Industrial production of polyhydroxyalkanoates using Escherichia coli: An economic analysis

Abstract

Disposal of plastic, in particular packaging, is a serious problem confronting many countries. Part of a solution lies in using biodegradable plastics such as polyhydroxyalkanoates (PHAs), which can be produced by bacterial fermentation. This paper presents an economic analysis of PHA production by fermentation using recombinant Escherichia coli, in order to identify areas where significant cost reductions are possible. Based on an annual production of 4300 tonnes of poly-hydroxybutyrate (PHB) from glucose supplemented with complex nitrogen sources, the break-even selling price per kilogram of plastic is US1995$6.08. A ten year plant life, 40% tax rate, 10% discount rate and a conservative process design based on existing technology are assumed. This cost is highly sensitive to PHB expression level and recovery strategy, and moderately sensitive to medium cost and cell growth yield on glucose. Maximum cell density achieved has little effect for the process design used in this analysis. At the same level of production, the cost can be easily reduced to between US 1995$5.63 kg-1 and US1995$3.59kg-1 by using dairy whey as a partial replacement for glucose as the carbon source. The price variation represents different constraints on whey availability and credits for whey disposal. Further price reduction will require significant changes to existing process technology. For example, a scenario incorporating 60% glucose substitution with concentrated dairy whey and a significantly altered processing strategy has the potential to reduce PHB production cost to US1995$2.67kg-1 . Significant work remains to develop and optimize such cost-effective designs.