Effect of hyperosmotic stress on reverse osmosis biofouling

• Main Author: Lee, Choon Kail
• Other Authors: Chong Tzyy Haur
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/71444
• Institution: Nanyang Technological University

Biofouling is an inevitable process in seawater reverse osmosis (SWRO), which adversely affects the membrane performance. Cleaning-in-place (CIP) method is commonly conducted to combat this issue. However, this may result in process downtime, membrane degradation, increased operation costs, and environmental contamination due to CIP chemicals disposal. As a more efficient and chemical-free alternative to conventional cleaning method, the engineered application of osmotic backwash by injecting a high salinity (HS) solution into the feed stream has been developing. Many past studies concentrate primarily on the physical cleaning mechanism of the osmotic backwash in removing biofilm, but not on how the hyperosmotic stress induced by the HS solution chemically alters the bacterial biofilm, leading to the detachment. Hence, this report aims to find out the optimal operating conditions for HS treatment in terms of HS treatment duration and salt concentration. Sodium chloride (NaCl) solution of 0.6 M with mix-culture bacteria (Bacillus sp. and Vibrio sp.) was used as model feed water to simulate the natural seawater. By varying the duration of HS treatment, the flux recovery was assessed as the parameter of cleaning efficiency. The biofilm compositions after cleaning were examined with a range of characterization analysis regarding the total cell numbers, cell viability, and extracellular polymeric substances (EPS) contents. The results demonstrated that 1 hour treatment using 2.4 M NaCl reduced the biofilm the most, generating the highest flux recovery. The theoretical explanation of detachment mechanism in a biochemical way was hypothesized to support the findings.