Denitrification Bioreactors Research Articles

Mesophilic condition favors simultaneous partial nitrification and denitrification (SPND) and anammox for carbon and nitrogen removal from anaerobic digestate food waste effluent

Three simultaneous partial nitrification and denitrification (SPND) bioreactors were established on ambient (30 °C), mesophilic (40 °C) and thermophilic condition (50 °C) at high dissolved oxygen levels (2–7 mg L−1) to remove nitrogen and carbon from anaerobic digestate food waste effluent (ADFE). The bioreactor performed best under mesophilic condition, with TN and COD removal efficiency of 96.3 ± 0.1% and 91.7 ± 0.1%, respectively. Free ammonia (FA) and free nitrous acid (FNA) alternately ensured selective inhibition of nitrite-oxidizing bacteria (NOB) in long-term operation of SPND systems. Candidatus Brocadia, known as anammox bacteria, was observed unexpectedly in the bioreactors. The analysis of microbial community and metabolic pathways revealed that mesophilic strategy stimulated SPND and anammox process. Mesophilic condition helped autotropic microbes resist the competitive pressure from heterotrophic bacteria, improving the balance between nitrifiers, anammox bacteria and other co-existing heterotrophs. Overall, this study offers new insights into the linkage among temperature, pollutant removals (carbon and nitrogen) and metabolic potential in the SPND bioreactors.

Performance on horizontal flow and folded plate denitrification bioreactor recycling waste sawdust and municipal sludge for continuously treating simulated agricultural surface runoff

Nitrogen removal from agricultural surface runoff is of great significance to protect the water quality and safety of groundwater and drinking water. The denitrification bioreactor uses wood-particle products and municipal sludge as solid carbon sources to treat agricultural surface runoff and the rule of total nitrogen produced by wood-particle products is still blank. In this study, a type of denitrification bioreactor with municipal sludge (MS) and Cunninghamia lanceolata sawdust (CLS) as solid carbon source to denitrify simulated agricultural surface runoff is designed. Results show that CLS can release approximately 0.86 ± 0.06 mg L−1 of nitrogen into the water, and the release process conforms to Non-Fickian transport (n = 0.46). The addition of MS is beneficial to increase the average degradation rate of NH4+-N (70.94%). Increasing the inflow rate is beneficial to increase the average degradation rate of NO2−-N, NO3−-N and TN. When the influent flow is 1.34 mL min−1, the average degradation rate of NO2−-N is as high as 61.61% while of TN is 86.04% in the CLS horizontal flow denitrification bioreactor. The average degradation rate of NO3−-N of CLS and MS (sludge-water volume ratio = 1:2) folded plate denitrification bioreactor is 95.72%, which is 17.46% higher than the horizontal flow type. Based on the principle of cleaner production, this study recycles waste CLS and MS as solid carbon sources in the bioreactor to continuously treat and simulate agricultural surface runoff. The device can not only degrade high-concentration nitrogen, but also prevent the generation of waste and waste of energy, which is a new surface runoff pollution control technology.

Carbon dioxide and methane emission of denitrification bioreactor filling waste sawdust and industrial sludge for treatment of simulated agricultural surface runoff

