PEP Review 2002-8
Polyhydroxyalkanoates from Organic Wastes
Published: September 2003
Poly(3-hydroxyalkanoates) are linear aliphatic polyesters composed of 3-hydroxy fatty acid monomers. They are biodegradable thermoplastics produced naturally by a number of bacteria as intracellular energy reserves. While PHAs have good properties that potentially could serve well in certain large volume applications such as packaging, a major barrier to their wide spread use is their high production cost.
In 2003 I-PHA Biopolymers Ltd. in Hong Kong announced that it had signed a technology license agreement with the University of Hawaii for PHA production technology based on fermentation of organic waste materials. The company plans to build a pilot plant in Yuen Long, Hong Kong for the production of PHA and organic fertilizers. After the pilot process is developed, the next production scale would be 3,000 tonnes/yr.
Organic wastes are potential low cost fermentation substrates for making PHA. U.S. residents, businesses and institutions produced more than 230 million tons of municipal solid waste (before recycling) in 2000. About 11%, or 26 million tons, were food scraps. Researchers at the University of Hawaii have developed a new technology that couples anaerobic digestion of food scraps with aerobic fermentation to make PHAs. Food wastes are digested in an anaerobic fermentor producing four major organic acids: acetic, propionic, butyric, and lactic acids. The fermentative acids are transferred through membranes into an air bubbling fermenter where they are utilized to produce PHAs in an enriched culture of R. eutropha. PHA composition may be controlled by membrane selection, which affects the relative rates of mass transfer of acids through the membrane. The University of Hawaii has applied for a patent and the application was published in 2003 (WO 03/062439).
Our economic evaluation, based on PEP's concept of the process, indicates that the use of organic waste as a fermentation substrate rather than glucose and propionic acid only modestly improves the process economics. Capital-related items still make up a large share of the overall economics. Recovery costs are a consequential portion of total costs. Efficient product recovery is a challenge for fermentation processes employing intracellular organisms such as R. eutropha.