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To gain insight regarding the orthophosphate influence on fatty acid dynamics and methane production during mesophilic anaerobic sludge digestion, batch experiments were conducted. The results showed that an orthophosphate concentration of 414 g P m −3 accelerated acetotrophic methanogenesis, acetogenesis and acidogenesis. Lower or higher concentrations slowed these processes down. Three modifications of the Anaerobic Digestion Model No. 1 (ADM1) were compared by simultaneously fitting them to a multi-experiment (7 batches), multi-variable (6 measured variables) data set. A modified ADM1 model including Haldane kinetics of orthophosphate inhibition gave the best description of the measured data while the model using non-competitive acetate inhibition showed the poorest results. It is notable that the multi-experiment, multi-variable data set could be fitted with a single parameter set. The model with Haldane kinetics of orthophosphate inhibition together with the proposed parameters can be considered as a first attempt to describe the observed orthophosphate inhibition of anaerobic digestion. [ABSTRACT FROM AUTHOR]

Sewage sludge is a polluting and hazardous waste generated in wastewater treatment plants with severe management problems. The high content in heavy metal, pathogens and micropolluting compounds limit the implementation of the available management methods. Anaerobic digestion could be an interesting treatment method, but must be improved since the biomethanisation of sewage sludge entails low biodegradability and low methane production. A sonication pre-treatment at lab scale is proposed to increase the organic matter solubilisation of sewage sludge and enhance the biomethanisation yield. Sonication time was optimised by analysing the physicochemical characteristics of sewage sludge (both total and soluble fraction) at different pre-treatment times. The pre-treatment time was fixed at 45 min under the study conditions given that the solubilisation of organic matter did not increase significantly at lower sonication times, whereas the concentration of total nitrogen increased markedly at higher times. The volatile fatty acids generation rate was also evaluated for the pre-treatment conditions. The anaerobic digestion of untreated and pre-treated sewage sludge was subsequently compared and promising results were obtained for loads of 1.0 g VS/L (VS, total volatile solids). The methane yield coefficient increased from 88 to 172 mL STP /g VS (STP, 0 °C, 1 atm) after the pre-treatment, while biodegradability was found to be around 81% (in VS). Moreover, the allowed organic loading rate and methane production rate observed for the sewage sludge reached values of up to 4.1 kg VS/m 3 ·d and 1270 L STP /m 3 ·d, respectively. [ABSTRACT FROM AUTHOR]

During advanced biological wastewater treatment, a huge amount of sludge is produced as a by-product of the treatment process. Hence, reuse and recovery of resources and energy from the sludge is a big technological challenge. The processing of sludge produced by Wastewater Treatment Plants (WWTPs) is massive, which takes up a big part of the overall operational costs. In this regard, anaerobic digestion (AD) of sewage sludge continues to be an attractive option to produce biogas that could contribute to the wastewater management cost reduction and foster the sustainability of those WWTPs. At the same time, AD reduces sludge amounts and that again contributes to the reduction of the sludge disposal costs. However, sludge volume minimization remains, a challenge thus improvement of dewatering efficiency is an inevitable part of WWTP operation. As a result, AD parameters could have significant impact on sludge properties. One of the most important operational parameters influencing the AD process is temperature. Consequently, the thermophilic and the mesophilic modes of sludge AD are compared for their pros and cons by many researchers. However, most comparisons are more focused on biogas yield, process speed and stability. Regarding the biogas yield, thermophilic sludge AD is preferred over the mesophilic one because of its faster biochemical reaction rate. Equally important but not studied sufficiently until now was the influence of temperature on the digestate quality, which is expressed mainly by the sludge dewateringability, and the reject water quality (chemical oxygen demand, ammonia nitrogen, and pH). In the field of comparison of thermophilic and mesophilic digestion process, few and often inconclusive research, unfortunately, has been published so far. Hence, recommendations for optimized technologies have not yet been done. The review presented provides a comparison of existing sludge AD technologies and the gaps that need to be filled so as to optimize the connection between the two systems. In addition, many other relevant AD process parameters, including sludge rheology, which need to be addressed, are also reviewed and presented.

This study examined the fate and effects of tylosin (TYL) on anaerobic digestion of swine wastewater at two concentrations of tylosin A (TYLA) using manure collected from swine fed with TYLA (TYLFED) or direct addition of TYLA (TYLADD) to antibiotic-free swine manure, to examine whether there are differences between the two TYL addition methods on methane production and other fermentation parameters. TYLA and tylosin D (TYLD) concentrations, pH, Chemical oxygen demand (COD), Total nitrogen (TN), and diversity of methanogenic archaea population were parameters used for this study. The results showed that concentrations of TYLA and TYLD in the TYLFED treatment were higher ( P < 0.05) than those in the TYLADD treatment. Methane production in the TYLFEDH and TYLFEDL was reduced by 35.52% and 37.06%, respectively, compared with the control during the 7 days addition period; but for TYLADDH and TYLADDL, the decrease ( P < 0.05) was only 12.98% and 7.84%, respectively. The diversity index of methanogenic archaea in the TYLFED treatment were lower than that in the control and the TYLADD on Day 4, but no difference ( P > 0.05) between the control and the TYLADD treatment was observed. pH, COD, and TN were not affected by treatment. Our results showed clear differences in the rate of methane inhibition by the two antibiotic inclusion methods; been higher for the TYLFED treatment than the TYLADD treatment. Since the former method resembles more under actual farm conditions, we suggested that studies on effects of antibiotic residues on anaerobic fermentation should adopt such an approach. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 808-813, 2014 [ABSTRACT FROM AUTHOR]

