Production of boiler feed water out of wastewater with micro-filtration and reverse osmosis: The new age challenge within reach

DOW Benelux is planning a new Boiler Feedwater (BFW) plant to replace the old one by the year 2000. The new plant will be designed for a maximum capacity of 750 m super(3)/h, and will produce more than 5 million m super(3) boiler feedwater annually. Sources for the production are either industrial water as supplied by the local water company Delta Nutsbedrijven, brackish water from the river Scheldt, or local available sweet wastewater. Delta Nutsbedrijven in cooperation with Grontmij and Camp Dresser & McKee worked out a plan based on the optimal use of available sweet (waste) water sources, which turned out to be the most economic solution. These sources comprise the wastewater as processed on the DOW site and the wastewater from the nearby communal wastewater treatment of the city Terneuzen. Following successful experiences abroad the process that was chosen included MEMCOR microfiltration followed by reverse osmosis, using DOW Filmtec membranes. The process has been tested in a 5 m super(3)/h pilot plant on communal wastewater for more than a year now and shows excellent results. Special emphasis was laid on the strategy to control bio-fouling as the wastewater contains high amounts of biodegradable organic matter and nutrients. The strategy that was opted for comprised: Proper design of the MF/RO (fluxes, recovery, pressure and type of installation); MEMCOR microfiltration with air back-wash as a proven pre-treatment for RO; Chemical addition to control bio-growth The objectives of the pilot test were: Prove the feasibility of the proposed scheme for re-use of wastewater; Establish definite design figures for the new BFW-plant. The paper will present the set-up of the pilot program and the results that were obtained, as well as their relation with the design and associated costs for boiler feedwater production. The results obtained will be presented against the background of experiences abroad.