Valorization of animal bone waste for agricultural use through biomass co-pyrolysis and bio-augmentation

Thermal treatment of animal bone waste (i.e., pyrolysis) is an alternative technology to sustainably manage slaughterhouse waste for agricultural uses. However, concentration of plant-available phosphorus (P) is limited in thermally treated animal bone (i.e., bone char). This study, therefore, aimed to develop sustainable methods to increase the P fertilizer value of animal bone waste through co-pyrolysis of animal bone with lignocellulose agricultural waste and bio-augmentation. Four types of bone chars were produced using two different pyrolysis temperatures (450°C and 850°C) and pyrolysis techniques (conventional and co-pyrolysis). These bone chars were then bio-augmented with four different phosphate solubilizing microorganisms (PSM). In vitro and incubation experiments were conducted to assess the fertilizing value of the products. The result showed that co-pyrolysis of animal bone with lignocellulose agricultural waste combined with bio-augmentation increased P solubility by 133–167%, at the lower production temperature. P solubility decreased considerably at a higher production temperature. However, it was increased by 16- to 21-fold when co-pyrolysis was coupled with bio-augmentation. Addition of co-pyrolyzed bone char enriched with PSM and organic carbon to soil increased P availability by 34 to 48% and PSM survival rate by 22 to 76%. The findings demonstrated that co-pyrolysis combined with bio-augmentation could be an efficient and low-cost strategy to improve the agricultural use of animal bone and to reduce the dependency on chemical fertilizer. This study has a significant importance particularly for developing countries, where the use of chemical fertilizer is limited due to its high price; and slaughterhouse waste has created an environmental concern.