Long-term performance and microbial mechanism in intertidal wetland sediment introduced constructed wetlands treating saline wastewater

Saline wastewater requires a clean and efficient treatment method to avoid frequent public health events and nonpoint source pollution. This study explored intertidal wetland sediment (IWS) as an inoculation source for long-term operation in saline constructed wetlands (CWs). Four CWs planted with Phragmites australis were set up. In two of them, IWS was introduced for saline wastewater treatment (150 mg/L NaCl) and salt-free treatment; and set other CWs as control groups. Nutrient removal rates, microbial community, and functional genus were detected in IWS-introduced CWs and control CWs over three years. The average removal rates of total phosphorus and chemical oxygen demand were 17.37% and 20.35% higher, respectively, in IWS-introduced CWs than in control CWs under a salty environment. No significant difference in NH4+-N removal was observed among all treatments (p > 0.05), and the removal rates in all treatments were above 90%. Results showed that IWSintroduced CWs achieved high levels of halophilic bacteria (Proteobacteria), denitrifying bacteria (Actinobacteria, Gammaproteobacteria), and anaerobic phosphate-accumulating organisms (PAOs) (Alphaproteobacteria, Anaerolineae) in the substrate. The bacterial community of the rhizosphere was dominated by "Pseudonocardiaceae," "Rhodobacteraceae," and "Rhizobiaceae" in the IWS-introduced CWs, known as COD-removing bacteria and aerobic PAOs. These bacteria chronically enhanced the pollutant removal performance, salt tolerance, and operational stability of CWs in three years. Overall, microbial augmentation through the IWS as an inoculation source in CWs is effective and has potential in long-term saline wastewater treatment.