Applicability of a Reverse Osmosis (RO) Membrane to the Treatment of Wastewater Contaminated with Nitrite, Nitrate, Iron and Manganese

In recent times, the practice of reverse osmosis (RO) membrane technology has become a feasible alternative tool for the wastewater reclamation and reuse. In this research we investigated the applicability of a commercial polyamide RO element to the treatment of municipal sewage-based synthetic wastewater contaminated with nitrite, nitrate, iron, and manganese. The results showed that the RO element achieved the complete removal of BOD, COD, and total coliform. Besides, the ions rejection rates were 98% for iron, 97% for manganese, 93% for chloride, 80% for nitrite, 77% for nitrate, and 45% for ammonia, respectively. Although, dissolved matters in feed water did not cause any significant fouling, organic aggregates and inorganic particles like iron (Fe) colloids decreased the permeate flux of the membrane. The permeate flux of membranes fouled by organic aggregates was successfully recovered to 79% of the initial flux by backwashing from the concentrate port with sodium hydroxide (NaOH) solution at the concentration of 1,000 mg-NaOH/L. The efficiency of NaOH in permeate flux recovery was inferred to be owing to hydrolyzation and solubilization of organic matter by NaOH. On the contrary, the permeate flux fouled by Fe colloids was completely recovered, when backwashing with the deionized water was applied just after the fouling, which suggested that the membrane fouling by Fe colloids was mainly caused by the physical clogging in the membrane.