Production and recovery of poly-β-hydroxybutyrate from whey degradation by azotobacter
Poly-β hydroxyl-butyrate, (PHB) is a biodegradable thermoplastic which can be extracted from a wide range of bacteria. PHB belongs to the class of bacterial polyesters collectively called polyhydroxyalkanoates, (PHAs). PHAs have properties similar to polypropylene and are important due to their complete biodegradability, with recognised potential applications in reducing disposable waste problems and in certain medical applications (Gostomski, and Bungay, 1996). These biodegradable thermoplastics can be used as packaging material and can be utilized as drug delivery systems, since these polymers are immunologically inert. Biodegradable polymers would help to reduce solid waste disposal problems associated with most plastics. The polymer which provides a reserve of carbon and energy, accumulates as intracellular granules. Several factors influence the economics of biodegradable polymer production. One factor is the cost of the substrate. The ability to produce biodegradable polymers from inexpensive and renewable carbon sources, such as xylose and lactose, may help to improve the economics of the process. Whey is the liquid part of milk that separates from the curd at the beginning of the cheese making process. In the past whey was considered waste. It was difficult to dispose of and sometimes contributed to environmental damage, for example by adding salt to soil or waterways. It is rich in nutrients and contains at least half the solids found in whole milk (Horton, 1993). Whey has a very strong polluting capacity, with a biological oxygen demand (BOD) of 40,000 to 45,000 mg/L (Hacking, 1988; Kemp and Quickenden, 1989). In recent years, value added products form wheyhave attracted much interest.