Influent Device Field Tests for Secondary Clarifier

Secondary clarifiers were field tested and evaluated at a major Maryland WTP. The test clarifiers were 47.26 m (155 ft.), diameter center-feed, peripheral-overflow clarifiers with a 4.57 m (15 ft.) SWD.This paper will discuss and evaluate inlet designs and will focus on the newer FEDWA design and how it impacts the RAS concentration.The Maryland (FEDWA) design is an improvement to the many EDI tub designs offered.The tub arrangement has several inherent process shortcomings. Recent studies have concluded the intended mass rotation within the outer well extends down below the well into the sludge blanket, and re-suspending solids.The FEDWA arrangement enhances the process characteristics by acting as a flocculation device as well as energy dissipating device. The FEDWA series of open baffles creates several areas of flow impingement, each consuming kinetic energy and promoting passive flocculation.Results of the field tests show an increase of RAS concentration for the FEDWA as compared to side by side data at the site. The clarifier had a 20 to 35% increase in RAS concentrations (up to 1.8%).