MBBR Retrofit vs. New Nitrifying Biotower

Carbon Footprint
Technology Comparison

The Analysis

A municipal landfill in Pennsylvania, which treats leachate in a 30,000 gallons per day on-site treatment plant, required an upgrade to their system to meet their NPDES permit limit for ammonia. Although capacity is sufficient, the treatment of ammonia, has been a challenge over the past few years, at times requiring the trucking of leachate to an off-site treatment and disposal facility.

Two options were evaluated:

  • An aerobic MBBR reactor using AnoxKaldnes™ K3 media to provide more aerobic treatment volume and greater fixed-film surface area. This would allow use of an existing anaerobic biotower.
  • A nitrification biotower with conventional packing media. This required construction of a new biotower.

Technology Design Data

The new design had to respond to two main requirements: achieve the targeted ammonia effluent concentration of 4.9 mg/l and utilize existing equipment and tanks to the extent possible

The system would be required to remove 150 lbs of ammonia per day over the operating range of 30,000 gal/day at 600 mg/l NH3 to 15,000 gal/day at 1,200 mg/l NH3 and to achieve an effluent NH3 averaging less than 4.9 mg/l (> 99% ammonia removal).

Evaluation Boundaries

For the conversion of the existing anaerobic biotower to an aerobic MBBR, the biotower was drained and the existing internal structures and media were removed for installation of the MBBR aeration grid and K3 media. A new concrete floor was installed in the tank over the original floor.

Conversion of the anaerobic biotower to aerobic with conventional packing media would not have provided adequate treatment due to insufficient fixed-film surface area. Also, the conversion would have been more complicated with conventional media due to the need for a media support platform. A new larger biotower would not fit within the existing building, making it necessary to construct a building extension. Therefore, construction included new building space, utilities for the building expansion and the new biotower tank with conventional packing media.

Both alternatives required equivalent new pH control systems and chemical consumption rates, and had equivalent aeration requirements utilizing an existing blower. Additional energy consumption was projected for the new biotower alternative due to heating, ventilation and lighting in the building expansion. Shipping of media was also taken into account since they would be shipped from different locations.

Carbon Footprint over Life Expectancy of the System*

 

Conclusions

The MBBR retrofit proved to be the easier and more economical upgrade of the existing leachate treatment system. It allowed re-use of an existing vessel and did not require expansion of the building. This resulted in lower capital cost and energy consumption projections. The transition from the old process to the upgraded process took only a few weeks to install. Effluent compliance was achieved less than a month after start-up of the upgraded system. The carbon footprint for an upgrade via retrofitting an existing tank is lower than an upgrade via new construction.

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