Multi-functional biochar preparation and heavy metal immobilization by co-pyrolysis of livestock feces and biomass waste

Biomass waste is a desirable additive in livestock feces biochar preparation due to its easy access, better moisture adjustment, and abundant organic content. In the present study, co-pyrolysis of livestock feces (PM: pig manure, CM: chicken manure) and biomass wastes (WC: wood chips, BS: bamboo sawdust, RH: rice husk, and CH: chaff) with different blending ratios was conducted at 600 degrees C to investigate the biochar characteristic and Cu/Zn immobilization performances. The results showed that WC and BS have more significant effect on the increase in fixed carbon content and heating value and the decrease in ash content of biochar. The biochar with lower pH and electrical conductivity is obtained from co-pyrolysis of manure with RH and CH. Compared with CM-based biochar, PM-based biochar presented better potential as fuel and soil remediation considering the higher heating value and lower aromatic H/C ratio. Specially, the residual fractions of Cu and Zn in PM biochar increased from 73.09% and 65.54% to 90.68% and 72.31% after 10 wt% BS addition and those in CM biochar increased from 81.07% and 73.57% to 88.87% and 84.11% after 10 wt% WC addition, which induced the lowest environmental risk of biochar. This work provided a strategy and direction for targeted enhancement in biochar characteristics with selective biomass addition during manure pyrolysis, which is beneficial to the local treatment and utilization of farm wastes.

Automated summary

This study investigated the co-pyrolysis of livestock feces and various biomass wastes to prepare biochar, finding that wood chips and bamboo sawdust significantly influenced the biochar characteristics by reducing ash content and increasing heating value. Co-pyrolysis of manure with rice husk or chaff produced biochar with lower pH and electrical conductivity. Addition of certain biomass led to increased residual fractions of Cu and Zn in biochar, reducing environmental risks.