Pumping surface water from a ditch into a denitrifying woodchip bioreactor could improve nitrate-nitrogen (N) removal by minimizing flow variabilities such as early flow cessation at a given subsurface drainage outlet and flashy drainage hydrographs. Few field-scale subsurface drainage bioreactors with pumping configurations have been assessed. Such evaluations would help better bound reasonable expectations of the benefits and drawbacks at these more advanced bioreactors. An underloaded "ditch diversion" bioreactor constructed in 2018 in Illinois, USA (LW: 4.6 x 9.1 m), was retrofitted with a solar-powered pumping system in 2021 and was then monitored for a 29-d period in 2022 and a 93-d period in 2023. The pumped bioreactor achieved N removal rates averaging 7.5 and 5.2 g N/m3-d and N removal efficiencies of 50 and 61% for the monitoring periods in 2022 and 2023, respectively. Pumping generally improved the bioreactor's performance compared to the same monitoring windows from the historic (non-pumped) 2019-2021 periods. Regression analysis indicated the addition of a pump slightly improved N load removal compared to what might be expected for a conventional bioreactor. The somewhat unintended diurnal batch mode operation resulting from the solar-powered pumping system boosted water temperature in the overnight batches. Bioreactor performance can be improved with a pump, especially at underloaded sites, but the additional complexity and cost need to be carefully weighed.

Indirect greenhouse gas emissions are a major source of uncertainty in global inventories. The contribution of dissolved N2O (dN(2)O) to indirect emissions is poorly understood, especially considering losses of dissolved gases that stem from subsurface agricultural drainage in nitrogen (N)-intensive corn (Zea mays L.) systems. To better quantify the impacts of recommended management on drainage losses of nitrate (NO3-) and dissolved gases, water quality was monitored during the growing season at replicated drainage plots in Illinois, USA. Four treatments were tested: pre-plant N application (224 kg N/ha with 60 % fall + 40 % preplant); split-N application (224 kg N/ha with 40 % preplant + 60 % side-dress); split-N + cereal rye (Secale cereale L.) cover crop; and 0 N control (n = 4). Dissolved N2O concentrations ranged from < 8-58 g dN(2)O-N/L while dissolved methane was consistently low (<3 g CH4-C/L). Environmental factors (temperature, drainage hydrology, soil inorganic N status) and N application events influenced dN(2)O concentrations and losses. Cumulative dN(2)O and NO3- loads followed the same trend: pre-plant N > split N > split + cover crop > 0 N control. The split N + cover crop treatment had a significant reduction in both NO3- load and dN(2)O concentration compared to pre-plant N application, highlighting the effectiveness of integrated management practices in reducing N losses to the environment. Split-N alone, while less effective in reducing losses, improved corn yield and agronomic efficiency, achieving the second lowest emissions factor (EF5 g). Future research should explore the long-term impacts of these management practices on cumulative dissolved greenhouse gas emissions to better inform climate-smart strategies.

Conservation drainage practices can mitigate water quality impacts of subsurface drainage, but their potential for climate change mitigation remains poorly understood. We summarized processes by which tile-drained croplands impact climate and assessed potential of conservation drainage practices to alter emissions of the greenhouse gases nitrous oxide (N2O) and methane (CH4) and stocks of soil organic carbon (SOC), compared using carbon dioxide equivalents (CO2e). Controlled drainage, bioreactors, saturated buffers, and water quality wetlands can decrease nitrate leaching with little or no increase in on-site N2O emissions, thereby decreasing indirect N2O emissions that would otherwise occur from downstream waters. However, under some conditions, CH4 emissions from bioreactors and especially from wetlands can counteract climate benefits of decreased indirect N2O emissions. Drainage water recycling could potentially increase direct soil N2O emissions while decreasing indirect N2O emissions, but these impacts might be mitigated through sub-irrigation and increased drainage intensity. Many conservation drainage practices are unlikely to markedly increase SOC, aside from saturated buffers. Expressed relative to the area of cropland treated by a given practice, saturated buffers may have the largest climate mitigation potential of examined practices due to the combination of efficient nitrate removal with low N2O emissions, lower risk of CH4 emissions, and high potential for SOC accrual. In sum, available data suggest that several conservation drainage practices can plausibly contribute to climate change mitigation as well as water quality improvement, although more comprehensive studies are needed to better constrain their effectiveness.