Abstract: In this study, the changes in sludge reduction, methane production and microbial community structures in a process involving two-stage thermophilic aerobic digestion (TAD) and mesophilic anaerobic digestion (MAD) under different solid retention times (SRTs) between 10 and 40 days were investigated. The TAD reactor (RTAD) was operated with a 1-day SRT and the MAD reactor (RMAD) was operated at three different SRTs: 39, 19 and 9 days. For a comparison, control MAD (RCONTROL) was operated at three different SRTs of 40, 20 and 10 days. Our results reveal that the sequential TAD–MAD process has about 42% higher methane production rate (MPR) and 15% higher TCOD removal than those of RCONTROL when the SRT decreased from 40 to 20 days. Denaturing gradient gel electrophoresis (DGGE) and real-time PCR results indicate that RMAD maintained a more diverse bacteria and archaea population compared to RCONTROL, due to the application of the biological TAD pre-treatment process. In RTAD, Ureibacillus thermophiles and Bacterium thermus were the major contributors to the increase in soluble organic matter. In contrast, Methanosaeta concilii, a strictly aceticlastic methanogen, showed the highest population during the operation of overall SRTs in RMAD. Interestingly, as the SRT decreased to 20 days, syntrophic VFA oxidizing bacteria, Clostridium ultunense sp., and a hydrogenotrophic methanogen, Methanobacterium beijingense were detected in RMAD and RCONTROL. Meanwhile, the proportion of archaea to total microbe in RMAD and RCONTROL shows highest values of 10.5 and 6.5% at 20-d SRT operation, respectively. Collectively, these results demonstrate that the increased COD removal and methane production at different SRTs in RMAD might be attributed to the increased synergism among microbial species by improving the hydrolysis of the rate limiting step in sludge with the help of the biological TAD pre-treatment. [Copyright &y& Elsevier]

Abstract: Pragmatic approach was adopted in order to reduce the amount of parameters necessary for determination, prior to simulation with Anaerobic Digestion Model No. 1 (ADM1). As a result common kinetic constants describing hydrolysis phase, applicable for a wide range of substrates, were determined and tested. Afterwards, this simulation methodology was tested against industrial scale biogas power plant, with 7 dam3 fermenter size, and feed with cattle manure and food waste. The result confirmed the applicability of ADM1 with modified kinetic constants in describing an existing biogas power plant. [Copyright &y& Elsevier]

Highlights: [•] Pathogen content was analysed in three different types of sludge. [•] Mesophilic and thermophilic processes produced Class B and Class A Biosolids. [•] The presence of C. perfringens prevented the obtaining of advanced treated sludge. [•] A two-stage digestion process is suggested for fully sanitation of the sludge. [ABSTRACT FROM AUTHOR]

Water resource recovery facilities have been described as creating breeding ground conditions for the selection, transfer, and dissemination of antibiotic resistance genes (ARGs) among various bacteria. The objective of this study was to determine the effect of direct addition of antibiotic and silver nanoparticles (Ag NPs, or nanosilver) on the occurrence of ARGs in thermophilic anaerobic digesters. Test thermophilic digesters were amended with environmentally-relevant concentrations of Ag NP (0.01, 0.1, and 1.0 mg-Ag/L; corresponding to ≈0.7, 7.0, and 70 mg-Ag/kg total solids) and sulfamethoxazole (SMX) that span susceptible to resistant classifications (1, 5, and 50 mg/L) as potential selection pressures for ARGs. Tetracycline (tet(O), tet(W)) and sulfonamide (sulI, sulII) ARGs and the integrase enzyme gene (/«ill) associated with Class 1 integrons were measured in raw sludge, test thermophilic digesters, a control thermophilic digester, and a control mesophilic digester. There was no apparent effect of Ag NPs on thermophilic anaerobic digester performance. The maximum SMX addition (50 mg/L) resulted in accumulation of volatile fatty acids and low pH, alkalinity, and volatile solids reduction. There was no significant difference between ARG gene copy numbers (absolute or normalized to 16S rRNA genes) in amended thermophilic digesters and the control thermophilic digester. Antibiotic resistance gene copy numbers in digested sludge ranged from 10³ to 106 copies per pL (≈8 X 10¹ to 8 X 104 copies per pg) of sludge as result of a 1-log reduction of ARGs (2-log reduction for mill). Quantities of the five ARGs in raw sludge ranged from 104 to 108 copies per pL (≈4 X 10² to 4 X 106 per pg) of sludge. Test and control thermophilic digesters (53 °C, 12-day solids retention time [SRT]) consistently reduced but did not eliminate levels of all analyzed genes. The mesophilic digester (37 °C, 20-day SRT) also reduced levels of sulI, sulll, and /«til genes, but levels of tet{O) and tet(W) were the same or higher than in raw sludge. Antibiotic resistance gene reductions remained constant despite the application of selection pressures, which suggests that digester operating conditions are a strong governing factor of the bacterial community composition and thus the prevalence of ARGs. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic digestion of organic waste plays an important role for the development of sustainable energy supply based on renewable resources. For further process optimization of anaerobic digestion, biogas production with the commonly used substrates, grass, maize, and green weed silage, together with industrial glycerine, were analyzed by the Weender analysis/van Soest method, and a simulation study was performed, based on the International Water Association’s (IWA) Anaerobic Digestion Model No. 1 (ADM1). The simplex algorithm was applied to optimize kinetic constants for disintegration and hydrolysis steps for all examined substrates. Consequently, new parameters were determined for each evaluated substrate, tested against experimental cumulative biogas production results, and assessed against ADM1 default values for disintegration and hydrolysis kinetic constants, where the ADM1 values for mesophilic high rate and ADM1 values for solids were used. Results of the optimization lead to a precise prediction of the kinetics of anaerobic degradation of complex substrates. [Copyright &y& Elsevier]

