Mitigation of Biological Fouling and control of SHMP Antiscalant agent for Brackish Water Reverse Osmosis Plants

Mohammed Saleh Al. Ansari

Department of Chemical Engineering, College of Engineering, University of Bahrain, PO box 32038, Sukhair Campus, Kingdom of Bahrain Tel: +973-3944-1110

Email: malansari@uob.edu.bh

Accepted 30 October 2012

Abstract

Sodium Hexametaphosphate (SHMP) is considered good antiscalant which is used to mitigate scaling in reverse osmosis membranes. The SHMP solution is made up in SHMP tank and dosed to the raw water via a point.  It was found that the SHMP tanks were the major source of biological infection and the results of the TBC values in the SHMP tanks were TNTC within 2 -days of make-up. SHMP is a polyphosphate whose degenerate into orthophosphate, is affected by factors of concentration, temperature, known nutrient for biological organisms to grow and colonize, a study on free phosphate in SHMP was carried out. Due to the presence of H₂S in the raw feed water, chlorine is not used even in trace levels. Hence, sodium metabisulfite (SBS) was used for sterilization of SHMP tanks and dosing lines. Extensive laboratory studies were conducted to determine the optimum dose concentration of SBS into SHMP tanks required to sterilize the solution but minimize the version to free phosphate. This paper discuss the addition of SBS in the SHMP tanks, its application and results to confirm the effectiveness of SHMP with SBS related to Micron Guard Filter (MGF) condition and R.O performance.

Keywords: SBS, SHMP, Reverse Osmosis; SHMP (sodium hexametaphosphate); RO (reverse osmosis); antiscalant