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• Offal wastewater (OWW) anaerobic digestion is technically viable in tubular digesters. • OWW anaerobic digestion leads to a biogas production rate>0.1 m3/m3dig d. • The integration of anaerobic technology in slaughterhouses would allow energy savings. • High organic loads favor the integration of biogas through boilers in slaughterhouses. • Biogas integration in slaughterhouses by cogeneration systems is economically viable. Anaerobic digestion (AD) has been a widely tested alternative for the management and valorization of wastewater from the animal slaughter process. However, the integration of AD in slaughterhouses depends on technical and economic aspects. In Colombian slaughterhouses AD integration is limited by the availability of land. In the present study, a techno-economic evaluation of the AD of offal wastewater (OWW) stream in a laboratory scale mesophilic tubular digester was carried out. The digester was operated at organic loading rates (OLR) of 0.28, 0.50, 1.0, 1.5 and 2.0 kg VS/m3 d. Boilers and a CHP (combined heat and power) system were considered for energy integration of biogas. For the economic study, the cost structure of a Colombian slaughterhouse was considered. The AD of OWW at 2.0 kg VS/m3 d OLR was unstable with risk of inhibition. Increasing the OLR from 0.28 to 1.5 kg VS/m3 d caused a reduction in the specific biogas production (SBP) from 0.474 to 0.069 m3/kg VS However, the biogas production rate (BPR) remained constant at around 0.105 m3/m3dig d for OLRs > 0.28 kg VSm3 d. Therefore, OWW anaerobic digestion in low-cost mesophilic biogas plants is technically feasible with OLRs between 0.28 and 1.5 kg VS/m3 d. The implementation of boilers is economically favorable for OLR ≥ 1.0 kg VS/m3 d. Nevertheless, feasibility is very sensitive to variations in the cost structure. The implementation of CHP was feasible in the range of OLRs evaluated and its viability is not affected by changes in assumed costs. [ABSTRACT FROM AUTHOR]

• Combined activated carbon supplement and feedstock microwave pretreatment studied. • Joint implementation effective in mitigating antibiotic resistance genes issue. • Average methane yield and CH 4 percentage increased by 10–41% and 6–29%, respectively. • Bacterial genus Treponema and methanogen genus Methanosarcina selectively enriched. • KEGG cluster and genome functional analysis validated enhanced microbial activity. Antibiotic resistance genes (ARGs) stemming from animal manure pose adverse impacts on human health and ecology and consequently cost more to treat the anaerobic digestate after manure fermentation. To jointly reduce the ARGs and improve the methane yield during anaerobic digestion (AD) of chicken manure, microwave pretreatment of manure and activated carbon supplementation were simultaneously applied and evaluated in an anaerobic digester (R1). For comparison, three other digesters, a digester (R2) fed with raw chicken manure without activated carbon, a digester (M1) fed with microwave-pretreated chicken manure and without activated carbon, and a digester (M2) fed with raw chicken manure supplemented with activated carbon, were operated in parallel. The results showed that after 47 days of AD operation, R1 achieved an 87–95% ARGs removal rate, significantly higher than that of R2 (34–58%). As the loading rate was 5.8–7.0 g volatile solids (VS)/L, the average methane yield of R1 was 0.287 L/g VS, which was 1.4-fold, 1.3-fold and 1.1-fold higher than that of R2, M1 and M2, respectively. The increased methane yield was ascribed to the combined effect of feedstock microwave pretreatment and activated carbon supplementation. Pyrosequencing analysis showed that the dominant bacterial phyla were Firmicutes , Bacteroidetes and Proteobacteria while the dominant archaeal genus were Methanosarcina , Methanothrix , Methanolinea , Methanomassiliicoccus , Methanospirillum , Methanoregula and Methanobacterium. The KEGG cluster analysis and functional analysis of genome from archaeal communities demonstrated that the dominant functions enhanced by substrate microwave pretreatment and activated carbon supplementation were linked to amino acid metabolism, carbohydrate metabolism, cell communication, energy metabolism, signaling molecules and interaction, and signal transduction. [ABSTRACT FROM AUTHOR]

