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

In this study, calcium peroxide (CaO 2 ) was added to two types of water to remove turbidity . The effects of CaO 2 on water quality, Ca content and microbial communities were also examined. The results showed that CaO 2 significantly improved the transparency of highly turbid water induced by algae. Compared with the control group, 5, 10, and 20 mg/L CaO 2 reduced the turbidity by 56.80%, 81.66%, and 82.54%, respectively. Considering the actual effect and cost, 10 mg/L CaO 2 was the recommended dosage. Furthermore, the addition of CaO 2 increased the degree of humification in the water and Ca content in the sediment. However, the addition of CaO 2 did not significantly increase the concentration of Ca 2+ in the water. Additionally, CaO 2 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 CaO 2 . At the genus level, Flavobacterium , Sphingomonas , Pseudomonas , and Limnohabitans , which occupied key nodes, were tolerant to CaO 2 , and CaO 2 had only a minor impact on the microbial ecological networks. Moreover, the eukaryotic rotifer community was destroyed. CaO 2 increased the abundance of chemotrophic heterotrophic functional groups but decreased that of the functional groups. These findings provide guidance for the use of CaO 2 to improve water turbidity and water ecological restoration.