Abstract

Globally, more than two billion tons of food are wasted each year, creating significant economic and environmental issues. Anaerobic digestion (AD), a process to convert organic waste to biogas, is a potential waste-to-energy alternative to landfilling wasted food (FW). Liquid digestate, a by-product of AD, is typically stored on-site in ponds prior to field application as a fertilizer, presenting risks of greenhouse gas (GHG) emissions and nutrient release to sensitive waterways. To assess this risk, we used a co-digestion (FW plus manure) facility and associated row-crop disposal system in an agricultural watershed in western New York, USA as a case study. A literature review of gaseous N and nitrate losses was complemented by targeted empirical measurements. We developed a mass balance model of nitrogen (N) across the digestate disposal pathway (storage and field application) and assessed nitrate and GHG losses relative to traditional manure and inorganic fertilizer practices. Sensitivity scenarios evaluated the volume of FW processed, crop type, and spreading practices. We validated results using the geospatial Soil and Water Assessment Tool (SWAT) and found good agreement between approaches. Digestate N content and seasonal variation in storage volume and application rate controlled nitrous oxide release at both stages. Ammonia volatilization was the dominant gaseous loss pathway, with nitrate leaching as the highest overall loss for digestate N. Field level losses for digestate were greater than stored manure or inorganic fertilizer, and increased significantly with higher application rates. However, at the watershed scale, current and two-fold greater FW processing levels did not substantially increase nitrate loss or global warming potential, as long as the field application rate remains constant. These findings suggest that sustainable diversion of FW from landfills to AD includes a decentralized strategy, with smaller digesters and sufficient storage and adjacent cropland.

Library of Congress Subject Headings

Food waste--Management; Food waste--Environmental aspects; Sewage--Purification--Anaerobic treatment

Publication Date

6-2-2020

Document Type

Thesis

Student Type

Graduate

Degree Name

Environmental Science (MS)

Department, Program, or Center

Thomas H. Gosnell School of Life Sciences (COS)

Advisor

Anna Christina Tyler

Advisor/Committee Member

Karl Korfmacher

Advisor/Committee Member

Thomas Trabold

Campus

RIT – Main Campus

Plan Codes

ENVS-MS

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