Fabrication and Performance Evaluation of a Cation Exchange Membrane Using Graphene Oxide/Polyethersulfone Composite Nanofibers.

Ion exchange membranes, especially cation exchange membranes (CEMs), are an important component in membrane-based energy generation and storage because of their ability to transport cations via the electrochemical potential gradient while preventing electron transport. However, developing a CEM with low areal resistance, high permselectivity, and stability remains difficult. In this study, electrospun graphene oxide/polyethersulfone (GO/PES) composite nanofibers were prepared with varying concentrations of GO. To fabricate a CEM, the pores of the electrospun GO/PES nanofiber substrates were filled with a Nafion ionomer. The pore-filled PES nanofiber loaded with 1% GO revealed a noticeable improvement in hydrophilicity, structural morphology, and mechanical properties. The 1% GO/PES pore-filled CEM was compared to a Nafion membrane of a varying thickness and without a nanofiber substrate. The CEM with a nanofiber substrate showed permselectivity of 85.75%, toughness of 111 J/m3, and areal resistance of 3.7 Ω cm2, which were 12.8%, 4.3 times, and 4.0 times better, respectively, than those of the Nafion membrane at the same thickness. The development of a reinforced concrete-like GO/PES nanofiber structure containing stretchable ionomer-enhanced membrane surfaces exhibited suitable areal resistance and reduced the thickness of the composite membrane without compromising the mechanical strength, suggesting its potential application as a cation exchange membrane in electrochemical membrane-based systems.

Evaluation of Efficiently Removing Secondary Effluent Organic Matters (EfOM) by Al-Based Coagulant for Wastewater Recycling: A Case Study with an Industrial-Scale Food-Processing Wastewater Treatment Plant.

The reuse of wastewater has been identified as an important initiative for the sustainable development of the environment; thus, the removal of secondary effluent organic matter (EfOM) to ensure the safety of reused wastewater is the key step and a subject of extensive research. In this study, Al2(SO4)3 and anionic polyacrylamide were selected as coagulant and flocculant, respectively, for the treatment of secondary effluent from a food-processing industry wastewater treatment plant to meet the standard regulatory specifications for water reuse. In this process, the removal efficiencies of chemical oxygen demand (COD), components with UV254, and specific ultraviolet absorbance (SUVA) were 44.61%, 25.13%, and 9.13%, respectively, with an associated reduction in chroma and turbidity. The fluorescence intensities (Fmax) of two humic-like components were reduced during coagulation, and microbial humic-like components of EfOM had a better removal efficiency because of a higher Log Km value of 4.12. Fourier transform infrared spectroscopy showed that Al2(SO4)3 could remove the protein fraction of the soluble microbial products (SMP) of EfOM by forming a loose SMP protein complex with enhanced hydrophobicity. Furthermore, flocculation reduced the aromaticity of secondary effluent. The cost of the proposed secondary effluent treatment was 0.034 CNY t-1 %COD-1. These results demonstrate that the process is efficient and economically viable for EfOM removal to realize food-processing wastewater reuse.

Insights into the minimization of excess sludge production in micro-aerobic reactors coupled with a membrane bioreactor: Characteristics of extracellular polymeric substances.

The production of excess sludge by the activated sludge system of wastewater treatment plants is a problem. In this study, the EPS characteristics on production and degradation were investigated in the real-scale food processing wastewater treatment system (i.e., a micro-aerobic reactor coupled with a membrane bioreactor (MAR-MBR)) with a treatment capacity of 150 t d-1, which could cater for the low production of excess sludge (i.e., 9 t·a-1; 76% moisture content). The total organic carbon concentrations in the different EPS fractions were in the following order: soluble EPS (S-EPS) < loosely bound EPS (LB-EPS) < tightly bound EPS (TB-EPS). Although the components (e.g., protein and humic acid-like substances) of each EPS fraction changed significantly throughout the MAR-MBR process owing to the low production of excess sludge, the degrees of change in S-EPS, LB-EPS, and TB-EPS were significantly different from the corresponding change in their relative molecular weights. Furthermore, the microbial community composition was beneficial for the release and degradation of EPS, and the regulation of gene functions via the MAR-MBR enhanced this process.

Modified bentonite as a conditioning agent for stabilising heavy metals and retaining nutrients in sewage sludge for agricultural uses.

The management and disposal of excess sludge are emerging issues owing to the high costs associated with treatment. In this study, the viability of a modified bentonite was investigated as a conditioning agent for the stabilisation of heavy metals (i.e., Cu, Zn, Cr, Pb, and Cd) and the retention of nutrient species (i.e., total nitrogen (TN), total phosphorus (TP), available nitrogen (available N), and Olsen-phosphorus (Olsen-P)) in sewage sludge for agricultural use. Five grams of modified bentonite resulted in the highest stabilisation rate of heavy metals and strongly contributed to the stabilisation of heavy metals. However, increased amounts of modified bentonite might increase the TN, available N, and TP losses in the conditioned sewage sludge. Through the analytic hierarchy process modelling, optimal concentrations of nutrient species and heavy metals remaining in the conditioned sewage sludge were achieved when the ratio of bentonite to sewage sludge was 1:12.5 (4 g bentonite : 50 g sludge). Moreover, the optimal mixing ratio of the conditioned sewage sludge to the soil (1:2) was suggested for agricultural use. Based on these observations, modified bentonite allowed the sewage sludge to be used as a fertiliser in agriculture by stabilising heavy metals and retaining nutrient species.

