Effect of sunlight in decontamination of coliforms and faecal coliforms from drinking water

ABSTRACT

Drinking water samples were collected during December 1997 to March 1998 from Mingalar market, Nyaungbinlay market, Thaketa, Pazundaung, Botataung, Lanmadaw, Anawrahta, Ahlone, Sanchaung and Papedan Townships, Yangon. The presumptive coliform and faecal coliform counts were tested on all water samples. The pH and temperature were also recorded during the experiment. The coliforms and faecal coliforms were identified by multiple tube method and the count of coliforms ranged from 17 to > 2400 MPN/100 ml and faecal coliform count ranged from <2 to 140 MPN/100 ml. The temperature ranged from 40 to 47C during the experiment. There was no association between coliform counts and temperature variation. Forty percent and 90 percent of the samples became free of coliforms after exposure to sunlight for six hours and seven hours, respectively. When exposed to sunlight, 33 percent and 77.8 percent of the samples became free of faecal coliforms after four and six hours respectively. Coliforms and faecal coliforms were totally absent after exposure for 12 hours. It was effective by using clear transparent plastic bottles but the opaque plastic bottles were not. After exposure to sunlight for 12 hours; regrowth of coliforms and faecal coliforms were not observed up to three months, provided that the exposed bottles were tightly closed.