Study of four new, field-based, microbiological tests : verification of the hydrogen sulfide (H₂S), Easygel®, Colilert and Petrifilm(tm) tests

Abstract

Currently, the U.N. defines water sources as "improved" (e.g. public taps, protected dug wells and springs, rainwater collection) and "unimproved" (e.g. surface waters, unprotected dug well and spring, and vended water). Although these water quality indicators are easy to measure, they do not reflect the actual quality of the drinking water source. A more accurate method of determining drinking water quality is to perform laboratory drinking water quality tests. Laboratory testing is especially difficult in developing countries where funds, technology, laboratory facilities, and trained laboratory personnel are lacking. Fortunately, over the last 30 years, scientists, researchers and inventors have developed a series of low-cost, microbiological, field-based tests. These include the Presence/Absence (P/A) hydrogen sulfide (H2S) test, the enumerative Easygel®, test, the 10-mL P/A Colilert test and enumerative PetrifilmTM test. However, the accuracy of these tests has never verified or established. The objective of this thesis is fourfold: (1) to verify the accuracy of the four field-based tests: the H2S tests (laboratory-made reagent for 10-, 20- and 100-mL sample volume, and industry-made HACH PathoScreenTM reagent), Easygel®, , Colilert and PetrifilmTM, by comparing them to two Standard Methods tests: Quanti-Tray® and membrane filtration; and to assess these tests based on two other factors: cost and practicality/ease of use; (2) to assess the suitability of the H2S producing bacteria as an indicator of fecal contamination; (3) to provide recommendations for the use of a single P/A test and a single enumerative test (PetrifilmTM or Easygel®, ) to be used on the field; and (4) to provide recommendations for a testing combination made up of one P/A test and one enumerative test. The tests used in this study were conducted on water samples collected from Capiz Province, Philippines, and from the Charles River, Cambridge, MA. The H2S-producing bacteria was found to be a valid indicator of fecal contamination. However, further testing is recommended to ensure that the H2S-producing bacteria meet all the WHO requirements for an ideal indicator of fecal contamination. The study recommends the use of the 20-mL H2S test and the Colilert test as a single P/A test for testing improved and unimproved water sources, respectively. The use of the Easygel®, test as a single enumerative test is recommended for testing improved water sources, and the use of the other enumerative tests (Easygel®, and PetrifilmTM) is strongly discouraged for unimproved sources. The combination of the 20-mL H2S test and Easygel®, combination is recommended for field-based microbiological drinking water quality testing.