Surface subsidence at denitrifying woodchip bioreactors treating subsurface drainage has been anecdotally noted but has not been consistently documented and is thus poorly understood. Subsidence is of concern due to safety and potential exacerbation of ponding within the bioreactor but could also indicate flow restrictions within the woodchip bed. This study used 3D light detection and ranging (LiDAR) surveying on handheld devices (iPhone 12 Pro, iPad Pro) to provide minimum estimates of surface subsidence at 17 full-size bioreactors across a range of ages (0.1 to 14 years). Bioreactors with woodchips extending to the surface subsided faster than bioreactors with soil covers with median subsidence rates over the entire surface of 7.3 and 1.0 cm/y, respectively. Maximum subsidence averaged 40 +/- 14 cm across all sites and tended to occur near the inflow manifold where subsidence could disproportionately impact hydraulic performance. Although these findings are limited to the bioreactors in the present evaluation and other sites may show different trends, it may be that subsidence is not reducible to aerobicity alone. Subsidence is not necessarily, on its own, the best individual indicator of the end of design life. In practice, checking for a consistent reduction in the amount of outflow over time is the best way to assess the need for a bioreactor woodchip recharge. Nevertheless, in this study, subsidence at full-size bioreactors was successfully approximated using a hand-held LiDAR device, and use of this method at additional sites is suggested, especially following bioreactor construction.

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/m3 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.

Although significant governmental investment has been provided to implement agricultural conservation practices (ACPs) for water quality improvement, eutrophication and hypoxia persist in coastal and fresh waters. A better understanding of the comparative effectiveness of ACPs is needed to improve environmental outcomes with the funding available. The objectives of this overview article are to (1) compare the performance and cost effectiveness among all the ACPs reviewed in both the first and second editions of the Special Collection and (2) present critical perspectives for researchers, policymakers, and funding entities seeking to improve water quality. The ten ACPs reviewed encompassed a range of goals, strategies, and landscape placement and varied widely in performance for their reduction of sediment, nitrogen (N), and phosphorus (P) and their cost-effectiveness. Three ACPs included performance measures for all three constituents: sediment, N, and P, whereas others focused only on N (nine ACPs) and/or P (six ACPs). The four ACPs that are considered "water management" practices: drainage water management, denitrifying bioreactor, saturated buffer, and constructed wetland were all effective in mitigating the effects of nutrients in subsurface drainage water and showed average nitrate-N load reductions of 40%-46%. In contrast, few practices were found effective in reducing dissolved P (DP) loss from agricultural fields. Four ACPs (residue and tillage management, conservation crop rotation, drainage water management, and nutrient management) demonstrated possible net economic benefits, while perspectives were provided for prioritizing financial assistance for other ACPs. Monitoring recommendations developed during the literature reviews highlighted the need for more long-term field-scale monitoring to better reflect multi-year climatic variability.

Adoption of edge-of-field conservation practices, such as denitrifying bioreactors, may be intrinsically linked to barriers associated with cost. However, most previous bioreactor cost efficiency assessments assumed values for either costs and/or nitrate removal. The objective of this work was to use actual construction costs as well as monitored nitrate removal to develop empirical cost efficiencies for eight full-size bioreactors in Illinois, USA. Capital construction costs were obtained via invoices or personal communications. A cash-flow discounting procedure was used to develop an equal annualized cost for each bioreactor assuming two media recharges over a 24-y planning horizon. These costs were combined with monitored nitrate removal based on one to six years of monitoring per site. Construction costs averaged $12,250 ± $7520 across the eight sites (or, $16,020 ± $9960 in 2023 price levels) but considering one of the sites was a paired bioreactor system, costs averaged $10,890 per bioreactor unit. Drainage treatment area-based cost averaged $132/ha-y and treatment area was strongly correlated with capital costs (R2 = 0.90; p = 0.001). The bioreactors averaged $108/m3 of woodchips and available federal government conservation programs could have offset an average of 70% of this cost. Monitored nitrate removal across 27 site-years resulted in a median of $33/kg N-y removed. This mass-based cost efficiency was higher than most previous assessments because the monitored nitrate removal for the study sites was lower than has been previously assumed or modeled. Future reporting about bioreactor recharge timing and cost will help guide assessment and planning. Water quality planning efforts should also consider the increasingly important engineering design costs, which were not included here. Suggested research and outreach to improve bioreactor cost efficiencies involves scaling the physical capacity of this technology for larger treatment areas, revisiting the use of low-cost non-standard fill media, and providing practical construction training.

