Denitrifying Bioreactors Research Articles

Characterizing the role of hydraulic retention time on nitrate removal indices in denitrifying bioreactors by nonlinear models

Denitrifying bioreactors (DNBRs) are a sustainable and cost-effective practice commonly used at the edge of fields to reduce nitrate from agricultural runoff. The hydraulic retention time (HRT) is a crucial variable that affects nitrate removal rate (NRR, g N m−3 d−1), nitrate removal efficiency (NRE, %), and nitrate concentration reduction per length (Nrd, mg N L−1 m−1). In this study, two nonlinear models, the developed Michaelis-Menten (MM) model and the Mitscherlich (MT) model, were developed to characterize the relationship between nitrate removal indices (NRR, NRE, and Nrd) and HRT. This study first utilizes nonlinear models to quantitatively understand the relationship between NRR, NRE, Nrd, and HRT. To verify the models, eight experiments were conducted under different conditions, including different scales (laboratory and field), media (woodchip, woodchip+biochar, woodchip+silage leachate, woodchip+biochar+silage leachate), and influent nitrate concentrations (6.8–70 mg N L−1). The results showed that the MT model outperformed the MM model and MT could accurately characterize the nitrate removal changes with HRT and provide the optimal HRT (HRTO). Overall, the model could be beneficial for designers and practitioners to optimize nitrate removal.

Flue gas Pb0 removal from sludge incineration through biological lead oxidation coupled denitrification

Lead (Pb0) in flue gas from sludge incineration can seriously harm human health especially lead poisoning and blood lead increase. Microbial lead (Pb0) oxidation associated with nitrate reduction might be poorly understood in eliminating Pb0 pollution in flue gas from sludge incineration. In this study, a denitrifying bioreactor (DBR) was investigated for Pb0 removal from flue gas. Pb0 removal efficiency achieved 87% in 60-day operation. Dominated Pb0-oxidating-denitrifying bacteria such as Azoarcus, Thauera and Stappia could realize bacterial Pb0 oxidation and nitrate reduction through the regulation of lead oxidation genes (katE, K07217, aoxA, aoxB, moxA) and denitrification gene (napAB and narHGI). The up-regulation of amino acids and polysaccharide biosynthesis, transporters and phosphatase-relevant genes provided evidence of their involvement in the transformation of lead. The bio-oxidation of Pb0 adsorbed on EPS was coupled with denitrification, where Pb0 and nitrate served as the electron donor and terminal electron acceptor, respectively, and thereby formed redox between Pb0 and nitrate. Pb2+ oxidized from Pb0 was intracellularly accumulated, and complexed with EPS by binding with –OH and P = O. Pb0-containing flue gas was bio-stabilized in the form of Pb5(PO4)3Cl and protein/polysaccharide-Pb2+. Pb0 in flue gas was adsorbed by denitrifying bacteria, oxidized to Pb2+ coupling with denitrification, and biostabilized to achieve the removal of Pb0 from flue gas. These results show that the DBR advanced treatmenttechnology is achievable and provide new possibilities for applying the denitrifying bioreactor to remove heavy metals from flue gas.

Effectiveness of denitrification bioreactors with woodchips, corn stover, and phosphate-sorbing media for simultaneous removal of drainage water N and P in a corn-soybean system.

Millions of acres of farmland in the midwestern United States (US) are artificially drained, and this contributes to the export of nitrogen (N) and phosphorus (P) from agricultural land to surface water. Using a 36-acre tile-drained farm field, effects of P-sorbing media in combination with a denitrifying bioreactor system constructed with woodchips (WC) and corn stover (CS) on reducing nutrient export in drainage water were tested for 3 cropping years (2018-2020). The field was divided into three subfields as replicates. In each subfield, the drainage water was divided and separately channeled into three bioreactors, each of which contains one of the three different substrates: WC, CS, and CS-WC (1:1 v/v mixture of CS and WC), randomly assigned. The outlet of each compartment contained a 2.25L flow-through chamber filled with activated iron (Fe) filings as P-sorbing material. Both WC and CS bioreactors were effective in removing drainage NO3 - with a 77% (WC), 86% (CS), and 89% (CS-WC) reduction in mean NO3 - -N concentration. For the three cropping years, the WC bioreactor reduced the total drainage inorganic N (NO3 - -N+NH4 + -N) load by 72%, but the CS bioreactor increased the total inorganic N load in the drainage water due to the substantial release of NH4 + with the decomposition of CS. The breakdown of CS also increased drainage P. The NH4 + and P release decreased with the decrease in the proportion of CS; thus, not more than 10% of CS is recommended for blending with WC to enhance the performance of a bioreactor. The P-sorbing Fe filing media reduced the P loads in drainage by an average of 19% during the 2-year study.

