Electrochemical oxidation has been demonstrated to be a useful method for removing biorefractory organic pollutants in mature landfill leachate but suffers from low efficiency in eliminating ammonium because of its resistance to being oxidized by HO• or free chlorine (FC) at decreased pH. Here, we propose a new bipolar membrane-electrochlorination (BPM-EC) process to address this issue. We found that the BPM-EC system was significantly superior to both the undivided and divided reactors with monopolar membranes in terms of elevated rate of ammonium removal, attenuated generation of byproducts (e.g., nitrate and chloramines), increased Faradaic efficiency, and decreased energy consumption. Mechanistic studies revealed that the integration of BPM was helpful in creating alkaline environments in the vicinity of the anode, which facilitated production of surface-bound HO• and FC and eventually promoted in situ generation of ClO•, a crucial reactive species mainly responsible for accelerating ammonium oxidation and selective transformation to nitrogen. The efficacy of BPM-EC in treating landfill leachates with different ammonium concentrations was verified under batch and continuous-flow conditions. A kinetic model that incorporates the key parameters was developed, which can successfully predict the optimal number of BPM-EC reactors (e.g., 2 and 5 for leachates containing 589.4 ± 5.5 and 1258.1 ± 9.6 mg L–1 NH4+-N, respectively) necessary for complete removal of ammonium. These findings reveal that the BPM-EC process shows promise in treating ammonium-containing wastewater, with advantages that include effectiveness, adaptability, and flexibility.
A novel Mg-loaded chitosan carbonized microsphere (MCCM) was prepared for simultaneous adsorption of ammonium and phosphate in this study, through the investigation of preparation procedures, addition ratio, and preparation temperature. Pollutants removals by MCCM were more acceptable with 64.71% for ammonium and 99.26% for phosphorus, compared with chitosan carbonized microspheres (CCM), Mg-loaded chitosan hydrogel beads (MCH) and MgCl 2 ·6H 2 O. Addition ratio of 0.6:1 (m chitosan : m MgCl2 ) and preparation temperature of 400 °C in MCCM preparation were responsible for pollutant removal and yield. The effect analysis of MCCM dosage, solution pH, pollutant concentration , adsorption mode and coexisting ions on the removal for both ammonium and phosphate indicated that pollutants removals were increased with increasing MCCM dosages, and achieved the peak at pH 8.5, but presented to be stable with Na + , K + , Ca 2+ , Cl − , NO 3 − , CO 3 2− and SO 4 2− , except for Fe 3+ .Adsorption mechanisms discussion implied that simultaneous ammonium and phosphate removal with MCCM was attributed to struvite precipitation, ion exchange, hydrogen bonding, electrostatic attraction and Mg–P complexation, suggesting that MCCM presents a new way for simultaneous concentrated ammonium and phosphate removal in wastewater treatment .
Yuqing Zhang,Junrong Li,Lili Si,Mingming Gao,Shuguang Wang,Xinhua Wang
Antibiotic shock may potentially impact the performance of promising microalgae-nitrifying bacteria consortia (MNBC) processes. This study investigated physiological behaviors of MNBC under sulfamethoxazole (SMX) shock (mg/L level) and verified a light regulating strategy for improving process performance. Results showed that SMX shock did not affect ammonium removal but caused nitrite accumulation, resulting from combined effects of excessive reactive oxidative species (ROS) production, inhibited microalgal photosynthetic activity, upregulated expressions of amoA and hao , and downregulated expression of nxrA . Moreover, high ammonium concentration aggravated nitrite accumulation and reduced ammonium removal owing to significantly reduced dissolved oxygen (DO). Increasing light intensity enhanced microalgal photo-oxygenation and promoted expressions of all nitrification-related genes, thus improving ammonium removal and alleviating nitrite accumulation. A central composite design coupled with response surface methodology (CCD-RSM) further demonstrated the negative impacts of SMX shock and high ammonium on MNBC and the effectiveness of the light regulation in maintaining stable process performance. This study provides theoretical basis for physiological responses and regulatory strategy of the MNBC process facing short-term antibiotic shock.
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