Porous floating Meretrix lusoria shell composite pellets immobilized with nitrate-reducing bacteria for treatment of phosphate and nitrate simultaneously from domestic wastewater

Removal of phosphate (PO43−) and nitrate (NO3−) from wastewater is essential to combat the major issue of eutrophication and other harmful associated threats. Hence, this study focused on designing feasibly applied adsorbents for efficient removal of PO43− and NO3−. A novel material, Porous Floating Meretrix lusoria Shell Composite (PFSC) pellet prepared from 75 to 85% soda lime silica, 6–16% dolomite and 4–14% M. lusoria F800 shell powder was able to float on water surface, which made it remarkable to apply, collect and reuse. PFSC pellets were found to effectively remove PO43−, and were used as the carriers for immobilization of various bacteria to develop Bacterial immobilized PFSC (Bac-immo-PFSC) pellets for NO3−removal from Domestic Wastewater (DWW). Highest NO3− removal was shown by immobilized PFSC pellets in the order of B. megaterium > P. aeruginosa > Pseudomonas sp. (Isolate 2) > Bacillus sp. (Isolate 4), respectively. Interestingly, the immobilization of PFSC pellets with mixed culture of B. megaterium and P. aeruginosa can remove 100% of NO3− alongwith removal of PO43−. Maximum adsorption capacity (Qmax) of PFSC pellets for PO43− and NO3− was 362 mg/g and 3.51 mg/g, respectively, whereas, among Bac-immo-PFSC pellets, Qmax of B. megaterium-immo-PFSC and P. aeruginosa-immo-PFSC pellets were 156 mgPO43−/g, 16.9 mgNO3−/g and 169 mgPO43−/g, 13.8 mgNO3−/g, respectively. This research identified higher expression of nitrous oxide reductase gene (nosZ) in case of B. megaterium, P. aeruginosafollowed by Isolate 2 and Isolate 4, respectively. Hence, the application of novel PFSC and Bac-immo-PFSC pellets can be easily applied for effective PO43− and NO3− removal and thus, can be easily collected and reused for wastewater treatment.