Author Type

Graduate Student

Date of Award

Summer 7-28-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

August 2026

Department

Civil, Environmental and Geomatics Engineering

College Granting Degree

College of Engineering and Computer Science

Department Granting Degree

Civil, Environmental and Geomatics Engineering

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Daniel E. Meeroff

Abstract

The increasing generation of high-strength organic wastes such as food waste and fats, oils, and grease (FOG) presents challenges for landfill capacity and waste management. Anaerobic co-digestion offers a sustainable alternative by converting these wastes into renewable energy and nutrient-rich digestate. This study evaluated the co-digestion performance of single fruit waste residuals and mixed food waste with wastewater sludge to identify substrate combinations that maximize methane production while maintaining process stability. Laboratory-scale batch experiments were conducted under mesophilic conditions using thickened waste activated sludge (TWAS) with varying proportions of food waste and co-substrates, including seaweed, aquatic weed, grease trap waste, and FOG. Performance was assessed based on methane yield, digestion stability, solids reduction, gas quality, siloxane formation, and heavy-metal behavior.

Results showed that simple co-digestion systems containing FOG with either single fruit waste or mixed food waste performed better than multi-substrate mixtures and TWAS-only controls. Addition of mixed household food waste slurry and scum-based FOG, each added at 10% on a volumetric basis resulted in a methane yield of 206 mL/gVS approximately double than that of the TWAS control (105 mL/gVS) while maintaining stable digestion conditions with methane content greater than 60%. Validation in larger digesters confirmed consistent methane enhancement and process reproducibility. Siloxane concentrations remained low across all systems varied within 0.8-5.8 mg/m3, indicating minimal gas treatment requirements. Although co-digestion mixtures introduced heavy metals into the system, heavy metals concentrations were below the applicable regulatory limits. Additionally, economic analysis showed that co-digestion at existing wastewater treatment plants achieved the lowest break-even cost, corresponding to an annual cost burden of $4,500 across 150 customers. These findings demonstrate that anaerobic co-digestion of food waste and FOG with wastewater sludge can enhance methane recovery, reduce landfill dependence, and maintain environmentally acceptable digestate quality.

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