Comparative Study on Performance and Organic Fouling of ZrO2 Ceramic Membranes in Ultrafiltration of Synthetic Water and Wastewater Treatment Plant Effluent

摘要

Adsorption of organic matter on ceramic membrane can lead to hydraulic-irreversiblefouling, which decreases the permeate flux and the cost-efficiency of membrane devices.In order to optimize the filtration process, detailed information is necessaryabout the organic fouling mechanisms on ceramic membranes. In this study, dead-end filtration experiments of both synthetic water and secondary effluent from a wastewatertreatment plant (WWTP) were conducted on a ZrO2 ceramic membrane.The experiment results of synthetic water showed that humic acid (HA) was ableto be adsorbed by the ZrO2 membrane and cause permeate flux decline; and thatHA-tryptophan mixture, at the same DOC level, promoted the filtration flux decline;DOC removal in the case of HA-tryptophan was lower than that of HA alone. Itseems that hydrophilic organic matter with low molecular weight have some specificcontribution to the organic fouling of the ZrO2 membrane. The results also suggestthat tryptophan molecules were preferentially adsorbed on the membrane at the beginning,exposing their hydrophobic sides which might further adsorb HA from the feed water. During the filtration of WWTP effluent, protein-like substances (mainlytryptophan-like) were also preferentially adsorbed on the membrane compared withhumic-like ones in the initial few cycles of filtration. More humic-like substances wereadsorbed in the following filtration cycles due to the increase of membrane hydrophobicity.A significant rise in hydraulic-irreversible flux decline was obtained by decreasingpH from near pHpzc to below pHpzc of the membrane. It suggests that a positivelycharged surface is preferred for HA adsorption. Ionic strength increase did not affectthe filtration of HA, but it lessened the hydraulic-irreversible flux decline of HA-tryptophan filtration. The adsorption of HA-tryptophan can be attributed to outersphere interaction while HA adsorption is mainly caused by inner-sphere interaction.The results of pre-ozonated HA filtration showed that pre-ozonation lowered theproportion of potential hydraulic-reversible foulants in HA. Filtration of pre-ozonatedWWTP effluent was also performed. Flux decline phenomenon similar to that of pre-ozonated HA was observed, and it is confirmed that smaller molecules have a strongeraffinity to ZrO2 membrane and tend to form hydraulic-irreversible fouling.