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KEE Triton® – Mountmellick Wastewater Treatment Plant Upgrade – The installation of new aeration and mixing units to reduce the carbon footprint and improve plant performance.

3.7kW Tritons® fixed on a tri-pontoon float. The Triton® can be bridge or side-wall mounted.

3.7kW Tritons® fixed on a tri-pontoon float. The Triton® can be bridge or side-wall mounted.


Mountmellick village is located approximately 15 miles northwest of Portlaoise, County Laoise, Republic of Ireland. As with all Irish towns, Mountmellick has grown greatly over the years. The existing plant was designed and installed in the mid 1970s, with further works being added later, the last being a sludge dewatering plant.

The existing plant design consisted of:

  • A Wham Mechanical Screen
  • An Oxidation Ditch for biological treatment. A 60m long ‘Race Track’ shaped ditch, each lane measuring 7m wide. The total average depth of the ditch was 1.57m with a total volume of 1,340m³.
  • Horizontal Brush Aeration System. As was the practice during the 1970s, consisting of 4 horizontal rotors, each 2m in length
  • Two final settlement tanks and sludge dewatering works.
  • An ‘activated sludge process’for the biological treatment stage.

The Challange

The design capacity of the works was 5,000PE and the discharge consent was 20mg/l BOD (Biological Oxygen Demand) and 30mg/l SS (Suspended Solids). The brush rotor aeration capacity had proved inadequate and was supplemented by Venturi Aerators. The combined horizontal brush and Venturi Aeration systems were unable to support the process oxygen demand and could not provide the necessary velocity profile in the ditch to ensure the minimum vital mixing requirement of the ditch contents. Consequently, the plant was failing consent.

In addition to the problems associated with the failure of consent, the high power demand to run the aeration system at Mountmellick (i.e. two 7.5kW drives for each horizontal brush rotors and two 13.50kW drives for each Venturi Aerator) also made it expensive to run at existing capacity. However, the need to increase plant capacity from 5000PE to 7000PE meant that the high power supply to the existing plant provided an opportunity to review the whole process performance of the aeration system and deliver a solution to reduce carbon footprint.

KEE Process was contacted by Laois County Council, to discuss how the Triton® aerators and mixers, could overcome the current process load issue facing the Mountmelick plant and explore the option to save power and increase the plant capacity.

After discussions with Laois County Council and their consultants at Nicholas O’Dwyers, KEE visited the site to review the existing plant design and formulate a proposal.

The Solution

After further liaison and evaluation of the actual dissolved oxygen requirements, it was agreed that the plant upgrade should be carried out in two phases using the KEE Process Triton® dual mode, fine bubble aerator/mixer.

  • Phase 1 upgrade – To address the urgent need to increase the process performance of the plant to meet the required environmental discharge consent and also reduce the overall carbon footprint.
  • Phase 2 – To increase the capability to upgrade the plant capacity upgrade from 5000PE to 7000PE and reduce maintenance requirements.

Based on the current load and the 20mg/l Biological Oxygen Demand consent for Phase 1, it was necessary to install four 3.7kW Tritons® to provide the supplemental Dissolved Oxygen and all the mixing for the oxidation ditch. These four Tritons® would provide complete mixing of the ditch and generate the optimum horizontal velocity of 0.3m/s to ensure that the suspended solids in the mixed liquor remained in suspension at all times.

Treatment processing target criteria for design upgrade:

Type of wastewater                                       Municipal

Dry Weather Flow (DWF)                              1,575m3/day

Full Flow to Treatment (FFT)                        3.3 x DWF = 5,184m3/day

Total influent BOD5 load                             420kg/day

Total influent nitrogen load                        77kg/day

Oxidation ditch approximate volume       1,340m3

Treatment objectives                                   BOD5<20mg/l
(no nitrification)

Although the stated environmental objectives did not require nitrification, we knew that the NH4-N in the influent would exert an oxygen demand due to the high retention time of 20 hours (at DWF) in the oxidation ditch. The projected AOR (actual oxygen requirement) of 959kg/day accounts for both carbonaceous BOD reduction and Nitrification. For carbonaceous BOD removal only, the AOR would be 773kg/day.

