generated from the beverage industry. The optimization of the biogas production potential of a single fed-batch anaerobic digester was operated at different temperatures (25, 35, and 45 ℃), pH (5.5, 6.5, 7.5, 8.5, and 9.5), and organic feeding ratio (1:3, 1:4, 1:5, and 1:6) with a hydraulic retention time of 30 days. The methane and biogas productivity of beverage wastewater sludge in terms of volatile solid (VS) and volume was determined. The maximum production of biogas (15.4 m3/g VS, 9.3 m3) and methane content (6.3 m3/g VS, 3.8 m3) were obtained in terms of VS and volume at 8.5, 35 ℃, 1:3 of optimal pH, temperature, and organic loading ratio, respectively. Furthermore, the maximum methane content (7.4 m3/g VS, 4.4 m3) and biogas production potential (17.9 m3/g VS, 10.8 m3) were achieved per day at room temperature. The total biogas and methane at 35 ℃ (30 days) are 44.3 and 10.8 m3/g VS, respectively, while at 25 ℃ (48 days) increased to 67.3 and 16.1 m3/g VS, respectively. Furthermore, the electricity-generating potential of biogas produced at room temperature (22.1 kWh at 24 days) and optimum temperature (18.9 kWh) at 40 days was estimated. The model simulated optimal HRT (25 days) in terms of biogas and methane production at optimum temperature was in good agreement with the experimental results. Thus, we can conclude that the beverage industrial wastewater sludge has a huge potential for biogas production and electrification. [ABSTRACT FROM AUTHOR]

Alkaline pretreatment (APT) is the promising disintegration pretreatment for the anaerobic digestion (AD) of sewage sludge (SS) to improve digestion efficiency and methane yields. In this study, the heavy metals (HMs) were observed to be leached from SS in the APT process, which could lower the HMs secondary pollution risk of the residual biosolids after AD in land application. The sequential chemical extraction (SCE) experiment was performed to determine the variation in HMs' distribution prior to and after the APT. The alkaline extracts were characterized in order to elucidate the HMs' release mechanism. The APT could cause significant release of Zn and Cu with a maximum release efficiency of 96.6% ± 4.6% and 62.7% ± 8.4% under the condition of 1.5 mol/L NaOH and 25 ℃, respectively. The release efficiency of Zn and Cu was reduced by 63.0% and 21.7%, respectively, due to the extra addition of 0.25 mol/L NaCl at a NaOH concentration of 1.25 mol/L in the APT process. The release of Zn and Cu may be attributed to a complex process including disruption of microbial cells in SS, solubilization of organic matters bounded with metals, and the chemical leaching reaction of minerals. This study demonstrates the possibility to remove the Zn and Cu from the SS in the APT process before the AD disposal. [ABSTRACT FROM AUTHOR]

This study aims to enhance the performance of a low-buffered anaerobic co-digestion of food waste and sewage sludge using an alkaline-based additive (waste seashell). Eighteen lab-scaled reactors were performed to evaluate the synergistic effects of waste seashell on methane production at different organic load. The addition of waste seashell showed significant synergistic effects with organic load on the anaerobic co-digestion performance in reducing the inhibitory level of volatile fatty acids and ammonia by (i) increasing buffer capacity of the systems, (ii) providing various slats, and (iii) changing the methanogenic pathway for achieving higher methane production yield. The addition of waste seashell with the concentration of 8 g/L, 20 g/L, and 26 g/L declined the propionic accumulation by 55%, 54%, and 49%, respectively, compared to their peer reactor at the same organic load. The utilization of waste seashell at 26 g/L increased the methane yield up to 219 mLCH4/gVS at an organic load of 15.6 gVS/L, represented 6.44, and 7.8-times higher methane yield and organic load increment, respectively, than that of conventional anaerobic co-digestion. However, at further increase of waste seashell and organic load, the anaerobic co-digestion showed low methane generation of 89.3 mL CH4/gVS due to the inhibitory impacts of calcium concentration on the biological process. [ABSTRACT FROM AUTHOR]

