The immobilized Alcaligenes faecalis strain WT14 for removing high strength nitrate and reducing nitrite accumulation

Microbial immobilization is considered as one of the effective denitrification techniques in the treatment of high load wastewater. In this study, the immobilized cells consisting of polyvinyl alcohol (PVA), sodium alginate (SA), and calcium chloride (CaCl₂) were inoculated with Alcaligenes faecalis strain WT14 to treat wastewater with high nitrate-nitrogen ($$-N) concentrations. After 48 h of wastewater treatment, 26.2-89.4% of total nitrogen (TN) was removed by the immobilized Alcaligenes faecalis strain WT14. The response surface methodology revealed the highest TN removal efficiency by Alcaligenes faecalis strain WT14 occurred at the immobilized ratio of 9.3% of PVA, 2.2% of SA and 1.9% of CaCl₂. Under the optimal ratio of PVA, SA, and CaCl₂, the conditions for the maximum denitrification efficiency and TN removal were pH of 7, temperature of 40°C, and shaking speed of 60 rpm·min^-1. Compared to the free cells, the immobilization cells had no obvious negative effect on denitrification efficiency, additionally reduced the nitrite accumulation, and thus improved the TN removal. Furthermore, the immobilized cells still maintained 95.4% of $$-N removal after the eighth cycle reuse. These results demonstrated the immobilized Alcaligenes faecalis strain WT14 can remove TN effectively and additionally reduce nitrite accumulation in treating high strength $$-N wastewater.