Correlation between empirical formulae based stoichiometric and experimental methane potential and calorific energy values for vegetable solid wastes

Abstract

Abstract The correlation between stoichiometric (sMP, sCEV) and experimental biochemical methane potential (eBMP) and calorific energy values (eCEV) of vegetable wastes were evaluated. The elemental composition based empirical formulae were simulated for vegetable wastes and calculated stoichiometric chemical oxygen demand (sCOD), sMP, sCEV and compared with experimental results. Among twelve vegetable wastes chosen, minimum total solids, volatile solids, eCEV, and eBMP were observed in bottle guard (4.2%), beetroot (79.37%), okra(12.9MJ\xa0kg−1), onion (0.15 Nm\xa0LCH4\xa0g−1VSr), whereas the maximum was recorded in beetroot (16%), radish (95%), tomato (19 MJ\xa0kg−1), tomato (0.42 Nm L CH4\xa0g−1VSr), respectively. Similarly, the minima sCOD, sMP and sCEV was recorded as 1.10gCOD\xa0g−1VS (okra), 0.40 Nm L CH4\xa0g−1VSr (onion), 15.89MJ\xa0kg−1 (Radish), whereas maxima was observed as 1.82 g COD. g−1VS (tomato), 0.62 Nm L CH4\xa0g−1VSr (tomato), 22.29 MJ\xa0kg−1 (tomato). The observed lower and higher biogas yield in onion and tomato waste was coincided with the recorded lower carbon to nitrogen (C/N) ratio (16.31), higher amino sulfoxides (sulfonic acid) content and higher C/N ratio, moisture, glucose and fructose content in the former and later respectively. However, the lowest biogas yield in banana plantain waste in spite of highest C/N ratio was attributed to the presence of high cellulose content. Interestingly, the ascending trend in carbon, hydrogen and nitrogen content per gram of dry vegetable waste was correlated well with increased eCEV, sMP, on contrast reverse trend was depicted for oxygen. Among five different reported sCEV model results correlated with present study, the ultimate analysis based Scheurer-Kestner’s model depicted high R 2 (0.89) compared to physical and proximate analysis based sCEV models for vegetable waste. Thus, the observed high correlation between sMP and eBMP (0.80), sCEV and eCEV (0.89), sCOD and eCEV (0.87) confirmed as an alternative short-term method that can replace tedious eBMP and eCEV for the design of biogas plants using vegetable organic solid wastes.