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Nitrogen (N) and phosphorus (P) losses to surface and coastal waters are still critically high across Europe and globally. Measures to mitigate and reduce these losses are being implemented both at the cultivated land surface and at the edge-of-fields. Woodchip bioreactors represent a new alternative in Denmark for treating agricultural drainage wa...
Citations
... This was consistent with the maximum subsided depths of 25 to 38 cm measured at four bioreactors ranging from 1.5 to 2.6 years old (Fig. 1b). Plauborg et al. (2023) assumed an additional 50 cm of woodchips would be required every six years for purposes of their cost modeling, and while they did not report subsidence, that value was within the range of other maximums documented here (Fig. 1b). ...
... Despite the many possible benefits of pumping surface water into an edge-of-field bioreactor, pumping adds system complexity and cost (Hartfiel et al., 2024;Plauborg et al., 2023). Bioreactors treating subsurface drainage are often in remote locations which can make it difficult to provide the practical day-to-day maintenance necessary for pumping set-ups. ...
... For example, a bioreactor treatment system in Iowa that was notably over-designed (i.e., too big) provided an ideal testing location for increased hydraulic loading via pumping from the nearby creek (Hartfiel et al., 2023a(Hartfiel et al., , 2023b. In Denmark, a pump was necessary at a large, three-chamber bioreactor because the inlet supply drain was found to be deeper than expected (Plauborg et al., 2023). Additional assessments of different pumping configurations and bioreactor designs would help better contextualize reasonable expectations of benefits and drawbacks at these more advanced bioreactors. ...
... Wastewater treatment applications tend to meet these criteria. Centralized treatment of large drainage areas in Denmark (120 ha treatment area; Plauborg et al., 2023) as well as pumped drainage outlets may also meet these criteria. ...
... The ambient and mid-height temperatures inside the WBRs increased by 2.5°C after the injection treatments but evaluated from a Q 10 temperature coefficient of 2.15 [54,55], this 2.5°C temperature increase could account for at most 35% of the increase in NRR across the six bioreactors (Table S5). Phosphorous is a key element that may limit N transformation rates in natural ecosystems [56,57] and the supply of soluble PO 4 -P in the PBS may have stimulated denitrification, although fresh woodchips are known to be a source of total P for at least 2-3 months in field-based WBRs [58]. The P concentration in the PBS (380 mg L −1 ) was four orders of magnitude higher than in the inlet water (0.028 mg L −1 ), but the potential effect on NRR remains speculative. ...
Woodchip bioreactors (WBRs) are biological systems designed to prevent excess nitrate (NO3-) leaching from agricultural fields to aquatic ecosystems. Nitrate is removed by microbial denitrification, but the enzyme-mediated process slows down at cold temperatures (<10°C), where NO3- removal in WBRs can be less than 20%. We studied the use of bacterial bioaugmentation in replicated test-scale WBRs (∼0.1 m3) as an environmental technology to increase NO3- removal at cold temperatures. Nitrate removal rates increased following injection of a nitrate-reducing inoculum (Pseudomonas proteolytica and Klebsiella sp.), but the effect disappeared within a week and was reproduced in control WBRs by injection of sterile medium (phosphate buffer saline). Metagenome analyses showed a shift in the bacterial community composition after bioaugmentation in the planktonic phase of the woodchip reactors, but not in the solid phase (woodchip matrix). Only in the planktonic phase, Pseudomonas and Klebsiella increased their relative abundance as monitored by 16S rRNA gene sequences. In addition, an increased abundance of genes related to NO3- transformation after bacterial inoculation was observed in the metagenomic sequences. After one week, bacterial community composition became similar to its initial state, indicating resilience of the WBR microbial communities. We conclude that improved inoculation methods are needed to unlock the potential of bioaugmentation to increase NO3- removal at cold temperatures and make it a relevant technology for practical use at field-scale.
... The samples studied in this work originated from the surface and waterlogged subsur face of a WBR in Dundelum, Haderslev, Denmark ( Fig. 2A), where nitrate-rich agricultural drainage water passes through a bed of woodchips (12). A schematic of the WBR can be found in Fig. S8. ...
... The WBR at Dundelum (544 m 2 ) was established in 2018 with a vertical (top-down) flow design and the filter matrix consisted of 100% willow woodchips (Ny Vraa I/S, DK, chip sizes 0.4-6 cm). The wet filter matrix was 1.2 m deep and was overlain by an unsaturated woodchip layer of 30-50 cm to allow for methane (CH 4 ) oxidation (12). In 2019-2020, total water flow to the WBR was 170 m 3 m −3 yr −1 with a total N load of 1,702 g N m −3 yr −1 and a total N removal efficiency of 46% (12). ...
