- With reference to microbiological contamination of marine gas oil:
(a) state the conditions that must be present for the microbes to live and multiply,(2)
(b) describe the effect of microbiological growth in the fuel;(2)
(c) explain how the contamination may be detected;(2)
(d) state how the risk of contamination may be reduced;(2)
(e) explain how the contamination may be removed.(2)
Microbiological Contamination of Marine Gas Oil
(a) Conditions for microbial growth (2 marks)
- Presence of water (free water or condensation in tanks).
- Suitable temperature and nutrients (hydrocarbon fuel provides food).
(b) Effects of microbial growth (2 marks)
- Formation of sludge and biomass that blocks filters and fuel lines.
- Production of acids and corrosive by-products that damage tanks and fuel system components.
(c) Detection methods (2 marks)
- Fuel sampling with microscopic/chemical analysis or dip-slide culture tests to reveal microbial colonies.
- Evidence of slimy deposits, filter blockages, or foul odour in tanks.
(d) Reducing the risk (2 marks)
- Regular draining of water from storage and service tanks.
- Use of biocides or additives to inhibit microbial growth.
(e) Removal of contamination (2 marks)
- Chemical treatment with biocides to kill microbes.
- Tank cleaning and fuel polishing/centrifuging to remove sludge, water, and dead biomass.