Carbon dioxide (CO2) and methane (CH4) produced by denitrification bioreactors in processing agricultural surface runoff have contributed to increasing proportion of greenhouse gases (GHG) emissions. It is the first time to monitor and quantify the emission flux of CO2 and CH4 produced by laboratory-scale denitrification bioreactors which recycled waste Cunninghamia lanceolata sawdust (CLS) and industrial sludge (IS) as fillers to process simulated agricultural surface runoff. Sludge-water ratio, inflow rate and water flow direction are used as experimental factors to study the effect on the emission flux of CO2 and CH4. Results show that emission flux of CO2 from denitrification bioreactors with different sludge-water ratio approached 20 mg m−2h−1, simultaneously the average emission flux of CH4 produced by all bioreactors was 1.785 mg m−2h−1. The addition of sludge increased the emission flux of CH4 and had no significant effect on the emission flux of CO2. Increasing the inflow rate reduced the CO2 emission flux from 21.57 to 1.27 mg m−2h−1, and at the same time increased the CH4 emission flux from 0.007 to 9.54 mg m−2h−1. The gravity flow of wastewater reduced the emission flux of CO2 and CH4. The emissions of CO2 and CH4 from folded plate denitrification bioreactor with CLS and industrial sludge with a volume ratio of 1:2 can be reduced by 24.67% and 73.3%, respectively. There was no need to add special gas collection and treatment devices because CO2 and CH4 emission fluxes produced by the folded plate denitrification bioreactor and gravity denitrification bioreactor are not enough to increase the greenhouse effect. This study quantified the CO2 and CH4 produced by denitrification bioreactors filling CLS and IS, and provided a reference for future research on the gases produced by the denitrification process.

Performance and microbial community of a novel PVA/iron-carbon (Fe–C) immobilized bioreactor for nitrate removal from groundwater

Abstract An efficient immobilized denitrification bioreactor functioning under anaerobic conditions was developed by combining bacterial immobilization technology with iron-carbon (Fe–C) particles. The effects of key factors on nitrate (NO3 −–N) removal efficiency were invested, such as the carbon-nitrogen ratio (C/N), pH and hydraulic retention time (HRT). Experimental results show that 100.00% NO3 −–N removal efficiency and a low level of nitrite (NO2 −–N) accumulation less than 0.05 mg L−1 were obtained under the condition of a C/N ratio of 3, pH 7.0 and HRT of 6 h. Meteorological chromatographic analysis showed that the final product of denitrification was mainly nitrogen (N2). The main component of precipitation formed in the bioreactor was characterized as Fe3O4 by X-ray diffraction. High-throughput sequencing analysis indicated that the dominant bacterial class in the Fe–C bioreactor was Gammaproteobacteria, while the dominant genera were Zoogloea and Azospira, the relative abundances of which were as high as 23.25 and 15.43%, respectively.

Techno-Economic Analysis of Constant-Flow Woodchip Bioreactors

HighlightsTechno-economic analysis was performed for multiple scales of bioreactors operated under a variety of conditions.The unit cost decreased as the bioreactor size increased.The unit cost increased in bioreactors with longer HRTs and bypass flow due to reduced treatment capacity.One large bioreactor was more cost-effective than multiple smaller bioreactors.Abstract. Woodchip denitrification bioreactors are a relatively new, edge-of-field technology used to reduce nitrate-nitrogen (NO3-N) from subsurface tile drainage. The removal rate of nitrate is influenced by many factors, including temperature, dissolved oxygen, and hydraulic residence time (HRT). The objective of this study was to conduct a techno-economic analysis (TEA) for four scales of woodchip denitrification bioreactors operating at three HRTs (2, 8, and 16 h), designed with bypass flow or with a low probability of bypass flow, to determine the cost to remove 1 kg of NO3-N at each bioreactor scale and at each HRT. Several assumptions were made: the flow rate required to achieve a 2 h HRT on a per m3 basis could be achieved at all scales, the same mass removal of NO3-N was achieved on a per cubic meter basis, and the 2 h HRT did not have any bypass flow at each scale. With these assumptions, the lowest unit cost was observed for the large-scale bioreactor sized to have a low probability of bypass flow at 16 h HRT, with a resulting cost of $0.74 kg-1 NO3-N removed. The highest unit cost was observed for the pilot-scale bioreactor designed with bypass flow to achieve a 16 h HRT at a cost of $60.13 kg-1 NO3-N removed. At longer HRTs with bypass flow, a greater percent removal of nitrate has been observed with a lower mass removal rate. By having a low probability of bypass flow in the design, a higher mass removal and percent removal of nitrate were observed, leading to the above results. Contrasting this trend, the total and annual costs were highest for the large-scale bioreactor and lowest for the pilot-scale bioreactor. However, it was determined that 783%, 280%, and 54% increases in total cost for the pilot-, small-, and medium-scale bioreactors would be incurred to implement the number of bioreactors (66, 24, and 4, respectively) required to treat the same volume of flow as one large bioreactor. These results can be used to inform future design decisions and inform stakeholders of the approximate unit cost of installing a denitrifying woodchip bioreactor over a range of expected field conditions. While a larger bioreactor with a low probability of bypass flow may represent a more cost-effective investment, the potential for unintended, negative byproducts needs to be considered in the design. Keywords: Denitrification, Nitrate, Tile drainage, Water quality, Woodchip bioreactor.

