Utilization of polyvinyl alcohol (PVA) with coal ASH to immobilize nitrifying bacteria for ammonia-nitrogen removal in shrimp culture wastewater recirculation system

Abstract

Immobilization of nitrifying bacteria using polyvinyl alcohol (PVA) and coal ash may be a effective methods to remove ammonia-nitrogen from recirculating aquacultural water. This could help improve water quality for shrimp culture and reduce capital and operating costs. The objective of this research was to investigate the effects of mixture ratio (%, PVA : coal ash) of 10.0%, 12.5%, and 15.0% (w/v) of pure PVA in combination with 3%, 5%, and 7% (w/v) of coal ash in gel beads, at hydraulic retention times (HRT) of 1, 2, and 4 hrs. A continuous nitrification bioreactor was fed with synthetic shrimp culture wastewater containing 2 mg/L ammonia-nitrogen for the determination of the removal efficiency under the optimum operating conditions of the mixture ratio and HRT. The results showed that the average NH3-N removal efficiencies were in the range of 76-96%. The average NH3-N removal efficiencies under different conditions were significantly different (p < 0.05). The NH3-N removal efficiencies were affected by the mixture ratios (%, PVA : coal ash) and hydraulic retention time (HRT). The average NH3-N removal efficiencies of the mixture ratio (%, PVA : coal ash): 10.0:3, 5, 7 were 87%, 94%, and 95% when operated at HRT 1, 2, and 4 hrs, respectively. But there were no significant differences related to the mixture ratio (%, PVA : coal ash) and HRT on chemical oxygen demand (COD) removal efficiencies (p < 0.05). The optimum operating conditions of the PVA-coal gel beads in synthetic shrimp culture wastewater was at the mixture ratio (%, PVA : coal ash) of 10.0:3, 5, 7 and HRT of 2 hrs., which yielded NH3-N and COD removal efficiencies of 93.64%, and 1.62%, respectively with an ammonia removal rate of 24.26 g/m3-day.The high removal efficiency and removal rate obtained in this research work indicates that coal ash could be mixed with PVA to immobilize nitrifier and the immobilized nitrifier technology has a high potential application for the removal of ammonia-nitrogen from recirculating aquaculture wastewater.