Experiments on sunlight inactivation of Escherichia coli were conducted from November 2006 to June
2007 in eight outdoors microcosms with different depths filled with maturation pond wastewater in
order to determine pond depth influence on sunlight inactivation of E. coli. The long-term aim was to
maximize sunlight inactivation of waterborne pathogens in waste stabilization ponds (WSPs) in sahelian
regions where number of sunny days enable longer exposure of wastewater to sunlight. The inactivation
was followed during daylight from 8.00 h to 17.00 h and during the night. Sunlight inactivation rates (KS),
as a function of cumulative global solar radiation (insolation), were 16 and 24 times higher than the corresponding dark inactivation (KD) rates, respectively in cold and warm season. In warm season, E. coli was
inactivated far more rapidly. Inactivation of E. coli follows the evolution of radiation during the day. In
shallow depth microcosms, E. coli was inactivated far more rapidly than in high depth microcosms.
The physical chemical parameters [pH, dissolved oxygen (DO)] of microcosms water were higher in shallow depth microcosms than in high depth microcosms suggesting a synergistic effect of sunlight and
these parameters to damage E. coli. To increase the efficiency of the elimination of waterborne bacteria,
the use of maturation ponds with intermediate depths (0.4 m) would be advisable in view of the high
temperatures and thus evaporation recorded in sahelian regions

Sunlight inactivation, Escherichia coli, Wastewater, Waste stabilization pond