Abstract: The mesophilic anaerobic digestion of wastewater derived from biodiesel manufacturing, in which total chemical oxygen demand (COD total) was found to be 428g/L, was studied at laboratory scale. Firstly, wastewater was acidified to recover its free fatty acid content. The resulting aqueous phase was then neutralized and subjected to coagulation–flocculation and electrocoagulation to demulsify the remnant organic matter. A 45% and 63% reduction in overall COD total was observed with the acidification–electrocoagulation and acidification–coagulation–flocculation pre-treatments, respectively. However, the anaerobic biodegradability of acidified-electrocoagulated wastewater was found to be the highest (98% COD), while the methane yield coefficient reached a mean value of 297mLCH4/gCOD removed (1atm, 0°C). Moreover, the allowed organic loading rate and the mean methane production rate were considerably higher for acidified-electrocoagulated wastewater. Consequently, the combination of acidification–electrocoagulation with anaerobic digestion might be a good alternative to efficiently purify wastewater derived from biodiesel manufacturing. [Copyright &y& Elsevier]

Abstract: This paper identifies key components of the microbial community involved in the mesophilic anaerobic co-digestion (AD) of mixed waste at Rayong Biogas Plant, Thailand. The AD process is separated into three stages: front end treatment (FET); feed holding tank and the main anaerobic digester. The study examines how the microbial community structure was affected by the different stages and found that seeding the waste at the beginning of the process (FET) resulted in community stability. Also, co-digestion of mixed waste supported different bacterial and methanogenic pathways. Typically, acetoclastic methanogenesis was the major pathway catalysed by Methanosaeta but hydrogenotrophs were also supported. Finally, the three-stage AD process means that hydrolysis and acidogenesis is initiated prior to entering the main digester which helps improve the bioconversion efficiency. This paper demonstrates that both resource availability (different waste streams) and environmental factors are key drivers of microbial community dynamics in mesophilic, anaerobic co-digestion. [Copyright &y& Elsevier]

Abstract: The main objective of this research was to propose two methods to quantify faecal coliforms and Salmonella spp. in both raw sludge and mesophilic digested sludge. Besides, a performance of a mesophilic digester operating at 30 and 20 days of solid retention time (SRT) was studied. The microbiological methods were carried out according to the Standard Methods (APHA, 1998) and to the American Environmental Protection Agency (US EPA, 1992) and new stages were suggested to determine pathogen concentrations in raw sludge as well as digested biosolids. The results showed that the anaerobic mesophilic digestion is able to remove high percentages of faecal coliforms and Salmonella spp. giving rise to digested sludge that can be classified as Class B biosolid, i.e. an effluent with faecal coliforms density less than 2 × 106 colonies g−1 total solids. Viable helminth eggs are not necessarily reduced in Class B biosolids. [Copyright &y& Elsevier]

Abstract: Mono fermentation of grass silage without the addition of manure was performed over a period of 345days under mesophilic conditions (38°C). A simulation study based on the IWA Anaerobic Digestion Model No. 1 (ADM1) was done in order to show its applicability to lignocellulosic biomass. Therefore, the influent was fractioned by established fodder analysis (Weender analysis and van Soest method). ADM1 was modified with a separate compound of inert decay products similar to the approach of Activated Sludge Model No. 1 (ASM1). Furthermore, a function, which described the influence of solids on the process of hydrolysis, has been integrated to reproduce reliable ammonium concentrations. The model was calibrated by using the modified Nash–Sutcliffe coefficient to evaluate simulation quality. It was possible to fit observed data by changing only hydrogen inhibition constants and the maximum acetate uptake rate. The extended ADM1 model showed good agreement with measurements and was suitable for modeling anaerobic digestion of grass silage. [Copyright &y& Elsevier]

