Biochar as a partial replacement of peat in pesticide-degrading biomixtures formulated with different soil types

Abstract

Biochar is a source of carbon with physico-chemical and biological properties that allow it to promote microbial growth, to absorb moisture and to improve the adsorption and/or degradation of pesticides. We evaluated the effect of biochar as a partial replacement of commercial peat in the pesticide-degrading biomixtures of a biopurification system known as biobed. Each biomixture was prepared with one type of soil (clay, trumao and sandy), straw, peat and biochar in different volumetric proportions. In each biomixture, the residual pesticide (atrazine, carbendazim, chlorpyrifos, isoproturon, iprodione and diazinon) concentration, the pH, and the levels of organic carbon (OC) and total Kjeldahl nitrogen (TKN) were measured at the beginning (day 0) and at the end (day 40) of the pesticide degradation assay. The obtained results demonstrated that at day 0, the pH of the biomixtures, regardless of soil type, increased incrementally with increasing amounts of biochar, whereas the OC and TKN values remain constant. At the end of the pesticide degradation assay, changes were observed in the biomixtures that demonstrated differences among their pesticide degradation abilities. In general, pesticide degradation was higher in the control biomixtures (without biochar) than in biomixtures prepared with biochar. An exception was the pesticide iprodione, which presented a highest degradation efficicency when biochar was included in the biomixture. Although the use of biochar as a replacement of peat in the biomixtures did not significantly improve pesticide degradation, a decrease in the initial residual concentration of the pesticides was observed. Therefore, biochar may represent an interesting material to replace peat in biomixtures designed to degrade and/or adsorb pesticides.