Optimization of Entrapping Conditions of Nitrifying Bacteria and Selection of Entrapping Agent

Sodium alginate and polyvinyl alcohol were selected as entrapping agents to immobilize nitrifying microbia. Through orthogonal tests, optimal conditions of entrapping nitrifying bacteria by the two agents were determined by ammonia nitrogen removal efficiency. The properties of the two immobilized microbial beads produced under their optimum embedding conditions were compared. Results indicate that the optimum embedding conditions of calcium alginate beads (briefly CA beads) were 10 ml of nitrifying bacteria, 4% of sodium alginate content, 3 mm in bead diameter and 24-hr crosslinking time. The optimum embedding conditions of polyvinyl alcohol beads (briefly PVA beads) were 10 ml of nitrifying bacteria, 10% of PVA content, 3 mm in bead diameter and 24-hr crosslinking time. Comprehensive comparisons on mechanical strength, stability, mass transfer property and ammonia nitrogen removal efficiency of the two immobilized microbial beads indicate that polyvinyl alcohol is a better embedding agent for nitrifying bacteria in wastewater treatment compared with sodium alginate.