Benthal Solids Properties Influencing ASB Design and Operating Practices

Abstract

Studies undertaken at two aerated stabilization basins (ASBs) treating industrial effluents showed that the benthal solids characteristics varied substantially with location in three dimensions. The top 15–30 cm layer of the deposited solids was found to be the most active biodegradation zone with relatively little activity in the deeper layers. Ammonia and phosphate were present in high concentrations throughout the benthal solids and thus are not believed to limit biological growth and its associated benthal solids degradation kinetics. The nutrient concentrations were particularly higher in the downstream cells than those in the upstream cells. Implementing a suitable strategy to recycle these nutrients could result in minimized discharge and cost savings when treating nutrient-deficient industrial wastewaters. Dewatering properties of the benthal solids also substantially varied from one cell of an ASB to another. The selection and dose optimization of the dewatering polymers should therefore be completed separately for individual cells (or major zones) within an ASB system. Insights provided in this paper could be instrumental in proposing remedies to enhance in situ degradation of benthal solids and to better design and operate ASBs treating industrial effluents.