Woodchip Filters Research Articles

Efficient Low-Cost Anaerobic Treatment of Wastewater Using Biochar and Woodchip Filters

Access to improved sanitation is often lacking in many low-income countries, and approximately 90% of the sewage is discharged without treatment into receiving water bodies. The aim of this study was the development and evaluation of an efficient low-cost wastewater treatment system for developing countries. Biochar and woodchips, potential locally available and inexpensive materials, were used for anaerobic wastewater filtration and their suitability evaluated in comparison to gravel as a common reference material. Filters were fed with raw sewage from a municipal full-scale wastewater treatment plant in Germany at 22 °C room temperature with a hydraulic loading rate (HLR) of 0.05 m∙h−1. This resulted in a mean organic loading rate (OLR) of 252 gCOD∙m−3∙d−1 and a mean organic surface load of 456 gCOD∙m−2∙d−1. To determine the influence of different filter materials, the removal efficiency of chemical oxygen demand (COD), total organic carbon (TOC), turbidity, and faecal indicator bacteria (FIB) E. coli and enterococci were tested. It was found that COD (up to 90%), TOC (up to 80%), FIB (up to 1.7 log10-units), and turbidity (effluent turbidity below 35 NTU) could be significantly reduced. The findings of this study demonstrate the potential of anaerobic filters (AFs) for wastewater treatment in low-income countries to reduce water pollution and comprehensively improve water quality. The performance of biochar filters was significantly better over the entire experiment compared to woodchip and gravel filters with respect to COD, TOC, turbidity, and FIB removal, indicating the superior properties of biochar for wastewater treatment.

Nutrient biofilters in the Virginia Coastal Plain: Nitrogen removal, cost, and potential adoption pathways

Excess nonpoint source nutrient loss presents one of the most vexing water management challenges for water quality managers. Agriculture is the single largest contributor of nutrients to the Chesapeake Bay, and achieving nutrient reduction targets for agriculture will be costly. Biofilters offer new opportunities to reduce nutrient loads from artificially drained agricultural land. Nutrient biofilters consist of organic carbon (C) medium, typically woodchips, that when saturated with nitrogen (N)-enriched waters supports the activity of naturally occurring soil microorganisms that convert bioavailable N into N gases via denitrification. This study estimates the cost and N removal effectiveness for a biochar-amended woodchip biofilter draining a 10 ha (25 ac) field planted in a corn (<i>Zea mays</i> L.)–soy (<i>Glycine max</i> [L.] Merr.) rotation in eastern Virginia as well as for alternative design scenarios for biofilters ranging 25 to 150 m³ (883 to 5,297 ft³) with either woodchips alone or biochar-amended woodchip C substrates. Nitrogen removal effectiveness is estimated using modeled site-specific influent loads and N removal effectiveness estimates derived from experimental trials in a pilot scale system on the Delmarva Peninsula. This analysis estimates N removal costs as a function of biofilter size, which directly relates to residence time, per unit of N removed. Modeled N removal estimates over a five-year period (2009 to 2013) for five bed volumes range from 88 to 391 kg (194 to 862 lb) for the woodchip biofilters (21% to 95% removal) and 132 to 412 kg (291 to 908 lb) for the biochar-amended woodchip biofilters (32% to 100% removal) of the 412 kg total N load exported to the biofilters during the five-year period. The N removal costs range from US$15 to US$48 kg⁻¹ y⁻¹ (US$6.82 to US$21.82 lb⁻¹ yr⁻¹) for the woodchip biofilter and US$15 to US$33 kg⁻¹ y⁻¹ (US$6.82 to US$15 lb⁻¹ yr⁻¹) for biochar-amended woodchip filters. While biofilters are determined to be cost-effective for N removal compared to conventional agricultural best management practices, agricultural producers may be reluctant to voluntarily adopt biofilters because of the relatively high initial installation costs and the lack of direct incentive payments for pollutant removal effectiveness. Nutrient trading programs offer some potential to enhance adoption, but not in the immediate future.

Nitrogen Removal in Permeable Woodchip Filters Affected by Hydraulic Loading Rate and Woodchip Ratio.

