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9 Páginas.-- 4 Figuras.-- 1 Tabla, Facilitating the anaerobic degradation of long chain fatty acids (LCFA) is the key to unlock the energy potential of lipids-rich wastewater. In this study, the feasibility of psychrophilic anaerobic treatment of LCFA-containing dairy wastewater was assessed and compared to mesophilic anaerobic treatment. The results showed that psychrophilic treatment at 15 ℃ was feasible for LCFA-containing dairy wastewater, with high removal rates of soluble COD (>90%) and LCFA (∼100%). However, efficient long-term treatment required prior acclimation of the biomass to psychrophilic temperatures. The microbial community analysis revealed that putative syntrophic fatty acid bacteria and Methanocorpusculum played a crucial role in LCFA degradation during both mesophilic and psychrophilic treatments. Additionally, a fungal-bacterial biofilm was found to be important during the psychrophilic treatment. Overall, these findings demonstrate the potential of psychrophilic anaerobic treatment for industrial wastewaters and highlight the importance of understanding the microbial communities involved in the process., The authors thank Arrabawn Dairies and Dairygold Co-Operative Society for providing the inoculum; Sandra O’Connor, Alison Graham, and Andrew Bartle for assisting reactor operations and Dr Anna Christine Trego for scientific discussions. The authors acknowledge the facilities and scientific and technical assistance of the Centre for Microscopy & Imaging at University of Galway (www.imaging.universityofgalway.ie). This work was supported by the Enterprise Ireland Technology Centres Programme (TC/2014/0016) and Science Foundation Ireland (19/FFP/6746 and 16/RC/3889), as well as the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement N° 101033411

New technologies development and renewable source exploitation are key tools to realize the European Green Deal and to boost the bio-based economy. In this context, fermentation of organic residues as food waste is an efficient method to obtain marketable products such as carboxylic acids widely applied in industrial production. Under favourable thermodynamic conditions, short chain fatty acids deriving from primary fermentation could be biologically converted into medium-chain fatty acids as caproate via chain elongation (CE) process, by using ethanol or lactate as electron donors. This study evaluates the effectivity of producing caproate from Food Waste extract rich in organics with in situ electron donor production. The test carried out at OLR 15 gCOD L

Chemical and thermal pretreatments of sewage sludge have proven to be effective to improve anaerobic digestion process by increasing methane production and sludge stabilization. In order to improve this technology towards sludge reduction combined with energy recovery, lab-scale experimentation was carried out to assess the efficiency of a 2-steps acid-alkali innovative pretreatment to enhance the anaerobic digestion process. Lab-scale results suggested to adopt some measures intended to ensure better anaerobic performances and imbalance risks prevention. The process allowed to achieve high sludge reduction efficiencies (up to 66% TSS removal), and to obtain high methane production yields (0.25 vs. 0.18 Nm/kgVS of the control) assuring high process stability. The electric energy recovery of the combined hydrolysis-digestion process, assessed on full-scale scenario, resulted higher with respect to a conventional digestion process. The sludge reduction obtained could imply cost savings of up to 32% compared to traditional scenarios.

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L−1d−1 with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L−1) was observed at OLR of 15 gCOD L−1d−1 with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process.

A novel biorefinery platform integrating thermal pretreatment and solid-liquid separation unit is here proposed to fully exploit food waste (FW) potential for production of valuable chemicals and energy through semi-continuous anaerobic bioconversion. The liquid fraction deriving from raw or pretreated FW, was fermented into volatile fatty acids (VFAs, from acetic to caproic acid) while the residual fraction was converted into biomethane. Thermal pretreatment effectively extracted a portion of the macromolecular organics, especially starch, to the liquid phase, promoting acidogenic fermentation and chain elongation pathways (0.43 gVFA g-1VSfed and 0.58 gVFA g-1VSfed with raw and pretreated extract, respectively). In parallel, anaerobic digestion of solid residue in 10 L reactors showed process stability and higher conversion rate for the pretreated residue (0.31 against 0.26 Nm3CH4 kg-1VSfed). The mass-transfer balance coupled with the economic assessment, calculated in terms of direct gross added value, indicated promising revenues by integrating the thermal upstream treatment.

The agricultural use of good quality sludge represents a value-added route to ensure growth sustainability in Europe, where raw material availability, for example, for phosphorus, is insufficient to meet demand. However, the possible presence of pathogens, pharmaceuticals and heavy metals requires specific regulations to minimize sludge-related health issues and environmental risks. The current regulation on sludge agricultural use applied by many EU countries is here presented and compared, highlighting scarce harmonization of the legislative framework among Member States. Actual issues, such as the fate of emerging micropollutants and microplastics in sludge-amended soils, and public health concerns regarding sludge spreading during the COVID-19 epidemic, are considered, too.

Anaerobic digestion is applied worldwide to treat food waste (FW) with the aim of obtaining renewable bioenergy by exploiting the methane gas produced. However, there are several problems in practical applications, primarily due to system instability. Although exhaustive knowledge regarding anaerobic microbial community composition has been established, few studies have investigated long-term correlations between microbial consortia, operative conditions and feedstock characteristics. Here, microbial community shifts as a response to feedstock variations were investigated in long-term semi-continuous systems, which were evaluated by an in situ cell detection method and 16S rRNA gene amplicon sequencing. FW digestion showed progressive system instability caused by the inhibition of methanogens, which resulted in volatile fatty acid accumulation and process failure at the low organic loading rate (OLR). Conversely, by co-digesting FW with waste-activated sludge (WAS), a stable process with methane yields of up to 0.27 Nm3 kg−1VSfed for OLR = 1.7 gVS L−1d−1 was achieved. This stabilizing effect was not related to the buffering capacity of WAS, but to its capacity to avoid volatile fatty acid accumulation and falls in pH by overcoming methanogenic activity inhibition. WAS addition promoted the establishment of a stable and active archaeal population in anaerobic co-digestion (AcoD) reactors. The continuous supply of trace elements together with the seeding of microbial functional groups were the main drivers that positively affected process stability.

More than 400 papers in the last 5 years have been published on FW into energy. Food waste complexity and composition affects anaerobic conversion. Scaling up of the AD process is fundamental to assess the real methane potential. Methanogenesis is often rate limiting step leading to pH drop and instability. Strategies to improve AD performances and stability are here reviewed.