... The wet filter matrix was 1.2 m deep and was overlain by an unsaturated woodchip layer of 30-50 cm to allow for methane (CH 4 ) oxidation (12). In 2019-2020, total water flow to the WBR was 170 m 3 m −3 yr −1 with a total N load of 1,702 g N m −3 yr −1 and a total N removal efficiency of 46% (12). ...
Freshwater ecosystems can be largely affected by neighboring agriculture fields where potential fertilizer nitrate run-off may leach into surrounding water bodies. To counteract this eutrophic driver, farmers in certain areas are utilizing denitrifying woodchip bioreactors (WBRs) in which a consortium of microorganisms convert the nitrate into nitrogen gases in anoxia, fueled by the degradation of lignocellulose. Polysaccharide-degrading strategies have been well described for various aerobic and anaerobic systems, including the use of carbohydrate-active enzymes, utilization of lytic polysaccharide monooxygenases (LPMOs) and other redox enzymes, as well as the use of cellulosomes and polysaccharide utilization loci (PULs). However, for denitrifying microorganisms, the lignocellulose-degrading strategies remain largely unknown. Here, we have applied a combination of enrichment techniques, gas measurements, multi-omics approaches, and amplicon sequencing of fungal ITS and procaryotic 16S rRNA genes to identify microbial drivers for lignocellulose transformation in woodchip bioreactors and their active enzymes. Our findings highlight a microbial community enriched for (ligno)cellulose-degrading denitrifiers with key players from the taxa Giesbergeria, Cellulomonas, Azonexus, and UBA5070 (Fibrobacterota). A wide substrate specificity is observed among the many expressed carbohydrate-active enzymes (CAZymes) including PULs from Bacteroidetes. This suggests a broad degradation of lignocellulose subfractions, including enzymes with auxiliary activities whose functionality is still puzzling under strict anaerobic conditions.
IMPORTANCE
Freshwater ecosystems face significant threats from agricultural runoff, which can lead to eutrophication and subsequent degradation of water quality. One solution to mitigate this issue is using denitrifying woodchip bioreactors (WBRs), where microorganisms convert nitrate into nitrogen gases utilizing lignocellulose as a carbon source. Despite the well-documented polysaccharide-degrading strategies in various systems, the mechanisms employed by denitrifying microorganisms in WBRs remain largely unexplored. This study fills a critical knowledge gap by revealing the degrading strategies of denitrifying microbial communities in WBRs. By integrating state-of-the-art techniques, we have identified key microbial drivers including Giesbergeria, Cellulomonas, Azonexus, and UBA5070 (Fibrobacterota) playing significant roles in lignocellulose transformation and showcasing a broad substrate specificity and complex metabolic capability. Our findings advance the understanding of microbial ecology in WBRs and by revealing the enzymatic activities, this research may inform efforts to improve water quality, protect aquatic ecosystems, and reduce greenhouse gas emissions from WBRs.
... Our study does not allow us to do a detailed cost analysis since the WFBs were constructed at the laboratory and the experiment was run at a university greenhouse facility with locally collected plant species. Considering only the expenses of construction materials, the cost for 1m 2 of WFBs was around $37. Woodchips bioreactor treating agricultural drainage water estimated 1.66 cm annual loss of woodchips layer (Plauborg et al., 2023). Accordingly, our WFBs should last more than six years if no woodchips are added. ...
Constructed wetlands and constructed floating wetlands are widely used for nitrogen (N) removal from surface water to combat eutrophication in freshwaters. Two main N removal pathways in freshwaters are plant biomass N uptake and denitrification, i.e. transformation of nitrate (NO3-) to nitrous oxide (N2O) or nitrogen gas (N2) by different microbes possessing nirK, nirS, nosZI, and nosZII genes. In this study, we tested woodchips-based floating beds (WFBs) as a nature-based and environment-friendly method to remove nitrate-nitrogen (NO3-N) from water. Moreover, we tested whether WFBs could support the growth of three selected plant species and the abundance of microbes on plant roots and woodchips as a proxy for WFBs’ denitrification potential. We conducted a greenhouse experiment for 90 days and measured NO3-N removal rates from water in WFBs mesocosms during five sampling occasions. Plant biomass production, biomass N uptake, and plant morphology related to N uptake and abundance of denitrifying organisms were measured at the end of the experiment. NO3-N removal rates were 29.17 ± 11.07, 28.18 ± 12.62, 25.28 ± 9.90, and 22.16 ± 7.79 mg L–1 d–1 m–2 (mean ± standard deviation) in Glyceria maxima, Juncus effusus, Filipendula ulmaria, and unplanted WFBs treatments, respectively for whole experimental period. N content in above- and belowground biomass of studied species ranged between 0.98 – 1.15 and 1.09 – 1.28 (% dry weight), respectively. Plant relative biomass production was 215 ± 61, 67 ± 18, and 7 ± 17 (% dry weight) for G. maxima, J. effusus and F. ulmaria, respectively. Denitrifiers were detected both on plant roots and woodchips, indicating WFBs’ denitrification potential. Our study highlights that WFBs could be applied to enhance NO3-N removal from surface water through plant biomass uptake and denitrification processes. Future studies should consider the long-term in situ application of WFBs for NO3-N removal from water.