Natural and modified zeolites (0.5-1.0 mm) from the Tasajera deposit in Cuba were used to enhance the anaerobic digestion process of synthetic substrates. Natural zeolites were modified by ionic exchange and by adsorption with nickel, cobalt and magnesium. The experiments were carried out by using an inoculum from a full-scale anaerobic reactor treating winery wastewater. Modified natural zeolites not only enhanced the anaerobic digestion process, but also increased the specific methanogenic activity (SMA) of the sludges. The textural and chemical surface characteristics of the modified zeolites were related to the process performance, volatile fatty acid (VFA) production and microbial communities found in the digesters. For the selected dose of modified zeolites [0.05 g/g of volatile suspended solids (VSS)], the lowest concentration was found for cobalt followed by nickel and magnesium. Based on the analyses of anaerobic biofilms, the heavy metal incorporated into the zeolite was shown to have a great influence on the predominance of species. For example, the presence of nickel and cobalt favoured Methanosaeta, while at the same dose magnesic zeolite stimulated the presence of Methanosarcina and sulfate-reducing bacteria (SRB). In digesters with modified zeolites and metal supplementations the values of SMA were higher than those obtained in the control and natural zeolite digesters. [ABSTRACT FROM AUTHOR]

Similar evolution was obtained for the stable carbon isotope signatures δ13CH4 and the modelpredicted relative rate of aceticlastic methanogenesis during mesophilic methanization of municipal solid wastes. In batch incubations, the importance of aceticlastic and hydrogenotrophic methanogenesis changes in time. Initially, hydrogenotrophic methanogenesis dominated, but increasing population of Methanosarcina sp. enhances aceticlastic methanogenesis. Later, hydrogenotrophic methanogenesis intensified again. A mathematical model was developed to evaluate the relative contribution of hydrogenotrophic and aceticlastic pathways of methane generation during mesophilic batch anaerobic biodegradation of the French and the Chinese Municipal Solid Wastes (FMSW and CMSW). Taking into account molecular biology analysis reported earlier three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H2/H2CO3 were considered in the model. The total organic and inorganic carbon concentrations, methane production volume, methane and carbon dioxide partial pressures values were used for the model calibration and validation. Methane isotopic composition (δ13CH4) evolution during the incubations was used to independently validate the model results. The model demonstrated that only the putrescible solid waste was totally converted to methane [ABSTRACT FROM AUTHOR]

The main obstacles existing in the biodegradation of primary sludge are particle de-amalgamation and the degradation-resisting structure of large-size particulate. Microwave irradiation solubilizes primary sludge by interaction of the electromagnetic field with polar particles in the sludge, which leads to a temperature increase in the irradiated sample. The influence of microwave irradiation on the characteristics and biochemical methane potential of microwave-pretreated primary sludge was studied in terms of microwave intensity (40 and 80% of total microwave power), sludge solid concentration (1 to 4% total solids, w/v) and pretreatment temperature achieved (35 to 90 °C). Microwave irradiation was found to increase the concentration of soluble chemical oxygen demand in the sludge. The ratio of soluble to total chemical oxygen demand increased from 2.5 to between 6 and 7% for primary sludge with 4% total solids concentration at a pretreatment temperature of 90 °C. In biochemical methane potential tests, biogas production rate increased with both pretreatment temperature and sludge total solids concentrations. For primary sludge with 4% total solids concentration pretreated to 90 °C, biogas production rate increased by 37% or resulted in a 28% reduction in required digestion time to achieve 85% of the ultimate biogas production. A first-order reaction model showed a constant increase in the biogas production rate coefficient with the increase in microwave pretreatment temperature. Microwave intensity in the range of pretreatment temperatures studied (35 to 90 °C) presented no obvious impact on primary sludge solubilization or anaerobic digestion in terms of ultimate biodegradation efficiency. [ABSTRACT FROM AUTHOR]

Effect of microwave pretreatment (MW) high temperature (175°C) and MW intensity to waste activated sludge digested with acclimatized inoculum in single- and dual-stage semi-continuous mesophilic anaerobic digesters at different sludge retention times (SRTs) (20, 10 and 5 days) were investigated. MW pretreatment led to similar sludge stabilization at low SRTs (5 and 10 days). Although lowering MW intensity slightly improved sludge solubilization, it had a negative effect on digestion at low SRTs. Single-stage digesters with MW pretreatment surpass dual-stage digesters performances. [Copyright &y& Elsevier]

High-solids anaerobic digestion can consistently achieve 55 to 60% volatile solids destruction after thermal hydrolysis pretreatment, which reduces its viscosity and increases the fraction of soluble organic matter. For feed sludge with total solids concentrations between 6.8 and 8.2%, the process is stable at hydraulic retention times of 9 to 12 days, significantly increasing the treatment capacity of existing digesters or, in treatment plants without spare capacity, helping to postpone, reduce, or even avoid costly infrastructure investments. Process stability is related to the high concentration of soluble organic matter in the digesters. High-solids temperature-phased digestion appears to be superior to high-solids mesophilic digestion, with respect to process flexibility and stability, biosolids stabilization, and biogas generation, although ammonia inhibition may have occurred. Implementation of high-solids digestion could significantly reduce operation and maintenance costs of solids-handling operations. [ABSTRACT FROM AUTHOR]