Sewage sludge is a type of urban waste generated as a byproduct of wastewater treatment in quantities ranging from 9 to 9.5 million tons (dry substance) in Europe. This waste can be considered a source of lipids, which can be converted into biofuels. Recovery of lipids from sludge is a critical step in the overall process, and the choice of the extracting solvent should satisfy efficiency as well as sustainability criteria. This study reports experimental optimisation of lipid extraction from sewage sludge using ethyl butyrate, a green bio-derivable solvent. Extraction conditions were optimised using the desirability function applied to the response surface methodology analysis of a Box–Behnken factorial design of experiments. By carrying out the extraction at 70 °C for 7 h, using an amount of solvent equal to the wet sludge, and without using any acids, 93.7% of the starting lipids were recovered. The extracted lipids were then efficiently converted into biodiesel (fatty acid methyl esters) through direct esterification promoted by AlCl3∙6H2O (catalyst). Furthermore, the residual sludge obtained after the extraction, different to that obtained using hexane, was found to be anaerobically digestible without any inhibition.

Methanogenic biomass plays a key role with regard to methane production during anaerobic bioconversion of organic substrates. In this study, the effect of two different acclimated inocula on digestion performances was investigated by means of anaerobic batch tests on untreated and sonicated waste-activated sludge. Organics solubilization and removal kinetics, the abundance and physiological conditions of archaeal cells on ultimate methane yield were evaluated. The simultaneous presence of Methanosarcina and Methanosaeta in the archaeal biomass, the higher initial archaeal cells relative abundance and their occurrence in the aggregated forms were the main factors positively affecting the conversion into methane. The presence of the acclimated inoculum at the start-up influenced positively the methane improvement due to sonication, and the methane-specific production increased from 0.335 ± 0.03 to 0.420 ± 0.05 Nm3/kg VSfed. Moreover, the better physiological state of methanogens permitted to appreci...

Biowaste valorization through anaerobic digestion is an attractive option to achieve both climate protection goals and renewable energy production. In this paper, a complete set of batch trials was carried out on kitchen waste to investigate the effects of mild thermal pretreatment, temperature regimen and substrate/inoculum ratio. Thermal pretreatment was effective in the solubilisation of macromolecular fractions, particularly carbohydrates. The ability of the theoretical methodologies in estimating hydrogen and methane yields of complex substrates was evaluated by comparing the experimental results with the theoretical values. Despite the single batch configuration, a significant initial hydrogen production was observed, prior to methane yield. Main pretreatment effect was the gain in hydrogen production; the extent was highly variable according to the other parameters values. High hydrogen yields, up to 113 mL H2/g VSfed, were related to the prompt transformation of soluble sugars. Thermophilic regimen resulted, as expected, in faster digestions (up to 78 mL CH4/gVS/day) and sorted out pH inhibition. The relatively low methane yields (342-398 mL CH4/g VSfed) were the result of the consistent lignocellulosic content and low lipid content. Thermal pretreatment proved to be a promising option for the enhancement of hydrogen production in food waste dark fermentation. (c) 2019 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

The reasons for the acidification problem affecting Food Waste (FW) anaerobic digestion were explored, combining the outcomes of microbiological data (FISH and CARD-FISH) and process modelling, based on the Anaerobic Digestion Model n°1 (ADM1). Long term semi continuous experiments were carried out, both with sole FW and with Waste Activated Sludge (WAS) as a co-substrate, at varying operational conditions (0.8–2.2 g VS L−1 d−1) and FW / WAS ratios. Acidification was observed along FW mono-digestion, making it necessary to buffer the digesters; ADM1 modelling and experimental results suggested that this phenomenon was due to the methanogenic activity decline, most likely related to a deficiency in trace elements. WAS addition, even at proportions as low as 10% of the organic load, settled the acidification issue; this ability was related to the promotion of the methanogenic activity and the consequent enhancement of acetate consumption, rather than to WAS buffering capacity. The ability of the ADM1 to model processes affected by low microbial activity, such as FW mono-digestion, was also assessed. It was observed that the ADM1 was only adequate for digestions with a high activity level for both bacteria and methanogens (FISH/CARD-FISH ratio preferably >0.8) and, under these conditions, the model was able to correctly predict the relative abundance of both microbial populations, extrapolated from FISH analysis.

In order to enhance anaerobic biodegradability of food waste (FW), thermal pretreatment was applied. The effectiveness in terms of biodegradability extent and process rate improvement was investigated. To this aim, Biomethane Potential tests were carried out under mesophilic and thermophilic conditions. The IWA anaerobic digestion Model 1 (ADM1), a powerful tool for modeling the anaerobic digestion (AD) of different substrates, was implemented to predict the methane production. Disintegration constant (k_dis) and maximum acetate uptake rate (km_ac) were identified as the most sensitive parameters and were calibrated over the observed methane production. Pretreatment improvement was more evident in enhancing parameters related to the process rate, such as solubilization extent (+153%) and disintegration constant (+18%), rather than increasing substrate biodegradability. Thermophilic conditions proved to be effective in speeding up the whole AD process, since all the kinetics were significantly improved (disintegration rate increased up to fivefold). Furthermore, it was demonstrated that, after k_dis and km_ac calibration, default thermophilic ADM1 parameters can be suitable to model FW digestion.

Single stage digestion tests were performed on food waste (FW) alone and mixed with olive husks (OH), to assess the influence of composition and pH on hydrogen and methane production. Process intensification with thermal pretreatment to further enhance the biological conversion of substrate constituents was investigated, too. Best performance in terms of H 2 production (up to 87 NL/kg VS fed ) was observed at initial pH 7 with the co-digestion of pretreated mix, because of the high amount of solubilized carbohydrates transformed rapidly during the first hours. Pretreatment of the sole FW enhanced hydrogen production only at initial pH 7, while successive methane production, ranging from 339 to 446 NL/kg VS fed , was not significantly affected. The strategy of co-digestion with untreated OH resulted encouraging to achieve contemporarily high methane and hydrogen conversion rates. The First Order/Modified Gompertz equation, the Logistic function and the Transference Function were used for experimental data fitting; the Modified Gompertz equation proved to be the best fit for this purpose.