[Note: AOR is the oxygen required under field conditions of temperature, elevation, desired dissolved oxygen operating concentration].

To provide the projected AOR, eight 3.7kW Tritons® were required, in addition to the existing horizontal brush rotors which would need to be retained. This process upgrade assumed that nitrification would be accepted as a future treatment objective. If this had not been the case then the Tritons on their own would have beeen sufficient to provide all the projected Dissolved Oxhgen (DO) and mixing for the 7000PE capacity.

Supply and Installation

Of all the aeration equipment on the market, Triton® aeration units are the easiest to install. There was no need to decommission the existing plant while installation was being carried out. The Tritons® fine bubble aerators were surface mounted and therefore neither the aeration tank or the oxidation ditch needed decommissioning, emptied, refurbished, refilled and re-commissioned. Tritons® can be bridge-mounted, wall-mounted, float-mounted or guiderail-mounted for SBR configuration.

Timing was of the essence to ensure that the treatment objectives were met and therefore the equipment was ordered whilst the installation format was being finalized. At the Mountmellick site Laois County Council and Nicholas O’Dwyer used a novel adaptation to use a ‘float-mount’ option where the floats were anchored to a steel bridge across the ditch with ‘H Frames’ attached to the bridge. This gave the operators the option to have fluctuating water levels as the H frame pivoted the Triton® floats to the bridge. The existing DO probes were used to control the brush aerators through the variable speed drives and, if the DO remained high, the Triton® blowers could be similarly controlled through the DO probes. At least four Tritons® had to be operating in the mixing mode to completely mix the ditch contents and therefore for Phase 1, the control philosophy was designed only to control the Triton® blowers operation to maintain the DO at between 1 and 2 mg/l.

After the Phase 1 installation was completed and within 20 minutes of the four Tritons® being commissioned, the mixed liquor DO concentration started to rise and it was evident that the units were re-suspending solids that had been settled out in the bottom of the ditch previously. Within two days of commissioning, the four Tritons® units were achieving 1-2mg/l DO constantly, with the existing brush rotors only coming on to assist at times of heavy load when the DO concentration started to drop.

Four out of the eight Tritons® for Phase 2 were operated in aeration and mixing mode at all times and the other four Tritons® were installed to operate in mixing and/or aeration mode when required. To ensure an even use, it was also decided that the Triton® operation would be alternated in ‘duty’ and ‘assist’ mode.

For Phase 1 the installed power was reduced from 42kW to 30kW and the treatment objectives were all achieved. Furthermore, the energy efficiency gains and optimisation objectives were achieved by controlling the aeration mode to provide oxygen as and when required whilst the mixing mode was always maintained to ensure the process performance. Thus, an energy saving over 28.5% was achieved and at the same time the environmental objective for effluent quality was met.

Phase 2 was designed to deliver the energy efficiency gains and carbon footprint objectives. The 45kW total installed power for Phase 2 provided a 40% increase in plant capacity whist requiring only a 3kW increase in power.

The carbon footprint can be further reduced if, as required by the consent for discharge, nitrification of the effluent was not pursued.

For more information on KEE Tritons® or any other wastewater treatment equipment and systems, please refer to our website at keegroup.com or call us on 01296 634500.

3.7kW Tritons® on a tri-pontoon float in position and fastened to the access gantry. The Triton® can be bridge or side-wall mounted.

3.7kW Tritons® on a tri-pontoon float in position and fastened to the access gantry. The Triton® can be bridge or side-wall mounted.




The wastewater treatment plant at the village of Keith in Aberdeenshire treats municipal wastewater from the village and effluent from a famous branded Whisky Distillery nearby.

The overall process on site includes inlet works with a grit chamber and screen for municipal wastewater. After this preliminary treatment, the municipal wastewater stream is mixed with the Distillery effluent and is processed through the first-stage high-rate biofilter tower. The effluent from the biofilter tower is then processed through radial flow-scraped primary settlement tanks and the settled effluent is discharged into a two-stage activated sludge basin consisting of two tanks of 7.92m x 7.92m x 4.65m deep (water depth 3.65m). The mixed liquor from the activated sludge plant is discharged through to three radial flow-scraped final settlement tanks and the settled effluent is discharged to a watercourse. The settled sludge is returned (RAS) to the activated sludge basin with excess sent to sludge storage.  Finally, supernatant from the sludge storage tank is returned to the feed for the high rate filter tower.

