Treatment Of Metal Cutting Evaporated Condensate By Iron-carbon Micro-electrolysis And Activated Sludge Combined Process

Evaporated condensate is derive from waste metal cutting fluid produced during the process of machining by removing oil through microfiltration membrane and evaporative condensation.It has the characteristics of high concentration of pollutants and poor biodegradability.The traditional advanced oxidation process such as Fenton process has high operation cost,while the combination of physicochemical method and biochemical method could not only satisfy the treatment effect but also give consideration to the cost efficiency of the method.In this study,the evaporated condensate was taken as the target wastewater,and the combined process of Fe-C micro-electrolysis and activated sludge treatment was proposed.The treatment effect of biochemical unit on wastewater,the optimization of combined process and continuous operation effect,the main principle of pollutant degradation by combined process were explored.It provides a technical plan and theoretical basis for the effective treatment of this kind of wastewater.The treatment effect of the biochemical unit on the wastewater was investigated and the operating parameters of Fe-C micro-electrolysis were determined at first.The results showed that the micro-electrolysis pretreatment could improve the biodegradability of evaporated condensate and could achieve higher treatment effect through sludge domestication.Fe-C micro-electrolysis achieved the highest degradation efficiency and biodegradability improvement of evaporative condensate with 30:1 gas-liquid ratio and 4 h reaction time.It was determined that the reaction of COD degradation by Fe-C micro-electrolysis followed the first-order reaction kinetics and the kinetic equation was estabilished.When the sludge domestication was completed,the COD and NH3-N removal rate of the system could reach more than 90%,and the sludge settling performance was good.Based on the above parameters,under the continuous operation,the combined process was optimized around the micro-electrolysis series,the internal reflux ratio and the stability of Fe-C filler treatment efficiency.The long-term operation effect of the combined process was investigated and economic and technical analysis was also carried out.The results showed that under three-stage micro-electrolysis series and 100%internal reflux ratio,the removal rate of organic matter by the combined process reached about 98%.Under this circumstance,the activation period of the micro-electrolysis filler was about 10 d,and the removal rate of COD by the activated micro-electrolysis filler could increased to more than 30%.The continuous operation of combined process showed that the removal rate of COD and ammonia nitrogen could maintained above 90%,the pH value of effluent was about 7.1,the Fe³⁺concentration was lower than 0.5 mg/L,and the sludge concentration was stable between 5000⁶000 mg/L during the later stage of operation with good sedimentation performance.The effluent quality index could meet the relevant requirements in"Water Pollutant Emission Limits of Gua ngdong Province"?DB44/26-2001?.After preliminary calculation,the operating cost of the combined process for treating evaporated condensate per ton was about 2.39 yuan when the daily amount was 100 m³/d.Finally,the principle of combined process for pollutant degradation was discussed.The results showed that micro-electrolysis could break the molecular structure of the main organic pollutants in the evaporated condensate,and gradually decompose into small molecules that are easily degraded.At the same time,some toxicity could also be reduced during the process,which reflects the improvement of biodegradability of wastewater by micro-electrolysis.The Fe³⁺produced by the micro-electrolysis pretreatment could promote the degradation of pollutants by the activated sludge system,and also improve the sludge settling performance and the sludge activity.