The humic substance analogue antraquinone-2, 6-disulfonate (AQDS) enhanced zero-valent iron based autotrophic denitrification: Performances and mechanisms.

Zero-valent iron based autotrophic denitrification (ZVI-AD) has attracted increasing attentions in nitrate removal due to saving organic carbon budget in wastewater treatment, but limited by the low reaction speed, poor electron transfer efficiency as well as the compaction/blocking by iron hydrolysis products. Humic substances (HS) were promising to regulate iron cycle and accelerate electron transfer by serving as electron mediators. In this study, HS analogue, antraquinone-2, 6-disulfonate (AQDS), was added to enhance ZVI-AD process. Results showed that the dosage of AQDS led to a NO3--N removal efficiency of 83.37 ± 3.98% within 96 h, which was 32.28 ± 1.25% higher than that in ZVI-AD system. The corrosion of ZVI and microbially nitrate reduction were both improved at the presence of AQDS. The addition of AQDS enriched the functional species, including autotrophic denitrobacteria namely Thauera and Hydrogenophaga, iron redox-related species namely Ferruginibacter and HS respiration related species namely Flavobacterium. The genes napA and napB related to electron transfer, nirK and nosZ related to the accumulation of intermediate products were also enriched by the addition of AQDS. AQDS addition boosted the electrons flowing to both abiotic and biotic nitrate reduction. Nitrate removal mechanism involved in ZVI-AQDS coupled system was proposed. This study provided an alternative strategy for improving ZVI-AD by HS.

Enhanced 4-bromophenol anaerobic biodegradation in electricity-stimulated anaerobic system: The key role of humic acid in reshaping microbial eco-interrelations and functions.

Electricity-stimulated anaerobic system (ESAS) has shown great potential for halogenated organic pollutants removal. Exogenous redox mediators can improve electron transfer efficiency to enhance pollutants removal in ESAS. In this study, humic acid (HA), a low-cost electron mediator, was added into ESAS to enhance the simultaneous reductive debromination and mineralization of 4-bromophenol (4-BP). Results showed that the highest 4-BP removal efficiency at 48 h was 95.43 % with HA dosage of 30 mg/L at - 700 mV, which was 34.67 % higher than that without HA. The addition of HA decreased the requirement for electron donors and enriched Petrimonas and Rhodococcus for humus respiratory. HA addition regulated microbial interactions, and enhanced species cooperation between Petrimonas and dehalogenation species (Thauera and Desulfovibrio), phenol degradation-related species (Rhodococcus) as well as fermentative species (Desulfobulbus). Functional genes related to 4-BP degradation (dhaA/hemE/xylC/chnB/dmpN) and electron transfer (etfB/nuoA/qor/ccoN/coxA) were increased in abundance by HA addition. The enhanced microbial functions, as well as species cooperation and facilitation, all contributed to the improved 4-BP biodegradation in HA-added ESAS. This study provided a deep insight into microbial mechanism driven by HA and offered a promising strategy for improving halogenated organic pollutants removal from wastewater.

Reductive potential from cathode electrode as an option for the achievement of short-cut nitrification in bioelectrochemical systems.

Nitrogen removal based on short-cut nitrification (SCN) have attract more attentions, in which stable nitrite accumulation is prerequisite. In this study, different reductive potential was applied to inhibit nitrite oxidizing bacteria for achievement of SCN in aerobic cathode chamber of bioelectrochemical systems with dissolved oxygen concentration of 3.5 mg/L. The results demonstrated that the applied potential facilitated nitrite accumulation with high ammonia oxidation rates. The maximum nitrate accumulation rate of 87.61% was obtained at -800 mV. The abundance of Nitrosomonas and Thauera increased while Nitrospira abundance declined with more negative reductive potentials. The activity of nitric oxide reductase was also evidently inhibited. The above-mentioned three genera were the keystone taxa in co-occurrence network with high degree and closeness centrality. Interestingly, total nitrogen (TN) removal was enhanced simultaneously in the absence of external organic carbon. Reductive potential would be a promising approach for achieving SCN and simultaneously TN removal.

Removing organic matters from reverse osmosis concentrate using advanced oxidation-biological activated carbon process combined with Fe3+/humus-reducing bacteria.

The high-concentration wastewater produced in the industrial reverse osmosis (RO) process contains a large amount of refractory organic matters, which will have serious impacts on the natural environment and human health. Among them, contaminants can be transformed by humus-reducing bacteria based on humus. In this study, O3- assisted UV-Fenton method was applied as pretreatment. Biological activated carbon (BAC) technology in which humus-reducing bacteria were the dominant bacteria, enhanced by electron donor and Fe3+, was used to dispose of RO concentrate (ROC). The results showed that water treatment process combining oxidation with biological filtration had a positive effect on the removal of stubborn contaminants in ROC. The system was strengthened by adding electron donor and Fe3+, and the chemical oxygen demand (COD) removal efficiency was up to 80.1%. However, when the removal efficiency of UV254 absorbing pollutants reached optimal value (87.3%), that means only Fe3+ was added.

Promotion by humus-reducing bacteria for the degradation of UV254 absorbance in reverse-osmosis concentrates pretreated with O3-assisted UV-Fenton method.

The primary pollutants in reverse-osmosis concentrates (ROC) are the substances with the UV absorbance at 254 nm (UV254), which is closely related to humic substances that can be degraded by humus-reducing bacteria. This work studied the degradation characteristics of humus-reducing bacteria in ROC treatment. The physiological and biochemical characteristics of humus-reducing bacteria were investigated, and the effects of pH values and electron donors on the reduction of humic analog, antraquinone-2, 6-disulfonate were explored to optimize the degradation. Furthermore, the O3-assisted UV-Fenton method was applied for the pretreatment of ROC, and the degradation of UV254 absorbance was apparently promoted with their removal rate, reaching 84.2% after 10 days of degradation by humus-reducing bacteria.

Synthesis and characterization of TiO2/graphene oxide nanocomposites for photoreduction of heavy metal ions in reverse osmosis concentrate.

In this study, graphene oxide (GO), titanium dioxide (TiO2) and TiO2/GO nanocomposites were synthesized as the catalysts for photoreduction of endocrine disrupting heavy metal ions in reverse osmosis concentrates (ROC). The morphology, structure and chemical composition of these catalysts were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Brunauer-Emmett-Teller analysis, Barrett-Joyner-Halenda, Fourier transform infrared spectroscopy and Raman spectroscopy. The photocatalytic experiments showed that TiO2/GO nanocomposites exhibit a higher photoreduction performance than pure TiO2 and GO. Under the optimal conditions, the removal rates of Cd2+ and Pb2+ can reach 66.32 and 88.96%, respectively, confirming the effectiveness of photoreduction to reduce the endocrine disrupting heavy metal ions in ROC resulted from the combined adsorption-reduction with TiO2/GO nanocomposites.