The aeration system for the activated sludge basin consists of two surface-mounted aerators driven by a 20kW common-geared motor through a propshaft delivering approximately 30kg/hour of dissolved oxygen.


The total BOD load to the plant from municipal and industrial sources is 570 kg/day and approximately 285kg of this is reduced through the high rate biofilter and the remaining 285kg/day is required to be treated through the activated sludge plant. The aeration tank capacity is 230m3 each and is normally operated at MLSS concentration of approximately 2000mg/l. One of the surface aerators in the existing aeration system had failed and a temporary venturi aeration system was installed to assist in oxygen supply.

KEE were requested to visit the site, analyse the situation and evaluate the process requirements to make a proposal to upgrade the aeration system. The factors to be taken into account included the need to upgrade the aeration system whilst the plant continued to operate (without decommissioning the plant) and to ensure that the new aeration device produced less than 60dB noise. KEE evaluated the existing process parameters and concluded that the plant could be operated at a higher MLSS concentration of up to 4000 mg/l at a substrate loading rate of 0.15g BOD/g MLSS.  The estimated dissolved oxygen demand on this basis would be approximately 33kg/hour.

KEE proposed to install four 5.6kW dual mode Triton processors to provide complete mixing of both the aeration basins and to supply up to 40kg/hour of dissolved oxygen. The Triton dual mode processor is an efficient aeration device which provides total (horizontal and vertical) mixing of the whole basin. It can be mounted from a wall or a bridge or can be supported from floats. The Triton can mix up to a depth of 10m and therefore is also ideal for upgrading existing aeration systems for total replacement or supplemental aeration. The Triton uses a low-power regenerative blower for air supply and a direct-coupled electric motor to generate a plume of fine bubble aeration which is able to penetrate through to the bottom of the tank. This  air/water mixer provides a long retention period for air bubbles and the resulting high efficiency oxygen transfer into the mixed liquor. By EPA definition the Triton is a fine bubble aerator.

triton-upgrade-002 triton-upgrade-003


The four Tritons were mounted from the side walls of the existing tanks and, once all the installation work was completed over two days, the electrical cabling was finalised. The blowers supplying air into the Triton were controlled through D.O. probes located in the aeration basin. Once all the electro mechanical work was complete the Tritons were switched on and the old aeration system switched off. The plant aeration system upgrade was achieved in less than one week’s time on site and without any downtime on the existing treatment process. There was no need to hire temporary plants to relieve activated sludge plant. Apart from large savings in capital and operating costs, the biggest benefit was that all the logistics and space problems associated with installing a temporary plant were avoided. The noise emitted by the new aeration system is much lower than specified and definitely lower than the previous system. The process performance of the plant has improved and the plant is able to meet its specified process objectives and has continued to do so for over twelve months.

For more information visit the KEE website.

KEE Process Logo


KEE seeks to identify and satisfy the needs of their customers by providing quality engineered solutions priced to offer value for money. KEE has over 60 years’ experience in wastewater treatment, process engineering, servicing and operation with over 350,000 installations worldwide. 

 The technologies and services offered by the KEE Group of companies are listed below:

Design, Installation and Operation of On-Site Plants

  • Anaerobic Reactors – The KEE Group offer design, installation and operation of on-site treatment plants. Their technologies include anaerobic digestion, aerobic processes including RBC and Submerged Aerated fixed film systems, extended aeration and SBR activated sludge processes, complemented with physical and physio-chemical processes. KEE also have a team of experienced process engineers and project engineers capable of delivering solutions to suit

Rotating Biological Contactor (RBC)

  • NuDisc© Single Piece Packaged RBC Treatment Plants
  • Modular Packaged RBC Treatment Systems
  • Large Diameter RBCs for site erection

Submerged Aerated Filters (NuSAF)

