Food waste is a desirable feedstock for anaerobic digestion because it is high in moisture and is an easily degradable material. However, mono-digestion of food waste often fails due to the accumulation of volatile fatty acids. Supplementing trace elements is one strategy to combat this issue. This study examined the effect of supplementing trace elements (iron, nickel, selenium, molybdenum, magnesium, zinc, calcium, copper, manganese, cobalt) on the methane yield and organic waste destruction of anaerobically digested food waste. Methane yield of food waste with and without the inorganic salt trace element was determined by the gas density-based biomethane potential method at mesophilic (37°C) conditions over 30 days. The three treatments were inoculum only, food waste and inoculum, and food waste and inoculum with an added trace element solution. There was no significant difference between treatments in terms of waste stabilization (percent volatile solids, total solids, and total chemical oxygen demand reduction) between treatments. The average cumulative biogas produced was 41% higher, and the average total cumulative methane produced was 23% higher in the treatment with the trace element supplement. Mean methane yield was not different (p > 0.05) between treatments over the 30 days, and there was no difference (p > 0.05) in biomethane potential between treatments.
In addition, greenhouse gas reduction potential was estimated from food waste streams in Montgomery, VA using anaerobic digestion. The purpose of this work was to (1) estimate the total mass of food waste produced in Montgomery, VA in a year, (2) use the results from the biomethane potential analyses to inform the sizing of a theoretical community digester in Montgomery, VA, and (3) estimate the greenhouse gas reduction potential of anaerobically digesting the food waste instead of sending it to landfill. Greenhouse gas reduction was calculated using the Climate Action Reserve Organic Waste Digestion Project Protocol guidelines. The greenhouse gas reduction potential was estimated as 6,532 tonnes of carbon dioxide equivalent per year (tCO2e/year), with approximately 693 m3 methane produced per day. In one year, the digester would generate an estimated 7370 kWh of energy which has the potential to power 149 homes for a year in Montgomery, VA. In addition, 4130 tonnes/year of composted digestate would be available as fertilizer for surrounding farms. / Master of Science / Currently, about one-third of the entire U.S. food supply is lost or wasted. A large portion of that food waste is sent to landfills, where it produces methane, a greenhouse gas. Instead, food waste can be broken down to produce biogas during anaerobic digestion. Anaerobic digestion is a process in which microorganisms break down organic materials in the absence of oxygen to produce biogas and digestate, a material used as a soil amendment or fertilizer. However, anaerobically digesting food waste often leads to process instability and failure due to a buildup of undesirable intermediates. Microorganisms in anaerobic digestion require certain trace elements (i.e., iron, copper) that food waste often lacks; therefore, supplementing key trace elements may improve the anaerobic digestion of food waste. This research aimed to assess the effect of supplementing key trace elements (iron, copper, zinc, calcium, magnesium, nickel, manganese, selenium, molybdenum, cobalt) on organic matter degradation and methane yield. Methane yield of food waste with and without the inorganic salt trace element was determined by the gas density-based biomethane potential method at mesophilic (37°C) conditions over 30 days. The average cumulative biogas produced was 41% higher, and the average total cumulative methane produced was 23% higher in the bottles containing a trace element supplement. No significant difference was seen in the two groups when comparing organic matter degradation. These results demonstrate that supplementing trace elements can improve biogas and methane production.
Greenhouse gas reductions from anaerobically digesting food waste instead of sending it to landfills were determined for Montgomery, VA. The results from the biomethane potential test informed the design of a theoretical community digester. Greenhouse gas reduction was calculated using the Climate Action Reserve Organic Waste Digestion Project Protocol equations. The greenhouse gas reduction was determined as 6,532 tonnes of carbon dioxide equivalent per year (tCO2e/year). The digester would produce approximately 693 m3 methane/day, which has the potential to power 149 homes for a year in Montgomery, VA. In addition, 4130 tonnes/year of compost would be produced and available as a fertilizer for surrounding farms.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110872 |
| Date | 15 June 2022 |
| Creators | Graff, Kelly Mackenzie |
| Contributors | Biological Systems Engineering, Ogejo, Jactone Arogo, Mukhopadhyay, Biswarup, Senger, Ryan S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-sa/4.0/ |
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