How to choose a wastewater treatment plant: flow rate and components

A wastewater treatment plant is chosen by starting from the quantity and type of water to be treated: domestic wastewater, wastewater from a business, oils to be separated. Then you decide whether you need a complete plant, such as a monoblock treatment plant or an activated sludge plant, or whether a tank with separate components is enough: blower, diffusers, control panel, manholes, covers and extensions. The polyethylene plants in the collection have diameters of up to about 2,100 mm and 230 or 400 V power supplies.

The types

• Activated sludge plant: treats the water with air and bacteria; for example the Rototec low-load activated sludge plant.
• Monoblock treatment plant: a single tank in which several stages of treatment take place, so there are fewer elements to connect.
• Biological tank: the tank in which the biological treatment or the settling of the sludge takes place.
• Trickling filter: a filter in which the water flows over a support medium. To feed it there is the lifting station for aerobic trickling filter.
• Oil separator: separates oils from the water, for workshops, car washes and car parks.
• Lifting station: pumps the water to the plant when it cannot be brought there by gravity.
• Blowers and diffusers: supply air to the tank. One example is the Rototec side channel blower; the diffuser disc distributes the air at the bottom.
• Control panels, timers: control blowers and pumps.
• Manholes, extensions and covers: for inspection, distribution and access. There are also anti-flooding and metering manholes.

How to choose by job

The features to look at

Material. The tanks are in polyethylene (PE, LLDPE), often corrugated, light, corrosion-resistant and suitable for burying. Other components, such as covers or fittings, are in polypropylene (PP), PVC or rubber.

Diameter and height. In the collection the diameters run from about 500 to 2,100 mm, and the heights up to 2,200 mm. The larger the tank, the more water it treats and the more space and handling equipment are needed.

Voltage. Blowers, pumps and panels run at 230 V or 400 V. Check that the available power supply is compatible.

Standard. Some products carry the standard UNI EN 12566 (parts 1 and 3), which concerns small wastewater treatment systems. It is a useful reference when you have to submit the permit application.

Model and compatibility. Blowers and diffusers have codes (such as HP302SF, HP402SF, HP502SF) linked to the power and the air volume. The component must suit the tank you have, not just the size.

Common mistakes

• Undersizing. A plant that is too small does not treat the water properly and clogs. Count the people or the real load, not just the minimum.
• Installing without a levelled bed. The buried tank goes on a flat base and must be backfilled while being filled with water, otherwise it deforms.
• Forgetting access. Without accessible manholes and covers, maintenance turns into an excavation.
• Choosing a component on price alone. A blower or diffuser that does not suit the tank uses more energy or does not oxygenate.
• Not having the sludge removed. The plant stops working properly if the sludge is not removed regularly.

Frequently asked questions

Do I need a discharge permit?

As a rule, yes: the discharge must be authorised by the competent authority, usually the municipality. Check before choosing the plant.

What is the difference between a septic tank and a treatment plant?

The septic tank does a first treatment, by settling. The treatment plant, with air and subsequent stages, takes the treatment further.

Who connects the blower and the panel?

An electrician, who connects them and protects them from water.

How often should the sludge be removed?

It depends on the plant and the load: follow the indications on the product page and carry out periodic checks through the inspection covers.

You will find tanks, plants and components in the Water Purification collection: the AMES technicians will help you choose the plant and spare parts and prepare a tailored quote.