Sustainable organic waste valorisation: A zero-waste approach

The annual increase in global organic waste generation emphasises the need to develop a sustainable management platform to address environmental concerns. This study aims to explore sustainable treatments for the conversion of organic waste into energy in pursuit of zero-waste. The organic waste generated from the animal feed industry (referred to as WF) was used for the model compound in this study. 8.5 wt% of lipids were extracted from the WF, which contained unidentified impurities. Acid-catalysed transesterification yielded less than 80 wt% biodiesel might be due to the reversible reaction. In contrast, non-catalytic transesterification resulted in a significantly higher biodiesel yield (95.6 wt%), suggesting that this method was more effective at converting impure lipids into biodiesel compared to acid-catalysed transesterification. These results indicate the potential advantages of the non-catalytic approach, particularly when dealing with impure lipid sources. To minimise the generation of waste in the process, the WF residue produced after lipid extraction was converted into combustible gas (syngas) through pyrolysis. CO₂ was used as a reactive medium in pyrolysis. In one-stage pyrolysis, the gas yield under CO₂ was comparable to that under N₂, indicating that CO₂ did not react effectively with the volatiles derived from the WF residue. Enhanced CO₂ reactivity was achieved via catalytic pyrolysis using a nickel-impregnated catalyst. Consequently, the combustible gas yield under CO₂ was much higher than that under N₂. This approach might contribute to maximising the efficiency of converting organic waste into renewable energy while simultaneously consuming CO₂ during pyrolysis, thereby enhancing the sustainability of this approach.