THE PERFORMANCE OF STABILIZATION RESERVOIRS AS A FUNCTION OF DESIGN AND OPERATION PARAMETERS

Stabilization Reservoirs were developed in Israel for the treatment and storage of wastewater for agricultural irrigation. These reservoirs were initially conceived just for seasonal storage of wastewater but soon the additional stabilization that they provide of effluents became evident. This paper formulates the first available equations for BOD and COD removal in Stabilization Reservoirs. Removal of BOD and COD is high (50 to 85%) in terms of annual means, but sharply changes during the year. Three models to predict BOD and COD removals as a function of design and operation parameters are developed based on a large amount of data from four different reservoirs. The percentage of fresh effluents within the reservoir has a negative effect on BOD and COD removals. High water levels, and their concomitant low area/volume relationships, have also a negative effect on removal efficiency due to poor oxygenation of the water column. The percentage of fresh effluents within the system is a hydraulic parameter better than Residence Time, to analyze the performance of non-steady state wastewater treatment systems. The quality of the effluents released for irrigation from Stabilization Reservoirs deteriorates during the second half of the irrigation season. This deterioration is due to both the increase in the percentage of fresh effluents within the reservoir, and the occurrence of dead areas and short-circuiting phenomena at low water levels. These problems must be resolved by proper design and operation of the reservoirs in order to obtain a more homogeneous effluent quality along the irrigation season.