Improvements in physicochemical and nutrient properties of sewage sludge biochar by the co-pyrolysis with organic additives.

Abstract

Sewage sludge (SS) has been suggested as a priming feedstock for biochar production that could simultaneously benefit the solid waste reuse and agricultural production. However, effects of organic additive (OA) addition on nutrient characteristic of SS biochar (SSB) are still unclear. Herein, a series of SSBs were produced from the co-pyrolysis of SS and OA with different types [reed straw (RS), brewers' spent grain (BSG), and sawdust (SD)] and addition rates (10%, 30%, and 50%) at 350 and 700°C, respectively, and their basic physicochemical and nutrient properties were also analyzed. The results indicated that OA addition greatly increased the carbon (C) content, while significantly decreased the yield, ash content, pH, electrical conductivity, and elemental ratios of H/C, N/C, and O/C of SSB. These changes in SSB physicochemical properties would be more beneficial to its potentials of soil improvement and C sequestration. Furthermore, OA co-pyrolytic SSBs generally demonstrated similar nutrient retention rate and higher available nutrient content (e.g., Olsen P, K, and NH4+-N) in relative to the SSBs from SS alone, indicating their excellent nutrient recovery capacity and higher nutrient utilization efficiency. Lastly, the SSBs produced from co-pyrolysis of SS and SD, BSG, and RS, respectively, with 50% addition rate and at 700°C were suggested as the best SSB kinds used for soil application due to their highest comprehensive quality scores. In sum, co-pyrolysis of SS and OA is recommended as a promising strategy to increase the benefits of SSB in both agricultural production and environment.