Aspect ratio and baffles impact hydraulic performance of full-size denitrifying bioreactors

Denitrifying woodchip bioreactors treating subsurface drainage in the US have high aspect ratios (i.e., length: width ratios; approximately 4:1) to encourage plug flow dynamics. Improved understanding of bioreactor hydraulics across aspect ratios would help assess possible increased flexibility for this practice to capture greater hydraulic loading or provide greater nitrate mass removal. The objective of this study was to assess the hydraulic impacts of aspect ratio and baffles using conservative tracer testing at full-scale denitrifying woodchip bioreactors. Fourteen tracer tests were performed at six bioreactors, spanning three design styles: (1) “conventional” bioreactors with high aspect ratios of ≥2.6:1; (2) a “wide” bioreactor with a low aspect ratio of 0.3:1; and (3) a relatively wide “advanced” bioreactor with baffles placed to route flow sinuously perpendicular (sideways) to the hydraulic gradient. The wide bioreactor had the most dispersion, the most short circuiting, and was the most well mixed based on the tanks-in-series model. The advanced design with baffles had higher volumetric efficiencies than the conventional and wide designs (2.9, 2.2, and 2.1, respectively) and trended toward the highest nitrate removals. The concept of baffles at relatively wide bioreactors merits additional field-scale assessment to increase hydraulic loading while maintaining hydraulic efficiency. The Morill Dispersion and Short Circuiting Indices were strongly and significantly correlated (Pearson's r: −0.88) across the fourteen tests as were the volumetric and hydraulic efficiency metrics (r: 0.87). While aspect ratio and baffles have been well studied in wetlands and other reactor types, this work is the first to establish these concepts using tracer testing at three woodchip bioreactor design styles.

Performance of denitrifying bioreactors in southern Alberta

Denitrifying bioreactors are an edge-of-field passive treatment technology that can reduce nutrient export from subsurface drainage waters to aquatic ecosystems. This technology is gaining popularity in many parts of the world including eastern Canada, but has not gained widespread acceptance in the Canadian prairies. This study evaluated the performance of pilot-scale denitrifying bioreactors for removing nitrate under agricultural field conditions in southern Alberta. Local agricultural residues– barley straw and hemp straw– were tested in comparison to wood chips for nutrient removal potential under varying retention times and temperatures during the growing season. Results from this study identified that the primary factors affecting nitrate-nitrogen removal in this region were temperature, flow rate, carbon source material and the age of the materials in the bioreactor. Both agricultural residues exceeded wood chip performance in the first year of operation, but all fill materials performed similarly in the second year of operation– the percent reduction of nitrate-nitrogen dropped from 72% to 34% and 55% to 32% for barley straw and hemp straw, respectively, while increasing from 27% to 29% for wood chips. These results indicate that more research is needed on the use of barley straw and hemp straw in bioreactors after an overwinter period.

Assessment of Wood Chips and Agricultural Residues as Denitrifying Bioreactor Feedstocks for Use in the Canadian Prairies

Highlights Performance of denitrifying bioreactors in Alberta was evaluated. Barley straw was more effective in reducing nitrate compared to wood chips. Hydraulic retention time, feedstock, and season are the primary factors affecting nitrate removal. Abstract. This study evaluated the performance of pilot-scale denitrifying bioreactors (LWD: 6 × 0.6 × 1m) filled with different carbon substrates, including barley straw, hemp straw, and woodchips, for removing dissolved nitrogen from simulated subsurface drainage at two representative geographic locations in Alberta. In this study, the bioreactors were tested under varying hydraulic retention times (4, 8, and 12 h) in the spring, summer, and fall of one year. Tracer studies were conducted to evaluate flow and dispersion characteristics. The mean of nitrate removal efficiency ranged from 19% to 87% during the spring, 44% to 95% during the summer, and 21% to 68% during the fall. We found that barley straw was more effective in reducing nitrate (45% to 95%) compared to wood chips (19% to 54%). This study is the first testing of the effect of different biomass types and hydraulic residence times on bioreactor performance in the Canadian prairies (Alberta) and will allow agricultural producers and regulators to assess the suitability of these systems within the region. Keywords: Bioreactor, Denitrification, Water quality, Wood chips, Agricultural residues, Subsurface Drainage.

