Application of Fenton sludge coupled hydrolysis acidification in pretreatment of wastewater containing PVA: Performance and mechanisms.

Hydrolysis acidification (HA) is widely used in pretreatment of macromolecular refractory wastewater to improve its biodegradability. However, because the biological activity could be inhibited by macromolecular substances to a certain extent, its application is limited. In this study, polyvinyl alcohol (PVA), as a classic macromolecular pollutant in TPD wastewater, was treated by the Fenton sludge-coupled HA process to investigate the effects of Fenton sludge addition on the HA performance and identify the probable mechanisms behind it. The results showed that approximately 40% of macromolecular PVA was hydrolyzed into small molecular substances with molecular weight (Mw) < 105 in the Fenton sludge-added reactor. Meanwhile, acidification efficiency (AE), volatile fatty acid production increased by 20.8% and 92.05 mg/L with Fenton sludge addition. The values of BOD5/COD changed from 0.091 of influent to 0.26 and 0.32 of effluent from the simple HA process and Fenton sludge addition HA process, respectively. These results proved that biodegradability was improved by the two processes and the Fenton sludge addition had a positive effect on HA. Further analysis found that 2-lines ferrihydrite involved in Fenton sludge might serve as an electron acceptor to participate in extracellular respiratory. Besides, the Fe2+ observed a positive effect of the sludge characteristics in agreement with the higher activity of dehydrogenase and extracellular polymeric substances (EPS) production. This study suggested that Fenton sludge can be recycled and used as an iron source to enhance HA for industrial wastewater pretreatment.

Effects of Fe/Fe-Mn oxides loaded biochar on anaerobic degradation of typical phenolic compounds in coal gasification wastewater: Performance and mechanism.

In this study, two kinds of magnetic biochar (BC) were synthesized by loading Fe (FeBC) and Fe-Mn oxides (FMBC) and their effects on anaerobic phenolics degradation were investigated. Compared with BC/FMBC, FeBC addition achieved the superior phenolics biodegradation even for 3,5-xylenol. Compared with control, FeBC addition enhanced CH4 production by 100.1 % with the lag time shortened from 9.5 days to 6.6 days while it increased to 11.2 days with FMBC addition. FeBC addition activated adsorption-biodegradation and Fe (III) reduction with the improved electron transfer activity, adenosine triphosphate and cytochrome C concentrations. Abundant phenol degrading bacteria, electroactive bacteria, syntrophic partners could be enriched by FeBC addition, contributing to the enhanced benzoyl-CoA and methanogenesis pathways. However, this enhancement was inhibited by FMBC addition owing to the accumulation of reactive oxygen species. This study provided novel insights into the application of magnetic BC to enhanced anaerobic treatment of phenolic wastewater.

Improved decolorization and mineralization of azo dye in an integrated system of anaerobic bioelectrochemical modules and aerobic moving bed biofilm reactor.

In this study, a stacked integrated system with anaerobic bioelectrochemical system (BES) and aerobic moving bed biofilm reactor (MBBR) was developed to improve the decolorization and mineralization of azo dye. This stacked BES-MBBR exhibited better performance with acid orange (AO7) decolorization of 96.4 ± 0.6% and chemical oxygen demand (COD) removal of 87.7 ± 4.4%. Contribution of each module in the BES and MBBR stages indicated that BES modules enhanced the pretreatment process in AO7 decolorization, and MBBR played an important role in further removal of COD. The mechanism analysis indicated that the azo bond was cleaved with reductive decolorization at biocathode in the anaerobic BES stages, and then the intermediate products can be further oxidized with COD removal in the aerobic MBBR stage. This work demonstrated that the integrated system with stacked anaerobic BES and aerobic MBBR could provide a promising way for the pretreatment and post-treatment of refractory wastewater.

Cu-coupled Fe/Fe3C covered with thin carbon as stable win-win catalysts to boost electro-Fenton reaction for brewing leachate treatment.

