International Biochar Initiative Pyrolysis and Gasification of Biosolids to Produce Biochar

The need to dispose of human-generated waste streams is growing in line with the expansion of urban population centers. This is particularly true for the byproducts of wastewater treatment. According to the US EPA, there are over 7 million dry tons of biosolids (stabilized sewage sludge) produced per year in the US. In 2004, 49% of biosolids were beneficially used—primarily for agricultural land application—with most of the remainder either landfilled or incinerated (NEBRA 2007). Because biosolids have a high nutrient content, land application as a fertilizer substitute is an appealing management strategy. Yet concerns around nutrient run-off and contamination of waterways have led to tighter environmental controls making land application increasingly tenuous. Promising alternate management strategies exist but are in early stages of development. Pyrolysis and gasification—a continuum of thermochemical conversion processes—have been shown to minimize harmful air emissions, while producing energy and biochar, a carbon-rich solid material with beneficial soil health properties. This white paper briefly explores experiences of pyrolysis and gasification of biosolids as a waste management strategy, and research into biosolids biochar (BSB) as a soil amendment.