Water Quality Management - River Dynamics and Integrated River Management - page 606

Chlorinated effluents are particularly prone to the phenomenon of bacterial regrowth where effluents
discharged with certain coliform levels quickly exhibit a marked increase in coliform levels. This
phenomenon is believed to be caused by the “organic food” in the sewage which is sufficient to provide
for a rapid growth of the coliform organisms. Lue-Hing et al. (1976) illustrated that coliform levels more
than 20 km downstream from the three major wastewater treatment plants in the Chicago area were
virtually the same before (1966) and after (1974) application of chlorination (Table 9.12). Further, Sedita
et al. (1987) found the cessation of chlorination at the major wastewater treatment plants in the Chicago
area on April 1, 1984, caused an increase in fecal coliform levels in the immediate downstream vicinity
of the plant, but 16.9 to 27.8 km downstream the fecal coliform levels were not statistically different
from those achieved prior to the cessation of chlorination.

Table 9.12 Fecal coliform levels before (1966) and after (1974) the application of chlorination at the three major
w astewater treatment plants in the Chicago area

Geometric mean fecal coliform
(counts/100 mL)

Wastewater treatment plant
downstream location

River kilometer
downstream

1966 1974

North side

Touhy Avenue 1.45 30,190 125

Damen Avenue 25.43 2,844 3,041

Stickney

Harlem Avenue 2.41 26,410 1,618

Upstream of Lemont Wastewater
Treatment Plant

23.98 13,960 11,245

Calumet

Ashland Avenue 3.70 44,500 2,464

Route 83 27.52 1,440 2,612

Ultraviolet (UV) —The effectiveness of UV disinfection is largely dependent on the applied UV dose,
suspended solids content, UV transmittal, non-disinfected microbial concentration, and the degree of
association of microorganisms with particles (USEPA, 2003b). UV radiation only is effective in destroying
microorganisms if it reaches the microorganisms, thus, the wastewater must be relatively free of turbidity
that can absorb UV energy and shield microorganisms. Nitrogenous compounds also can have an adverse
effect on UV disinfection systems as UV-absorbing compounds (WERF, 2005). The advantages of UV
versus chlorine disinfection are (Geosyntec, 2008):
(1) UV efficiency for protozoa of concern ( Cryptosporidium parvum and Giardia lamblia ) is
significantly greater than chlorine efficiency.
(2) Proven ability to disinfect pathogenic bacteria and viruses. There are no significant differences between
the efficacy of chlorine and UV radiation as a disinfectant for the reduction of fecal coliforms and E. coli .
(3) Formation of harmful by-products by UV is negligible at conventional UV doses.
(4) Increased safety compared to the storage and handling of chlorine.
(5) Increasing costs of chlorination due to regulation curbing chlorine discharge, thus, mandating
dechlorination.
6) UV technology has become increasingly more reliable and predictable with regard to performance.
Ozonation —The high reactivity of ozone makes it useful for disinfection, color removal, the degradation
or conversion of organic micropollutants, the reduction of chemical oxygen demand, and effluent oxygenation
(Geosyntec, 2008). The effectiveness of ozone disinfection depends on the ozone dose, the quality of the