Odpowiemy w 24h
Od poniedziałku do piątku

How does a domestic sewage treatment plant work?

A domestic sewage treatment plant is a solution used where there is no possibility of connecting to the sewage system, and we are looking to avoid investing in inconvenient and expensive septic tanks.

There are several types of wastewater treatment plants available:

  • drainage treatment plants,
  • biological treatment plants,
  • plant treatment plants.

This division is a major simplification, because each type of sewage treatment plant has a biological treatment stage, but this nomenclature is the most common. All types are linked by the fact that the processes are divided into:

  • mechanical processes in anaerobic conditions,
  • biological processes in aerobic conditions.

Drainage treatment plants consist of a septic tank and a drainage system located in the ground. The septic tank is where the processes of mechanical treatment, retention of solid fractions, rotting and mineralization in anaerobic conditions and averaging the composition and temperature of wastewater take place. This is where mineral parts, which are not subject to cleaning and must be periodically removed by the gully emptier fleet (usually once a year), are stored.

Here, biological treatment takes place under drainage on a washed gravel bed of appropriate grammage. Oxygen for bacteria is supplied through the ventilation system - from low ventilation at the end of each line to high ventilation - deaeration of the sewer riser. This method also requires the cyclical addition of bacteria. The accepted length of drainage should not be less than 10 meters per 1 resident. Additionally, the solution requires well-drained soil and a low level of groundwater. The durability of the drainage system is limited due to the cyclical clogging of the space in the ground and around the gravel, and ranges from a few to several years.

Biological treatment plants combine mechanical (anaerobic) and biological (aerobic) treatment in one or more tanks. There is no treatment in the ground, as in the case of drainage treatment plants. Thanks to a high efficiency, the wastewater is so effectively treated that it is possible to discharge it, for example, into a river, after obtaining the appropriate permits.

As in the case of drainage treatment plants, the processes begin in the first chamber - the so-called primary sedimentation tank. Here, the lighter parts are retained on the surface - mostly fats, and the heavier mineral ones are left at the bottom. The composition and temperature of the waste water is averaged. In the case of RotoSET and EasySET sewage treatment plants, the sedimentation tank also plays a major role as a buffer that accepts temporary increased wastewater discharges. This way, the hydraulic flow through the system is stable and the cleaning efficiency is much higher.

The next stage consists in biological wastewater treatment under aerobic conditions. Depending on the adopted technology, aerobic bacteria may develop in a biological bed or appear in the form of activated sludge. RotoSET wastewater treatment plants work in the technology of rotating biological contactors, and EasySET operate by means of sprinkling biological beds. A major advantage is the enhanced process stability, no need to add bacteria, biopreparations and the addition of activated sludge - both at start-up and during operation. In terms of the basic parameters of BOD5, COD and suspended solids, the treated sewage corresponds to the second class of flowing water purity, thanks to which it is possible to discharge it directly into a watercourse or into the ground.

A major advantage of biological treatment plants is the ability to control the composition of the liquid flowing out of the devices into the environment. In recent years, there has been a noticeable focus on this type of sewage treatment plant in Poland and in a number of European Union countries.

In plant sewage treatment systems, or hydrophyte systems, mechanical (anaerobic) processes take place in a separate septic tank, while biological (aerobic) processes occur in a properly designed plot filled with gravel, crushed stone or rock rubble. Carefully selected plants that live in the plot integrate organic compounds into their mass through the root system, causing wastewater treatment. After passing through the plot, the liquid is fed to the collecting well, which allows it to be controlled.

Is there a “one and only” solution? Depending on the type of facility, plot area, investor’s requirements, soil and water conditions as well as the available budget, our specialists are able to propose an optimized solution specially for you.

The opinions about household sewage treatment plants vary

Domestic sewage treatment plants have been used for several dozen years. Depending on the region, soil and water conditions and, above all, the adopted solutions, they do not enjoy a good reputation everywhere. The available media contain both positive and negative reviews. The former predominate, but in order not to be 'clever after a harm', we recommend that you read the text below.

As is usually the case with the purchase, in the long run, what is cheap turns out to be fragile, problematic and more expensive. Certainly, this does not mean that spending more gives us a guarantee of quality and a sense of well-invested funds. When choosing a sewage treatment plant, we should take into account plenty aspects, the most important of which are:

  • Effectiveness of operation,
  • Convenience of use (necessary activities, smell, noise),
  • Technical conditions (required surface, recess of connections),
  • Purchase costs,
  • Operating costs,
  • Access to components.

A certain group of people may see the convenience of use, including odor-free and quiet operation, no need to add bacteria and minimized maintenance, as the most important, while others will appreciate a small installation area or low purchase costs. Before making your purchase, you should answer one important question: What is the most important to me?

Drainage sewage treatment plants are characterized by low purchase and operating costs, quiet operation, but unfortunately, they require a large plot area, well-drained soil and a low level of groundwater. When betting on this solution, first remember that the service life of the drainage system is limited and after a few to several years the system will become clogged, which is associated with extensive expenditure related to the installation of a new drain. With this solution, it is necessary to add bacteria that will support the operation of devices and accept temporary unpleasant odors when ventilating the drainage lines; especially with falling pressure.

Biological treatment plants require much less land for installation because both mechanical and biological treatment processes take place in the device. There are a number of biological treatment plant technologies available on the market:

  • Wastewater treatment plants with a rotating biological contactor RBC,
  • Sewage treatment plants with sprinkling biological beds,
  • Wastewater treatment plants with active sludge,
  • Sequential sewage treatment plants with SBR activated sludge,
  • Wastewater treatment plants with a moving submerged bed,
  • Wastewater treatment plants with a fixed submerged bed.

How to choose the right solution for yourself?

If you seek solutions characterized by convenience of use, odorlessness, high efficiency of operation with low operating costs, the rotating biological contactors technology may be the best solution for you. A major advantage is the high efficiency of operation with a simultaneous lack of mechanical aeration, and thus odor-free work. A low-power engine operating under the cover of the sewage treatment plant is characterized by low electricity demand and generates no noise. The foolproof design means that it contains no components such as blowers, solenoid valves, diffusers or mechanical or mammoth pumps, thanks to which this technology is rather ‘not cheap’.

A more budget-friendly, but also very interesting alternative are sewage treatment plants that work in the technology of sprinkling biological contactors. Their main advantage is the foolproof construction without mechanical components inside the tank. Compared to activated sludge or fluidized beds, there are no devices such as diffusers, solenoid valves, engine, but only a small blower. There are no additional bacteria, no active sludge, and the processes of creating a biological membrane are automatic and require no intervention from the user. All this has a remarkably positive effect on low operating costs in the short and long term.

When choosing a technology, please keep in mind local conditions and your individual expectations.