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The growing concern about residual antibiotics in the water environment pushes for innovative and cost-effective technologies for antibiotics removal from wastewater. In this context, various microbial electrochemical systems have been investigated as an alternative to conventional wastewater technologies that are usually ineffective for the adequate removal of antibiotics. This review article details the development of stand-alone and hybrid or integrated microbial electrochemical systems for antibiotics removal from wastewater. First, technical features, antibiotics removal efficiencies, process optimization, and technological bottlenecks of these systems are discussed. Second, a comparative summary based on the existing reports was established to provide insights into the selection between stand-alone and hybrid systems. Finally, research gaps, the relevance of recent progress in complementary areas, and future research needs have been discussed. [ABSTRACT FROM AUTHOR]

Anaerobic bioreactors for source‐separated blackwater are mostly operated at low organic loading rates (OLRs) due to low biodegradability and the potential of ammonia inhibition. In this study, an anaerobic biofilm reactor having conductive carbon fibers as the media was investigated for the high‐rate treatment of blackwater collected from vacuum toilets. The bioreactor was operated at different OLRs ranged from 0.77 to 3.01 g COD/L‐d in four stages for a total operating period of ~ 250 days. With the increase of OLRs, the specific methane production rate increased from 105.3 to 304.6 ml/L‐d with high methane content in biogas (75.5%–83%). The maximum methane yield was achieved at hydraulic retention time (HRT) of 15 days. Highest organics and suspended solids removal (80%–83%) were achieved at 20‐days HRT, while increased OLRs resulted in diminished removal efficiencies. The state variables, including pH, total ammonia nitrogen, short‐chain volatile fatty acids, and soluble chemical oxygen demand, indicated the system had a great capability to withstand the high OLRs. Microbial community analysis revealed that the high performance might be attributed to direct interspecies electron transfer (DIET) facilitated by potentially electroactive bacteria (e.g., Syntrophomonas, Clostridium) and electrotrophic archaea (e.g., Methanosaeta and Methanosarcina species) enriched on the carbon fibers. Practitioner points: An anaerobic biofilm reactor was investigated for biomethane recovery from source‐separated blackwater.Conductive carbon fibers were utilized as the media to stimulate enrichment of potentially electroactive methanogenic communities.The bioreactor was operated at ambient temperature for over 250 days.High methane production rate and high‐quality biogas were achieved at OLRs ranged from 0.77 to 3.01 g COD/L‐d.Microbial community analysis suggested direct interspecies electron transfer (DIET) between specific electroactive bacteria and electrotrophic archaea. [ABSTRACT FROM AUTHOR]

In this study, mesophilic acidogenic fermentation, thermophilic acidogenic fermentation, and thermal hydrolysis process (THP) were compared to generate sludge liquors for bioenergy recovery with microbial electrolysis cells (MECs). The results showed that THP at 170 °C was the most effective for hydrolysis of particulate organics in sewage sludge, while fermentation under thermophilic temperature led to the highest accumulation of volatile fatty acids (VFAs) in sludge liquor. However, THP yielded the highest percentage of acetate in VFAs, which resulted in superior MEC performance compared to fermented sludge liquors in terms of current density (2.7 vs. ~1.3 A/m2), coulombic efficiency (50% vs. 31–34%), bio-H 2 potential (1114 vs. 839–881 mL), and H 2 production rate (50.3 mL/d vs. 28–32 mL/d). The utilization sequence of the VFAs was found to be acetate > butyrate > propionate. Overall, our results show that generating sludge liquors through THP could provide a feasible solution to produce bio-H 2 from sewage sludge; however, coulombic efficiencies should be further improved before practical application. • MECs were operated with sludge liquors produced through three different processes. • Thermal hydrolysis process (170 °C) led to superior MEC performance. • Sludge liquors from fermentations (38 °C and 55 °C) showed comparable performance. • VFAs degradation profiles followed the order of acetate > butyrate > propionate. [ABSTRACT FROM AUTHOR]

