Introduction

In this post, we’ll explore the practical process of Denitrification, the second stage in reducing Total Nitrogen (TN) in treated sewage effluent. Denitrification converts Nitrates (NO₃) into Nitrogen (N₂) and Oxygen (O₂) gases, which are safely released into the atmosphere.

Recap of Total Nitrogen Reduction

1. Nitrification: Converts Ammonia (NH₄) to Nitrates (NO₃).

2. Denitrification: Converts Nitrates (NO₃) to Nitrogen (N₂) and Oxygen (O₂) gases.

1. Sewage Parameters 6 Part 1: Total Nitrogen

2. Sewage Parameters 5 Parts 1 & 2: Ammonia (NH4)

Conditions Required for Denitrification

To achieve denitrification in a package sewage treatment system, the following conditions must be met:

1. Nitrate-Rich Effluent:

   • Effluent must first undergo nitrification to convert Ammonia (NH₄) into Nitrates (NO₃).

2. Carbon Source:

   • A carbon source (e.g., incoming raw sewage or an external source) is required for bacterial respiration.

3. Anoxic Environment:

   • An environment where no active aeration occurs, but small amounts of oxygen may be present.

   • Oxygen levels must remain low, as higher levels will inhibit denitrification.

How Denitrification Works

Certain bacteria respire using nitrogen instead of oxygen in an anoxic environment, converting:

• Nitrates (NO₃) → Nitrogen Gas (N₂) + Oxygen Gas (O₂)

This process is less energy-efficient than aerobic respiration, so conditions must be carefully controlled to prevent nitrification from being inhibited by excessive oxygen.

Typical Denitrification Setup

1. Anoxic Tank:

   • A tank sized to hold 8 hours of average flow is placed at the inlet of the treatment plant.

   • Raw sewage (carbon source) is mixed with nitrified effluent.

2. Recirculation of Nitrified Effluent:

   • Nitrified effluent from the treatment plant’s outlet is recirculated to the inlet of the anoxic tank.

   • A 50:50 mixture of raw sewage and nitrified effluent is maintained in the tank.

3. Gas Removal:

   • Denitrification produces oxygen and nitrogen gases.

   • These gases are removed to maintain anoxic conditions, typically using a submerged mixing pump.

Challenges of Denitrification

• Temperature Sensitivity: Efficiency decreases in colder climates.

• Control of Anoxic Conditions: Requires precise monitoring of oxygen levels and recirculation rates.

• Energy Usage: Many systems rely on pumps to move effluent between tanks.

Denitrification with the BMS Blivet

The BMS Blivet simplifies denitrification by combining it with other treatment stages:

1. Hydraulic Lift:

   • The Blivet creates net hydraulic lift, allowing recirculation of nitrified effluent under gravity rather than by pumping.

2. Primary Settlement as Denitrification Zone:

   • The Blivet’s primary settlement area acts as the anoxic zone, eliminating the need for separate tankage.

3. Integrated Process:

   • Incoming raw sewage provides the carbon source.

   • Nitrified effluent is recirculated under gravity, mixing with the carbon source to achieve denitrification.

4. Performance:

   • Effluent quality achievable with the BMS Denitrifying Blivet:

     • BOD ≤ 10 mg/l

     • SS ≤ 10 mg/l

     • Ammonia ≤ 5 mg/l

     • Total Nitrogen ≤ 10 mg/l

For Larger Flows

For larger systems, a separate denitrification/balance tank may be required. BMS offers expert design and manufacturing of such tanks to suit specific needs.

About BMS

BMS is a quality manufacturer of package products for wastewater and stormwater treatment:

• Established: 1986

• Global Reach: Exported to over 50 countries.

• Family Business: A third-generation company with deep expertise.

BMS Product Range

BMS provides a wide array of surface water and wastewater treatment products, including:

• Attenuation systems

• Interceptors

• Holding tanks (chemical-resistant options available)

• Hydrobrakes

• Rainwater harvesting tanks

• Vortex silt/oil/debris separators

• Fully fitted pumping stations

• Recyclone: A plug & play vehicle wash water recycling system

View the full product catalogue here

Additional Services by BMS

• Free Design Service: For sewage treatment, pump stations, and surface water management.

• Operation and Maintenance: Full services for existing installations, including repair, advice, and testing.

• Free CPD Presentations: Available for sewage treatment and surface water management, delivered at your location.

We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience.  Contact us today.

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