Use of biochar to improve sewage sludge quality in Maluti-A-Phofung Municipality, South Africa

Research on wastewater treatment processes in Maluti-a-Phofung Municipality (South Africa) has revealed that substandard wastewater management in this region contributes to terrestrial and aquatic pollution. Because this pollution poses a threat to the environment, there is a pressing need to reduce the environmental impact of poorly managed sewage sludge in the region. Biochar has been regarded as a cost-effective way of reducing chemical toxicity in terrestrial environments. In the present study, we aimed to investigate the effectiveness of biochar in the remediation of the toxicity of sewage sludge using the earthworm Eisenia fetida. Sewage sludge was collected from a local wastewater treatment plant and E. fetida were exposed to 0, 25, 50, and 100% non-amended and 10% biochar-amended sludge. After 28 days, survival, biomass and reproduction were assessed. Separately, in clean artificial soil, E. fetida was exposed to 5, 10 and 15% biochar amendment for 96 hours to determine if biochar amendment alone could be harmful to E. fetida. The results showed no significant differences in all parameters between the worms exposed to non-amended sludge and 10% biochar-amended sludge. Assessment of acetylcholinesterase and catalase activities in the earthworms that were exposed to biochar via clean soil revealed that 10% and 15% biochar amendment rates caused the worms to experience significant levels of neurotoxic and oxidative stress (p < 0.05). These findings reveal that biochar alone is likely to have adverse effects on soil organisms, and amendment rates higher or equal to 10% are not suitable to alleviate the toxic effects of sewage sludge.