Abstract
The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.
Highlights
Nitrogenous contamination of surface waters is a serious environmental problem, causing eutrophication of rivers, lakes, and near-shore marine environments [1,2] and raising the likelihood of toxic algal blooms in receiving waters [3,4]
We quantified the effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and microbial community composition of an aerobic denitrification reactor at a bench scale
Our results showed that increased HRT and the reduction of influent nitrate-N concentration promoted the denitrification process, with HRT having the stronger effect on aerobic denitrification process and microbial community composition
Summary
Nitrogenous contamination of surface waters is a serious environmental problem, causing eutrophication of rivers, lakes, and near-shore marine environments [1,2] and raising the likelihood of toxic algal blooms in receiving waters [3,4]. Accumulation of nitrogenous wastes is a problem in aquaculture systems [5], posing toxicity to cultured organisms [6,7,8,9]. In recirculating aquaculture systems (RASs), the low rate of water replacement may lead to the accumulation of nitrate-N in rearing water, to concentrations as high as 400–500 mg/L [11], bringing about the need for conversion of nitrate-N to N2 via denitrification. The denitrification process in biological treatment of wastewater is affected by environmental conditions [12,13,14]. Dissolved oxygen (DO) concentration, temperature, C/N ratio, carbon source, pH, nitrate loading rate, and hydraulic retention time (HRT) affect the performance of the aerobic denitrification process [15,16,17,18].
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