This study, for the first time, documented microbial community shifts in response to the changes in anode potential in a microbial electrolysis cell (MEC) operated with primary sludge. At an anode potential of −0.4 V vs. Ag/AgCl, the MEC showed COD and VSS removal efficiencies of 73 ± 1% and 75 ± 2%, respectively. The volumetric current density and specific hydrogen production rate were 23 ± 1.2 A/m3, and 145 ± 4.1 L/m3-d, respectively. The anodic microbial community was consisted of various fermentative/hydrolytic bacteria (e.g., Bacteroides and Dysgonomonas) and anode-respiring bacteria (Geobacter), while different hydrolytic/fermentative bacteria were abundant in suspension. The MEC showed substantially inferior performance along with a higher accumulation of various volatile fatty acids when the anode potential was switched to more positive values (0 V and +0.4 V). Both biofilms and suspended communities were also shifted when the anode potential was changed. Notably, at +0.4 V, Geobacter genus entirely disappeared from the biofilms, while Paludibacter species (known fermentative bacteria) were selectively enriched in biofilms. Also, the relative abundance of genus Bacteroides (known hydrolytic bacteria) substantially decreased in both biofilms and suspension, which was correlated with the inferior hydrolysis of VSS. Quantitative comparison of biofilms and suspended microbial communities at different anode potentials revealed a sharp decrease in bacterial cell numbers in anode biofilms after changing anode potential from −0.4 V to +0.4 V. By contrast, bacterial cell numbers in suspension were slightly decreased. Collectively, these results provide new insights into the role of anode potential in shaping key microbial players associated with hydrolysis/fermentation and anodic respiration processes when MECs are operated with real biowastes. Unlabelled Image • Impact of changing anode potentials on primary sludge fed MEC was studied. • Changes in biofilms and suspended bacterial communities were evaluated. • Superior MEC performance was achieved only at −0.4 V vs. Ag/AgCl. • Higher anode potentials adversely affected ARB and hydrolytic bacteria. • Key fermentative bacteria were also influenced by anode potentials. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the addition of conductive materials can promote direct interspecies electron transfer (DIET) between bacteria and methanoarchaea. This study demonstrated that carbon fibers could significantly stimulate methanogenic conversion of propionate and butyrate as co-substrate, while only butyrate was completely degraded in the unamended control bioreactor. In the carbon fibers-amended bioreactor, specific methane production (mL-CH 4 /g COD Initial ) and methanogenesis rate (d −1 ) increased by around 2.4 and 6.7 times, respectively. Various electroactive bacteria were abundant in the carbon fibers-amended bioreactor, whereas different known fermentative bacteria were abundant in the control. Moreover, carbon fibers substantially increased the abundance of Methanosaeta species. These results suggest that electroactive bacteria could be involved in DIET with Methanosaeta species enabling co-degradation of propionate and butyrate. Additionally, electrical conductivities of the biomass were comparable in both configurations, indicating that carbon fibers were the primary route for DIET. [ABSTRACT FROM AUTHOR]

Engineering strategies to reduce greenhouse gases (GHGs) emissions by inhibiting methanogenesis in oil sands tailings have rarely been examined. In this study, we explored the potential impact of chemical treatment (lime) and biological treatment using enzymes (lysozyme and protease) on inhibiting methane emissions from tailings. Overall, treatment with protease 3%, lysozyme 3%, and lime 5000 ppm reduced CH 4 production (by 52%, 28%, and 25%, respectively) and were weakly associated with the archaeal abundance. Enzymes treatment resulted in a higher reduction in CH 4 production compared with lime treatment. A 3% lysozyme treatment suppressed CH 4 production (the change in methane was 0.48 mmol) and reduced the degradation of hexane throughout the experiment. Similarly, 3% protease suppressed CH 4 production throughout the experiment (the change in methane was 0.78 mmol), which could be attributed to the pH reduction to pH 4.9 at week 23 resulting from the formation of volatile fatty acids. Another possible mechanism could be the formation of toxic compounds, such as high nitrogen content, after protease treatment that inhibited the microbial community. The toxicity effect to Vibrio fischeri was greater with lysozyme 3% and protease 3% treatment than with lime treatment (124 TU and 76 TU, respectively). Lime treatment resulted in the highest reduction in 16S rRNA gene copies from 5.7 × 106 cells g−1 (control) to 2.7 × 105, 1.71 × 105, and 1.4 × 105 cells g−1 for 1600, 3500, and 5000 ppm treatments, respectively. This study supports further work to examine and determine the optimum conditions (e.g., enzyme and lime dosages) for CH 4 inhibition. [Display omitted] • The impact of enzymatic and lime treatment on methanogenic inhibition was studied. • Enzymatic treatment provided higher methane reduction than lime treatment. • Enzymatic treatment had a more toxic effect towards Vibrio fischeri than lime. • 3% Protease provided the highest reduction in methane production from tailings. • Lime treatment led to the highest reduction in 16S rRNA and archaeal gene copies. [ABSTRACT FROM AUTHOR]

