Zeta potential of commercial RO membranes: influence of source water type and chemistry

Streaming potential measurements have typically been performed on reverse o smosis (RO) and nanofiltration (NF) membranes using simple solution chemist ries that are representative of those found in natural waters and wastewate rs. In this investigation, streaming potential measurements were performed on RO membranes using actual membrane feed waters. Tertiary wastewater effl uents which serves as membrane feedwater at the Orange County Water Distric t (Fountain Valley, California) and river water from the Brazos River (Braz os, Texas) were used. Additionally, the effects of glutaraldehyde (a membra ne storage agent) and atrazine (a pesticide) on membrane surface charge wer e evaluated. The pesticide was evaluated in the presence and absence of hum ic acid. Results showed a more positive zeta potential in the presence of t he Brazos River water, most likely due to the presence of divalent cations (Ca2+ and Mg2+). For the tertiary wastewater effluent, adsorption of organi c acids in the wastewater effluent may have been the cause of the more nega tive zeta potential in,the low pH range and the presence of divalent cation s may have been the cause of the more positive zeta potential in the high p H range. The glutaraldehyde and atrazine showed little effect on the surfac e charge of the membranes. However, atrazine in the presence of humic acid showed a significant effect on the zeta potential, causing the membrane to have a less negative surface charge than in the presence of the humic acid alone.