Methane and Hydrogen Sulfide Production from Co-Digestion of Gummy Waste with a Food Waste, Grease Waste, and Dairy Manure Mixture

Choudhury Choudhury,Lansing Lansing

doi:10.3390/en12234464

Abstract

Co-digestion of dairy manure with waste organic substrates has been shown to increase the methane (CH4) yield of farm-scale anaerobic digestion (AD). A gummy vitamin waste (GVW) product was evaluated as an AD co-digestion substrate using batch AD testing. The GVW product was added at four inclusion levels (0%, 5%, 9%, and 23% on a wet mass basis) to a co-digestion substrate mixture of dairy manure (DM), food-waste (FW), and grease-waste (GW) and compared to mono-digestion of the GVW, DM, FW, and GW substrates. All GVW co-digestion treatments significantly increased CH4 yield by 126–151% (336–374 mL CH4/g volatile solids (VS)) compared to DM-only treatment (149 mL CH4/g VS). The GVW co-digestion treatments also significantly decreased the hydrogen sulfide (H2S) content in the biogas by 66–83% (35.1–71.9 mL H2S/kg VS) compared to DM-only (212 mL H2S/kg VS) due to the low sulfur (S) content in GVW waste. The study showed that GVW is a potentially valuable co-digestion substrate for dairy manure. The high density of VS and low moisture and S content of GVW resulted in higher CH4 yields and lower H2S concentrations, which could be economically beneficial for dairy farmers.

Highlights

Anaerobic digestion (AD) of organic substrates with dairy manure, known as co-digestion, can increase biogas production and result in higher return on investment for dairy farmers [1].Biogas produced from AD is a combination of 50–75% methane (CH4 ) and 25–50% carbon dioxide (CO2 ), with trace levels (0.01–1%) of hydrogen sulfide (H2 S) that can be used as a source of renewable energy for heat and power generation [2]
The co-digestion mixtures 0–23% gummy vitamin waste (GVW).dairy manure (DM).FW.GW had a significantly higher percent CH4 in the biogas compared to the mono-DM digestion (p-value < 0.0001; Table 3)
The negligible CH4 production and low pH values in the mono-GVW, FW, and GW treatments compared to the higher CH4 production (336–374 mL CH4 /g volatile solids (VS)) and pH range (7.88–7.95) in treatments that co-digested GVW, FW, GW, and DM showed that the buffering capacity of the added co-substrates is important to mitigate accumulation of volatile fatty acids (VFA) and lowered pH [3,21]

Summary

Introduction

Anaerobic digestion (AD) of organic substrates with dairy manure, known as co-digestion, can increase biogas production and result in higher return on investment for dairy farmers [1].Biogas produced from AD is a combination of 50–75% methane (CH4 ) and 25–50% carbon dioxide (CO2 ), with trace levels (0.01–1%) of hydrogen sulfide (H2 S) that can be used as a source of renewable energy for heat and power generation [2]. Limitations from mono-digestion of organic materials arise from substrate properties, such as unbalanced C:N ratios, recalcitrance in the feedstock, high concentrations of long chain fatty acids, and deficiency in trace minerals required for the growth of methanogens [1,3]. These limitations can lead to unfavorable economics for dairy farmers using AD to generate energy on-farm [1,4]. A review by Mata-Alvarez et al (2014) reported that co-digestion of carbon (C)-rich organic matter with cattle and poultry manure resulted in up to 3.5 times more CH4 production than the CH4 potential of the individual substrates [3]. Moody et al (2011) determined the biomethane potential of a wide range of food waste substrates and concluded that co-digestion of manure and Energies 2019, 12, 4464; doi:10.3390/en12234464 www.mdpi.com/journal/energies

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