Pretreatment of Petrochemical Secondary Effluent by Micro-flocculation and Dynasand Filtration: Performance and DOM Removal Characteristics

A pilot scale micro-flocculation and dynasand filtration process was used to pretreat the petrochemical secondary effluent. The suspended solids (SS) and the dissolved organic matter (DOM) removal characteristics were investigated. The results showed that the optimized poly aluminum ferric chloride (PFAC) dosage was 10 mg/L during the experiment. In this dosage period, the SS removal rate was as high as 50.58 % with the effluent SS of 15.38 mg/L when the influent SS was 33.53 mg/L. The COD removal rate was 10.42 %. The DOM fraction with large apparent molecular weight (MW) higher than 3 k was removed more significantly than that of small molecular DOM. Resin fractionation showed that the micro-flocculation and dynasand filtration process could preferentially remove the hydrophobic neutrals (HON) and hydrophobic acids (HOA) of DOM, so it could be suitable as the pretreatment unit. When oxidized by catalytic ozonation, the ozone consumption of COD removal for filtrated effluent was 1.2 g-O-3/g-COD while it was 1.6 g-O-3/g-COD for untreated petrochemical secondary effluent, saving 25 % of ozone consumption. The micro-flocculation and dynasand filtration is a suitable pretreatment process for petrochemical secondary effluent, especially when the subsequent unit is the catalytic ozonation process.