ارزيابي روش هيدروژن سولفايد در تعيين آلودگي مدفوعي منابع آب آشاميدني

Evaluation of hydrogen sulfate technique in determining fecal contamination of drinking water sources

Aims. Fecal contamination determining in drinking water sources is a communicated problem, especially in locations without laboratory equipment. An alternative low-cost test for fecal contamination in drinking water is the hydrogen sulphide (H2S) method. Methods. Totally, 116 drinking water samples were collected from piped supplies, dug wells and surface water. The water quality was determined by the standard of most probable number (MPN), P/A, EC-M and H2S techniques. The influence of incubation period, incubation temperature and concentration of fecal coliform were tested by H2S method. Also the efficiency, predictive value for +ve, predictive value for -ve, specificity and sensitivity of H2S method were examined in comparison of a reference methods. Results. 91.66% of positive samples in standard MPN technique were positive for H2S method with black precipitation. More than 90% of positive samples in standard MPN technique were positive by H2S method with black precipitation. In addition, the color changes would have been violent if the MPN had increased in sample. Temperature is the important factor to reduce the required incubation period. In fact, at higher temperature (45 °C) the bottles turned black just after 6 hours of incubation. The sensitivity, specificity, predictive value for +ve, predictive value for -ve and accuracy of H2S test is 90.91, 67.74, 83.33, 80.77 and 82.56%, respectively. Conclusion. The results of H2S tests are visual and therefore it is simple for the operator to distinguish the contamination, as a black color change occurs when bacteria levels in drinking water are high.