We evaluated the chronic impact of oxytetracycline (OTC) on performance and antibiotic resistance development during the mesophilic anaerobic digestion (AD) of antibiotic-containing biomass. Mesophilic AD was conducted in a completely stirred tank reactor by constantly feeding municipal excess sludge spiked with increasing concentrations of OTC (0–1000 mg L −1 ) under a solid retention time of 20 days over a period of 265 days. Results showed that methane generation of mesophilic AD was inhibited when the OTC concentration in digested sludge was increased to around 18,000 mg kg −1 (OTC dose, 1000 mg L −1 ), due to the inhibition of fermenting and acidogenic bacteria. Metagenomic sequencing and high-throughput quantitative PCR analysis demonstrated that tetracycline resistance genes were the most dominant type (38.47–43.76%) in the resistome, with tetG , tetX , tetM , tetR , tetQ , tetO , and tetL as the dominant resistant subtypes throughout the whole experimental period. The relative abundance of these tet genes increased from 2.10 × 10 −1 before spiking OTC (OTC concentration in digested sludge, 8.97 mg kg −1 ) to 2.83 × 10 −1 ( p  < 0.05) after spiking OTC at a dose of 40 mg L −1 (OTC concentration in digested sludge, 528.52 mg kg −1 ). Furthermore, mobile genetic elements, including integrons, transposons, and plasmids, were also enriched with the increase in OTC dose. Based on partial canonical correspondence analysis, the contributions of horizontal (mobile element alteration) and vertical (bacterial community shift) gene transfer to antibiotic resistome variation were 29.35% and 21.51%, respectively. Thus, considering the inhibition of hydrolytic acidification and enrichment of antibiotic resistome, mesophilic AD is not suggested to directly treat the biomass containing OTC concentration higher than 200 mg L −1 . [ABSTRACT FROM AUTHOR]

• Swine manure anaerobic digestion (AD) at 55 °C raised 47.9% methane than at 35 °C. • More oxytetracycline (OTC) led to less methane from mesophilic and thermophilic ADs. • Adding 400 mg/L OTC reduced energy conversion efficiencies of ADs by 21.4–48.4%. • More than 63.0% and 72.5% OTC were removed via mesophilic and thermophilic ADs. • Methanolinea was bearable to high content OTC in mesophilic and thermophilic ADs. Anaerobic digestion (AD) technology is a valuable method for producing biogas fuels and treating livestock wastes such as swine manures concurrently. However, the effect of emerging antibiotics on the AD process is still undiscovered. In this study, the influence of oxytetracycline (OTC) on the AD process was investigated under mesophilic (35 ± 0.5 °C) and thermophilic (55 ± 0.5 °C) conditions, respectively. The presence of OTC significantly inhibited the production of methane in AD process, where the methane yields decreased by 58.6% and 73.3% in mesophilic and thermophilic ADs when the initial concentration of OTC was 400 mg/L, respectively. Besides, OTC can be markedly degraded by the AD process with a removal efficiency higher than 90% when the OTC initial concentration is lower than 10 mg/L. Furthermore, a higher concentration OTC led to a lower biomethane yield, energy conversion efficiency, and contaminant removal during both mesophilic and thermophilic ADs. With adding of 400 mg/L OTC, Clostridium sensu stricto 1 (32.9%) and Anaerolinea (29.3%) are dominant to biodegrade organic matter during mesophilic and thermophilic AD systems. Correspondingly, Methanosaeta was functional in producing biomethane in both mesophilic (60.8%) and thermophilic (56.4%) AD systems. Additionally, Methanolinea was bearable to high concentrations of OTC during mesophilic and thermophilic AD processes. [ABSTRACT FROM AUTHOR]