Quorum sensing signals regulate various functions within activated sludge processes such as formation of microbial aggregates. Disturbance of this signaling system, known as quorum quenching (QQ), provides opportunities for eliminating some problems related to biological wastewater treatment (e.g., biofouling and excess sludge production). However, it is poorly understood how and to what extent QQ systems can affect the microbial aggregation processes and the following floc formation. In particular, an in-depth structural characterization at the scale of microbial aggregate while considering nutrient conditions in the reactor is still largely disregarded. Here, we evaluated the QQ effects at the short-term time scale (i.e., after 4 h for the exogenous period and 19 h for exogenous/endogenous period), by combining advanced techniques for microbial characterization (flow cytometry, CARD-FISH, and confocal laser scanning microscopy) and conventional physical-chemical assessments. The results indicated that by implementing QQ agents (immobilized Acylase I enzyme in porous alginate beads) the abundance of single cells and suspended microbial aggregates in the supernatant did not show significant changes during the exogenous period. Conversely, at the end of the exogenous/endogenous period a significant increase of single prokaryotic cells, small and large microbial aggregates favored the growth of grazers, including free-living nanoflagellates and ciliates. Flocs became looser and thinner than those in the control reactor, thus affecting the sludge settling behavior. Inability of microbial community in degradation of soluble protein during the endogenous period confirmed that the QQ agents are likely to inhibit the secretion of protease enzyme within microbial communities of activated sludge.

Stability and performance of long term semi-continuous Anaerobic Digestion of food waste at semi-pilot scale is here evaluated based on the integration of multiple lines of evidence. In order to elucidate the main microbial components, the core microbiome dynamics were assessed by high-throughput 16 S rRNA gene sequencing over the reactor operation together with the data related to the AD performances. The experimental reactor, after a successful start-up, was operated for more than 200 days at a moderate OLR (Organic Loading Rate) of 1.6 ± 0.4 g VS L−1d−1. The availability of readily biodegradable substrate, in particular carbohydrates, favored the fermentative functional redundancy of bacteria promoting the rapid accumulation of acetate first, and propionate afterwards, due to limited methanogenesis. The prolonged operation, despite the moderate OLR, nurtured propionate accumulation, because H2 concentration exceeded the level capable to render the reaction endergonic, hampering the propionate uptake process. The application of a Pulsed Feeding strategy increased the hydrogenotrophic Methanomicrobiales favoring the consumption of propionate most likely through hydrogen utilization.

Background Recent studies have suggested that addition of electrically conductive biochar particles is an effective strategy to improve the methanogenic conversion of waste organic substrates, by promoting syntrophic associations between acetogenic and methanogenic organisms based on interspecies electron transfer processes. However, the underlying fundamentals of the process are still largely speculative and, therefore, a priori identification, screening, and even design of suitable biochar materials for a given biotechnological process are not yet possible. Results Here, three charcoal-like products (i.e., biochars) obtained from the pyrolysis of different lignocellulosic materials, (i.e., wheat bran pellets, coppiced woodlands, and orchard pruning) were tested for their capacity to enhance methane production from a food waste fermentate. In all biochar-supplemented (25 g/L) batch experiments, the complete methanogenic conversion of fermentate volatile fatty acids proceeded at a rate that was up to 5 times higher than that observed in the unamended (or sand-supplemented) controls. Fluorescent in situ hybridization analysis coupled with confocal laser scanning microscopy revealed an intimate association between archaea and bacteria around the biochar particles and provided a clear indication that biochar also shaped the composition of the microbial consortium. Based on the application of a suite of physico-chemical and electrochemical characterization techniques, we demonstrated that the positive effect of biochar is directly related to the electron-donating capacity (EDC) of the material, but is independent of its bulk electrical conductivity and specific surface area. The latter properties were all previously hypothesized to play a major role in the biochar-mediated interspecies electron transfer process in methanogenic consortia. Conclusions Collectively, these results of this study suggest that for biochar addition in anaerobic digester operation, the screening and identification of the most suitable biochar material should be based on EDC determination, via simple electrochemical tests. Electronic supplementary material The online version of this article (10.1186/s13068-017-0994-7) contains supplementary material, which is available to authorized users.

Thermophilic bacteria have recently attracted great attention because of their potential application in improving different biochemical processes such as anaerobic digestion of various substrates, wastewater treatment or hydrogen production. In this study we report on the design of a specific 16S rRNA-targeted oligonucleotide probe for detecting members of Coprothermobacter genus characterized by a strong protease activity to degrade proteins and peptides. The newly designed CTH485 probe and helper probes hCTH429 and hCTH439 were optimized for use in fluorescence in situ hybridization (FISH) on thermophilic anaerobic sludge samples. In situ probing revealed that thermo-adaptive mechanisms shaping the 16S rRNA gene may affect the identification of thermophilic microorganisms. The novel developed FISH probe extends the possibility to study the widespread thermophilic syntrophic interaction of Coprothermobacter spp. with hydrogenotrophic methanogenic archaea, whose establishment is a great benefit for the whole anaerobic system.

High-frequency ultrasounds have recently gained interest as oxidative technique for sonochemical degradation of organic contaminants in water. In this study an innovative approach applying 200. kHz ultrasounds to improve both sludge anaerobic biodegradability and decontamination is proposed. Digestion tests were performed on batch reactors fed either with untreated or sonicated sludge, at different food/inoculum (F/I) ratio, in the range 0.3-0.9. First order kinetic highlighted a decreasing trend of the hydrolysis rate by increasing F/I, both for untreated and sonicated sludge. Positive effect of ultrasounds on specific biogas production was evident, but the conversion rate for pretreated sludge was strongly affected by F/I, and decreased by increasing F/I. Anionic surfactants anaerobic removal occurred in all tests, but the effect of ultrasounds was significant only at F/I. = 0.3. By pretreating sludge with high frequency ultrasounds, low F/I was the ideal ratio improving both sludge anaerobic digestion and decontamination. © 2014 Elsevier Ltd.

