Effect of lake destratification on water quality parameters

Abstract

Scope and Method of Study: The objectives were: (1) Determine the effect of the pump's operation on the water quality parameters of a stratified lake; (2) Optimize design for minimum head loss, construct and evaluate a rigid diffuser for the lake destratification pump; and (3) Determine the relationships of shaft power, RPM and pump flow rate both with and without the diffuser.

The relationship between flow (Q) and power with a varying propeller RPM was determined both without a diffuser and with an optimum diffuser. The effect of the pump's operation on the lake was determined by observing: temperature, dissolved oxygen, alkalinity, pH, BOD5, surface turbidity, and composite algae samples. The effect on fish was not observed.

Findings and Conclusions: The pump was capable of destratifying the lake without the diffuser attached. The destratification efficiency during this initial period of seven days was 6.0%. Fifteen days of operation were required to lower the stability to nearly zero. The destratification efficiency for this period was 4.6%. Destratification of all physical-chemical parameters was observed. A longer period of time is required to destratify DO then is necessary for thermal destratification. Although there were some changes in algae species predominating in the lake, there was no real shift from blue-green to green algae predominance. No significant improvement in diffuser efficiency was found in comparing the rigid metal diffuser with the flexible fabric diffuser. Using a propeller with greater pitch increased flow with the same power consumption. With a diffuser attached this pump was capable of moving 0.991 m3/sec from near the surface to near the lake bottom using 373 watts.