In this study, swine manure containing sulfachloropyridazine sodium (SCPS) and zinc was subjected to mesophilic (37 °C) anaerobic digestion (AD). The absolute abundances (AAs) of antibiotic resistance genes (ARGs) were evaluated, as well as intI1 and intI2 , and the degradation of SCPS according to variation in the amount of bio-available zinc (bio-Zn). In digester that only contained SCPS, the concentrations of SCPS were lower than that digesters both contain SCPS and Zn. Compared with the control digester, the addition of SCPS increased the AAs of sul1 , sul3 , drfA1 , and drfA7 by 1.3–13.1 times. However, compared with the digester with SCPS but no added Zn, the AAs of sul3 , drfA1 , and drfA7 were decreased by 21.4–70.3% in the presence of SCPS and Zn, whereas sul1 and sul2 increased 1.3–10.7 times. There were significant positive correlations ( P < 0.05) between the concentrations of SCPS with several ARGs and bio-Zn. [ABSTRACT FROM AUTHOR]

This study presents a multi-criteria evaluation of energy recovery from wastewater sludges by the traditional anaerobic digestion pathway versus the emergent hydrothermal liquefaction (HTL) pathway. The two pathways were assessed considering the following 12 criteria: process stability, volatile solids reduction, process time, energy recovery, energy yield, net energy yield, energy return on investment, net power yield, energy density of the resulting biofuel, potential for methane emissions, effluent quality, and technology readiness. Experimental results from HTL of primary and secondary sludges and literature data on mesophilic and thermophilic anaerobic digestion are used here to quantify the above criteria for assessment. Although the two anaerobic pathways ranked better than the HTL pathway on the basis of energy return on investment (5.5–19.8 vs. 1.5), when all the 12 criteria were taken into consideration by the multi-criteria decision making approach, the HTL pathway outranked both the anaerobic pathways with a preference ranking of + 0.44 compared to − 0.28 in anaerobic digestion. It is recommended that developing technologies for recovering energy from the solid residue of HTL, the biochar, the energy return on investment by the HTL pathway could be improved from 1.5 to 2.42. • Evaluated energy recovery from sewage sludges by hydrothermal liquefaction (HTL). • Derived 12 performance criteria to compare HTL vs. anaerobic digestion (AD). • Used multicriteria decision-making (MCDM) method to compare HTL vs. AD. • MCDM method ranked HTL higher than both mesophilic and thermophilic AD. [ABSTRACT FROM AUTHOR]

The feasibility of co-digestion of chicken manure (CM) and maize silage (MS) without water dilution was investigated in 5-L digesters. Specific methane production (SMP) of 0.309 L CH 4 g −1 volatile solids (VS) was achieved but only at lower %CM. Above a critical threshold for total ammonia nitrogen (TAN), estimated at 7 g N L −1 , VFA accumulated with a characteristic increase in acetic acid followed by its reduction and an increase in propionic acid. During this transition the predominant methanogenic pathway was hydrogenotrophic. Methanogenesis was completely inhibited at TAN of 9 g N L −1 . The low digestibility of the mixed feedstock led to a rise in digestate TS and a reduction in SMP over the 297-day experimental period. Methanogenesis appeared to be failing in one digester but was recovered by reducing the %CM. Co-digestion was feasible with CM ⩽20% of feedstock VS, and the main limiting factor was ammonia inhibition. [ABSTRACT FROM AUTHOR]

Two-stage mesophilic anaerobic digestion of waste activated sludge was conducted to enhance methane production by low-temperature thermal hydrolysis. Two steady stages were evaluated: the first acidogenic stage was operated at sludge retention times of 2 d, and the second methanogenic stage was controlled at hydraulic retention times of 8 d. Thermal hydrolysis results showed that more chemical oxygen demand, proteins and carbohydrates were released from sludge as temperature increased from 50 to 120°C. Protein-like substances were major components from three-dimensional (3D) excitation–emission matrix analysis, and their fluorescence intensities were matched with temperatures. Sludge extracellular structure was disintegrated from scanning electron microscope analysis when the temperature was beyond 80°C. The volatile fatty acids (VFAs) and methane production had positive relation to the soluble organic matters after low-temperature hydrolysis. About 100°C was the suitable temperature for sludge digestion, and corresponding VFAs and biogas productions were 1,672 mg/L and 123 mL/gVSS, respectively. [ABSTRACT FROM AUTHOR]