Denitrifying Bioreactor In Situ Woodchip Bulk Density

Highlights The bulk density of woodchips in denitrifying bioreactors in the field is unknown. In situ bulk density estimation methods were developed for use during construction or excavation. Dry bulk densities of aged woodchips at bioreactor bottoms were lower than previous literature values. Moisture and particle size and density explained some, but not all, of the variation in in situ bulk densities. Abstract. Woodchip bulk density in a denitrifying bioreactor governs system hydraulics, but this prime physical attribute has never been estimated in situ. The objectives were twofold: (1) to establish estimates of in situ woodchip bulk density at bioreactors in the field, and (2) evaluate causal factors for and resulting impacts of these estimates. Proof-of-concept bulk density methods were developed at a pilot-scale bioreactor using three ways to estimate volume: surveying the excavated area, pumping the excavation full through a flow meter, and using iPhone Light Detection and Ranging (LiDAR). These methods were then further tested at two new and three old full-size bioreactors. Additional ex situ (off-site) testing with the associated woodchips included analysis of bulk density along a moisture gradient and particle size, particle density, wood composition, and hydraulic property testing. In situ dry bulk densities based on the entire volume of the new bioreactors (206-224 kg/m3) were similar to values from previous lab-scale studies. In situ estimates for woodchips at the bottom of aged bioreactors (22-mo. to 6-y) were unexpectedly low (120-166 kg/m3), given that these woodchips would presumably be the most compacted. These low moisture-content corrected dry bulk densities were influenced by high moisture contents in situ (>70% wet basis). The impacts of particle size and particle density on bulk density were somewhat mixed across the dataset, but in general, smaller woodchips had higher dry bulk densities than larger, and several woodchips sourced from the bottom of bioreactors had low particle densities. Although dry bulk densities in the zone of flow in bioreactors in the field were shown to be relatively low, the resulting permeability coefficients under those packing conditions did not differ from those of the original woodchips. The LiDAR-based volume estimation method was the most practical for large-scale, full-size evaluations and allowed high precision with small features (e.g., vertical reactor edges, drainage fittings). Keywords: Compaction, Cone penetrometer, Drainable porosity, LiDAR, Moisture content, Survey.

Influence of metabolism and microbiology on organic micropollutants biotransformation in anoxic heterotrophic reactors.

There is scarce information about the biotransformation of organic micropollutants (OMPs) under anoxic conditions. In this study, a heterotrophic denitrifying bioreactor was set up to study the fate of several OMPs from metabolic and microbiological points of view. Primary metabolic activity was increased by adding progressively higher nitrogen loading rates during the operation (from 0.075 to 0.4gN-NO3- L-1 d-1), which resulted in an important shift in the microbial population from a specialized biomass to a more diverse community. Such a change provoked a significant increase in the removal efficiency of erythromycin (ERY), roxithromycin (ROX) and bisphenol-A (BPA), and some bacterial taxa, such as Rhodoplanes, were identified as possible indicators related to the biodegradation of these compounds. The increasing primary metabolic activity in the reactor did not enhance the OMP-specific removal rates, suggesting that the bacterial composition is more influential than cometabolism.

Flow analysis and hydraulic performance of denitrifying bioreactors under different carbon dosing treatments