  • Single piece NuSAF© Systems,
  • Modular Packaged NuSAF© Treatment Systems
  • Large NuSAF© – in on-site constructed concrete tanks

Activated Sludge Systems

  • Extended Aeration, Sequencing Batch Reactors (SBR)
  • Oxidation Ditch

Fine Bubble Aeration & Mixing Systems

  • KEE Triton Aerator/Mixer

Attached Growth Airlift Reactor (AGAR®)

  • Moving Bed Biological Reactor (MBBR)
  • Integrated Fixed Film Activated Sludge (IFAS)

Dispersed Air Flotation (DAF)

  • pre-treatment of industrial and food processing wastewater
  • KEE Microfloat® – Dispersed Air Floatation Technology,  for pre-treatment of industrial and food processing wastewater to reduce FOG, BOD, COD & SS. The KEE Microfloat system achieves the same result as conventional DAF systems without the need to use a high-pressure pump and venturi. It incorporates a system to produces extremely fine bubbles 10 to 50 micron air bubbles into the water to float the light fractions

Primary and Final Settlement Tanks

  • GRP Hopper Bottom Settlement Tanks – A range of advanced design Hopper Bottom GRP Settlement Tanks for small wastewater treatment plants.

Grease Management System – Biological Solution to Fat, Oil and Grease (FOG)

  • KEE Bio-GuardThe grease digester that’s the biological solution for the removal of Fat, Oil and Grease.


KEE Services Logo

For full information on KEE Technologies and Services visit the KEE Group website
or call 01296 634500


KEE Tritons® Dual mode Processor (Aerator/Mixer)


Dairy Crest Davidstow Creamery in Camelford is the largest cheddar cheese manufacturer in the UK. The process of collecting and processing milk is a 24/7 operation and therefore in a cheese-making facility like Davidstow effluent is generated round the clock on a daily basis and needs to be treated and disposed of continuously. Effluent from the cheese-making process contains high fat content and BOD/COD concentration.

The Creamery upgraded the effluent treatment plant during 2002/2003 and currently has DAF, a balancing tank, two aerobic reactors and a final clarifier. One of the aerobic reactors is MBR and the second reactor is an extended aeration system.

The original design was based on the MBR treating 60% of the total load and the extended aeration system expected to treat the balance. Due to various operational matters and high power consumption, the site was operating with the extended aeration system, consisting of a 5,000 m3 reactor, treating approximately 60% of the flow. The extended aeration system used helixor aerators for providing oxygen to the mixed liquor and the air was provided by Roots blowers at approximately 0.7bar pressure.

Approximately two-thirds of the helixors were still operational and this meant that one-third of the reactor was not being aerated and consequently was not effective in providing any treatment. The reactor was lacking in adequate mixing and due to the reduced operational volume of the reactor it was necessary to maintain high MLSS at around 7,000mg/l.

A further complication was introduced with high-pressure air at high temperatures increasing the bulk liquid temperature to 23ºC. The combination of high MLSS concentration, high bulk liquid temperature, lack of adequate mixing and the need to operate the reactor at a DO of 3.0-3.5mg/l meant that the blowers were consuming around 150kW of power. It was necessary to replace the disfunctional helixor aerators, as gradually more helixors were beginning to fail and the process was at risk of becoming unstable.

In order to replace helixor aerators, it would be necessary to de-commission the 5,000m3 extended aeration reactor, re-install the aerators and then re-commission the plant.

Whilst this refurbishment was being carried out, the Creamery would have had to make arrangements to dispose of 5,000m3 of mixed liquor and dispose of 850m3/d of high strength effluent for the duration of the refurbishment. Disposal of effluent would need to be continued after the plant had been re-commissioned and until the process was fully established and the effluent discharged from the plant was within consent. In addition to these logistical issues and the high cost of mixed liquor and effluent disposal, the Creamery also had concerns with the ageing Roots blowers, which were consuming approximately 3,600kWh of electrical power, associated maintenance and extremely high levels of noise. It would also be necessary to install 60kW of mixing power to optimise plant performance thereby increasing the power consumption to 5,040kWh/d.

