LPWRP - ENR - How It Works
Denitrification is the process of reducing nitrate (NO3) to nitrogen gas (N2) in the absence of dissolved oxygen by denitrifying microorganisms.

How does Denitrification happen ?

The influent entering into the denitrification filter complex contains residual nitrates from the final clarifiers. Utilizing denitrifying microorganism, these residual nitrates are trapped and converted to nitrogen gas.

The denitrifying organisms get their oxygen by taking it off of the nitrate molecules contained in the influent. When bacteria break apart the nitrate (NO3) to gain oxygen (O2), the nitrate is reduced to nitrous oxide (N2O), and, then to nitrogen gas (N2). Nitrogen gas has low water solubility and ultimately released into the atmosphere as gas bubbles. Denitrifying microorganism uses carbon as a source of energy. To provide a readily biodegradable carbon source, methanol is added to the influent.

The Denitrification process implemented at the LPWRP is depicted in the figure below.

Denitrification Process

The treated influent from the denitrification filters enters the UV disinfection chamber to treat pathogens and is collected in the clear well. The effluent in the clear well will have little or no dissolved oxygen (DO) and therefore reaeration of the effluent is provided in the post aeration tanks before discharging into the Little Patuxent River.

denitrification Building

Where does Denitrification occur ?

The denitrification occurs in the gravity downflow packed bed sand filter. Listed below are the three processes that occur in the denitrification filter :


  • Normal Filter Cycle
    Influent passes through the filter media and contacts the denitrifying microorganism.
    The microorganism utilize the oxygen on the nitrate and leaves nitrogen gas bubbles in the filter bed.
    The filter media also traps residual suspended solids.
  • Nitrogen Release Cycle
    Small bubbles of nitrogen gas trapped in the filter bed cause headloss ( clogs filter ) therefore, the gas bubbles must be periodically washed out from the filter.
    A short backwash cycle releases the trapped bubbles of nitrogen gas into the atmosphere.
  • Full Backwash Cycle
    A complete backwash cycle cleans the filter media which releases the remaining nitrogen gas and removes suspended solids trapped during the normal filter cycle.
    Click on the buttons below to see the three processes in action.

    Does Deni