Abstract:

I-landers (Belgium) is confronted with reactive phosphorus concentrations in streams and lakes which are three to four times higher than the 0.1 mg.I. ; environment limit set by the Water framework Directive. Much of the excessive P input in surface walers is derived from agriculture. Specifically, direct P input from artificial!} installed subsoil drainage pipes which shun-circuits the buffering capacity of the subsoil is suspected to be one of the major sources, hi this stud}, we aim to develop simple and cheap fillers that can be directly installed in the field to reduce P concentration from farm drain water. To achieve this, our specific objectives included; (1) determining the link between physical size distribution, bulk density and initial saturated hydraulic conductivity (Ksal) of tiller materials. (2) evaluating P removal efficiency} and durability of the filler materials. (3) determining the cumulative P sorption until saturation point and subsequently test P desorption efficiency and (4) assessing the performance of the fillers under a pilot field trial. I lie filter materials used were made of iron coaled sand and mixtures of iron coaled sand with glauconite. We determined Ksal using the constant head method and Darcy's equation, particle size distribution by sieving the materials through sieves of 0-5 mm mesh size and bulk density by measuring dry mass per volume. I lie method of Murph}' and Kiley was employed to analyse P using a spectrophotometer. We found that Ksal is linked to particle size distribution and bulk density by the equation; Ksal 0.00-1 ¦ 0.004*1)20 :0.010*1)10 - 3.013*TXP-06*BD. We also found that the filter with the highest P removal efficiency was Grobbendonk 90/10% with 98.84% P removal efficiency but had a lower saturated sorption capacity of 538.9 mg.kg1. The most durable filler was Grobbendonk 100% with P sorption capacity at breakthrough point of 942.2 mg P kg . We estimated that Grobbendonk 100% was able to realise 62% of its total sorption capacity in the laboratory experiment (942.2 mg P.kg ' out of 1500 mg P.kg1). Therefore, our best filler in terms of both efficiency and durability was Grobbendonk 100%. Similarly. our field trial identified Grobbendonk 100% as the best filler with estimated sorption capacity breakthrough point of 985 mg P.kg ‘. P removal efficiency of 74% and achieving (>5.7% of its estimated saturated sorption capacity. Based on these findings, we suggested that the experiment to determine the maximum sorption capacity of the filters be concluded so that we can compare the capacity of the fillers used in relation to their total capacity saturation. We also suggested that a comprehensive large scale field trial be conducted for best performing filters to validate both the laboratory and pilot trial results.