Variations in generation of vegetable, fruit and flower market waste and effects on biogas production, exergy and energy contents

In India, large quantities of centrally generated wastes from vegetable, fruit and flower wholesale markets (VFF) are mostly disposed without treatment at open dumpsites. To implement sustainable waste treatment system including an adapted substrate management for Indian cities, detailed information on temporal mass and compositional fluctuations of VFF are fundamental. This article investigates the sources, extent and influence of fluctuating VFF characteristics, and examines its impact on biogas production and energy potentials. A comprehensive analysis of VFF in the city of Chennai revealed strong fluctuations of individual waste component shares of 34.5-142.9% (vegetables), 40.5-185.9% (fruits) and 33.0-244.9% (flowers) throughout the monitored year. Waste amounts occur independently of fresh vegetable, fruit and flower amounts entering the urban area. Specific biogas yields (SBY) of VFF varied from 403.7 to 570.5 mL(N)/g oDM during the analysis period of 4 months. A comparative analysis between calculated and measured SBY revealed that measured SBY are on average 9.7-22.4% lower, partly due to unfavourable C/N ratios. Despite fluctuations in VFF composition, monthly variations in theoretically available energy contents are not particularly pronounced if an adapted substrate management is applied for anaerobic treatment of VFF.