The riser pipe sludge removal device was developed in the early 1960s. At the time, Rex Chain Belt (now Envirex/Siemens) patented the current Tow-Bro™ / unitube header product. As a result, hydraulic removal for activated sludge final clarifiers became the standard. To overcome this patent and still hold to hydraulic removal of activated sludge, the riser pipe design was developed and promoted. It was marketed and furnished heavily in the Northeast part of the USA by Dorr-Oliver, Walker, and Eimco who were the main players at that time. There have been various names for the product over the years such as: riser pipe, pipe organ, site well clarifier (so that it can be seen when there is a clogging problem), and suction removal pipe device.
The general thinking was that a competitive offering was needed that could overcome the dominance of the Tow-Bro™ with unique features that it did not include. The riser pipe offered the plant operators the ability to see the sludge in the sludge box and the ability to control the sludge withdrawal rate from each area/region in the tank. There are several different flow control device designs for the pipes as they discharge into the sludge box. The two main control layouts are: 1) individual compartments with a submerged orifice gate and 2) a pipe over pipe design with a submerged orifice to control flow by varying the size of the orifice.
Despite these unique design features, there was not a lot of concern given to uniform pick up of sludge, the size of the pipes, low flow velocities, or pipe clogging problems. There were also thoughts at the time that the heavier sludge settles out near the center of the basin, making uniform pick up across the basin diameter less critical. There were some designers that also specified and promoted a heavy solids line at the center of the tank with scrapers directing the sludge into a heavy solids hopper. The outer area towards the wall then would be considered for the riser pipe removal of sludge.
After the Tow-Bro patent ran out in the mid-to-late seventies most manufacturers furnished the same header design configuration as the Tow-Bro™. The original equipment will now be 20 to 40 years old and in need of replacement at many plants.
