Heavy metal immobilization and microbial community abundance by vegetable waste and pine cone biochar of agricultural soils

- Vegetable waste and/or pine cone biochars immobilized Pb in soils.
- Vegetable waste biochars were most efficient in Pb immobilization.
- Torrefied biomass at 200 °C was most beneficial for soil microbial properties.
- Vegetable waste biochars were most efficient in improving soil chemical properties.
- Biochars were not effective for As immobilization in soils.

In order to determine the efficacy of vegetable waste and pine cone biochar for immobilization of metal/metalloid (lead and arsenic) and abundance of microbial community in different agricultural soils, we applied the biochar produced at two different temperatures to two contaminated soils. Biochar was produced by vegetable waste, pine cone, and their mixture (1:1 ww−1) at 200 °C (torrefied biomass) and 500 °C (biochar). Contaminated soils were incubated with 5% (ww−1) torrefied biomass or biochar. Sequential extraction, thermodynamic modeling, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy were used to evaluate the metal immobilization. Microbial communities were characterized by microbial fatty acid profiles and microbial activity was assessed by dehydrogenase activity. Vegetable waste and the mixture of vegetable waste and pine cone biochar exhibited greater ability for Pb immobilization than pine cone biochar and three torrefied biomass, and vegetable waste biochar was found to be most effective. However, torrefied biomass was most effective in increasing both microbial community and dehydrogenase activity. This study confirms that vegetable waste could be a vital biomass to produce biochar to immobilize Pb, and increase the microbial communities and enzyme activity in soils. Biomass and pyrolytic temperature were not found to be effective in the immobilization of As in this study.