Evaluating the nutrient removal efficiency of biochar in a small stream- A case study of Västankvarn farm

Abstract

The study evaluated the nutrient removal efficiency of a two-stage biochar filtration in an agricultural stream at Västankvarn Gård in Finland. The removal efficiency was calculated as the total nitrogen( TN) and total phosphorus( TP) removal through adsorption by biochar. The system consisted of a sac biochar filter placed across the stream and a downstream box biochar filter. Water samples were collected once every two weeks over a four-month period and analyzed for TN and TP. The results showed extremely high nutrient loads throughout the monitoring period. Statistical analysis indicated no significant difference between influent and effluent concentrations for either nutrient, demonstrating that the biochar filters did not achieve measurable nutrient reduction. Factors contributing to the poor performance included extremely high nutrient concentrations, limited water–biochar contact, sediment clogging, rapid flow-through, and the use of unmodified biochar. A moderate correlation between streamflow and nutrient concentrations showed that both high-flow events and continuous agricultural inputs influence water quality. Although the system was ineffective in nutrient removal, the study provides an important foundation for future field research. The findings suggest that integrated treatment approaches and continuous monitoring are essential for managing nutrient pollution in agricultural streams that ultimately discharge into the Baltic Sea.