In this study, an effective enrichment technique was applied to isolate different bacterial strains with capabilities to denitrogenate carbazole (CAR), as a model compound for nitrogenous polyaromatic hydrocarbons (NPAHs). Twenty-four different CAR-denitrogenating bacterial strains were isolated from mineral coke samples. From all, a Gram +ve bacterial isolate designated BS1 showed a higher biodenitrogenation (BDN) efficiency relevant to the well-known biodenitrogenating bacterium strainPseudomonas resinovoransCA10, recording 77.15 and 60.66% removal of 1000 ppm CAR with the production of 119.79 and 102.43 ppm anthranilic acid, and 121.19 and 90.33 ppm catechol, as by-products, respectively. BS1 was identified by 16S rDNA gene sequence analysis to beBacillus clausiiBS1 (NCBI GenBank Accession no. KF985981) with a similarity of 99.14%. The CAR-BDN pathway was also elucidated using high-performance liquid chromatography (HPLC) and gas chromatography mass spectrometry analysis (GC/MS), which proved further metabolism of catechol to muconic acid. [ABSTRACT FROM PUBLISHER]

Understanding the toxic effect of silver nanoparticles (AgNPs) on various biological wastewater treatment systems is of significant interest to researchers. In recent years, microbial electrochemical technologies have opened up new opportunities for bioenergy and chemicals production from organic wastewater. However, the effects of AgNPs on microbial electrochemical systems are yet to be understood fully. Notably, no studies have investigated the impact of AgNPs on a microbial electrochemical system fed with a complex fermentable substrate. Here, we investigated the impact of AgNPs (50 mg/L) exposure to a biofilm anode in a microbial electrolysis cell (MEC) fed with glucose. The volumetric current density was 29 ± 2.0 A/m3 before the AgNPs exposure, which decreased to 20 ± 2.2 A/m3 after AgNPs exposure. The biofilms produced more extracellular polymeric substances (EPS) to cope with the AgNPs exposure, while carbohydrate to protein ratio in EPS considerably increased from 0.4 to 0.7. Scanning electron microscope (SEM) imaging also confirmed the marked excretion of EPS, forming a thick layer covering the anode biofilms after AgNPs injection. Transmission electron microscope (TEM) imaging showed that AgNPs still penetrated some microbial cells, which could explain the deterioration of MEC performance after AgNPs exposure. The relative expression level of the quorum signalling gene (Lux R) increased by 30%. Microbial community analyses suggested that various fermentative bacterial species (e.g., Bacteroides , Synergistaceae_ vadin CA02, Dysgonomonas , etc.) were susceptible to AgNPs toxicity, which led to the disruption of their syntrophic partnership with electroactive bacteria. The abundance of some specific electroactive bacteria (e.g., Geobacter species) also decreased. Moreover, decreased relative expressions of various extracellular electron transfer associated genes (omc B, omc C, omc E, omc Z, omc S, and pil A) were observed. However, the members of family Enterobacteriaceae, known to perform a dual function of fermentation and anodic respiration, became dominant after biofilm anode exposed to AgNPs. Thus, EPS extraction provided partial protection against AgNPs exposure. Unlabelled Image • Impact of AgNPs was studied for a biofilm anode fed with a fermentable substrate. • AgNPs exposure disturbed syntrophy between fermentative and electroactive bacteria. • Fermentation efficiency reduced, followed by a decrease in current density. • AgNPs exposure induced EPS excretion and altered EPS composition. • AgNPs exposure influenced expressions of EET and QS genes. [ABSTRACT FROM AUTHOR]

The addition of conductive materials in anaerobic digestion (AD) is a promising method for boosting biomethane recovery from organic waste. However, conductive additives have rarely been investigated for the high-solids anaerobic digestion (HSAD). Here, the impact of adding carbon cloth in the solid phase of an HSAD system with percolate recirculation was investigated. Furthermore, spatial patterns of microbial communities in suspended biomass, percolate, and carbon cloth attached biofilm were assessed. Carbon cloth increased biomethane yield from source-separated organics (SSO) by 20% more than the unamended control by shortening the lag phase (by 15%) and marginally improving the methanogenesis rate constant (by ∼8%) under a batch operation for 50 days. Microbial community analysis demonstrated higher relative abundances of the archaeal population in the carbon cloth amended reactor than in unamended control (12%–21% vs. 5%–15%). Compared to percolate and suspension, carbon cloth attached microbial community showed higher enrichment of known electroactive Pseudomonas species along with Methanosarcina and Methanobacterium species, indicating the possibility of DIET-based syntrophy among these species. [Display omitted] • Carbon cloth led to a 20% higher methane yield in high-solids anaerobic digestion. • Relative abundance of the archaeal population increased by carbon cloth addition. • Spatial variations in microbial communities suggested DIET-based syntrophy. • Known DIET-active microorganisms were highly enriched on the carbon cloth surface. [ABSTRACT FROM AUTHOR]