Septage, which is made up of liquid and solid materials pumped from septic tanks, can be a potential co-digestion resource for sewage sludge. This study was conducted to evaluate possibility of co-digestion of sewage sludge and septage. Biochemical methane potential tests were performed using primary sludge, secondary sludge and septage. The mixing ratio of the septage ranged from 30% to 62% (by volatile solid wt.) based on the typical ratio of the septage transported to municipal WWTP plants and the sewage sludge generated in the plants. The co-digestion of sewage sludge and septage showed synergistic effects on the methane potential due to the enhanced C/N ratio. The observed methane potential of co-digestion substrate was 8–16% higher than the predicted value based on weighted average of mono-digestion substrate's methane potentials. The maximum synergistic effect on methane potential was observed when 42% (by volatile solid wt.) of the septage was co-digested. In conclusion, the septage can be a suitable resource for co-digestion with sewage sludge. [ABSTRACT FROM AUTHOR]

Purpose: Following anaerobic co-digestion of various types of organic waste in wastewater treatment plants, the digestate can be directly used as fertilizer, particularly at small facilities. Cultivation of photosynthetic bacteria (PSB) using this digestate is promising for improving fertilizer quality. Therefore, in this study, we evaluated the growth characteristics of PSB in sewage samples. Methods: Laboratory-scale PSB cultivation experiments were performed using culture medium or sewage samples. Carotenoids, pufM copy numbers, and microbial structures were analyzed. Results: Rhodospirillaceae grew in the filtrate of digested sludge samples, whereas it did not grow in the unfiltered digested sludge samples. Addition of acetate at 400 mg/L per day promoted the growth of PSB. Comparison of the carotenoids, pufM copy numbers, and microbial structures in the culture liquids showed that carotenoid measurements can be performed to monitor PSB growth. The specific growth rate of PSB in the digested sludge samples was approximately 0.3 day−1 when the suspended solid concentration was < 1 g/L but decreased to 0.2 day−1 when this concentration was 10 g/L. Conclusion: PSB can be cultivated in sewage samples containing other types of bacteria, particularly at low suspended solid concentrations. This technology can enhance fertilizer utilization, contributing to regional recirculation of energy and resources from small-scale waste and wastewater treatment systems. [ABSTRACT FROM AUTHOR]

The objective of this research was to evaluate anaerobic co-digestion of guinea pig manure (GP) with Andean agricultural residues such as amaranth (AM), quinoa (QU) and wheat (TR) in batch biodigesters under mesophilic conditions (37 0C) for 40 days. As microbial inoculum, sewage treatment sludge was used in two inoculum/substrate ratios (ISR of 1 and 2). In terms of methane production, the best results occurred in treatments containing AM and QU as co-substrate and an ISR of 2. Thus, the highest methane production yield in the GP:AM biodigesters (25:75) and GP:QU (25:75) with 341.86 mlCH4/g VS added and 341.05 mlCH4/g VS added, respectively. On the other hand, the results showed that methane production with an ISR of 2 generated higher yields for guinea pig waste and the methane fraction of the biogas generated was in a range from 57 to 69%. Methane production kinetics from these raw materials was studied using five kinetic models: modified Gompertz, logistic equation, transfer, cone and Richards. The cone model adjusted best to the experimental values ​​with those observed with r2 of 0.999 and RMSE of 1.16 mlCH4/g VS added. Finally, the highest biodegradability (experimental yield/theoretical yield) was obtained in the GP-AM biodigesters (25:75) with 67.92%. [ABSTRACT FROM AUTHOR]

Plastics fragmentation into smaller debris, namely, micro- and nano-plastics (MPs and NPs), is a matter of global concern because of their wide distribution in terrestrial and marine environments. The latest research has focused mainly on aquatic ecosystems, and fragmentation of bioplastics into micro- and nano-particles (MBPs and NBPs) is not considered. The distribution, concentration, fate and major source of MPs, NPS, MBPs and NBPs in agroecosystems still need to be understood. The use of composts and sewage sludge from the organic fraction of municipal solid waste (OFMSW) treatment plants as soil amendments is likely to represent a major input of these debris. The present review provides insights into the current evidence of pollution from micro- and nano-particles of both fossil- and bio-origin in the OFMSW treatment, and aims at evaluating if the recycling of organic waste and its application as a soil fertilizer outweigh the risk of pollution in terrestrial environments. Huge unpredictability exists due to the limited numbers of data on their quantification in each source of possible solution. Indeed, the major hurdles arise from the difficult to quantify the micro-, especially the nano-, particles and subsequently assess the concentrations in the environments, as well as bioaccumulation risks, and toxic effects on organisms. [ABSTRACT FROM AUTHOR]

