| As the water resources become scarce, wastewater recycling is becoming more and more urgent. The main problem is that salts and recalcitrant organic pollutants need to be effectively removed and mineralized, respectively. Now various technologies have been developed to deal with the wastewater containing salts and organics. However, the technologies used for salt removal can only concentrate the organics instead of mineralization, thus resulting in secondary pollution, while the technologies intended for organics mineralization can not effectively remove the salts. In this paper, we firstly investigated the desalination performance of capacitive deionization (CDI) using ordered mesoporous carbon (OMC) electrodes, and studied the organics degradation performance of heterogeneous Fenton reaction using OMC supported catalysts, then we tried to remove salt and mineralize organics simultaneously by combining CDI and electrochemical oxidation using carbon electrodes. The main conclusions were as follows.(1) OMC was prepared by the evaporation-induced triconstituent co-assembly method, using triblock copolymer F127, resol phenolic resin and tetraethoxysilane (TEOS) as raw material. The effect of preparation conditions such as stirring time, HCl concentration, the ratio of TEOS/resol/F127 and ethanol evaporation temperature was studied in terms of OMC surface area and pore size. It showed that HCl concentration played an important role. The optimized stirring time was no more than 8 h, HCl concentration was 0.2 mol/L, ethanol evaporation temperature was 60℃ and TEOS/resol/F127 (mass ratio) was 2.08: 0.5:1.0.(2) OMC was studied as electrodes for CDI in comparison with a commercial activated carbon (AC) and self-prepared activated carbon hollow fiber (ACHF). The electrosorption isotherm was fitted by Langmuir or Freundlich equation, with the maximum electrosorptive capacity of OMC determined as 10.1 mg/g, and rate constant was 0.085 min-1 fitted by pseudo-first-order kinetics. The main advantage of OMC vs AC or ACHF was that the adsorption and desorption rate were faster. Furthermore, the influence of working conditions and OMC characteristics on desalination performance was investigated. The results showed that the applied voltage and flow rate exhibited an optimum value, and a too-high or too-low value was not favorable towards desalination. Electrode with thinner thickness was better. The surface properties are important for initial desalination. However, these groups had a negligible effect on the long-term desalination stability. Besides, large surface area and pore diameter were more favorable towards long-term stability.(3) The desalination behavior of membrane capacitive deionization (MCDI) and asymmetric capacitive deionization units was investigated. The results showed that the MCDI unit displayed a large desalination capacity up to 25 mg/g which were 2.5-3 times of CDI unit. Current efficiency of MCDI unit was more than 100%. The performance of MCDI unit remained almost unchanged during 50 charge/discharge cycles, while the capacity decreased by 50% in CDI unit. The asymmetric capacitive deionization unit which used unmodified ACHF as anode and ACHF modified by H2O2 or HNO3 as cathode displayed better specific capacity and current efficiency than symmetric capacitive deionization, which used unmodified ACHF as both electrodes.(4) The heterogeneous Fenton reaction using OMC or AC supported iron catalysts was investigated for 4-chlorophenol degradation. The results showed that mesopore wasmore favorable to iron oxide dispersion than micropore. At the optimized working conditions (Fe/OMC catalyst calcination temperature of 300℃, pH of 3, H2O2 of 6.6 mmol/L, reaction temperature of 30℃),96% of 4-chlorophenol and 47% of TOC would be degraded after 270 min of reaction time. Fe/OMC catalyst could be recycled for several times. Hydroxyl radical was mainly produced by the reaction of H2O2 with iron ion leached from the solid catalyst. OMC supported bimetallic iron and copper catalyst showed better catalytic ability than monometallic catalyst. However, the metal leaching was worse.(5) A new technology for simultaneous desalination and mineralization of biorefractory organic pollutants was developed. The mechanism of salts and organics removal was carefully studied, and the electrode reusability was also examined. At the optimized conditions (NaCl of 1000 mg/L, phenol of 100 mg/L, reaction temperature of 40℃, applied potential of 2.0 V, O2 flow rate of 500 mL/min), the specific desalination ability reached 40 mg/g, phenol and TOC removal efficiency reached 91% and 65%, respectively after 300 min of reaction time. The specific energy consumption of TOC and NaCl removal was 89 kWh/(kg TOC) and 4.2 kWh/(kg NaCl), respectively, i.e. the process can simultaneously remove 0.011 kg TOC and 0.24 kg NaCl per consumption of 1 kWh power. The removal of phenol was attributed to physical adsorption, electrochemical direct oxidation and chlorine-mediated oxidation, and the salt removal was because of electrosorption. The electrode stability was maintained by polarity reversal.The technology is a promising low-cost method for simultaneous desalination and mineralization of low-concentration biorefractory organics which may be applied in wastewater tertiary treatment and reclamation. |
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