Particle size, inoculum-to-substrate ratio and nutrient media effects on biomethane yield from food waste

Abstract

This study investigates the effects of particle size reduction at different inoculum-to-substrate ratios and nutrient media supplementation on the assessment of biomethane production from food waste, under batch mesophilic conditions. Two different food waste samples were used and the best method for testing biomethane potential was chosen based on their characterisation and methane yields. Results obtained indicate that Inoculum-to-substrate ratios of 3:1 and 4:1 helped to stabilise test reactors with smaller particle sizes of 1 mm and 2 mm, respectively. Consequently, an overall biomethane yield increase of 38% was reported (i.e., from 393 NmLCH 4 gVS-1 added to 543 NmLCH 4 gVS-1 added). This could potentially imply a better assessment of energy outputs from anaerobic digestion of food waste (i.e., 43.5% higher energy output as electricity from biogas, using commercial scale Combined Heat and Power (CHP) units). Although nutrient media supplementation did not enhance methane yield from optimum inoculum-to-substrate ratio (3:1) and particle size (1 mm), it was found that its application helped to stabilise food waste digestion by avoiding volatile fatty acids accumulation and high propionic-to-acetic acid ratio, consequently, improving the overall test kinetics with 91% lag time reduction from 5.6 to 0.5 days. This work supports the importance of key variables to consider during biomethane potential tests used for assessing methane yields from food waste samples, which in return can potentially increase the throughput of anaerobic digestion system processing food waste, to further increase the overall energy output.

Enhancing bioenergy production from food waste by in situ biomethanation: Effect of the hydrogen injection point

“…Waste samples were collected from the University of Leeds’ student refectory for 5 days in separately monitored bins. FW sorting, storage and characterisation method follow the methods described in a previous study (Okoro‐Shekwaga et al, 2020). The characteristics of the FW used in this study are presented in Table 1, which includes pH, total solids (TS), volatile solids (VS), total chemical oxygen demand (TCOD) and total VFA (TVFA).…”

“…Wheaton bottles (160 ml) were used as batch anaerobic reactors with 75 ml working volumes and held in a water bath to maintain reactor temperature at 37°C. An inoculum‐to‐substrate ratio (ISR) of 3:1 based on VS was adopted according to previous ISR optimisation tests (Okoro‐Shekwaga et al, 2020). The experiments were set up to include a blank (inoculum only), control (inoculum and FW without H 2 injection) and test (inoculum and FW with H 2 injection) reactors.…”

Anaerobic digestion of food waste at varying operating conditions

“…Okoro -Shekwaga et. al., 2020 Food waste Mesophilic anaerobic sewage sludge from sludge treatment plant 33:100 ,1:2,1:1,2:1,4:1 TS% varied-4.4% and 10.5%, Temperature maintained at 37±1°C, agitated using shaker at 60 rpm High organic fraction increased risk of acidification but also contributed to high methane, S: I ratio< 0.33 resulted in higher methane yield Kawai et al, 2014 Food waste…”

Investigation on Recycling Dry Toilet Generated Blackwater by Anaerobic Digestion: From Energy Recovery to Sanitation

“…A cumulative biogas production curve is then obtained and the BMP value is typically expressed as a function of added volatile solids (VS) (mL•CH4/g•VS) [17]. However, the results of BMP tests can be influenced by inoculum characteristics (origin, concentration and activity), experimental conditions (gas measurement system, operational parameters, chemical parameters and inoculum to substrate ratio) [18], particle size and the nutrient media of the substrate [19].…”