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The widespread application of antibiotics has caused a large number of their residues in the water and posed a serious threat to the ecological environment and human health. Advanced oxidation processes (AOPs) are a promising way to deeply remove such emerging organic pollutants in wastewater treatment. Recently, the AOPs based on sulfate radical (SO4–·) have become a global research hotspot owing to their characteristics of economic efficiency, wide application range, and high stability. In this review, traditional and emerging methods for persulfate activation (such as heating, ultraviolet (UV), carbon-based materials, metal-organic frameworks (MOFs), and transition metals) and their research progress in the degradation of antibiotics in water are summarized integrally. The main factors influencing the activation of persulfate by different methods, as well as the mechanism and pathway of antibiotic degradation, are discussed thoroughly, and the toxicity of antibiotic degradation intermediates is also evaluated. Finally, the developing trend prospects for advanced oxidation technology of active persulfate.

•A single bioelectrode achieved in-situ coupling of reduction and oxidation processes.•Alternating current boosted azo dye initial reduction and subsequent mineralization.•Bidirectional EET in electro-biofilms through cytochromes, pili, and redox mediators.•A collaborative microbiome facilitated efficient bioelectro-metabolism of azo dyes.•Multiple mechanisms of alternating current-driven bioelectrode were deciphered.

A methane-producing microbial electrolysis cell (MEC) is a promising energy-recovery technology, yet its performance is generally inhibited by the insufficient cathode/anode ratio. In this study, a novel stacked stainless-steel-mesh cathode was designed to investigate the effect of the cathode/anode ratio on methane production in semi-continuous MECs. Overall, energy recovery was significantly enhanced by increasing the cathode/anode ratio. The methane production rate in R3 (cathode/anode ratio of 4 cm2/cm3) reached 0.14 m3m–3day–1with an applied voltage of 0.9 V, which increased by 56–180% compared to the methane production rates in R2 (2.5 cm2/cm3) and R1 (1 cm2/cm3). The overall energy efficiency in R3 was 66–94% higher than the overall energy efficiencies in R2 and R1. The cathode area was sufficient for obtaining and maintaining a maximum current when the cathode/anode ratio was higher than 2.5 cm2/cm3. According to electron balance analysis, when the cathode/anode ratio was less than 2.5 cm2/cm3, the methane production enhancement was mainly attributed to the promotion of bioelectrochemical performance, while the sole biomass contribution was enhanced and led to further improvement in overall methane production when the ratio was above 2.5 cm2/cm3. In general, increasing the cathode/anode ratio of the staked-style cathode would be an effective strategy to improve the methane production in the membraneless MECs.

Autotrophic denitrification can be driven using zero valent iron (ZVI) as an electron donor. Balancing the competitive reactions of abiotic nitrate removal and biotic nitrate removal by H2is the key problem for iron-assisted autotrophic denitrification. Hence, H2production by ZVI corrosion plays an important role in the iron-assisted nitrate reduction process, which determines the nitrate reduction rate and the end product. However, few studies concentrate on the effect of soluble H2on ZVI corrosion and the performance of iron-assisted autotrophic denitrification. A hydrogen-rich solution is obtained by dual-chamber MFCs, which is usually directly discarded. The present study aimed to demonstrate that the dissolved hydrogen can be feasibly applied in iron-assisted autotrophic denitrification to accelerate nitrate reduction during ZVI corrosion. It was observed that a continuous dissolved hydrogen supply viaelectrolysis promoted and stabilized the performance of iron-assisted autotrophic denitrification. The average nitrate removal was 47.3% ± 0.2% in ZVI reactors with dissolved hydrogen-rich water (DH reactors), and 30.2% ± 0.3% in ZVI reactors without dissolved hydrogen-rich water (control reactors). Moreover, the concentration of nitrite was 0.04 mg L−1in the DH reactors compared with 0.50 mg L−1in the control reactors. No other intermediates (e.g.N2O) were found in both the autotrophic denitrification reactors. Finally, the hydrogen-rich water enriched the denitrifying bacteria and increased the abundance of specific functional genes, resulting in the promotion of hydrophobic denitrification during the iron-assisted nitrate removal.

