In this study, a modified bipolar membrane electrodialysis system equipped with a "back-to-back" soil compartment was fabricated for simultaneous removal of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from contaminated soils. The results showed that the soil solution pH had a significant effect on the Cr(III) and Cr(VI) desorption, and the desorption data fit well with the Elovich kinetic model. Current density had an obvious effect on Cr(III) and Cr(VI) removal, cell voltage, soil pH, current efficiency, and specific energy consumption, and the optimal current density was 2.0 mA/cm 2 . The removal efficiencies of Cr(III) and Cr(VI) were both 99.8%, while Cr(III) and Cr(VI) recoveries were somewhat lower at 87 and 90%, respectively, because some Cr(III) and Cr(VI) were adsorbed by the membranes. An energy consumption analysis indicates that the back-to-back soil compartment equipped system increased the current efficiency and decreased the specific energy consumption. When a system equipped with two back-to-back soil compartments was used to remove chromium from soil, the current efficiency increased to 28.8% and the specific energy consumption decreased to 0.048 kWh/g. The experimental results indicate that the proposed process has the potential to be an effective technique for the treatment of soil contaminated with heavy metals.
For industrial wastewater with high chemical oxygen demand (COD) and nitrogen, traditional wastewater treatment processes fail to achieve stable removal of typical pollutants under the conditions of variable raw water quality and low energy consumption. In this study, a novel pre-and post-physicochemical synergistic oxic−hydrolytic and denitrification−hydrolytic and denitrification−oxic (P2PC-O/H/H/O) process with in situ sludge separation in respective bioreactors was developed, in which signature pollutants and TN were completely removed through an optimized allocation of energy and carbon source. The 180-day full-scale operation showed that optimal removal of COD and TN (with removal rates of 97.5 and 94.5%, respectively) can be obtained at influent loading rates of 1.5−1.7 kg COD (m 3 days) −1 and 0.11−0.13 kg TN (m 3 days) −1 . In this process, O1 reactor ensured organic matter removal and pre-nitrification. Double H (H1 and H2) reactors allowed deep removal of TN through combined and coupled denitrification pathways. O2 reactor consolidated the overall treatment performance through decarbonization and nitrification. By P2PC, the refractory and easily biodegradable total organic carbon (TOC) was separated, achieving a qualitative and fractional utilization of electron donors. Analysis of the microbial community in the whole process indicated that Nitrosomonas (0.7−2.4%) and Nitrospira (0.3−1.7%) played a major role in nitrification. Ottowia (15.4−19.6%) and Limnobacter (1.8−7.4%) dominated in eliminating organic matter. The P2PC-O/H/H/O process with a four-sludge regime enabled a spatial allocation of functional microorganisms. The operation cost of the full-scale process was approximately 1.335 USD m −3 . In short, this P2PC-O/H/H/O process, with high efficiency and stability in signature pollutant removal, will be a promising wastewater treatment technology to revolutionize the existing anaerobic− anoxic−oxic (A/A/O) process, adding a new dimension to industrial wastewater management.
The novel oxic-hydrolytic and denitrification-oxic (O/H/O) process has attracted intensive attention from the industry and academia and has been applied in coking wastewater treatment practice in recent years. However, there has yet been a mechanism model that can systematically guide the design and operation of the O/H/O process in optimization. In this study, a two-step nitrification−denitrification activated sludge model no. 3 for coking wastewater (TCW-ASM3) model was established. The addition of new components and processes enables TCW-ASM3 to accurately simulate the biological reaction processes in the O/ H/O system. The simulation results show that the increase in the step feeding ratio (R1) will lead to the increase in biological effluent chemical oxygen demand (COD) and total nitrogen (TN). To meet the TN effluent target (TN < 50 mg/L), R2 > 320% was needed. The energy consumption under this effluent constraint (COD < 200 mg/L, TN < 50 mg/L) was 4.873−5.752 kWh/m 3 . The foregoing results showed that the O/H/O process could be adjusted in different modes according to the pollutant characteristics and effluent targets. This study is the first report of the O/H/O process model, which is capable of providing strategies of multiple targets for the pollutant removal from industrial wastewaters with high toxicity and high C/N ratio.
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