Effect of Copper Suplementation on Biogas Yield from Co-Digestion of Cattle Dung and Jatropha Curcas Fruit Coat

Abstract

Limited understanding exists regarding the role of copper as a trace additive in cattle dung–Jatropha curcas fruit coat (CD–JFC) co-digestion systems, particularly under ambient mesophilic conditions. This study therefore aimed to evaluate the effect of low-dose copper supplementation on biogas yield during batch anaerobic co-digestion of CD and JFC. Experiments were conducted in 2 L laboratory-scale digesters operated over 30 days at 25–35°C, comparing mono-digestion, co-digestion, and co-digestion with copper addition (4.45 g). Co-digestion improved cumulative biogas yield by approximately 47% relative to cattle dung mono-digestion, confirming enhanced substrate synergy. The inclusion of copper resulted in a further ~7.4% increase compared to co-digestion without copper. While this suggests a stimulatory effect, the relatively small absolute gain indicates that the influence of copper under the tested conditions is modest. Typical batch digestion behavior, including lag, active production, and stabilization phases, was observed; however, no direct process monitoring or yield normalization was performed, limiting mechanistic interpretation and cross-study comparability. Consequently, copper supplementation in this context should be interpreted as appearing to enhance biogas yield rather than providing definitive performance improvement. Given the laboratory-scale setup and short hydraulic retention time, further research is required to optimize copper dosage, evaluate long-term process stability, and assess potential environmental implications associated with metal accumulation in digestate.