Dirk Schoenen

Biodosimetry : Model calculations for u.v. water disinfection devices with regard to dose distributions

Abstract The increasing importance of disinfection of drinking water by u.v. radiation makes it necessary to determine the u.v. dose which is applied to the water by u.v.-disinfection plants. In Austria a minimum microbicidal dose of 400 Jm −2 at a wavelength of 253.7 nm is demanded for drinking water, the control of it shall be assured by type testing. A method was developed in using calibrated spores of Bacillus subtilis as biodosimeter which are added to the inflowing water, and after determination of their survival rate in the plant one can deduce the applied dose from it. This procedure is unproblematic as long as all microorganisms receive the same dose on their way through the reactor. But in some cases, and probably this is the normal case, not all microorganisms receive the same dose. It follows that a dose distribution will exist among the test organisms which have passed through the reactor. The dose (reduction-equivalent dose or RED) which is deduced from the survival rate of the microorganisms passing flow-through systems for u.v.-disinfection of wastewater or drinking water in general is different from the arithmetic mean of the dose distribution. The RED depends on the special form of the dose distribution and on the specific shape of the survival curve of the test organisms. The broader the dose distribution and the higher the u.v.-susceptibility of the microorganisms, the lower is the measured RED. But if the survival curve of the microorganisms used would have a shoulder ( D s > D m ), and the dose distribution would overlap with the shoulder the RED may increase. We investigated by calculations and by experiments the influences on the test results obtained by this method.

Invertebrate colonization of granular activated carbon filters

Results of biological sampling of granular activated carbon (GAC) filtrate taken between May 1994 and August 1995 at three different treatment plants along the river Rhine indicate that GAC filters are colonized by invertebrates. Dominating organism groups were rotifers and nematodes. Depending on operational characteristics, mainly regeneration intervals and backwashing procedures, the filter colonization can lead to an output of organisms in high numbers with the filtrate. Examples are given for the development of filter colonization and for the influence of different backwashing procedures to reduce numbers of invertebrates in GAC filters. These findings underline the establishment of a complex food web in a GAC filter, the consequences of which still remain to be investigated in detail.

Giardia and Cryptosporidium in backwash water from rapid sand filters used for drinking water production.

Backwash water from rapid sand filters of a treatment plant using surface water from small rivers for drinking water production was examined with the aim of determining the degree of their potential contamination with Giardia cysts and Cryptosporidium oocysts. Simultaneous investigations were carried out for both protozoans from November 1993 to February 1994. Water samples were concentrated by continuous flow centrifugation (11 backwash water samples) or by using polypropylene cartridge filters (12 raw water samples and 39 backwash water samples). Parasites were identified by the direct immunofluorescence assay. Ten out of 12 raw water samples tested were positive for Giardia (range: 2-103/ 100 L) and 8 out of 12 were positive for Cryptosporidium (range: 0.8-109/100L). Eight of 11 backwash water samples collected by continuous flow centrifugation were positive for Giardia (range: 3-86/100 L) or Cryptosporidium (range: 1-69/100 L). Out of 39 samples collected using cartridge filters, 34 were positive for Giardia (range: 1.4-374/100 L) and 33 for Cryptosporidium (range: 0.8-252/100 L). Overall, Giardia, Cryptosporidium, or both were detected in 92% of the backwash water samples. The results have clearly shown that backwash waters were contaminated with Giardia and Cryptosporidium and the supernatant returned to the raw water after the sedimentation process was not free from cysts and oocysts.

Bench scale experiments for the evaluation of a membrane filtration method for the recovery efficiency of Giardia and Cryptosporidium from water

Abstract The method of membrane filtration was evaluated regarding the recovery efficiency of Giardia cysts and Cryptosporidium oocysts from water. Equal volumes of distilled water were contaminated with a defined numbers of cysts and oocysts (1×10 2 , 1×10 3 , 5×10 3 and 1×10 4 parasites l −1 ) and filtered through a special membrane filter apparatus. After filtration, the recovered cysts and oocysts were identified using phase contrast microscopy and the number of cysts and oocysts were counted using a Neubauer haemocytometer. The average recovery rate obtained for Giardia cysts was 78.7% (range 61.1–105.9%), and for Cryptosporidium oocysts 42.1% (range 30.8–52.2%). The method had a superior efficiency for Giardia cysts comparable to Cryptosporidium oocysts, but there are no significant differences in recovery for Giardia cysts and Cryptosporidium oocysts using different initial concentrations of parasites.

