Natural gas for production of single-cell protein
The past and the future
By Professor Dr. Techn. John Villadsen
March 2006
Abstract
Large-scale production of commodity chemicals by fermentation routes may well become one of the fastest moving enterprises of the early 21st century. Among the most promising processes is the production of animal feed from natural gas, a cheap and abundantly available natural resource.
Currently animal feed rich in protein is produced from fishmeal, but progressive overfishing of the oceans leads to rapidly increasing prices of fishmeal, and the price of e.g. aquaculture fish is consequently being driven up, thus drastically aggravating the nutritional problems faced by third-world populations.
A fermentation process in which methane from natural gas is used as a carbon source for a bacterial culture found in the natural habitat can be utilised in an industrial production of a highly rich product. The only other raw materials are O2, NH3 (or ammonia salts) and a few other minerals. This product is at least nutritionally equivalent to high-quality fishmeal (LT) and furthermore free from dioxin and heavy metals.
The final product is a bright, brownish powder of uniform quality and with a P-content much smaller than fishmeal, thus giving rise to no environmental problems. The fish fed with UniProtein are generally healthy, requiring no costly vaccination during growth, and the digestibility of UniProtein is at least on par with high-quality fishmeal.
The fermentation is conducted in continuous mode with a holding time of the liquid medium around 5 hours. Gas (CH4 and O2) is sparged into the bioreactor, and with a holding time of 60 -100 s the conversion of O2 is around 95%.
The two main process challenges are
• to maximise the conversion of the carbon source to give a high protein yield and a
high productivity in the reactor.
• to ensure that CH4 and O2 are transferred from the gas phase at a rate that corresponds
to the rate of the carbon consumption by the microorganism.
Extensive studies conducted from the mid-1980s with Mr Busch Larsen in his Danish company Dansk BioProtein and at Danish universities, in particular the Technical University of Denmark (DTU), have led to an order of magnitude increase in the metabolism of the microorganism, and various sources of culture instability have been eliminated.
In recent years further research headed by UniBio A/S with financial support from the Danish Ministry of Climate and Energy, the Danish engineering company Ramboll and DTU has led to qualitative improvements of the reactor design, thus making the overall energy input to the process much smaller.
Production plants of 100,000 tonnes SCP per year or more can now be constructed using a modular design with bioreactors of 100 m3 capacity servicing a common downstream product recovery unit with centrifuges, homogenisation units, ultra-filters and spray driers.
It is estimated that at least 20 such plants can be erected in different parts of the world with readily available natural gas. These plants will serve just to cover the current deficit of high- quality fishmeal.
Apart from the obvious use of the product as animal feed, research in Denmark and Norway has shown that the product can easily be modified to serve as a rich diet for human consumption, and industrial applications for SCP are also being developed.
Video: Visualisation of factory on Trinidad & Tobago