Denitrifying woodchip bioreactors successfully remove nitrates from reverse osmosis desalinization brine. On-farm desalination plants only operate for several hours per day in batch mode, meaning bioreactors should also operate in batch cycles, although this type of bioreactor operation is relatively unstudied. This study compared two tests of three cycles of 24 h per week with two treatments each (Test 1 8 vs. 24 h, and Test 2 8 vs. 12 h). Cylindrical pilot-scale bioreactors were filled with 130 kg of citrus woodchips and an average of 322 L of brine. The results show that the treatments with longer saturation periods of 24 and 12 h exhibited higher removal rates under operational conditions (i.e., 8 h flooding based on a 24 h cycle) than the 8 h treatment. However, the nitrate removal rates of the 8 h treatment were higher under fill cycle conditions (i.e., 8 h flooding based on an 8 h cycle). Dissolved organic carbon liberated from the woodchips was greater in treatments with longer drying periods (i.e., treatments with shorter saturation periods). Batch bioreactors should be considered under applicable conditions to increase nitrate removal rates.

Nitrate (NO3-) removal in denitrifying bioreactors is influenced by flow, water chemistry, and design, but it is not known how these widely varying factors impact the production of nitrous oxide (N2O) or methane (CH4) across sites. Woodchip bioreactors link the hydrosphere and atmosphere in this respect, so five full-size bioreactors in Illinois, USA, were monitored for NO3-, N2O, and CH4 to better document where this water treatment technology resides along the pollution swapping to climate smart spectrum. Both surface fluxes and dissolved forms of N2O and CH4 were measured (n = 7-11 sampling campaigns per site) at bioreactors ranging from <1 to nearly 5 years old and treating subsurface drainage areas from between 6.9 and 29 ha. Across all sites, N2O surface and dissolved volumetric production rates averaged 1.0 ± 1.6 mg N2O-N/m3-d and 24 ± 62 mg dN2O-N/m3-d, respectively, and CH4 production rates averaged 6.0 ± 26 mg CH4-C/m3-d and 310 ± 520 mg dCH4-C/m3-d for surface and dissolved, respectively. However, N2O was consistently consumed at one bioreactor, and only three of the five sites produced notable CH4. Surface fluxes of CH4 were significantly reduced by the presence of a soil cover. Bioreactor denitrification was relatively efficient, with only 0.51 ± 3.5 % of removed nitrate emitted as N2O (n = 48). Modeled indirect N2O emissions factors were significantly lower when a bioreactor was present versus absent (EF5: 0.0055 versus 0.0062 kg N2O-N/kg NO3-N; p = 0.0011). While further greenhouse gas research on bioreactors is recommended, this should not be used as an excuse to slow adoption efforts. Bioreactors provide a practical option for voluntary water quality improvement in the heavily tile-drained US Midwest and elsewhere.

Pumped denitrification bioreactors are currently being assessed in the field to extend the use of traditional, subsurface drainage bioreactors. Pumped bioreactors for the treatment of drainage ditches, surface waters, and cisterns intercepting drainage were evaluated to provide a basis of the unit cost of bioreactor operation ($ kg NO3-N removed -1) under a variety of scenarios. The unit costs were modeled using a techno-economic analysis. The variables assessed in the analysis included nitrate removal rate, bioreactor lifespan, and operating periods, which were assumed. To evaluate the impact of these variables on the unit cost, a sensitivity analysis was conducted where one variable was adjusted (e.g., lifespan) while the other variables were kept the same as a traditional bioreactor. The cistern and supplemental surface water bioreactors were larger in size and had similar unit costs ranging from similar to$5 to $27 kg NO3-N removed -1 for all scenarios except for the low mass removal and worst -case scenarios. The smaller, ditch diversion bioreactor had unit costs in the best- and worst -case scenarios in the range of $24 to $619 kg NO3-N removed -1, respectively. A breakeven analysis indicated increasing the mass removal rate of the bioreactors and ensuring an operating period greater than 6 -months had the greatest impact on reducing the unit cost compared to a traditional bioreactor. Overall, the larger -scale surface water and cistern bioreactors had comparable, but slightly higher, unit costs than traditional bioreactors under most scenarios evaluated. This information can be used to optimize and inform of the potential of pumped bioreactor systems.