The potential of a mesophilic-thermophilic-mesophilic anaerobic digestion system was investigated with respect to improvement of both digestion and sanitation efficiencies during treatment of liquid cattle manure. The pilot plant produced a high methane yield from liquid dairy cattle manure of 0.24 m³ (kg VSfed)-1. Considering the low system loading rate of 1.4–1.5 kg VS (m³ d)-1, digestion efficiency compared to conventional processes did not appear improved. The minimum guaranteed retention time in the tubular thermophilic reactor was increased compared to a continuously stirred tank reactor. Levels of intestinal enterococci in raw liquid manure as determined with cultivation methods were reduced by 2.5–3 log units to a level of around 10² cfu/mL. This sanitizing effect was achieved both during mesophilic-thermophilic-mesophilic and thermophilic-mesophilic treatment, provided the thermophilic digester was operated at 53–55°C. A change in feeding interval from 1 h to 4 h did not significantly alter methane yield and sanitation efficiency. It was proposed that a two-stage, thermophilic-mesophilic anaerobic digestion system would be able to achieve the same sanitizing effect and equal or better digestion efficiency at lower costs. [ABSTRACT FROM AUTHOR]

Abstract: The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35–37°C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20–40 days and an organic loading rate of some 1kgVS/day. The solids content of the sludge fed to the digesters was in the range 2.6–3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07–0.18m3/kgVSfed. The specific gas production per kilogram of volatile solids destroyed was in the range 0.5–0.9m3/kgVSdestroyed and the reduction of the volatile solids concentration was in the range 13–27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07m3/kgVSfed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed. [Copyright &y& Elsevier]

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from chickpea flour was carried out in a laboratory-scale, mesophilic (35 °C) fluidised-bed reactor with saponite as bacterial support. Soluble chemical oxygen demand (SCOD) removal efficiencies in the range of 96.8–85.2% were achieved in the reactor at organic loading rates (OLR) of between 0.58 and 2.10 g chemical oxygen demand (COD)/l per day, hydraulic retention times (HRT) of between 14.9 and 4.5 days and average feed COD concentration of 9.1 g/l. Eighty-five percent of feed COD could be removed up to OLR of 2.1 g COD/l per day. The yield coefficient of methane production was 0.34 l of methane (at STP) per gram COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favourable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. Experimental data indicated that a total alkalinity in the range of 1090–2130 mg/l as CaCO3 was sufficient to prevent the pH from decreasing to below 7.2 for OLR of up to 2.7 g COD/l per day. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3–0.4) for OLR and HRT up to 2.7 g COD/l per day and 3.5 days, respectively. For a HRT of 2.8 days (OLR of 3.00 g COD/l per day) the start of acidification was observed in the reactor. [Copyright &y& Elsevier]

Conventionally treated sewage sludge may contain high concentrations of potentially pathogenic microorganisms and additional treatment is required to minimise the risks to health if it is to be recycled to agricultural land. Mesophilic anaerobic digestion (MAD) is the most widely used process in the UK for stabilising sludge prior to agricultural recycling, but little is known about the fate of a number of enteric pathogens as the sludge passes through the treatment processes. The aim of this study was to determine the efficiency of MAD in removing the bacterial enteric pathogens, Salmonella senftenberg, Listeria monocytogenes and Campylobacter jejuni which were added as a spike to the digester feedstock, together with the die-off of indigenous Escherichia coli already present in the sludge. The primary sludge digestion stage of MAD was found to achieve a log removal of 1.66 for E. coli, 2.23 for L. monocytogenes and 2.23 for S. senftenberg. However, the extent of die-off was a function of the numbers of pathogens in the feed and as these increased the log removal also increased. The numbers of C. jejuni were not affected by primary sludge digestion. Additional die-off was provided by secondary sludge digestion with log removals of 1.70 for E. coli, 2.10 for S. senftenberg and 0.36 for C. jejuni. [Copyright &y& Elsevier]

Evaluates the comparative process stability and efficiency of mesophilic anaerobic digestion for reactor configurations. Stability of pH and volatile fatty acid; Importance of microbial consortia for the removal of propionate; Addition of nutrients into the reactors.

