Construction of a Powdered Activated Carbon (PAC) Plant for the Elimination of Trace Substances

Cause

Herforder Abwasser GmbH operates a wastewater treatment plant with a capacity of 250,000 PE at the Goebenstraße site in Herford. The sewage treatment plant was built in 1994 according to the principle of biological filtration (Biostyr®). As part of the WFD assessment, new requirements were imposed relating to the construction of a plant for the elimination of micropollutants. After carrying out and evaluating pilot tests, it was decided to install a Powdered Activated Carbon plant (PAC plant) as a fourth purification stage for trace elimination.

Process

The new plant essentially consists of the following components: Mixing and equalization tank with inlet pumping station; PAH contact tank, Actiflo® tank in compact design; PAH dosing system; polymer and iron III dosing system; filtration and drainage system.

After the inlet pumping station, the wastewater flow is routed via a three-line MID control section and then conveyed into the PAC contact tanks. It is then fed into the pre-coagulation tank of the Actiflo® compact system. The chemical dosing of the precipitant from the iron III dosing system also takes place in this feed line. In the subsequent coagulation tank, colloids are destabilized and microflocs are formed using agitators.

In the downstream flocculation tank, both the dosing of the polymer flocculant and the addition or recirculation of the microsand take place. After this two-stage flocculation process, the water enters the lamella settling tank with a rake system. The treated water then flows through the lamellas and leaves the Actiflo® compact system via the clear water discharge channels.

To improve the effluent quality, a secondary filtration system is installed, which is designed as a disk filter and forms a common functional unit with the Actiflo®.