Parasitic and bacterial contamination in collards using effluent from treated domestic wastewater in Chiang Mai, Thailand.

Thailand often has inadequate water supply for agriculture during the dry season. The reuse of treated wastewater treatment plants could solve this problem. Treatment of domestic wastewater of Chiang Mai municipality by the aerated lagoon system (AL) releases more than 25,000 m3 of treated water everyday. The reuse of wastewater in agriculture is an efficient use of water, especially in tropical countries or in drought zones. The objective of this study is to demonstrate the possibility of using treated wastewater in growing edible vegetables, ie collards (kale), without pathogenic parasite and bacterial contamination. Collards (Brassica oleracea var acephala) were grown using either the treated wastewater from the aerated lagoon system (AL) or ground water (GW). Three cropping times were scheduled in February, May and July, 2000. Samples of water from AL system and GW were taken two times per month (the consecutive weeks) from February to July and examined for bacteria and parasites. Irrigation water (IW) that was normally used in agriculture was also collected, at the same time of the AL and GW collection, for bacteria and parasite investigation. A soil sample was taken before and after each crop for parasite examination. Collards were also collected at the end of the crop for parasite investigation. The results showed that GW seems to be a clean water since no pathogenic bacteria were found although small amount of Escherichia coli was noted in May. For AL and IW, similar number and types of bacteria were found. They were Aeromonas sobria, A. hydrophila, E. coli, Citrobacter freundii, Pseudomonas aeruginosa, non-pathogenic type of Vibrio cholerae. The small number of Salmonella enteritidis gr E was found in AL in April. After investigating 12 samples in 6 months of each kind of water, ie GW, Al, and IW, no parasite was found. Only unidentified free living nematodes were found in IW but those parasites are non pathogenic. A small number of unidentified free living nematodes (UFLN), a natural parasite, were found in soil after cropping. After each cropping time, similar number of hookworm was found in the plots which used either GW or AL. Collards grown by using either GW or AL showed no harmful parasite contamination. We conclude that the effluent from wastewater treatment, using aerated lagoon system, of Chiang Mai municipality could be safely used for growing collards.

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

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.