AWWA WQTC71612

Chloramines are unstable at neutral pH, even without the presence of reactive inorganic ororganic substances, and auto-decompose by complex sets of reactions that ultimately result in theoxidation of ammonia and the reduction of active chlorine. Granular activated carbon (GAC)filters become biologically activated carbon (BAC) filters due to microbiological growth whichoccurs after the ozonation process. To compare filter efficiency, chloramine decay tests werecarried out to observe the chloramine decay patterns of filter effluents during the dry and wetseasons. The auto-decomposition rate increased with decreasing pH. Chloramine disinfects andreacts with microorganisms. The residual chloramines of Log 9.0 CFU HPC/mL sampledecreased by 20% within 1 hour of incubation time. 90% of the chloramine was consumed within96 hours of incubation time. Chloramine was initially consumed to kill bacteria, and then reactedwith dead bacterial matter. Monochloramine decay also occurred through reactions with inorganicions such as nitrite, bromide, and ferrous iron, and with inorganic carbon from GAC particles.Oxidation of bromide by monochloramine is rapid under the conditions of chloramination. Theoxidation of ferrous iron by monochloramine has apparently never been investigated at thequantitative level. This may be because of the belief that the reactions are too slow to be ofeconomic relevance. Monochloramine might also react with GAC fines, but 0.1 mg/L GAC finedid not affect the monochloramine loss within 140 hours. BAC filtration can remove NOM andparticle matter through microbiological processes. Particle matter and the growth ofmicroorganisms from the filter media contribute to pressure head loss. Heterotrophic Plate Count(HPC) from the initial samples taken after filter backwashing showed a decrease until 3 hoursafter backwashing, then increased until 24 hours as the BAC filter matured. The residual chlorineincreased after 1 hour of backwashing. The sample taken 1 hour before backwashing showed adecrease in residual chlorine because matter might have come out of the mature filter because ofthe high loss of head. Over 80% of the residual chlorine was consumed within 96 hours. Thelignite GAC and bituminous GAC did not show a difference in chloramine consumption. Thechloramine demand was greater during the wet season than the dry season. Samples werecollected immediately after backwashing during the wet and dry seasons, and incubated for 96hours. Results showed a chloramine demand of 9.4 mg/L during the wet season, while the dryseason demand was 7.7 mg/L. Includes 8 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2009

Number of Pages:

21

File Size:

1 file , 1 MB