Comparison of flocculant aids as pretreatment reagent for membrane filtration process by fingerprint analysis of organic matters in secondary effluent

Abstract

Coagulation/flocculation is becoming a conventional and beneficial pretreatment for membrane filtration of wastewater, but how to choose coagulant/flocculant aid and optimal dosage is still a key issue in practice. Two cationic flocculant aids, polyacrylamide (PAM) and Kuriverter EP-301 (EP), were compared for the removal of organic matters from secondary effluents of municipal wastewater plant using FeCl3 as coagulant. EP achieved a better performance than PAM in terms of membrane filtration factor (MFF) and removal of suspended solids, turbidity and dissolved organic carbon. Optimal dosage for PAM was 30 mg Fe/L FeCl3 and 1 mg/L PAM, at which MFF was 2.13, while when 30 mg Fe/L FeCl3 and 1 mg/L EP was injected, MFF was 1.47. Optimal dosage for EP was 50 mg Fe/L FeCl3 and 2 mg/L EP, at which MFF was as low as 1.04. Fingerprint analysis method was first used to analyze the removal characteristics of dissolved organic matters fraction by PAM and EP flocculation. It was found that EP could remove more hydrophobic fractions (HO) than PAM. Moreover, EP could remove part of hydrophilic fractions (HI), while PAM had no effect on HI fractions. Hydrophobic acids (HOA) with MW > 5,000 Da were the major subfraction removed largely by coagulation/flocculation and EP could remove more of it than PAM. Larger MW (>107 Da) and three-dimensional molecular structure made EP more effective based on polymer bridging mechanism and charge neutralization.