Performance of Gravity Thickener in Cairo WWTP

Gravity thickeners most commonly used in wastewater treatment plants in Egypt. Gravity thickeners designed so as sedimentation happens due to physical reactions only, but what actually happens is that due to other incomprehensible reactions the sedimentation efficiency is affected. The main goal of the present work is to study the gravity thickener behavior and determine the affecting factors on its gravity thickening working. Determine the best mixing ratio between primary & secondary sludge for thickener from different three wastewater treatment plants in in Egypt (El Berkah WWTP, Zenein WWTP & El- Gabal Al. Asfar contract (16)). The experimental work was conducted from the primary sludge was the sludge resulting from primary sedimentation tank of each WWTP while the waste activated sludge is the sludge resulting from final sedimentation tank. The laboratory experiment was mixing the two different types of with different ratios (starting from the set value of El- Gabal Al. Asfar contract (16) which was (30 % Primary sludge (PS) + 70% Waste activated sludge (WAS)) in the blending tank) and different retention times from (0 to 40 hour). The lab experimental results show that the best mixing ratio between primary sludge (PS) and waste activated sludge (WAS) is (40 % PS + 60 % WAS). From TSS curves the best mixed ratio between primary sludge (PS) and waste activated sludge (WAS) with the gravity thickener is found (40 % PS+ 60 % WAS). This was because TSS curve shows that the slope of the line simulates results of mixed ratio (40 % PS + 60 % WAS) is the highest slope compared with the other mixed ratios lines and this slope simulates the thickening concentration ratio. From the batch-scale lab experiments also find, the big effect of biological action was presentable after 16 hrs must be taken into consideration when thickener designing and it prove that hydrolysis phase by anaerobic action can be happened from start settling by gravity thickener depends on the sludge characteristics and sludge age.