Abstract Microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) is a promising technology for enhancing biomethane recovery over conventional AD, while external energy input is required for its operation. A few previous reports suggested that periodic power supply in MEC-AD systems could improve their performance with synthetic substrates, while significant gaps remain in understanding the underlying fundamental features of such operation schemes. Here, the impacts of intermittently applied potential on a sewage-sludge fed MEC-AD system were investigated to shed new light on microbial syntropy, and functional methanogenesis pathways under continuous (24 h/d) vs. intermittent (12–18 h/d) applied potential modes. In general, sludge hydrolysis and methane production increased with a more extended switch-off period of applied potential. The results showed that periodic applied potential could improve direct interspecies electron transfer (DIET) based syntrophy between anodic electroactive bacteria ( Geobacter sp.) and known electrotrophic methanogen ( Methanobacterium ). Consistently, extracellular electron transfer (EET)-related genes ( omc C, omc Z, omc B, omc E, omc S, and pil A) were upregulated due to switching between on and off modes of applied potential. It was found that the intermittent application of applied potential was also effective in alleviating microbial competition between methanogens and acetogens in the biocathode. Such microbial competition was evident due to excessive H2 production under continuous applied potential mode. These results indicate the potential of operationally flexible MEC-AD systems for more economic sustainability. Zakaria, B. S., & Dhar, B. R. (2022). Intermittent energization catalyzes direct interspecies electron transfer in electro-anaerobic digestion of sewage sludge.  Chemical Engineering Journal ,  442 , 136177. https://www.sciencedirect.com/science/article/pii/S1385894722016758?casa_token=vFmTzDA227AAAAAA:7nYw0Tb5_-BX98NayUTYR9p3Ww6k8o9HYph5aiIGCsdVAKAr42h2ATShVE4lDCXvjJiuEAz472zo

Abstract Microplastics (MPs)/nanoplastics (NPs) have been widely detected in wastewater treatment plants (WWTPs). They are captured mainly by sludge and unavoidably move into the anaerobic digestion (AD) process. Recent studies suggested that MPs/NPs could induce oxidative stress to the microbiome in digesters. The thermal hydrolysis process (THP) has been implemented for sludge pretreatment in many full-scale WWTPs. To date, there is limited knowledge about how THP can influence MPs/NPs-induced stress during AD. This study systematically investigated the impact of THP (80 and 160 °C) on AD of sewage sludge exposed to different levels (50–150 μg/L) of polystyrene nanoplastics (PsNPs), one of the most found MPs/NPs in WWTPs. Compared to the control, higher PsNPs levels of 100 and 150 μg/L decreased methane yields by 17.98 and 29.34%, respectively. Moreover, reactive oxygen species (ROS) levels increased by 17.18 and 34.84%. Our results demonstrated that THP counteracted the suppression of methane production imposed by such PsNPs concentrations, with decreased ROS levels. Also, THP reduced antibiotic resistance gene (ARG) propagation that can be encouraged by PsNPs, thus minimizing the ARG transmission risks of digestate biosolids. These findings suggest that THP holds a high promise to further develop as a remediation method for MPs/NPs in WWTPs. Azizi, S. M. M., Haffiez, N., Zakaria, B. S., & Dhar, B. R. (2022). Thermal hydrolysis of sludge counteracts polystyrene nanoplastics-induced stress during anaerobic digestion.  Acs Es&T Engineering ,  2 (7), 1306-1315. https://pubs.acs.org/doi/abs/10.1021/acsestengg.1c00460?casa_token=5pNQ5rmpODIAAAAA:MksCIcuecK-GmbCKtosFDkEUk9pQ0b-XiXr27jzJ00Q6XJC_gbFn1QEIpslYKty5zFvb6vJf-HeKF9v1fg

