Coolgreany Wastewater Treatment Plant 

Until 2009, Coolgreany was served by a septic tank constructed in the early 1960s.  Due to EPA licensing and more onerous discharge limits a new wastewater treatment was required on a greenfield site.  

Due to the sensitive character of the receiving waters the client required a wastewater treatment plant tasked with treating the domestic wastewater for 2,400PE to an extremely high standard. The stipulated effluent parameters were:
• BOD5 ≤5mg/l
• Suspended Solids ≤5mg/l
• Phosphorus ≤1mg/l
To ensure that the above standard was met, a rigorous design and review process was undertaken to ensure that all complex issues were identified and then careful consideration was given to addressing these issues. 

Plant Description:
To meet this stringent standard Molloy Engineering designed and built a wastewater treatment plant based on the proven Sequential Batch Reactor technology.  The specification stipulated twin streams of equal capacity.

An important feature of the supplied system is the provision of a Human Machine Interface (HMI), which uses the latest generation of 19” touch-screen panels for easy operation and also for registering, recording and storing all relevant process parameters.  The HMI facilitated easy adjustment of process settings. The HMI exceeded the specification.  The control panel includes an automatic dial out facility, which informs caretakers of serious faults, should they occur.  All alarms and operational activities can be monitored remotely via SCADA by the client.  The HMI records and displays the key process parameters. This enables the plant operator to review plant performance when the site is unattended. This is essential in the event of problem solving.

  • The supplied equipment and materials were selected to provide optimum functionality, process control, maintainability, user friendliness and longevity.

The plant consists of:

  • Inlet works with flow measurement and 3mm two fine screens of 140m3/hr capacity overflow channel and manual coarse screen.  This exceeded the specification. To ensure that no unpleasant odours are generated, screenings are automatically placed in an endless plastic bag and the unit is totally enclosed.
  • Inlet buffer tank with two submersible pumps.  A mixer was also provided to reduce the settlement of sludge.  The buffer tank acts as a storm tank when required.
  • Reactor tanks with one floating turbine each.   The high efficiency oxygen input turbines are controlled by a variable speed drive based on a feedback signal from an oxygen sensor.  Therefore, the turbine only runs enough to achieve the desired oxygen level in the mixed liquor.  The turbine is inverter controlled using the DO probe signal to minimise power consumption.  The turbine operates as mixer during anoxic phases of the process (also reducing power consumption).
  • Cylindrical tanks were chosen for all process tanks as they offered the optimum shape for mixing, reducing power consumption and preventing dead zones.
  • Sludge storage tank with decanting mechanism. The sludge being produced on site is considerably higher in % Dry Solids, as compared with the specification. 
  • Outflow attenuation tanks to prevent shock loading of the sensitive receiving waters. These attenuation tanks are equipped with a flow measurement device to measure final outflow.
  • An access platform was provided to permit easy access to the reactors and sludge tank.
  • A control house with separate rooms for the MCCs, generator, stores room and toilet/shower room.
  • A chemical dosing station with emergency bunded storage.   A flocculent is dosed to achieve the phosphate standard.
  • Standby generator to ensure continuous functionality of the plant, during times of power cuts or electricity supply issues.
  • The final effluent is used as wash water for site equipment, which saves on expensive and valuable potable water. 
  • A 1.0km trunk sewer was constructed from the village to the treatment plant.  This sewer passed through a number of private gardens.  The sewer was 300mm diameter concrete. Careful planning and management was required to ensure it was completed safely and with minimal effect to the residents of the gardens.

Process outcome
A number of final effluent samples were taken each week during the intensive three month process proving period for analysis at an INAB certified laboratory.  Results were regularly noted as follows:

  • <2mg Suspended Solids/litre
  • <1mg BOD5/litre


This type of highly reliable plant has also been used to great effect in:
• Derrinturn, Co. Kildare
• Aughrim, Co. Wicklow, and
• Carrig-on-Bannow, Co. Wexford.

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