Leveraging Acid-Hydrolyzed Corn Stover and Pig Manure as Substrates for Optimized Biogas Production: A Circular Economy Approach

One of the most promising energy generation techniques for sustainable development is the production of biogas from waste. This study exploited corn stover (CS), abundant waste material in corn plantations, as feedstock with pig manure (PM) as inoculum in biogas production. The CS was pretreated via acid hydrolysis using sulfuric acid. In the batch experiment of acid-hydrolyzed CS, the hydraulic retention time (HRT) and the ratio of corn stover and pig manure (CS/PM ratio) were used as variables in the design of the experiment using the central composite design of the response surface methodology. The effects of these variables on biogas yield were investigated through analysis of variance and 3D surface plots. The best conditions of HRT and CS/PM ratio that would result in optimal biogas yield were also determined via numerical optimization using the built-in feature of the Design Expert software used in data analysis. Additionally, the biogas compositions were determined via gas chromatography analysis. Results showed that the biogas production was significantly affected by CS/PM ratio, with yield peaking at 2:1 to 3:1 (w/w) CS/PM ratio. On the other hand, HRT did not significantly affect biogas production, with an insignificant change in yield even at a variable time. Numerical optimization revealed that the best conditions, such as 10 days of HRT and a 2:1 (w/w) CS/PM ratio, yielded 10.4 L of biogas out of 1000 g feeding concentration (667 g CS and 333 g PM). Based on the gas compositional analysis, the 10.4 L biogas composed of the following: methane of 4.49 L (43.13%), carbon dioxide of 3.88 L (37.29%), nitrogen of 0.19 L (1.85%), and other gases of 1.84 L (17.73%). With published and known purification techniques of biogas using a cleaning device, the desired methane gas can be obtained for various applications.