The electro-Fenton oxidation is one of the powerful approaches for achieving the complete mineralization of organic pollutants in water. The key dilemma for efficient industrial application of electro-Fenton oxidation is the complicated post-processing of iron sludge, and the cost and risk associated with H2O2 transportation and storage. Herein, Cu-coupled Fe/Fe3C covered with carbon layer on carbon felt (Cu-Fe/Fe3C@C), engineered by a hydrothermal reaction followed by the consequent thermal-treatment in N2 atmosphere, as a self-supported integrated cathode were used for an onsite oxygen reduction reaction and a Fenton oxidation reaction. Experimental evidences demonstrate that, at the operating potential of -1.1 V, Fe3C can selectively catalyze O2 into H2O2 by 2e reduction pathways with assistance of metal Cu. Meanwhile, metal Fe and Cu incorporated into Cu-Fe/Fe3C@C simultaneously motivate the onsite Fenton oxidation arose by H2O2. Such a win-win catalyst presented high activity in the electro-Fenton process. In acidic environment, the efficient mineralization rate of methylene blue, nitrobenzene, phenol, and bisphenol A can reach more than 70% in 60 min, as well as the excellent stability and durability due to the protection of graphited carbon layer. Compared with tradition electrochemical degrade system, the prepared Cu-Fe/Fe3C@C electrode as cathode for practical refractory brewing leachate treatment reveal more efficient decolorization and mineralization, saving 14.3% of electricity.

Bioelectrochemical systems with a cathode of stainless-steel electrode for treatment of refractory wastewater: Influence of electrode material on system performance and microbial community.

The large-scale application of the bioelectrochemical system (BES) is limited by the cost-effective electrode materials. In this study, five kinds of stainless-steel materials were used as the cathode of the BES coupled with anaerobic digestion (BES-AD) for the treatment of diluted N, N-dimethylacetamide (DMAC) wastewater. Compared with a carbon-cloth cathode, BES-AD with a stainless-steel cathode had more engineering due to its low cost, although the operating efficiencies were slightly inferior. Stainless-steel mesh with a 100 µm aperture (SSM-100 µm) was the most cost-effective electrode and the implanted BES exhibited better COD removal efficiency, electrochemical performance and biodegradability. Analysis of microbial community revealed the synergetic effect between exoelectrogen and fermentative bacteria had been strengthened in the SSM-100 µm cathode biofilm. Function analysis of the microbial community based on PICRUSt predicted metagenomes revealed that the metabolic pathways of xenobiotics biodegradation and metabolism in the SSM-100 µm cathode were stimulated.

Tire pyrolysis wastewater treatment by a combined process of coagulation detoxification and biodegradation.

Recycling waste tires through pyrolysis technology generates refractory wastewater, which is harmful to the environment if not disposed properly. In this study, a combined process of coagulation detoxification and biodegradation was used to treat tire pyrolysis wastewater. Organics removal characteristics at the molecular level were investigated using electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that nearly 90% of the organic matter from the wastewater was removed through the process. Preference of the two coagulants for different classes of organics in tire pyrolysis wastewater was observed. The covalently bound inorganic-organic hybrid coagulant (CBHyC) used in this work had a complementary relationship with biodegradation for the organics removal: this coagulant reduced toxicity and enhanced the biodegradation by preferentially removing refractory substances such as lignin with a high degree of oxidation (O/C > 0.3). This study provides molecular insight into the organics of tire pyrolysis wastewater removed by a combined treatment process, supporting the advancement and application of waste rubber recycling technology. It also contributes to the possible development of an effective treatment process for refractory wastewater.

Removal of refractory organics in wastewater by coagulation/flocculation with green chlorine-free coagulants.

