Application of a full-scale wood gasification biochar as a soil improver to reduce organic pollutant leaching risks

BACKGROUND: The application of biochar to sandy loam soil to reduce leaching of three representative pollutants (a persistent hydrocarbon (phenanthrene; logKOW 4.46), a herbicide (isoproturon; logKOW 2.50), and an antibiotic (sulfamethazine; logKOW 0.28)) were investigated. The wood-derived biochar evaluated in our laboratory study was the solid co-product of a full-scale gasifier feeding a combined heat and power plant. The research aimed to demonstrate multiple environmental benefits with the innovative use of this biochar as a soil improver.

RESULTS: Batch sorption experiments indicated 5% biochar added to soil enhanced the partitioning coefficient (Kd) by factors of 2 for phenanthrene and 20 for both sulfamethazine and isoproturon. Column leaching experiments indicated a reduced porewater flow rate, up to 80% slower in the column amended with 5% biochar, and reduced pollutant leaching risks. Numerical models interlinked batch and column study observations.

CONCLUSION: (i) Biochar enhanced sorption for the hydrophobic pollutant phenanthrene, and also the less hydrophobic pollutants sulfamethazine and isoproturon; (ii) reduced porewater flow rates following biochar amendment gave rise to greater opportunity for pollutant-solid interaction; (iii) mixing with soil resulted in biochar fouling affecting pollutant partition, and (iv) irreversible retention of pollutants by the soil was an important mechanism affecting pollutant transport.