NITROGEN REMOVAL EFFICIENCY OF DENITRIFYING BACTERIA ISOLATED FROM AQUACULTURE PROCESSING WASTEWATER IN NITRATE-RICH ENVIRONMENT

Abstract

Denitrifying bacterial strain III-8, isolated from aquaculture processing wastewater and selected based on their ability to reduce nitrate and nitrite without ammonification was identified by traditional culture methods combined with 16S rRNA gene sequencing and searching the Genbank. As the results, III-8 was identified as Achromobacter xylosoxidans. Factors affecting denitrification efficiency such as NaCl concentration, biofilm carrier presence and microbial cell density were investigated in an experimental moving bed biofilm reactor (MBBR) system using artificial wastewater as well as aquaculture processing wastewater. In artificial wastewater with a loading of 140 mg ml^-1 N-NO₃^-, strain III-8 showed a nitrogen removal efficiency up to 100 % in the salt free medium and 88 % in 3 % salt concentration biofilm carrier containing system with an initial cell density of 10⁸ cfu ml^-1. In aquaculture processing wastewater with the same loading, the average nitrogen removal rate after 36 hours of treatment was found to be of 9.1 gN m^-3 h^-1 with 100 % efficiency. The high initial microbial density could be secured by aerobic propagation in a proper culture medium.