Contrasting Finished Water Stabilization Approaches at Two Full-Scale Indirect Potable Reuse Plants

Indirect potable reuse plants, such as those located in Southern California, Singapore, and Australia, often use reverse osmosis (RO) membranes as part of the treatment process for removal of many constituents, including trace organics, nutrients, and dissolved solids, including divalent ions and large fractions of monovalent ions. Rejection of some of these ions, including bicarbonate (HCO3−) and calcium (Ca2+), creates RO permeate with low pH and insufficient calcium that must be stabilized before distribution to avoid corrosion of downstream infrastructure. Chemicals, such as lime, are typically used for water stabilization; however, lime often increases finished water turbidity due to impurities, which can lead to numerous issues associated with solids deposition, including difficulty complying with water quality requirements established by the end user. This paper will compare and contrast stabilization approaches utilized at two full-scale indirect potable reuse (IPR) plants.