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Roxarsone (ROX) is a typical organoarsenic feed additive, and most of ROX is excreted unchanged in manure and wastewater. The stability and mobility of ROX result in the environmental risk of arsenic contamination spreading. The degradation of ROX to arsenate (As(V)) can reduce the mobility and environmental risk. Riboflavin is a photosensitizer and can catalyze ROX to As(V), but it is not stable in water environment. In this study, riboflavin-derivative 2′,3′,4′,5′-tetraacetylriboflavin (RTA) was used to replace riboflavin as photosensitizer. The possibility of ROX photodegradation using riboflavin-derivative (RTA) as photosensitizer was investigated. The results showed that RTA was more stable than riboflavin in water environment. ROX was degraded to arsenite (As(III)) by RTA in 90 min under simulated sunlight irradiation and 50 min under natural sunlight irradiation, and further to As(V). The degradation was inhibited under acidic or alkaline pH conditions, while was favorable under neutral pH conditions. The mechanisms of ROX degradation by RTA were further explored. 1O2, O2 − and excited RTA played important role in the RTA-sensitized ROX photodegradation. The photocatalytic degradation of roxarsone by RTA can reduce mobility of arsenic and the environmental risk caused by organoarsenicals.

Biochar as a multi-functional material has been widely used in the fields of catalysis and pollutant removal, but its feasibility to enhance biologic nitrobenzene reduction with the mixed culture and the long-term impact on nitrobenzene removal and microbial structure are lack of a clear clarification. This study aimed at evaluating the feasibility of biochar to enhance anaerobic reduction of nitrobenzene with a mixed culture. We initially investigated the effect of the biochar addition on nitrobenzene removal in short-term experiments and then possible enhancement mechanisms for the biochar were explored. Additionally, the impacts of different key parameters on biological nitrobenzene reduction were studied in the presence of biochar. Moreover, the long-term influence of the biochar on biological nitrobenzene removal with the mixed culture was also evaluated. The results showed that the estimated pseudo first-order rate constant of nitrobenzene removal in the presence of 1.0 g L−1 biochar was four times higher than that without biochar addition. The possible enhancement mechanisms may be owing to that biochar could activate the nitrobenzene molecules and accelerate the electron transfer between microbe and nitrobenzene. Additionally, the stimulating level of the biochar on biological nitrobenzene removal remarkably varied under different conditions. Long-term experiments demonstrated that biochar could not only increase nitrobenzene removal rate but also improve the system stability, which may be related to the shift of microbial communities that the relative abundance of nitrobenzene reduction related bacteria as well as electrochemically active bacteria was enriched in biochar addition systems.

The research on developing cobalt silicate (Co2SiO4)-based materials with high energy and power densities for energy storage devices has sprung up in the field of transition metal silicates (TMSs)-type supercapacitors (SCs). However, the electrochemical performances of the reported Co2SiO4-based materials are not enough desirable owing to the poor conductivity and narrow voltage ranges originated from the intrinsic shortcomings of Co2SiO4. Herein, we design a double-sandwich-like composite, C@Co,CoO/Co2SiO4/rGO/Co2SiO4/C@Co,CoO (denoted as C@Co,CoO/Co2SiO4/rGO) architecture, to improve the electrochemical performance of Co2SiO4, where, reduced graphene oxide (rGO) is inside, both sides of rGO are coated by Co2SiO4, and carbon@cobalt/cobalt oxide (C@Co,CoO) are formed on the surface of Co2SiO4. This integrated construction can not only avert the sluggish mass/electron transfer progress caused by the conventional Co2SiO4, C@Co,CoO and rGO multi-phase mixture system, but also improve the cycle stability by protecting Co2SiO4 from the dissolution and structural collapse during the electrochemical process. As expected, the double-sandwich-like C@Co,CoO/Co2SiO4/rGO displays promising electrochemical performances. At 0.5 A·g−1, it achieves the specific capacitance of 360 F·g−1 (324 C·g−1) in the potential interval of − 0.4 V ∼ 0.5 V, and super long lifespan with 88 % after 15,000 cycles. Moreover, the hybrid supercapacitor (HSC) device C@Co,CoO/Co2SiO4/rGO//AC displays the capacitance with 687 mF·cm−2 at 1 mA·cm−2, energy density with 1.373 Wh·m−2 at 1.5 W·m−2, and even shows practical application for lightening the LED bulb. This work provides an idea for the preparation of the integrated double-sandwich-like carbon/TMSs/carbon architecture to boost the electrochemical performance of TMSs.

