Tideflex Effluent Diffusers Improve Water Quality, Allow for City Growth


Foreseeing industry growth and overall city expansion, the City of Cedar Rapids, Iowa, Wastewater Treatment Plant sought a new permit that would increase the total allotted daily discharge and allow for the release of higher amounts of regulated compounds. In order to obtain a better permit, the plant needed to enact a significant reduction to the pollutant concentrations being produced by its current level of discharge.

"In the winter, during low river flow, it was hard to meet the required concentrations of certain pollutants, such as ammonia and biological and chemical oxygen demand," said Operations Specialist Chris Hatch. "We were meeting our water quality regulations but foresaw the increase in city industry would make that an even harder goal to reach in the next 10 years."


The city consulted engineering firm Howard R. Green for a means of lowering dilution-zone pollutant concentrations without further restricting the current discharge operation. The firm concluded that the city’s existing outfall line could be redesigned into a multi-port diffuser that would significantly enlarge the dilution zone and mix the effluent more rapidly with the receiving water body. An effluent diffuser would also be a more reliable and cost-effective option than altering the treatment process or installing a second outfall line.

Tideflex® Engineers recommended a Tideflex® Effluent Diffuser Valve with a rubber riser and a 45-degree rubber elbow to be attached to each of 73 ports spaced evenly across the length of a single outfall pipe. The unique duckbill design of the Tideflex® created a pressure drop across the valve that maximized the velocity of the discharging effluent and increased mixing speed, reducing pollutant concentrations at each discharge point.


Because Cedar Rapids is a city that is continually expanding, Hatch knew that a system working efficiently at the time of installation would eventually have to be upgraded. Howard R. Green and Tideflex® Technologies worked together to engineer a diffuser system that would meet the city’s current needs and still allow for future increases in capacity without any major redesign requirements.

Because the Tideflex® Valves are constructed entirely of durable, flexible elastomers, they will not rust, break or erode, problems that are common with metal diffuser products. The duckbill design of the Tideflex® prevents backflow into the header pipe as backpressure from the receiving water body effects drop-tight sealing.

Tideflex® Technologies also vulcanized the closed portion of the Tideflex® Valves, limiting the number of ports in operation to maintain adequate velocities within the line at the plant’s current rate of flow. If and when the rate of flow is significantly increased, the Tideflex® can easily be slit open to increase overall system capacity.

With this much more efficient and environmentally friendly means of discharging its wastewater effluent, the City of Cedar Rapids was able to obtain a better permit. "The new permit regulations are much easier to meet," Hatch said, "and they allow the city a lot of future growth."

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