Biocidal agents (BAs) are widely used in environmentally safe toilet complexes (ESTC) of passenger railcars to suppress microbial activity in fecal sludge (FS). The subsequent disposal of BA-containing FS at municipal sewage treatment facilities adversely affects their work due to the loss of activated sludge. The antimicrobial properties of BAs based on quaternary ammonium compounds (QAC) and polyhexamethylene guanidine (PHMG), as well as methods for its neutralization, have been studied. It was confirmed that BAs based on QAC and PHMG have an antimicrobial effect on various groups of bacteria, reducing their number by 10–100 or more times. It was found that FS contains two groups of microorganisms with different sensitivities to BA. Methods for the deactivation of BA antimicrobial action in FS were tested with (1) a deactivating agent; (2) incubation with thermophilically digested wastewater sludge as a source of the methanogenic microbial community; and (3) chemical deactivation via acidification or alkalization. The highest efficiency was obtained from thermophilic anaerobic digestion with the pretreatment of FS with a strong acid. [ABSTRACT FROM AUTHOR]

The power system needs flexible electricity generators. Whilst electricity generation from anaerobic digestion (AD) of sewage sludge has traditionally been baseload, transforming the generation capacity into a modern flexible operator is an opportunity to further valorise the resource. This work aims to demonstrate that AD of sewage sludge can support flexible generation and be operated dynamically in a relevant operational environment, to promote full scale implementation. A demonstration scale plant (20 m3 conventional AD reactors) was used to test several feeding regimes designed to return a biogas production rate that matches the demand. Two demand profiles are defined, either by common corporate power purchase agreements or by the main balancing mechanism used by the grid operator in UK. Demand-driven biogas production is demonstrated in this relevant operational environment, and the flexibilisation performance is positive in all scenarios. The value of the biogas increases by up to 2%, which outperforms the results obtained at pilot scale. Additionally, an increase in biogas yield is observed. Whilst transitional imbalances are recorded, they last for few hours and the overall stability is not affected. In conclusion, these trials demonstrate demand-driven biogas production is a feasible operational solution and full-scale implementation is possible. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion of sludge from recycled pulp and paper industry (RPPS) with vinasse effluent from alcohol distilleries (VW) was performed under mesophilic conditions (37 °C) at laboratory scale, using one-liter continuous stirred tank reactors (CSTRs). The physicochemical parameters were monitored during the process. The average pH and alkalinity were 7.7 and 1000 mg CaCO3 Kg−1, respectively, indicating that the process is working well without the risk of acidification. The methane yield and biodegradability of this mixture were determined. The methane yield was about 112 (NmL CH4 g−1 VS added) and biodegradability reached 73%. Nevertheless, in monodigestion of RPPS, the methane yield was 94 (NmL CH4 g−1 VS added) and biodegradability 65%. The anaerobic co-digestion of (RPPS) with (VW) at a proportion of (70:30) improved methane production by 16% and biodegradability by 11%. Bioenergy recovery from industrial (RPPS) is promoted by co-digestion with (VW), and the removal efficiency of 73% indicates the performance of the process adopted. A kinetic study was performed using five models Richards, modified Gompertz, Logistic, Cone, and first order. The results show that Richards' was the most appropriate model for adjusting methane production from (RPPS) and (VW) co-digestion. [ABSTRACT FROM AUTHOR]

This study examines whether vapothermal pre-treatment is technically feasible and brings economic advantages for a subsequent anaerobic co-fermentation of reeds together with sewage sludge. This is illustrated by the example of remote sites located close to constructed wetlands in the Persian Gulf states. Thus, eight different biogas plant configurations with an installed electric power between 75 and 450 kW, each with and without vapothermal pre-treatment, are investigated in detail related to technical and economic figures. Within the technical assessment, suitable plant components are chosen and overall plant layouts are designed and dimensioned. Furthermore, the requirements on the substrate by means of quantity, pre-treatment and storage capacities are investigated. Based on this, an economic evaluation following the annuity method is performed in order to calculate the respective electricity production costs. The results show that the thermal energy required for vapothermal pre-treatment can be obtained completely from the residual heat of the combined heat and power unit used in each case. Additionally, the specific electricity production costs can be reduced by a vapothermal pre-treatment up to 7 % related to the systems without pre-treatment. Furthermore, a comparison shows that vapothermal pre-treatment can compete with other pre-treatment methods such as steam explosion and hydrothermal pre-treatment for plants with higher installed electric capacity. In addition, it is shown that the considered cases can compete with the production of electricity using diesel as a fuel at a fuel equivalent price of 1.00 € [ABSTRACT FROM AUTHOR]