In this study, enhanced degradation of high-concentration pyridine and simultaneous denitrification were achieved in an Electricity assisted bio-photodegradation system (EBPS) with a photoanode zone, a biocathode zone and an aerobic zone. The recombination of photoelectron-hole pairs was significantly suppressed in EBPS, which could not only improve the pyridine oxidation in photoanode zone, but also accelerate the biodegradation process in biocathode zone. NH4+ produced from pyridine degradation could be effectively nitrified into NO2- and NO3- in aerobic zone, which was recirculated into biocathode zone to serve as electron acceptor for accelerating pyridine biodegradation. When influent pyridine concentration was as high as 1250 mg L-1, pyridine was completely degraded without adding any extra electron donors, and complete denitrification was achieved in biocathode zone. Microbial community analysis confirmed the enrichment of the pyridine biodegradation species (Rhodococcus, Hydrogenophaga, Truepera and Thermovirga), denitrification species (Thiobacillus, Thioalkalispira and Rhodococcus) and electroactive species (Thiobacillus, Thermovirga, Hydrogenophaga, Thioalkalispira and Rhodococcus). Furthermore, the mechanism of pyridine metabolism, denitrification and extracellular electron transfer processes in EBPS was investigated, utilizing Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2). The results showed that the genes involved in pyridine degradation, denitrification and extracellular electron transfer were remarkably enriched in EBPS, indicating the crucial role of photoelectrical stimulation. This study provided a sustainable technical approach for simultaneous removal of pyridine and nitrogen in wastewater.

With the development of the degradation of persistent organic pollutants in the wastewater, antibiotics have been considered as emerging pollutants. Their lasting effects on the entire ecosystems directly resulted in irreversible damage all over the world. Electro-Fenton, photo-Fenton, photoelectro-Fenton and solar photoelectro-Fenton processes have been adopted to the elimination of antibiotics for the considerable efficiency. The mechanism, advantage, disadvantage, and the impacts of key parameters for each method are discussed based on the recent works, respectively. The cost aspects of electro-Fenton and photo-Fenton are analyzed for practical application. The degradation pathway as well as the toxicity evaluation of the antibiotics is reviewed. Finally, research needs and unfilled gaps have been proposed, including blocks from unpredicted impurities, pilot-scale study for the remediation of polluted water, pretreatment of antibiotic effluent, cognition of high-performance electrode, and characterization of intermediates. All of them suggested that electro-Fenton and photo-Fenton could be adopted as an ecological and efficiency ways for the elimination of antibiotics.

The anaerobic technology plays a fundamental role in both energy recovery and pollutant removal from wastes. However, it usually suffers from several bottlenecks, such as low reaction rates and poor system stability. To compensate for these limitations, the use of electrical stimulation to promote the anaerobic process, named as electricity-stimulated anaerobic system (ESAS), has been recently proposed. It has been demonstrated that the ESAS can improve energy recovery and pollutant removal substantially, through the regulation of metabolic pathways and electron transfer process by electrical stimulation. This paper comprehensively reviews the research progress of ESASs, covering the application of this system for energy recovery and pollutant removal, the possible enhancement mechanisms in the view of electron transfer process, response of microorganisms under electrical stimulation, as well as the strategies to manipulate such systems. Perspectives on future trends in the development of ESASs are also discussed. It is expected that the review will attract more attention to this promising technology and contribute to its further development.

The performance and possible mechanisms of iodinated contrast medium diatrizoate (DTA) removal by sulfide-modified nano-sized zero-valent iron (S-nZVI) without the presence of oxygen were investigated in this study. It was shown that the degradation efficiency of 30 μM DTA was observably enhanced by 2 g L−1 S-nZVI (S/Fe = 0.25) compared to nZVI. Kinetic analysis indicated that the three-step deiodination process of DTA removal by S-nZVI could be appropriately fitted by pseudo-first-order kinetic model. The first-step kinetic rate constant of DTA removal reached to 2.22 h−1 with the utilization of S-nZVI, which was 5.2 times higher than that of nZVI. The enhancement mechanism for DTA removal by S-nZVI was confirmed as accumulating more atomic hydrogen (H*) via the inhibition of hydrogen recombination. Moreover, it was found that the degradation rate of DTA was optimal when the S/Fe ratio attained at 0.25. The DTA removal performance exhibited a promoting trend with the increasing of S-nZVI dosage, while the existence of humic acid or artificial groundwater environment showed an inhibition effect on the degradation rate of DTA by S-nZVI. Additionally, the comparison of reduction capacity between S-nZVI and nZVI was evaluated in continuous flow systems, indicating that S-nZVI would likely present more practical application prospects on DTA removal than nZVI.

The dispersion behavior of an upflow anaerobic sludge blanket (UASB) reactor for acidogenesis was investigated, and its flow patterns were simulated. Compared with the single-zone axial-dispersion model (with squared difference from 130 to 450), a two-zone axial-dispersion model (with squared difference from 1 to 7) was found to be more appropriate for simulating the dispersion characteristics of the acidogenic UASB reactor. A sensitivity analysis of the key model parameters was performed, and the axial dispersion coefficient was identified as the most important factor in the dispersion modeling of the reactor, implying that the acidogenic UASB reactor was potentially dispersion-controlled. The flow patterns, including mixed and plugging degrees, at different hydraulic loading rates were evaluated. The ratio of plug volume to mixed volume (Ip/Im) decreased with the increasing specific gas velocity (image) when the image value was low, but increased markedly with the increasing image after the image exceeded 0.7.