In microbial electrolysis cells (MECs), methanogenic communities were sensitively affected both by hydrogen production rate, which were regulated by external voltages, and by initial cathodes, which were determined by reactor startup mode. Hydrogenotrophic methanogens, such as Methanobacterium, Methanococcus, Methanocorpusculum, and Methanoculleus, were enriched in the anode biofilm with a high voltage (0.7 V), which promoted a hydrogen production rate of 0.99–1.10 mL H2per mL reactor in a 24 h batch operation, compared to 0.08–0.09 mL H2per mL reactor at low applied voltage (0.3 V). Acetoclastic methanogens were only obtained from Methanosarcina, which competed with anode respiring bacteria in the anode biofilm, and they were largely detected in open circuit reactors (control). GeoChip analysis revealed that MECs with the largest hydrogen yields had the highest microbial diversity of methanogens. The cathodic products (hydrogen, methane) can simultaneously make the anodophilic community structure comprehensive and diverse despite the use of only a single substrate (acetate) in MECs. The results indicated that the evolution of microbial communities was substantially affected by external voltage and initial operational modes, but methanogen communities were inevitably affected by cathodic products. Higher applied voltage positively affected the relative abundance of cytochrome gene among the overall detected genes, and methanogens were consequently promoted by high coulombic efficiency and fast hydrogen production rate. This research can help in understanding of improving or regulating the quality of products from MEC reactors in the future.

Carboxylic acids, particularly short chain (C2 and C3) fatty acids, are the preferable carbon source for many bioprocesses. Production efficiency of volatile fatty acids (VFAs) recovery from waste activated sludge (WAS) is limited by unbalanced nutrient components. In this study, a low-cost alternative approach (i.e., co-digestion with vinegar residue (VR)) to enhance C2–C3 VFAs recovery from WAS is reported. Compared to sole WAS digestion, concentration of total VFAs, C2–C5, increased by 187%, 74% and 44%, when co-digested with thermal-assisted alkaline (TA), ammonium hydroxide (AH) and sulfuric acid (SA) pretreated VR, respectively. Based on composition analysis, this improvement was mainly due to C2–C3 VFAs production. The hydrolysis rate constants in co-digestion tests, e.g., kh_TA= 0.0045 h−1, were also higher than that observed during mono-digestion (0.0018 h−1). Addition of VR greatly increased the hydrolysis of WAS, particularly with TA, thus enhancing the subsequent acidification process. High-throughput sequencing illustrated that certain groups of microbes (particularly hydrolytic and acid-producing bacteria), such as Acetobacterium, Proteiniclasticum, Cloacibacillus, Acinetobacterand Gemmobacter, were enriched in WAS and VR co-digestion. Further investigation of canonical correlation analyses showed that characteristic conditioning of digestion feedstock was an efficient strategy to restructure the inherent microbial community in WAS. The proposed concept in this study may be practical to simultaneously reduce operational, sludge transport and disposal costs of WWTPs.

AbstractRapid hydrolysis of waste activated sludge (WAS) can be achieved by improving activities of extracellular enzymes under proper temperature conditions. As short-chain fatty acids (SCFAs) accumulation is always consumed by methanogens under anaerobic conditions, and considering that the micro-aerobic condition can inhibit the activities of methanogens, in this study, effects of temperature (55–75°C) on thermophilic micro-aerobic fermentation of WAS were investigated. Results showed that the highest soluble chemical oxygen demand (SCOD) yield was obtained at 60°C (4,407 ± 80 mg/L, 36 h), 2.0 times higher than that obtained at 75°C (2,180 ± 40 mg/L, 36 h), the corresponding hydrolysis rate was 0.6689 d−1. The highest SCFAs yield was 2,928 ± 12 mg COD/L at 60°C and 36 h, 4.9 times higher than that obtained at 75°C (594 ± 10 mg COD/L, 36 h). The analysis of SCFAs composition showed that acetic acid (HAc) accounted for the most percentage (>40%), followed by n-valeric (n-HVa) (20–25%), and propionic acids (HPr) (10–15%). Total suspended solids removal efficiency reached 18.7% after 192-h fermentation at 60°C. These results suggested that the optimal thermophilic micro-aerobic conditions for WAS hydrolysis and SCFAs accumulation from WAS were 60°C and 36-h fermentation time.

