Production of biocomposite materials from activated sludge: polyhydroxyalkanoates reinforced with filamentous bacteria
| Author(s) | Liang, Xiangmin | |
| Date Accessioned | 2023-08-21T23:04:35Z | |
| Date Available | 2023-08-21T23:04:35Z | |
| Publication Date | 2023 | |
| SWORD Update | 2023-06-26T19:09:59Z | |
| Abstract | Polyhydroxyalkanoates (PHAs) are intracellular microbial polyesters that serve as bacterial carbon and energy storage substances. They share similar properties with many petroleum-based polymers, thus attracted significant interest due to their potential biodegradability and environmental benefits. In order to improve the mechanical properties of PHAs, many types of natural plant-based fibers have been successfully used as reinforcement agents of PHA-based composites. The overall goal of this research is to obtain both the matrix (PHA copolymer) and the reinforcement agents (filamentous bacteria) for biorenewable composites from adapted wastewater treatment systems, thus, develop biocomposite materials that are derived entirely from microorganisms growing naturally in wastewater treatment processes. ☐ Biocomposite materials with commercially available poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as matrix and filamentous bacteria as reinforcement were fabricated by melt extrusion and 3D printing. Filamentous bacteria were cultivated and enriched in a laboratory membrane bioreactor. Low dissolved oxygen, and nitrogen and phosphorus limited conditions were provided in the MBR, resulting in proliferation of filamentous bacteria with the sludge volume index as high as 703 mL/g. Sphaerotilus spp. were identified as the dominant filamentous bacteria by 16S rRNA gene sequencing. A relative abundance of these filamentous bacteria was 19% in the mixed cultures. The morphology of filamentous bacteria was observed using optical microscopy and atomic force microscopy (AFM). The aspect ratio (length to width ratio) of the filamentous bacteria was 346. ☐ The thermal properties of PHBV and filamentous bacteria were evaluated by differential scanning calorimetry and thermogravimetric analysis. The results suggested that the processing temperature of these composite materials should be around 185 °C to minimize thermal degradation of both commercial PHBV and filamentous bacteria. Tensile properties (e.g., tensile strength, elongation at break, and tensile modulus) and notched impact strength of composites with different fiber contents were also evaluated. The results showed that tensile modulus and notched impact strength of the composite with 20% fiber content (mass basis) increased 12% and 95%, respectively. ☐ AFM-based nanoindentation method was used to examine the mechanical properties of filamentous bacteria. The measured Young’s modulus of Sphaerotilus spp. was 91.4% higher than that of non-filamentous bacteria. The Halpin-Tsai and Tsai-Pagano equations were used to determine the theoretical Young’s modulus of filamentous bacteria-reinforced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The predicted values closely matched the experimental values, indicating that filamentous bacteria were randomly oriented and uniformly distributed in PHBV. ☐ A sequencing batch reactor was operated to enrich for PHA-accumulating bacteria, and the production of PHBV by the enriched cultures was maximized by a fed-batch reactor. The highest PHA content of 59% dry cell weight was obtained with 68% PHB and 32% PHV. PHBV extracted from the bacterial cells in the fed-batch reactor had a purity of 99.3%. A membrane bioreactor was used to cultivate filamentous bacteria-dominating cultures (19% relative abundance of Sphaerotilus spp.). Differential scanning calorimetry and thermogravimetric analysis of microbial PHBV suggested that the melt extrusion and 3D printing temperatures to be 170 °C and 180 °C, respectively, to minimize the thermal degradation of PHBV. Mechanical tests showed that the tensile modulus and notched impact strength of microbial PHBV improved by 57% and 45%, respectively, following the addition of 20% membrane bioreactor sludge. ☐ The research presented in this dissertation demonstrated that both biopolymer matrix and the natural fiber reinforcement for the composite materials can be recovered from microorganisms present in wastewater treatment systems. This development of biocomposite materials that are derived entirely from microorganisms growing naturally in wastewater treatment processes will help reduce the quantity of waste sludge from wastewater treatment plants and produce a green alternative to petroleum-based composite that are environmentally friendly, biodegradable, and sustainable. | |
| Advisor | Cha, Daniel K. | |
| Degree | Ph.D. | |
| Department | University of Delaware, Department of Civil and Environmental Engineering | |
| DOI | https://doi.org/10.58088/45rv-8m06 | |
| Unique Identifier | 1397065807 | |
| URL | https://udspace.udel.edu/handle/19716/33167 | |
| Language | en | |
| Publisher | University of Delaware | |
| URI | https://login.udel.idm.oclc.org/login?url=https://www.proquest.com/dissertations-theses/production-biocomposite-materials-activated/docview/2833375823/se-2?accountid=10457 | |
| Keywords | 3D printing | |
| Keywords | Filamentous bacteria | |
| Keywords | Mechanical properties | |
| Keywords | Melt extrusion | |
| Keywords | Polyhydroxyalkanoates | |
| Title | Production of biocomposite materials from activated sludge: polyhydroxyalkanoates reinforced with filamentous bacteria | |
| Type | Thesis |