Performance of a Woodchip Bioreactor for the Treatment of Nitrate-Laden Agricultural Drainage Water in Northeastern Germany

Abstract

Reactive barriers, such as denitrifying bioreactors, have been identified as a clean-upoption for nutrient-laden agriculture runoff. Here we tested a 20 m long, 3.75 m wide and 2.2 mdeep woodchip bioreactor receiving tile drainage water from a 5.2 ha field site, aiming at testing thehydraulic functioning of a dual-inlet system and quantifying its impact on nutrient loads (nitrogen,reactive phosphorus, organic carbon) in a region with a drainage season taking place in thehydrological winter (November to April). The hydraulic conditions in the dual-inlet bioreactorsystem developed differently than expected; asymmetric flow rates led to long average hydraulicretention times and a highly dispersed residence time distribution, which was revealed by abromide tracer test. With a nitrate load reduction of 51 to 90% over three drainage seasons, thewoodchip bioreactor proved at the same time to be very effective under the winter conditions ofnortheastern Germany. The bioreactor turned from an orthophosphate source in the first year ofoperation into an orthophosphate sink in the second and third year, which was not expected becauseof anoxic conditions (favorable for denitrification) prevailing within the woodchips. Besides anefficient nutrient retention, the woodchip bioreactor contributed to the total organic carbon load ofreceiving waters, which impairs the overall positive role of bioreactors within intensivelyagriculturally used landscapes. We consider this promising low-maintenance biotechnologyparticularly suitable for single drainage pipes with high discharge and high nitrate concentrations.

Low temperature Moving Bed Bioreactor denitrification as mitigation measure to reduce agricultural nitrate losses

“…These removal efficiencies achieved during the last 63 days of the drainage season are comparable with or even higher than other available denitrification technologies to mitigate nitrate. For example, Gosch et al (2020) reported similar nitrate removal efficiencies in a woodchip bioreactor, i.e., varying between 51% and 90%, together with the release of nitrite in the first month of operation (up to 10.8 mg NO 2 -N/L). A system combining a surface-flow constructed wetland with a woodchip bioreactor showed a lower removal of Total Nitrogen, i.e., 8% and 51% (Pugliese et al, 2020b).…”

“…Constructed wetlands, mimicking natural wetlands and their water self-cleaning processes, are proposed as a potential solution to the problem of agricultural drainage (Borin and Tocchetto, 2007;Kleimeier et al, 2018). Also, woodchip bioreactors have gained interest as an alternative measure (Gosch et al, 2020;Hartz et al, 2017;Hoover et al, 2016;Randall and Mulla, 2001). Furthermore, controlled drainage systems, saturated buffer zones and integrated buffer zones are commonly applied (Carstensen et al, 2020).…”

Pharmaceutical Attenuation Differs within Woodchip-Based Lignocellulose Bioreactors across Nitrate- and Sulfate-Reducing Conditions

“…In turn, this respiration can be applied toward the sustainable treatment of trace organic contaminants. Passive infiltration designs that deploy woodchips have been implemented in tile drains to facilitate nitrate attenuation in agricultural runoff . The targeted respiration of sulfate, which is pervasive in surface waters and certain mining-impaired waters, has been applied in reactors designed to immobilize the otherwise challenging and problematic metals such as zinc and copper through the formation of metal sulfides and other immobilization processes but less so for pharmaceutical attenuation.…”

Cost effectiveness, nitrogen and phosphorus removal in field-based woodchip bioreactors treating agricultural drainage water

“…For two 100 m 3 woodchip bioreactors, Carstensen et al (2019) found that 67-85% of the annual loading of particulate P was retained, but in some years the bioreactors acted as a sink and in other years as a source of phosphate. Thus, Gosch et al (2020) found that a bioreactor (76.5 m 3 ) turned from acting as a phosphate source in the rst year of operation to a phosphate sink in the second and third year.…”