Research Of Coagulation As Pretreatment For Microfiltration

The combination technology of Membrane and Coagulation/Sedimentation has been widely applied in reclaim water treatment. This research of coagulation as the pretreat process of Continuous Microfiltration (CMF) is based on analysis of a reclaimed water inflow quality, molecular weight distribution and UV254. Bench and 3m3/h pilot scale tests were developed. During the research, the effects of coagulation condition, such as coagulants, retention time, on coagulation and CMF combination process were fully discussed. The results have instructive significance for practice. The main conclusion is as following:Polyaluminium Chloride (PACl) had great removal of turbidity, Total Phosphor (TP) and COD, especially for giant module and hydrophobic matters, but it had poor ability for small module matters. The removal of Color, COD and TP increased as the dose of PACl increased. CMF could hardly screen giant molecule and hydrophobic matters but has removal for small molecule matters. The Transmembrane Pressure (TMP) increased rapidly, and poorly recovered after back wash when low coagulation doses were applied, while TMP increasing rates grown slower and had better recovery when high coagulation doses were applied. Rapid agitation speed was the dominant factor for turbidity removal; PACl dosages could greatly affect the TP removal; agitation speed had little influence for TP removal.Pre-chlorination coagulation and CMF system had better removal effect of color, turbidity, NH3-N, TP, and COD than single Coagulation-CMF system. Pre-chlorination improved color, NH3-N, TP, COD removal but could hardly affect turbidity removal; organic matters removal of all molecule weight ranges were increased, heterocyclic, polycyclic aromatic hydrocarbon, unsaturated organic compounds at molecule weight ranges different were removed by pre-chlorination. With the increased concentration of pre-chlorination, chlorine oxidation enhanced. Pre-chlorination had poor ability to remove the organic matters under 1kDa, TMP increased rapidly and badly recovered when low chlorine added, and TMP increase rate slowed down as chlorine concentration increased.