Effect of saline drainage water on performance of denitrification bioreactors

Abstract Excessive use of nitrate fertilizers in agriculture causes harm to humans and the environment. The most suitable nitrate removal process is heterotrophic biological denitrification. The purpose of the present study was to evaluate the performance of three shapes of denitrification bioreactors: triangular, rectangular and semicircular. The main element that was used to remove nitrate was beech woodchips. The concentration of inlet nitrate was 75 mg/l and the salinity of the solution was 1 ds/m and 5 ds/m, for a period of six months. The results showed that the efficiency of the triangular bioreactor with a salinity level of 1 ds/m was 90%, which is more efficient than the rectangular and semicircular bioreactors with performances of 55.8% and 53.8%, respectively. The results also indicated that at a salinity level of 5 ds/m, the semicircular bioreactor with a performance of 50.8% inlet nitrate removal was the best of the three shapes of bioreactors tested, the efficiencies of the triangular and rectangular bioreactors were 49.9% and 48.6% respectively. Also, it was observed that at the salinity level of 1 ds/m, a high hydraulic retention time had a high positive effect on denitrification, on the other hand at the salinity level of 5 ds/m, there was better performance of denitrification if the hydraulic retention time was lower.

A novel insight on nitrate removal from high-contaminated ground waters: acid citric as carbon sources and ozone treatment

ABSTRACT The elevated levels of nitrate in ground waters are severe menace for human health and environment. The present study examined a new approach for removal of nitrate from high-contaminated ground waters (100 mg.L−1). Citric acid as carbon sources was employed to evaluate the nitrate removal from bioreactors filled with four media: polypropylene, polyethylene, porous Pumice stone and sand collected from local river within 20 month operation. Furthermore, ozonation process was employed to eliminate the residual carbon sources in effluent before transfer to local water network. The denitrification bioreactors seeded with denitrifying bacteria collected from local wells showed high removal efficiency (62–81%). Furthermore, the ozonation process with concentration level of 5 gr.h−1 significantly reduced the chemical oxygen demand. The result indicated that denitrifying bioreactor with citric acid as carbon source is a promising method for nitrate removal from ground water.

Nitrogen removal in recirculating aquaculture water with high dissolved oxygen conditions using the simultaneous partial nitrification, anammox and denitrification system

The efficient removal of nitrogen pollutants in the aquaculture systems is still a challenge due to the low concentration of organic carbon and high concentration of dissolved oxygen (DO) in the wastewater. The simultaneous partial nitrification, anammox and denitrification (SNAD) bioreactor was firstly used for the treatment of aquaculture wastewater in recirculating aquaculture system. The bioreactor operated for 180 days without adding extra organic carbon. After 60-day operation, the bioreactor reached the stable stage with the average concentration of ammonia/nitrate/nitrite/COD in the effluent with 0.26/0.75/0.47/0.27 mg/L. The Pseudoxanthomonas was the dominant genus in the biofilm samples. The typical nitrogen functional bacteria and genes for nitrification, anammox and denitrification were detected with different abundance in different procedures along the bioreactor. Network analysis revealed the significant correlations between nitrogen functional bacteria and genes. The SNAD bioreactor achieved the effective removal for nitrogen and COD under high DO conditions in recirculating aquaculture system.