Rapid hydrolysis of waste activated sludge (WAS) can be achieved by improving activities of extracellular enzymes under proper temperature conditions. As short-chain fatty acids (SCFAs) accumulation is always consumed by methanogens under anaerobic conditions, and considering that the micro-aerobic condition can inhibit the activities of methanogens, in this study, effects of temperature (55–75°C) on thermophilic micro-aerobic fermentation of WAS were investigated. Results showed that the highest soluble chemical oxygen demand (SCOD) yield was obtained at 60°C (4,407 ± 80 mg/L, 36 h), 2.0 times higher than that obtained at 75°C (2,180 ± 40 mg/L, 36 h), the corresponding hydrolysis rate was 0.6689 d−1. The highest SCFAs yield was 2,928 ± 12 mg COD/L at 60°C and 36 h, 4.9 times higher than that obtained at 75°C (594 ± 10 mg COD/L, 36 h). The analysis of SCFAs composition showed that acetic acid (HAc) accounted for the most percentage (>40%), followed by n-valeric (n-HVa) (20–25%), and propionic acids (HPr) (10–15%). Total suspended solids removal efficiency reached 18.7% after 192-h fermentation at 60°C. These results suggested that the optimal thermophilic micro-aerobic conditions for WAS hydrolysis and SCFAs accumulation from WAS were 60°C and 36-h fermentation time.

To recover resource from waste activated sludge (WAS) presents great roles on developing carbon-neutral operation of wastewater treatment plants. This study was conducted to evaluate SCFAs production potential from anaerobic fermentation of WAS by a novel strategy, i.e., low temperature assisting potassium ferrate (PF) treatment. Results showed that the maximal SCFAs production reached 217 mg chemical oxygen demand (COD)/g volatile suspended solids (VSS) with the shortened fermentation time of six days, and the sum of acetic and propionic acids reached 128 mg COD/g VSS. Meanwhile, the potentially recovered carbon source, in terms of SCFAs, soluble polysaccharides and proteins, reached 437 mg COD/g VSS. The mechanism study indicated that both solubilization and hydrolysis steps were accelerated, supporting by the highest accumulations of soluble organics and ammonia nitrogen, while methanogenesis step was inhibited, supporting by the lowest methane production. In addition, it is noted that low temperature treatment facilitated organics release from extracellular polymeric substance (EPSs), with the removal efficiencies of 51.1% for polysaccharides and 44.3% for proteins, while PF facilitated cell lysis. Interestingly, compared with low temperature followed by PF treatment, PF followed by low temperature treatment performed better on facilitating disintegration of both cells and EPSs, with the highest soluble polysaccharides and proteins of 439 and 1845 mg COD/L. Also, the acid-producing bacteria was greatly enriched, with total percentage of 29.5%. The findings of this study may provide some potential solutions for SCFAs production enhancement from WAS.

Conditioning of extra carbon sources has been widely reported to facilitate fermentation of waste activated sludge (WAS). Soy sauce residue (SSR) was a relatively untapped carbon source for sludge conditioning. This batch study aimed to evaluate the possible implementation of SSR for volatile fatty acids (VFAs) production from WAS. To upgrade the bioavailability of feedstock, three typical pretreatment methods were conducted, i.e., ammonium hydroxide (AH), sulfuric acids (SA) and thermal assisted alkaline (TA). AH pretreated test (AH-PT) outperformed due to a relatively strong structure decomposition of cellulosic materials as revealed by infrared spectroscopic analysis and crystal index. As a result, performed a high hydrolysis rate of 4449 mg COD/d, 1.12-1.23-fold higher than that in TA and SA pretreated tests (TA-PTand SA-PT), and 7.8-fold higher than that in the Control test. Meanwhile, a volatile fatty acids (VFAs) contribution of 401.2 mg COD/g SSR∙L and a maximum acidification rate of 3.59 d–1was recorded, with a high sum proportion of mall molecular acetic and propionic 82.2%, 11%–70% increase over the other three tests. Besides, speciation process characterized with functional genus differentiation was identified by microbial diversity and distribution investigation and canonical correspondence analysis (CCA). Finally, a potential market value of 0.49–0.65 Billion €/year was preliminary estimated, showing promise of resource recovery from both WAS and SSR instead of extensive disposal.