Treatment and recycling of organic waste play important roles in an integrated waste management system by producing a stabilized material that can be utilized as a source of nutrients and as a soil conditioner. In this study, the viability of composting for the recycling of sewage sludge and also the possible effects of pretreatment under various conditions on the quality of the end-product were examined. Waste sewage sludge was obtained from a wastewater treatment plant in Hamedan, Iran, and was subjected to aerobic and anaerobic digestions. After analyzing the physicochemical properties of the digest, both treated sludges were composted. A third reactor was also set as control by direct composting of sewage sludge without pretreatment. The composting process was controlled by the measurement of the physicochemical properties of the substrate during and at the end of the process. The results of the analyses showed a substantial decrease in the C/N ratio, pH, volatile solids (VSS), total organic carbon, as well as pathogenic populations; however, a significant increase was observed in the ash and nitrogen contents in the compost obtained after anaerobic digestion. Accordingly, it was decided that the compost obtained, especially after anaerobic digestion, showed adequate degrees of maturity and stability and reflected characteristics, which based on national and international standards made it suitable for agricultural use. [ABSTRACT FROM AUTHOR]

The increasing demand for a Thermal Hydrolysis Process (THP) to pretreat municipal sludge upstream Anaerobic Digestion (AD) opens the opportunity to further develop and optimise this technology. The optimal THP temperature remains unclear due to the production of refractory compounds at high temperature. A compilation of literature data was conducted to investigate the existence of a temperature sweet spot for the THP applied to municipal sludge. All related reports (n = 43) were included. The THP temperature range impact was assessed in the range of 100 °C–200 °C on four AD and dewatering performance indicators (CH4 production, Volatile Solid Reduction (VSR), Dewaterability (DW) and filtrate quality). Other parameters potentially affecting the performance indicators were also considered. These parameters include the type of sewage sludge and operational conditions related to THP and AD. The impact of all parameters on performance indicators was evaluated with a Kruskal–Wallis statistical test. For THP temperature optimisation, a pairwise comparison, using a Wilcoxon test, was made. A temperature optimum in the [140–160] °C range was proposed. It seemed to minimize the production of refractory compounds, while maximising AD and dewatering performances. It is noteworthy that above 160 °C, the concentration in refractory compounds and soluble COD increases sharply, thus leading to a potential deterioration of WWTP effluent quality. Optimal THP temperature range for an optimal outcome on both sludge and wastewater treatment lines. [ABSTRACT FROM AUTHOR]

The coupling of biological and thermal technologies allows for the complete conversion of wastes into energy and biochar eliminating the problem of sludge disposal. The valorisation of fatty residues as co-substrate in a mesophilic digester of a wastewater treatment plant was studied considering an integrated approach of co-digestion and pyrolysis. Four digested samples obtained from co-digestion of sewage sludge and butcher's fat waste were studied by thermogravimetric analysis. The activation energy corresponding to the sludge pyrolysis was calculated by a non-isothermal kinetic. Arrhenius activation energy was lower for the pyrolysis of a digested grease sample (92 kJ mol−1 obtained by OFW and 86 kJ mol−1 obtained by Vyazovkin) than for the pyrolysis of sewage sludge and its blends (164–190 kJ mol−1 obtained by OFW and 162–190 kJ mol−1 obtained by Vyazovkin). The analysis of the integrated approach of anaerobic co-digestion and pyrolysis of digestates demonstrated that the addition of 3% (w/v) of fat to the feeding sludge results in a 25% increase in the electricity obtained from biogas (if a combined heat and power unit is considered for biogas valorisation) and increasing the fat content to 15% allows for covering all thermal needs for drying of digestate and more than doubles (2.4 times) the electricity production when the scenario of digestion and pyrolysis is contemplated. [ABSTRACT FROM AUTHOR]

