Effect of pyrolysis conditions on Biochar properties with a focus on p fractionation

Transforming biosolids into biochar, through pyrolysis, could result in increased sustainability of waste management. Biosolids were collected at Mount Martha Water Recycling Plant, Melbourne. Influence of pyrolysis conditions (temperature, heating rate and residence time) on physico-chemical properties of biosolids, phosphorus fractionation and phosphorus forms were investigated. Twelve different biochar samples were produced at 400, 500 and 600 ºC, at two heating rates (5 and 20 ºC/min) and at two residence times (30 and 120 minutes). Biochar yield, pH, EC, elements (C, H, N, S and O) and BET surface area were analysed. Sequential extraction of P in biosolids and resultant biochar was done using Hedley method. Characterisation was completed with SEM images and results from 31P liquid state NMR. Increased temperatures would not only increase the alkalinity, decrease the electric conductivity and increase the adsorption capacity by increasing the surface area but also converted the readily available P to less available pool, so that this nutrient would be provided to soil slowly for long term if applied to soil. The results showed that temperature along with residence time and heating rate had a significant effect on the characteristics observed, therefore all these factors need to be carefully considered when preparing biochar for use as a soil amendment