Lysimeter Experiments to Determine the Ability of Soil to Reduce Concentrations of BOD, Available P and Inorganic N in Dirty Water

Abstract

Lysimeter experiments were conducted to determine the ability of different soils to reduce levels of biochemical oxygen demand (BOD) and concentrations of molybdate reactive phosphorus (MRP) and ammonium-N (NH4 +-N) in dirty water and the impact of applications on nitrate leaching. An additional experiment investigated the effect of dirty water components on leaching quality. This information is required to assess the potential risk of dirty water applications on polluting groundwater and to assess the use of such soils in the development of treatment systems for dirty water. Intact and disturbed soil lysimeters, 0.5 and 1m deep were constructed from four soils; a coarse free-draining sandy loam, a sandy loam over soft sandstone, a calcareous silty clay over chalk and a sandy loam over granite. For the coarse free-draining sandy loam, lysimeters were also constructed from disturbed soil with and without the addition of lime, to assess if this could increase phosphorus immobilisation. Levels of BOD and concentrations of MRP, NH4 +-N and nitrate (NO3 − -N) of leachates were measured following dirty water applications at 2 and 8 mm day−1 under laboratory conditions. Under the daily 2mm application, all soils were effective at treating dirty water, reducing concentrations of BOD, MRP and NH4 +- N by ≥ 98% but NO3 −-N concentrations increased up to 80 mg l−1 from the 0.5 m deep lysimeters of the sandy loam over granite. Soils were less effective at reducing levels of BOD, MRP and NH4 +-N at the 8 mm daily rate of application, with maximum NO3 − -N concentrations of leachates of 200 mg l−1 from disturbed soils.