Denitrifying bioreactors are an effective approach for removing nitrate from a variety of non-point wastewater sources, including agricultural tile drainage. However, compared to alternate mitigation approaches such as constructed wetlands, nitrate removal in bioreactors may decline with time and low temperature, resulting in poor long-term nitrate removal rates. To address the low nitrate removal rates in bioreactors, the addition of an external carbon source has been found to be an effective method for enhancing and maintaining nitrate removal rates. While carbon dosing has led to a significant improvement in nitrate removal, some of the possible adverse effects of carbon dosing, such as clogging and reduction in hydraulic efficiency, remain unknown and need to be investigated. Using observations from both field and mesocosm trials, we compared the hydraulic performance of bioreactors with and without carbon dosing. The pilot-scale field bioreactor (58 m3 total woodchip volume, 25 m3 saturated volume, referred to as field bioreactor in this work) treated drainage water from a paddock of a dairy farm. The bioreactor received an exogenous carbon dose of 8% methanol (v/v) at 10 mL min−1 and 5 mL min−1 in the 2020 and 2021 drainage seasons, respectively. The field bioreactor had a statistically higher hydraulic conductivity in 2018 when not carbon-dosed of 4601 m day−1, reducing to 1600 m day−1 in 2021 which was the second year of carbon dosing. Field observations could not establish whether the addition of liquid carbon could affect the bioreactor's internal hydraulics performance, such as actual hydraulic retention time (AHRT), despite a significant decline in hydraulic conductivity in the field bioreactor. Separate experiments on replicated bioreactor mesocosms were conducted to investigate the effects of carbon dosing on the internal hydraulic parameters of bioreactors. These mesocosm bioreactors had previously been used to study the long-term effects of methanol dosing on bioreactor performance, such as nitrate removal under steady-state conditions. The mesocosm and field bioreactors shared some characteristics, such as the use of methanol as an external carbon source, but the mesocosm experiments were hydrologically controlled contrary to the field bioreactor's transient operating conditions. We found that methanol dosing in either carbon or nitrate limiting conditions had no significant effects (p-value >0.05) on internal hydraulic parameters (e.g., effective utilization of media) when compared to control bioreactors. The present study offers insight into the long-term hydraulic performance of bioreactors and may help develop small-footprint bioreactors that incorporate external carbon dosing.

Constant carbon dosing of a pilot-scale denitrifying bioreactor to improve nitrate removal from agricultural tile drainage

Denitrifying bioreactors are effective tools for removing nitrate from agricultural drainage water. However, as woodchips age with time, a shortage of labile carbon supply limits nitrate removal by microbial denitrification when high nitrate pulses occur in drainage waters. In this study, we investigated the potential of methanol dosing at a constant rate to increase nitrate removal rates in a 58 m3 pilot-scale bioreactor (25 m3 saturated volume) installed on a dairy farm for two consecutive drainage seasons. The drainage water in the bioreactor had a mean hydraulic retention time (HRT) of 12.7 days and 13.5 days in the 2020 and 2021 drainage seasons. With 14.4 L of methanol solution (8% v/v) added per day, the seasonal nitrate removal rates were 8.6 g N m−3 d−1 in 2020 and 5.1 g N m−3 d−1 in 2021 when the methanol dosing rate was halved. Both rates (2020 and 2021) were enhanced as compared to seasonal rates of 0.67–1.60 g N m−3 d−1 in previous years (2017 and 2018) when the bioreactor was not dosed. When there were very large pulses of nitrate into the bioreactor, which exhausted added methanol, nitrate was observed at concentrations above limiting ranges (> 3 mg N L−1) at the outlet on several occasions in 2021. Cumulative nitrate load reductions of 1859 g N and 1620 g N occurred in 2020 and 2021, respectively, resulting in overall nitrate removal efficiencies of 85 and 73%, respectively.Methanol concentrations decreased by order of magnitude along the bioreactor length, from mean inlet concentrations of 327 mg CH3OH-C L−1 in 2020 (higher dosing rate) to concentrations of <50 mg CH3OH-C L−1 at the outlet. The mean methanol removal rates of 106 g CH3OH-C m−3 d−1 in 2020 and 109 g CH3OH-C m−3 d−1 in 2021. A 90% (2020) and 100% (2021) overall methanol removal efficiency was calculated. With methanol dosing, sulfate removal occurred in the bioreactor, with an average sulfate removal rate of 8.5 g SO42−-S m−3 d−1 in 2020 and 0.5 g SO42−-S m−3 d−1 in 2021. This work demonstrated that methanol additions to bioreactors could enhance denitrification rates even when nitrate was limiting without considerable losses of methanol being released to the receiving waters.

Denitrifying bioreactor woodchip sourcing guidance based on physical and hydraulic properties

