Biochar for Nutrient Recapture From Dairy Wastewater: Phosphate Recovery.

Sorption capacity of biochar for pesticides and other organic compounds has been studied in the recent years, but there is very little research on its sorption capacity for agronomic nutrients. Use of biochar for recapturing excess nutrients from agricultural pollutants such as dairy wastewater can offer a solution for controlling the pollution while improving soil productivity and carbon sequestration. In this project, we aim to determine the sorption capacity of biochar for three major nutrients in dairy wastewater namely nitrogen (N), phosphorous (P), and potassium (K). Here, we report the phosphate sorption-desorption study. The nutrient concentrations in this study were chosen to represent the range of concentrations commonly observed in dairy wastewater (0-50ppm for PO₄). The amount of phosphate adsorbed increased with increasing initial solution concentration of PO₄, and up to 1.06 mg phosphate /g of biochar was adsorbed at the highest concentration. Most of the phosphate sorbed by biochar (82-97%) was strongly associated with biochar and could not be desorbed under the same solution conditions. We also found that biochar released small amount of phosphate to soil solution (up to 0.005 mg/g of biochar). Similarly, each gram of biochar in our experiment released up to 3.44 mg K, 0.03 mg Na, 0.13 mg Mg, 0.01 mg NO₃, 0.13 mg NO₂, 0.27 mg SO₄ and 0.16 mg Br to soil solution. Our findings suggest that biochar can offer an excellent alternative for recovering the excess phosphate from dairy wastewater, which can later be applied to poor quality soils to enhance fertility and carbon sequestration potential of these soils.