Development of composite index for predicting membrane fouling potential in SWRO pretreatment

A model for water quality index is proposed. This index is based on the input quality variables such as concentration of turbidity, chlorophyll-a, ATP, absorbance at 260 nm and TOC. The index can be used for estimation of water quality before SWRO since the existing water quality metrics such as SDI and its derivatives do not provide reliable estimation for potential fouling. The impact of input variables was approximated by the second order function. The level of impact of input variables (such as concentration of chlorophyll-a; ATP; absorbance; TOC and turbidity) is characterized by weight factors. The target function – Z(X_j) was assumed to be proportional to the probability of membrane fouling that, in turn, proportional to SDI. The target function implies cumulative-composite structure. It includes imbedded sub-models f(X_j) for different fouling factors, X_1-X_5. The proposed model can be applied in different characteristic locations such as seawater intake, the points before and after pretreatment. The developed model can represent mathematical background for the software for monitoring and management of feed water quality in desalination. Individual weight factors and target function in real time can be used as a component in the early warning system.