Effect of Biochar Amendment in Woodchip Denitrifying Bioreactors for Nitrate and Phosphate Removal in Tile Drainage Flow

Rasa Vismontienė,Arvydas Povilaitis

doi:10.3390/w13202883

Abstract

Biochar has received increased attention in environmental applications in recent years. Therefore, three pilot-scale denitrifying bioreactors, one filled with woodchips only and the other two enriched with 10% and 20% by volume of biochar from deciduous wood, were tested under field conditions for the removal of nitrate (NO3-N) and phosphate (PO4-P) from tile drainage water in Lithuania over a 3-year period. The experiment showed the possibility to improve NO3-N removal by incorporating 20% biochar into woodchips. Compared to the woodchips only and woodchips amended with 10% biochar, the NO3-N removal effect was particularly higher at temperatures below 10.0 °C. The results also revealed that woodchips alone can be a suitable medium for PO4-P removal, while the amendment of biochar to woodchips (regardless of 10% or 20%) can lead to large releases of PO4-P and other elements. Due to the potential adverse effects, the use of biochar in woodchip bioreactors has proven to be very limited and complicated. The experiment highlighted the need to determine the retention capacity of biochar for relevant substances depending on the feedstock and its physical and chemical properties before using it in denitrifying bioreactors.

Highlights

To maintain high crop production, modern agriculture uses large amounts of mineral fertilizers to create more favorable conditions for plant growth
To assess the efficiency of NO3-N and PO4-P removal in tile drainage flow, three pilotscale denitrifying bioreactors were built at the field laboratory of Agriculture Academy at VMU in Kaunas, Lithuania
Compared to the pure woodchips and the woodchips mixed with 10% biochar, the NO3-N removal effect was more pronounced at low temperatures

Summary

Introduction

To maintain high crop production, modern agriculture uses large amounts of mineral fertilizers to create more favorable conditions for plant growth. This practice can result in increased levels of nutrients (i.e., inorganic forms of N and P) leaching from the soil and rapidly entering surface waters through tile drainage systems [1,2]. With the rapidly increasing human population, agriculture is expected to become even more intense with likely larger negative impacts on water environments [7]. The core of the bioreactor is a drainage trench filled with woodchips through which the tile flow is directed. Under anaerobic conditions, chemically bound oxygen is used by heterotrophic bacteria to oxidize carbon, while NO3-N is reduced to N gases [12,13]

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Conclusion