Anaerobic digestion (AD) of fruit and vegetable market waste (FVMW): potential of FVMW, bioreactor performance, co-substrates, and pre-treatment techniques

Abstract

Fruit and vegetable marketplace waste (FVMW) is an appealing alternative for energy production and should be utilized as a single substrate in anaerobic digestion (AD)–based biogas plants at an industrial-scale level in subtropical climatic countries. India alone generates 961,000 tons of FVMW annually from the major fruit and vegetable markets (FVMs). Utilization of FVMW to produce useful energy by AD could be helpful in meeting the ever-increasing energy demands of these countries. AD of fruit and vegetable waste (FVW) by two-phase systems has revealed good results in terms of stability, performance, and biogas generation; however, innovative approaches like plug flow tank reactor (PFTR) with passive solar heating with no mixing and no energy heating coupled with heat balance models and resistance network–based heat balance models need to be researched for subtropical climatic conditions in order to optimize the economics and energy balance of an AD system. Food waste and slaughter house wastes could be utilized successfully as co-substrates with FVW. C/N ratio is a critical performance parameter in the AD systems involving co-substrates; however, the synergistic relationship among co-substrates and characteristics, viz., macro- and micronutrients of individual co-substrates, must be investigated to improve the AD process. The optimum proportions of co-substrates could be determined by individual substrate characterization, biomethanation potential (BMP), and biodegradation kinetic models, thereby saving time and money as compared with random experimentation. Thermal, ultrasonic, and electrical pre-treatment in addition to physical pre-treatment could be effectively used for pre-treating FVW; however, synergy between co-substrates and pre-treatment method must be researched in order to justify the increased cost in extra pre-treatment.