Operational experience from hybrid RO system at SAFI wastewater re-use RO plant

Abstract

Operation of wastewater treatment plants can be very challenging due to the high fouling tendency of wastewater. Much knowledge has been gained over the past few years to guide design engineers on the optimum design for wastewater reverse osmosis (RO) plant. The implementation of this knowledge helps to improve the operation and performance of many wastewater plants. One such example is the SAFI (BESIX Group Company) plant in Ajman, UAE. Here, an microfiltration (MF) and RO plant was installed in 2010 to treat sewage effluent in order to supply high quality water for industrial and domestic reuse. The 6,800 m3/d plant treats secondary effluent with MF and RO. There are two RO trains designed to operate at 18.6 l/m2 h and 75% recovery, for treating municipal treated effluent with 2,000–4,000 mg/l of total dissolved solids (TDS). When operation started in 2010, the rate of fouling on RO membranes was extremely high, with up to 66% flow decline in 3 months of operation. This was eventually attributed to higher than design operation temperatures, lack of regular biocide disinfection, absence of flushing and cleaning system, and no flux balance between the RO stages. A detailed analysis was made of the fouled elements, and it was found that the primary issue was biofouling. This paper will review the actions that were taken to correct the fouling issue and stabilize the RO performance. One of the key factors, which ultimately resolved the problem was the membrane change, from single element type to two different types of membranes, on each RO stage to better balance the flux between RO stages. This and other changes have resulted in the plant now to achieve the production goals with stable operation.