The Water Authority of Istanbul, which owns a biological wastewater treatment plant, serves a population of about 15 million people in the city of Istanbul. To meet strict environmental regulations, the Water Authority approached Marine Consultants Group (MCG) in spring 2017 to find a suitable product to provide adequate diffusion for its marine wastewater outfall.
MCG worked with Proco to design and engineer duckbill diffusers to accommodate outfall sewage from the treatment plant through an 87-in.-diameter steel pipe. The pipe extends 1.35 miles (2,230 meters) along the bottom of the ocean and discharges at approximately 154 ft below sea level.
There were several challenges Proco needed to keep in mind for this project. One concern was that passing marine vessels might damage diffusers and duckbill check valves. To address this concern, Proco needed to determine the appropriate diffuser length, which in this project was approximately 741.5 ft at the farthest end of the 1.5-mile run on outfall pipe.
Previously, engineers and contractors were often required to blind-flange some of the ports so they would be functional with lower flow rates and opened to allow for maximum flow rates. Maximum flow was calculated to handle requirements with a 20-year future outfall rate. However, the present flow rate will not be functioning at maximum output, and as a result, Proco and MCG needed to design appropriately sized check valves to alleviate this concern.
Installation
MCG recommended that the Water Authority use Proco ProFlex Style 710 duckbill check valves for this project. Each port discharge was equipped with two 10-in.-diameter (250-mm) duckbill check valves.
Duckbill valves are frequently used to prevent backflow in deep marine outfall and diffuser projects. The Proco ProFlex 710 duckbill check valves provided several advantages for this marine outfall. First, there was no need to blind-cap some of the ports during the first years of operations. Secondly, the use of these duckbill check valves eliminates the need to blind-flange ports since the lines can operate with full efficiency from the initial startup, which decreases maintenance and reduces diver time to add additional valves in the future.
Preventing saline intrusion into the line when there is no inlet pressure is another benefit of using duckbill check valves for this project. Different head pressures between seawater and discharge water cause seawater to enter the line when there is low head pressure or when there is no inlet flow. If this backflow is not prevented, the ports may be blocked or plugged, and marine life can enter the lines. As a result, the calculated and engineered dilution ratios will not be achieved.
Finally, duckbill check valves increase the jet velocity and provide a better dilution value than traditional flap gates, even with low flow rates.
In addition to these benefits, the Proco ProFlex Style 710 duckbill check valves’ highly engineered elastomer maintains its memory after a long period of staying open or staying in a closed position. Elastomeric check valves are 100% barnacle- and algae-resistant, which is an important feature for a saltwater project.
Proco’s engineering team also provided full assistance with supplying the head loss calculations.
Results
Following the installation of the Proco ProFlex Style 710 duckbill check valves, the finished assembly was charged with air to allow buoyancy and then dragged into a determined position and allowed to drop to the sea floor. This allowed the valves to become operational and allow the appropriate outfall diffusion through each of the 46 valves.
The system has been a fully functional success for the region, and Proco continues to offer assistance and engineering expertise on systems comparable to this on a globally active basis.
