Full Description

Ultraviolet (UV) irradiation is gaining more attention as an alternative disinfectant to conventional chemical disinfectants in water treatment systems. Recent technological improvements make this alternative disinfectant increasingly cost-competitive and effective. UV irradiation at disinfection doses does not produce harmful disinfection byproducts (DBP) and has been shown to be very effective for inactivation of pathogenic bacteria as well as the protozoan parasites Cryptosporidium parvum and Giardia lamblia (Chang et al, 1985, Sobsey, 1989, Bukari et al, 1999, Clancy et al, 2000, Shin et al, 2001, Craik et al, 2001, Linden et al, 2002). However, UV irradiation does not leave a residual in the treated water (Oppenheimer et al, 1997) and there are other waterborne pathogens that are considerably resistant to UV irradiation, including some important human enteric viruses (Meng and Gerba, 1996). Therefore, this study determined the kinetics and extent of inactivation of pathogenic microorganisms by various doses of monochromatic, low-pressure (LP) UV followed by free and combined chlorine. A highly UV-resistant virus (Adenovirus 5), a highly chlorine-resistant parasite (C. parvum) and a human pathogenic bacterium (Salmonella typhimurium) were included in this study. Adenovirus type 5 (AV5) was propagated in A549 cells. Infected cell lysates were frozen and thawed three times and extracted by homogenizing in an equal volume of chloroform. The supernatant was recovered by low speed (5,000 x g) centrifugation for 15 minutes at 4 oC. This virus extract was further purified by centrifugal ultrafiltration (Centricon 100) and dispersed by filtration through 0.2 um pore size polycarbonate filters pre-treated with 0.1 % Tween 80 solution in water. AV5 was assayed by TCID50 method on confluent layers of A549 cells grown in 24-well tissue culture plates. Cryptosporidium parvum oocysts (Iowa strain) were purchased from Pat Mason, Pleasant Hills Farm, Troy, Idaho. Shed oocysts collected daily from experimentally infected 3-day old Holstein calves were screened to remove large debris and hair and then purified and dispersed by processing through discontinuous sucrose gradients, followed by cesium chloride (CsCl) gradients (1.15 g/ml, 1.15 specific gravity). Oocysts recovered from CsCl gradients were washed in phosphate buffered saline (PBS, pH 7.2), resuspended in buffer solution containing antibiotics and stored at 4 oC. Cryptosporidium parvum infectivity assays were done in Madin-Darby Canine Kidney (MDCK) cell cultures (ATCC CCL 34) as described in a previous study (Shin et al, 2001). Salmonella typhimurium 1537, an Ames test strain for chemical mutagens, was grown in tryptic soy broth without dextrose (Difco #0862-17). Overnight cultures of S. typhimurium grown to mid-exponential log phase were washed three times and diluted into PBS for disinfection experiments. S. typhimurium 1537 was assayed on tryptic soy agar (Difco #0368-17) by the spot plate technique for colony growth. Also discussed are: low-pressure UV irradiation system and radiometry; petri factor and dose determinations; experimental protocol of UV disinfection experiments; glassware and reagents for chemical disinfection experiments; free chlorine and monochloramine solutions and measurement of chlorine residuals; experimental protocol for chemical disinfection experiments; and, data presentation. Includes 13 references, figures.

Product Details

Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 7File Size: 1 file , 260 KB