Microfiltration system as a pretreatment for RO units: Technical and economic assessment

Microfiltration (MF) seems to be a very attractive pretreatment technique that is increasingly being used in drinking water, seawater, and wastewater applications. Recently, it has been used as a pretreatment in reverse osmosis applications. This paper presents the results of a research project on the viability and the economics of MF as a pretreatment technique for a seawater reverse osmosis (SWRO) system. The overall performance of the MF unit indicates that the SDI of the surface seawater feed ranges between 0.26 and 3.10% with an average SDI value of 2.24. SDI of surface seawater feed is above 6.5%. Average filtrate flowrate is 3.20 m(3)/h. The optimal backwash interval is 10 min at variable feed flowrate. The MF unit is capable of reducing COD and BOD values and producing good quality water suitable as a feed for RO systems. The techno-economic study revealed that the total unit water costs produced by beachwell, MF and conventional surface pretreatment systems are 11.082, 12.264 and 28.153 fils/m(3),(dagger) respectively. It is clear that the beachwell system is the most cost-effective among the three available techniques for seawater pretreatment. If for some reason the beachwell system is not technically feasible, then the MF system is the next most cost-effective system for seawater pretreatment. It has the added advantage of better water quality.