Production of Polyhydroxybutyrate (PHB) from batch fermentation of hemp wastes via co-fermentation of Cupriavidus necator with Paraburkholderia sacchari

Abstract

Polyhydroxybutyrate (PHB) is a biopolymer from the polyhydroxyalkanoates (PHA) family, produced as a result of secondary metabolic reactions for energy storage in cells. It has gained considerable attention due to its biodegradability, biocompatibility, mechanical properties and potential to replace petrochemical based plastics, addressing the growing environmental concerns related to plastic pollution. Moreover, PHB is a promising material for applications in packaging, agriculture, biomedical devices, and more. However, challenges in its production, including high production costs and resource demands, hinder its large-scale adoption. The price for biodegradable plastics is approximately 20-30% higher than traditional plastics and the total production cost is heavily influenced by the cost of raw materials costs such as feedstock and water resources. As a result, optimizing its production process is critical for improving its economic viability and sustainability. In this study, hemp biomass has been explored as an alternative feedstock to produce PHB. Hemp biomass is a byproduct of the textile industries and hemp seed processing industries that is obtained as a remnant part after bast fiber and seed are removed from the shoot system of the plant. Being rich in cellulose and hemicellulose, hemp biomass can be processed into glucose and xylose rich hydrolysate that can be consumed by bacteria such as Cupriavidus necator and Paraburkholderia sacchari to produce PHB. C. necator can produce PHB from glucose and lignin while P. sacchari can coferment glucose and xylose to produce PHB. This thesis focused on exploring various factors that affect PHB production from hemp hydrolysate using two different microorganisms. Chapter 1 entails the literature review of the relevant information regarding hemp biomass as feedstock and PHB production procedures via C. necator and P. sacchari. In chapter 2, pretreatment parameters for alkaline treatment of hemp biomass were optimized and the PHB production capacity of the two bacteria, in individual and combined manner, in hemp hydrolysate were studied. Pretreatment of hemp biomass with 1% sodium hydroxide for 1 h at 130°C was observed to be significantly superior during pretreatment optimization. Similarly, hydrolysate with C. necator only achieved maximum PHB yield of 0.433 g/g sugars (specifically from glucose) at 48 h from the start of fermentation while combination of C. necator and P. sacchari showed significant effects on utilization of both glucose and xylose in the hydrolysate to produce maximum yield of 0.341 g/g sugars at 48 h. To reduce water demand during washing of solids prior to hydrolysis, unwashed solids were processed under different alternatives in chapter 3 where maximum PHB yield of 0.65 g/g sugars was obtained for liquid hot water pretreated hemp solids and undetoxified prehydrolysate using C. necator, which consumed lignin derivatives and sugars in the media. Finally, chapter 4 concluded the findings and understanding of this research study along with recommendations for future experiments.