Evaluation of an innovative polyvinyl chloride (PVC) ultrafiltration membrane for wastewater treatment

The use of ultrafiltration (UF) employing a polyvinyl chloride (PVC) membrane (LH3-1060-V) as pretreatment for a reverse osmosis (RO) system treating secondary water effluent at the Scottsdale Water Campus was investigated. Membrane fouling tendency was evaluated, foulants were characterized, and chemical cleaning was optimized. Feed and permeate water qualities were indexed to address the effect of UF as a pretreatment on the RO process, in view of RO design and scale calculations. The results showed that the pilot plant operated stably for 102 days with a chemical cleaning interval of 69 days. The transmembrane pressure (TMP) ranged from 35.44 to 71.15 kPa, and the normalized flux was 72 L/(m2 h) at 20 °C. The majority of the foulants were organic compounds (tannins, fulvic acids, humic acids, amino sugars, etc.) along with a few inorganic ones (iron, calcium, etc.). SEM–EDX mapping showed that most of the foulants deposited on the inner surface of the fiber. The best cleaning sequence for the fouled membrane was found to be 2% sodium hydroxide–0.5% citric acid, as 97% of the initial membrane flux was restored. The PVC-UF membrane efficiently removed turbidity, suspended solids and color, with removal efficiencies of 96.41%, 88.33%, and 50.00%, respectively. The UF pretreatment was found to enhance the RO average permeate flux and recovery by 34% and 21%, respectively, compared to the simulated conventional pretreatment system.