Case study ——
State-of-the-Art Wastewater Treatment Facility at Blue Plains for DC WASA

Manufacturing units engineered to withstand the harsh conditions of wastewater treatment facilities while delivering an energy recovery efficiency of at least 65%.

The District of Columbia Water and Sewer Authority (DC WASA) required fully outdoor air handling units for its state-of-the-art Blue Plains wastewater treatment facility.

Project Details

  • 12 identical rooftop units
  • Two-level stacked plate heat exchangers
  • 18,800 CFM of outdoor airflow and 15,250 CFM of exhaust airflow
  • Built entirely (100%) of 316 stainless steel
    • Fans
    • Dampers
    • Unit cabinet/housing
    • Structural frame
    • Belt guards
    • Spring isolator cages
    • Fiberglass floor grating for return air
  • 1,000 MBH corrosion-resistant direct-fired burner
  • Programmable DDC controller with BACnet communication protocol
  • NEMA 4X electrical wiring
At least 65%
energy recovery

Context

A design tailored to the demands of wastewater treatment.

During the initial assessment of this application, the primary objective was to take a closer look at the harsh operating environment of this wastewater treatment plant. The main chemical compound that had to be considered was hydrogen sulfide gas (H2S).

Need

The units had to withstand the harsh conditions found in wastewater treatment facilities while delivering energy recovery efficiency of at least 65%.

Solution

As a leader in the potash mining sector, Bousquet Applied developed and refined a custom 304/316 stainless steel unit for potash mine applications, avoiding the need for a fully aluminum and galvanized steel construction.

Results

The 304/316 stainless steel construction of the units also incorporates features such as a riveted panel assembly system, a formed and welded stainless steel sheet metal frame, specialized coatings for the gas burners, and other key components to prevent corrosion and premature failures caused by this harsh environment. Every element, regardless of size, is critical to maintaining the integrity of the unit. From large fans down to nuts and bolts, each component plays a key role in the unit’s structural integrity, since the unit is only as strong as its weakest link. That is why Bousquet Applied paid special attention to the fans, motors, belt guards, spring mounts, sensors, wiring, dampers, actuators, gas manifolds, heat exchangers, hinges, handles, supports, window trims, access ladders, switches, nuts and bolts, and more.

One of the main points of comparison between a potash environment and a wastewater environment is hydrogen sulfide gas, which is relatively well tolerated by aluminum surfaces. This makes it possible to use epoxy-coated aluminum plate heat exchangers, maximizing energy recovery without concern for premature corrosion.

The selected aluminum heat exchanger provides 65.7% sensible energy recovery efficiency and 78.8% latent energy recovery efficiency. This relatively high efficiency will significantly reduce natural gas heating demand, since these units will operate continuously.

Annual natural gas savings are estimated at 17,733 m3 (638,000 ft3) per unit.

This is equivalent to a reduction of 3,898 tons of CO2 emissions per year for the facility!

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