PRETREATMENT OF THE MUNICIPAL WASTE-WATER FEED FOR REVERSE-OSMOSIS PLANTS

Potable water can be produced at a reasonable cost if reverse osmosis (RO) technology can be applied to renovate secondary/tertiary wastewat er effluent. This implementation would yield many advantages to Kuwait , namely satisfying the increasingly agricultural, industrial and dome stic demands for good quality water free of viruses and bacteria, pres erving the natural strategic water resources, reducing environmental p ollution resulting from direct discharge of secondary/tertiary municip al effluents to the sea and meeting unexpected emergency cases of shor tages in fresh water production for certain applications. Membrane fou ling is the most important obstacle that has to be overcome for succes sful RO. Membrane fouling usually results in reduction of the permeate production rate, an increase in salt passage with time and/or membran e damage. Causes of fouling include scaling, plugging of membrane pore s by suspended matter, biological fouling and degradation of the membr ane itself. Membrane fouling is very much aggravated with the use of w astewater effluent as a feed for RO systems. The Kuwait institute for Scientific Research (KISR) is implementing a research project to desal inate tertiary treated wastewater using RO in Kuwait. This paper descr ibes the process of designing a proper pretreatment process capable of producing a substantial reduction in potential membrane foulants. Res ults obtained from laboratory and pilot studies revealed that fast mix ing, coagulation, flocculation and sedimentation using FeIII, cationic polyelectrolyte and a sanitizing agent can produce an acceptable qual ity of effluent feed for the RO process. This paper discusses the prog ress made in establishing proper pretreatment of this feed to meet the requirements of RO membrane manufacturers.