To optimise the process it would also be advisable to introduce lateral mixing in the reactor and again this would have added to the power costs and additional electro-mechanical equipment to be maintained.

Tritons® Dual mode Processor (Aerator/Mixer)

KEE Process has been working with the Davidstow Creamery and their Consultant, Mr. D. Sharpe of Lanson Microbe, for some time to evaluate installation of KEE’s dual-mode Triton® processor which provides efficient mixing and fine bubble aeration for mixed liquors in any activated sludge system configuration. The Tritons® can be installed without de-commissioning the reactor and whilst the existing treatment process is ongoing thereby eliminating the logistics of emptying the reactor contents and finding a temporary solution for disposal of the effluent.

The Tritons® are surface-mounted fine bubble aerators and the aerator operates under water surface, thereby eliminating the atomisation and aerosol effect of the air-water mixture. The blower supplying low-pressure air is a high-efficiency regenerative unit and is quiet in operation. The Triton® injects a plume of fine bubble air and water mixture into the water and this action ensures that air reaches deep into the tank bottom up to a depth of 10m. The air-water mixture forms a cone-shaped plume which increases in its zone of influence with depth and this ensures that all the tank contents are completely mixed. As the Triton® uses low-pressure air, the mixed liquor temperature is not elevated and thus the energy required for process is minimised.

The blower can be controlled using a DO probe and PLC to facilitate effective dissolved oxygen in the mixed liquor as required. During the low-load conditions the blower would switch off but the Triton® would continue to provide efficient mixing to the reactor contents. The benefits of a well-mixed activated sludge reactor are that all the installed volume of the reactor is actively participating in the treatment process, the DO concentration throughout the reactor is homogenised and is always available throughout the tank and all the other tank contents, i.e. activated sludge and the substrate are uniformly distributed and this enables the reactor to operate as a completely stirred tank reactor. The system can therefore be operated at the desired DO set point of between 1.5mg/l and 2mg/l instead of 3.5mg/l previously.

KEE Process provided the necessary process engineering input to the creamery and re-evaluated the reactor design for treating 850m3/d of creamery effluent with influent COD load of 1,682kg/d (2,000mg/l) at a design MLSS concentration of 4,000mg/l, F:M ratio of 0.053, and mixed liquor temperature of 20ºC. The consent for final effluent for the Creamery is BOD < 13mg/l, SS <20mg/l, NH4-N < 5mg/l and PO4-P < 1mg/l/.

KEE concluded that the process required between two and three 48.5kW Tritons® for oxygen requirements but two would suffice for mixing. It was decided to install two 48.5kW Tritons® and these would provide the necessary mixing of the mixed liquor and almost 85% of the oxygen demand. The balance of the oxygen would be provided by the retained existing helixor aeration system as and when necessary. In effect, the Tritons® took over as the primary aeration system and provided the critical mixing vital to any activated sludge process. The Creamery could have installed three Tritons®, in which case the reactor would have been able to handle 30% more load than at present and this option still remains available to the Creamery. In fact the reactor is capable of treating a lot more load with 4 No. Tritons® but beyond that the process becomes limited by the solids handling capacity of the final clarifier.

The Tritons® were installed and commissioned and the existing aeration system was kept switched on to supplement any necessary deficiency in oxygen demand. The Creamery and Mr D. Sharpe monitored the existing variable speed Roots blower operation and concluded that they only need to operate at their lowest speed. They also monitored the D.O. concentration in the reactor and this was found to be consistently uniform compared to before the installation of the Tritons®. They also commented that the Tritons® were extremely quiet in operation.

Power Saving

Since commissioning the Triton® Dual Mode Processors, the power consumption is 2,580kWh/day and this represents a 28.3% drop in energy consumption compared with the previous aeration system. The annual power saving is 372,300kWh. More importantly, the contents of the reactor are now completely mixed thereby providing a true CSTR with uniform distribution of substrate and D.O. With mixing taken into account the annual power saving would be 897,900kWh. In addition to the power saving the noise from the Roots type blower is eliminated.


