Highly advanced diaphragm valves employed against toxic substances

Upgrading the "Alte Schanze" seepage water treatment plant

The "Alte Schanze" landfill has been used as a rubbish dump for domestic waste and similar commercial waste since 1979. Its seepage water treatment plant was commissioned in 1997. PFT analyses that started in 2014 revealed that the limits for introduction to the waste water treatment plant Sande were clearly exceeded. Consequentially, another treatment stage had to be implemented in the form of an activated carbon filtration system, which is fitted with SISTO diaphragm valves and KSB pumps.

Abfallverwertungs- und Entsorgungsbetrieb Kreis Paderborn (recycling and waste disposal company of the district of Paderborn), A.V.E. for short

A.V.E. operates the "Alte Schanze" disposal centre for the just over 300,000 inhabitants and businesses of the 10 towns and municipalities of the Paderborn district. The landfill 8 km south of Paderborn spans an area of approximately 90 hectares. This area also comprises a modern recycling and disposal centre for domestic waste and similar commercial waste.

Special materials

Using an activated carbon filtration system only makes sense when the specified limits for chemical oxygen demand and filterable substances can already be undercut upstream of the activated carbon stage.

Waste water analyses have also shown a high chloride content. This is why all system components that will come into contact with the fluid handled had to be made from special plastics and special stainless steels, e.g. all pipes, valves and pumps as well as their lining. This also applies to the control valve lining.

New treatment technology

Commissioned by A.V.E., an analysis by Chemisches und Veterinäruntersuchungsamt Ostwestfalen-Lippe (chemical and veterinary examination authority) revealed an excessive concentration of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The results markedly exceeded the reference value for life-long consumption without health risks recommended by the TWK (Drinking Water Commission of the German Ministry of Health). Consequentially, another treatment stage had to be implemented.

Treatment by means of activated carbon adsorption in the additional treatment stage is state of the art in industry and seepage water treatment as well as in drinking water treatment systems. As the values of chemical oxygen demand and filterable substances were much too high for using an activated carbon filtration system, a method had to be found that would significantly lower these values within the clarification process in the existing lamella clarifier that will continue to be used.

A detailed look at this treatment technology may help to explain:

The new treatment procedure involves the waste water to be treated in a floatation unit, an ozone unit and six fixed-bed reactors (denitrification and nitrification stages), followed by the final clarification. The chemical oxygen demand values can be reduced in this way. The filterable substances values have to be lowered by installing additional fuzzy filters upstream of the activated carbon filtration system.

The water passes through the fuzzy filters and is then transported to the inlet tank of the activated carbon by means of gravity. The waste water collects in the inlet tank from where two redundant Etabloc feed pumps transport it to the connection point at the valve blocks. The valve blocks serve to establish a rolling series control system for the water to pass through the activated carbon adsorbers. The control system is fully automatic using PLC and electrically actuated SISTO diaphragm valves.

After the waste water has passed the four activated carbon adsorbers connected in series, it reaches the discharge storage tank. From the discharge storage tank, two redundant Etabloc discharge pumps transport the waste water to the flushing water tank or, if this tank is full, in the direction of the pumping station via the existing treatment plant discharge measuring unit (MID).

The system is designed in such a way that all activated carbon adsorbers can be by-passed. A connection line from the inlet line to the discharge tank is provided for this purpose, controlled by two electrically actuated diaphragm valves of the type SISTO-20.

For controlling the systems, diaphragm valves with ECTFE lining were selected as none of the movable parts of diaphragm valves will be surrounded by the fluid handled. This is particularly important for the control of activated carbon adsorbers as the high chloride content can lead to salts being deposited and frequently to activated carbon entering the valve blocks.

The time between the opening and closing of these diaphragm valves is relatively long. Deposits may form at system components that are situated in the waste water. The diaphragm valves, however, remain unaffected and reliably open and close as required.

Diaphragm valves that need to be opened and closed frequently are fitted with an electric actuator; diaphragm valves intended for maintenance work only are fitted with a handwheel.

What is special about diaphragm valves is that all mechanical parts are located outside the wetted area. The only valve parts in contact with the fluid handled are the inner surface of the valve body and the diaphragm itself. The moving parts are maintenance-free.

The diaphragm valves of the SISTO-20 type series with their unique sealing system, consisting of a spiral-supported, completely enclosed diaphragm, provide tight sealing to atmosphere and tight shut-off at operating pressures of up to 16 bar. 

Apart from diaphragm valves, a number of swing check valves of the type SISTO-RSK have also been installed in the system. The SISTO swing check valves are coated with corrosion-resistant ECTFE. SISTO-RSK valves offer an almost entirely free passage and their pre-loaded valve disc reliably prevents surge pressure.

Customer: 

Abfallverwertungs- und Entsorgungsbetrieb Kreis Paderborn (recycling and waste disposal company of the district of Paderborn), A.V.E. for short

Plant:

Landfill seepage water treatment

Project data:

Swing check valves:

- Discharge pumps: 2 x SISTO-RSKS PN 16 / DN 80

- Feed pumps: 2 x SISTO-RSKS PN 16 / DN 125

- Emergency by-pass pump: 1 x SISTO-RSKS PN 16 / DN 50

- Flushing water pump: 1 x SISTO-RSKS PN 16 / DN 200

Diaphragm valves:

- Emergency by-pass pump: 2 x SISTO-20 PN 16 / DN 50

- Discharge pumps: 4 x SISTO-20 PN 16 / DN 80

- Treatment plant discharge: 1 x SISTO-20 PN 16 / DN 80

- Activated carbon feed pump: 4 x SISTO-20 PN 16 / DN125

- Flushing water pump: 4 x SISTO-20 PN 16 / DN 200

- Flushing water connection line: 8 x SISTO-20 PN 16 / DN 125

- Treatment plant discharge: 2 x SISTO-20 PN 16 / DN 80

- Valve block: 40 x SISTO-20 PN 16 / DN 80

- Valve block: 2 x SISTO-20 PN 16 / DN 125

Redundant feed pumps:

- 6 x Etabloc made of 1.4408

Redundant discharge pumps:

- 2 x KWP F 065-050-0201 made of Noridur

Project year:

2019