Fishery byproducts were acidogenically fermented with agricultural wastes (corncob, cabbage waste, and fruit peel), and fishery acidogenic fermentation broth (FFB) was used to observe sludge reduction and biogas production in anaerobic co-digestion. The experiment was conducted using a batch test for 30 days in mesophilic conditions. Samples with FFB showed a short response delay time of 1.50–3.06 (day), and total solid (TS) and volatile solid (VS) removal efficiencies of 23–43% and 20–30%, respectively, which were higher than those without FFB. In addition, the process produced 2.63–3.86 times more biogas with a methane content of over 70%. These results indicate that FFB improves the biodegradability of sewage sludge and that microbial communities were activated in a short time during the anaerobic co-digestion process. In particular, the highest TS and VS removal efficiency, biogas production, and high methane content were observed in FFB with corncobs. This suggests that nutrients such as sugar and minerals in corncobs may have positively affected the activity of methane-producing archaea. The anaerobic co-digestion process, which combines FFB and sewage sludge, enhanced the treatment efficiency of sludge and has an advantage of energy recovery. [ABSTRACT FROM AUTHOR]

The requirements for enhanced technologies, such as pyrolysis and anaerobic digestion, are crucial to improve food waste and sewage sludge and address the difficulty in disposing of hardly biodegradable residues. The pyrolysis process was applied to two waste streams, namely hardly biodegradable residues and sewage sludge, at 500 °C with a heating rate of 25 °C min−1 to obtain hardly biodegradable residues biochar (DBR-Char) and sewage sludge biochar (SS-Char). The two biochars were then used as additives during anaerobic digestion of food waste treatment to enhance biogas production and reactor robustness to achieve average methane contents in biogas up to 75% compared with the control. Biochar addition also improved process stability, with the Methanosaeta/Methanothrix 99.55% in the CK1 (reactor with inoculum, food waste, and DBR-Char) and 98.13% in the CK2 (reactor with inoculum, food waste, and SS-Char) as the dominant genera among the anaerobic consortia. This study averted the hardly biodegradable residues and sewage sludge disposal challenges via pyrolysis and offered biochar utilization to promote reactor stability and biogas production in food waste fermentation. [ABSTRACT FROM AUTHOR]

Direct landspreading of anaerobic digestates is the most common digestate management strategy. Nevertheless, digestate post-treatment can be unavoidable, especially for environmental services providers operating large-scale anaerobic digestion (AD) facilities. This review aims to assess the technical feasibility of achieving value-added products from digestates from urban and/or centralized AD plants (UC-AD). An exhaustive effort was dedicated to identifying and clarifying the available processing technologies and specific issues that can be related to UC-AD digestates. The valorization options were classified according to the final product destination. The result is a useful information source for assessing digestate valorization pathway given a local market and context. Agriculture was the first destination to be considered, as it allows a more direct closing of nutrient and carbon cycles. Several processes exist either for concentrating desirable characteristics of digestates, enhancing organic matter stability or producing pure and reformulated fertilizers. Thermal conversion processes are either under development or full-scale demonstration. They allow to valorize the solids through the production of biofuels and/or biochar and in the coming future, to start a whole biorefinery system. Similarly, biomass harvesting processes such as microalgae are under upscaling, enabling to valorize the nutrients of the digestate liquid phase while producing renewable biomass from sunlight. Several value-added products were already obtained in laboratory to pilot conditions from UC-AD digestates, for example, biopesticides, biosurfactants and composite materials. Adding to technical challenges, the quality variation of digestates, regulation barriers, public acceptance and the difficult access to new markets are among the main obstacles to UC-AD digestates valorization into value-added products. [ABSTRACT FROM AUTHOR]