The requirement for enhanced stabilization processes to obtain a more stable, pathogen-free sludge for agricultural use is an increasing challenge to comply with in the waste hierarchy. With this in mind, the Routes European project ('Novel processing routes for effective sewage sludge management') is addressed to assess innovative solutions with the aim of maximizing sludge quality and biological stability. In order to increase anaerobic stabilization performances, the sequential anerobic/aerobic process and the thermophilic digestion process, with or without integration of the thermal hydrolysis pre-treatment, were investigated as regards the effect on sludge stabilization, dewaterability and digestion performances. Thermal pre-treatment improved anaerobic digestion in terms of volatile solids reduction and biogas production, but digestate dewaterability worsened. Fluorescence in situ hybridization (FISH) quantification showed an increase of methanogens consistent with the increase of biogas produced. The aerobic post-treatment after mesophilic digestion had a beneficial effect on dewaterability and stability of the digested sludge even if was with a reduction of the potential energy recovery. © IWA Publishing 2014.

A 2-year sampling campaign was conducted in three wastewater treatment plants of various sizes in the Rome area to assess the occurrence of nutrients and micropollutants among primary, secondary and digested sludge. The primary purpose was to evaluate the quality of different sludge types and their suitability for agricultural use. Primary sludge was consistently more polluted than secondary in terms of organic micropollutants, whereas heavy metals partitioned equally among the sludge types. In digested sludge, the heavy metal concentrations were always below limit values proposed for agricultural utilisation. In contrast, organic micropollutants concentrated during anaerobic digestion and affected the quality of the digested sludge. Secondary sludge resulted less polluted and richer in nitrogen and phosphorus (up to three times) than primary sludge and is hence more suitable for agricultural use. Separate processing of primary and secondary sludge might therefore be an innovative option for sludge management that could maximise the possibilities of agricultural use of secondary sludge and limit disposal problems only to primary sludge. In fact, primary sludge could be easily treated and disposed of by conventional processes including thickening, anaerobic digestion, centrifugation and incineration, whereas the difficult digestibility of secondary sludge could be improved by disintegration pre-treatment before stabilisation.

Ultrasounds pretreatment aims to convert waste activated sludge, characterized by recalcitrant particulate organics, into a soluble, more biodegradable form, maximizing anaerobic stabilization and biogas recovery. Objective of this work was the assessment of the efficiency of high frequency ultrasounds, as 200 kHz, to improve sludge anaerobic digestion performances. Parallel batch anaerobic digestion tests were performed to evaluate anaerobic biodegradability of 20 or 200 kHz sonicated secondary sludge, operating at food/inoculum ratio of 0.5 and 1. Ultrasound pretreatments, independent on the frequency, accelerated the initial hydrolysis phase, and the effect was more marked working at high inoculum content. Moreover, the biogas produced by the sonicated sludge was always higher than that produced by the untreated one. This gain seemed to be independent on the F/I ratio for the digestion of the 20 kHz pretreated sludge, while, in the case of sludge treatment at 200 kHz, the biogas improvement was particularly high (about 40%) at F/I=0.5. In fact, at F/I=1, the biogas gain was only +4% due to an evident slowdown of the biogas production of the sonicated sludge, due to the accumulation of soluble organic substances, evidenced by the soluble COD pattern, suggesting discoupling between hydrolysis and methanogenesis. Fluorescence In Situ Hybridization (FISH) analysis allowed to highlight the establishment in the anaerobic biomass of different methanogens responsible for the biogas production depending on the extent of readily biodegradable substrates availability for the methanogenesis or on the amount of inoculum utilised at the start up of the anaerobic digestion process.

Anaerobic treatments have been successfully employed for more than one hundred years to stabilize sewage sludge. The main aim of sludge anaerobic digestion is the degradation and destruction of organic matter, with consequent sludge stabilization and pathogen reduction. One of the advantages of the fermentative system over aerobic treatment is the production of biogas (i.e., an available source of energy), which in some cases can be exploited to satisfy part of the energy requirements of the treatment plant. Nevertheless, inadequate knowledge of the principles governing the process often prevents satisfactory digester management, and thus there is an evident need for reliable kinetic models in order to improve performance and optimize the control strategies. In the present review, an overview of the anaerobic digestion models proposed in the specialized literature is presented. Models are grouped according to the degree of substrate characterization and thus of complexity (in terms of number of equations ...

Separation between primary and secondary sludge treatment could be a valuable solution for sludge management. According to this approach, secondary sludge can be conveniently used in agriculture while primary sludge could be easily dried and incinerated. It follows that some concern may arise from incinerating primary sludge with respect to the current practice to incinerate mixed digested sludge. Incineration of primary and mixed digested municipal sludge was investigated with a lab-scale equipment in terms of emissions of products of incomplete combustion (PICs) during incineration failure modes. PICs can be grouped in three sub-categories, namely aliphatic hydrocarbons (alkanes and alkenes), compounds with a single aromatic ring, and polycyclic aromatic hydrocarbons (PAHs). After-burning temperature was the most important parameter to be controlled in order to minimize emissions of alkanes and alkenes. As for mono-aromatic compounds, benzene and toluene are the most thermally resistant compounds, and in some cases, an after-burning temperature of 1100 °C was not enough to get the complete destruction of benzene leading to a residual emission of 18 mg/kgsludge. PAHs showed an opposite trend with respect to aliphatic and mono-aromatic hydrocarbons being the thermal failure mode the main responsible of PIC emissions. A proper oxygen concentration is more important than elevated temperature thus reflecting the high thermal stability of PAHs. Overall, obtained results, even though obtained under flameless conditions that are different from those of the industrial plants, demonstrated that separation of primary and secondary sludge does not pose any drawbacks or concern regarding primary sludge being disposed of by incineration even though it is more contaminated than mixed digested sludge in terms of organic pollutants.

