Wastewater treatment outside agglomerations – passive systems

Oczyszczanie ścieków

Few of us realize that treating wastewater outside of agglomerations, mainly in rural areas with distinctive, dispersed development, presents significant challenges. It is estimated that more than 300 millioncubic meters of wastewater from there enters the environment annually without treatment. Hence, ways and methods are still being sought that can ensure their effective purification. One solution is passive systems that in some way mimic the processes naturally occurring in marshes and bogs. It is an ecological and low-cost alternative to conventional wastewater treatment plants.

Wastewater treatment – rural challenges

Released in partnership with Idea 3W and the Bank Gospodarstwa Krajowego, the report “The State of Technology of Sink Stations in Poland” indicates that the homes of 10.5 million Poles are not connected to a combined sewer system. This is mainly a problem for residents of rural areas. In the Lodz and Lublin provinces, for example, this applies to 75% of people living outside agglomerations.

At the same time, CSO data cited by the authors of the aforementioned report indicate that only 7% of wastewater from unsanctioned areas reaches treatment plants. This means that more than 300 million m³ of wastewater per year ends up untreated in the environment. To illustrate the scale of the problem: this is half the volume of Poland’s largest lake – Sniardwy. This invisible polluter has been leaking into groundwater for many years, poisoning the intakes from which we draw our drinking water. A recent amendment to the Water Law aims to tighten the system. Municipalities have been given a tool to effectively discipline residents and fight against waste disposal companies that dispose of waste illegally.

This means that in the not-too-distant future a huge amount of wastewater, which has been outside the system until now, will find its way to treatment plants in small towns. These facilities are not prepared for this. Some of them are outdated, but even the newer ones can’t handle several times the amount of wastewater. Trouble is already brewing today, with the amount of water going to the treatment plant rising sharply due to heavy rainfall. Extensive modernization and construction of new facilities will be required. That’s why it’s a good idea to get an idea of the available treatment technologies in advance, and learn about their strengths and weaknesses.

Passive constructed wetland wastewater treatment systems

Hydrophytic treatment plants are a popular solution in rural areas in countries such as Germany, the Czech Republic, Denmark, France and Italy. Specific guidelines for the construction of such facilities were created there. They serve towns and communities with populations ranging from tens to thousands. They are also gaining popularity in Poland.

Hydrophytic treatment plants mimic the hydraulic and habitat conditions typical of natural wetland ecosystems. A variety of microorganisms inhabiting the filter beds (stone, gravel, sand) and water-loving plants are responsible for the biological purification process. Microorganisms play a key role, degrading and assimilating carbon compounds, retaining phosphorus compounds and heavy metals, and being responsible for removing nitrogen compounds. It is a natural and ecological solution, where no chemicals are used.

Such passive facilities, compared to traditional treatment plants, are much cheaper to maintain. They use less energy and require less human labor. In them, for example, it is not necessary to precisely control the treatment conditions or properly aerate the wastewater. A properly commissioned passive system works effectively for years without much human intervention. Microorganisms adapt to changing conditions – the amount of matter to process or temperature. A good example is the facility in the Czech town of Velka Jasenice, which has been operating in our Central European climate for more than two decades. Importantly, they are friendly to local residents: they look natural and do not emit unpleasant odors.

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Sewage treatment plant in the village of Velka Jasenice

Hydrophytic wastewater treatment plant in the village of Białka in the municipality of Debowa Kloda (Lublin Province).

The village of Bialka is located on the picturesque Bialskie Lake. There are 200 people living here on a daily basis. On summer weekends, the number rises to as many as 2,500. A major challenge, therefore, was the management of wastewater. In addition, the village lies in Natura 2000 areas. In 2020. A hydrophytic wastewater treatment plant with a capacity of 180m3/day was put into operation. The facility was designed by scientists from the University of Life Sciences in Lublin. In addition to wastewater fed through the combined sewer system, it also accepts sewage that is hauled in by a septic tanker.

According to the municipality’s mayor, such large fluctuations in the number of residents throughout the year mean that a treatment plant other than a hydrophytic one would either not be able to handle wastewater during the peak tourist season, or the investment and operating costs would be unacceptable to the municipality.

Wastewater treatment
Hydrophytic wastewater treatment plant in Bialka (Debowa Kloda municipality)

In the future, the municipality plans to expand the treatment plant. This will only require the addition of new filters, without having to upgrade the entire plant.

Passive wastewater treatment system in Udrzynek, Brańszczyk municipality (Mazowieckie voivodeship).

A biological-mechanical wastewater treatment plant based on sequencing biological reactors (SRBs) was in operation in Udrzynek. During heavy rains, it often failed (due to significantly increased sewage inflow from the sewer system). Municipal authorities decided to renovate the existing facility and add a hydrophytic system. The biological-mechanical treatment plant accepts a constant volume of wastewater. The remainder goes to a hydrophytic treatment plant, which copes well with varying amounts of incoming waste. The new part was launched in June 2022. The passive nature of the facility allows it to maintain a low rate for its services, which in the municipality of Brasinchik is 5.5 zloty/m3.

The treatment plant was designed and built by RDLS, a spin off from the University of Warsaw, which is among the entities working with Idea 3W, which supports innovation in the areas of water, hydrogen and coal.

Wastewater treatment
Sewage treatment plant in Udrzynek – hydrophytic part
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Sewage treatment plant in Udrzynek – biological-mechanical part

Another local government in the Mazovian province that has decided to build a hydrophytic treatment plant is the municipality of Wyśmierzyce. The investment, which began this year, is 95% financed by the Bank Gospodarstwa Krajowego’s coordinated Strategic Investment Program under the Polish Order. The treatment plant, which will serve 600 p.e., will be built under a design-and-build formula by November 2024.

For more on passive constructed wetland wastewater treatment systems, visit the RDLS website.

Photo author: Lukasz Rodek

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