Use of anaerobic sludge digester is a common practice around the world for solids digestion and methane generation from municipal sewage sludge. Understanding microbial community structure is vital to get better insight into the anaerobic digestion process and to gain better process control. However, selective analysis of viable microorganisms is limited by DNA-based assays. In this study, propidium monoazide (PMA)-PCR with 16S rRNA gene sequencing analysis was used to distinguish live and dead microorganisms based on cell membrane integrity. Microbial community structures of PMA-treated and PMA-untreated anaerobic digester sludge samples were compared. Quantitative PCR revealed that 5–30% of the rRNA genes were derived from inactive or dead cells in anaerobic sludge digesters. This caused a significant decrease in the numbers of operational taxonomic units and Chao1 and Shannon indices compared with that of the PMA-untreated sludge. Microbial community analysis showed that majority of the viable microbiome consisted of Euryarchaeota, Bacteroidetes, Deltaproteobacteria, Chloroflexi, Firmicutes, WWE1, Spirochaetes, Synergistetes, and Caldiserica. On the other hand, after the PMA treatment, numbers of Alphaproteobacteria and Betaproteobacteria declined. These were considered residual microbial members. The network analysis also revealed a relationship among the OTUs belonging to WWE1 and Bacteroidales. PMA-PCR-based 16S rRNA gene sequencing analysis is an effective tool for uncovering viable microbiome in complex environmental samples. [ABSTRACT FROM AUTHOR]

Hydrochars produced from hydrothermal carbonisation of faecal simulant (FS) at 180 °C for 30 min and sewage sludge treated via CAMBI process at 165 °C for 30 min were used for adsorption of organic pollutants in effluent from an anaerobic digester (AD). The adsorption potential of the hydrochars investigated was compared with that of a commercial powdered activated carbon (PAC). It was found that the CAMBI and FS hydrochars were effective only after chemical activation. KOH activation increased chemical oxygen demand (COD) removal from 33.0 to 59.6% and 75.2% for FS and CAMBI, respectively. Extra activation with HCl improved the adsorption efficiency of FS, increasing COD removal to 79.3%, but not for the CAMBI hydrochar even though its surface area was increased. Acidic pH aided organics removal for both hydrochars. PAC adsorption capacity was the highest (> 90%), and this was not affected by pH. All the adsorbents could successfully remove the organics in a very short time as 30 min. The optimum dosage of the hydrochars to reach a high uptake of organics was 30.0 g/L. The adsorption reaction followed a pseudo-second-order kinetic model for all the hydrochars. The adsorption onto the hydrochars correlated well with Temkin isotherm model and followed a type II and IV isotherm type, except PAC which was described by the Langmuir isotherm with a high adsorption capacity of 400.0 mg/g. The study demonstrated that hydrochars of FS and CAMBI activated with KOH are efficient and sustainable adsorbents for the removal of organics from AD effluent. [ABSTRACT FROM AUTHOR]

The effect of Aso volcanic limonite was explored in anaerobic digestion using waste sewage sludge (WSS). In this study, methane and hydrogen sulfide were remarkably inhibited when Aso limonite was mixed with WSS as well as a significant reduction of ammonia. Although pH was lowered after adding Aso limonite, methane was still inhibited in neutralized pH condition at 7.0. Hydrolysis stage was not influenced by Aso limonite as supported by the result that a high protease activity was still detected in the presence of the material. However, acidogenesis stage was affected by Aso limonite as indicated by the different productions of organic acids. Acetic acid, was accumulated in the presence of Aso limonite due to the inhibition of methane production, except in the highest concentration of Aso limonite which the production of acetate may be inhibited. Besides, the production of propionate and butyrate reduced in accordance to the increased concentration of Aso limonite. In addition, Archaeal activity (methanogens) in WSS with Aso limonite was low in agreement with the low methane production. Thus, these results indicate that Aso limonite influences the acidogenesis and methanogenesis processes, by which the productions of methane and ammonia were inhibited. On the other hand, in the contactless of Aso limonite during the anaerobic digestion of WSS (Aso limonite was placed in the area of headspace in the vial), Aso limonite had the adsorptive ability for hydrogen sulfide from WSS, but not for methane. This contactless system of Aso limonite may be a practical means to remove hydrogen sulfide without inhibiting methane production as an important bioenergy source. [ABSTRACT FROM AUTHOR]

The wastewater sludge stabilization by anaerobic digestion is sufficient to reduce the organic content of the sludge, so that it can be safely disposed of without causing odor problems and pathogen contamination, while producing energy in form of biogas. Efficiency of anaerobic digestion in terms of biogas/methane production and organic removal can be enhanced by pretreating the sludge prior to anaerobic digestion. This study compares the effects of microwave (MW), combined hydrogen peroxide/microwave (H2O2/MW), and combined hydrogen peroxide/heat (H2O2/heat) pre-treatments on the digestion efficiency and methane production potential of wastewater sludges. The methane productions were also estimated by using modified Gompertz equation through the calculation of the kinetic parameters. The pre-treatments applied to sludge samples speeded up the hydrolysis step and improved the biodegradability of the organics by increasing their solubility. Application of MW, combined H2O2/MW, and combined H2O2/heat pre-treatments increased the methane yields by 64%, 38%, and 19%. The modified Gompertz model fitted well to the experimental results (R2 of 0.999, 0.983, 0.997, and 0.998 for control, MW, H2O2/MW, and H2O2/heat, respectively). [ABSTRACT FROM AUTHOR]