Thermophilic bacteria have been isolated from several terrestrial, marine and industrial environments. Anaerobic digesters treating organic wastes are often an important source of these microorganisms, which catalyze a wide array of metabolic processes. Moreover, organic wastes are primarily composed of proteins, whose degradation is often incomplete. Coprothermobacter spp. are proteolytic anaerobic thermophilic microbes identified in several studies focused on the analysis of the microbial community structure in anaerobic thermophilic reactors. They are currently classified in the phylum Firmicutes; nevertheless, several authors showed that the Coprothermobacter group is most closely related to the phyla Dictyoglomi and Thermotoga. Since only a few proteolytic anaerobic thermophiles have been characterized so far, this microorganism has attracted the attention of researchers for its potential applications with high-temperature environments. In addition to proteolysis, Coprothermobacter spp. showed several metabolic abilities and may have a biotechnological application either as source of thermostable enzymes or as inoculum in anaerobic processes. Moreover, they can improve protein degradation by establishing a syntrophy with hydrogenotrophic archaea. To gain a better understanding of the phylogenesis, metabolic capabilities and adaptations of these microorganisms, it is of importance to better define the role in thermophilic environments and to disclose properties not yet investigated.

Nowadays, several technologies and management strategies are proposed for upgrading wastewater treatment plants (WWTPs) in order to improve sludge stabilization or minimize sludge production. In order to make sure that this leads to overall improvements, their techno-economic and environmental performance has to be carefully evaluated. In response to this, the techno-economic and environmental performance was assessed for a considered model reference WWTP upgraded with separate treatment and disposal for primary and secondary sludge to provide guidance to research, policy and investment efforts. This paper departs in an experimental campaign carried out within the EU project "ROUTES" and describes an assessment of an upgrade of a WWTP, involving wet oxidation of primary sludge and thermophilic anaerobic digestion (integrated with thermal hydrolysis pre-treatment) for secondary sludge. The reference plant and the upgrade implied different disposal routes for the resulting sludges: incineration for the stabilized sludge deriving from the reference WWTP; agricultural land application for the secondary stabilized sludge from the upgraded plant and landfilling for the solid residue deriving from the wet oxidation process (as non-hazardous waste). The mass balance carried out for both reference and upgraded WWTPs showed a reduction of total sludge production (up to 45%) for the upgraded WWTP. The additional energy demand of the upgraded solution (+22.4 Wh/(PE d), PE: population equivalent) was partially balanced by the electric energy produced by combined heat and power unit installed in the upgraded WWTP (-18.08 Wh/(PE d)). The integrated assessment showed that the upgraded solution, although resulting in an increase of WWTP technical complexity, may contribute to environmental and economic advantages. The paper provides guidance in terms of which aspects need a more thorough evaluation when this upgrade is considered in real cases.

Anaerobic digestion (AD) is one of the few sustainable technologies that both produce energy and treat waste streams. Driven by a complex and diverse community of microbes, AD may be affected by different factors, many of which also influence the composition and activity of the microbial community. In this study, the biodiversity of microbial populations in innovative mesophilic/thermophilic temperature-phased AD of sludge was evaluated by means of fluorescence in situ hybridization (FISH). The increase of digestion temperature drastically affected the microbial composition and selected specialized biomass. Hydrogenotrophic Methanobacteriales and the protein fermentative bacterium Coprothermobacter spp. were identified in the thermophilic anaerobic biomass. Shannon-Weaver diversity (H?) and evenness (E) indices were calculated using FISH data. Species richness was lower under thermophilic conditions compared with the values estimated in mesophilic samples, and it was flanked by similar trend of the evenness indicating that thermophilic communities may be therefore more susceptible to sudden changes and less prompt to adapting to operative variations. © 2014 Springer-Verlag Berlin Heidelberg.

Anaerobic digestion has been recognized as the most appropriate stabilization technology for approaching sludge reuse task, in part because of the methane production involved. The mesophilic anaerobic processing train can be upgraded by adding a pre-treatment step or by increasing the digestion temperature to thermophilic conditions. In this study, semi-continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digesters were operated for 180 days at low (0.7-1.0 kg VS/m(3) d), medium (1.4-1.8 kg VS/m(3) d) and high (2.8-3.7 kg VS/m(3) d) organic loading rates (OLRs). The impact of ultrasound and thermal hydrolysis pre-treatments on the mesophilic and thermophilic digestion efficiency, respectively, was assessed by performing parallel digestion tests. The increase of soluble COD (Chemical Oxygen Demand) and colloidal surface charge after the sludge pre-treatments suggested biopolymers solubilization and changes in surface floc properties. Thermal hydrolysis enhanced the release of lipids and long chain fatty acids, while ultrasounds application resulted in proteins being the main component of the released matter. Operating the digesters at OLRs between 0.7 and 1.4 kg VS/m(3) d the methane conversion rate was not significantly affected by the temperature increase up to thermophilic conditions, whereas the integration of the pre-treatments accelerated the organic conversions, resulting in a noticeable methane gain (up to +51%). Conversely, at higher organic loads, the TAD yields were significantly higher with respect to the MAD ones, assuring the sustainable economic benefit of operating smaller anaerobic digesters to obtain higher methane productions. Nevertheless, the colloidal charge increase during thermophilic digestion impaired the sludge filterability much more rapidly than in mesophilic conditions. (C) 2015 Elsevier ay. All rights reserved.

The European Union (EU) Project Routes aimed to discover new routes in sludge stabilization treatments leading to high-quality digested sludge, suitable for land application. In order to investigate the impact of different enhanced sludge stabilization processes such as (a) thermophilic digestion integrated with thermal hydrolysis pretreatment (TT), (b) sonication before mesophilic/thermophilic digestion (UMT), and (c) sequential anaerobic/aerobic digestion (AA) on digested sludge quality, a broad class of conventional and emerging organic micropollutants as well as ecotoxicity was analyzed, extending the assessment beyond the parameters typically considered (i.e., stability index and heavy metals). The stability index was improved by adding aerobic posttreatment or by operating dual-stage process but not by pretreatment integration. Filterability was worsened by thermophilic digestion, either alone (TT) or coupled with mesophilic digestion (UMT). The concentrations of heavy metals, present in ranking order Zn > Cu > Pb > Cr ~ Ni > Cd > Hg, were always below the current legal requirements for use on land and were not removed during the processes. Removals of conventional and emerging organic pollutants were greatly enhanced by performing double-stage digestion (UMT and AA treatment) compared to a single-stage process as TT; the same trend was found as regards toxicity reduction. Overall, all the digested sludges exhibited toxicity to the soil bacterium Arthrobacter globiformis at concentrations about factor 100 higher than the usual application rate of sludge to soil in Europe. For earthworms, a safety margin of factor 30 was generally achieved for all the digested samples. © 2014 Springer-Verlag Berlin Heidelberg.