Unregulated and event-driven agricultural tile drainage discharge poses several challenges that potentially limit the nitrate (NO) removal performance of woodchip-based wetlands constructed to intercept subsurface tile drain flows. Laboratory column tests were conducted to evaluate the biogeochemical response of mixed reactive media (woodchips-seashells and woodchips-Filtralite mixtures) at two woodchip ratios to changes in hydraulic loading rate (HLR). The tests involved continuous loading of aerated artificial drainage water spiked with NO-N and tritium (HO) breakthrough experiments. Flow-normalized NO reduction rates ranged from 0.35 to 3.97 g N m L, corresponding to N removal efficiencies of 5 to 64%, depending on HLR and filter mixtures. At high HLRs, oxic conditions prevailed in the woodchip filters, resulting in reduced N removal. At low HLRs, progressively lower pore-water velocities extended the period for consumption of terminal electron acceptors, increasing N removal. When increasing the content of mineral material, N removal declined, probably due to a lower denitrifying biomass at lower woodchip mass. The effect of woodchip ratios on solute transport characteristics was difficult to assess. However, woodchip media including a mineral fraction of crushed seashells demonstrated the highest N removal rates and efficiencies, most likely due to the alkalizing effect of the seashells. In conclusion, filter mixtures consisting of woodchips and seashells were the most effective material for N removal in subsurface flow-constructed wetlands treating agricultural drainage water.

Assessment of intermittently loaded woodchip and sand filters to treat dairy soiled water

Land application of dairy soiled water (DSW) is expensive relative to its nutrient replacement value. The use of aerobic filters is an effective alternative method of treatment and potentially allows the final effluent to be reused on the farm. Knowledge gaps exist concerning the optimal design and operation of filters for the treatment of DSW. To address this, 18 laboratory-scale filters, with depths of either 0.6 m or 1 m, were intermittently loaded with DSW over periods of up to 220 days to evaluate the impacts of depth (0.6 m versus 1 m), organic loading rates (OLRs) (50 versus 155 g COD m−2 d−1), and media type (woodchip versus sand) on organic, nutrient and suspended solids (SS) removals. The study found that media depth was important in contaminant removal in woodchip filters. Reductions of 78% chemical oxygen demand (COD), 95% SS, 85% total nitrogen (TN), 82% ammonium-nitrogen (NH4N), 50% total phosphorus (TP), and 54% dissolved reactive phosphorus (DRP) were measured in 1 m deep woodchip filters, which was greater than the reductions in 0.6 m deep woodchip filters. Woodchip filters also performed optimally when loaded at a high OLR (155 g COD m−2 d−1), although the removal mechanism was primarily physical (i.e. straining) as opposed to biological. When operated at the same OLR and when of the same depth, the sand filters had better COD removals (96%) than woodchip (74%), but there was no significant difference between them in the removal of SS and NH4N. However, the likelihood of clogging makes sand filters less desirable than woodchip filters. Using the optimal designs of both configurations, the filter area required per cow for a woodchip filter is more than four times less than for a sand filter. Therefore, this study found that woodchip filters are more economically and environmentally effective in the treatment of DSW than sand filters, and optimal performance may be achieved using woodchip filters with a depth of at least 1 m, operated at an OLR of 155 g COD m−2 d−1.

Suspended Sediment and Phosphorus Removal in a Woodchip Filter System Treating Agricultural Wash Water.

Woodchip filters have received attention in recent years for their ability to sustain denitrification activity across multiyear time frames. However, in some freshwater aquatic ecosystems, P rather than N is the nutrient considered most responsible for eutrophication. Previous studies have indicated that woodchip filters have limited ability to remove dissolved P, but in agricultural terrain, P export in watercourses is often dominated by particulate P (PP). Woodchip media, because of their high porosity and permeability and the surface roughness of the particles, could be effective for PP removal. In this study, we tested a woodchip filter for its ability to remove suspended sediment and associated PP at a farm in southern Ontario, Canada, where vegetable wash water with extremely high total suspended solids (TSS) was generated. The treatment system consisted of a 12.3-m concrete sedimentation tank and a slightly larger woodchip filter (16.1 m) installed in a subsurface trench. During 7 mo of full-scale operation, treating 10.8 m d, the filter system removed 71% of influent total P (TP) averaging 8.8 mg L and 99% of TSS averaging 5800 mg L, with most of the removal occurring in the tank and a lesser amount (6-16%) occurring in the woodchip filter. Almost all of the TP removal was associated with PP (91% removal) because dissolved P, averaging 1.5 mg L in the wash water, was little changed. Woodchip filters, when coupled with a solids settling tank, have the potential to provide high-capacity, low-maintenance treatment of suspended solids and associated particulate P in turbid waters.

