| The huge production of industrial water and wastewater in China has resulted in an imbalance between the supply and demand of water resources and an increase in water pollution.In recent years,with the goal of near-zero or zero liquid discharge(ZLD),the dual-membrane method of "ultrafiltration-reverse osmosis"(UF-RO)combination has been increasingly recognized for the deep treatment and reuse of industrial wastewater.However,it is difficult to treat the reverse osmosis(RO)concentrated water produced by the dual-membrane method,which has become one of the key issues limiting the near-zero discharge of wastewater.Therefore,this paper combines the topic of "Research,Development and Demonstration of Key Technologies for Pollutant Reduction and Water Reuse in Chemical Industrial Parks with Near-Zero Discharge of Wastewater" funded by the 13th Five-Year National Key Research and Development Programme,and takes the reverse osmosis(RO)concentrated water generated in the process of regeneration of the wastewater from the ecological wetland of the Shanghai Chemical Industrial Zone as the research object,and explores the effect and mechanism of treating the RO concentrated water of chemical parks by electrochemical method and its coupling process through small and pilot experiments,with the aim of providing references for the treatment of the RO concentrated water.Firstly,the effectiveness of the flow-through electrode system for treating reverse osmosis concentrated water was examined.The results showed that the removal effect was influenced by the number of electrode groups,water inlet method,current density,water inlet flow rate,initial pH and electrode area-to-water ratio A/V.Under the conditions of 4 electrode groups,anode-cathode circulation water inlet method,current density of 28 mA/cm2,initial pH of 8,inlet flow rate of 12 mL/min and electrode areato-water ratio A/V of 40.2 m-1,the best effect was achieved for concentrated water after 120 min of treatment,with the removal rates of 92.2%,52.2%and 43.0%for COD,TOC and TN,respectively.The maximum kinetic constants for COD and TN removal were 0.02051 min-1 and 0.00071 L/(mg·min),respectively,and the lowest energy consumption for removing unit mass of COD was 1.1 kWh/gCOD.Secondly,the mechanism of the flow-through electrode system for the treatment of reverse osmosis concentrated water was explored.The results showed that in continuous flow mode,decreasing the electrode spacing,increasing the current density and decreasing the influent water flow rate would result in lower pH of anode effluent,higher pH of cathode effluent,more active chlorine produced,and the better the removal of COD and TN.The removal of pollutants is attributed to anodic oxidationcathodic reduction,the indirect oxidation of active chlorine has a contributing effect on the removal of COD and TN,and the increase in the number of electrode groups is conducive to the production of active chlorine.The organic matter in the reverse osmosis concentrated water was fluorescent,chain and ring compounds containing benzene rings and nitrogen atom hybridisation mainly,and the flow-through electrode system could effectively degrade 46 organic pollutants among them.Finally,the effectiveness of electrochemical methods to reduce pollutants in reverse osmosis concentrated water was verified on a pilot scale.Using individual electrochemical treatment of RO concentrated water,both increasing current intensity and decreasing influent flow rate were beneficial for COD and TN removal,and achieved 86.1%COD removal and 47.4%TN removal at 500 L/h influent flow rate and 800 A current intensity,with an average energy consumption of 13.43 kWh/ton of concentrated water.The ozone-biological effluent was further treated by electrochemical method,and the COD of the wastewater could be reduced from 84 mg/L to 13 mg/L under the optimal conditions,and the total COD removal reached more than 90%,with an electrochemical contribution of 44.7%;TN were all removed electrochemically,and the concentration was reduced to less than 15 mg/L.The combined process could remove five types of DOM in the reverse osmosis concentrated water and effectively degrade 49 characteristic organic pollutants therein.Electrochemical oxidation is more useful in organic matter removal,and the oxidation capacity is better than ozone.Calculation and analysis of the operational energy consumption and cost of the near-zero wastewater discharge process in the chemical park yielded that the energy consumption of the electrochemical process unit was 1.13 kWh/ton of wastewater,which accounted for 27.3%of the total;the total energy consumption of the process was 4.18 kWh/ton of wastewater,and the total treatment cost was less than 5 yuan/ton of wastewater;electrochemical process and combined processes have good treatment efficiency in treating reverse osmosis concentrated water. |
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