Modeling and Optimization of Anaerobic Biogas Digestion Process of Pig Dung Using Response Surface Methodology

Abstract

In this study, the optimum methane yield and the requisite data which
accounted for the effects of the independent variables on the yield of
the response were investigated. The yield of methane via anaerobic
digestion (AD) of pig dung was modeled and optimized with response
surface methodology (RSM) using least square approach for the
prediction of the response. Central composite design (CCD) with
mixture design produced 32 batch anaerobic digestion experiments
which were randomly executed in order to investigate hydraulic
retention time (HRT) (10 – 14 days), temperature (45 – 65 °C),
moisture content, (90 – 94 %), pH (6.8 – 7.2) and carbon to nitrogen
ration (C/N) (0.5 – 2.5) on the methane yield. Linear and interaction
models were developed and further subjected to optimization
technique using genetic algorithm (GA) optimization criteria with
analysis of variance (ANOVA) employed in determining the degree
of accuracy of the RSM models utilized. Results obtained showed
optimum methane yield of 95.63 % which was obtained at HRT,
temperature, moisture content, pH and carbon – nitrogen ratio of 13
days, 50 °C, 88 %, 6.96 and 1 respectively. Coefficient of
determination, R
2
(65.02%), sum of square error, SSE (213.13), sum
of square residual, SSR (396.13), and total sum of square, SST (609.23)
values indicated model predictive accuracy and ability to navigate the
design space.