Activated Sludge Ditch Technologies

Wastewater treatment facilities can rely on Veolia's extensive biological experience and proven technologies. We offer a wide range of solutions for activated sludge treatment providing our clients guaranteed total process performance with a single point of responsibility. The core offerings in our activated sludge systems are based on Phased Isolation Ditch technology, or Phased Isolation Technology. Veolia also provides many additional system configurations for enhanced biological nutrient removal such as A/O®, A2/O, and An/O systems, providing flexibility in meeting the diverse requirements of plants. 

Phased Isolation Technologies for Enhanced Nutrient Removal

Phased Isolation Technology is a type of continuous flow activated sludge process wherein one or more reactors alternate between oxic and anoxic phases. Phase alternation is based on either a timed sequence of online nutrient monitoring. These systems offer very efficient enhanced nutrient removal without multiple reactor zones or multiple mass recycle loops. This technology includes the BIO-DENITRO™, BIO-DENIPHO™ and Double Ditch (D-Ditch) treatment systems.

Improved BIO-DENITRO™ Oxidation Ditch


1) Same flexible process as BIO-DENITRO Classic for TN removal

2) Now More Energy Efficient

  • Fine bubble aeration
  • Choice of Blowers to Fit the Application
  • No Internal MLSS Recycle

3) Simpler O&M

  • No Need for Precise Water Level Control
  • No Automated Weirs
  • No Rotors, Gearboxes
  • Less Maintenance

4) Simpler Construction

  • Less Concrete
  • Simpler, More Modular Geometry
  • Easier to Construct Common Walls with EQ, Digesters, etc.
  • Smaller Footprint, Much More Flexible Fit Onto Project Sites

5) Additional Savings

  • 20 - 30% lower capital cost
  • 30 - 40% lower operating cost
12.0 MGD with Secondary Anoxic Zones

BIO-DENIPHO™ for Enhanced Phosphorus Removal

  • Expansion of the BIO-DENITRO, utilizing a similar configuration and mode of operation with the addition of a Block and Hong Anaerobic Selector
  • Biological phosphorus removal achieving TP <1 mg/L, resulting in highly efficient BNR system

BIO-DENIPHO™ Process Diagram


Double Ditch (D-Ditch) for Nitrification

  • All processes, including settling, occur within two reactors
  • Reduced plant maintenance, secondary settling tanks are not required
  • Continuous flow; no batching, no decanters, no post equalization required
  • Achieves exceptional effluent quality of BOD and TSS <10 mg/L, complete nitrification, and total nitrogen removal to less than 8 mg/L
  • Advanced storm flow control made to ensure maximum treatment with no solids washout during wet weather events
  • Ease of future expansion and upgrade for increased nitrogen removal or flow by adding secondary clarifiers to convert to BIO-DENITRO
  • Ideal solution for 1 MGD and smaller plants with future growth plans or future tightening of nutrient limits

Additional Biological Treatment Solutions

Veolia's additional biological treatment solutions are superior alternatives to other multi-stage BNR systems. We apply the A/O and A2/O processes in both oxidation ditch and rectangular tank layouts. These processes can be applied to existing activated sludge and oxidation ditch plants resulting in significantly improved performance.

A/O® (Anaerobic/Oxic) for Phosphorus Removal

Veolia's A/O Ditch process utilizes the Block and Hong Anaerobic Selector for biological phosphorus removal followed by a single or multiple oxidation ditches.

A2/O (Anaerobic/Anoxic/Oxic) for Denitrification

Veolia's A2/O process incorporates an anoxic zone between the anaerobic selector and oxic zones for nitrate reduction. For more stringent TN limits, a secondary anoxic zone can be added for additional denitrification.

Process Control Features

Veolia's biological treatment systems are equipped with a PLC based control panel for enhancing the plant's daily operation. The PLC based control panel is provided of preprogrammed operational modes for ease of operation. Veolia also offers customized plant-wide SCADA systems.The SCADA system monitors and controls the process while storing relevant data that can be used to compute and report plant performance, allowing the operators to gain valuable insight into the operation of the plant. As a result, operators become more confident in the plant's capabilities and are able to optimize the plant's performance.

Veolia's Biological Process Engineers work side by side with our Instrument and Controls Engineers on each project. Therefore, expert process knowledge goes into every Veolia integrated process control system provided.

  • Customizable PLC based control
  • SCADA system including 2-D and 3-D rendered graphics
  • Use of open architecture software
  • Point-and-click navigation and control
  • 24-hour alarm monitoring and notification

STAC (Superior Tuning and Control)

Veolia's Phased Isolation Technologies can be design or upgraded with dynamic phase control, optimizing energy usage and TN removal.

  • Dynamically control phase lengths in response to incoming nitrogen loading
  • Improve total nitrogen (TN) removal by 2-4 mg/L than with a time-based, phase length system
  • Obtain energy savings from optimization of operation of ditch aeration equipment