AWWA JAW57217

In an effort to better control formation of disinfection byproducts (DBPs), the USEnvironmental Protection Agency's recently promulgated Disinfectants/DBP Rule requiresthat US surface water treatment plants whose influent and effluent waters meet certaincriteria practice enhanced coagulation. Although this treatment technique has been shownto effectively reduce natural organic matter, and consequently DBPs, questions have beenraised concerning its effect on other aspects of water treatment such as particle andpathogen removal. The current study was designed to investigate the influence of decreasedcoagulation pH levels (an integral component of enhanced coagulation) on removal ofCryptosporidium oocysts as well as on reduction of total organic carbon (TOC), turbidity, andparticle counts. A series of pilot-plant trials was conducted in which commonly usedcoagulants (ferric chloride, alum, and polyaluminum chloride) were used at various pHlevels to treat river water spiked with large numbers of Cryptosporidium oocysts. The resultsshowed that TOC removal is significantly enhanced by coagulation at lower pH levels andthat all three coagulants are effective in removing Cryptosporidium oocysts duringconventional treatment (mean removal = 4.3 log units). However, turbidity and particlecounts appear to be unreliable indicators of oocyst removal. Finally, the investigationsuggested that lowering coagulation pH does not interfere with removal of Cryptosporidium.However, questions remain concerning the use of alum at pH 5. Includes 22 references, table, figures.

Product Details

Edition:

Vol. 94 - No. 11

Published:

11/01/2002

Number of Pages:

11

File Size:

1 file , 380 KB