Coagulation/flocculation is considered an economical and practical technology to remove refractory organic matter from wastewater. Coagulants containing chlorine may release chloride ions into water, thereby resulting in corrosion. A green chlorine-free coagulant of polyaluminum ferric silicate (PSAF) was synthesized to treat non-oily (e.g., humus wastewater) and oily refractory wastewaters (e.g., lubricating oil wastewater). Results showed that the highest removal efficiency of humus substances in non-oily wastewater achieved 96.0% at pH 7.0 using PSAF alone. When treating oily wastewater, the dosage and addition sequence of PAMALAM significantly affected the coagulation performance. The removal efficiencies of turbidity, chemical oxygen demand, and total nitrogen were increased by 0.3, 1.8, and 5.9 folds, respectively, with the optimal adding sequence of PSAF +0.08% PAMALAM. More fulvic acid-like substances can be removed during this process. The analysis of zeta potential and floc properties revealed that charge neutralization, sweep, and adsorption/entrapment mechanisms existed during the single PSAF coagulation process, and PAMALAM mainly improved the adsorption, bridging, and sweep function.

Coupling of Fe-C and aerobic granular sludge to treat refractory wastewater from a membrane manufacturer in a pilot-scale system.

A novel pilot-scale system based on aerobic granular sludge (AGS) as a biological treatment step was proposed to treat refractory wastewater from a membrane manufacturer. The components of the system included a microelectrolysis Fe-C filter, a hydrolysis acidification bioreactor (HA), sequence batch reactor 1 (AGS SBR1), sequence batch reactor 2 (AGS SBR2), and a membrane bioreactor (MBR). The Fe-C filter effectively improved the biodegradability of the wastewater components and introduced some byproducts (such as Fe2+, Fe3+, and Fe minerals) that are beneficial for the cultivation and stability of the AGS. Ideal conditions for aerobic granulation were maintained in the SBR, such as alternating feast and famine conditions. A selection pressure, including a hydraulic shear force and settling time, was also created therein. The results showed that the AGS was formed successfully in both SBR1 and SBR2, the sludge volume index after 30 min (SVI30) and mean particle size reached 34.2 mL/g and 720 µm, and 36.7 mL/g and 610 µm, respectively, and a satisfactory nutrient removal capacity was achieved in the system. During the entire experimental period, the microbial community changed significantly; enrichment of microbes with the secretion of extracellular polymeric substances (EPS), granule stabilization functions in the AGS, and the differentiation of microbes corresponding to the function of each unit were observed. The use of Fe-C, application of SBRs, and use of dewatered sludge as an inoculant played key roles in the cultivation and stability of the AGS.

Functional graphene oxide membrane preparation for organics/inorganic salts mixture separation aiming at advanced treatment of refractory wastewater.

Some refractory organic matters or soluble microbial products remained in the effluents of refractory organic wastewater after biological secondary treatment and need an advanced treatment before final disposal. Graphene oxide (GO) was known to have potential to be the next generation membrane material. The functional organics/inorganic salts separation GO membrane preparation and application in wastewater advanced treatment could reduce energy or chemicals consumption and avoid organics/inorganic salts mixed concentrate waste problems after nanofiltration or reverse osmosis. In this study, we developed a novelty GO membrane aiming at advanced purification of organic matters in the secondary effluents of refractory organic wastewater and avoiding the organics/inorganic salts mixed concentrate waste problem. The influence of preparation conditions including pore size of support membrane, the number of GO layers and the applied pressure was investigated. It was found that for organics/inorganic salts mixture separation membrane preparation, the rejection and flux would achieve balance for the support membrane at a pore size of ~0.1µm and the number of GO layers of has an optimization value (~10 layers). A higher assemble pressure (~10bar) contributed to the acquisition of a higher rejection efficiency and lower roughness membrane. This as prepared GO membrane was applied to practical secondary effluent of a chemical synthesis pharmaceuticals wastewater. A good organic matter rejection efficiency (76%) and limited salt separation (<14%) was finally obtained. These results can promote the practical application of GO membrane and the resourcelized treatment of industrial wastewater.