Effect of calcium silicate hydrates (CSH) on phosphorus immobilization and speciation in shallow lake sediment

Abstract

Phosphorus is considered as the main factor in fostering eutrophication. Calcium silicate hydrates (CSH) were studied for immobilization of phosphorus in shallow lake sediment. The impacts of CSH amendment on phosphorus release from sediment and phosphorus speciation in the sediment were investigated under different operating conditions including CSH dosage, contact time, and pH. The laboratory experimental results demonstrated that CSH could effectively inhibit phosphorus release from the sediment. The optimal CSH dosage was 50mg·g−1 for phosphorus immobilization in the sediment with total phosphorus of 470mg·kg−1. CSH was more effective for the immobilization of soluble reactive phosphorus than for total phosphorus. Water pH had significant effect on phosphorus immobilization in the sediment by CSH. CSH addition led to the increase of pH, in particular the conversion of ferric phosphate (Fe-P) to calcium phosphate (Ca-P). Fe-P is an active inorganic phosphorus species with a high release rate at high pH, while Ca-P is tightly adsorbed to the sediment. At CSH dosage of 100mg·g−1 the proportion of Fe-P decreased by 19%, and Ca-P increased by 20.5% in the sediment. CSH dosage of 50mg·g−1 led to a substantive increase of Ca-P proportion in sediment from 520mg·kg−1 to 781mg·kg−1 in 7days, thereby reducing the potential risk of phosphorus release from sediment. The practical application of using CSH to control phosphorus release from shallow lake sediment was discussed.