Date of Award

Fall 2019

Document Type


Degree Name

Master of Science (MS)


Civil and Environmental Engineering

First Advisor

Zitomer, Daniel H.

Second Advisor

Mayer, Brooke K.

Third Advisor

McNamara, Patrick J.


Organic polymer plastics are often short-lived commodities for single-use that result in landfill buildup and persistence in the environment. Plastic waste accumulation can cause ecological damage. Plastic production continues to outpace plastic waste management and perpetuates the growing epidemic of plastic pollution. More efficient handling of plastics would be beneficial. One improvement involves biodegradable plastics (i.e., bioplastics), particularly polylactic acid (PLA) and polyhydroxyalkanoates (PHA), which can alleviate environmental concerns stemming from mismanagement. Yet, there are currently no bioplastic waste management strategies scalable to handle the millions of pounds of bioplastics that enter the waste stream. Therefore, new bioplastic resource recovery options were investigated through anaerobic co-digestion, a potential solution that can take advantage of existing digesters to convert bioplastic to biogas containing methane for renewable energy. Bioplastics biodegrade, but their potential to completely biodegrade on a time-scale compatible with current anaerobic digestion technologies is largely unknown. Accordingly, base-catalyzed thermal pretreatments were investigated to increase biodegradation rates. Batch experiments revealed pretreatments at 55 °C, pH 12 for PHAs and 90 °C regardless of pH for PLA produced the greatest increase in subsequent bioconversion to methane. Polyhydroxybutyrate (PHB) showed the highest rate of methane recovery and was selected for high-rate anaerobic co-digestion investigations simulating full-scale anaerobic digestion at municipal water resource recovery facilities. Synthetic municipal primary solids were co-digested with untreated or pretreated PHB at a 15 d retention time and resulted in 79-93% and 84-98% bioplastic conversion to methane, respectively, corresponding to a 5% additional increase when pretreated. Microbial communities analyzed via Illumina sequencing showed archaea were unchanged in response to PHB co-digestion, whereas the bacterial community changed, with increased relative abundance of Kosmotoga, Deferribacter, Geobacter, and Ruminococcus. Therefore, these taxa may be important for PHB biodegradation. The results of the current study suggest anaerobic co-digestion at municipal water resource recovery facilities is a feasible waste management option for PHB bioplastics, which may help to alleviate challenges associated with contemporary single-use plastics. Near complete conversion of PHB bioplastic to methane in just over two weeks signals a great compatibility with completely-stirred tank reactor co-digestion.

Included in

Engineering Commons