Application of calcium peroxide for efficient treatment of surface water turbidity: Mechanisms and microbial community responses

In this study, calcium peroxide (CaO2) was added to two types of water to remove turbidity. The effects of CaO2 on water quality, Ca content and microbial communities were also examined. The results showed that CaO2 significantly improved the transparency of highly turbid water induced by algae. Compared with the control group, 5, 10, and 20 mg/L CaO2 reduced the turbidity by 56.80%, 81.66%, and 82.54%, respectively. Considering the actual effect and cost, 10 mg/L CaO2 was the recommended dosage. Furthermore, the addition of CaO2 increased the degree of humification in the water and Ca content in the sediment. However, the addition of CaO2 did not significantly increase the concentration of Ca2+ in the water. Additionally, CaO2 first decreased the richness and diversity of the bacterial and fungal communities. However, this effect gradually disappeared over time. The abundance of cyanobacteria decreased to 0 after 168 h. Actinobacteria and Compilobacteria were also inhibited by CaO2. At the genus level, Flavobacterium, Sphingomonas, Pseudomonas, and Limnohabitans, which occupied key nodes, were tolerant to CaO2, and CaO2 had only a minor impact on the microbial ecological networks. Moreover, the eukaryotic rotifer community was destroyed. CaO2 increased the abundance of chemotrophic heterotrophic functional groups but decreased that of the functional groups. These findings provide guidance for the use of CaO2 to improve water turbidity and water ecological restoration.