Treating wastewater with nature-based solutions in Modena
The GrowGreen team in Modena is working on designs for nature-based treatment of canal waters from the urbanised eastern area of the city. The proposed nature-based solutions are being used for the first time by the City of Modena and the public-private partnership that manages water for the city.
The project aims to reduce flood peaks and treat wastewater in the canal itself. It also aims to improve the environment by re-naturalising a part of the countryside around the canal and improving the quality of water entering the river network from the canal. Currently, sewage from Modena East is discharged into the canal during heavy rainfall. The water then enters the rivers, contributing to an overall decline in water quality.
The nature-based solutions designs are based on the chemical, physical and biological processes that occur in nature to purify water. The two types of nature-based solution used are a grassed canal and a dry swale.
The grassed canal solution means that the canal’s banks are planted with erosion-resistant plants chosen according to the specific local conditions. The vegetation will help to take up water from the canal, oxygenate the water through root systems and absorb some pollutants. To ensure that water stays in the canal long enough for these processes to take place, the flow will be controlled by a sluice gate. The slower flow will also encourage solids to be deposited on the channel floor.
The dry swale will be used to temporarily store mixed rainwater and wastewater during rainfall. The water will be treated by ‘bio-retention’ processes. It will be filtered through artificial soil containing the plants, bacteria and animals that help to remove pollutants.
The canal before and during works to create the dry swale
The solutions will be carefully monitored. Water samples will be taken from the canal both up and downstream of the nature-based solutions. The samples will be tested for various pollutants, allowing the solutions’ effectiveness to be assessed. The effectiveness will also be compared over time, to ensure that the solutions are stable in the long term.