Research And Design Of Biological Treatment Of Coke Plant Wastewater

Components are complex in coke plant wastewater, in which contains high concentration of ammonia nitrogen and a number of toxic and refractory organic compounds and great changes usually happen to water quality and water flow. Most of the original treatment processes were conventional activated sludge method,through which the CODCr and ammonia nitrogen removal were not favorable and the effluent concentration couldn't attain the wastewater drainage level,which brought severe harm to our environment and human body.lt had been demonstrated that using anaerobic acidification as pretreatment anddenitrification-carbonization-nitrification as secondary biological treatment to remove ammonia nitrogen in coke plant wastewater was a cost effective technology.In this research, firstly, six efficiently predominant bacteria of degradating refractory organic compounds and nitrogen removalbacteria after they were cultured and domesticated and immobilized in certain condition, were thrown into carbonization, nitrification and denitrification reactor individually. Then biogradation pathway and biogradation process analysis and influence factors to biological nitrogen removal were investigated in individual reactor. Secondly, these predominant bacteria were used in compound nitrogen removal process of treatment of coke plant wastewater,meanwhile,nitrogen removal process and operating parameters were studied.Thirdly, the process A1-A2-O-M conditions and operating parameters were summarized as following:The total hydraulic retention time was 51 hours,among which 10.5h for anaerobicA1 stage,12.5h for anoxic A2 stage and 20h for aerobic O stage,8h for aerobic M stage.The pH value of the anaerobic reactor was maintained at 6.5 ~ 7.5.Recycled ratio of mixed liquid to the anoxic reactor influent was 3.5~ 5.0MeOH must be added to anoxic unit as an external carbon source in the denitrification process.The ratio of BOD; to TN was 10.6.In aerobic O stage.the temperature was maintained in 25~32'C and the pH value here should be maintained in the level of 7.7~8.2 by the addition of sodium bicarbonate and the remaining alkalinity in the effluent was 100~200mg/L and the dissolved oxygen(DO) was at 6.59~6.83mg/L.Less than 0.05kgCODCr/(kgMLSS-d) of CODcr loading rate and less than 0.01 kg NH4+ - N /(kgMLSS-d) of ammonianitrogen loading rate should be controlled in the feed of aerobic O stage.Given the above conditions,up to 87.7-93.9% of CODCr and up to 86.5~92.4% of ammonia nitrogen could be removed.The optimum technology A1-A2-O-M, which had been compared was chosed as the suitable process for the treatment of the coke plant wastewater. And then, the process was researched and designed accordance with an actual project. When the influent concentration of CODCr and ammonia nitrogen were less than 700mg/L and 300mg/L respectively, the average effluent concentration of CODCr and ammonia nitrogen was less than 100mg/L and 25mg/L each, the two indices of which had attained the primary and secondary national standard about wastewater discharge GB8978-1996 respectively.Lastly,the project buget and economic analysis were carried out for the after-researches.