Recovery Efficiency of Cryptosporidium from Water with a Crossflow System and Continuous Flow Centrifugation: a Comparison Study

A crossflow system and continuous flow centrifugation were tested with regard to the recovery rate of Cryptosporidium oocysts from water. Equal volumes of tap water were contaminated with specific numbers of oocysts. With the crossflow system, an average recovery of 9.8% was obtained when using a concentration of 2 x 10(2) oocysts/L. Recovery rates achieved with the continuous flow centrifuge were more satisfactory: Starting with a concentration of 80 oocysts/L, we obtained an average recovery of 12.9%. The technique of continuous flow centrifugation was found to be more efficient for collection of Cryptosporidium oocysts from water than the crossflow system.

Biological Test for the Detection of Low Concentrations of Infectious Cryptosporidium parvum Oocysts in Water

An in vivo SCID mouse infectivity assay was used to determine its capacity to detect the infectivity of low concentrations of Cryptosporidium parvum oocysts in water. This biological test can be applied to demonstrate oocysts infectivity in water samples derived from drinking water supply and/or environmental sources.

Requirements for the Catchment, Treatment, and Surveillance of Drinking Water To Avoid the Transmittance of Pathogenic Bacterial, Viral, and Parasitic Organisms

Measures devised for guaranteeing the supply of epidemiologically and hygienically sound drinking water are generally based on observations made during epidemics and the follow-up scientific studies. Despite the high level standards that have been attained in the treatment of drinking water, the drinking water-derived outbreaks still keep cropping up even in the industrialized countries. The outbreaks of the parasites Giardia lamblia and Cryptosporidium parvum, and the recent outbreak in Canada caused by Toxoplasma gondii, again focused our attention to the possible infection risk posed by pathogens in drinking water. The circumstances of the cryptosporidia outbreak in Milwaukee in 1993 can be considered as typical for such outbreaks in which parasites have caused human disease. There are generally two ways of avoiding the transmittance of pathogens by drinking water: (i) use of uncontaminated groundwater, or (ii) treatment of the potentially contaminated one. All surface waters have to be considered potentially contaminated, while the purity of the groundwater depends on the local conditions. Routine disinfection of drinking water should be used to minimize the residual risk posed by pathogens. For purification of fecally contaminated water it is utterly inadequate. Testing of water for pathogens followed by more extensive decontamination measures in the case of positive findings appears to be of little value. Anforderungen an die Gewinnung, Aufbereitung und Uberwachung von Trinkwasser zur Vermeidung einer Ubertragung von bakteriellen, viralen und speziell parasitaren Krankheitserregern Die Masnahmen zur Versorgung mit einem seuchenhygienisch einwandfreien Trinkwasser beruhen im Wesentlichen auf den Beobachtungen, die bei Epidemien bzw. Ausbruchen gemacht werden konnten oder auf Grund der wissenschaftlichen Untersuchungsergebnisse, die bei derartigen Zwischenfallen gewonnen werden konnten. Trotz der hohen Sicherheitsstandards, die mittlerweile bei der Trinkwasserversorgung erreicht worden sind, treten auch in den Industrielandern immer wieder trinkwasserbedingte Ausbruche auf. Die Ausbruche durch die Parasiten Giardia lamblia und Cryptosporidium parvum sowie der Ausbruch durch Toxoplasma gondii in Kanada haben die Aufmerksamkeit wieder auf die mogliche Infektionsgefahrdung durch Krankheitserreger im Trinkwasser gelenkt. Die Verhaltnisse, unter denen der Cryptosporidien-Ausbruch in Milwaukee aufgetreten ist, konnen als typisch fur die Ausbruche angesehen werden, bei denen die Parasiten zu den Erkrankungen gefuhrt haben. Die Umstande stimmen aber auch weitgehend mit denen uberein, die in der Vergangenheit zu den klassischen bakteriellen und viralen Seuchen wie Cholera, Typhus, Hepatitis A und Poliomyelitis gefuhrt haben. Zur Vermeidung einer Ubertragung von Krankheitserregern mit dem Trinkwasser gibt es zwei grundsatzlich unterschiedliche Moglichkeiten: die Gewinnung von unbelastetem Grundwasser oder die Aufbereitung bei potentiell kontaminiertem Wasser. Alle Oberflachenwasser mussen als potentiell kontaminiert gelten, bei Grundwassern ist es von den ortlichen Gegebenheiten abhangig. Die routinemasige Desinfektion von Trinkwasser sollte zur Minimierung des Restrisikos durch Krankheitserreger im Wasser eingesetzt werden, aber nicht um ein offensichtlich fakal kontaminiertes Wasser in einen seuchenhygienisch einwandfreien Zustand zu versetzen. Die Untersuchung des Wassers auf Krankheitserreger erscheint wenig hilfreich. Beim Nachweis von Krankheitserregern haben moglicherweise schon Infektionen stattgefunden.

