Experiment series in environmental engineering: Experiment 8 (NUS ChBE, AY 2004/2005, Semester 1)

Potential contamination of natural water samples by microorganism is always a problem that must be properly controlled due to its potential consequences on public health. The microbiological testing of water to determine the presence of microorganism in water is expensive and tedious. Thus the concept of indicator organism is introduced. For the case of detecting fecal contamination of water, the indicator organism is total coliform. The objective of this experiment is to undertake a microbiological examination of 3 water samples (tap water, drain water and Escherichia. coli contaminated water control) by the Most Probable Number method and the IMViC test procedure. The tap water has no coliform bacteria present and is safe. The drain water MPN index is 1.100 per 100 ml at 95% confidence level and that of E.coli contaminated water is 75 per 100ml at 95% confidence level. The standard for drinking water (US EPA) is zero coliform CFU in 100 ml of water sample at 95% confidence level so the tap water meets the criteria. Only E. coli is detected in the E.coli contaminated water in the IMViC test but E.coli together with Enterobacter aerogenes is detected in the drain water thus indicating that the drain water may be contaminated by fecal pollution. Further studies can be conducted to verify this result and to investigate the likely sources of this fecal contamination. Done by: Luo Jinjing, Lian Juan, and Ng Wenfa