You have installed your sewage treatment plant successfully and have started using it. And, it all seems to be working well. This is where you as customer / house owner have to take responsibility. Don’t forget that maintaining your plant well is key to its long life.

The manufacturer’s installation guide will have details of how you need to maintain your sewage treatment plant. You can even talk to your service engineer about the steps to be taken to maintain your sewage treatment plant. It is important to note that it is the end user’s responsibility to ensure that maintenance is performed on the system at the appropriate time. Maintenance will ensure good operation and avoid environmental pollution caused by any potential faults. Environmental enforcement agencies will hold the owner of the plant responsible for ensuring compliance with any consent parameters imposed on the site.

It is extremely important that your sewage treatment plant is desludged and serviced at the prescribed intervals so that the maximum working life of the components is obtained and that effluent quality does not deteriorate. Servicing and desludging should be carried out in accordance with the size of the plant. It’s better to purchase a sewage treatment plant from a reputed manufacturer like Harlequin MFG who will provide you with all the information required on steps involved in maintaining your sewage treatment plant.


Desludging prevents a decrease in effluent quality and minimises any potential damage to the sewage treatment plant. The desludging interval ranges from 6 to 12 months depending on the size of the plant. Failure to desludge the system at the appropriate time may cause excessive solids to build up. This could result in solids washout which can pollute water courses or block soakaway systems. Both primary and final settlement chambers must be emptied in this order to avoid excess transfer of solids through the aeration chamber. It is important not to desludge the aeration chamber which contains the active bacteria attached to the media. Once desludging is complete the plant should be refilled immediately with water (waste or clean) to re-balance internal and external pressures on the plant. The quality of effluent produced would depend on what enters the plant. Soakaways, drains and the emptying of primary tanks remain the responsibility of the sewage treatment plant owner.

It is the installer’s responsibility to check the plant internally for damage. It is also the installer’s responsibility for the electrical supply, safety, connection, suitability and testing non-interference with other electrical systems as well as the ducting, hoses, venting and sealing.

Most sewage treatment plants are not designed to have any non-biological waste going into or out of the plant.

Some dont’s to keep in mind


Maintenance Activities to be carried out

  • Check the operation of the blower
  • Check the operation of the diffusers for any bubbles
  • Check the inlet and outlet stilling zones are clear of debris and remove any obstructions.
  • Check the blower ventilation is un-obstructed
  • Check the biomass growth on the filter media. The biomass should be a light brown colour, not white or grey. The odour in the plant should be ‘earthy’. There should not be a noticeable ‘rotten eggs’ smell.
  • Check the final effluent. If this is cloudy or contains many suspended particles, then the final settlement tank is likely to require desludging.
  • The air blower filter must be checked/cleaned/replaced (if necessary) every 3 months, particularly on sites which are prone to dusty conditions.
  • The diaphragms should be changed every 18 months.
  • It is recommended that the valve boxes be replaced every three years to maintain optimum performance.
  • A full service on the sewage treatment plant should be performed once every 24 months.

The full service should ensure that the following aspects of the system are functioning correctly:

  • Checking all chambers for damage
  • Checking the full air system including the air blower and diffusers
  • Checking lid seals and air blower chamber
  • Checking ventilation system
  • Checking electrical connections at the plant.

Harlequin Sewage Treatment Solutions

At Harlequin, we manufacture two type of Sewage Treatment Plants to meet all our customer’s needs, along with a septic tank range. We work very closely with a number of installers. This allows us to recommend only the best and most reliable installer to our customers.

To find out more about our products or guidance on maintaining one of our sewage treatment plants products, contact our team on 028 9261 1077 or email


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