Sludge Blanket Formation
The first sedimentation tank containing the floc blanket has been constructed. Flocs enter the tank and do not appear to be breaking up, so it has been determined that our entrance pipe was large enough. The hydraulics are working correctly and the water levels are as calculated. We also measured the flow rate of the sedimentation tank and the sludge hopper, and both were very close to the design rates.
Over the past week we have been observing how the floc blanket has been forming. Sludge has been piling up slowly and a suspension of flocs has begun to form. By the end of the first week it was very clear that a thin floc blanket had formed in the tank. Although some floc were noticed to still be making it up to the effluent manifold a large number of flocs were being captured by the floc blanket. The flocs forming the blanket were relatively large, up to 5 mm in diameter. The top of the blanket was forming around the level of the sludge hopper. This tells us that the hopper is successfully controlling the level of flocs in the tank. Hopefully with more time for development the floc blanket performance will improve as the floc blanket thickens, and the smaller flocs noticed toward the top of the tank will be captured.
It was observed that upward flow through the tank seemed slightly faster in the front corner of the tank by the effluent manifold. Upon tank draining, it was observed that the sludge at the bottom of the tank formed a conical shape. The evenness of the conical shape demonstrates that flow seems to be flowing uniformly out of the inlet and up through the tank, and thus the slight increase in flow noticed at the top of the tank is not significant, and it is not leading to a large amount of scour at the bottom of the tank. Flow irregularity is a concern because it is one of the main causes of blanket instability and poor blanket formation.