Sludge anaerobic digestion is a wastewater treatment plant crucial point for the impact mitigation on environment. Such process reduces the disposable sludge volume and pollution potential, generating biogas. Despite its crucial role, sludge digestion microbiology is not clearly understood. In this work, the characterization of the microbiota into digesters fed by primary and secondary sludges was performed. Two sampling sessions were conducted and more than 120 samples were extracted and analyzed by PCR-DGGE. Cluster analysis on DGGE profiles suggested the presence of diverse communities associated with different sludge characteristics (ANOVA, p < 0.01) and Shannon's diversity index showed higher evenness into the secondary one. Moreover, the comparison of community structure based on DNA and bacterial rRNA genes highlighted the presence of unexpressed bacterial genome, leading to a potential functionality overestimation using a DNA-based approach (Shannon index mean − 16%, t test, p < 0.05). This approach has proven to be suitable for a first useful assessment of microbial community dynamics during the anaerobic digestion process. [ABSTRACT FROM AUTHOR]

The presented study summarizes laboratory tests results to define the inhibition effect of selected pharmaceuticals on biogas production under anaerobic digestion conditions. Two sets of inhibition tests were realized: (i) with real anaerobic sludge (from municipal wastewater treatment plant (WWTP) where sludge is present and includes a wide spectrum of pharmaceuticals over a long period) and (ii) with laboratory sludge (sludge without pharmaceuticals). Methanogenic tests lasting 20 days were performed with three analgesics (diclofenac, ibuprofen, and tramadol), two antibiotics (amoxicillin and ciprofloxacin), β-blocker (atenolol), three psychoactive compounds (carbamazepine, caffeine, and cotinine), and a mixture of these compounds. All tests were performed with two concentrations of pharmaceuticals (10 μg/L and 500 μg/L). Results of the methanogenic tests showed the different behaviors of the investigated sludges in the presence of individual pharmaceuticals. Stimulation of anaerobic digestion was mostly detected for laboratory (unadapted) sludge (e.g., the addition of ibuprofen at a concentration of 500 μg/L increased biogas production by 61%). On the other hand, pharmaceuticals inhibited biogas production for real sludge (e.g., the addition of ciprofloxacin 500 μg/L decreased biogas production by 52%). [ABSTRACT FROM AUTHOR]

This study was conducted to demonstrate enhanced phosphate release in mesophilic anaerobic digestion of sewage sludge in relation to sulfate reduction. Sulfate was added as sulfuric acid to influent sewage sludge at the three levels, 0, 461 and 922 mg-S/L (0, 14.4 and 28.8 mmol/L, respectively). The sewage sludge used was one without artificial modification for 70 days, and then chemically pre-precipitated one artificially prepared by adding 4 g/L (17.9 mmol/L) of FePO4·4H2O for 77 days (influent total phosphorus of 302 and 855 mg/L, respectively). The anaerobic digesters were operated at 35 °C and 20 days hydraulic retention time. The phosphate concentration in digested sludge at the final stage reached 7.3, 89 and 112 mg/L for the sewage sludge without artificial modification, and 114, 258 and 461 mg/L for the chemically pre-precipitated sewage sludge, at the three levels of sulfate addition respectively. The phosphate concentration was almost proportional to the sulfate concentration added, indicating that the introduction of sulfate to anaerobic digestion can enhance phosphate release. The enhanced phosphate release was attributable to sulfate reduction to sulfide and subsequent release of phosphate from ferric or ferrous phosphate. In addition to the above mechanism involving sulfate reduction, phosphate release was estimated to occur from ferric phosphate along with iron reduction. A possible disadvantage of involving sulfate reduction is that part of the methane is lost due to the consumption of methane precursors. [ABSTRACT FROM AUTHOR]