Pedahzur, R., Division of Environmental Sciences, Grad Schl Applied Sci and Technology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Nasser, A.M., Division of Environmental Sciences, Grad Schl Applied Sci and Technology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Dor, I., Division of Environmental Sciences, Grad Schl Applied Sci and Technology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Fattal, B., Division of Environmental Sciences, Grad Schl Applied Sci and Technology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Shuval, H.I., Division of Environmental Sciences, Grad Schl Applied Sci and Technology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

The effect of baffles on the performance of an ineffective, single-celled stabilization pond with theoretical retention time of 5-10 days, was investigated. The efficiency of the pond was evaluated by comparing the microbiological and chemical quality of pond's influent and effluent, as well as by hydraulic tests. Removal of indicator microorganism (1 log) and BOD 5 (55%) remained unchanged, regardless of the number of baffles. Tracer study findings were characterized by the appearance of a peak of tracer within 15-20 hours after injection of the tracer, followed by a long 'tail' of lower concentration. These findings, along with optical observations, indicated that the baffles succeeded in channeling influent flow to the planned routes (resulting in increased traveling distance of the wastewater). However, the actual retention time of the influent, particularly a small but important fraction of it, remained short regardless of baffle installation. The lack of mixing caused by thermal stratification of the water column resulted in rapid bottom flow in the cool hypolimnion. These findings may explain, in part, the lack of success in improving treatment efficiency.