Optimizing nitrate removal in woodchip beds treating aquaculture effluents

Nitrate is typically removed from aquaculture effluents using heterotrophic denitrification reactors. Heterotrophic denitrification reactors, however, require a constant input of readily available organic carbon (C) sources which limits their application in many aquaculture systems for practical and/or economic reasons.A potential alternative technology for removing nitrate currently applied for treating surface and drainage water is based on using wood by-products as a carbon source for denitrification.Using lab-scale horizontal-flow woodchip filters, the current study investigated the potential of optimizing woodchip reactors for treating aquaculture effluent. A central composite design (CCD) was applied to assess the effects of simultaneously changing the empty bed contact time (EBCTs of 5.0–15.0h; corresponding to theoretical hydraulic retention times of 3.3–9.9h) and bicarbonate (HCO3−) inlet concentration (0.50–1.59g HCO3−/l) on the removal rate of NO3−N, and additional organic and inorganic nutrients, in effluent deriving from an experimental recirculating aquaculture system (RAS).Volumetric NO3−N removal rates ranged from 5.20±0.02 to 8.96±0.19g/m3/day and were enhanced by adding bicarbonate, suggesting that parts of the removal was due to autotrophic denitrification. The highest N removal rate (8.96±0.05g/m3/day) was achieved at an EBCT and HCO3− combination of 15h and 1.59g HCO3−/l. Bicarbonate inlet concentration as a single factor had the strongest effect on N removal rates followed by the interaction with EBCT, and EBCT2 (quadratic term).The study thus indicates that woodchip beds may be applied and optimized for removing nitrate from aquaculture effluents. Statement of relevanceThis study is a relevant contribution to research in aquaculture as it presents an alternative method for removing nitrates from aquaculture effluents especially for less intensive fish farms. Furthermore, it shows how this method can be optimized to yield higher removal rates of nitrate.

An investigation into the removal of Salmonella and enteric indicator bacteria from the separated liquid fraction of raw or anaerobically digested pig manure using novel on-farm woodchip biofilters

The objective was to investigate the removal of Salmonella and enteric indicator bacteria from the liquid fraction of raw and anaerobically digested (AD) pig manure in woodchip biofilters over a 14week (98day) period. Antibiotic susceptible Salmonella Infantis was detected in one influent material (liquid fraction of raw manure) on two occasions but was not found in the effluent at any time point. Furthermore, mean coliform reductions of 56% were observed in the biofilters treating the liquid fraction of raw manure. However, a mean increase of 228% was found in those treating the liquid from AD manure, despite the fact that the microbial challenge to these biofilters was lower. In addition, relatively high coliform counts were still present in the effluent from both biofilter treatments, especially in the systems treating the liquid fraction of AD manure. However, findings for Escherichia coli and Enterococcus were more promising, with reductions observed for both treatments (10 and 18.5% for E. coli and 71 and 87% for Enterococcus). Moreover, E. coli and Enterococcus were at, or just above, the limit of detection in the final effluents. Overall, although, there are no microbial limits for discharge or washwaters, the woodchip filter effluent would appear safe for discharge to waterways or use on-farm as regards Salmonella, E. coli and Enterococcus but not coliform. In conclusion, woodchip biofilters offer potential as a low-cost sustainable novel treatment option for the removal of pathogens from the liquid fraction of pig manure.

Comparison of a Stratified and a Single-Layer Laboratory Sand Filter to Treat Dairy Soiled Water from a Farm-Scale Woodchip Filter

Washing-down parlours and standing areas, following milking on dairy farms, produce dairy soiled water (DSW) that contains variable concentrations of nutrients. Aerobic woodchip filters can remove organic matter, nutrients and suspended solids (SS) in DSW, but the effluent exiting the filters may have to be further treated before it is suitable for re-use for washing yard areas. The performance of a single-layer sand filter (SF) and a stratified SF, loaded at 20 L m−2 day−1, to polish effluent from a woodchip filter was investigated over 82 days. Average influent unfiltered chemical oxygen demand (CODT), total nitrogen (TN), ammonium–N (NH4–N), ortho-phosphorus (PO4–P) and SS concentrations of 1,991 ± 296, 163 ± 40, 42.3 ± 16.9, 27.2 ± 6.9 and 84 ± 30 mg L−1 were recorded. The single-layer SF decreased the influent concentration of CODT, TN, NH4–N, PO4–P and SS by 39, 36, 34, 58 and 52 %, respectively. Influent concentrations of CODT, TNT, NH4–N, PO4–P and SS were decreased by 56, 57, 41, 74 and 62 % in the stratified SF. The single-layer SF and the stratified SF were capable of reducing the influent concentration of total coliforms by 96 and 95 %, respectively. Although a limited amount of biomass accumulated in the uppermost layers of both SFs, organic and particulate matter deposition within both filters affected rates of nitrification. Both types of SFs produced final water quality in excess of the standards for re-use in the washing of milking parlours.

