Effect of cement-based composite pellets on phosphorus removal and microbial community structure in eutrophic water

Phosphorus (P) removal still faces challenges in eutrophic water treatment. Combining adsorption and biological reactions can efficiently reduce the P concentrations, achieving long-term function. In this study, five kinds of pellets were produced using cement, bentonite, and organic carbon (rice husk powder) with mass ratios of 100%:0%:0% (M1), 95%:5%:0% (M2), 92.5%:5%:2.5% (M3), 90%:5%:5% (M4), and 85%:5%:10% (M5) for phosphorus removal in eutrophic water. The static adsorption experiment revealed that both Langmuir and Freundlich models were suitable for describing the adsorption characteristics. The P-bonding energy (K-L) and adsorption capacity (K) followed the order of M1 < M2 < M3 < M4 < M5. The adsorption processes conformed to the Pseudo-second-order kinetic model. The adsorption capability of pellets decreased with increasing pH levels. The Cl-, NO3-, and SO42- showed negligible effects on adsorption, while CO32- reduced the adsorption amount. In the dynamic experiment, all the pellets have sustained P removal efficiency with the average removal rates of 58.54% (M1), 60.78% (M2), 63.97% (M3), 66.81% (M4), and 72.05% (M5). The presence of CaHPO42 H2O in pellets after P removal indicated phosphate precipitation and ion exchange. The attached microbes in pellets exhibited an increase in Proteobacteria abundance contributed to biological phosphorus removal and long-term effectiveness. Hence, this study introduces innovative cement-based pellets for phosphorus removal in eutrophic water, establishing a possibility for practical applications.