Water recycling using sequential membrane treatment in the electronics industry

Sony Display Device in Singapore (SDS) has taken the radical initiative of installing a water recycling system (WRS) that draws over half its feed Tom reclaimed municipal wastewater. Pretreated plant wastewater collected fi-om three fabrication processes is blended with filtered secondary sewage and processed through a dual membrane treatment system comprising Memcor continuous microfiltration (CMF) and reverse osmosis (RO). The resulting reclaimed water provides a process water feed for the factory that has lower TDS than potable water. The microfiltration system uses polypropylene hollow-fibre membranes to condition the water prior to RO. It achieves a silt density index (SDI) consistently less than 3.5 by removing particles greater than approximately 0.2 microns. The RO units employ cellulose acetate hollow-fibre membranes and reduce TDS to not greater than 100 mg/L. The WRS has operated successfully since July 1998. Its output of 2100m’ of reclaimed water per day is blended with Public Utilities Board (PUB) water and supplied to the demineralization plant and cooling tower. Total reclaimed water has reached 1,225,000m3 in the past 2 years, equivalent to 40% of SDS’s total water usage.

Prior to installing the WRS, SDS used some 4000 m3/d of potable PUB water. The WRS has operated successfully since July 1998. Its output of 2100 m3 of reclaimed water per day is blended with 1900 m3 of PUB water and supplied to the DI plant and cooling tower. Total reclaimed water has reached 1,225,OOOm3 during the past 2 years. In addition to reducing potable water consumption by 40%, WRS has obtained savings in demineralization chemical consumption for regeneration and is expected to achieve a satisfactory return based on projected PUB water price rises and government tax incentives for installation of wastewater recycling facilities.