Few studies have addressed whether in-field practices to reduce nitrate-nitrogen (NO3-N) leaching might increase nitrous oxide (N2O) emissions, which could undermine attempts to mitigate agricultural N pollution. Over a 3-year period, we assessed the impacts of N application timing and cereal rye (Secale cereale L.) cover crop on subsurface drainage NO3-N leaching and N2O emissions to quantify changes in total N loss and corresponding social and environmental damage costs under continuous corn (Zea mays L.). While NO3-N losses were reduced by 37% with the combination of in-season split N application and cereal rye cover crop relative to pre-season N application, soil N2O emissions increased by 26%, highlighting a tradeoff between N loss pathways. As a result, total N losses and social and environmental damage costs from each system were not different. These results demonstrate the importance of addressing agricultural N pollution using a holistic framework accounting for the environmental and social risks of both NO3-N losses and N2O emissions.

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.

Highlights Saturated buffers redistribute tile drainage water below riparian buffers to reduce nitrate-nitrogen loading. NRCS Conservation Practice Standard 604 guides saturated buffer design in the USA. Annual edge-of-field nitrate-nitrogen loss reductions averaged 46 ± 24% and 9.4 ± 5.9 kg N/ha/y. Further research on design, siting, and mechanisms will enhance performance. Abstract. It is a pivotal time in the development of saturated buffers as a conservation drainage practice. Field data have demonstrated that this practice can effectively reduce nitrate loads in subsurface drainage. The compilation and assessment of current knowledge for this relatively new practice is timely to help identify future opportunities. This review summarizes the state of the science for saturated buffers in the US within the context of this special collection’s emphasis on performance and cost. Suggested research areas are identified to improve understanding of saturated buffer function and performance and to refine design processes and criteria to accelerate adoption. As currently designed, saturated buffers removed an average of 46 ± 24% (mean ± sd) of the N load that would have otherwise entered receiving waters (9.4 ± 5.9 kg N removed/ha-y; n = 30 site-years). Cost efficiencies, which generally trended around $3 to $5/kg N removed per year, were considered relatively efficient compared to similar nitrate removal practices (range: $1.20 to $9.20/kg N/y), with planning level costs between $25 and $66/ha treated/y. As adoption is scaled, engineering design costs need to be considered unless the design model can be simplified. Future research should refine design processes, management, and siting criteria to facilitate scaled adoption for water quality goals. Additional studies on nutrient cycling within saturated buffers are needed to fill gaps about nitrogen and phosphorus dynamics and the role of buffer vegetation. Saturated buffers have significant nitrate reduction potential for tile-drained landscapes, but design adaptations may be needed to facilitate adoption in varied landscapes. Keywords: Denitrification, Edge-of-Field, Nitrate, Nonpoint-source pollution, Saturated riparian buffer, Subsurface drainage, Tile drainage, Water quality.

Bromide (Br-) tracer tests are an important environmental monitoring method for assessing internal hydraulics in denitrifying woodchip bioreactors. The objective was to assess performance of relatively new high-frequency Br-sensing technology to help resolve challenges associated with sampling uncertainty and failure during bioreactor tracer tests. A Seametrics TempHionTM Bromide Logger was used to: (1) continuously log Br-concentrations at least every 30 s during three tracer tests in the field and (2) determine Br-concentrations in sample bottles post-hoc following eight tracer tests (sampling frequency in the field: every 2 to 300 min). Both were compared to lab-analyzed Br-concentrations. The sensor underreported Br-concentrations at two real-time tracer tests and overreported during one test, but this mainly impacted the tracer metric of percent recovery. While Br-sensor deployment during a tracer test is the ideal use of this convenient tool, use of the sensor post-hoc in collected bottles matched the lab-analyzed concentrations more closely based on the Root Mean Square Errors and the Mean Absolute Errors. The sensor's ability to collect large amounts of high-resolution con-centrations did not necessarily add value because most tracer metrics were interpolated with reasonable accuracy from the discrete lab-analyzed samples. The relatively continuous nature of the sensed concentrations, however, along with ease of deployment were important sensor benefits.

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.

