Comparison of two agitation systems air lift and paddle wheel in high rate algal channel
The purification technique of wastewater by High Rate Algal Ponds (HRAP) is distinguished from the traditional lagoon by a shorter residence time, a shallow depth and constant mechanical agitation. This agitation can be done by a water jet, a paddle wheel, or an air lift. A comparison of the hydrodynamic behaviour of the two agitation systems most often used for wastewater treatment systems similar to High Rate Algal Ponds (air lift and paddle wheel) was undertaken. Power energy consumed by these two agitation systems is compared for typical effluent circulation rates usually encountered in this type of wastewater treatment process. The purification performances for both agitation systems are also analyzed. The results showed that energy consumption using the air lift is about 3 to 5 times less costly than the paddle wheel. This advantage is also confirmed in terms of treatment efficiency since better removal of nitrogen and phosphorus using the air lift system is observed. This study shows that good functioning of the High Rate Algal Ponds can be obtained using the air lift as the agitation system.