Vermeidung einer Übertragung von Cryptosporidien und Giardien mit dem Wasser

Die Ausbreitung von Krankheitserregern — Bakterien, Viren und Parasiten — mit dem Wasser stellt immer noch einen der wesentlichen gesundheitlichen Risikofaktoren dar. Offensichtliches Zeichen dieser Gefährdung sind nicht nur die Ausbrüche von Cholera in Südamerika oder Hepatitis in Indien, sondern insbesondere die in den letzten Jahren beobachteten Epidemien durch Cryptosporidien und Giardien in einigen Industrieländern. Die Ubertragung von Krankheitserregern mit dem Wasser kann nur durch umfassende hygienische Schutzmaßnahmen, die auf mehr als 100 jährigen Erfahrungen und Erkenntnissen beruhen, ausgeschlossen werden. Die Desinfektion liefert, wie schon lange bekannt, einen wichtigen, aber allein keinen ausreichenden Schutz für eine einwandfreie Trinkwasserversorgung. Namentlich die Übertragung von Parasiten-Dauerformen mit dem Wasser kann nur durch Gewässerschutz und Aufbereitung ausgeschlossen werden. Die herkömmlichen Trinkwasserdesinfektion mit Chlor, Chlordioxid oder UV-Strahlen ist jedoch nicht nur bei Parasiten unwirksam, sondern auch bei bakteriellen und viralen Krankheitserregern, wenn sie sich bei einem stark verschmutzten Wasser in Partikeln fäkalen Ursprungs befinden. Water-borne transmission of agents of disease (bacteria, viruses and parasites) continues to be one of the essential health risks. Not only outbreaks of cholera in South America or of hepatitis in India but also epidemics caused by cryptosporidia and giardias in a number of industrialized countries which have been observed in recent years are obvious manifestations of this risk. A water-borne transmission of agents of disease can only be excluded by instituting comprehensive hygienic measures which are based on more than 100 years of experience and knowledge. It has been known for a long time already that disinfection provides an important element of protection to ensure a safe water supply; however, if applied alone, it does not provide adequate protection. In particular, a water-borne transmission of persistent forms of parasites can be excluded only by water pollution control and water treatment. The common processes of drinking water disinfection using chlorine, chlorine dioxide, or UV irradiation will be ineffective not only in the control of parasites but also where viral and bacterial agents are present in particles of faecal origin.

Beobachtungen über parasitenbedingte Ausbrüche durch Trinkwasser und Maßnahmen zu deren Vermeidung Teil III: Seuchenhygienische Anforderungen