The objective of this work was to determine the partitioning of the pollutant load in urban wastewater in order to improve the conventional sewage treatment. In addition to settling tests, physical fractionation of COD in the degritted influent of Roma-Nord sewage treatment plant was performed via sequential filtration through sieves and membrane filters of the following pore size: 150-100-50-25-1-0.2 μm, and 100 kD (about 0.02 μm). Biodegradability studies were also performed on the different size fractions. Size fractionation showed that COD in Roma-Nord sewage is predominantly associated with settleable and supracolloidal (> 1 μm) particles, each size range including about 40% of total COD. Biodegradability tests indicated that the large fraction of COD associated with supracolloidal particles, which are not removed in the primary treatment, is characterised by slow degradability. This suggests that removal of these particles prior to biological treatment may greatly improve the overall treatment scheme. Preliminary pilot plant coagulation tests with lime at pH 9 showed that lime-enhanced primary treatment may increase COD removal efficiencies from typical 30-35% up to 65-70%, by inducing almost complete removal of the COD fraction associated with supracolloidal particles.

Thermal hydrolysis pretreatment coupled with Thermophilic Anaerobic Digestion (TAD) for Waste Activated Sludge (WAS) treatment is a promising combination to improve biodegradation kinetics during stabilization. However, to date there is a limited knowledge of the anaerobic biomass composition and its impact on TAD process performances. In this study, the structure and dynamics of the microbial communities selected in two semi-continuous anaerobic digesters, fed with untreated and thermal pretreated sludge, were investigated. The systems were operated for 250 days at different organic loading rate. 16S rRNA gene clonal analysis and Fluorescence In Situ Hybridization (FISH) analyses allowed us to identify the majority of bacterial and archaeal populations. Proteolytic Coprothermobacter spp. and hydrogenotrophic Methanothermobacter spp. living in strict syntrophic association were found to dominate in TAD process. The establishment of a syntrophic proteolytic pathway was favoured by the high temperature of the process and enhanced by the thermal pretreatment of the feeding sludge. Proteolytic activity, alone or with thermal pretreatment, occurred during TAD as proven by increasing concentration of soluble ammonia and soluble COD (sCOD) during the process. However, the availability of a readily biodegradable substrate due to pretreatment allowed to significant sCOD removals (more than 55%) corresponding to higher biogas production in the reactor fed with thermal pretreated sludge. Microbial population dynamics analysed by FISH showed that Coprothermobacter and Methanothermobacter immediately established a stable syntrophic association in the reactor fed with pretreated sludge in line with the overall improved TAD performances observed under these conditions.

The behaviour of four metals (Cr, Cu, Pb, Zn) during sewage sludge incineration was studied in eight pilot plant tests performed with a rotary kiln (RK) and a fluidised bed (FB) furnace. To simulate sludge co-incineration with hazardous wastes, in three FB tests feed sludge was mixed with chlorinated organic compounds. Chromium and copper showed similar concentrations both in bottom or cyclone ash and in fly ash, even at high chlorine input and high combustion temperature. In contrast, zinc and lead concentrations in fly ash produced in RK tests are one or two orders of magnitude higher than those in bottom ash. However, not even these two metals showed significant enrichment in FB tests carried out at high chlorine input. The predictive capability of a thermodynamic model was checked by comparing predicted metal volatilisation in the combustion chamber with experimental metal enrichment in the fly ash. Large discrepancies were observed in FB tests carried out at high chlorine content, where Pb, Zn, and Cu are predicted to volatilise in great extent, andin RK tests where zinc volatilisation is not predicted. Likely explanations of these discrepancies are the very short solid residence times in the FB furnace (non equilibrium conditions) and the incomplete mixing conditions in the RK furnace (pyrolysis pockets). From the environmental impact point of view, the pilot tests suggest that sludge incineration with fluidised bed furnace is safer than the one using rotary kiln furnace.

Olive husks, typical solid by-products from the olive oil industry, were selected to carry out anaerobic digestion tests. Before digestion, olive husks were subjected to ultrasonic or thermal pretreatments in order to release the organic matter into solution. Both sonication and thermal pretreatment allowed to solubilize the particulate matter with 22% and 72% increase in soluble organics of olive husks, respectively. Nevertheless, such pretreatments caused the release of unwanted molecules in solution, with the related risks of inhibition of the methanogenic process. Biochemical Methane Potential (BMP) tests on olive husks mixed with olive-mill wastewater and dairy wastewater, either pretreated or not, showed that ultrasound pretreatment resulted in 15% increase in volatile solids reduction and a 13% increase in biogas production, while after thermal pretreatment no benefits were observed.

The performance of thermophilic digestion of waste activated sludge, either untreated or thermal pretreated, was evaluated through semi-continuous tests carried out at organic loading rates in the range of 1–3.7 kg VS/m 3 d. Although the thermal pretreatment at T = 134 °C proved to be effective in solubilizing organic matter, no significant gain in organics degradation was observed. However, the digestion of pretreated sludge showed significant soluble COD removal (more than 55%) whereas no removal occurred in control reactors. The lower the initial sludge biodegradability, the higher the efficiency of thermal pretreated digestion was observed, in particular as regards higher biogas and methane production rates with respect to the parallel untreated sludge digestion. Heat balance of the combined thermal hydrolysis/thermophilic digestion process, applied on full-scale scenarios, showed positive values for direct combustion of methane. In case of combined heat and power generation, attractive electric energy recoveries were obtained, with a positive heat balance at high load.

This paper deals with the comparison of ultrasound (mechanical) and ozone (chemical) pre-treatment on the performances of excess sludge semi-continuous digestion. Sludge solubilisation has been investigated by varying specific energy input. For each pre-treatment, long anaerobic digestion tests were carried out by two parallel digesters: one reactor, as control unit, was fed with untreated waste activated sludge, and the other one was fed with disintegrated sludge. To evaluate and compare the efficacy of both pre-treatments, the specific energy was maintained approximately the same. The digestion tests were carried out to investigate the feasibility of anaerobic digestion performance (total biogas production, volatile solids removal, sludge dewaterability) and to assess the heat balance. Results obtained from the digestion of sonicated sludge at 4% disintegration degree (∼2500 kJ/kg TS) showed that the ultrasound pre-treatment may be effective both in increasing VS destruction (+19%) and cumulative biogas production (+26%). On the contrary, the digestion test with ozonized sludge (ozone dose of 0.05 g O 3 /g TS corresponding to ∼2000 kJ/kg TS) did not indicate a significant improvement on the digestion performances. By doubling the ozone dose an improvement in the organics removal and cumulative biogas production was observed. Relevant differences in terms of colloidal charge and filterability were discussed.