Enhanced nitrogen removal of low carbon wastewater in denitrification bioreactors by utilizing industrial waste toward circular economy

Aquaculture needs practical solutions for nutrient removal to achieve sustainable fish production. Passive denitrifying bioreactors may provide an ecological, low-cost and low-maintenance approach for wastewater nitrogen removal. However, innovative organic materials are needed to enhance nitrate removal from the low carbon effluents in intensive recirculating aquaculture systems (RAS). In this study, we tested three additional carbon sources, including biochar, dried Sphagnum sp. moss and industrial potato residues, to enhance the performance of woodchip bioreactors treating the low carbon RAS wastewater. We assessed nitrate (NO3−) removal and microbial community composition during a one-year in situ column test with real aquaculture wastewater. We found no significant differences in the NO3− removal rates between the woodchip-only bioreactor and bioreactors with a zone of biochar or Sphagnum sp. moss (maximum removal rate 31–33 g NO3−-N m−3 d−1), but potato residues increased NO3− removal rate to 38 g NO3−-N m−3 d−1, with stable annual reduction efficiency of 93%. The readily available carbon released from potato residues increased NO3−-N removal capacity of the bioreactor even at higher inflow concentrations (>52 mg L−1). The microbial community and its predicted functional potential in the potato residue bioreactor differed markedly from those of the other bioreactors. Adding potato residues to woodchip material enabled smaller bioreactor size to be used for NO3− removal. This study introduced industrial potato by-product as an alternative carbon source for the woodchip denitrification process, and the encouraging results may pave the way toward growth of blue bioeconomy using the RAS.

Tile-Drain and Denitrification Bioreactor Water Chemistry for a Soybean (<i>Glycine max</i>(L.) Merr.)-Corn (<i>Zea mays</i> L.) Rotation in East-Central Missouri (USA)

Nitrogen transport from agriculture production fields raises the specter of environmental degradation of freshwater resources. Our objectives were to document and evaluate nitrate-N, ammonium-N, phosphorus and other nutrients emanating from a 40-ha controlled subsurface irrigation drainage technology coupled in series with a denitrification bioreactor. The intent of the denitrification bioreactor is to create an environment for anoxic microbial populations to support denitrification. We monitored the tile-drainage effluent and denitrification bioreactor water chemistry under a corn-soybean rotation to estimate the nutrient concentrations and the competence of the denitrification bioreactor to foster denitrification. Nitrate-N bearing tile drainage effluents ranged from less than 1.5 to 109 mg NO3- -N/L, with the nitrate concentration differences attributed primarily to the: 1) timing of nitrogen fertilization for corn, 2) soil mineralization and residue decomposition, and 3) intense rainfall events. The denitrification bioreactor was highly effective in reducing drainage water nitrate-N concentrations providing the rate of water flow through the denitrification bioreactor permitted sufficient time for equilibrium to be attained for the nitrate reduction reactions. The nitrate-N concentrations entering the denitrification bioreactor ranged from 0.4 to 103 mg NO3- -N/L in 2018, whereas the outlet nitrate concentrations typically ranged from 0.3 to 5.2 mg NO3- -N/L in 2018. Nitrate tile-drainage effluent concentrations in 2019 were marginal, given soybeans obtain nitrogen from biological nitrogen fixation. Nutrient uptake by corn reduced the soil nitrate leaching pool and created nitrogen-bearing biomass, features important for formulating best management practices.