Evaluation of technologies for sequestering carbon in agricultural land by using organic filter underdrains

Technology for storing carbon in the subsoil of agricultural land using organic filter materials in underdrains was evaluated as an activity for sequestering CO2 to mitigate global warming. First, the quantity of carbon remaining in wood chips and rice husks in underdrains was determined over 11 years after construction. Moreover, the quantity of CO2 emissions from the construction of two underdrain types was calculated. Then, a survey was conducted to investigate the effect on greenhouse gas emissions of the filter material. The results indicate that greenhouse gas emissions would not increase. The quantity of storage carbon in the wood chip filter material of underdrains during their 15-year service life was estimated to be 6.76 tCO2eq ha−1. Rice husks, in contrast, were found ineffective in storing carbon. Therefore, the selection of the filter material for underdrains is important. The value of storage carbon in the wood chip filter material is similar to the amount of carbon sequestered by no-till farming, which is now being implemented as a global warming countermeasure based on soil management in agricultural land.

Performance of a woodchip filter to treat dairy soiled water

The milking process on dairy farms produces wastewaters, known as dairy soiled waters (DSW), which contain variable concentrations of nutrients. The most common method of disposal is by application to land. However, this practise can result in the pollution of nearby receiving water bodies. A laboratory study, comprising two sets of 0.5m, 1m and 1.5m-deep filters loaded at two loading rates, examined the performance of woodchip filters in treating DSW. The filters comprised de-barked Sitka spruce (Picea sitchensis) woodchips. Dried DSW was reconstituted to 1% and 3% suspended solids (SS) concentrations and was applied at 28L/m(2).d to the surface of the filters at loading rates of 280gSS/m(2).d and 840gSS/m(2).d, respectively. Filters were loaded for a maximum of 277 days. The filters achieved substantial decreases in SS (>99%), chemical oxygen demand (COD) (>97%) and total nitrogen (TN) (>89%). The dominant treatment mechanism appears to be physical filtration, but sorption and biological uptake likely also play a role. As the filters are aerobic, mineralisation and nitrification occur, but gaseous N losses are probably not significant. Woodchip shows potential as a filter medium for treating DSW, significantly decreasing the concentrations of SS, COD and TN.

On-farm treatment of dairy soiled water using aerobic woodchip filters

Dairy soiled water (DSW) is produced on dairy farms through the washing-down of milking parlours and holding areas, and is generally applied to land. However, there is a risk of nutrient loss to surface and ground waters from land application. The aim of this study was to use aerobic woodchip filters to remove organic matter, suspended solids (SS) and nutrients from DSW. This novel treatment method would allow the re-use of the final effluent from the woodchip filters to wash down yards, thereby reducing water usage and environmental risks associated with land spreading. Three replicate 100 m 2 farm-scale woodchip filters, each 1 m deep, were constructed and operated to treat DSW from 300 cows over an 11-month study duration. The filters were loaded at a hydraulic loading rate of 30 L m −2 d −1, applied in four doses through a network of pipes on the filter surface. Average influent concentrations of chemical oxygen demand (COD), SS and total nitrogen (TN) of 5750 ± 1441 mg L −1, 602 ± 303 mg L −1 and 357 ± 100 mg L −1, respectively, were reduced by 66, 86 and 57% in the filters. Effluent nutrient concentrations remained relatively stable over the study period, indicating the effectiveness of the filter despite increasing and/or fluctuating influent concentrations. Woodchip filters are a low cost, minimal maintenance treatment system, using a renewable resource that can be easily integrated into existing farm infrastructure.

Treatment of dairy soiled washwater using a woodchip filter

Treatment of dairy soiled washwater using a woodchip filter