DISTRIBUTION AND REMOVAL OF GIARDIA AND CRYPTOSPORIDIUM IN WATER-SUPPLIES IN GERMANY

This study has been conducted, to estimate the distribution of Giardia and Cryptosporidium in German water supplies and the removal efficien cy of surface water treatment plants for Giardia and Cryptosporidium b y conventional treatment. Water samples from six surface water treatme nt plants in different parts of Germany were simoultaneously examined for Giardia and Cryptosporidium. Investigations for both parasites wer e carried out in the period from July 1993 until December 1995. The re sults confirmed the occurrence of Giardia and Cryptosporidium in surfa ce and raw water, in intermediate steps after treatment, in back wash water, in the first filtrate and in final water. Giardia or Cryptospor idium or both have been found in 76.2% of me investigated raw water so urces. The average number of the detected Giardia cysts was 88.2/100 l (max.1314/100 l), and the average number of Cryptosporidium oocysts w as 116/100 l (max. 1081/100 l). In the intermediate steps (including f locculation and several steps of filtration), Giardia or Cryptosporidi um or both have been found in 33.3% (50/150) of the samples. 14.9% of drinking water samples (7/47) were positive for Giardia (max. 16.8/100 l) and 29.8% (14/47) were positive for Cryptosporidium (max. 20.8/100 l). Overall, Giardia and Cryptosporidium, or both were detected in 38 .3% of the drinking water samples. The parasites have been found in ne arly all of the investigated backwash water samples. The filtrate of a rapid sand filter was analysed immediately after-filter backwashing d uring the ripening period of the filter. Good elimination results were obtained by optimizing relevant water treatment process, but a low fl occulant dose following sudden variation in the raw water quality, cau ses a breakthrough of Cryptosporidium into the treated water. Although water treatment technologies are effective to remove Giardia and Cryp tosporidium, the results clearly show that Giardia and Cryptosporidium evade the filler harries in the absence of visible treatment deficien cies and low turbitidy level, and contaminate final water. (C) 1998 IA WQ. Published by Elsevier Science Ltd.