Significance of Pretreatment in Enhancing the Performance of Dry Anaerobic Digestion of Food Waste: An Insight on Full Scale Implementation Strategy with Theoretical Analogy

Abstract

The aim of this study was to treat food waste containing 25% total solids (TS) through dry anaerobic digestion (dry AD) process at various pressures (0.5 to 2.5 kg/cm2) and different time duration (20 to 100 min) to understand the impact of pretreatment in enhancing the methane generation potential along with insights on scale up. The findings revealed that vs. reduction and methane yield of 60% and 0.25 L CH4/(g VSadded) can be achieved with pretreated food waste at two kilograms per square centimeter, while pretreatment of food waste at 2 kg/cm2 for 100 min enhanced the vs. reduction from 60% to 85% and methane yield from 0.25 to 0.368 L CH4/(g VSadded). However, the net energy indicated that 40 min of pre -treatment at two kilograms per square centimeter can be a suitable option as methane yield and vs. reduction of 0.272 L CH4/(g VSadded) and 70%, respectively was achieved. The vs. reduction and the methane yield of 45% and 0.14 L CH4/(g VSadded), respectively was obtained from untreated food waste which illustrated that pretreatment had significantly impacted on the enhancement of methane generation and organic matter removal which can make the dry AD process more attractive and feasible at commercial scale.

Effects of co-substrates’ mixing ratios and loading rate variations on food and agricultural wastes’ anaerobic co-digestion performance

“…However, focusing on SMY profile, mono-digested FW produced the lowest volume of methane compared to co-digested feedstocks which ascertained the important role played by the co-substrates in terms of biogas composition enhancement. 20 , respectively, and confirmed the positive impact of agricultural residues on FW anaerobic cotreatment. Thus, C:N ratio and macro-and micronutrients balancing ensured by co-substrate addition boosted the development of methanogenesis phase and, in turn, affected the methane production efficiency [55].…”

“…In fact, the identified C:N ratio of different organic materials depicts that the abundance of nitrogen contents, particularly for FW and CM or the carbonaceous aspect of WS, makes those residues unsuitable for anaerobic mono-digestion [50]. Therefore, different substrates were combined at different ratios to balance the C:N ratio greater than or equal to 20 20 . However, it is worthy to mention that despite the diversity of the raw materials used in terms of carbon and nitrogen content, balanced C:N ratios for all the trials within the requested range of 20-40 were noted [51].…”

“…Thus, in the European Union (EU), pasteurization at 70 °C for 1 h is the defined standard for meat-containing wastes from food processing, food waste from households and restaurants, and slaughterhouse waste of animals which are then suitable to deliver products for human consumption such as biofertilizers [16] [17]. Moreover, several studies evaluate various approaches intending to examine the removal rate of pathogenic microorganisms achieved through thermal pretreatment [18]; chemical pretreatment such as ozonation; electro-technology such as pulsed electrical field or highvoltage discharge [19]; or physicochemical methods such as ultrasound technology, microwave irradiation, or hydrostatic pressure [20]; however, it should be mentioned that the thermal sanitization is most commonly applied. In this context, Zhang et al (2020) tested the effect of pasteurization at 70 °C for 1 h on anaerobic treatment of various organics and revealed that the disinfection can positively impact the methane yield of some specific substrates, such as potato waste and animal blood, whereas pasteurization of food waste, cattle slurry, and card packaging had no significant impact on methane yield during anaerobic digestion [21].…”