Starting lake Velnezers treatment with ALUM method

Starting lake Velnezers treatment with ALUM method

Join the first ALUM treatment demonstration in the Baltics, where lake Velnezers will be purified from historical phosphorus pollution using a special boat designed for the lake!

The ALUM treatment method has been successfully used in lakes in Sweden for more than 60 years. The method works by binding phosphorus compounds with aluminum salts, where the excess phosphorus deposits in the lake sediments in the form of insoluble compounds. The ALUM treatment method is safe and fast, and the improvement of water quality can be observed within a few days, as the transparency of the water increases.

During the last year, Latvian Institute of Aquatic Ecology in cooperation with partners from Sweden, has carried out careful monitoring of the state of the lake and developed a model to calculate the exact dosage of aluminum salts to be added. Currently, all the necessary preparations have been made so that the treatment of lake Velnezers is successful.

During the week from October 14-18 there will be an info tent near lake Velnezers (Riga, Malienas street 64), where you can get all your questions answered about cleaning the lake and meet the project team.

Moreover we invite you to join on October 16, when starting at 10.30 AM there will be treatment demonstrations and speeches from representatives of LHEI, Swedish company “Vattenresurs” and Riga municipality.

Why was lake Velnezers chosen for the treatment?

Fish in the lake are suffocating.

We carried out feasibility study of the lake and it confirms that the ecological condition of the lake is poor and this is proven by the lack of oxygen in the water. On February 22, 2024 local residents reported a mass fish die-off. During a lake test by LHEI scientists, it was found that the dissolved oxygen concentration was only 0.83 mg/l at the surface level. As the ice sheet formed, the amount of oxygen decreased rapidly. Fish died due to lack of oxygen. Mass fish mortality events in winter is typical in nutrient-rich (eutrophic) lakes – such as Velnezers, but the planned treatment with the ALUM method will improve thissituation. Read more here.

There are few fish in Velnezers, they are thin and starved

In Fall 2023 more than 80 local residents and media representatives gathered at lake Velnezers to observe the scientific fishing, the purpose of which was to assess and demonstrate the health of the fish population before the lake was treated. The results showed that the fish community of Velnezers could be more depleted than predicted. Six species of fish found in Latvia were caught in the lake. In total, a third of the fish stomachs were empty. Most of the fish caught were young and small in size.

Ubiquitous aluminum: is there cause for concern?

There is no reason to worry. Aluminum is all around us – in the soil and sediments, in food and its packaging, and even in drinking water (aluminum salts are used in the preparation of drinking water). In the Baltic countries, the method of ALUM treatment in lakes has not been used until now, because there is a fear of aluminum as a chemical element, there is a lack of the necessary knowledge and there is a belief that it is too expensive. Within the framework of the TRUST ALUM project, both the efficiency and safety of the method will be demonstrated by careful monitoring of the lake ecosystem (water quality, fish and macrophytes, etc.) before and after cleaning. Technical regulations for the implementation of the ALUM method in the practice of cleaning heavily polluted lakes in the Baltics have been prepared and a guide for responsible parties and experts has been created.

Answers to the most frequently asked questions about the ALUM method are available here.

About TRUST ALUM project

Lake overgrowth or eutrophication can be prevented by reducing the presence of biogenic elements, mainly phosphorus compounds, in the water. However, a series of recovery measures did not bring the desired result, because the lakes has already historically accumulated a large amount of phosphorus compounds. The availability of phosphorus in highly polluted and urban lakes can be limited by the ALUM method, which is based on the use of polyaluminum chloride (abbreviated as PAC in English) to precipitate phosphorus in the form of insoluble compounds in lake sediments and remove it from the circulation cycle.

The ALUM treatment method has a number of advantages – it is fast (water transparency increases within a few days), the method physically affects only lake sediments and deeper layers, and the long-term effectiveness of the method can be measured over several decades. On the other hand, the prerequisites for the successful application of the method are a seasonal feasibility study of the lake and creation of a model for calculating the correct dose of polyaluminum chloride, the introduction of external phosphorus must be prevented, and the lake must have a suitable buffer capacity (pH).

The activities take place within the framework of the TRUST ALUM project (Interreg Baltic Sea Region Program 2022-2027), in which nine organizations from Latvia, Estonia, Lithuania and Sweden cooperate in popularizing and implementing the ALUM water treatment method in the Baltic States. More about the project.

Additional resources:

Watch a recording of the informative seminar: https://e.pcloud.link/publink/show?code=kZQvo1ZtESqL70qNabj8FBqYTWYs8xqwquk

Watch the TV3 news story about research in lake Velnezers (in Latvian): https://www.tv3.lv/dzivesstils/dzivnieki/velnezera-zivis-cer-izglabt-ar-baltija-lidz-sim-nepielietotu-metodi/