The effects of incubation period and temperature on the Hydrogen sulphide (H2S) technique for detection of faecal contamination in water

Abstract

A total of 171 water samples from 3 sources were analyzed for the presence of faecal contamination by standard MPN, P/A, EC-M and H2S techniques at different temperatures and incubation times. Analysis of water samples by H2S technique showed that the incubation period of H2S bottles is highly dependent on temperature and concentration of faecal coliform bacteria. Incubation temperature was changed from 22 to 45°C. At higher temperatures (45°C) the bottles turned to black after a 6 h incubation period. Correlation of H2S technique with P/A and MPN techniques were 75.4 and 71%, respectively. Furthermore, the P/A technique showed a correlation of 60.9% with standard MPN technique. In relation to the faecal coliform and by using EC-M technique, we obtained a correlation percentage of 65.1, 56 and 62.3% for standard MPN, H2S and P/A techniques, respectively. This study indicated that incubation period and temperature had significant effects (P = 0.05) on the efficiency of H2S technique. The times when H2S bottles take to turn black is dependent on the number of faecal bacteria, an indicator of the risk that pathogenic organisms are present. Based on the results obtained in this study, we concluded that H2S technique is a reliable method that can be used as an alternative for indication of faecal contamination and drinking water quality surveillance. By using this technique at high t emperatures, rapid screening of large number of water samples in a short period can be profitable especially when the number of drinking water sources is high.