Characterization of Nitrifying Bacterial Community in a Mariculture Wastewater Treatment Using SBR System

Abstract

Sequencing batch reactors (SBR) have been used in the biological treatment of aquaculture wastewater. In this study, we investigated the microbial community of a SBR that used diatomite earth (20 g/L) as the sludge carrier material. Marine wastewater in which ammonia content was 42.08 to 55.88 mg/L was supplied to the SBR every 12 h over a treatment period of 65 days. During the first 20 days, the concentration of NH4-N decreased gradually, while nitrite (NO2-N) became the major nitrogen compound, reminiscent of the development of an ammonia-oxidizing process. Over the next 20 days, the concentration of NH4-N decreased further due to conversion to NO3-N. More than 99% of the NH4-N was converted to NO3-N over a period of 40-65 days. Denaturing gradient gel electrophoresis (DGGE) assay showed that bacteria of the genus Flavobacterium were present during the entire treatment period, while α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, and Sphingobacteriia started to accumulate after the first 20 days. Fluorescence in situ hybridization (FISH) assay identified Nitrobacter and Nitrosomonas as the main bacteria involved in the conversion of NH4-N to NO3-N. Diatomite earth therefore acted as an efficient sludge carrier by shortening the settling time and facilitating bacterial colonization. This SBR was capable of rapid removal of NH4-N. This warrants further investigation at the pilot-scale in an actual mariculture farm.