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Untreated sewage sludge potentially contains a wide range of enteric pathogens that present a risk to human health. Mesophilic anaerobic digestion (MAD) is the most-favoured process for sewage sludge treatment in the United Kingdom. It is a well-established approach to sludge stabilisation, but the mechanisms responsible for pathogen removal are poorly understood. Operational data collected by Thames Water from conventional MAD sites were statistically scrutinised to examine the effects of primary and secondary digestion on the removal of the enteric indicator bacteria, Escherichia coli, by using the IBM SPSS statistical software package for ANOVA, post-hoc and multiple regression analysis. The results showed that the process temperature conditions at the MAD plants were equivalent to or exceeded the minimum estimated by the analysis necessary to comply with the 2 log10 removal standard for E. coli. The results also showed that primary digestion conditions (specifically temperature) sublethally damaged E. coli and increased decay in secondary digestion and therefore over the whole digestion process. [ABSTRACT FROM AUTHOR]

The presence of high levels of sulfate and metal ions (e.g., iron and copper), introduced with substrate feeding or by chemical or electrochemical pretreatment, may impose complex chemical and biological interactions in anaerobic digestion. To effectively investigate the effects of those ions on anaerobic digesters, this study used dairy manure as the model substrate and applied response surface methodology for design and data analysis. The response variables evaluated in this study included H2S concentration and production, biomethane and carbon dioxide production, and acetate and total volatile fatty acids in digestate. Ferrous was found effective in controlling H2S concentration, while cupric lost its effectiveness at the end of 45 days digestion. It was found that copper and sulfate exerted severe inhibition to overall microbial activities as well as methane generation. Ferrous showed slight inhibition on methane generation at baseline concentrations of the other additives, but stimulated methane production when VS (dairy manure fiber) content was high. Co-digestion of feedstock introducing sulfate and copper components should be cautiously done in order to maintain high performance of digester. To the contrary, Fe can be effective both in sulfide control and methane production stimulation, and is recommended for use in anaerobic digestion that requires sulfide control when digestion substrate contains high levels of lignocellulosic biomass. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1405-1416, 2017 [ABSTRACT FROM AUTHOR]

Brewer's spent grain (BSG), the residual solid fraction of the final mash process of malting, is a main waste fraction of beer production, recently considered as possible substrate for biovalorization by anaerobic digestion (AD). In this article, the biomethanization of BSG was evaluated by performing biochemical methane potential (BPM) tests. The obtained specific methane production (SMP) was 0.284 LCH4·g-1COD. The process was modelled by implementing the Anaerobic Digestion Model No.1 (ADM1) into AQUASIM software with the focus on the disintegration and hydrolysis step. The calibrated disintegration rate for BSG was equal to 0.823 d-1 and the hydrolysis rate constants varied from 0.124 d-1 for lipids to 1.056 d-1 for proteins. The obtained results showed a good efficiency in treating BSG with anaerobic digestion. The practical conversion degree of the biowaste COD into methane was equal to 81.1%, a high value for a substrate with an elevated solid content. Moreover, the estimated values of disintegration and hydrolysis rates complied with the retention time values generally adopted in an anaerobic digestor. [ABSTRACT FROM AUTHOR]

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]

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]

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]