Determination of the suitable condition for producing biogas from the co-digestion of broiler manure and stillage

Abstract

Renewable energy has gained more interest in the last two decades as the fossil fuel has been depleted and its use contributes to global warming problem. This research aimed to investigate the method to produce biogas from broiler manure (BM), a waste with bedding material that has been generated in large amounts in Thailand. In The first objective of this work was to examine the optimum condition for pretreating BM using the thermal-alkali pretreatment process. Lime was chosen as an alkali substance. Full factorial design (FFD) was used to design the experiments with three factors, i.e. temperature, lime concentration, and pretreatment duration. According to FFD results, the optimum condition for pretreating BM was at 150°C, 3% w/v Ca(OH)₂ solution, and 1 h pretreatment duration. The highest lignin removal efficiency from BM was 49.9%.

The second objective was to investigate the effects of C/N ratio on efficiency of biogas production by co-digesting BM with stillage. Three different C/N ratios were chosen, i.e. 30, 40, and 50. The highest methane yield (247.73±6.10 mlCH₄/gVS) was achieved from stillage as the sole substrate. The similar methane yields found from the non-pretreated BM (164.39±6.05 mlCH₄/gVS) and the pretreated BM (160.70±0.93 mlCH₄/gVS). Same for the co-digestion at C/N 30, the methane yield obtained from the pretreated BM co-digested with stillage (141.37±6.99 mlCH₄/gVS) was not significantly different from the non-pretreated BM co-digested with stillage (154.53±5.79 mlCH₄/gVS). From the results, it could conclude that the thermal-alkali pretreatment could not achieve to increase the biogas production and the co-digestion between BM and stillage had an antagonistic effect in biogas production. Gomperzt model was found to fit better to the BMP results than the first-order model for all the experiment results. Within the relatively shorter period of time (around 5 or 7 d), Gompertz model could predict more than 95% of the final methane production.