Numerous substances of anthropic origin, such as pharmaceuticals and chemical products, are present in trace concentration in wastewater. Such micropollutants are only partially eliminated in conventional wastewater treatment plants, and are thus released to the environment. Once in the nature, these substances can cause adverse effects on the aquatic environment and deteriorate the quality of drinking water supplies.
In the framework of “stratégie Micropoll”, a programme implemented by the Swiss Federal Office for the Environment (FOEN), Membratec performed a series of pilot scale tests at the wastewater treatment plant of Vidy in Lausanne between 2009 and 2012. The process applied in Vidy consists in adsorbing micropollutants onto powder activated carbon (PAC) which is then separated from wastewater on ultrafiltration membranes (UF). The PAC is dosed in a contact bassin, filtered on membranes and finally reintroduced into the biology.
With the PAC-UF process, applying a dosage of 10 to 20 mg/L PAC, the removal of the majority of targeted micropollutants was above 80% and comparable to other tested processes, such as ozone. After recirculation in the biological treatment, PAC is finally eliminated with wastewater sludge and incinerated. This guaranties a complete elimination of micropollutants and no by-product formation.
Moreover, the filtered water is free of suspended solids and microorganisms, thanks to a membrane cut-off of 0.02 µ m. Latest results of the pilot-scale tests done at Vidy show that the PAC-UF process is energetically sustainable (≤ 0.1 kWh/m3) and that high (>65 L/hm2) and lasting filtration fluxes can be achieved with a limited chemical consumption.
The latest developments, in particular the increased filtration fluxes, open new perspectives for this process which has been proven to be competitive in terms of treatment quality and costs: Micropollutant treatment can now be coupled to the total elimination of the suspended solids and microorganisms.