Fem avloppsreningsverk med MBR-process och strikta utsläppskrav

This report is only available in Swedish. English summary is available in the report.

Summary

Several wastewater treatment plants (WWTPs) in Sweden will in the near future be given stricter effluent regulations concerning phosphorus, nitro-gen and BOD. Many of these are also expecting an increased load due to a growing population. Implementation of membrane technology (MBR) is a possibility for these plants to both increase their treatment capacity as well as ensuring to comply with the future stricter regulations. Membrane tech-nology is also very space efficient and the capacity of a plant can therefore often be increased without the need of more land.

Since there are no municipal WWTPs with membrane technology in operation in Sweden, it is important to learn from other plants in other countries. With this as a background, the authors of this report visited five MBR WWTPs in the USA, in March 2018. All visited plants where selected to be as similar as possible to Swedish WWTPs concerning cli-mate, effluent regulations and recipient.

The MBR process is generally working well for all visited plants. The operation is stable and they are complying with their effluent regulations. However, there are some common general challenges that several of the visited plants are experiencing. It is difficult to find coating of the mem-brane tanks that is light enough to be lifted but at the same time stable enough to walk on. Corrosion has been noted on equipment handling hypo chlorite, but not if the equipment is made of plastic material. Since the hypo chlorite is degrading with time storage should not exceed one month usage. All visited plants have had problems with foaming in the biological treatment step, but this has been reduced by installing sprinklers containing water or a chlorine solution. For some plants, the power of the crane used to lift membranes had to be increased, since fouled membranes weighed more than initially expected.

The membranes are continously cleaned using hypo chlorite and citric acid, based on a specific cleaning schedule. After some time, the plants ahve adusted the cleaning schedule to their specific needs, and they are all satisfied with the cleaning effect on the membrane capacity. The two plants continously monitoring effluent phosphate have both noted an increase in effluent phosphate concentrations in connection to membrane cleaning with citric acid. This effect has also been noted at the MBR pilot scale treatment line at Hammarby Sjöstadsverk in Stockholm, Sweden (operated by IVL Swedish Environmental Research Institute and Stock-holm Vatten och Avfall).

The main focus at the visited plants is to comply with the effluent require-ments and not much focus is being out on resource and energy effieciency, such as chemical used for phosphorus and nitrogen removal and energy used for aeration in the biological treatment step and in the membrane tanks.

Coworkers: Klara Westling

Year: 2019.0

Report number: C377

Authors: Klara Westling, Sofia Andersson

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