Methane production from low-strength wastewater (LSWW) is generally difficult because of the low metabolism rate of methanogens. Here, an up-flow biofilm reactor equipped with conductive granular graphite (GG) as fillers was developed to enhance direct interspecies electron transfer (DIET) between syntrophic electroactive bacteria and methanogens to stimulate methanogenesis process. Compared to quartz sand fillers, using conductive fillers significantly enhanced methane production and accelerated the start-up stage of biofilm reactor. At HRT of 6 h, the average methane production rate and methane yield of reactor with GG were 0.106 m3/(m3·d) and 74.5 L/kg COD, which increased by 34.3 times and 22.4 times respectively compared with the reactor with common quartz sand fillers. The microbial community analysis revealed that methanogens structure was significantly altered and the archaea that are involved in DIET (such as Methanobacterium) were enriched in GG filler. The beneficial effects of conductive fillers on methane production implied a practical strategy for efficient methane recovery from LSWW.

Recently, a new oxygenic pathway has been proposed based on the disproportionation of NO with putative NO dismutase (Nod). In addition to a new process in nitrogen cycling, this process provides ecological advantages for the degradation of substrates in anaerobic conditions, which is of great significance for wastewater treatment. However, the Nod distribution in aquatic environments is rarely investigated. In this study, we obtained the nod genes with an abundance of 2.38 ± 0.96 × 105 copies per gram of dry soil from the Zoige wetland and aligned the molecular characteristics in the corresponding Nod sequences. These Nod sequences were not only found existing in NC10 bacteria, but were also found forming some other clusters with Nod sequences from a WWTP reactor or contaminated aquifers. Moreover, a new subcluster in the aquifer-similar cluster was even dominant in the Zoige wetland and was named the Z-aquifer subcluster. Additionally, soils from the Zoige wetland showed a high potential rate (10.97 ± 1.42 nmol of CO2 per gram of dry soil per day) for nitrite-dependent anaerobic methane oxidation (N-DAMO) with low abundance of NC10 bacteria, which may suggest a potential activity of Nod in other clusters when considering the dominance of the Z-aquifer subcluster Nod. In conclusion, we verified the occurrence of Nod in an alpine wetland for the first time and found a new subcluster to be dominant in the Zoige wetland. Moreover, this new subcluster of Nod may even be active in the N-DAMO process in this alpine wetland, which needs further study to confirm.

ABSTRACTThe processes and mechanisms of community assembly and its relationships to community functioning are central issues in ecology. Both deterministic and stochastic factors play important roles in shaping community composition and structure, but the connection between community assembly and ecosystem functioning remains elusive, especially in microbial communities. Here, we used microbial electrolysis cell reactors as a model system to examine the roles of stochastic assembly in determining microbial community structure and functions. Under identical environmental conditions with the same source community, ecological drift (i.e., initial stochastic colonization) and subsequent biotic interactions created dramatically different communities with little overlap among 14 identical reactors, indicating that stochastic assembly played dominant roles in determining microbial community structure. Neutral community modeling analysis revealed that deterministic factors also played significant roles in shaping microbial community structure in these reactors. Most importantly, the newly formed communities differed substantially in community functions (e.g., H2production), which showed strong linkages to community structure. This study is the first to demonstrate that stochastic assembly plays a dominant role in determining not only community structure but also ecosystem functions. Elucidating the links among community assembly, biodiversity, and ecosystem functioning is critical to understanding ecosystem functioning, biodiversity preservation, and ecosystem management.IMPORTANCEMicroorganisms are the most diverse group of life known on earth. Although it is well documented that microbial natural biodiversity is extremely high, it is not clear why such high diversity is generated and maintained. Numerous studies have established the roles of niche-based deterministic factors (e.g., pH, temperature, and salt) in shaping microbial biodiversity, the importance of stochastic processes in generating microbial biodiversity is rarely appreciated. Moreover, while microorganisms mediate many ecosystem processes, the relationship between microbial diversity and ecosystem functioning remains largely elusive. Using a well-controlled laboratory system, this study provides empirical support for the dominant role of stochastic assembly in creating variations of microbial diversity and the first explicit evidence for the critical role of community assembly in influencing ecosystem functioning. The results presented in this study represent important contributions to the understanding of the mechanisms, especially stochastic processes, involved in shaping microbial biodiversity.