Rj. Daviescolley et al., SUNLIGHT INACTIVATION OF ENTEROCOCCI AND FECAL-COLIFORMS IN SEWAGE EFFLUENT DILUTED IN SEAWATER, Applied and environmental microbiology, 60(6), 1994, pp. 2049-2058
Inactivation (loss of culturability) by sunlight of enterococci and fe
cal coliforms within sewage effluent diluted in seawater was investiga
ted in held experiments. In most experiments, 500-ml flasks of pure si
lica were used to confine activated sludge effluent diluted to 2% (vol
/vol) in seawater. Inactivation of bacteria in these basks (diameter,
0.1 m) was faster than in either open chambers (depth, 0.25 m) or patc
hes of dyed effluent (depth of order, 1 m), probably because of the lo
nger light paths in the latter two types of experiment, which caused g
reater attenuation of sunlight. Inactivation of 90% of enterococci gen
erally required 2.3 times the insolation required for 90% inactivation
of fecal coliforms, because of both the presence of larger initial sh
oulders on survival curves and a lower final inactivation rate. Two pa
rameters are required to model inactivation of enterococci, a shoulder
constant as well as a rate coefficient. The depth dependence of inact
ivation rate for both fecal indicators matched the attenuation profile
of UV-A radiation at about 360 nm. Inactivation by UV-B radiation (29
0 to 320 nm), which penetrates much less into seawater, is of minor im
portance compared with the UV-A and visible radiation in sunlight, con
trary to expectations in consideration of published action spectra for
bacterial inactivation.