  • Tritons® can be installed in new plant, or in existing plants for supplemental aeration and/or mixing or for refurbishment.
  • Tritons® can be installed without de-commissioning the aeration reactor.
  • Tritons® are surface-mounted dual-mode processors and provide complete mixing and fine bubble aeration of the reactor whilst operating under water surface.
  • With complete mixing of the reactor contents, the process is completely optimised for performance and energy consumption with lower operational MLSS concentration.
  • The upgraded aeration system enables operation of the reactor at under 2mg/l DO and, apart from saving energy, it also enables control of DO in the anoxic selector tank.
  • Use of Tritons® enables lower MLSS concentration in operation and this will reduce solids loading on the final clarifier which, in turn, improves final clarifier effectiveness in removing solids or enables operation of the reactor at higher SSVI.
  • The use of high-pressure blowers leads to increased temperature of reactor contents thereby increasing energy consumption.
  • It is possible to treat more flow and load in the same reactor by adding further Tritons® to improve mixing or provide additional D.O. or both.

KEE, a BSI Certified Company (IMS, QMS, OHS & EMS) offers domestic and industrial wastewater treatment solutions including lifetime operation and maintenance using RBC, SAF, SBR and Extended Aeration. With 60 years’ experience and over 350,000 installations, KEE have the expertise in design, build and operation of all wastewater treatment plants.

For full information on KEE Technologies and Services call 01296 634500 or visit: The KEE Group Website




The patented new Dual Mode Processor called the Triton Aerator/Mixer.

This new technology overcomes the previous limitations of oxidation ditch technology and can be used to revitalise existing oxidation ditches and technology.

Oxidation ditch technology is one of the oldest ways of treating wastewater. Whilst it enables wastewater to be treated to a high standard, including nitrification and de-nitrification, it does have significant limitations.

The process requires aerated and mixed liquor to continuously move through the aeration ditch. Brush rotors and disc rotors aerate and mix the liquor but, because they can only maintain the necessary fluid velocity of 0.3 – 0.4m/s in a shallow depth of no more than 2m, the footprint area of the oxidation ditch is extremely large.

The Triton Aerator and Mixer Aerator is an energy efficient, dual mode (aeration and mixing) process aerator that is capable of nitrification and de-nitrification all in one unit. With two propellers and a regenerative blower, it is able to operate either as an anoxic mixer with the blower turned off, or a very efficient aerator/mixer with the blower turned on.

With its two mixing propellers, the Triton is able to achieve significant velocities in depths of up to 10m. This means the oxidation ditch basin can now be built up to 10m deep, therefore significantly reducing the footprint area.

The Triton Aerator/Mixer’s primary and secondary propellers inject air bubbles (defined by the Environmental Protection Agency as “fine bubble”) into a high velocity stream (plume) below the surface of the water and provide flow linkage mixing in multiple unit arrangements.

The Triton can also be used to revitalise existing oxidation ditch systems with failing brushes or disc rotors. If the rotors have totally failed, the Triton can replace them.


Franklin’s plant has two oxidation ditch systems operating in parallel, each of which treats 4536m3/day, with influent BOD of 185mg/l and TSS of 90mg/l. The Oxidation Ditch Wastewater Treatment Plant at Franklin was failing to meet the consent of 15mg/l BOD and 23mg/l TSS. Because the rotors required daily lubrication, maintaining them was a time consuming and costly exercise. So when the rotors fractured and failed four years ago, the decision was made to upgrade the plant by replacing the brush rotors with the Triton Aerator/Mixer.

During the upgrade each ditch was fitted with four Triton each rated 18.6 kW. This represents a maximum of just over 2kWh of electrical energy per kg of BOD or 0.4 kWh/m3 flow.

The final effluent quality from the refurbished oxidation ditch is testimony to the excellence of the Triton. The result of the upgrade was final effluent with BOD of between 2 and 3mg/l and TSS well below 15mg/l. Independent velocity measurements at extremities are well above the minimum 0.3m/sec, therefore guaranteeing that no solids deposit would develop in the basin. At the same time, maintenance requirements have been substantially reduced to a simple lubrication task once every six months.

For full information on KEE Fine Bubble Aeration visit:

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