Characterization of ammonia remover Bacillus albus (ASSF01) in terms of biofilm-forming ability with application in aquaculture effluent treatment.

Abstract

Presence of higher concentration of ammonia (> 0.5 mg/L) as well as nitrite (> 0.2 mg/L) in aquaculture environment create difficulties for fish survival. The existing methods for removal of these pollutants are time-consuming. A stable biofilm-based system for ammonia removal from aquaculture wastewater was developed in the current study to overcome the limitations of conventional treatment processes. In order to do so, initially the bacterial candidate was well characterized and tested for rapid biofilm development. The ammonia bioremediating Bacillus albus (ASSF01), from the activated sludge of shrimp farm, with a generation time of 67 min 12 s in suspension culture, was a structured biofilm former. The staining based measurement showed biofilm initiation from the very first hour of incubation. This finding was further validated using scanning electron microscopy (SEM), profilometry, and ellipsometry with Brewster angular microscopy (BAM). Hurst exponent (H) calculation using the profilometer and ellipsometer data yielded a value of H of above 0.9 and 0.62, indicating positive correlation or persistence behavior, hence a stable biofilm former. Each method of biofilm measurement, in spite of variation in complexity and sensitivity, was equally effective for biofilm progression analysis. The generation time of ASSF01 upon immobilization was 15 min and 36 s, ensuring rapid development of stable system. Response surface methodology (RSM)-based optimization of aquaculture wastewater treatment by the isolate in a biofilm reactor at ambient temperature revealed the optimum influent concentration of ammonia (3.2 mg/L), nitrate (6.89 mg/L), and phosphate (1.17 mg/L) to be reduced to discharge level (as per aquaculture requirement) with 14 h of hydraulic retention time. This study demonstrates the potential of the isolate as an efficient bioremediant for treating ammonia-containing aquaculture wastewater in a single unit biofilm reactor, ensuring rapid stabilization, environmental protection, and aquaculture sustenance.