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Surprising, isn’t it? You may be seeing this water filtering system for the first time. As the first filtering stage was carried out in the six chambers located on this floor. Each and every one of them sheltered a three meter high layer of coke, an industrial material extracted from grey porous charcoal. Side rooms used to store around 90 tons of coke while intermediate rooms had a capacity of 70 tons.

What does charcoal have to do with water treatment, one might ask? Take a look on top of the coke layer! There is a steel pipeline network. Water was pulverized through the pipe vents. When fine drops entered into contact with air, iron compounds from water is oxidized. Iron oxides, insoluble in water, were then retained on the coke filtering layer. The rusty color of the coke from these spaces is the living proof of iron compound filtering system. The rust from the walls comes from the water drops that never reached the filter.  Plus, gases dissolved are also released as a result of aerial application, which gives a strange smell to raw water -  hydrogen sulphide and ammonia.

Inside the rooms, you can still see today the venting installation, where jets of water used to spring out, being scattered shaping an open umbrella. It is also worth noticing the venting system with natural circulation – the spiral openings in side walls and the “funnels” in the roof framing which maintained the oxidation process. 

And then what ? What happened with the iron free water after sitting in the coke layer? Well, in every room, under the coke layer, there were perforated steel floorings, where filtered water could drain. Today, the first side room is empty, so you can see the perforated floorings.

Whenever the filtering layer was full of oxides, the coke had to be cleaned. Every 3 years, coke was removed via the openings visible on the south front of the building, through the steel doors, using conveyors, in order to be washed. It took around 3 months to clean the coke from one room only, through hard human labor. Coke was being replaced only under special circumstances.

A glass desk was installed in the last chamber, where you see a layer of washed coke.

After aeration and iron removal stages, water went to the next filtering stage, that is for manganese removal using Bollmann filters. Please, follow the stream down!