In this work, the impact of granular activated carbon (GAC) on the mesophilic and thermophilic anaerobic digestion of chicken manure and the structure of microbial communities was investigated. These results demonstrated that GAC supplementation effectively enhanced the consumption of produced organic acids in the mesophilic and thermophilic batch tests, accompanied by faster biomethane production in the presence of GAC than from reactors without GAC. However, since the free ammonia level was 3–6 times higher in the thermophilic reactors, this led to the instability of the anaerobic digestion process of the nitrogen-rich substrate at thermophilic temperatures. Bacteroidia and Clostridia were the two main bacterial classes in the mesophilic reactors, whereas the class Clostridia had a competitive advantage over other groups in the thermophilic systems. The archaeal communities in the mesophilic reactors were mainly represented by representatives of the genera Methanosarcina, Methanobacterium, and Methanotrix, whereas the archaeal communities in the thermophilic reactors were mainly represented by members of the genera Methanosarcina, Methanoculleus, and Methanothermobacter. New data obtained in this research will help control and manage biogas reactors in the presence of GAC at different temperatures. [ABSTRACT FROM AUTHOR]

Invasive plant species threaten native species and habitats causing ecologic, economic and social burden. When creating climate friendly solutions by utilizing plant biomasses in biogas and fertilizer production, safety should be ensured concerning the use of residues. This study concentrates on the treatment of biomasses containing invasive plant material by tunnel and windrow composting, and by farm-scale and laboratory-scale anaerobic digestion (AD) in mesophilic conditions. Germination of the nationally settled and harmful invasive species Lupinus polyphyllus Lindl. was investigated after these processes. In addition, the role of the conditions found in the processes that destroyed seeds were studied, such as the time of exposure, temperature and static pressure. Dormant seeds are well protected against harsh conditions and can survive through various stress factors, but also become vulnerable as more factors are combined and time of exposure is extended. Our results suggest that the risks involved for the utilization of harmful invasive species increase with mesophilic temperatures and single treatments if the processing conditions are not stabile. One-month treatment with windrow composting showed a high risk for dormant seeds of L. polyphyllus seeds to survive, whereby extending the processing time reduced it substantially. Hard coated seeds can thus be broken with a combination of thermophilic temperatures, moisture and static pressure. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) appears to be a popular unit operation in wastewater treatment plant to treat waste activated sludge (WAS) and the produced methane gas can be harvested as renewable energy. However, WAS could inhibit hydrolysis stage during AD and hence pre-treatment is required to overcome the issue. This paper aimed to study the effect of electrochemical pre-treatment (EP) towards efficiency of AD using titanium coated with ruthenium oxide (Ti/RuO2) electrodes. The investigation has been carried out using in-house laboratory batch-scale mesophilic anaerobic digester, mixed under manipulation of important operating parameters. Optimization was performed on EP using response surface methodology and central composite design to maximize sludge disintegration and dewaterability. By operating at optimal conditions (pH 11.65, total solids 22,000 mg/L, electrolysis time 35 min, current density 6 mA/cm2, and 1000 mg/L of sodium chloride), the pre-treated WAS in terms of mixed liquor volatile suspended solids (MLVSS) removal, soluble chemical oxygen demand (sCOD), capillary suction time (CST) reduction, and extracellular polymeric substance (EPS) were 38%, 4800 mg/L (increased from 935 mg/L), 33%, and 218 mg/L, respectively. Following AD, the volatile solids (VS) removal and chemical oxygen demand (COD) removal by EP were enhanced from 40.7% and 54.7% to 47.2% and 61.5%, respectively, at steady-state. The biogas produced from control and electrochemical pre-treated WAS were in the ranges of 0.12 to 0.17 and 0.2 to 0.24 m3/kg VSfed, respectively, and the volume of biogas produced was 44–67% over the control. Based on the results obtained, suitability of EP for WAS prior to AD was confirmed. [ABSTRACT FROM AUTHOR]

Waste activated sludge (WAS) from wastewater treatment plants is an important reservoir of antibiotic resistance genes (ARGs). The fate of ARGs in this process was not revealed previously. The present study applied metagenomic approach to examine the occurrence and fate of ARGs in thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM), by comparison with mesophilic alkaline fermentation followed by mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The removal efficiency of two-stage anaerobic digestion (AD) to total ARGs is higher than that of one-stage AD. The hydrogen and methane production stages of two-stage AD processes have dissimilar impact on the fate of ARGs. Macrolide, lincosamide, and streptogramin (MLS) resistance genes were enriched, especially in the hydrogen production reactors of TM and MM processes. Statistical analysis of metagenomic profiles analysis suggested that bac A may be the differential ARG subtype of two-stage AD process. ARG-like sequences encoding antibiotic efflux pump, antibiotic inactivation and antibiotic target alteration mechanisms were identified as the dominant ARGs resistance mechanisms in all samples. Procrustes analysis showed that microbial community composition structured the resistome. Co-occurrence patterns between ARGs and microbial phylogeny revealed that 26 bacterial species might be potential hosts of 94 ARG subtypes. ga1 • Two-stage anaerobic digestion caused a more great elimination of the total ARGs. • MLS were enriched in hydrogen production reactor of two-stage anaerobic digestion. • bac A may be the differential ARG subtype of two-stage anaerobic digestion. • Microbial community composition determined the ARGs composition. [ABSTRACT FROM AUTHOR]

