SORPTION OF NUTRIENTS AND HEAVY METALS BY BIOCHAR AMENDED POTTING SOIL AS A VEHICLE FOR CLIMATE CHANGE

Biochar is produced from the pyrolysis of biomass under anoxic conditions. High porosity, cation exchange capacity, and charge density allow biochar to remove heavy metals and nutrients from solution and retain them. Batch experiments were conducted by dissolving biochars derived from different parent material in ultrapure water overnight. X-Ray Fluorescence analysis revealed 90-100% loss of Fe, Mn, Ti, Zn and Pb in two of three biochars. Oak biochar had almost no leaching by ultrapure water and was chosen for nutrient retention tests.

Potting soils were amended with finely crushed and sieved (<250µm) biochar in a 1:1 ratio by volume. The mixture was packed into chromatography columns and leached top-down with 100ppm of nutrient-enriched ultrapure water via peristaltic pump, to simulate water percolating through topsoil. Eluate was collected periodically and nutrient concentrations were measured via ion chromatography. Preliminary results have been inconsistent except for nitrate sorption by "Miracle-Gro Organic Choice" which displayed 93-100% sorption for the first 1-2hrs and 61% at 3hrs. Saturation occurred at about 4hrs. Percentage sorption of nitrate by biochar amended soil decreased exponentially with time.

Improved nutrient retention in topsoil means potentially better crop yield. This requires faster uptake of carbon dioxide and water required for growth via photosynthesis. Many studies measure biochar’s ability to cause increase in plant height, volume, size and number of fruits. These results do not offer an effective way to quantify growth rate and thus carbon uptake. Later stages of this study will measure CO2 uptake to assess biochar’s ability to sequester carbon via increased photosynthesis. Column leaching experiments will examine biochar’s ability to leach and retain of heavy metals Cd, Pb, Cu and Zn which can inhibit photosynthesis rates.

The carbon sequestration abilities of biochar are further enhanced by the fact that plants grown in biochar amended soil can be pyrolyzed to create new nutrient rich biochar, thus creating a carbon sink by limiting the release of carbon by oxidation death and decay. The most challenging task will be to generate biochar from a readily available source in an economical fashion, which can restrain contaminants and prevent leaching of nutrients in the soil.