Examination for intestinal parasites and enteric bacteria in the wastewater and treated wastewater from the city of Chiang Mai, Thailand.

ABSTRACT

An attempt to use treated wastewater for agriculture in the Chiang Mai area was made, but the re-use process had to be performed under a condition that limited the risks liable to leave pathogens present in the water. The objective of our study was to examine the intestinal parasites and enteric bacteria in the wastewater and treated wastewater from the Chiang Mai University campus as well as the treated wastewater from the Chiang Mai municipality. The raw wastewater (RW), primary treatment effluent water (PE), treated wastewater using the activated sludge system (AS) from the Chiang Mai University campus and treated wastewater using the aerated lagoon (AL) system from the Chiang Mai municipality were examined for intestinal parasites and enteric bacteria by using the centrifugal sedimentation and conventional methods respectively. The ground water (GW) and the irrigation water (IW) were used for comparison. All kinds of water were collected and examined twice a month for 6 months (February to July 2000). None of human intestinal parasites were found from any wastewater, whereas the RW and PE water contained hookworm larva, Ascaris egg and Taenia egg on some occasions. A small amounts of pathogenic bacteria that can cause severe diarrhea were detected. Salmonella enteritidis gr E was isolated from the AL water in April, while Vibrio cholerae type O139 was detected from the PE water in June. Some pathogenic bacteria that might cause gastroenteritis, such as Aerobacter spp, Citrobacter spp, Pseudomonas spp and Escherichia coli were also found in all kinds of water. Between the two types of treated wastewater, the bacteria found in AS water was less than that in AL water in terms of both amount and type of bacteria. The treated wastewater from the city of Chiang Mai, compared to natural water such as irrigation water, appears to be safe to use for agriculture.