Denitrifying bioreactors using woodchips reduce nitrate loads in agricultural outflows, but there is a lack of practical guidance for woodchip selection from a hydraulic design perspective. The objectives of this study were to develop relationships between particle size, porosity, bulk density, and saturated hydraulic conductivity (Ksat) for a range of commonly available woodchip types to improve woodchip selection guidance and default design model values. Twenty woodchip types from across the US Midwest had their sizes quantified using both sieve analysis and manual axis measurements. Bulk and particle densities and porosity of the twenty types were measured using relatively easy “jar tests” and a selected eight types had bulk density determined across four compaction levels in larger permeameters. Saturated hydraulic conductivity was determined for six types each at three compaction levels. Mean conductivities generally ranged from 3.1 to 7.4 to 0.51–1.8 cm/s for uncompacted and highly compacted woodchips, respectively, and this work newly documented maximum limits of woodchip compaction occurred generally at bulk densities of 190 to 260 kg/m3. Woodchip types with D50 in the 13.5–16.8 mm range had predictable and relatively consistent drainable porosity and Ksat values across bulk densities, facilitating the development of predictive models (R2 ≥ 0.51; p < 0.0001). Even so, Ksat values were highly variable both within and between woodchip types, especially at the lowest compaction level, which creates challenges for precisely estimating this term for design models. Woodchip types with D50 > 12 mm and D90 > 26 mm with uniformity coefficients of 2–3.1 that were chip-shaped (length: width ratio < ∼3.5) were recommended for standardized denitrifying bioreactor designs.

Paired denitrifying bioreactors with wide orientation for increased drainage flow capacity

Denitrifying bioreactors are a conservation drainage practice for reducing nitrate loads in subsurface agricultural drainage. Bioreactor hydraulic capacity is limited by cross-sectional area perpendicular to flow through the woodchip bed, with excess bypass flow untreated. Paired bioreactors with wide orientations were built in 2017 in Illinois, USA, to treat drainage from a relatively large 29 ha field. The paired design consisted of: a larger, Main bioreactor (LWD: 6.1 × 18.3 × 0.9 m) for treating base flow, and 2) a smaller, Booster bioreactor (7.8 × 13.1 × 0.9 m) receiving bypass flow from the Main bioreactor during periods of high flow. Over three years of monitoring, the paired bioreactor captured 84–92% of the annual drainage discharge which demonstrated an expanded cross-sectional area could improve bioreactor flow capture, even for a large drainage area. However, the paired bioreactors removed 6–28% of the annual N load leaving the field (1.8–5.6 kg N ha−1 removed; 52–161 kg N), which was not a notable improvement compared to bioreactors treating smaller drainage areas. The design operated as intended at low annual flow-weighted hydraulic retention times (HRTs) of usually ≤2 h, but these short HRTs ultimately limited bioreactor nitrate removal efficiency. Daily HRTs of <2 h often resulted in nitrate flushing. The Main bioreactor had higher hydraulic loading as intended and was responsible for the majority of flow captured in each year although not always the most nitrate mass removal. The Booster bioreactor provided better nitrate removal than the Main at HRTs of 3.0–11.9 h, possibly due to its drying cycles which may have liberated more available carbon. This new design approach tested at the field-scale illustrated tradeoffs between greater flow capacity (via increased bioreactor width) and longer HRT (via increased length), given a consistent bioreactor surface footprint.

First Demonstration of Nitrate Reduction Using Woodchip Bioreactor Technology at a Small Community Wastewater Treatment Plant

Eutrophication can be accelerated by excess amounts of reactive Nitrogen (Nr) entering aquatic ecosystems. Historically, the circa 1960 Bolton Wastewater Treatment Plant, Warren County, New York (USA), discharged plant effluent for final polishing to natural sand infiltration beds, which entered the groundwater and then tributaries to Lake George. The absence of a denitrification unit process at the Bolton facility resulted in the construction of a woodchip bioreactor and a corresponding demonstration project to evaluate denitrification of plant effluent prior to sand bed discharge. This Denitrifying Bioreactor (DNBR) installation was the first real time, in-situ application of this “green technology” for a small wastewater treatment plant world-wide. The Bolton DNBR reduced nitrate-nitrogen concentrations in the tertiary effluent by 38% when compared with untreated tertiary effluent. Here we show that wastewater denitrification using this passive, environmentally compatible technology offers a low-cost, effective tool for small community wastewater treatment plants where excess Nr is problematic. Combined with diligent plant operator attention, this innovative treatment should move beyond concept into full scale field applications for other small community wastewater treatment plants globally, using lessons learned at the Bolton facility.

