Pilot Study Of Catalytic Ozonation-BAC For High Ammonia Nitrogen And Heavily Polluted Water Treatment

Serious source water pollution in China makes conventional drinking water treatment ineffective. More and more water plants have adopted advanced treatment processes, among which the most popular one is ozonation– biological activated carbon (BAC). However, poisonous and harmful trace refractory organics are found constantly. Removing such matters by ozone alone is limited so that catalysts are introduced into this system to improve removal efficiency. Further, different catalysts have various mechanisms. Therefore, three-stage catalytic ozonation process coupled with three kinds of catalysts is proposed to removal refractory organics and control bromated.In this study, aiming at river-net source water with high ammonia nitrogen and high organics in south China, 120m~3/d pilot study of three-stage catalytic ozonation process was proceeded for ten months. To research and select reasonable processes, water treatment units ahead could be switched or surpassed, which supplied three kinds of influent for advanced treatment. Result showed that effluent water qualities met the national standards all around the year by BAF, coagulation-precipitation, filter and three-stage catalytic ozonation-BAC processes treated. Even if water temperature was 5℃～8℃in winter, effluent oxygen consumption < 2.6mg/L, ammonia nitrogen < 0.5mg/L, UV254 < 0.03cm-1, Mn < 0.5mg/L, turbidity <0.2NTU, bromated < 5μg/L, THMsFP < 45μg/L.Meanwhile, influence of ozone stage and BAC stage was analysed, including temperature and water quality controlled by nature condition and a large munber of artificial controllable factors, such as ozone dosage, feeding methods, ozone contacting time, catalysts performance, EBCT, flow direction, carbon lay height and so on. It was suggested that less ozone dosage, one point feeding, shorter contacting time and no catalysts adding were benefit for ammonia nitrogen control; Comparing to zone feeding methods, contacting time and whether catalysts adding or not, oxygen consumption was more affected by ozone dosage, water temperature and aging of BAC; Effluent Mn was below 0.05mg/L and had nothing to do with feeding ozone or not; Catalysts could reduce bromate around 77% from 28.4μg/L to 6.5μg/L and improve removal of THMsFP in BAC stage around 30%.At last, considering the feasibility of engineering, the scope of operation parameters were set and water quality indexes were affected by them in different trends and degrees. Based on influence factors analysis for above water quality indexes, four novel system optimization methods were proposed, namely scoring method, vital index extraction, contribution rate statistics and classification, which were simple handle, easy understanding and had practical engineering value.