[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.