What goes on at a wastewater treatment plant?

A modern wastewater treatment plant is like a fine-tuned production line. Wastewaters go through a multi-stage cleaning process, each stage of which is closely monitored and precisely managed.

At all Finnish treatment plants, the processing of wastewaters collected by the sewage network includes the same three stages: mechanical, biological and chemical treatment.

The first step is separating sand and large pieces of solid materials, such as paper, from the wastewater. Next, the water is aerated and conveyed to a biological process, the most common one of which is the activated sludge method based on microbial action: a growing mass of microbes binds organic substances and is later removed.

The cleaning performance is improved by adding ferrous sulphate or some other suitable chemical to the process to precipitate phosphorus. Some treatment plants additionally use intensified nitrogen removal. The final step is clarification. The sludge produced at the wastewater treatment plant can be processed further, making it suitable for soil quality improvement or landscape gardening. It can also be used for biogas production.

While the treatment process is highly efficient and removes more than 95% of many pollutants, it is still being developed further. The next challenges to be tackled are viruses and drug residues in wastewaters and microplastics contained in the sludge.

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