Methane production capacity in mesophilic conditions of waste from two food industry plants was assessed in a semi-pilot (6 L, fed-batch) and pilot (300 L, semi-continuous) scale. This was carried out in order to evaluate the convenience of producing heat and electricity in a full scale anaerobic digester. The pilot test was performed in order to obtain more reliable results for the design of the digester. Methane yield, returned from the pilot scale test, was approximately 80% of that from the smaller scale test. This outcome was in line with those from other studies performed in different scales and modes and indicates the success of the pilot scale test. The net electricity produced from the digester accounted for 30–50% of the food industry plants’ consumption. The available thermal energy could cover from 10% to 100% of the plant requirements, depending on the energy demand of the processes performed. [ABSTRACT FROM AUTHOR]

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]

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]

[Display omitted] • iARGs accounted for most ARGs during anaerobic digestion of cow manure. • AD increased absolute abundance of eARGs and bARGs. • Potential hosts of iARGs and eARGs were similar. • bARGs may spread between bacteria or across bacterial genera. • eARGs and bARGs were directly driven by physicochemical factors (e.g., pH). The fate of intracellular antibiotic resistance genes (iARGs), extracellular ARGs (eARGs) and bacteriophage ARGs (bARGs) during anaerobic digestion (AD) of cow manure is unclear. Thus, the characteristics of iARGs, eARGs and bARGs during mesophilic AD (MAD) and thermophilic AD (TAD) of cow manure were investigated. The absolute abundances of iARGs decreased by 69.82% after TAD. After MAD and TAD, the total absolute abundances of eARGs increased by 63.5 times and 67.6 times, respectively, whereas those of the bARGs increased by 47.60% and 59.22%. eARGs were mainly derived from the non-specific lysis of Firmicutes, Bacteroidetes, while bacteriophages had a wide range of hosts. The variations in iARGs, eARGs and bARGs were affected by the microbial hosts but also directly driven by physicochemical factors (e.g., pH). Overall, the findings of this study revealed that there may be a risk of eARGs and bARGs disseminating during the AD of cow manure. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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 removal efficiency of nine pharmaceutical compounds from primary sludge was evaluated in two different operating conditions: (i) in conventional Mesophilic Anaerobic Digestion (MAD) alone and (ii) in a co-treatment process combining Mesophilic Anaerobic Digestion and a Thermophilic Aerobic Reactor (MAD-TAR). The pilot scale reactors were fed with primary sludge obtained after decantation of urban wastewater. Concerning the biodegradation of organic matter, thermophilic aeration increased solubilization and hydrolysis yields of digestion, resulting in a further 26% supplementary removal of chemical oxygen demand (COD) in MAD-TAR process compared to the conventional mesophilic anaerobic digestion. The highest removal rate of target micropollutants were observed for caffeine (CAF) and sulfamethoxazole (SMX) (>89%) with no substantial differences between both processes. Furthermore, MAD-TAR process showed a significant increase of removal efficiency for oxazepam (OXA) (73%), propranolol (PRO) (61%) and ofloxacine (OFL) (41%) and a slight increase for diclofenac (DIC) (4%) and 2 hydroxy-ibuprofen (2OH-IBP) (5%). However, ibuprofen (IBP) and carbamazepine (CBZ) were not degraded during both processes. Anaerobic digestion affected the liquid-solid partition of most target compounds. Sorbed fraction of pharmaceutical compounds on the sludge tend to decrease after digestion, this tendency being more pronounced in the case of the MAD-TAR process due to much lower concentration of solids. Image 1 • A hybrid digester was implemented to evaluate pharmaceutical compounds removal. • MAD-TAR allowed a better removal of VSS (76%) compared to MAD (47%). • Removal higher than 90% was found for CAF and SMX whatever the process. • Moderate (DIC, 2OH-IBP) to high (OXA, PRO, OFL) removal was observed in MAD-TAR. • Biodegradable compounds removal was correlated with their fraction in liquid phase. [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]