This study explored the fate of mobile genetic elements (MGEs) in anaerobic digestion (AD) system with four nanoparticles (NPs) added, including carbon NPs, Al 2 O 3 NPs, ZnO NPs, and CuO NPs. 16S rRNA amplicon sequencing and quantitative PCR to investigate the microbial community, MGEs abundance and the potential host in the AD process. The results of high-throughput sequencing showed that ZnO NPs and CuO NPs significantly reduced the microbial diversity and significantly changed the microbial community structure. Simultaneously, the absolute abundance of MGEs increased by 145.01%, 159.67%, 354.70%, and 132.80% on the carbon NPs, Al 2 O 3 NPs, ZnO NPs, and CuO NPs. The enrichment rate of tnpA -03 in ZnO NPs group was the highest, which could reach up to 2854.80%. Co-occurrence analysis revealed that Proteobacteria harbored the vast majority of MGEs followed by Firmicutes. Redundancy analysis and variation partitioning analysis showed that metabolites were the main factors that shifted the succession of bacterial communities. Moreover, there were significant positive correlations between metabolites and part MGEs (such as tnpA -01, tnpA -02, tnpA -03, tnpA -04, tnpA -05, tnpA -07 and IS CR1). This study provides a new perspective that NPs increase the risk of antibiotic resistance through MGEs during AD process. ga1 • NPs changed microbial communities and reduced bacterial diversity in anaerobic digestion. • The abundance of total MGEs increased in the anaerobic digestion with NPs. • Proteobacteria and Firmicutes were potential hosts of MGEs. • Metabolites were the major factors of the shift in bacterial communities and MGEs. [ABSTRACT FROM AUTHOR]

This study explored the effect of eight antimicrobials on the efficiency of biogas production in the anaerobic digestion (AD) process of cattle manure. The microbiome involved in AD, presence and number of genes mcrA, MSC and MST specific for Archaea, and antibiotic resistance genes (ARGs) concentration in digestate (D) were examined. Supplementation of antibiotics to substrate significantly lowered biogas production. Amoxicillin caused a 75% decrease in CH4 production in comparison with the control samples. Enrofloxacin, tetracycline, oxytetracycline, and chlortetracycline reduced the amount of biogas produced by 36, 39, 45 and 53%, respectively. High-throughput sequencing of 16S rRNA results revealed that bacteria dominated the Archaea microorganisms in all samples. Moreover, antibiotics led to a decrease in the abundance of the genes mcrA, MSC, MST, and induced an increase in the number of tetracyclines resistance genes. Antibiotics decreased the efficiency of the AD process and lowered the quantity of CH4 obtained, while stimulating an increase in the number of ARGs in D. This work reveals how antimicrobials affect the cattle manure AD process and changes in microbial biodiversity, number of functional genes and ARGs in the digestate due to drugs exposure. It also, provides useful, practical information about the AD process. [ABSTRACT FROM AUTHOR]

Hot water extraction (HWE) removes hemicellulose from woody biomass to give improved end products while producing a sugar-rich by-product stream, which requires proper treatment before disposal. Hot water extracted Norway spruce (Picea abies) at two different pretreatment conditions (140 °C for 300 min (H140) and 170 °C for 90 min (H170)) generated hydrolysate as a by-product, which was used in mesophilic anaerobic digestion (AD) as substrate. H140 gave a higher methane yield (210 NmL/g COD—chemical oxygen demand) than H170 (148 NmL/g COD) despite having a lower concentration of sugars, suggesting that different levels of inhibitors (furans and soluble lignin) and recalcitrant compounds (soluble lignin) affected the methane yield significantly. Organic loads (OLs) had a negative effect on the methane yield, as observed during AD of H170, while such an effect was not observed in the case of H140. This suggests that the decrease in methane yield (32%) of H170 compared to H140 is primarily due to inhibitors, while the decrease in methane yield (19%) of H140 compared to the synthetic hydrolysate is primarily due to recalcitrant substances. Therefore, both OL and pretreatment conditions must be considered for efficient anaerobic digestion from hydrolysate for enhanced methane production. [ABSTRACT FROM AUTHOR]

The fate of diverse antibiotic resistance genes (ARGs) in anaerobic digestion (AD) system under different temperature remains largely unknow. This study employed the shotgun metagenomic sequencing and 16S rRNA amplicon sequencing approaches and investigated the shifts of composition and abundance of more than 1360 ARGs, as well as microbial community, in a temperature-raising AD system (from 35 °C to 55 °C) treating municipal sewage sludge. Results suggested that the six ARGs, inlcuding mac B, tet A(58), bcr A, evg S, mtr A, and ole C, were predominated in digested sludge. More than 407ARG subtypes (30%) could be largely reduced under high temperature condition. Thermophilic AD (55 °C) provided a better removal for tetracycline, macrolide, penam, fluoroquinolone, acridine dye, and peptide resistance genes when compared to mesophilic AD (35 °C). The removal rates of these genes reached 29.7%–32.3%. In addition, at the end of thermophilic digestion process, the relative abundance of Firmicutes increased (from 18.22% to 74.89%), while Proteobacteria and Chloroflexi both decreased, from 36.39% to 6.80% and 20.29%–2.64%. This study further proposed the underlying mechanisms of effective elimination of ARGs under high temperature by: (1) the reduction of genes encoding antibiotic efflux pump, (2) the promotion of sludge biomass degradation rate, (3) the loss of microbial community diversity in AD systems, and (4) the inactivation of multidrug-resistant bacteria. The significance of current study is in characterizing the fate of ARGs across AD process, which allows to correlate diverse genetic properties with digesters' operational condition. Results provided an insight into the manipulation of AD technology (e.g. temperature) to efficiently remove ARGs from municipal sewage sludge. • Fate of ARGs in a temperature-raising anaerobic digester was investigated. • More than 1360 ARG subtypes were identified by metagenomics approach. • Effective reduction of ARGs under thermophilic condition was confirmed. • Underlying mechanisms of ARGs removal were proposed. [ABSTRACT FROM AUTHOR]

