EFFECTIVENESS OF RICE HULL BIOCHAR ON THE ADSORPTION OF SOLUBLE PHOSPHORUS IN A BATCH EQUILIBRIUM STUDY

Phosphorus is an essential nutrient for agriculture and a contributor to impaired water quality as it leaves agricultural fields. In northwest Ohio, drainage tiles aid in removal of excess field water, allowing phosphorus to enter drainage ditches without passing through buffer strips. This research seeks to demonstrate that the addition of a phosphorus adsorbing material into agricultural soil would act to remove soluble phosphorus, holding on to the nutrient until it can be taken up by growing plants. We focused on using biochar made from rice hulls (SynTerra Energy) as the sorbent and hypothesized that the quantity of phosphorus and rate with which it is adsorbed would increase in the presence of biochar.

To test this hypothesis, a US EPA batch equilibrium study will be conducted. Silty clay soil, common to northwest Ohio, and the rice hull biochar will be treated with calcium chloride and 1.0 mg/L potassium phosphate solution. These mixtures will be shaken for 24 hours and then tested for the concentration of phosphorus in solution at equilibrium (P_max in mg phosphorus per kg adsorbing material) using the US EPA ascorbic acid. A kinetics study will also be conducted to determine the phosphorus adsorption rate (mg phosphorus per L per hour) of the rice hull biochar. The biochar and the silty clay will be treated with the calcium chloride and potassium phosphate solution and then shaken for 5 minutes, 30 minutes, 1 hour and then 4 hour intervals until equilibrium is reached. The concentration of phosphorus in solution will be determined using US EPA ascorbic acid method. The P_max and adsorption rate will determine how much biochar needs to be integrated into a silty clay soil to adsorb phosphorus from agricultural fields. Preliminary adsorption results show that biochar can adsorb 1.4-2.3 ug phosphorus per gram more than silty clay soil. The goal of this experiment is to determine if biochar stops soluble phosphorus from entering waterways adjacent to agricultural fields.