In 2005, NEFCO contracted with a noted hydraulic modeling firm and began a study of the performance of the Density Current Baffle using Computational Fluid Dynamic (CFD) software. One result of that effort is NEFCO’s Stamford Baffle 2.0, the first major advance in Density Current Baffle performance in twenty years. Stamford Baffle 2.0 can reduce TSS by as much as 80%. Stamford Baffle 2.0 combines a 30° inclination angle with a greater horizontal projection from the clarifier wall calculated as a function of the diameter of the clarifier. The study demonstrated that these two features, operating in concert, are able to intercept a greater volume of rising solids and redirect those solids on a more horizontal trajectory toward the center of the tank. Subsequent field results confirmed that Stamford Baffle 2.0 reduced total suspended solids by nearly 80% and produced a 35% increase in overall hydraulic capacity. SB 2.0 is not simply a baffle; it is an integral piece of process equipment that makes the clarifier more effective.
The SB 2.0 is the result of over five years of computer hydraulic analysis and modeling.
The SB 2.0 offers an unprecedented improvement in clarifier performance in terms of reduced TSS and increased hydraulic capacity.
The SB 2.0 features a 30° inclination angle as measured down from the horizontal and a greater horizontal projection from the clarifier wall, calculated as a function of the clarifier diameter.
Density currents form in all activated sludge clarifiers. The dense influent cascades downward and become a current moving in a horizontal plane just above the sludge blanket, attracting lighter solids and short-circuiting the main clarification volume of the tank. The density currents carry the solids to the tank wall and deposit them into the effluent channel, increasing effluent suspended solids and reducing the clarifier’s hydraulic capacity. An EPA consultant, working at the Stamford, CT WWTP in the early 1980’s, conceived of an inclined baffle mounted to the clarifier wall that would intercept these currents and redirect them toward the center of the tank. Several years later, NEFCO implemented that concept by designing and installing the first full-scale, fiberglass Density Current Baffle at the Stamford plant.
The original NEFCO Stamford Baffle was inclined at 45° and had a relatively small horizontal projection factor. That baffle reduced the clarifier’s total suspended solids (TSS) by roughly 40%. The design quickly became the industry standard. NEFCO’s baffle included two proprietary features: an integrally molded support bracket that simplified installation, and gas vents molded into the mounting flange at the top of the baffle. The 45° baffle continues to be produced by others.
Stamford Baffle 2.0 retains all of the unique features of the original NEFCO Baffle. The baffle is comprised of individual baffle sections or “modules”. Each module combines the baffle panel, the bracket, the vents and the mounting and stiffening flanges in a one-piece molded fiberglass unit that offers a number of advantages:
1. The solid integral bracket at the end of each baffle panel reduces the current velocity below the baffle and contributes to settling.
2. With the integrally molded bracket and other reinforcements, this baffle requires only one bracket per panel.
3. The one-piece, modular design cuts installation time in half.
The Stamford Baffle 2.0 Baffle System is readily converted to NEFCO’s new Dual Surface Baffle. This dual surface configuration is designed for larger clarifiers operating at very high flows, including combined sewer configurations.
In clarifiers with outboard launders, the baffle mounts to the clarifier wall with the bottom of the baffle positioned mid-way between the top of the sludge blanket and the bottom of the weir. In clarifiers with inboard launders, the baffle will perform most effectively mounted to the tank wall below the launder, so long as there is sufficient vertical clearance to mount the baffle with the bottom of the baffle two feet or more above the top of the blanket. If there is insufficient vertical clearance, the baffle should be mounted to the lower inboard corner of the launder trough. The width of the launder should be included in calculating the horizontal projection of the baffle, but the projection should never be less than 24”.
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