... Two higher estimates for bioreactors have been developed by DeBoe et al. (2017) at $15 to $40/kg N-y and by Law et al. (2023) at $13 to $88/kg N-y. Most recently, Plauborg et al. (2023) reported cost efficiencies for the first two years of five bioreactors in Denmark averaged $50/kg N-y but the drainage treatment areas (45-129 ha) were larger than those typical for bioreactors in the US Midwest. Improved bioreactor cost efficiencies in modelling studies occurred when bioreactors were scaled to treat greater hydraulic loads (Easton et al., 2019) and when the frequency of woodchip replacement was reduced (Lepine et al., 2018). ...
... Design work by a private firm could add 50-100% of the installation cost, averaging an additional ≈$7500 per bioreactor (L. . This was higher than the advisory costs described by Plauborg et al. (2023) for large bioreactors in Denmark which were approximately 20% of the total construction cost at $1500 to $4300 per site. Batching a number of practice implementation sites together (e.g., the "Batch and Build" approach in Kult, 2022) can help leverage an economy of scale for private engineering firms to bid on such projects. ...
... This relationship was not significant in the current work (m 3 volume versus EAC R 2 : 0.23; p value: 0.28; excluding private farm #3 in the model due to free labor and fill media). Additionally, Plauborg et al. (2023) recently reported that establishment costs of large bioreactors in Denmark were independent of the bioreactor size. ...
Freshwater ecosystems can be largely affected by neighboring agriculture fields where potential fertilizer nitrate run-off may leach into surrounding water bodies. To counteract this eutrophic driver, farmers in certain areas are utilizing denitrifying woodchip bioreactors (WBRs) in which a consortium of microorganisms convert the nitrate into nitrogen-gases in anoxia, fueled by the degradation of lignocellulose. Polysaccharide-degrading strategies have been well-described for various aerobic and anaerobic systems, including the use of carbohydrate-active enzymes, utilization of lytic polysaccharide monooxygenases (LPMOs) and other redox enzymes, as well as the use of cellulosomes and polysaccharide utilization loci (PULs). However, for denitrifying microorganisms, the lignocellulose-degrading strategies remain largely unknown. Here, we have applied a combination of enrichment techniques, gas measurements, multi-omics approaches, and amplicon sequencing of fungal ITS and procaryotic 16S rRNA genes to identify microbial drivers for lignocellulose transformation in woodchip bioreactors, and their active enzymes. Our findings highlight a microbial community enriched for lignocellulose-degrading denitrifiers with key players from Giesbergeria, Cellulomonas, Azonexus, and UBA5070 (Fibrobacterota). A wide substrate specificity is observed among the many expressed carbohydrate active enzymes (CAZymes) including PULs from Bacteroidetes. This suggests a broad degradation of lignocellulose subfractions, even including enzymes with auxiliary activities whose functionality is still puzzling under strict anaerobic conditions.
Understanding the world through a lens of phosphorus (P), as Dr. Andrew Sharpley aimed to do, adds a deeper dimension for water quality work in the heavily tile‐drained US Midwest where nitrate is often the nutrient of biggest concern. Denitrifying woodchip bioreactors reduce nitrate pollution in drainage water, but dissolved phosphorus leached from the organic fill is a possible pollution tradeoff. Recent work by Dr. Sharpley and others defined such tradeoffs as strategic decisions in which a negative outcome is accepted with prior knowledge of the risk. In this vein, we assessed 23 site‐years from full‐size bioreactors in Illinois to determine if bioreactors were a net dissolved reactive phosphorus (DRP) source and, if so, to determine flow‐related correlation agents (1904 sample events; 10 bioreactors). DRP was removed across the bioreactors in 15 of 23 site‐years. The 23 site‐years provided a median annual DRP removal efficiency of 12% and a median annual DRP removal rate of 7.1 mg DRP/m ³ bioreactor per day, but the ranges of all removal metrics overlapped zero. The highest daily bioreactor DRP removal rates occurred with high inflow concentrations and under low hydraulic retention times (i.e., under higher loading). Dr. Sharpley was one of the first to explore losses of DRP in subsurface drainage and performed decades of useful applied studies that inspired approaches to management of P loss on both drained and undrained land. We seek to honor this legacy with this practical study of the DRP benefits and tradeoffs of denitrifying bioreactors.