In this work, we investigated the impact of iron nanoparticle, including magnetite nanoparticles (Fe 3 O 4 NPs) and nanoscale zero-valent iron (nZVI), on the anaerobic digestion (AD) performance. Moreover, the evolutions of antibiotic resistance genes (ARGs), class 1 integrons-integrase (intI 1) and potential hosts of ARGs were also investigated. The optimal addition of Fe 3 O 4 NPs and nZVI to promote methane production was 0.5 g/L and 1 g/L, which led to 22.07% and 23.02% increase in methane yield, respectively. The degradation rate of organic matter was also enhanced with the addition of Fe 3 O 4 NPs or nZVI. The results of high-throughput sequencing showed that the reactors with iron NPs exhibited significant differences in microbial community structure, compared to the reactors with the non‑iron NPs. Iron NPs have caused the relative abundance of the dominant bacteria (Proteobacteria, Firmicutes and Actinobacteria) generally decreased, while the dominant archaea (Euryarchaeota) increased in AD sludge. Quantitative PCR results revealed that iron NPs accelerated the reductions in total absolute abundance of ARGs, especially a beta-lactamase resistance encoded gene (bla OXA). Network analysis displayed that the attenuation of ARGs was mainly attributed to the decline of potential hosts (Proteobacteria, Firmicutes and Actinobacteria). Meanwhile, environmental factors (such as pH, soluble chemical oxygen demand and heavy metals) were also strongly correlated with ARGs. Unlabelled Image • Iron NPs promoted methane production and organic matter degradation in anaerobic digestion. • Iron NPs changed microbial communities and reduced microbial diversity in anaerobic digestion. • The absolute abundance of total ARGs decreased in the anaerobic digestion with iron NPs. • Proteobacteria , Firmicutes and Actinobacteria were potential hosts of ARGs. • The potential host of ARGs was the main driving factor for the fate of ARGs and intI 1. [ABSTRACT FROM AUTHOR]

• Algal biochar enhanced co-digestion of algal biomass and food waste for biomethane. • 75% algal biomass + 25% food waste mixture co-digestion showed a synergistic effect. • Average methane yields enhanced by 12–54% due to 15 g/L of algal biochar amendment. • Proteiniphilum enriched in mesophilic reactor like Defluviitoga in thermophilic one. • Biochar shifted methanogens towards a balance of two flexible methanogenic pathways. The impact of algal biochar addition on mesophilic and thermophilic anaerobic co-digestion of algal biomass and food waste was investigated with a focus on semi-continuous operations and functional microbial communities. Under batch co-digestion, the highest co-digestion synergy was observed for a mixture of 25% food waste and 75% algal biomass. During semi-continuous co-digestion of 25% food waste-75% algal biomass mixture, biochar amended digesters exhibited a 12–54% increase in average methane yield (275.8–394.6 mL/gVS) compared to the controls. Elevated temperature induced narrow distributions of volatile fatty acids (VFAs) by inhibiting the production of branched VFAs. Genus Proteiniphilum was selectively enriched by 3.2 folds in mesophilic digesters with biochar amendment while genus Defluviitoga was selectively enriched in thermophilic digesters due to elevated temperature. Methanogenic communities were significantly different in mesophilic and thermophilic digesters. Biochar amendment contributed to shifts in the predominant methanogens leading to a more balanced state of two methanogenic pathways. [ABSTRACT FROM AUTHOR]