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The graphs show that as plant flow rate decreases, the effluent turbidity also decreases, until we reach 50 ml/min. At 25 ml/min, we found that the effluent turbidity is unstable but seems to be greater than that of 50 ml/min. From this, we conclude that the optimal flow rate of this flocculator and sedimentation tank is approximately 50ml/min50 ml/min. This is much lower than the 100 ml/min flow rate the plant was designed for. This is most likely due to slight inaccuracies in construction of the sedimentation tank that caused the flow rates in each of the lamellas to be different, resulting in a settling time that was lower than expected. Thus, when plant flow rate was decreased, resulting in a longer settling time, the flocs had a more reasonable amount of time to settle out, and effluent turbidity decreased.

To verify that the lamellas in the sedimentation tank experienced varied flow rates, we added red dye to the last column of the flocculator, and observed its progress through the plant. We saw that the red dye proceeded mostly through the last 3-4 lamellas of each side of the sedimentation tank, and that it moved the fastest through the last one. Also, upon further observation, we saw that at 100 ml/min, medium and small sized flocs were being carried up these channels in the sedimentation tank and leaving the tank to the effluent water supply.

Simply by observing the Demo Plant as experiments were being run, we saw that the largest flocs were created at a flow rate of 50 ml/min. These results also show us that the G-theta in our plant is high enough at 50 ml/min to create very large flocs. However, at 25 ml/min, the flocs were very small, showing that the G-theta was no longer large enough to create flocs.

Conclusion