A Review on Influential Factors on Polyhydroxyalkonates (PHA) Production with Feast /Famine Regime Using Waste Sludge from Biological Wastewater Treatment

Due to the increased use of plastic materials in the daily lives of human all over the worlds and the concerns about the negative impacts of petroleum based plastics on aquatic and soil environments, the researchers have attempted to introduce biodegradable alternatives to such plastics. The non-biodegradability of petroleum based plastic is due to the large and long polymer molecules and the strong bonds between them, which ultimately makes it very difficult and even impossible for microorganisms to break down the molecules. The bioplastics are simply decomposed into their constituent units by the activity of living organisms and do not remain in the environment. Polyhydroxyalkonates (PHAs) are among the biodegradable polymers that have been received attention in the recent years. PHAs are polyester compounds that are produced by bacteria under special conditions. Feast/famine methodology is one of the methods for PHA production from bacteria. In this method, a sequencing batch recator (SBR) is used to supply feast and famine conditions, so that bacteria which are capable to produce PHA, compete with other microorganisms and obtain the maximum amount of PHA from the culture medium. In this review article, the method of feast/famine and the influential factors on producing PHA including feed type, feast/famine ratio, feed to microorganism (F/M) ratio, dissolved oxygen and nutrients concentration are investigated.