The Captivator System — an important step toward a net-zero energy consuming WWTP

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The Captivator System improves a conventional anaerobic process by capturing and converting BOD to biogas that otherwise requires aeration energy. The system utilises a VLR Contact Tank to help biomass maximise the absorption of soluble BOD. A Folded Flow DAF applied to the liquid stream removes and thickens the majority of biomass and incoming sludge at high overflow rates.

The system can be applied to both new and existing plants, and can tilt new plant economics to favour anaerobic digestion. It can:

  • Generate up to 40% more biogas
  • Reduce aeration energy up to 40%
  • Lower capital costs by up to 20%
  • Shift a plant’s energy balance toward net-zero energy usage

In the Captivator System, primary clarification and separate sludge thickening is replaced with a modified contact stabilisation process in front of a DAF. The contact stabilisation process is an aerated contact tank that is fed both raw influent and waste activated sludge.

Toward Net-Zero Energy Use

Whereas a 30 MGD conventional plant might use 1000 kW of electricity in aeration, and only produce 500 kW from biogas, a plant with a Captivator System would only need 600 kW for aeration and could generate 700 kW from biogas. The additional biogas is generated by digesting captured BOD instead of treating it in a biological reactor. This frees up a portion of the tank volume required by a conventional process for biological treatment.


VLR Aerated Contact Tank

Helps biomass absorb BOD. Low energy disc aeration is incorporated into a space-efficient design.

Folded Flow DAF

Efficiently removes and thickens biomass and incoming SS. The DAF eliminates considerable footprint and capital costs associated with primary clarifiers and sludge thickeners. It also reduces grit sent to the digester and related maintenance costs.

Integrated Control System

Fine tunes performance of the system and provides seamless controls across technologies and eliminates unnecessary PLCs.


The Captivator System is ideal for the following applications:

  • The design of new wastewater plants, looking for more biogas production for conversion to energy
  • WWT plants looking to reduce aeration energy and drive to a net-zero energy plant
  • The retrofit of existing wastewater plants, providing a capacity increase with a more efficient use of existing space and tankage

Key benefits

  • Cost-effective — Provides a cost-effective alternative to primary clarifiers and separate sludge thickeners, lowering capital costs by up to 20%
  • Reduced footprint — Reduces the footprint of biological step of an activated sludge plant
  • Less energy — Reduces aeration energy up to 40%, shifts a plant energy balance toward net-zero energy usage
  • More biogas — Generates up to 40% more biogas
  • Economical — Improves the economics of converting biogas to electricity


The Captivator System can be combined with other technologies to create even greater process and project efficiency. For example, a Dystor Gas Holder with JetMix Hydraulic Digester Mixing can be combined into a solution to increase gas storage, operational flexibility and digestion efficiency. Waste or direct heat generated from biogas can provide energy for a low temperature Sludge Belt Dryer. FlowSheet Solutions projects are strongly supported with cross technology experts and a dedicated point of contact.


Stepping towards net-zero energy consumption.


1300 661 809,


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