ZusammenfassungDie seuchenhygienischen Anforderungen an das Trinkwasser leiten sich aus den Beobachtungen von Praxiszwischenfällen ab. Eine der bekanntesten und auch heute noch uneingeschränkt gültigen Anforderungen zur Bereitstellung eines seuchenhygienisch unbedenklichen Trinkwassers ist von Robert Koch nach der Choleraepidemie von 1892 in Hamburg aufgestellt worden. Seine Forderung war, Oberflächenwasser, das für die Trinkwasserversorgung genutzt wird, muss durch Filtration aufbereitet werden, und nach der Filtration darf die Koloniezahl maximal 100/ml betragen. Die Praxisbeobachtungen mit parasitenbedingten Ausbrüchen und die Tatsache, dass die Parasiten nicht durch die üblicherweise zur Trinkwasserdesinfektion eingesetzten Mittel abgetötet werden, haben gezeigt, dass nur durch Gewässerschutz und eine leistungsfähige Aufbereitung ein sicherer Schutz gewährleistet werden kann. Entsprechend dem Multibarrieresystem müssen Rohwasserbelastungen und Leistungsfähigkeit der Aufbereitung aufeinander abgestimmt sein. Nach der Aufbereitung vor der Desinfektion des Trinkwassers darf das Wasser keine mikrobiologisch nachweisbaren Fäkalindikatoren mehr aufweisen.AbstractOur contemporary approach to securing drinking water free of disease-causing microorganisms derives essentially from the observation of and learning from earlier disease outbreaks. One of the best-known suggestions for controlling the quality of drinking water comes from Robert Koch. After the 1892 cholera outbreak in Hamburg, which afflicted 16,956 people of whom 8,605 eventually died, Robert Koch insisted that the surface water, which served as a source of drinking water, should be filtered. After filtration the colony count was supposed not to exceed 100/mL. The parasites Giardia and Cryptosporidia are transmitted by the fecal-oral route just like the classical epidemic microorganisms of cholera and typhoid fever. Hygienically safe water supply can be secured not by water analysis, but by appropriate measures aimed at elimination of possible parasites in water. The water-borne parasites differ from other bacterial and viral water contamination by their higher resistance to disinfection. The commonly used drinking water disinfectants are not effective with these parasites. The microorganisms thus have to be removed from the water naturally by the passage of the water in the underground or artificially by an appropriate filtration or flocculation filtration. The higher the fecal contamination of the source water, the more efficient the filtration process has to be. Water can be considered parasite-free only when no fecal material is detectable after the filtration before disinfection. The filtered water should not contain E. coli, coliform bacteria, fecal Streptococci and Clostridium perfringens. Such water should have the properties of a well-protected ground water. And even then the last step of the water treatment process should be disinfection, which further diminishes the residual risk of infection.

Studies on the lethal effect of ultraviolet light onTrichomonas vaginalis

Following cultivation in Asami medium, centrifugation and resuspension in saline or in water from a medicinal spring,Trichomonas vaginalis trophozoites were exposed to well-defined doses of ultraviolet (UV) light (254 nm). We used 24- and 48-h-old trichomonads at concentrations of 1×105 and 5×104 trophozoites/ml in a total volume of 20 ml for these studies. The apparatus for UV irradiation was especially constructed for batch experiments. After irradiation at doses ranging from 80 to 160 mJ/cm2, the mobility of the parasites was reduced and morphological alterations appeared: rounding of the cells, vacuolization of the cytoplasm and even cytolysis. A dose of 401.7 mJ/cm2 killed 99.8% of the 48-h-old trichomonads when irradiation occurred in saline at a cell density of 1×105 trichomonads/ml and 98.9% when irradiation was done at a cell density of 5×104 trichomonads/ml. A dose of 362.1 mJ/cm2 killed only the more sensitive 24-h-old trichomonads. In mineral water, 241 mJ/cm2 was sufficient to kill up to 99.5% of the 48-h-old trichomonads. When 48-h-old trichomonads that had been exposed to a radiation dose of 160–240 mJ/cm2 were subcultured, they lost their ability to propagate. At a dose of 80 mJ/cm2, both the trichomonads that had been harvested during the log phase and the 48-h-old organisms suspended in mineral water lost their ability to propagate on subculture. These results indicate that 24-h-old trichomonads were more sensitive than 48-h-old organisms. Furthermore, the experiments demonstrated that a higher dose of UV radiation must be applied toT. vaginalis trophozoites than to the more sensitive bacterial strainEscherichia coli ATCC 11229 so as to achieve comparable killing results.