Ultrasounds represent an effective technology in many research fields. In sewage sludge treatment, low-frequency ultrasound, particularly at 20 kHz, are widely used for sludge disintegration before the anaerobic digestion, while in the last years novel application of high-frequency ultrasound regards the decontamination of water and wastewater through sonochemical reactions. The innovative approach presented in this paper is the treatment of sewage sludge with ultrasound at 200 kHz for obtaining efficient sludge disintegration and the removal of the linear alkylbenzenesulphonates (LAS) at the same time. Results of the sonolysis experiments showed that native LAS degradation up to 40% can be achieved with low power input in less than 1h. The degradation pattern was different for each LAS homologue (from C10 to C13), because of their physical-chemical properties, in particular as regards the alkyl chain length. This high-frequency ultrasound irradiation resulted effective also in terms of floc disintegration and soluble organic matter release, in particular for energy inputs higher than 30,000 kJ/kg TS. The disrupting effect of the 200 kHz treatment was also evaluated by microscope analyses and determination of the extracellular polymeric substances release in the liquid phase.

In this work the potential of high frequency ultrasounds as pretreatment for sludge anaerobic digestion has been assessed. Irradiation with 200 kHz ultrasounds was efficient in disintegrating the floc structure increasing the available fraction of soluble organic matter (up to seven times at 25,000 kJ/kg TS). Batch anaerobic digestion tests were carried out on lab-scale reactors fed either with untreated or disintegrated sludge inoculated with anaerobic sludge, at different feed/inoculum ratio (F/I = 0.5 and 1). Degradation of particulate matter, biogas production and related microbial community composition (estimated by fluorescence in situ hybridization, FISH) were investigated. Sludge ultrasounds pretreatment led to an overall improvement of the digestion performances, with a maximum biogas gain of 40% at F/I = 0.5. FISH showed a key-role of Methanosarcina spp. in the main reactions of biogas synthesis.

The objective of this work was to maximize the digestibility of biological sludge to elucidate the feasibility of a new sludge management strategy to recover good quality sludge for agricultural use. The combined effects of organic loading rates (from 0.7 to 2.8 g VS L −1 d −1 ) and the degree of disintegration by anaerobic digestion of sonicated activated sludge were discussed, and the thermal and energetic balances were evaluated. Despite low sonication inputs, sludge digestion performance improved in terms of solids degradation and biogas production depending on the soluble organic load. The biogas production by sonicated sludge was higher (up to 30%) with respect to the control. Filterability improved during digestion of sonicated sludge at medium OLR due to a significant abatement of the fines. Thermal balances indicated that sonication may be a proper system to guarantee self-sustaining WAS mesophilic digestion. Nevertheless, thickening is a pre-requisite to achieve a positive energy balance.

In the coming years, large European wastewater treatment plants (WWTPs) will need to dispose of sludge by transforming it into inert material by thermal processes. In fact, the present European landfill directive 99/31 has restricted this disposal route which was practically abandoned by countries, where the implementation of the directive criteria in national legislations was very stringent, either imposing a limit of the organic carbon to 4 - 5 % in the wastes to be disposed (Germany) or including a leachate test with the very stringent limit of dissolved organic carbon of 80 mg/L (Italy). Moreover, guidelines for agricultural utilization, will become progressively more stringent due to increasing health concerns about the widespread diffusion of pathogenic and organic micropollutants in the environment (European Commission, 2000). Regardless, agricultural utilization involving large amounts of sludge to be spread on land does not seem feasible for the following reasons: ? need of large extensions of fields and therefore long distances to be covered from WWTPs to the site of spreading; ? need of large storage volume required when sludge cannot be used (winter periods and when the fields are flooded); ? large WWTPs are often polluted by non-controlled industrial discharges that might hinder agricultural utilization of resulting sludge. A more sustainable sewage sludge management system might be attained through a separation of primary and secondary sludge before their treatment and disposal. It would thus be possible to maintain agricultural utilization for biological sludge (secondary) and to convert to inert material by incinerating (on- or off-site) only the primary sludge (Mininni et al. 2004). In fact, characteristics of primary and secondary sludge are quite different in terms of quality (pollutants and nutrients) and in terms of suitability for thickening, digestion and dewatering. Secondary sludge is expected to be less polluted than primary sludge and should be segregated and treated separately from primary sludge, thus sustaining its agricultural utilisation. A sampling campaign carried out in Italy to assess the quality difference between primary and secondary sludge has highlighted that enrichment factors of organic micropollutants in primary sludge increase with respect to those in secondary sludge in the order of hydrocarbons, extractable organic halogens (EOX), anionic surfactants measured as methylene blue active substances (MBAS). Sludge separation may also give flexibility to sludge management, decreasing dependence on conventional disposal options (as required in the European Directive 2008/98), as sludge of good quality (biosolids) can be recovered for agricultural utilization while the remaining primary sludge can be treated by incineration. The challenge in the coming years will be assuring sludge management the greatest flexibility as well as maximizing the recovery of valuable products and energy sources while reducing disposal only to inert materials, which no longer contain useful compounds. One of the main goals in secondary sludge processing is improving the performance of anaerobic digestion. Secondary sludge contains up to 70 % of bacteria, so the above objective can only be achieved by accelerating the hydrolysis, which is the limiting step in the anaerobic process. Sludge disintegration treatments are able to disrupt biomass flocs and cell walls and to cause the release of the intracellular organic material. This treatment results in acceleration in the biological breakdown of particulate organic material into soluble, readily biodegradable fractions. The subsequent increase in biodegradable material improves bacterial kinetics, resulting in lower sludge quantities and, in the case of anaerobic digestion, increased biogas production. The technologies already in use for sludge disintegration, such as ultrasounds, by means of shear forces, have shown that energy input can account for 1-2 kWh/kg TS (Khanal et al., 2007, Müller, 2001). In this context, IRSA has carried out anaerobic digestion tests with sonicated secondary sludge, in batch and semi-continuous mode, investigating the effect of pre-treatment on digestion performances and on particle surface charge, affecting dewaterability. It is worth noting that ultrasound pre-treatment (specific energy 5,000 kJ/kg TS, i.e., about 1.4 kWh/kg TS) considerably accelerates the reaction rate (doubling the k values), and biogas production increases by about 30 % with respect to the control reactor without sonication (Braguglia et al., 2008). A second way to increase performance of secondary sludge anaerobic digestion is by thermal pre-treatment. The Cambi process may give even better results due to the drastic conditions of this disintegration process (temperature of 160 - 170 °C, pressure of 6 - 9 bar, residence time of more than 20 minutes). The Cambi process combined with anaerobic digestion allows increased VS removal and biogas production of 40 - 50 % in comparison with conventional sludge anaerobic digestion without disintegration. Certainly, disintegration and digestion technologies of secondary sludge need to be optimised, taking into account both energy balance and sludge quality (reduction of volatile solids, dewaterability). In this paper, the energy balance of different treatment options will be presented. The conventional treatment routes with mixed (primary + secondary) sludge thickening, digestion, mechanical dewatering and on-site incineration or on-site drying and off-site coincineration will be compared with advanced options where the primary and secondary sludge are kept separate. Primary sludge treatment is performed by the conventional route, whereas secondary sludge is thickened by dynamic thickening and then disintegrated by sonication or thermal treatment and then digested. This analysis points out that the advanced options are much more convenient than the conventional ones in terms of reduction of exhaust gas from the drying-incineration process and in terms of total energy requirements.

