Effect of Calcium Peroxide Composite Tablets on Water Remediation and Phosphorus Control in Sediment

Two types of calcium peroxide composite tablets (CPCTs) were prepared, and the inhibition effect on the release of endogenous phosphorus and the influence on the overlying water by mixed-dosing were investigated. The CPCTs were made of calcium peroxide (CaO2), calcined water purification sludge, and hydroxypropyl methylcellulose (HPMC), which were directly pressed into composite tablets, among which Tablet-B (T-B) contained ferrous sulfate (FeSO4) and Tablet-A (T-A) did not. Both the tablets agreed well with the Langmuir and Freundlich isothermal models; the theoretical maximum adsorption capacities of T-A and T-B on phosphorus were 110.908 mg·g-1 and 106.390 mg·g-1, respectively. Compared with the control group, the pH of overlying water was increased, the concentration of Chl-a was decreased by 42.75% and 60.82%, and the DO was increased by 53.73% and 63.30% in group A and B, respectively. The DIP of the overlying water decreased significantly by 54.93% and 25.11% in group A and B, respectively. For the interstitial water in sediment, the DIP in layer Ⅰ (0-2 cm) decreased significantly by 74.81% and 65.66% in group A and B, and the DIP in layer Ⅱ (2-4 cm) decreased significantly by 46.23% in group B, but not obviously in group A. The DIP in layer Ⅲ (4-6 cm) remained unchanged in group A and B. For phosphorus fractions in sediment, the proportion of NH4Cl-P in TP was significantly increased (layer Ⅰ: 16.87% and 13.11%; layer Ⅱ: 12.99% and 11.02%, in group A and B, respectively), and the proportion of Al-P in TP was significantly decreased (layer Ⅰ: 7.58% and 13.91%; layerⅡ: 9.86% and 7.28%, in group A and B, respectively). The other phosphorus fractions did not change significantly. Both T-A and T-B dosing can improve the microbial activity of the surface sediment, though T-A can improve the microbial activity more significantly.