Thesis
The design, construction and commission of a fermentation plant, with gas recycle for the production of biomass from north sea gas and simple nitrogenous medium
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 1973
- Thesis identifier
- T140(1973)
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The purpose of this project was to design, build and commission a fermentation system for the production of biomass from north sea gas. The need for unconventional sources of protein and the status of biomass in this context was assessed. The advantages of microorganisms grown on different substrates as a source of biomass was discussed with particular reference to the use of hydrocarbon substrates. The extra cooling and oxygen requirements of hydrocarbon fermentations was noted and the influence of these factors on the overall process costs noted. The additional treatment of liquid and solid hydrocarbon grown biomass to remove potentially carcinogenic residues was compared unfavourably with biomass derived from gaseous hydrocarbons, where no such residues occur. The historical background and present state of research into the microbiological aspects of natural gas fermentations was reported and especial reference made to the difficulty of isolating methane oxidisers in pure culture. The comparative success of mixed cultures of methane oxidisers grown in fermenters was considered as a significant feature of these organisms. The rare use of gas recycle techniques in microbiological work was noted and the advantages of such a system in the reduction of substrate costs was discussed. The advantages of isolating methane oxidisers capable of growth at high temperatures (40°C or over) was examined. It was noted that the higher costs of oxygen supply and cooling for natural gas fermentation may offset the cost advantage of using the cheapest widely available carbon substrate. A fermentation plant was built comprising of two 5 litre fermenters used either as a multistage chemostat, or two single stage units, or as conventional batch fermenters, for the production of biomass from north sea gas at 40°C. The fermenters used were selected partially on the basis of an industrial standard of manufacture and were capable of high rates of gas transfer. This was considered essential to offset the relatively low solubilities of both oxygen and natural gas in water at the temperature used. A gas recycle scheme was used and several control loops were incorporated so that the concentration of the gases in the circulating gas mixture was automatically kept constant. Since a closed cycle was in operation, only one of the two major constituents of the gas mixture - oxygen - was controlled on the basis of concentration changes. The other - methane - was controlled by means of pressure changes which occurred due to microbial growth on these gases. A special device was designed so that in the event of the ethane in natural gas not being consumed, any build up of the ethane was prevented by an automatically controlled purging arrangement. An Integrator/photo cell device was used to record the total flow of gas through the ethane purge route. Extensive use was made of recorders so that continuous traces of the various fermentation parameters could be compared. A new type of dissolved oxygen electrode employing a silicone nylon reinforced membrane was described. At the high rates of agitation in the fermenters both vessels were completely full of a gas/liquid foam emulsion so that conventional volume control during continuous culture was impossible. A method of volume control was designed based on the differential measurement of current consumed by the fermenter stirrer motors at different volumes of liquid (i.e. at different foam densities). Changes in current consumption were detected by a photocell which operated flow inducers to remove culture fluid or deliver fresh medium. The fermentation plant was situated in safety cubicles at a considerable distance from the nearest autoclave. Steam sterilisation of large quantities of liquid medium was therefore impractical and an automatic filtration rig was built which enabled automatic delivery of sterile medium to reservoirs in the vicinity of the fermenters. The transfer of medium from the reservoirs to the fermenters was automatically operated. Only bulk medium preparation was manual. The explosive nature of methane/oxygen mixtures necessitated the consideration of safety features in detail. Several fail safe devices were incorporated into the plant and much use was made of intrinsically safe or flame proofed equipment. A mixed culture of micro-organisms was isolated in the equipment described, which was able to oxidise both ethane and methane in batch culture at 40°G. The culture appeared to consist of a Gram- rod together with a Gram+ rod and a Gram+ yeast.
- Resource Type
- DOI
- EThOS ID
- uk.bl.ethos.880501
- Funder
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