How To Choose The Right Type Of Sewage Treatment System

How To Choose The Right Type Of Sewage Treatment System

The good, the bad and the ugly of waster water treatment

questionWhether you have a fosse septic that’s failed it’s inspection, whether you renovate old buildings or whether you’re building new homes from scratch, at some point you will need to think about the waste water and how you’re going to deal with it.

But what is the ideal type of system for you?

Here we look at the options currently available, giving a brief explanation of how they work and the pros and cons of each type. With this guide you should be able to make the right decision about which type of system best meets your needs and best suits your property.

The Systems

There are three broad categories of system that are approved for use in France

  • Open Filter Systems
  • Compact Filter Systems
  • Microstations

They each have their advantages and their disadvantages and, how suitable they are depends on what you want from your system.

Open Filter Systems

There are two main types of open filter system, those that combine a fosse and filter bed and those that use a plant based filtration system either with or without a septic tank (fosse toutes eaux).

Fosse and Filter Bed Systems

How They Work

planThe conventional “fosse toutes eaux” with filter bed works by collecting all waste water in the fosse itself where it is separated and the lighter suspended solids are digested by aerobic bacteria and the heavier sludge waste digested by anaerobic bacteria. As this usually only results in a reduction of pollutants, some germs and pathogens still remain and these could pose a real threat of contamination or disease if released directly into waterways. As such the effluent then needs to pass through a filtration process where the remaining waste and toxic particles are removed before the resulting liquid is either allowed to soak away or be siphoned off.

Advantages

  • Proven to be effective in purifying waste water without requiring any electrical input
  • An environmentally sustainable method for the treatment of contaminated water
  • Environmentally friendly in that they do not need an electrical input to function
  • Cheap to run as no electrical input is required
  • Suitable for all property types including holiday homes and gites

Disadvantages

  • A sizeable amount of land is required for the filter bed, and this is land that can then not be used for other purposes such as parking or building.
  • The size of the system often means that costs of installation, the level of disruption and the time taken to complete the installation are higher when compared to other systems.
  • Open filter beds do not cope well in extreme climates, often freezing solid at low temperatures, dying off during high temperatures or flooding during extremes of rain. Any of these situations will prevent the system from working effectively
  • As the filtering material is not compact or enclosed, these systems are prone to flooding and clogging making them ineffective and potentially harmful to the environment.
  • Due to a tendency to clog, the filtering material needs to be replaced on a regular basis with the old media being disposed of in a controlled way
  • As these systems require gravity to disperse the waste water throughout the system they often require a pumping system to overcome land lie difficulties

Suitability

  • Suitable for all property types including second homes and gites
  • Suitable where a low carbon footprint is desired or where the environmental impact is of greatest importance
  • Not suitable for properties with little land area
  • Not suitable for areas with a high water table, where there is susceptibility to flooding or which are likely to suffer climatic extremes
  • Not suitable for problematic terrain

Plant Based Systems

How They Work

plantsThere are two main types of reed bed system, those that pass the water through a fosse first and those that release effluent directly on to the reed bed filtration system. The way in which the reed beds work is relatively simple. The reeds used are chosen because they have the ability to transfer oxygen from their leaves, down through their stems and out via the root system and this results in a very high level of micro-organisms at the root level. This not only encourages aerobic digestion but also anoxic digestion (bacterial action that occurs in water depleted of dissolved oxygen, a situation created by the use of the reeds) and anaerobic bacterial action. As the waste water moves through the mass of reed roots, the bacterial action breaks down the pollutants in the water and clarifies it.

Advantages

  • Proven to be effective in purifying waste water without requiring any electrical input
  • Environmentally friendly in that they do not need an electrical input to function
  • Cheap to run as no electrical input is required well proven
  • An environmentally sustainable method for the treatment of contaminated water
  • Beneficial for wildlife
  • Suitable for all property types including holiday homes and gites

