Denitrification bioreactors application to order decrease nutrient losses via drained agricultural areas

Abstract

In order to improve the agricultural productivity, in the second half of the last century too wet soils in Lithuania were intensively drained by various means of agricultural drainage. The draining of agricultural areas by means of tile drainage – is an effective tool for the removal of excess moisture from the soil, but while entering into drains water leaches various nitrogen compounds (NO3 in particular) and other biogenic substances not assimilated by plants. The increased inflow of these substances into surface water bodies leads to their eutrophication. Research results indicate that the inflow of nitrogen from tile drained agricultural areas is a significant source of this pollution. The solution of the above mentioned problem using purely agronomic or severe economic activity limitation measures often does not reach the expected results due to the diversity of natural factors and changeable climatic conditions. It is obvious that technological innovations in tile drainage systems design and implementation are necessary. The first attempts to apply biotechnologies for the removal of nitrogen in tile drainage water were started in the US in 2001. The main idea of these technologies is based on the direct installation of bioreactors into the trenches of tile drainage systems. The performance of bioreactors is based on denitrification process which takes place under oxygen limited conditions in a specifically constructed trench filled with organic material where the tile water is diverted. At the time, the denitrifying bacteria utilize oxygen to process (oxidize) the available carbon and herewith converts nitrates being in a water into nitrogen gas. Laboratory scale tests have revealed, that during the analysed period of 235 days in bioreactor with deciduous woodchips the reduction of nitrate-nitrogen mass was reached 51% compared with the total amount observed in the inflow mass