Enhancement of Methane Production from Vegetable, Fruit and Flower Market Wastes Using Extrusion as Pretreatment and Kinetic Modeling

Organic wastes from wholesale vegetable, fruit, and flower markets are one among the major sources of centralized waste generation in urban cities, which are predominantly disposed at dumpsites. Sustainable solution for the effective treatment and disposal of these wastes from Indian urban centers needs to be explored. Anaerobic digestion (AD) process coupled with extrusion as a pretreatment prior to AD was studied to increase methane production from vegetable, fruit, and flower market wastes. The detailed waste characterization and bio-methane potential (BMP) tests of vegetable, fruit, and flower market wastes were carried out. From the results of BMP tests, the highest specific methane yield (SMY) of 332.7 mL_N/g oDM (31% increase) was obtained for extruded fruit market wastes compared with non-extruded wastes, which showed SMY of 253.9 mL_N/g oDM. Similarly, the SMY of vegetable and flower market wastes was significantly increased (p < 0.05) to 319.6 mL_N/g oDM (+ 35.5%) and 188.1 mL_N/g oDM (+ 42.3%), respectively, as a result of extrusion pretreatment. Further, AD of extruded wastes showed 11.4–17.2% increase in the oDM reduction in concurrence with the increased SMY. The energy potential of extruded and non-extruded wastes varied between 6.4–10.9 MJ/kg DM and 4.7–9.4 MJ/kg DM, respectively. In addition, from the profile of bio-methane production, it is observed that the extruded wastes reached 95% of SMY in 14–17 days unlike non-extruded wastes, which took 17–23 days to reach the same value thereby attaining steady-state condition faster than non-extruded wastes. Among the three models used, the logistic model showed best fit with R² value of 0.96–0.98 with minimum SMY deviation < 2.8% than first-order kinetic and modified Gompertz models. Results of the study revealed that extrusion pretreatment of wholesale vegetable, fruit, and flower markets wastes prior to AD was found to be effective in increasing the methane production during anaerobic treatment of these wastes from urban centers.