The wastewater treatment plant in Leksand, Sweden was built in the 1960s and has since been renewed many times. A major rebuilding took place during 1979-80, including the incorporation of a biological step. Recently, another upgrade was necessary due to a higher capacity demand partly caused by the added treatment of the wastewater from the nearby city of Insjön. The planning began in 2015, identifying the location and designing new pools and biological steps. The project continued until early 2019, when the new facilities started operations.
H2S is an air pollutant well-known in the sewage treatment industry. It is emitted from the wastewater, diffusing in the surrounding air. Disturbing odor problems are often related to H2S emissions, due to the high sensitivity of the human nose for this compound. Since new facilities were going to be built, increasing the wastewater load, a system for treating H2S was mandatory. This case was particularly complex because various streams needed to be treated, with a diffused H2S emission.
A complex problem required an advanced solution, treating all streams with a combination of catalysis and ozonation. Most of the H2S was removed with two units of the Nodora Cat, the catalytic version of our widely used Nodora air treatment system. The main difference between the two versions is the material composing the filter. Our Rubicat™ catalyst was used in this version of the Nodora Cat. It is designed to selectively remove H2S from polluted air streams, even at high concentrations. Ozone was used as final polishing step, ensuring zero odor emissions. The ozonation step included three Ozonetech RENA Pro ozone systems. These units are the most powerful ozone systems in our portfolio, producing highly concentrated ozone. The oxidant is injected into the ventilation ducts just after the catalytic stage, using the ventilation system as reaction chamber.
An optimal configuration was obtained by splitting the ozone flow and injecting it into different process streams, according to the various requirements. This configuration resulted in a very accurate usage of the produced ozone, optimizing the energy consumption and operational costs.
Our combined Nodora Cat and Ozonetech RENA Pro system proved to be very effective at removing H2S and all related issues. No H2S was detected after the Nodora Cat stage with the ozonation stage abating the remaining odorants and ensuring no H2S or odor emissions, even in case of high peaks. Measuring the pollutant concentration at the outlet of the system, the H2S removal was 100%, confirming the effectiveness of the tailored solution.