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Microbial electrolysis cells (MEC), coupled with sulfate-reducing bacteria (SRB), was used to degrade sulfate-rich wastewater that is deficient in electron donors. However, because of the impact of electric double layers (EDLs), salt crystals formed on the electrode, thereby potentially retarding the continuity of sulfate removal during the whole operation. Here, an improved MEC reactor using intermittent electric field was established. It works better in sulfate removal for a longer period, which was higher than the conventional MEC reactor by 2.18-fold after 10 days. Observation on the activity of lactic dehydrogenase (LDH) and ATP revealed that the formation of salt crystals on the electrode led to plasmatorrhexis. Conversely, improved reactor contributed to extracellular substances production and prevented the salt crystal formation, which was conducive to biofilm formation as further verified by detection through SEM. Electrochemical impedance spectroscopy tests showed that the cathodic microorganisms accelerated electron transfer whereas the salt crystals increased the charge transfer resistance. High-throughput sequencing analysis illustrated that improved reactor could maintain the competitiveness of SRB in the microbial community for a longer period. Moreover, the improved reactor resulted in high species diversity, thereby showing the significant resistance of the microorganisms to arduous environments. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cell (MEC) coupled with sulfate-reducing bacteria (SRB) was used to degrade sulfate-rich wastewater which was deficient in electron donors. Results confirmed that SRB could trigger vigorous synergy with an applied current. An applied electrical field of 1.5 mA (R1) resulted in the highest sulfate removal, which was 14.9% higher than that of the control reactor (R0). In addition, organic-substance consumption decreased with the increase of applied current. The concentration of lactic dehydrogenase (LDH), an indicator of cell rupture, increased by 3.59 times at 2.5 mA; that of ATP, an indicator of cell metabolism, sharply decreased under 2.5 and 3.5 mA. This finding indicated that high current led to plasmatorrhexis, low growth rate, and metabolic activity, subsequently reduced sulfate-reduction efficiency. Conversely, a proper current resulted in the enhancement of extracellular secretion, which was conducive to biofilm formation as further confirmed by detection through SEM. Electrochemical impedance spectroscopy (EIS) illustrated the SRB in the biofilm could accelerate the rate of direct electron transfer to cathode. Genus-level results further revealed that the dominant bacterium Desulfovibrio , an SRB, was richer in the cathode biofilm and R1, compared with R0. [ABSTRACT FROM AUTHOR]

Sulfate reducing bacteria (SRB) is identified as the primary organisms responsible for the treatment of heavy metal wastewater. However, most heavy metals can inhibit the growth of SRB during heavy metal treatment processes. Sulfide is a metabolic product of SRB and it can precipitate or reduce heavy metals. This study focused on the effects of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity. First, we considered the existence style of various heavy metals with and without sulfide addition by sequential extraction experiments. Second, the particle size distribution was evaluated and the cell structure during the metabolism of a SRB culture, containing different heavy metals, was analyzed by particle size distribution and TEM analyses. Third, the evolution of sulfate under the influence of different concentrations of heavy metals with and without sulfide addition was investigated to evaluate SRB activity. The results indicated that sulfide played an important role in alleviating and even eliminating the toxicity of Cu(II), Hg(II) and Cr(VI). We also discuss the mechanism of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity. [ABSTRACT FROM AUTHOR]

Abstract: The current study focused on the influences of various pretreatments, including alkaline, ultrasonic and thermal pretreatments on biological sulfate reduction with waste activated sludge (WAS) as sole electron donor. Our results showed that thermal and ultrasonic pretreatments increased the sulfate reduction percentage by 14.8% and 7.1%, respectively, compared with experiment with raw WAS, while alkaline pretreatment decreased the sulfate reduction percentage by 46%. By analyzing the WAS structure, particle size distribution, organic component, and enzyme activity after different pretreatments, we studied the effects of these pretreatments on WAS as well as on the mechanisms of how biological sulfate reduction was affected. The reduction of WAS and variation of WAS structure in the process of sulfate reduction were investigated. Our results showed that biosulfidogenesis was an efficient method of diminishing WAS, and various pretreatments could enhance the reduction efficiency of volatile solid in the WAS. [Copyright &y& Elsevier]

Given that the consumption of organic substances entails costly biodesulfurization, the characteristics of the bacterial community in a reactor should be determined to increase the desulfurizing rate under low organic loading condition. In this study, the bacterial community distribution in the expanded granular sludge bed reactor used to treat sulfate-containing wastewater with low organic loading rate was determined by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and 16S rDNA clone library analyses. DGGE results showed that the predominant bacteria were stable and accounted for ~90 % sulfate removal efficiency. Differences in band positions and intensities indicated that the distribution and abundance of bacteria were affected by their positions in the reactor. Typical bands were identified in the bacterial community comprising Desulfovibrio, Desulfomicrobium, Thiomonas, Acinetobacter, Bacteroidetes, and Chloroflexi. Their functions in the reactor were also discussed. The possible links between the functional and microbial responses were also investigated based on the characteristic and spatial distribution of each bacterium in consortium. [ABSTRACT FROM AUTHOR]