Effect of Biochar Amendment in Woodchip Denitrifying Bioreactors for Nitrate and Phosphate Removal in Tile Drainage Flow

Biochar has received increased attention in environmental applications in recent years. Therefore, three pilot-scale denitrifying bioreactors, one filled with woodchips only and the other two enriched with 10% and 20% by volume of biochar from deciduous wood, were tested under field conditions for the removal of nitrate (NO3-N) and phosphate (PO4-P) from tile drainage water in Lithuania over a 3-year period. The experiment showed the possibility to improve NO3-N removal by incorporating 20% biochar into woodchips. Compared to the woodchips only and woodchips amended with 10% biochar, the NO3-N removal effect was particularly higher at temperatures below 10.0 °C. The results also revealed that woodchips alone can be a suitable medium for PO4-P removal, while the amendment of biochar to woodchips (regardless of 10% or 20%) can lead to large releases of PO4-P and other elements. Due to the potential adverse effects, the use of biochar in woodchip bioreactors has proven to be very limited and complicated. The experiment highlighted the need to determine the retention capacity of biochar for relevant substances depending on the feedstock and its physical and chemical properties before using it in denitrifying bioreactors.

Initial Validation of a Replicated Field-scale Denitrifying Bioreactor Facility in a Boreal Environment

Denitrifying bioreactor technology, where a solid carbon source (woodchips) acts as a reactive medium to intercept agricultural tile drainage water, has been successfully used to convert N (NO3-) to di-nitrogen (N2) gas. Four replicated field-scale (24 m long x 3 m wide x 1 m deep), bioreactors were built and operated at the St. John’s Research and Development Centre and were successful at removing a notable amount of nitrate (N) from agricultural subsurface drainage water. The objective of this study was to investigate the internal flow dynamics of one of these field-scale bioreactors as a proxy for the others. The hydraulic conditions in the bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention time (HRT) and a highly dispersed residence time distribution, which was revealed by a sodium chloride tracer test. To measure the internal flow a known amount of sodium chloride (salt) was added to water before it entered the bioreactor and samples were collected in 30 minutes intervals. The temperature of water samples taken from the inlet, outlet, and sample ports ranged from 14.5 to 18.4°C With a N removal of 62 to 66% the bioreactor proved at the same time to be very effective under the boreal environment of Newfoundland and Labrador (NL). Mass removal rate (MRR) was calculated to evaluate the performance of woodchip bioreactor. The average MRR was 3.87 gm-3day-1 and the highest was 7.19 gm-3day-1 respectively. The theoretical retention time was calculated to be approximately 10.64 h based on the active flow volume, the length and depth of the system. In comparison the observed retention was 18.18 h

Design flow and nitrate removal evaluation of a wide denitrifying bioreactor with baffles

A relatively wide denitrifying woodchip bioreactor (LWD: 16.8 × 10.7 × 0.91 m) was installed with two flow-routing baffles in Illinois, USA with the design objectives of minimizing inflow manifold-related flow restrictions while maintaining both a relatively consistent footprint and nitrate-removal performance compared to conventional designs. This wide design did not improve the percentage of flow from the field that was treated (generally about 40% of flow treated) compared to other sites. However, the Richards-Baker flashiness index (0.74 to 0.91) and probability of exceedance evaluations indicated site drainage was flashy which might have accounted for the lower than expected performance. Nitrate removal was consistent with other bioreactors despite the new design ideas (22–24% edge of field N loss reduction; 0.72 to 1.3 g N removed m−3 d−1). Within the context of the need for accelerated conservation drainage practice adoption across the US Midwest, trying to account for flow uncertainties like flashiness with site-specific designs could be a bottleneck for bioreactor design and implementation. It may be worthwhile to explore possible benefits of a simpler design approach (e.g. standardized plug-and-play designs) since there are many factors at play in bioreactor performance.

Effect of Wheat-Straw Biochar on Nitrate Removal in Laboratory Denitrifying Bioreactors

Denitrifying bioreactors are an innovative nitrate-reduction strategy that reduces NO3-N with carbon substrate. In this study, application of biochar as a carbon substrate in DNBRs and the effect of biochar application rate and bioreactor heights on nitrate and ammonium concentration in the laboratory were investigated. Four mixtures of soil–biochar–wheat straw content of B0 = 0 (control treatment), B1 = 10, B2 = 20, and B3 = 30 percent of biochar were used. Also, to evaluate the effect of bioreactors heights, four heights 30, 60, 90, and 120 cm were used. The results showed that the nitrate concentration removal for control, B1, B2, and B3 treatment was 74.5, 81, 86.4, and 90.6% and biochar application rate, and bioreactor height have a significant effect on NO3-N removal and ammonium concentration. The results also showed that NO3-N removal and ammonium concentration increased with time. The effluent pH value of bioreactors does not have any particular trend during the experiment.

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.

