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In this study, the performances of a conventional anaerobic baffled reactor (ABR) and an ABR combined with microbial electrolysis cells (MECs) for enhancing degradation of volatile fatty acids (VFAs) were evaluated in 55°C. The ABR-MECs system achieved a total chemical oxygen demand (COD) removal rate of 97.2% and a methane yield of 236 ± 5 mL g−1 CODremoved at organic loading rate (OLR) of 6.9 kg COD m−3 d−1, which were higher than those of the ABR with 77.6% and 207 ± 5 mL g−1 CODremoved, respectively, at OLR of 5.1 kg COD m−3 d−1. The pyrosequencing analysis confirmed that the introduction of MECs into ABR was conducive to establishing stable functional communities of syntrophic fatty acids oxidizing bacteria (SFOB), exoelectrogens and hydrogenotrophic methanogens, such as Syntrophobacter (5.4%), Thermodesulfovibrio (2.0%), Methanobacterium (43.8%), Methanolinea (20.4%). The content of unclassified bacteria increased from 12.4% in the ABR system to 52.3% in the ABR-MECs system. In contrast, the proportion of aceticlastic methanogens decreased from 50.1% in the ABR to 24.5% in the ABR-MECs system. The improved performance of the thermophilic ABR-MECs system resulted from phase separation, wide ecological niche and intensification of methanogenesis process via functional microbes, which significantly enhanced the degradation of propionic acid and acetic acid. [ABSTRACT FROM AUTHOR]

The anionic detergent sodium dodecyl benzene sulfonate (SDBS) inhibits anaerobic solid waste fermentation process in mesophilic anaerobic digesters. In this study, the effect SDBS on the performance of anaerobic digestion (AD) of mixture of sewage sludge, food waste, and green waste serving as substrate was investigated. The batch experiments were conducted with five SDBS concentrations namely 0, 0.01, 0.02, 0.05, 0.1, and 0.2 g/g (SDBS/dry sludge) under mesophilic condition (37 ± 1 °C) and lasted for 63 days. The results showed that the presence of SDBS remarkably increased the release of protein and carbohydrate, and resulting in the serious accumulation of volatile fatty acids (VFAs), especially for propionate accumulation. Likewise, the observed variations in enzyme activities associated with different stage of AD revealed that methanogenesis was quite sensitive to SDBS and inhibited by the increase of SDBS addition. Meanwhile, the presence of SDBS decreased the pH value and the concentration of free ammonia, but increased the concentration of NH4+-N. Furthermore, the production of biogas was reduced by SDBS. In conclusion, SDBS addition has a negative impact on anaerobic co-digestion. On the one hand, methanogens were severely inhibited and biogas yield decreased remarkably, on the other hand, the accumulation of VFAs was excessive. Thus, the presence of surfactant (SDBS) in the municipal organic waste should be concerned during the waste disposal via anaerobic digestion process. [ABSTRACT FROM AUTHOR]

Surfactants are widely used and discharged into wastewater treatment plants, which might influence the anaerobic digestion (AD) treatment of municipal waste. In this study, the effects of typical anionic surfactants sodium dodecyl benzene6 sulfonate (SDBS) and non-ionic surfactants APG, on mesophilic anaerobic co-digestion of sludge, food waste, and green waste were investigated. Results indicated that at 5 mg/g, the biogas production was inhibited in SDBS supplemented systems while stimulated in APG-added reactors, with the methane yield of 146.58 L/g VS consumed. At 15 mg/g, the biogas production in both SDBS and APG supplemented reactors was both inhibited. It means the negative or positive effect of APG on AD depends on the dose of APG supplementation. The 16S rRNA gene analysis demonstrated the microbial community structure in the digester was changed due to the addition of surfactant. Bacteroidia significantly increased with the addition of APG and SBDS, while the increase of Clostridia only occurred in APG-added system. The variation of microbial Communities' structure in APG and SDBS-added digesters might give an explanation for the different efficiencies in these two systems. Thus, the effects of surfactants on the efficiency of AD should be considered during the disposal of municipal organic waste. [ABSTRACT FROM AUTHOR]

The anaerobic bio-treatment of lower COD/SO4 2- ratio wastewater constitutes a bottle-aqneck due to the limited carbon source. In this type of environment, interactions between acidogenic fermentation bacteria and methane-producing bacteria (MPB) are aided by syntrophic fatty acid oxidation bacteria present in the functional niche; MPB and sulfate-reducing bacteria (SRB) compete with each other due to the availability of sulfate. Therefore, introduction of syntrophic fatty acid oxidation bacteria into an SRB dominated culture can achieve maximum utilization of the substrate, weakening the competition of MPB. In this study, the mixed culture of dominant syntrophic propionate oxidation bacteria (SPOB) and SRB was established and characterized at 35°C. The dominant SPOB and SRB were enriched in a continuous flow stirred-tank reactor and in batch experiments, respectively. Subsequently, an equal proportion of the enriched sludge was mixed and incubated in conical flasks with propionate as the sole substrate. Six parallel experiments (SP1-SP6) were conducted and two of them (SP2 and SP4) were chosen. The results revealed that the sulfate removal efficiencies of SP2 and SP4 were 91.83% and 93.03%, respectively. Furthermore, the outcome of the microbial analysis showed that the dominant microbial communities included Uncultured Smithella spp., Uncultured Desulfobacteraceae bacterium and sequences related to members of the family Desulfovibrio. Excess propionate was mainly syntrophically decomposed via sulfate reduction. Findings from this study could provide valuable information for the establishment of new processes and the regulation of parameters in the treatment of lower COD/SO4 2- ratio wastewater. [ABSTRACT FROM AUTHOR]

Anaerobic baffled reactor (ABR) processes play an increasingly important role in wastewater treatment and resource recycling by its ingenious construction and excellent performance. The authors aim to introduce new research progresses and applications of ABR in the last two decades, focusing mainly on the following aspects: presenting and comparing its development and application instances, discussing the optimization of operating regulation and mathematical models, stating existing problems in current researches, suggesting possible improvements, and proposing future research perspectives. The contributions of this review involve enhancing ABR treatment efficiency and operation stability to provide information for colleagues. [ABSTRACT FROM AUTHOR]