Isolation and immobilization of new aerobic denitrifying bacteria

Nitrate is considered to be one of the most widely present pollutants leading to eutrophication of environment. The purpose of this work was to isolate and identify new aerobic denitrifying bacteria from nitrate-contaminated sediments and utilize modified immobilized techniques for immobilizing isolates to improve nitrate removal efficiency. Using traditional enrichment approach, three purified aerobic bacteria (HS-N2, HS-N25 and HS-N62) capable of NO3−–N removal from sediments were obtained. According to their physiological properties and 16S rRNA gene sequences analysis, isolates HS-N2, HS-N25 and HS-N62 were identified as Salmonella sp., Bacillus cereus and Pseudomonas sp. respectively. After cultivating at 37 °C with 150 rpm shaking, the percentages of NO3−–N removal by isolates HS-N2, HS-N25 and HS-N62 were 95% in 24 h, 100% in 24 h and 96% in 12 h, respectively. Due to its higher removal rate of NO3−–N, HS-N62 was selected for immobilization with polyvinyl alcohol (PVA)-sodium alginate (SA) and powder activated carbon. The removal efficiency of NO3−–N by immobilized HS-N62 pellets was enhanced with no nitrite accumulation. Immobilized pellets exhibited more desirable denitrification after 24 h under stressful batch conditions, indicating they had stable and strong denitrifying capabilities.