Nutrient reclamation in muddy creek : effects of used biochar water filters on soil fertility and plant growth

Abstract

This study investigates the efficacy of corn cob-based and waste wood-based biochar as recycled soil amendments following their utilization in nutrient-contaminated water filtration. Biochar, produced through the pyrolysis of high-carbon materials under controlled anaerobic conditions, possesses significant potential in agricultural applications due to its unique structure and high carbon content. Historically, biochar and activated charcoal have been employed for water purification, owing to their superior adsorptive properties, which effectively capture harmful nutrients and pathogenic microorganisms like Escherichia coli. The use of agricultural residues such as corn cobs for biochar feedstock mitigates deforestation and promotes sustainable agricultural practices in regions where tree biomass is scarce. This study comprised an open-air pot trial growing turnips with various types of biochar before and after they were used to filter a stream polluted with nitrogen and phosphorus. Two different sizes of biochar made from wood and one biochar made from corncobs were placed in the stream for one month to produce filterchar. They were then removed and incorporated into the soil for the pots at a rate of 5% by weight. At the end of the pot trial, soil samples from the pots were sent to a lab for testing, and a simple test of soil water holding capacity was conducted. There was no significant difference in plant growth between corn cob filterchar and the control; however, wood feedstock filterchar increased plant growth by 100% versus the unamended control and 180% versus the fresh biochar control. There was also a significant increase in soil water holding capacity with all the biochar treatments. The results of this study show the potential for spent biochar water filters to be recycled as plant fertilizer to create a closed loop system of nutrient reclamation. Wood based filterchar had a clear advantage over unused biochar and no treatment, but corn appeared to be less effective as a soil additive. More research is needed to assess the difference between feedstocks and the optimization of both filtration and soil amendment.