|Author:||Ma, Tsz-chun Terry|
|Title:||Microbial synthesis and characterization of physiochemical properties of polyhydroxyalkanoates (PHAs) produced by bacteria isolated from activated sludge obtained from the municipal wastewater works in Hong Kong|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Polyesters -- Synthesis
Polymers -- Biodegradation
Sewage -- Purification -- Activated sludge process
|Department:||Department of Applied Biology and Chemical Technology|
|Pages:||xxviii, 216 leaves : ill. ; 30 cm|
|Abstract:||Polyhydroxyalkanoates (PHAs) are microbial-synthesized biopolymers that accurnulate as intracellular carbon and energy reserve materials in numerous micro-organisms. PHAs are attractive in research fields since they are biodegradable, biocompatible and possess properties similar to those of the conventional plastics such as polypropylene and polyethylene. Among many bacteria isolated from municipal activated sludge, Bacillus cereus (TRY2) was chosen and used for poly(3-hydroxybuytrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] biopolymers production because (1) it could produce HV% as high as 73.1% (in shake-flask fermentation) of the copolymer; (2) production of the copolymers could be achieved simultaneously with the cell growth and (3) desirable copolymers could be generated in a short period of time by means of batch fermentation (within 24 hours). In addition, as an environmental and clean production project, an investigation was conducted to find out whether wastewater treatment and polyhydroxyalkanoates (PHAs) production could be done at the same time in the simplest way in order to reduce sludge volume and produced valued product simultaneously. The study was divided into two parts. The first part studied the physical properties of P(3HB-co-3HV) copolymers with different HB to HV ratio produced by Bacillus cereus (TRY2) isolated from activated sludge. A 15 L B. Braun computer-controlled fermenter containing complex media including sodium propionate was used to perform the batch fermentation. Fermentation condition of 30 C, pH 7 (+- 0.05), 300 rpm stirring speed and 24 hours incubation period were kept constant throughout each of the experiments. The mol% of 3HV PHBV copolymers extracted for physical properties measurements after harvesting the cells were 0.05%, 22.6%, 39.2%, 54.1% and 69.1% respectively. Each of the copolymer films prepared after recovery process was used for Differential Scanning Calorimetry (DSC) analysis [for detection of glass transition temperature (Tg) and melting temperature (Tm)], Thermogravimetric Analysis (TgA) [for detection of the temperature at the onset of weight loss (TO), the temperature at the maximum rate of weight loss (TP), the temperature of complete degradation] and polymer purity (TF)], Water Resistance Test [for detection of degree of water absorption (in %) and degree of soluble matter loss (in %) after immersion of water at room temperature (25 to 30 C) and 60 C] and Tensile Testing (tensile strength and initial modulus analysis). The second part of the project was to study the possibility of wastewater treatment [measured by means of total organic carbon (TOC) and chemical oxygen demand (COD) reduction of activated sludge samples] and productivity of PHAs at the same time by Bacillus cereus (TRY2) (isolated from activated sludge), Pseudomonas spp. (TOB17) (isolated from activated sludge), recombinant Bacillus DH5帢 (recombinant bacteria that created by our team) and a combination of the above three bacteria. Each of the above bacteria, and the mixture of three was allowed to grow in 4 different media -(1) complex media including sodium propionate, (2) synthetic wastewater, activated sludge collected from (3) Tai Po and (4) Yuen Long wastewater treatment plants, HK. Their PHA production (mg of PHA / L of media used), COD reduction (in %) and TOC reduction (in %) after 24 hours shake-flask fermentation were measured and investigated. Culture condition of 30 C and 250 rpm stirring speed were maintained at constant throughout all the above experiments. The results were satisfactory that the maximum COD and TOC reduction of the sewage sludge were 53.5% and 67.5% respectively and, overall 391 kg of PHA could be produced from the sewage sludge everyday in Hong Kong. Different mol% of 3HV in P(3HB-co-3HV) copolymers possessing different physical properties that may be suitable for different PHA products applications, e.g. surgical suture and drug containers, etc., but further optimizations of the production are necessary to lower the cost of production and to increase their acceptance. In addition, it is possible to produce PHA and reduce wastes simultaneously according to the findings of this project. Again, optimization will be needed to further increase the yield of PHA produced and to assure it is of high purity after extraction for industrial applications in order to pursue the government in support of PHA industry.|
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