Abstract Coal gasification wastewater (CGWW) is a typical toxic and refractory industrial wastewater. Here, a novel phenol and ammonia recovery process (IPE) was employed for CGWW pretreatment, and the coupled system assemble by the IPE process with A2/O system (IPE-A2/O) were operated to enhance the treatment performance of CGWW. The results showed that the IPE pre-treated effluent had a higher BOD 5 /COD ratio and lower refractory compounds compared to a typical process (MIBK). Subsequent A2/O biological treatment indicated that the A2/O-p system (A2/O system followed IPE process) obtained a higher average COD removal of 92% compared to 87.7% of the control (A2/O-m, A2/O system followed MIBK). The GC–MS analysis suggested that the content of alkanes in the IPE-A2/O effluent was lower than that of the MIBK-A2/O. The high-throughput sequencing revealed Levilinea, Alcaligenes , Acinetobacter , Thauera and Thiobacillus were the core genera in A2/O system. The genera Alcaligenes , Acinetobacter , Thauera and Thiobacillus in the degrading consortium were enriched in the A2/O-p system, leading to increased removals of organic pollutants and TN. These results suggested that the IPE process was a feasible pretreatment method, and the coupled IPE-A2/O system was an alternative technique for treating CGWW. Graphical abstract Unlabelled Image Highlights • A novel phenol and ammonia recovery process was employed to treat real CGWW. • The pre-treated process significantly improved the effluent biodegradability. • The pre-treated process facilitated the COD removal in A2/O system. • Microbial community structure was shaped by the pre-treated wastewater. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Asymmetric MCDI with only anion-exchange membrane (AMCDI-AEM) is proposed. • AMCDI-AEM shows better performance compared with CDI. • AEM with high IEC and low resistance and water uptake favors desalination. • AEM plays a stronger role than CEM in membrane-assisted CDI application. Abstract Membrane capacitive deionization (MCDI) usually contains both anion and cation exchange membranes (AEM, CEM) to restrict the ion desorption during charging and re-adsorption during discharging in capacitive deionization (CDI). In this study, different from conventional MCDI, an asymmetric membrane capacitive deionization (AMCDI) device packing an AEM only (AMCDI-AEM) was constructed, where the AEM was lab-synthesized from poly (2, 6-dimethyl-1, 4-phenylene oxide). The effect of the AEM properties, such as ion exchange capacity, water uptake and membrane resistance on the desalination performance of AMCDI-AEM was systematically discussed. The results indicate that an AEM with high ion exchange capacity, low membrane resistance and low water uptake is beneficial for AMCDI-AEM. Furthermore, AMCDI packed with a commercial cation exchange membrane only (AMCDI-CEM) and a conventional MCDI device were also assembled to stress the importance of AEM application. Although the charge efficiency of AMCDI-AEM is lower than a full MCDI cell (54.7 vs 95.0%) due to the unprotected cathode, AMCDI-AEM device shows comparable salt adsorption capacity to MCDI (7.4 vs 7.2 mg g−1), and is much better than that of CDI (2.3 mg g−1) and AMCDI-CEM (1.5 mg g−1), suggesting that AEM plays a stronger role than CEM for membrane-assisted CDI application. By using a single AEM and commercial activated carbon electrode, this work provides an opportunity to reduce membrane cost for the industrialization of MCDI technology. [ABSTRACT FROM AUTHOR]

Coal gasification wastewater is a typical high phenol-containing, toxic and refractory industrial wastewater. Here, lab-scale anaerobic-anoxic-oxic system was employed to treat real coal gasification wastewater, and methanol was added to oxic tank as the co-substrate to enhance the removal of refractory organic pollutants. The results showed that the average COD removal in oxic effluent increased from 24.9% to 36.0% by adding methanol, the total phenols concentration decreased from 54.4 to 44.9 mg/L. GC-MS analysis revealed that contents of phenolic components and polycyclic aromatic hydrocarbons (PAHs) were decreased compared to the control and their degradation intermediates were observed. Microbial community revealed that methanol increased the abundance of phenolics and PAHs degraders such as Comamonas , Burkholderia and Sphingopyxis . Moreover, functional analysis revealed the relative abundance of functional genes associated with toluene, benzoate and PAHs degradation pathways was higher than that of control based on KEGG database. [ABSTRACT FROM AUTHOR]