Hydrogen producer microalgae in interaction with hydrogen consumer denitrifiers as a novel strategy for nitrate removal from groundwater and biomass production

Low-soluble and hazardous hydrogen gas which is used in current water denitrification processes was substituted by microalgae as a novel approach for biological nitrate removal. Bioremediation of nitrate-contaminated groundwater was evaluated by three batch cultures of hydrogen consumer denitrifiers (HCD), microalgae, and HCD-microalgae consortium at a similar inoculated total biomass of about 0.025 g. Microalgae contained three species of Chlorella vulgaris, Ettlia sp., and Chlamydomonas reinhardtii with an initial cell number of 60 × 104 cell/mL and subsequently C. vulgaris as dominant strain. High nitrate concentration of about 221 mg/L was entirely removed in hydrogen-injected denitrification bioreactor containing HCD in <24 h with N removal rate of 86 mg/L/d. However, it released sCOD into the environment and did not remove phosphorus efficiently. The consortium of HCD and microalgae could offset the lack of hydrogen for dissimilation of nitrate and produced N removal rate of 78 mg/L/d at lowest HCD/microalgae inoculated mass ratio of 0.26. Microalgae played the main role for assimilation of phosphorus and mitigation of the produced sCOD in both photobioreactors containing microalgae alone or their consortium with HCD. The maximum biomass productivity of 0.32 g/L/d and settling efficiency of 0.6 were obtained at highest inoculated HCD/microalgae mass ratio of 2.33. However, the performance of the consortium in terms of nitrate removal was better in lower ratio of HCD/microalgae, which can be applied in large-scale application.

Denitrification behavior in a woodchip-packed bioreactor with gradient filling for nitrate-contaminated water treatment

Woodchip solid-phase denitrification bioreactors (SPDRs) are widely applied to remove NO3− from water. In this study, two SPDRs with different woodchip filling patterns, namely a gradient filling bioreactor (G-SPDR) and a uniform filling bioreactor (U-SPDR), were constructed and their denitrification performances were investigated. Analysis of the NO3− removal pathway along the water flow path showed that NO3− removal rates could be enhanced using the G-SPDR (35.66–174.55 mg N·L−1·d−1) compared to the U-SPDR (25.17–111.72 mg N·L−1·d−1) at an appropriate flow rate (0.3–1.8 mL·min−1). In addition, the G-SPDR promoted complete denitrification with low NO2− accumulation. Chamber model analysis showed that the maximum NO3− removal rate was closer to the inlet in the G-SPDR. Furthermore, the optimum reaction height was 25 cm for the G-SPDR and 35 cm for the U-SPDR, implying that gradient filling could reduce the size of the bioreactor. Therefore, gradient filling is a promising and cost-saving method to construct SPDRs for the bioremediation of NO3− contaminated water.

Investigating the Effect of Different Hydraulic Cross Sections of Denitrification Beds on the Amount of Effluent EC

Nitrate loadings from agricultural drainage to surface water resources cause’s serious water quality concerns in many parts of the world. Denitrification bioreactors are suitable option for removing nitrate from agricultural drainage water. The objectives of this study was to investigate the effect of different hydraulic cross sections of denitrification beds on the amount of effluent EC. In this study, three denitrification beds were constructed with a semicircular, triangle and a rectangle cross sections, filled with wood chips of beech tree. Samples were taken from the outlets of all three beds at a depth at 25 and 50 cm from the bottom of the bed for two months. EC of the samples was meassured using EC-meter. After determining the EC of the samples, data were analyzed by T-test and Univariate tests. The results showed that the shape of the cross-section of the denitrification beds and the saturation depth had a significant effect on EC and the amount of EC of the outflow was increased.

Simultaneous partial nitrification, anammox and denitrification (SNAD) process for nitrogen and refractory organic compounds removal from mature landfill leachate: Performance and metagenome-based microbial ecology

In this study, a simultaneous partial nitrification, Anammox and denitrification (SNAD) bioreactor was constructed for mature landfill leachate treatment, which exhibited favorable NH4+-N (98.9–99.9%), TN (90.7–94.9%) and bio-refractory organic compounds (46.2–67.7%) removal efficiencies. Stoichiometric analysis demonstrated that the synergy of ammonium-oxidizing bacteria and Anammox bacteria dominated TN removal (96.1–97.2%). NO3−-N produced in Anammox could be further reduced through (partial) denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The results highlighted that humic-like and their intermediates might serve as the electron donor for these (partial) denitrifiers and DNRA bacteria to remove NO3−-N, and could be effectively removed from mature landfill leachate in SNAD bioreactor. Metagenomic characterization further demonstrated that phyla Chloroflexi, Chlorobi and genera Nitrosomonas, Ignavibacterium and Aminiphilus might be responsible for such humic-like degradation. Overall, this work offers new insights into the metagenome-based bioinformatic roles for the previously understudied microorganisms in SNAD bioreactor for mature landfill leachate treatment.

