Water Treatment Ultrafiltration Theory And Technology Research

This paper mainly studied the characteristics of ultrafiltration for the removal ofbacteria, turbidity, and humic acid (HA). Experiments were also carried out to examine theeffects of turbidity and coagulation pretreatment on HA removal. The mechanism of UFseparation was analyzed, and the UF flux decline was preliminarily discussed.The results show that UF is efficient for the removal of bacteria and turbidity with the99% removal of bacteria achieved and residual turbidity within 0.02 NTU in the treatedwater; the UF resulting TOC and UV₂₅₄ removals of HA are 30% and 40%; there is noobvious difference of HA removals between the UF membrane with a MWCO of 10kdaltons and the other one with a MWCO of 1 kdaltons. Bacteria, turbidity and HA areremoved by the sieving mechanism of size exclusion which depends on the membraneMWCO. The decline of the membrane flux is mainly attributed to the cake layer formation,but the HA cake layer leads to much worse membrane flux decline than turbidity cake layerdoes.The presence of turbidity improves the UF removal of HA. the bigger the turbidity, thehigher the HA removal. But the membrane flux decline is aggravated due to the morecompact cake layer formation than HA alone.Aluminum coagulation pretreatment enhances the UF removal of HA and greatlyameliorates the effect of HA on the membrane flux decline. At pH=7.0 the mechanism isadsorption of HA on the amorphous solid-phase Al(OH)₃(s), while at pH=5.0 themechanism is charge-neutralization. In terms of the removal of HA (TOC, UV₂₅₄) and themembrane flux decline, the effect of coagulation under pH=7.0 condition turns out to be muchbetter than that under the condition of pH=5.0.The result of HPLC indicates that direct UF has low removal of small molecule HA,while coagulation pretreatment can enhance the removal of UF of small molecule HA whichattributes to the higher removal of HA.