Use of dairy sludge for biodiesel production and soil amendment

Abstract

The primary objective of this study is to enhance the recycling of dairy sludge by extracting lipids for biodiesel production, evaluating the efficiency of two (trans)esterification methods, and repurposing the defatted sludge into biochar fertilizer. Lipid extraction was performed using a chloroform/methanol solvent mixture, which yielded an extract comprising 18.7% of the initial sludge mass. Analysis revealed the presence of free fatty acids, saponified fatty acids, and other impurities along with triglycerides within the extract. Biodiesel production involves both non-catalytic (trans)esterification and conventional acid/base catalytic (trans)esterification. The non-catalytic approach demonstrated a seven-times higher efficiency than the conventional approach, which was attributed to its resilience against impurities. After lipid extraction, the phosphorus (P) content in the residual material increased by 13.1% compared to the original sludge, suggesting its potential as a phosphorus source. The residual material served as feedstock for biochar production, increasing the total phosphorus (TP) concentration within the resultant biochar. Biochar analysis revealed a non-apatite inorganic phosphorus (NAIP) fraction of 3.6%. Moreover, the biochar exhibited a plant-available P content of 514 mg/kg, as determined using the Olsen method. Oat seeds cultivated in biochar-amended soil exhibited promising growth outcomes. These findings suggest the potential of dairy sludge as a dual solution for fossil fuel dependency and P resource depletion. Innovative utilization of this waste stream mitigates environmental burdens and promotes sustainable practices.