Ex situ simultaneous nitrification-denitrification and in situ denitrification process for the treatment of landfill leachates

The objective of this research was to investigate the ex situ simultaneous nitrification–denitrification (SND) and in situ denitrification process and to evaluate its application for treating landfill leachates at long-term operations. Based on the predicted contaminant concentrations, two sets of laboratory-scale bioreactor landfill systems (an ex situ nitrification and in situ denitrification bioreactor as well as an ex situ SND and in situ denitrification bioreactor) were operated continuously for about 48 weeks. The recirculated leachate quantity and effluent characteristics of leachates were regularly monitored and analyzed by using the standard method. The ex situ SND and in situ denitrification process obtained a better leachate removal performance compared with the ex situ nitrification and in situ denitrification process, while the ex situ SND process can reduce the energy costs. However, the leachate treatment performance of this process was generally unsatisfactory as the contaminant concentrations do not meet the discharge standard within the forecasted time. These results further proved that the effectiveness of the treatment decreases along with an increasing landfill age. Therefore, further research must be performed to optimize the treatment efficiency of the bioreactor.

Performance of Saturated Riparian Buffers in Iowa, USA.

Nitrate from artificial drainage pipes (tiles) underlying agricultural fields is a major source of reactive N, especially NO, in surface waters. A novel approach for reducing NO loss is to intercept a field tile where it crosses a riparian buffer and divert a fraction of the flow as shallow groundwater within the buffer. This practice is called a saturated riparian buffer (SRB), and although it is promising, little data on the performance of the practice is available. This research investigated the effectiveness of SRBs in removing NO at six sites installed across Iowa, resulting in a total of 17 site-years. Water flow and NO in the tile outlets, diverted into the buffers, and NO concentration changes within the buffers were monitored throughout the year at each site. Results showed that all the SRBs were effective in removing NO from the tile outlet, with the average annual NO load removal ranging from 13 to 179 kg N for drainage areas ranging from 3.4 to 40.5 ha. This is NO that would have otherwise discharged directly into the adjoining streams. The annual removal effectiveness, which is the total NO removed in the SRB divided by the total NO draining from the field, ranged from 8 to 84%. This corresponds to an average removal rate of 0.040 g N m d with a range of 0.004 to 0.164 g N m d. Assuming a 40-yr life expectancy for the structure and a 4% discount rate, we computed a mean equal annual cost for SRBs of US$213.83. Given the average annual removal of 73 kg for all site-years, this cost equates to $2.94 kg N removed, which is very competitive with other field-edge practices such as denitrification bioreactors and constructed wetlands. Thus, SRBs continue to be a promising practice for NO removal in tile-drained landscapes.

Twenty Years of Riparian Zone Research (1997-2017): Where to Next?

Riparian zones have been used for water quality management with respect to NO in subsurface flow and total P (TP), sediments, and pesticides in overland flow for decades. Only recently has the fate and transport of soluble reactive P (SRP), Hg, emerging contaminants, and greenhouse gas (GHG) fluxes (NO, CO, and CH) been examined in riparian zones. Overall, riparian zones are efficient at reducing emerging contaminants in subsurface flow and only function as hot spots of methylmercury production in the landscape when dominated by Hg-rich wet organic soils. However, riparian zones do not provide consistent benefits with respect to SRP removal or GHG emissions. Although most existing riparian models almost exclusively focus on NO removal, recent developments in riparian models demonstrate the potential for using easily accessible digital environmental datasets to simulate and scale up riparian functions beyond NO removal to include SRP, TP, and GHG dynamics. To further inform integrated watershed management efforts, more research should be conducted on how various practices, including stream restoration, subsurface drainage, two-stage ditches, beaver dam analogues, denitrification bioreactors and permeable reactive barriers, artificial wetlands, and short-rotation forestry crops affect riparian water and air quality functions. Riparian zone benefits should be discussed not only with respect to water and air quality, but also in terms of recreation, habitat for wildlife, and other ecosystem services. More research is needed to fully address potential water quality or air quality tradeoffs associated with riparian zone management in a multicontaminant-multiuse landscape context.