Contributions of enhanced endogenous microbial metabolism via inoculation with a novel microbial consortium into an anoxic side-stream reactor to in-situ sludge reduction for landfill leachate treatment.

In-situ sludge reduction plays a significant role in reducing excess sludge production. This study investigated the role of beneficial microorganisms (BM) in the anoxic-oxic-settling-anoxic (A-OSA) process associated with the in-situ sludge reduction efficiency under synthetic landfill leachate treatment. The rates of excess sludge reduction with the inoculation of BM increased up to 53.6% (calculated as total suspended solids) and 38.3% (calculated as total volume), respectively. Side-stream reactors, as important components of the A-OSA process, were further studied to explore change of parameters related to in-situ sludge reduction. With the inoculation of BM, the release and conversion of extracellular polymeric substances and the dehydrogenase activity (increasing rate = 60.9%) were increased. Species richness and microbial diversity, as well as the microbial community composition (e.g., hydrolytic and fermentative bacteria), were improved via bioaugmentation. Moreover, potential gene functions of microorganisms were positively regulated and the abundance of gene expressions (e.g., nirK, norB) for in-situ sludge reduction could be improved.

Evaluation of foam-glass media in a high-rate filtration process for the removal of particulate matter containing phosphorus in municipal wastewater.

Foam-glass as an effective filter media in a high-rate filtration process was evaluated for the removal of particulate matter containing phosphorus in municipal wastewater. The foam-glass with a low sphericity exhibited a higher porosity (60.2%) and a lower apparent specific gravity (0.50 g/cm3) compared with a conventional sand media (35.1% and 1.19 g/cm3). In particular, the high porosity of the foam-glass increased its surface area for capturing particles with coagulation, leading to a significantly decreasing head loss in the filtration bed column, resulting in a significantly longer filtration duration (more than 2 times) and a slightly higher removal of contaminants (approximately 4.8% for a suspended solid and 2% for the total phosphorus). Additionally, while backwashing of the conventional sand media required about 30% of the bed volume, the low specific gravity of the foam-glass media could be expanded to 100% of the volume due to its lower energy demand. Based on these advantages, it is expected that the foam-glass media will have a vital role as an alternative media in high-rate filtration processes.

Combined use of polymeric ferric sulfate and chitosan as a conditioning aid for enhanced digested sludge dewatering.

In this study, the effects of polymeric ferric sulfate (PFS) and chitosan (CTS) on the dewatering characteristics of the digested activated sludge (e.g. filtrate turbidity, specific resistance of filtration (SRF), and cake moisture content) were investigated. The combined conditioning of PFS and CTS improved the settleability of the digested sludge more effectively than when using of PFS alone. The SRF value of the digested sludge decreased to 2.08 × 1012 m/kg after conditioning with 50 mg/g PFS and 10 mg/g CTS. Furthermore, a minimum moisture content of 68% was obtained when 40 mg/g PFS and 10 mg/g CTS were used to condition the digested sludge. At a fixed dose of PFS, the concentrations of extracellular polymeric substances, including polysaccharides (C/C0 = 2.1), proteins (C/C0 = 2.7), and deoxyribonucleic acids (C/C0 = 7.8) in the supernatant were increased considerably with an increase in CTS dose (0-10 mg/g). Phosphorus could be recovered efficiently as a result of charge neutralization and the adsorption-bridging effects of CTS, which promote the release of phosphorus from the digested activated sludge. The concentrations of heavy metals in the digested sludge conditioned with 40 mg/g PFS and 10 mg/g CTS satisfied the agricultural safety requirements. These results indicate that conditioning the digested sludge with combinations of PFS and CTS improves its dewatering performance and enables its direct use as a fertilizer.

Non-selective rapid electro-oxidation of persistent, refractory VOCs in industrial wastewater using a highly catalytic and dimensionally stable IrPd/Ti composite electrode.

Volatile organic compounds (VOCs) are highly toxic contaminants commonly dissolved in industrial wastewater. Therefore, treatment of VOC-containing wastewater requires a robust and rapid reaction because liquid VOCs can become volatile secondary pollutants. In this study, electro-oxidation with catalytic composite dimensionally stable anodes (DSAs)-a promising process for degrading organic pollutants-was applied to remove various VOCs (chloroform, benzene, toluene, and trichloroethylene). Excellent treatment efficiency of VOCs was demonstrated. To evaluate the VOC removal rate of each DSA, a titanium plate, a frequently used substratum, was coated with four different highly electrocatalytic composite materials (platinum group metals), Ir, IrPt, IrRu, and IrPd. Ir was used as a base catalyst to maintain the electrochemical stability of the anode. Current density and electrolyte concentration were evaluated over various ranges (20-45 mA/cm2 and 0.01-0.15 mol/L as NaCl, respectively) to determine the optimum operating condition. Results indicated that chloroform was the most refractory VOC tested due to its robust chemical bond strength. Moreover, the optimum current density and electrolyte concentration were 25 mA/cm2 and 0.05 M, respectively, representing the most cost-effective condition. Four DSAs were examined (Ir/Ti, IrPt/Ti, IrRu/Ti, and IrPd/Ti). The IrPd/Ti anode was the most suitable for treatment of VOCs presenting the highest chloroform removal performance of 78.8%, energy consumption of 0.38 kWh per unit mass (g) of oxidized chloroform, and the least volatilized fraction of 4.4%. IrPd/Ti was the most suitable anode material for VOC treatment because of its unique structure, high wettability, and high surface area.