The physicochemical and structural properties of the AMX (homogeneous AEM), AMA (semi-homogeneous AEM) and HAEM (heterogeneous AEM) were characterized systematically to examine their effects on membrane fouling from sodium dodecyl sulfate (SDS) in electrodialysis. Results demonstrated that the fouling of three AEMs was closely related to their membrane structure, and the denser membrane structure caused more SDS accumulated on the membrane surface to make the severer membrane fouling. The existence of SDS in the dilute solution caused the desalination rate of AMX, AMA and HAEM decreased by 42.3%, 15.3% and 9.2%, respectively. Different fouling layer was formed on the surface of AMX and AMA except HAEM, which was demonstrated firstly by element mapping of membrane cross-section. Electrochemical impedance spectroscopy (EIS) suggested the ionic migration through the fouled AMX was restricted completely, different from the transmembrane migration of partial ions through the fouled AMA and HAEM. Compared with the fouled AMA and HAEM, the performance of the fouled AMX caused by SDS was more difficult to be recovered due to its denser membrane structure. [ABSTRACT FROM AUTHOR]

The recent thrust in utilizing microbial electrolysis cell (MEC) has led to accelerated attention in environmental decontamination. One key factor that governs this process is electron transfer efficiency. In this study, neutral red (NR) is involved as electron transfer mediator to investigate whether it could contribute to MEC performance. Afterwards, influence of electrode material selection on NR addition system was also studied. The results indicate MEC with NR shows better electrochemistry activity, which means sulfate-reducing bacteria (SRB) can response to electron transfer mediator NR. Further study reveals graphite felt triggers a better synergy with NR to facilitate electron utilization efficiency of the system subsequently maintains bacteria metabolic activity for a longer time. Sulfate removal in this reactor reaches 79.0% with electron utilization efficiency of 54.2%. To explore the mechanism, electrode bioelectrochemical property, microorganism activity and community were investigated. Electrode morphology analysis confirms graphite felt affords abundant space for the growth of electroactive microorganisms especially SRB and promotes electron exchange through cooperating with NR, which fits in with electrochemical impedance spectroscopy (EIS) analysis. High-throughput sequencing analysis confirms improved reactor can fortify the population dominant of SRB in the community which greatly raises electron utilization efficiency of SRB. [ABSTRACT FROM AUTHOR]

• ZVI promotes removal of COD, phenolics and heterocyclics in coking wastewater. • Accumulation of 2(1H)-quinolinone is decreased by ZVI during quinoline degradation. • The abundance of phenolics and NHCs degraders is increased with ZVI addition. • ZVI promotes xenobiotics degradation and its downstream metabolic pathways. • Reduced ORP by ZVI is the main driving force of microbial community succession. Coking wastewater (CWW) has long been a serious challenge for anaerobic treatment due to its high concentrations of phenolics and nitrogen-containing heterocyclic compounds (NHCs). Herein, we proposed and validated a new strategy of using zero-valent iron (ZVI) to strengthen the anaerobic treatment of CWW. Results showed that COD removal efficiencies was increased by 9.5–13.7% with the assistance of ZVI. GC-MS analysis indicated that the removal of phenolics and NHCs was improved, and the intermediate 2(1H)-Quinolinone of quinoline degradation was further removed by ZVI addition. High-throughput sequencing showed that phenolics and NHCs degraders, such as Levilinea and Sedimentibacter were significantly enriched, and the predicted gene abundance of xenobiotic degradation and its downstream metabolic pathways was also increased by ZVI. Network and redundancy analysis indicated that the decreased oxidation-reduction potential (ORP) by ZVI was the main driver for microbial community succession. This study provided an alternative strategy for strengthening CWW anaerobic treatment. [ABSTRACT FROM AUTHOR]

• Global softness of the NHCs was employed to correlate with the ozonation efficiency. • Higher global softness of NHCs resulted in a greater degradation efficiency. • Fewer N atoms in heterocyclic ring generated more OH from ozone dissociation. • Reactive sites for both O 3 and radical attack were located by FO theory. • Combined DFT and TOF-MS results were used to identify the hydroxylation products. Nitrogen-containing heterocyclic contaminants (NHCs) have aroused intense environmental issues in waterbody because of their high toxicity and strong recalcitrance against natural degradation. In this study, ozonation degradation on four typical NHCs - benzotriazole (BTA), benzimidazole (BMZ), indazole (IDZ), and indole (IDO) was carried out to investigate the effects of N atoms on degradation efficiency. Global softness of the NHCs was calculated by density functional theory (DFT) and correlated with ozonation efficiency. It was discovered that higher global softness of the NHCs resulted in the greater degradation efficiency. Mineralization results together with the quenching tests results suggested that NHCs with ortho-positioned N atoms in heterocyclic ring are easier to be mineralized, while the presence of para-positioned N atoms increased the recalcitrance for destruction. Apart from hydroxyl radicals, superoxide radicals and singlet oxygens were also identified by electron paramagnetic resonance (EPR) spectra. Condensed Fukui index was employed to probe the potential active sites for both direct ozone oxidation and radical-based attack. Single point energies were further calculated among these active sites to seek the initial-stage hydroxylation intermediates. Combined the calculation results with the identified intermediates from time-of-flight mass spectroscopy (TOF-MS), degradation routes of the NHCs were proposed. This study discovered structure-dependent behavior of NHCs on ozonation efficiency and envisaged a more accurate strategy for establishing the degradation pathway. [ABSTRACT FROM AUTHOR]