Using the Conservation Practice Effectiveness (CoPE) Database to assess adoption tradeoffs

The newly published Conservation Practice Effectiveness (CoPE) Database compiles information on the effectiveness of a suite of conservation practices developed to treat contaminants in surface runoff and tile drainage water from agricultural landscapes. Traditional conservation practices such as no-tillage and conservation crop rotation are included in the CoPE Database, as well as novel practices such as drainage water management, blind inlets, and denitrification bioreactors. This will be particularly useful to conservation planners seeking new approaches to water quality problems associated with dissolved constituents, such as nitrate (NO₃) or soluble phosphorus (SP), and for researchers seeking to understand the circumstances in which such practices are most effective. Another novel feature of the database is the presentation of information on how individual conservation practices impact multiple water quality concerns. This information will be critical to enabling conservationists and policy makers to avoid (or at least be aware of) undesirable tradeoffs, whereby great efforts are made to improve water quality related to one resource concern (e.g., sediment) but exacerbate problems related to other concerns (e.g., NO₃ or SP). Finally, we note that the CoPE Database can serve as a source of the soft data needed to calibrate simulation models assessing the potential water quality tradeoffs of conservation practices, including those that are still being developed.

A cascade of a denitrification bioreactor and an aerobic biofilm reactor for heavy oil refinery wastewater treatment

The performance of an efficient denitrification bioreactor–aerobic biofilm reactor cascade for heavy oil refinery wastewater treatment was investigated. Optimum operation parameters for denitrification were found as follows: (1) hydraulic retention time of 8 h; (2) C/NO3−–N molar ratio of 3.75 with acetate as the carbon source; (3) 20% (v/v) carrier filling ratio in the denitrification bioreactor. Under such optimal conditions, a volumetric removal of 0.82 kg N m−3 d−1 was obtained. As an alternative low-cost carbon source to acetate, secondary DAF effluent (COD/NO3−–N mass ratio of 5.4) was also detected and a stable activity of denitrification was achieved with adding 25% volume fraction of secondary DAF effluent. Effluent COD of the subsequent aerobic biofilm reactor further decreased satisfying the requirements of the current discharge standards. High-throughput sequencing results exhibited that Rhodocyclaceae and Comamonadaceae were the dominant denitrifiers in the denitrification reactor and Pseudomonas was the dominant microbe in the aerobic biofilm reactor.

Bacterial community analysis of marine recirculating aquaculture system bioreactors for complete nitrogen removal established from a commercial inoculum

An experimental recirculating aquaculture system was constructed under ambient seawater conditions to compare microbial community diversity of nitrifying and denitrifying biofilters that were derived from a commercial inoculum used for aquarium applications. Next generation sequencing revealed distinct and diverse microbial communities in samples analyzed from the commercial inoculant and the denitrification and nitrification biofilters. In all samples, communities were represented by a few dominant operational taxonomic units (OTUs). Bacteria having the capacity to carry out ammonia and nitrite oxidation were more abundant in the nitrification biofilter. Similarly, the proportion of the bacterial taxa known to carry out heterotrophic and autotrophic denitrification and participate in sulfur cycling were found in the denitrification bioreactor, and likely originated from the ambient environmental water source. Our results indicated that environmental seawater can be a favorable enhancement to the bacterial consortium of recirculating aquaculture systems biofilters.