Objective: To study growth and 1,3-propanediol production kinetics of Clostridium diolis under batch cultivation conditions in bioreactor.
Theory: Basic concepts and Need for production of 1,3-propanediol
The escalating global energy demands, skyrocketing fuel prices, environmental concerns and a predilection for use of cleaner, inexhaustible and environment friendly resources over the exhaustible and dwindling petrochemical resources call for green production of industrially important metabolites. In the recent past there has been an increasing interest in the production of biodiesel as a popular alternative transportation fuel. It is a non-toxic fuel which is derived from vegetable or animal fats by the process of trans-esterification. Huge amounts of glycerol are available (1 gallon of crude glycerol is left behind for every 10 gallon of biodiesel produced) against a meagre demand. This has led to a steep decline in glycerol prices with even shutting down of glycerol production plants by Dow Chemicals and P&G. Thus innovative strategies befitting the disposal of this enormous waste glycerol stock are required to increase the sustainability and economic viability of biodiesel plant. An interesting way is the bioconversion of this ‘waste product’ to a ‘high-value added’ product such as 1,3-propanediol (1,3-PD).
1,3-PD is an organic compound with noticeable properties particularly for polycondensation reactions to synthesize polyesters, polyethers and polyurethanes. It has gained commercial attention as an important monomer to synthesis a new polyester polytrimethylene terephthalate (PTT) which is principally used in the manufacture of carpet and textile fibres but also finds applications as engineering thermoplastics, films and coatings. 1,3-PD has enormous other uses in chemical and cosmetic industry e.g. solvent, adhesives, resins, lubricant, antifreeze, cosmetics, detergents, water-based inks, immunosuppressive drugs, repellents, fragrances etc. The classic production route to this valuable monomer is the chemical process which entails the use of high pressure and temperature, expensive catalysts and accumulation of toxic by-products. Biological alternative to chemical synthesis for 1,3-PD is possible by the use of microorganisms belonging to the genera Clostridium, Klebsiella, Enterobacter and Citrobacter which can use glycerol for bioconversion to 1,3-PD.
Though bio-based production presents a cleaner, environmentally favourable route to 1,3-PD, the major bottleneck in the batch cultivation process is inhibition from both substrate and product which reduces the overall growth and product formation rates. Thus it becomes rather difficult and tricky to design fresh nutrient feeding strategies in selected fed-batch/continuous cultivations as it invariably features a scenario of cultivation when the culture is either starving or inhibited during the entire cultivation period. The conventional trial and error approach of nutrient feeding strategy for high productivity cultivation is laborious, frustrating, time-consuming and inefficient. In such a case, a mathematical model-based approach appears to be intelligent, fast, reliable and productive. The model can be used as a ‘tool’ to design fresh nutrient feeding strategies for maximum 1,3-PD production during fed-batch &/or continuous cultivation processes which can then be experimentally implemented to optimize the fermentation in minimum experiments.