Wastewater Treatment Plants Comparison Information

SUSPENDED GROWTH or BLOWN AIR Wastewater Treatment Plants

(NOT to be confused with the AirFlow from Klargester!)


Suspended growth or “blown air” wastewater treatment plants in France ( WWTP ) are the most common type of WWTP in France as they are generally the cheapest and easiest to manufacture. Unfortunately, this type of wastewater treatment plant is highly likely to either under-aerate releasing untreated sewage and contaminating the environment or over-aerate causing bacteria to not settle-out and contaminating the environment. This can be prevented by using diffusers and/or effluent filters which requires higher levels of maintenance to either clean, service or replace diffusers and/or effluent filters. Suspended growth systems are typically unable to reduce total Nitrogen to acceptable levels in order to better protect public health from the harmful effects of nitrates either – this is a very French problem. Disastrously inefficient and uncertified blown air wastewater treatment systems produced by “cottage industries” in France in a variety of CE marked containers and without any means of through-flow control – which have then been traditionally pressure sold at inflated margins, are one of the main reasons that France has dragged its feet introducing the new European wastewater treatment regulations. Any search for “fournisseurs de micro stations d’épuration France” (semi-hidden link to klar-environnement.com) will come up with any number of uncertified products that are best avoided, along with a handful of certified ones that you can compare – ask for a copy of their EN12566-3 certification, and if they don’t have one or seem reluctant then walk away! Klar Environnement welcomes fair competition as we are confident in the quality of Klargester products and our unbeatable price promise – but misleading potential clients with “claims” of “compliance” with EN12566-3 is unacceptable.


The suspended growths generally blow air into the wastewater using an air pump or blower. The air is injected into the wastewater in order to keep the solids, paper and food particles in suspension in the waste water during aerobic treatment. Going through a minimum of two stages or chambers, the systems rely completely on the mixing of the air with liquid, organic matter and solids in suspension to create the conditions for the bacteria to digest the sewage. One of the key functions of these types of wastewater treatment plants is to match the amount of air to the amount of both liquid and organic matter (nominal and biological loading) coming into the system.

Regardless of the method, it is the amount of air being delivered to the amount of wastewater and biological loading that is of importance. The vast majority of these wastewater treatment systems are set to supply a steady amount of air and they rarely adjust the amount of air being injected into the liquid and organic matter even when there are daily or seasonal changes (e.g. holidays) in either of the amount of liquid and/or organic matter. Therefore, it is generally accepted that suspended growth wastewater treatment systems using the principles of extended aeration through direct air injection suffer with the problem of over-aeration (too much air for the wastewater). This over-aeration causes the microorganisms to become too thin and light and therefore causes them not to settle out in the final clarification stage. This results in bursts of bacteria being released leading to progressive failure of the drain field over time and the pollution of water with bacteria. At times of higher biological and wastewater loadings, these domestic sewage treatment systems can become under-aerated which results in insufficient treatment and subsequent contamination of the environment.

Service / Maintenance

The suspended growth wastewater treatment plants typically recommend:

  • Four times per year changing of air pump filter
  • Twice a year checking of sludge levels, especially in holiday home usage
  • Annual checking and servicing of the fine bubble diffusers inside the tank
  • Annual checking and servicing of effluent filters inside the tank

Environmental Benefits

This type of wastewater treatment plants should be more ecologically friendly than a septic tank system, but this will depend on monitoring and maintenance and you could do better considering the use of energy for the results achieved.


Whilst these types of wastewater treatment plants may be cheap, (but not always), their long term reliability and ecological impact should be questioned. When comparing wastewater treatment plants be certain you are not paying a premium product price for a WWTP that can fail to deliver the best results for you and the environment. Be especially careful about any suspended growth or blown air wastewater treatment plants that are not presented complete with their EN 12566 – 3 CE certification to European regulations, as this is the category of waste treatment plants where you find the majority of untested WWTP ‘s. Why waste any money on an untested wastewater treatment plant? Click here to continue and read about Aeration and Filtration type wastewater treatment plants. or skip straight to the summary on wastewater treatment plants here (link to summary page)