Denitrification and Dissimilatory Nitrate Reduction to Ammonium (DNRA) Activities in Freshwater Sludge and Biofloc from Nile Tilapia Aquaculture Systems

Abstract

Suspended organic sludge from freshwater and biofloc Nile tilapia systems were examined for the presence of denitrifying and dissimilatory nitrate reduction to ammonium (DNRA) activities under nitrate and sulfide stimulation. Initial nitrate concentrations at 25 and 100 mg NO 3 --N/L were added to the freshwater sludge and biofloc samples to simulate low and high nitrate levels that are normally found in aquaculture systems. The results showed that freshwater sludge and biofloc both had denitrifying activity immediately after nitrate addition. However, ammonium accumulated in the biofloc reactors but not in the freshwater reactors, indicating the activity of DNRA in the high C/N biofloc particles. The influence of sulfide on nitrate reduction was also studied by adding different concentrations of sulfide along with 100 mg NO 3 --N/L. The results showed that elevated sulfide concentrations partially inhibited denitrification in the freshwater sludge and caused nitrite and ammonium accumulation, in which ammonium formation was probably responsible by DNRA activity. In sulfide-added biofloc reactors, ammonium accumulated at the same level as found in the biofloc reactors without sulfide. Therefore, DNRA bacteria residing in the biofloc aquaculture system were more likely to be heterotrophs that did not use sulfide as their electron donor.

Distinct Microbial Community Performing Dissimilatory Nitrate Reduction to Ammonium (DNRA) in a High C/NO₃⁻ Reactor

“…The growth and activity of DNRA microorganisms decrease denitrification efficiency, and increase the waste load on nitrification as well as total nitrogen discharged with the effluent. DNRA activity was previously detected in anaerobic digester systems ( 1 , 2 , 13 , 21 ), a pilot plant treating sulfate (SO 4 2− )- and NO 3 − -containing wastewater ( 14 ), a lab-scale denitrifying reactor ( 4 ), and aquaculture nitrogen removal systems ( 10 ). The extent of DNRA measured among these studies suggests its competitive potential in high organic-loaded wastewaters; however, the microorganisms responsible for the process have rarely been identified in these environments.…”

Effects of dietary protein content on hybrid tilapia (Oreochromis aureus × O. niloticus) performance, common microbial off-flavor compounds, and water quality dynamics in an outdoor biofloc technology production system

“…Another anaerobic, bacterially mediated nitrogen transformation is dissimilatory nitrate reduction to ammonium (DNRA), where nitrate is reduced to nitrite and nitrite is reduced to ammonium and that may contribute substantially to nitrogen cycling (Burgin and Hamilton, 2007;van den Berg et al, 2016;). Concurrent DNRA and denitrification was observed in sludge from a freshwater tilapia biofloc system (Chutivisut et al, 2014), although DNRA is reported to occur preferentially when labile organic carbon concentration is high and nitrate-N concentration is low (Burgin and Hamilton, 2007). The observed gain in TAN in settling chamber effluent supports the hypothesis of DNRA activity.…”

Core microbiome involved in nitrite removal in shrimp culture ponds

“…As a key intermediate of the N cycle, nitrite generated from nitrate by denitrification and ammonia by nitrification can effectively convert into ammonium that is recycled by DNRA (Giblin et al, 2013). Chutivisut et al (2014) found that the activity of DNRA bacteria and denitrifiers could be simultaneously stimulated in biofloc reactors after a high nitrate concentration (25 mg NO 3 − ‐N/L) was added. In this study, the abundance of nitrate reduction genes ( narG and napA ), which was higher than that of nitrite reduction genes ( nirK and nirS ), implied that the nitrate reduction rate was higher than that of nitrite, which theoretically led to the accumulation of nitrite (Table 1).…”