Abstract This study examined the significance of propionate to acetate (HPr/HAc) ratios on microbial syntrophy and competition in microbial electrolysis cell-assisted anaerobic digestion (MEC-AD). In addition to molecular biology and phylogenetic analysis, a numerical MEC-AD model was developed by modifying Anaerobic Digestion Model No.1 to predict the effects of different HPr/HAc ratios (0.5, 1.5, 2.5, and 5). The HPr/HAc ratios of 0.5 and 1.5 maintained efficient syntrophy among electroactive bacteria, hydrogenotrophic methanogens , and homoacetogens, leading to higher methane yields. In contrast, higher HPr/HAc ratios of 2.5 and 5 were detrimental to methanogenesis . Both microbial community analysis and numerical modeling results suggested that higher propionate levels could promote the enrichment of H2-utilizing acetogens , thereby triggering their competition with hydrogenotrophic methanogens . Moreover, protein fraction in extracellular polymeric substances and the relative expression of genes associated with extracellular electron transfer in both anode and cathode biofilms were markedly decreased with increasing HPr/HAc ratios, indicating partial inhibition of microbial electroactivity. Overall, these results illuminate deep insight into anaerobic syntrophy, contributing to the process kinetics and methane yields in MEC-AD systems. Furthermore, from a practical viewpoint, the results can also be helpful in effective control of MEC-AD operation without propionate accumulation. Zakaria, B. S., Guo, H., Kim, Y., & Dhar, B. R. (2022). Molecular biology and modeling analysis reveal functional roles of propionate to acetate ratios on microbial syntrophy and competition in electro-assisted anaerobic digestion.  Water Research ,  216 , 118335. https://www.sciencedirect.com/science/article/pii/S0043135422002986?casa_token=dvdElqnzVt4AAAAA:hij7MyMcnKap3LUkEIGZ1TWpkv60XQb8NdYGtfYuQPWunC5nmwSA04QTzMKHnErr5Oz3tp_k-l-z

Abstract Remediation of oil sands tailings is a crucial environmental aspect of the Canadian oil sands industry. Because of the poor released water quality and slow consolidation of tailings, engineered non-natural strategies to improve the consolidation of tailings are warranted. Here, we investigated enzymatic treatment (using cellulase, protease, and lysozyme) to accelerate the dewatering of fluid fine tailings (FFT). Our findings illustrated that lysozyme (0.5% and 1%) significantly improved FFT dewatering by increasing the water recovery (WR) up to 20% compared with the other enzymes (up to 12%) or the control (2%). Moreover, lysozyme treatment resulted in the highest increase in ionic strength (0.038 to 0.1 mol L−1), decrease in diffuse double layer (DDL) thickness (1.54 × 10−7 to 9.40 × 10−8 cm), and increase in zeta potential (−34.7 to −14.8 mV). Increased methane production was observed for cellulase (0.5% and 1%), lysozyme (0.5% and 1%), and protease (0.5%). The enhanced dewatering could be linked to the ebullition of methane gas resulting from the methanogenic activity, which created pathways for the trapped water release. In addition, the dissolution of carbonate minerals during the release of methane gas increased ionic strength and decreased the DDL of the FFT. Lysozyme 1% treatment was also the most effective in reducing naphthenic acid fractions (1934.6 to 243 ng mL−1); however, the released water had high toxicity toward Vibrio fischeri and had a slight decrease in microbial populations . This study provides a fundamental insight into enzymatic treatment for oil sand tailings. Allam, N. E., Anwar, M. N., Kuznetsov, P. V., Ulrich, A. C., & Dhar, B. R. (2022). Enzyme-assisted dewatering of oil sands tailings: Significance of water chemistry and biological activity.  Chemical Engineering Journal ,  437 , 135162.  https://www.sciencedirect.com/science/article/pii/S1385894722006672?casa_token=lYPZtZzz3QoAAAAA:nP_E2g-lU8XBVMwt5_Ku-WlXztSXxC_AX3e4_YGgrVyFqZG-wiFqSZPxUbZyESp_4ouFl_WRApMP

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