Abstract
In this paper, the anaerobic co-digestion of three different organic wastes, including livestock manure, slaughterhouse waste, and agricultural by-products (ABs), was carried out to enhance the efficiency of mono-digestion of livestock manure. The characteristics of co-digestion were evaluated at different mixing ratios. The experiment was performed using the Batch test and was divided into two parts. The first experimental section (EXP. 1) was designed to evaluate the seasonal characteristics of ABs, which are the different ratios of fruits and vegetables, where the mixing ratio of spring (fruits:vegetables = 3:7) showed the highest biogas yield (0.24 m3/kg volatile solids). The second experiment (EXP. 2) was conducted by using ABs in the ratio that gave the highest biogas yield in EXP. 1 in combinations of three wastes livestock manure, slaughterhouse waste, and ABs. The highest CH4 yield was 0.84 m3/kg volatile solids (VS), which was obtained with a mixing ratio that had even amounts of the three feedstocks. In addition, the results of the second biochemical methane potential test, which assessed the digestive efficiency according to the mixing ratio of the three types of organic waste, showed that the CH4 production rate of the merged digestion was approximately 1.03–1.29 times higher than that of the mono-digestion of livestock manure. The results of our experiment were verified using the modified Gompertz model, the results of which were relatively similar to the experimental results.
Highlights
The significant increase in energy consumption in recent times due to the increase in population has become a global issue
We aimed to (i) evaluate the efficiency of anaerobic co-digestion using three different substrates, including swine manure, slaughterhouse waste, and agricultural byproducts (ABs), to enhance the efficiency of anaerobic digestion and biogas production; in addition, elemental analysis was conducted on each feedstock to confirm the characteristics of the substrates; (ii) perform biochemical methane potential test (BMP test) on ABs to determine the effect of the mixing ratio of fruits and vegetables to evaluate biogas production potential from each substrate; (iii) apply a modified Gompertz model to investigate the practical result of the BMP test
Fruits contain sugar and are rapidly converted into volatile fatty acids (VFAs) by acid-fermenting bacteria. This can cause the accumulation of VFAs, which can cause a rapid decrease in the pH inside the reactor [31]
Summary
The significant increase in energy consumption in recent times due to the increase in population has become a global issue This increase in energy consumption has, in turn, led to an increase in the demand for fossil fuel, such as coal, oil, and natural gas, which are used as primary energy sources, thereby resulting in higher costs of fossil fuels [1]. The main stages of the process of anaerobic digestion are hydrolysis, acidogenesis, acetogenesis, and methanogenesis [9]. The VFAs are transformed into acetate, H2, and CO2, as well as new cellular material. At the stage of methanogenesis, which is the last stage, the acetate, H2, and CO2, formate, or methanol are converted into methane, CO2, and new cellular material [10]
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