Date of Award

August 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Member

Amy E Landis

Committee Member

Claire Dancz

Committee Member

Karen High

Committee Member

Prathap Parameswaran

Committee Member

Bradley Putman

Abstract

Organic waste streams often include bioplastics, such as polylactic acid (PLA) and food waste. PLA is a plant-derived bioplastic intended to replace petroleum based plastics; it is often used to make utensils and food packaging. Recently, managing food waste and PLA are becoming more and more complex as the amounts disposed continue to increase. PLA and food waste are often comingled during disposal since PLA is touted as being compostable. However, PLA does not degrade at the same rate as food waste in compost facilities. As such, PLA builds up within compost facilities and has to be screened out and ultimately is sent to landfills. Thus, PLA is not actually achieving the sustainability or landfill waste diversion goals that were originally envisioned for the product. And PLA does not become part of the soil amendment that can be produced from composting food waste. Despite the benefits of composting food waste, both food waste and PLA are commonly disposed of in landfills; sending food waste and PLA to landfills without energy recovery are unexploited sources of energy. Most landfills in the US do not capture methane generated from the degradation of organic wastes. Anaerobic digestion is a renewable energy technology that converts organic waste to value products under anaerobic conditions and could be a viable waste management option for food waste and PLA.

The aim of this dissertation is to develop waste management methods for anaerobic digestion of food waste and PLA with energy recovery. In order to enhance the degradation of PLA, an alkaline pretreatment was investigated for its potential to accelerated degradation of PLA and its performance when anaerobically digested with food waste. The dissertation further investigates the environmental impacts associated with this new technique through life cycle assessment. The anaerobic digestion system was evaluated for Sittee River, Belize. The aim of the international research component was to quantify the amount of food waste generated by the community, to estimate the environmental and cost impacts of implementing waste to energy solutions in a rural developing community, and to evaluate whether or not waste could be used to meet local cooking needs for Sittee River’s local school.

Results from this dissertation showed that the best food waste to inoculum ratio was 1.42 g chemical oxygen demand (COD)/g volatile solids (VS) due to its short lag time, highest CH4-COD recovery and methanogenic yield. In addition, amorphous (i.e. thin film) and crystalline (i.e. plastic cup) PLA reached near complete solubilization at 97% and 99% respectively, when alkaline pretreatment was applied. Furthermore, this dissertation shows that treating PLA with alkaline pretreatment has the greatest solid reduction of PLA and maximum production of methane when combined with food waste and anaerobic digested sludge. Incorporating anaerobic digestion as a waste management technique in rural communities, like Sittee River, Belize, may reduce greenhouse gas emissions while providing a cost effective fuel for cooking. Lastly, the life cycle assessment found that sending food waste and treated PLA to anaerobic digestion emits the least amount of CO2 equivalent emissions when compared to landfill and compost.

The outcomes from this dissertation not only develop novel and innovative technical and computational solutions to determine the best method to recover energy and biosolids value, but also provide real solutions for wastewater treatment plants and developing, rural communities. In addition, this research was used to evaluate the waste management techniques of Sittee River, Belize (a rural developing community) and provide recommendations for a renewable source of energy for cooking school lunches.

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