Denitrifying Woodchip Bioreactor Leachate Tannic Acid and True Color: Lab and Field Studies

HighlightsOak leached more tannic acid, true color, and chemical oxygen demand (COD) than ash and mixed hardwood chips.The factors became similar (tannic acid, COD) or below stream levels (true color) after flushing.Eleven site-years of field bioreactor data showed decreasing tannic acid and true color over time.Post-startup tannic acid was lower in bioreactor outflow than in area streams.True color did not appear to be a reliable indicator of leachate tannic acid at low concentrations.Abstract. Woodchips have been a preferred denitrifying bioreactor medium to date, but concerns about potential harmful effects of tannins in the leachate have precluded the use of oak chips in many installations. A study was conducted to compare the suitability of oak (genus Quercus) woodchips as a denitrifying bioreactor medium relative to other types of woodchips, both in lab leachate tests and in the context of observed bioreactor leaching in the field. Assessment measures included the content of tannic acid and other compounds in the leachate, as well as leachate color, which can often be high during startup. An 84-day leaching test using rectangular bioreactor cells filled with either oak (Quercus rubra), ash (Fraxinus spp. L.), or a generic hardwood blend showed that oak initially leached higher concentrations of tannic acid, true color, and chemical oxygen demand (COD) than the other two media. The significant differences in leached concentrations among the three wood types were eliminated after a finite leaching period. Tannic acid and true color in 11 site-years of field bioreactor outflow data generally decreased over time, except following a dry period when one of the bioreactors received no drainage inflow for more than two months. The lab and field results indicated the capability of woodchip bioreactors to flush at least these two analytes to ambient stream levels. True color did not appear to be the best parameter for estimating the tannin content of woodchip leachate due to discrepancies at low concentrations. Mass normalized tannic acid leaching ranged from 0.03 to approximately 40 mg tannic acid g-1 woodchip across the lab and field assessments. Oak initially leached more tannic acid, color, and COD than the other wood types, but the eventual similarity among the wood types after flushing with a sufficient number of pore volumes meant that any potentially negative environmental impacts would likely be limited to the startup period or possibly after dry periods. Oak initially eluted higher mean total nitrogen (TN) concentrations than the other wood types, but the treatments were not significantly different by day 3, indicating that biological N removal was not significantly inhibited, even with high concentrations of tannic acid. Keywords: Chemical oxygen demand, Oak, Tannin, Water quality, Wood leachate.

Bacteria and virus removal in denitrifying bioreactors: Effects of media type and age

Denitrifying bioreactors are simple, low-cost ecotechnologies designed to reduce nitrate (NO3−) present in septic tank effluent and drainage water. Recent studies indicate that, in addition to significant reduction in NO3− loads, these systems are also able to remove microbial contaminants from municipal wastewater. However, the removal of microbial contaminants in denitrifying bioreactors remains poorly characterised and factors that control removal in denitrifying bioreactors remain unexplored. In this study, the removal efficiency of faecal indicator bacteria Escherichia coli (E. coli) and total coliforms (TC) as a model for bacterial pathogens and F-specific RNA bacteriophage (FRNA bacteriophage) as a model for viruses was assessed for mesocosm-scale (∼700 L) bioreactors receiving municipal wastewater. Systems were filled with two different slow-release carbon sources: woodchip and coconut husk. The effect of media age on attenuation of microbial contaminants was assessed by comparing the performance of 8-year old systems with equivalent newly constructed woodchip and coconut husk bioreactors. Additionally, removal performance of these carbon substrates was compared to that of gravel, a non-carbon substrate commonly used in subsurface flow (SSF) constructed wetlands. Substantial reduction of E. coli, TC and FRNA bacteriophage from primary treated municipal wastewater was achieved in all bioreactors. Mean annual log10 removal efficiencies were similar between microbial indicators ranging from 1.4 to 1.9 for TC, 1.3 to 1.8 for E. coli and 1.3 to 2.0 for FRNA bacteriophage. All denitrifying bioreactors showed consistent year-round performance and long-term performance which did not markedly change in the ninth year of operation. The woodchip or coconut husk bioreactors achieved microbial effluent quality within the same range of log10 removal rates achieved in gravel-based systems. This suggests that denitrifying bioreactors, as well as reducing N loads, can effectively reduce microbial contaminants in wastewater, providing a complimentary disinfection role. Further research is needed to increase understanding of factors affecting removal of microbial contaminants in denitrifying bioreactors to support design of these systems for microbial contaminant removal.