Phosphorus removal in denitrifying woodchip bioreactors varies by wood type and water chemistry

Ana Paula Sanchez Bustamante-Bailon,Laura E Christianson,Andrew Margenot,Richard A C Cooke

doi:10.1007/s11356-021-15835-w

Ana Paula Sanchez Bustamante-Bailon, Laura E Christianson + Show 2 more

Open Access

https://doi.org/10.1007/s11356-021-15835-w

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Abstract

Denitrifying woodchip bioreactors are a practical nitrogen (N) mitigation technology but evaluating the potential for bioreactor phosphorus (P) removal is highly relevant given that (1) agricultural runoff often contains N and P, (2) very low P concentrations cause eutrophication, and (3) there are few options for removing dissolved P once it is in runoff. A series of batch tests evaluated P removal by woodchips that naturally contained a range of metals known to sorb P and then three design and environmental factors (water matrix, particle size, initial dissolved reactive phosphorus (DRP) concentration). Woodchips with the highest aluminum and iron content provided the most dissolved P removal (13±2.5 mg DRP removed/kg woodchip). However, poplar woodchips, which had low metals content, provided the second highest removal (12±0.4 mg/kg) when they were tested with P-dosed river water which had a relatively complex water matrix. Chemical P sorption due to woodchip elements may be possible, but it is likely one of a variety of P removal mechanisms in real-world bioreactor settings. Scaling the results indicated bioreactors could remove 0.40 to 13 g DRP/ha. Woodchip bioreactor dissolved P removal will likely be small in magnitude, but any such contribution is an added-value benefit of this denitrifying technology.

Highlights

Denitrifying woodchip bioreactors, woodchip-filled trenches where maintenance of anoxic conditions enhance denitrification, are a simple on-farm technology promoted for nitratenitrogen (NO3-N) treatment in agricultural drainage waters and effluents worldwide (Schipper et al 2010)
The 84% dissolved reactive P (DRP) concentration reduction by the field bioreactor woodchips was significantly greater than the concentration changes caused by the white oak and cypress (p = 0.006 and 0.005, respectively, for pairwise multiple comparison Tukey tests) and was not significantly different from the four other treatments
The significant differences in DRP concentrations over the batch tests demonstrated the possibility for woodchips to influence P dynamics in a bioreactor, both positively and negatively

Summary

Introduction

Denitrifying woodchip bioreactors, woodchip-filled trenches where maintenance of anoxic conditions enhance denitrification, are a simple on-farm technology promoted for nitratenitrogen (NO3-N) treatment in agricultural drainage waters and effluents worldwide (Schipper et al 2010). Woodchips can obviously act as a physical filter to trap sediment and particulate P (Choudhury et al 2016; Sharrer et al 2016), but beyond this, woodchip bioreactors have provided dissolved reactive P (DRP) removal ranging from 0.01 to 0.88 g DRP/m3-day (Dougherty 2018; Hua et al 2016; Sharrer et al 2016; von Ahnen et al 2018) with Weigelhofer and Hein (2015) reporting removal as high as 166 g phosphate-P/m3-day for straw-filled bioreactors. Dissolved P load and concentration reductions by woodchips across bioreactor literature have been as high as >50% (Dougherty 2018; Hua et al 2016; Husk et al 2018), though most reported reductions are more moderate (≈10%; Goodwin et al 2015; Warneke et al 2011; Zoski et al 2013). While DRP removal has been observed across a variety of studies, P removal in woodchip bioreactors has not been systematically tested

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