The olive oil production is an important industrial sector in many Mediterranean areas, but it is currently struggled by the necessity of a proper valorisation of the olive mill solid waste or alperujo. The alperujo is the main by-product generated during the two-phase olive oil extraction, accounting for up to 80% of the initial olive mass. The alperujo is a source of valuable compounds, such as the pomace olive oil or highly interesting phenolic compounds. In the present research, a novel biorefinery approach has been used for phenolic compounds recovery. However, the extraction of these valuables compounds generates different exhausted phases with high organic matter content that are required to be managed. This study consists of the evaluation of the anaerobic biodegradability of the different fractions obtained in a novel biorefinery approach for the integral valorisation of alperujo. The results show that the different phases obtained during the biorefinery of the alperujo can be effectively subjected to anaerobic digestion and no inhibition processes were detected. The highest methane yield coefficients were obtained for the phases obtained after a two-months storages, i.e., suspended solids and liquid phase free of suspended solids, which generated 366 ± 7 mL CH4/g VS and 358 ± 6 mL CH4/g VS, respectively. The phenol extraction process reduced the methane yield coefficient around 25% due to the retention of biodegradable compounds during the extraction process. Regardless of this drop, the anaerobic digestion is a suitable technology for the stabilization of the different generated residual phases, whereas the high market price of the extracted phenols can largely compensate the slight decrease in the methane generation. [ABSTRACT FROM AUTHOR]

The performance of a single-stage semi-pilot scale reactor in anaerobically digesting food waste was examined and its microbial community composition investigated using high-throughput 16S rRNA gene sequencing. Highest biogas yield (1.01 L/g VS added), highest removal efficiency for chemical oxygen demand (COD) (95.84%) and volatile solid (VS) (92.7%) were achieved during 124-day HRT. When the hydraulic retention time (HRT) reduced from 124 days to 62 days, ammonia and volatile fatty acids (VFA) concentration in the reactor gradually increased while pH, biogas yield, removal efficiency for VS and COD decreased gradually. This was likely due to the accumulation of volatile fatty acid (VFA), which resulted in scum accumulating in the reactor. The abundance of acid-producing bacteria resulted in the accumulation of VFA in the reactor, which is a critical factor that could explain process failure. Hydrogenotrophic methanogenesis was the main pathway for producing methane from hydrogen and carbon dioxide during the 124-day HRT. The decline in hydrogenotrophic methanogens at 62-day HRT inhibited the decomposition of VFA and accelerated the transfer of the amino acid degradation pathway, which further enhanced VFA accumulation. However, the dominant methanogens failed to degrade the excessive acetate at 41-day HRT. This metabolic discrepancy ultimately led to process deterioration. • Stability and performance of the AD were significantly affected by different HRTs. • Microbial community was investigated by 454 pyrosequencing technique. • A significant microbial shift was observed during decreased HRT operations. • Proliferation of acid-producing bacteria resulted volatile fatty acid accumulation. [ABSTRACT FROM AUTHOR]

This study was on the comparison of hydrothermal treatments at 170 °C (steam injection) and 220 °C (steam explosion) to solubilize the organic matter contained in residual strawberry extrudate, focusing on phenolic compounds that were susceptible to be extracted and on sugars. After the extraction step, the remaining strawberry extrudate phases were subjected to anaerobic digestion to generate biogas that would compensate the energy requirements of the suggested hydrothermal treatments and to stabilize the remaining waste. Hydrothermal treatment at 220 °C allowed the recovery of 2053 mg of gallic acid eq. per kg of residual strawberry extrudate. By contrast, after hydrothermal treatment at 170 °C, only 394 mg of gallic acid eq. per kg of residual strawberry extrudate was recovered. Anaerobic digestion processes were applied to the de-phenolized liquid phase and the solid phase together, which generated similar methane productions, i.e., around 430 mL CH4/g volatile solids, after both 170 °C and 220 °C hydrothermal treatments. Considering the latest observation, hydrothermal treatment at 220 °C is a preferable option for the valorization of residual strawberry extrudate (RSE) due to the high solubilization of valuable phenolic compounds that can be recovered. [ABSTRACT FROM AUTHOR]