Emerging Trends in Chemical Engineering Review Article
Co-Digestion of Sewage Sludge and Food Waste for Enhanced Bio-fertilizer Production
Abstract
This study investigated the production and effectiveness of liquid and solid biofertilizers derived from co-digested water treatment plant sludge and food waste, with the aim of enhancing soil fertility and plant growth while ensuring microbiological safety. Biofertilizer samples were formulated at three concentrations (100%, 75%, and 50% sludge-based mixtures) and evaluated for physicochemical quality, microbial composition, and agronomic performance on test crops. The microbial assessment of liquid formulations revealed total viable counts ranging from 1.57 × 10⁶ to 2.35 × 10⁶ CFU/mL, coliform counts between 1.87 × 10⁴ and 3.84 × 10⁴ CFU/mL, fungal populations of 3.67 × 10³–5.65 × 10³ CFU/mL, and helminth egg loads of 0.7–2.7 eggs/L. Solid biofertilizers showed higher microbial densities, with viable counts of 3.75 × 10⁶–4.65 × 10⁶ CFU/g, coliform counts of 1.88 × 10⁴–2.74 × 10⁴ CFU/g, fungal counts of 5.67 × 10³–7.41 × 10³ CFU/g, and helminth egg counts of 0.7–1.7 eggs/g, all within international safety limits. Morphological and biochemical characterization indicated the dominance of beneficial microbial species such as Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Aspergillus niger, demonstrating active participation in nutrient cycling and organic matter decomposition. Plant growth evaluation showed that biofertilizer treatments significantly improved growth metrics compared to the control. Root length increased by 150% (50% sludge), 200% (75% sludge), and 275% (100% food waste) relative to the control, outperforming NPK which showed a 75% increase. Above-ground parameters such as plant height and leaf count also followed similar enhancement trends across sampling intervals. Overall, the findings confirm that biofertilizers derived from co-digested sludge and food waste possess adequate nutrient quality, beneficial microbial populations, and strong plant growth–promoting effects. The study demonstrates that integrating waste -derived biofertilizers into agricultural systems can provide a safe, nutrient-rich, and sustainable alternative to synthetic fertilizers.
Keywords
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