Graduate Thesis Or Dissertation
 

Disinfection of settled and unsettled trickling filter effluent by chlorination

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6q182n68s

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  • The colicidal efficiency of chlorine in both settled and unsettled trickling filter effluent samples was determined by means of a series of tests in which each sample was analyzed, at given time intervals, for suspended solids, pH, residual chlorine (orthotolidine and iodometric) and coliform count. A dye-tracer study, using Rhodamine B dye, was conducted on a typical circular settling tank and the flow characteristics evaluated. The results of the two studies were analyzed individually and then combined to compare the coliform disinfection obtained by chlorinating settled effluent in a contact chamber with that obtained by chlorinating unsettled effluent in a settling tank. Based on this study, the following conclusions were made: 1. In general, the colicidal efficiency and residual chlorine tended to decrease as the suspended solids concentrations of the samples increased. 2. The orthotolidine method for determining chlorine residual was found to be an unreliable indicator when used on trickling filter effluent, with chlorine residuals of 5.0 or less. 3. Chlorination of the settled filter effluent showed better coliform disinfection than did chlorination of the unsettled. At a chlorine dosage of 1 mg /l, coliform regrowth occurred in both the settled and the unsettled samples after 2 hours of contact. The dosages of 2, 4, 5 and 8 mg/l all gave complete disinfection (less than 0.0001% coliforms remaining) in less than 3 hours contact. The difference in the coliform disinfection rates of the settled and the unsettled samples decreased as the chlorine dosage was increased. At dosages of 4 mg/l and higher the difference in disinfection rates became insignificant. 4. The dye-dispersion data revealed several undesirable features in the flow pattern through the settling tank. The effects of turbulent short-circuiting and stagnant areas were very pronounced. The dispersion index for the tank was approximately four times higher than the maximum value usually associated with settling tanks with acceptable flow characteristics. 5. The colicidal efficiency obtained by chlorinating settled effluent in a contact chamber was found to be consistently higher than that obtained by chlorinating unsettled effluent in a final settling tank. The difference was found to be small and insignificant at chlorine dosages greater than 2 mg/l. At dosages of 2 mg/l and lower, the concentration of coliforms in the settling tank effluent averaged 2 to 4 times higher than the average concentration of coliforms in the contact chamber effluent. This difference is quite significant and should be considered when comparing the cost of chlorinating (at dosages near 2 mg/l) in a final settling tank with the cost of building and operating a contact chamber.
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  • File scanned at 300 ppi using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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