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Figure 1: TMS Clearwell Configuration

 

Clearwells

    Clearwells are located at water treatment plants and are designed to provide sufficient contact time (CT) of the disinfectant to kill pathogens prior to distribution. Clearwells are typically operated in plug flow and this process can be much more efficient by using baffles. Baffles increase the baffling factor which is a measure of the short-circuiting characteristics of the tank. Baffles maximize the amount of time the water stays in the tank by preventing the water from quickly short-circuiting from the inlet to the outlet pipe.

    Distribution storage tanks by contrast are most efficient by encouraging complete mixing as discussed in the AwwaRF report Water Quality Modeling of Distribution System Storage Facilities (Grayman et al, 2000). The TMS is designed to achieve complete mixing but is also used in clearwells in two cases:

• Without the use of baffles, The TMS can provide a minor improvement in baffling factor. The AwwaRF report Improving Clearwell Design for CT Compliance (Crozes et al. 1999) stated that a 40% improvement in CT can be achieved with the use of inlet or inlet/outlet diffuser piping. Note, the regulatory agency may require the baffling factor to be proven by CFD, scale model, or tracer study.
• With the use of baffles, the TMS is and inlet diffuser, Figure 1, designed to ensure that a homogenous mixture of water (thru the depth) moves thru the baffles. Even with baffles, a single inlet pipe can produce recirculation areas and dead zones. The baffles still control the CT of the tank. The TMS eliminates recirculation areas and dead zones near the inlet.

US Patent No. 7,104,279
Canada Patent No. 2,409,009