Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy

Anaerobic co-digestion (AcoD) with suitable substrate ratios may have the potential to improve biogas process and could play a better role in nutrient management for biocircular economy. The goal of this study was to enhance biogas yield from AcoD of cow manure (CM) and canteen food waste (CFW), and pertinent co-digestion of suitable substrate ratios for nutrient management i. e NPK from linear to biocircular economy, using ruminant intestinal fluid as a source of inoculum. A mesophilic (37 +/- 1 degrees C) laboratory-scale AcoD with varying CFW/CM ratios of (0:1, 1:4, 2:3, 1:1, 3:2, 4:1, and 1:0) based on wet weight was performed. The AcoD systems of different CFW/CM ratios were evaluated with a loading rate of 400 g/L in the presence of 100 g cow intestinal fluid (CIF) inoculation. All experimental AcoD systems yielded greater biogas (147-300 cm3/g VS) than the mono-digestion in which only CM (135 cm3/g VS) and CFW (146 cm3/g VS) were digested anaerobically. The AcoD system of CFW/CM with 4:1 showed the highest biogas yield (300 cm3/g VS), and VS and COD reduction rate (39.51% and 65.15%, respectively), and nutrient contents (6.53%). Moreover, the experiment results were verified by modified Gompertz model. This work provided a window of opportunity to examine the anaerobic co-digestion technology beyond biogas production and to put the current low-cost technology to use for nutrient management and as a better component of the biocircular economy for agriculture in Pakistan in order to achieve sustainable development goals.