Comparative analysis of biogas production from expired fruit concentrates: Insights from correlation and PCA techniques

Abstract

• Expired fruit concentrates (mango, pineapple) are suitable for biogas production • PCA showed that time, BOM and stirrer speed are pivotal for biogas production • Acidity content of fruit concentrates affected VFA and inhibited methanogenesis • Key microbial populations contributing to CH 4 yield during AD were identified • pH buffering with natural alkaline (cow dung) was helpful in stabilizing AD Expired fruit concentrates from agro-industrial processes, such as mango and pineapple, are typically discarded as waste, contributing to environmental pollution and economic losses. Valorizing these carbohydrate-rich wastes through biogas production presents a sustainable strategy for renewable energy generation and circular economy development. This study investigates the anaerobic digestion of expired mango and pineapple concentrates in a mesophilic continuous stirred tank reactor (CSTR) (Biogas Test Plant BTP2). The substrates were homogenized and co-digested with cow dung slurry as inoculum. Sample characterization (moisture, total solids (TS), volatile solids (VS), ash) followed APHA (2012) and ASTM D2974 protocols. Biogas production and composition (CH₄, CO₂) were monitored daily. VFA and TIC were determined through potentiometric titration according to Nordman’s method. Microbial community profiling was conducted using rRNA gene sequencing . Principal component analysis (PCA) and Pearson correlation analysis were applied to identify the main operational drivers influencing methane yield. Results showed that cow dung (control) produced the highest cumulative methane yield (41.5 L; 68.7% CH₄), followed by mango (30.6% CH₄) and pineapple (28.5% CH₄). PCA revealed that pH stability, VFA accumulation, and stirring speed were significant drivers of methane production efficiency. Microbial analysis identified Firmicutes and Syntrophomonas as dominant contributors to methanogenesis across all reactors. This study innovatively combined PCA, correlation analysis, and microbial community profiling to evaluate biogas production from expired fruit concentrates in a CSTR system. The findings highlight the potential of these agro-industrial wastes for renewable energy generation and contribute to advancing sustainable waste management practices