Pre-treatment of SWRO pilot plant for desalination using submerged MF membrane process: Trouble shooting and optimization

Abstract

The membrane pre-treatment process is a hot issue in SWRO (seawater reverse osmosis) desalination. However, fouling control is essential to operate the membrane pre-treatment process. If such control fails, the operation expenditure will be increased by the need to replace membranes or add more chemicals to clean foulants. The submerged membrane process could treat feed water of low quality, like a membrane bioreactor in sewage treatment. In this research, a pilot test was performed to develop a membrane pre-treatment system which could produce less fouling feed water with an RO system and be operated stably in spite of variations in the quality of seawater. A submerged type MF (micro filtration) membrane was tested for about two years in a pilot plant (200 m 3/day) as a pre-treatment process to SWRO desalination. A conventional pre-treatment process was installed to compare the performance with the membrane pre-treatment process using the same feed water from the open intake system. The membrane process was operated with 1) high flux condition, 2) low flux condition, 3) low flux condition with coagulation and 4) high flux condition with coagulation. The average turbidity of the submerged MF permeate was 0.07 NTU, while that of the conventional process was 0.23 NTU. The SDI value of the membrane process was consistently lower than that of the conventional process. The RO recovery of each pre-treatment process showed the same result. The RO system of the membrane pre-treatment showed a higher flux (11.03 LMH) than that of the conventional pre-treatment (8.27 LMH) when the operating pressure was the same (49 bar). There were several trouble-shooting events due to the growth of micro-organisms, foam generation, and membrane fouling, which were addressed by pre-chlorination, increased soak time after CEB, and coagulation optimization, respectively. This paper covers every aspect of the pre-treatment process from planning to operate the SWRO pilot plant.