A wastewater treatment plant has a tertiary filter that discharges over an 8' weir at elevation 18', it falls 5' to elevation 13' (bottom of filter effluent chamber), goes through a 16" 90 deg bend mounted on the side of the chamber down to an opposite faced 90 then runs 20 feet to a contact chamberwith a control elevation of 9'.
The water over the weir is causing excessive air entrainment since there is no pool of water in the effluent chamber. It is then compounded once it falls again over the 90 bend at an even faster velocity. The water level in the contact chamber is approximately 6' deep. The main contains so much air, it causes a massive air burp in which water splashes over the edge which is 1.5' higher than the controlled water surface.
Flow rate is between 1 and 3 mgd.
We have tried an orifice plate on the discharge but the flow rate varies too much to keep a pool of water in the chamber at low flow and overflows the chamber at high flow. We have tried an internal weir in the effluent chamber to create a pool in the chamber, but the fall in the 90 still entrained too much air. We have also tried throttling the downstream valve, but the flow range was to great and had problems with siphoning and sucking the chamber down. We can not install a riser in the contact chamber due to a pump bypass vault that parralels the filters but is at elevation 11'.
I was thinking a modulating float valve might work, but Im afraid I dont have enough head or control volume (3'x10'x5'). I was also thinking of a multi-pipe weir inside of the filter chamber, maybe 3-6" pipes..
Any thoughts. Have a small construction budget.
I will try to link to a diagram in the A.M as I know this is confusing.
The water over the weir is causing excessive air entrainment since there is no pool of water in the effluent chamber. It is then compounded once it falls again over the 90 bend at an even faster velocity. The water level in the contact chamber is approximately 6' deep. The main contains so much air, it causes a massive air burp in which water splashes over the edge which is 1.5' higher than the controlled water surface.
Flow rate is between 1 and 3 mgd.
We have tried an orifice plate on the discharge but the flow rate varies too much to keep a pool of water in the chamber at low flow and overflows the chamber at high flow. We have tried an internal weir in the effluent chamber to create a pool in the chamber, but the fall in the 90 still entrained too much air. We have also tried throttling the downstream valve, but the flow range was to great and had problems with siphoning and sucking the chamber down. We can not install a riser in the contact chamber due to a pump bypass vault that parralels the filters but is at elevation 11'.
I was thinking a modulating float valve might work, but Im afraid I dont have enough head or control volume (3'x10'x5'). I was also thinking of a multi-pipe weir inside of the filter chamber, maybe 3-6" pipes..
Any thoughts. Have a small construction budget.
I will try to link to a diagram in the A.M as I know this is confusing.
