Performance of precipitation and electrocoagulation as pretreatment of silica removal in brackish water and seawater

Abstract Continuous increase in the world’s population is posing serious threat to the fresh water reserves all over the world. Seawater desalination processes have been proven to be one of the most promising processes to supplement the increasing demand for fresh water, due to the limitless nature of seawater. One of the biggest problems related to the membrane desalination process is the fouling and scaling of reverse osmosis (RO) membrane. Among all the foulants, silica is considered to be one of the most difficult inorganic foulant to deal with in membrane desalination due to its chemical complexity. This study compares some of the most commonly used pretreatment techniques of silica removal, analyses the characteristics of dissolved silica in both brackish water and seawater bodies, along with silt density index (SDI) tests. It was found that silicate salts are difficult to be dissolved in brackish water and seawater, and the fouling propensity of membrane is not a function of silica concentration (from 15–200 mg/L) in the feed water. Also, Al 3+ exhibited superior silica removal efficiency than Fe 3+ , and a removal efficiency of 90.2% was reported when using electrocoagulation on brackish water where the silica concentration was around 28 mg/L.