Disadvantages

  • Unless the site has a decent gradient, it is not usually possible to avoid the need for electrical power when designing a reed bed system
  • A sizeable amount of land is required for the filter bed, and this is land that can then not be used for other purposes such as parking or building
  • The size of the system often means that costs of installation, the level of disruption and the time taken to complete the installation are higher when compared to other systems
  • Reed beds are not a long term solution and even when they are designed and maintained properly, they will only be viable for up to a maximum of 7 to 10 years. Refurbishment after this will include the removal and replacement of not only the reeds, but the entire gravel bed
  • Reed beds do not cope well in extreme climates, often freezing solid at low temperatures, dying off during high temperatures or flooding during extremes of rain. Any of these situations will prevent the system from working effectively
  • As the filtering material is not compact or enclosed, these systems are prone to flooding and clogging making them ineffective and potentially harmful to the environment.
  • Reed beds require a regular maintenance programme to ensure the effectiveness of the system. This maintenance invariably puts the person maintaining the system into contact with some potentially very nasty bacteria and viruses.
  • Mosquito and flies may be a problem during the summer months as they tend to breed in the reed beds, the beds also tend to attract rodents particularly in the winter and some snakes tend to be abundant in reed beds, making their nests, laying their eggs and hibernating in the dense bottom vegetation

Suitability

  • Suitable for all property types including second homes and gites
  • Suitable where a low carbon footprint is desired or where environmental impact is of greatest importance
  • Suitable where providing a habitat for wildlife is important
  • Not suitable for properties with little land area
  • Not suitable for areas with a high water table, where there is susceptibility to flooding or which are likely to suffer climatic extremes
  • Not suitable for problematic terrain

Compact Filter Systems

How They Work

compactAn advancement in filter systems that negates many of the problems associated with open filter systems is the development of compact filters systems which contain the filtering media in an enclosed unit. These systems work on a similar principal to the traditional fosse and filter bed system as they are still 2 part systems comprising a “fosse toutes eaux” and a self contained filtering system but they use the latest technologies to reduce the space required and to limit the chances of flooding by enclosing the filtering media.

Advantages

  • The filtering materials tend to also have a longer life and are more dense with greater absorbing surface which means they take up less land than the traditional systems.
  • Environmentally friendly in that they do not need an electrical input to function
  • Cheap to run as no electrical input is required well proven
  • An environmentally sustainable method for the treatment of contaminated water
  • Suitable for all property types including holiday homes and gites
  • Eligible for “l’éco-prêt à taux 0%” (interest free loan)

Disadvantages

  • As these systems work on the downward movement of water they usually require a pump to either discharge the water or overcome land-lie difficulties.
  • In the majority of systems, the filtering media needs to be replaced on a regular basis with the old media needing to be disposed of in a controlled manner
  • Although they take up less room than open filter systems, they tend to be larger than some microstations as they require both the fosse and the filtering units
  • These systems tend to be more expensive than microstations to purchase

Suitability

  • Suitable for all property types including second homes and gites
  • Suitable where a low carbon footprint is desired
  • Not suitable for problematic terrain

Microstations

How They Work

microMicrostations remove the need for any kind of filtering process as they work by passing the waste water through a series of chambers where the waste is broken down by bacterial action which is accelerated due to a forced movement of air controlled by a compressor. These systems are made up of numerous chambers, basically a settlement chamber for waste separation and bacterial pre-treatment, an aeration chamber where the remaining liquid effluent undergoes enhanced biologically treatment and a clarification chamber which removes any remaining fine solids before the effluent can be discharged.

Advantages

  • As these systems are more compact they are easy to transport and easier and quicker to install often making the purchase and installation costs cheaper when compared to other systems
  • Easy to maintain as they have no working parts and no media to be replaced

Disadvantages

  • As they run off electricity they are susceptible to power cuts and should therefore be fitted with an alarm warning system.
  • The reliance on electrical input means that these systems are unlikely to be approved for holiday or secondary homes or properties where habitation is intermittent.

Suitability

  • Suitable for properties with minimal land space
  • Suitable where installation and long term maintenance costs are a consideration
  • Suitable where the level of disruption to existing gardens is a concern
  • Not suitable for second homes and gites
  • Not suitable where power supply failures are common
  • Some systems may be less suitable for areas of bedrock

Conclusion

There are three main types of system all of which work in different ways and all of which have both advantages and disadvantages and all of which have different suitability factors. Which is the best system for you depends on how you will use that system, be it intermittently or all year round, on the type and size of land available and on your views regarding carbon footprint. Once you know the type of system you want, you can start looking at which individual system within that type will best suit your requirements and the constraints of your property.

And that, is the very topic of our article next month. Entitled “How To Choose Your Ideal System” it will take you through the 10 things you need to consider before parting with any money.