​ Solids Transfer, Treatment and Disposal 

● Mixed sludge from the wastewater treatment process is pumped via a 12-mile long, 16-inch, high density polyethylene pipeline from CWWTP to SWWTP for further treatment and processing.

● On average, 1.8 to 2.2 million gallons per day of mixed sludge is pumped from CWWTP to SWWTP.

● The mixed sludge from CWWTP is blended with primary/activated sludge from SWWTP, which has “active" microorganisms in it that treats the wastewater, and thickened using gravity belt thickeners. After thickening, the sludge is pumped through a group of closed tanks that serve as digesters where bacteria anaerobically break down the solids to methane, carbon dioxide, ash and stabilized solids, etc. The sludge is then pumped to the dewatering facility, where it is further dewatered and thickened using belt filter presses to about 16% solids content.

● These solids are taken to the 1,100-acre on-site Dedicated Land Disposal (DLD) fields or the 200-acre sludge-only landfill (Monofil) for disposal. This eliminates the cost of off-site transport and disposal of the treated waste and is also environmentally friendly.

● The plant processes and disposes of over 150 tons of solids/day.

Cogeneration – Ameresco's Combined Heat and Power (CHP) System

● The CHP system uses the biogas generated from the plant's digesters to produce electrical energy and heat, concurrently, which is provided to the plant.

● This is an on-site installation, public-private partnership between the City of Dallas and Ameresco.

● It is located on a 2.5-acre tract of land (leased premises) at the SWWTP. Ameresco began operations in February 2011 and will run for a 20-year contract period.

● This installation enables the city to reduce its dependence on the electrical grid. About 45% of electricity used at the plant is supplied by biogas CHP. The city also gets 1,200 million gallons per year of hot water for SWWTP's heating needs from this environmental recycling system.

● The CHP results in reduction of about 43,000 tons/year of CO2 emissions (greenhouse gas); significant reductions in particulate matter, mercury, Sox and Volatile Organic Compounds (VOCs). These reductions improve air and environmental quality.

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