Drinking water treatment in three steps

Step 1: ozonisation

Ozone treatment for purification of raw and waste waters is done in three vessels connected in parallel. The water passing through them is enriched with ozone which reacts with the water substances to be oxidised. Remaining traces of residual ozone will later be discharged completely during the process. Basically, the requirements for valves vary substantially with regards to startup, draining or separate operational air release in these ozone reactors. The valves must be designed for large flow rates, whereas they should be able to respond reliably to relatively small pressures.

TASK // Efficient bleeding and venting during startup and operation

Whilst large air quantities are rapidly released or supplied during startup and draining, only small quantities of air and residual ozone accumulate when the ozone reactors are in operation. The valves installed there must be designed correspondingly for both dimensions. If an exhaust venting capacity of 800 Nm³/h is required for filling and 600 Nm³/h for draining, only a minimal counterpressureis sufficient to close the valves.

SOLUTION // Startup bleeding and venting valve EB 3.51 and bleeding and venting valve for continuous operation EB 1.12

When being combined, the two ozone-resistant Mankenberg bleeding and venting valves EB 3.51 and EB 1.12 fulfill any requirement for an efficient ozonisation process. The startup bleeding valve EB 3.51 reacts reliably at a system pressure starting from just 0.05 bar. It closes safely with ozone-resistant elastomers and its large seat diameter allows for evacuation of large air quantities at low pressures. As continuous bleeding valve for the operating range from 0 to 2 bar, the EB 1.12 is ideally suited to discharge the residual ozone arising in the exhaust air. It reacts reliably to the operating pressure of 0.16 bar that is usually available as counter-pressure for closing the valve.

Step 2: rapid filtration

After the ozone treatment, the raw water to be purified goes through a rapid filtration process. This takes place in four filter chambers switched in parallel. In contrast to ozonisation, an extra startup bleeding is not required in this case. This task is performed by the separate exhaust air dampers that are also used to flush the vessels with air. Residual ozone may arise during all the processes of the rapid filtration step. It must continuously be supplied to the residual ozone destruction plant and it is mandatory that all valves be designed for this purpose.

TASK // Rapid bleeding and venting of the fast filtration step

With 2,800 Nm³/h required for draining and 10 Nm³/h for separate air release during operation, the volume range within the rapid filtration step is really large. To cover the requirements in this area, a combination of valves with specific characteristics is the best way to a convincing overall concept.

SOLUTION // Vacuum breaker VV 34, combined bleeding and venting valve EB 1.74 and bleeding and venting valve for continuous operation EB 1.12

During draining of the fast filtration line the vacuum breaker VV 34 DN 200 is recommended for rapid ventilation. In this system solution it does not assume any function for the startup and / or continuous bleeding and venting operation because this task is being fulfilled by the valve EB 1.74 DN 100. For operational air release in the pipelines the EB 1.12 G ¾ is installed. All Mankenberg components of this concept are ozone-resistant.

Step 3: activated charocal filtering

Filtration through activated charcoal is and continues to be the final process for drinking water treatment also in the most advanced fine filter water-works. Even the residues of medi­caments and hormones can be effectively removed from the water in this way. The process runs under excess pressure in four closed filter vessels switched in parallel. This last step on the way to clean drinking water is also subject to specific requirements with which the valves in the plant must comply in a practical way.

TASK // Complete bleeding and venting in a closed system

800 Nm³/h startup air release, 2.800 Nm³/h air intake during discharge and 10 Nm³/h operational air release: This range must be covered by a valve solution at solely 0.12 bar operating pressure. In the closed system of the activated charcoal filtration this can be achieved by a combination of two proven Mankenberg components.

SOLUTION // Combined bleeding and venting valve EB 1.74 and vacuum breaker VV 34

For bleeding in the startup and operation phase, one EB 1.74 DN 100 per each of the four activated charcoal vessels has been installed. The vacuum breaker VV 34 DN 200 ensures fast air intake during the discharge phase in this section. Just like for any other Mankenberg solution, different types of connections offer many possibilities for individual planning or adaptation to existing systems.

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