Winter cover crops are widely promoted for multiple ecosystem services although nutrient leaching from the plant biomass and subsequent transport of those nutrients is possible after freeze-thaw events. The objective of this study was to determine the effect of freeze-thaw conditions on both runoff and drainage or leachate water quality from two common cover crops. Rainfall simulations were performed on packed columns (20 cm diam.; 56 cm length) that included triplicate combinations of cereal rye (Secale cereale L.), forage radish (Raphanus sativus L. var. longipinnatus), and bare soil and a heavy, light, and no freezing treatment. The two cover crops reduced runoff total suspended solids concentrations and nitrate leaching compared with a bare soil control, confirming many cover cropping benefits. The heavy freezing conditions (including two nights of <-15 degrees C) resulted in significantly higher total phosphorus and nitrate concentrations in both runoff and leachate from the cereal rye, which had been killed, compared with unfrozen cereal rye. Some of the conditions tested in this lab-scale study could be considered extreme (e.g., 10.1 cm h(-1) rainfall x 2 h, -15.7 degrees C) but these results nonetheless help demonstrate the importance of effective conservation practices for both surface and subsurface flows as well as for multiple water quality parameters in the face of increasing weather variability.

Agricultural phosphorus (P) loss, which is highly variable in space and time, has been studied using the hot spot/hot moment concept, but increasing the rigor of these assessments through a relatively newer "ecosystem control point" framework may help better target management practices that provide a disproportionate water quality benefit. Sixteen relatively large (0.85 ha) subsurface drainage plots in Illinois were used as individual observational units to assess dissolved reactive P (DRP) concentrations and losses within a given field over four study years. Three plot-months were identified as DRP control points (one export and two transport control points), where each plot-month contributed >10% of the annual DRP load from the field. These control points occurred on separate plots and in both the growing and nongrowing seasons but were likely related to agronomic P applications. Elevated soil test P, especially near a historic farmstead, and soil clay content were spatial drivers of P loss across the field. The nongrowing season was hypothesized to be the most significant period of P loss, but this was only documented in two of the four study years. A cereal rye (Secale cereale L.) cover crop did not significantly reduce DRP loss in any year, but there was also no evidence of increased drainage P losses due to freezing and thawing of the cover crop biomass. This work confirmed annual subsurface drainage DRP losses were agronomically small (<3% of P application rate), although the range of DRP concentrations relative to eutrophication criteria still demonstrated a potential for negative environmental impact. The control point concept may provide a new lens to view drainage DRP losses, but this framework should be refined through additional within-field studies because mechanisms of P export at this field were more nuanced than just the presence of tile drainage (i.e., a transport control point).

Woodchip drainable porosity and saturated hydraulic conductivity are important denitrifying bioreactor design parameters, but both strongly depend upon woodchip bulk density (or, how tightly woodchips are packed). These properties are relatively easy to estimate with packed columns in the lab, but woodchip bulk density in full-size bioreactors is relatively unknown. The overall objectives of this body of work were to (1) develop and test a proof-of-concept in situ woodchip bulk density estimation method and (2) use the new method to calculate bulk densities at two new and three old full-size bioreactors in Illinois, USA. Proof-of-concept testing involved excavating a pilot-scale bioreactor at the University of Illinois South Farms (Urbana, Illinois, USA) in three lifts and correcting the excavated woodchip masses by an appropriate moisture content. The volume of each of the three lifts was estimated using three methods: laser level surveying; lining the excavation with plastic and pumping the volume full through a flow meter; and capturing the excavation with iPhone LiDAR then using open-source volume software (SiteScape app, Cloud CompareTM). These three volume estimation methods are described in detail in this extended abstract proceedings paper. The survey method consistently resulted in the largest volume estimate for each lift, whereas the flow meter and LiDAR methods resulted in volumes within 3% of each other. Each method had limitations and advantages, but overall, cellphone-based LiDAR imaging plus open source volume software was an accurate and relatively easy volume estimation method for in situ bioreactor woodchip volumes.

Woodchip cost and sourcing availability may be barriers for denitrifying bioreactor implementation. This survey comparison of nutrient composition improves understanding of the spectrum of widely available wood media. Sixteen new woodchip types purchased from bulk suppliers and six chipped debris media sourced for free at the supplier were analyzed for carbon (C), nitrogen (N), phosphorus (P), cellulose, and lignin. Results were presented in context of woodchips harvested from saturated and unsaturated portions of operational bioreactors. The municipal debris was not significantly different from the bulk woodchips in C or cellulose concentrations (e.g., medians 46.7 vs 47.7 %C, respectively) but had significantly greater N and P concentrations (e.g., 0.45 vs 0.27 %N, respectively). The lower C:N, C:P, and lignin:N ratios of the chipped debris versus bulk supplier (e.g., C:N of 103 vs 177, respectively) highlighted that the role of macronutrients in supporting a diverse “bioreactor ecosystem” (e.g., decomposers who make C available) is not fully understood. Useful ranges of nutrient and fiber composition were provided for future modeling efforts.