Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

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.

Nitrate Water Contamination from Industrial Activities and Complete Denitrification as a Remediation Option

“…− concentration [87,88]. During mining, tailings that are transported to the surface from the pits are piled next to the mine, where the residual explosives are washed off and dissolve in rain water, which eventually flows into nearby streams and rivers, resulting in elevated NO 3 − concentrations [9,19,22].…”

The Application of Design of Experiments in the Hatchery Wastewater Treatment through Biological Method

“…These may imply that three days was long enough for the microbes to remove nitrate-N, as the maximum removal was achieved on day 3. Also, the removal of nitrate through the denitrification process requires a large amount of oxygen [5,17]; therefore, a longer retention time causes the reduction of oxygen, consequently reducing the amount of nitrate removed. According to Lu et al [18], 0.7h was the optimum hydraulic retention time for nitrogen removal instead of 12 h. Similarly, the decrease of hydraulic retention time from 30 to 5 h had caused a remarkable increment in nitrite oxidation activity [12].…”

“…COD and nitrogen are the two main indicators indicating poor wastewater quality. Also, the accumulation of nitrogenous wastes in aqua culturing systems has given rise to the toxicity to microorganisms [5]. The continuous production of wastes from domestic and industrial sectors occurs at an alarming rate nowadays, and disposal of wastes regularly takes place without proper treatment and management [3].…”

Riboflavin enhanced denitrification of artificial wastewater under low C/N condition in cold season

“…Low temperature below 15 °C inhibits the denitrification activity and functional gene expression, rapidly lowering the nitrogen removal efficiency (Racys et al 2018). A common engineering resolution of this issue in cold seasons (such as winter) is to enhance the hydraulic/sludge retention time, or to decrease the nitrogen load rate (Song et al 2020). Elsewhere, new bioreactors such as the moving bed biofilm reactor (MBBR) and biocharpacked SBR were developed to solve this problem (He et al 2018;Kowalski et al 2019).…”