The goal of this study was to follow and compare dewaterability parameters of untreated and “pre-sonicated” sludge during semicontinuous anaerobic digestion by particle charge density and sludge filterability measurements. Floc disintegration due to sonication resulted in a significant increase of soluble COD and colloidal charge density. It is interesting to note that in all the tests despite the higher specific charge density and soluble COD values of the sonicated feed, the digested sludge at steady state present in both reactors statistically comparable values, independently on the pretreatment. The biological hydrolysis of the untreated sludge causes a large release of dispersed charged fines whereas the digestion of the sonicated sludge is characterized by a significant removal of fines and colloids already present in the pretreated feed. The amelioration of the filterability during the digestion of the sonicated sludge in test #2 suggest that anaerobic digestion may be very effective for degrading fine dispersed particles produced by mechanical pre-hydrolysis. Nevertheless, ultrasound pre-treatment does not improve the dewaterability of the digested sludge with respect to the untreated one. Optimisation of both disintegration degree and hydraulic residence time is necessary to improve the dewaterability of the digested sonicated sludge.

Results of three semi-continuous anaerobic tests were reported and discussed. Each test was carried out by two parallel anaerobic reactors fed with waste activated sludge, either as it was sampled from the sewage treatment plant of Rome North or previously disintegrated by ultra-sound treatment. Activated sludge was sonicated at the energy input of 5,000 or 2,500 kJ kg−1 dry solids corresponding to a disintegration degree of approximately 8 or 4%, respectively. Sonication proved to be effective both in increasing VS destruction and cumulative biogas production. The best increase of VS destruction (from 30 to 35%) was achieved in test #3 carried out at high organic load (10 d residence time) and low energy input (2,500 kJ kg−1 dry solids). The best increase in cumulative biogas production (from 472 to 640 NL after 67 d of tests i.e.) was obtained in test #1 at low organic load (20 d residence time) and high energy input (5,000 kJ kg−1 dry solids). Specific biogas production varied in the tests carried out with untreated sludge (0.55 – 0.67 Nm3 kg−1 VS destroyed) but was practically unchanged for all the tests with sonicated sludge (0.7 Nm3 kg−1 VS destroyed).

Degradation kinetics of particulate matter in anaerobic digestion of secondary sludge, untreated and sonicated, was investigated by carrying out batch tests at different feed/inoculum ratio (F/I) (in the range of 0.1-4.0). Particulate COD degradation data were analysed using the four equations most widely utilized to model the hydrolysis process and the related kinetic parameters were evaluated. The increase of F/I results in a correspondent increase of the process rate up to one order of magnitude in the investigated interval for both untreated and sonicated sludge. The maximum step increase is observed in the range of 0.1-2.0 while for F/I varying from 2.0 to 4.0 only a modest enhancement of the process kinetics is detected. The effect of sonication on kinetics is not appreciable at low F/I, due to the low fraction of fed sludge and to the consequent strong substrate limitation, whereas at high F/I a slight increase is evidenced.

An experimental campaign was carried out on a hospital and cemetery waste incineration plant in order to assess the emissions of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polycyclic aromatic hydrocarbons (PAHs). Raw gases were sampled in the afterburning chamber, using a specifically designed device, after the heat recovery section and at the stack. Samples of slags from the combustion chamber and fly ashes from the bag filter were also collected and analyzed. PCDD/Fs and PAHs concentrations in exhaust gas after the heat exchanger (200-350 degrees C decreased in comparison with the values detected in the afterburning chamber. Pollutant mass balance regarding the heat exchanger did not confirm literature findings about the de novo synthesis of PCDD/Fs in the heat exchange process. In spite of a consistent reduction of PCDD/Fs in the flue gas treatment system (from 77% up to 98%), the limit of 0.1 ng ITEQ Nm(-3) at the stack was not accomplished. PCDD/Fs emission factors for air spanned from 2.3 up to 44 mu g ITEQ t(-1) of burned waste, whereas those through solid residues (mainly fly ashes) were in the range 41-3700 mu g ITEQ t(-1). Tests run with cemetery wastes generally showed lower PCDD/F emission factors than those with hospital wastes. PAH total emission factors (91-414 mu g kg(-1) of burned waste) were in the range of values reported for incineration of municipal and industrial wastes. In spite of the observed release from the scrubber, carcinogenic PAHs concentrations at the stack (0.018-0.5 mu g Nm(-3)) were below the Italian limit of 10 mu g Nm(-3).