What does “treatment” mean?

The GLSD wastewater treatment plant provides two types of treatment: wastewater treatment and sludge/solids treatment. These two types of treatment are described as follows:
Wastewater Treatment: Virtually all the wastewater entering the GLSD plant passes through the main pumping station known as the Riverside Pump Station. This station has the capacity to pump up to 120 million gallons per day of wastewater. At the treatment plant, the wastewater passes through four stages of treatment:

  • Primary Clarification for removal of solids in the wastewater;
  • Aeration Treatment for removal of organics remaining in the wastewater after primary clarification;
  • Disinfection to destroy harmful pathogenic organisms in the treated wastewater;
  • Discharge back to the Merrimack River.

Sludge/Solids Treatment: Both the primary clarification and aeration treatment processes produce sludge, which also must be treated. The “Biosolids Improvement Project” completely revamped the treatment of sludge at the GLSD. The following summarizes the new sludge treatment system:

  • Gravity Thickening for initial removal of water from sludge produced by the Primary Clarification process. Covers have been added to these tanks for odor control.
  • Gravity Belt Thickening for initial removal of water from sludge produced by the Aeration Treatment process.
  • Anaerobic Digestion: This process receives the sludge from the two thickening processes. Anaerobic Digestion is a biological process that performs several functions:
  • Breaking down organic matter into simple compounds thereby stabilizing the sludge and reducing its odor potential;
  • Reducing the concentration of pathogenic organisms present in the sludge, and producing methane gas that can be utilized as a fuel.
  • Centrifuge Dewatering removes additional water from the sludge transforming it into a solid material that is then sent to the onsite drying facility where it is processed and converted into dry pellets that can be utilized as a fertilizer and soil conditioner.
  • Although not part of the sludge treatment process, the Biosolids Improvement Project also includes a new “Biofilter” for control of odors produced during sludge processing.
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