Aggregate Characteristics on Permeability of Microfiltration and Ultrafiltration in Pre-coagulation Membrane Filtration Hybrid Process

摘要

Effect of aggregates chareacteristics under different pre-coagulation pH and alum dose on microfiltration (MF) and ultrafiltration (UF) membrane permeability and removal efficiency of humic acids (Has) was studied. The water production rate of MF was far much higher than that of UF under all the same pre-coagulation conditions because of lower intrinsic resistance and higher initial flux of MF membrane compared to UF. Meanwhile, when pre-coagulation alum dose increased to 20mg/L and above, the Has removals were both enhanced to 95% from less than 5% of direct MF and 20% of direct UF respectively. Insufficient and excessive dose were both detrimental to filtrate for MF and UF membrane under different pre-coagulation mechanism. Under complexation-charge neutralization condition, more small particles were produced for high electrical repulsion by underdose and overdose to augment specific resistance of cake layer. The optimum cake permeability of two membranes was when aggregates formed near isoeletric point. Under sweep coagulation condition, low removal of Has and serious pore blocking occurred under insufficient alum dose, because some fine particles of comparable size to membrane pores were present in feed suspension and penetrate membrane pore without impeding by enough cake layer. However, hydrolysis Al(OH)3 precipitates as direct contaminant loading aggravated cake resistance when overdosed, in particular for MF.