Chemistry of alkaline and non-alkaline scaling in community RO for brackish water treatment operated with and without antiscalant doses

Abstract

About 3,500 small community based reverse osmosis (RO) plants have been installed in Rajasthan, India to comply with the recent Government of India guidelines for drinking water quality in rural areas. This paper presents the performance of four RO plants of Bharatpur, which face frequent replacement of membrane modules primarily due to accelerated scaling of carbonates and sulphates of calcium. A detailed chemical analysis of different streams from these plants was carried out to assess the reasons of scaling through a mass balance approach. The chemical analysis was substantiated through ion balance and the scaling potentials were analysed through different saturation indices. Efficacy of antiscalant usage plants was further assessed through mass balance approach followed by detailed characterization of the RO membrane to understand the complete fouling process, which brought out subtle differences in brackish and seawater desalination. The membranes adopting commonly used antiscalant showed an enhanced life span of 2–2.5 year by reducing calcium carbonate scaling but not calcium sulphate scaling. This study highlights the requirement of customized antiscalant application according to the feed characteristics. With a better understanding of the fouling phenomenon, this study would help enhance the life of membrane in RO plants treating brackish water.