Several university and college pilot projects are determining the metal contamination of rainwater running off copper and zinc roofs. The contaminated rainwater from these roofs reaches the sewage treatment plant in an untreated condition, thus making the sewage sludge unusable due to heavy metal contamination. The resulting sewage sludge is generally disposed of.
Significance of Measuring Metal Contamination in Rainwater
Researchers were seeking simple solutions for heave metal removal from the contaminated rainwater prior to sending into infiltration pits. Although copper and zinc are vital trace elements for many animals and plants, they can be hazardous to aquatic organisms when present at slightly increased concentrations. In order to facilitate approval processes for the infiltration of metal contaminated water, heavy metals have to be removed from the water.
It is necessary to install several filters in underground precast concrete manholes for cleaning the rainwater running off the metallic roofs before the actual infiltration, allowing concentrated collection and easy disposal of the materials that are harmful to the water.
Flowmeters can be used to measure the minimally conductive water coming off the metallic roofs for accurate measurement of the metal concentration in the rainwater. It is also necessary to place the sampling equipment prior to and subsequent to the filters for accurate measurement of heavy metal and solid contamination.
KROHNE’s Simple Solution
After reaching the rainwater outlet pipe, the contaminated rainwater is allowed to pass through KROHNE electromagnetic flowmeters (EMF) to reach the filter hoppers at a rate of roughly 25L/s. The size of the filter hoppers vary with the rainwater quantity. The filtered water is then passed through the porous concrete-made partially transmitting infiltration pipes of DN300 and DN400 sizes.
For this purpose, KROHNE provides the OPTIFLUX 7300 C of DN40 and DN80 sizes to address the overflowing issue of the EMFs in the respective protection category (Figures 1 and 2). The average flow velocity is roughly 1–2m/s, but the DN40 and DN80 sizes can handle the optimum flow velocity of 7m/s. The current output yields the flow signal with 4– 20mA.
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Figure 1. The OPTIFLUX 7300 C
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Figure 2. Installed OPTIFLUX 7300 C
Key Features of OPTIFLUX 7300 C
The key features of the OPTIFLUX 7300 C are listed below:
- Optimized flow profile with reduced pressure loss due to the special shape of the measuring tube
- Capacitive electrodes allow non-contact measurement
- Unobstructed flow cross-section, measurement even with high solid content
- Long-term stability
- Unprecedented measurement accuracy
- Electrical conductivity of = 0.05µS/cm
- Broad size range from DN25 to DN100
- Compact design not only facilitates installation, but allows for safe and reliable operation
- Inherently stable, abrasion-proof, vacuum-proof advanced ceramic measuring tube
- Highly smooth ceramic surface with roughness of Ra < 0.8µm
- Food-safe operation as it eliminates dead space or gaps in measuring tube
The OPTIFLUX 7300
The OPTIFLUX 7300 is an EMF featuring a ceramic liner, non-wetted capacitive electrodes and the IFC 300 converter (Figure 3). The electrodes are large-area capacitor plates installed behind the ceramic liner. Non-contacting capacitive signal pick-up is another advantage of the OPTIFLUX 7300, eliminating unnecessary catalytic action with metallic components. In addition, the insulation of electrodes ensures safety.
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Figure 3. The OPTIFLUX 7300 consisting of stainless steel sensor housing (1), ceramic liner (2) and capacitor plates for signal pick up behind the liner (3).
The OPTIFLUX 7300 is designed to avoid leakage along the electrodes and through the ceramic liner. The IFC 300 converter allows stable flow measurements. The OPTIFLUX 7300 has found use in:
- Noisy applications
- Mediums that have the tendency to create an insulting film
- Low conductivities
- Applications with high vibrations
- Toxic, abrasive and oxidizing mediums
The ceramic tube in the OPTIFLUX 7300 is smooth, non-porous, and CIP / SIP resistant, making the flowmeter ideal for applications demanding hygienic conditions. It is inherently strong, non-permeable and exhibits resistance to extreme and broad range of chemicals, making it suitable for applications in the chemical industry.
Measuring Principle
The flow of an electrically conductive fluid via an electrically insulated pipe under a magnetic field generates a voltage ‘U’ (Figure 4) within the fluid as expressed below:
U = v * k * B * D
Where, v = mean flow velocity; k = factor correcting for geometry; B = magnetic field strength; and D = inner diameter of flow meter.
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Figure 4. Measuring principle of the OPTIFLUX 7300
Here, a current passing through a pair of field coils generates the magnetic field. The electrodes pick the signal voltage ‘U’ up, which varies proportionally with the mean flow velocity ‘v’ and so the flow rate ‘q.’ The signal voltage is amplified, filtered and converted into signals for totalizing, recording and output processing.
Conclusion
Filtering and subsequent disposal of contaminated rainwater coming off metallic roofs can be done easily with KROHNE's measurement and control technology. Storage and disposal of heavy metals become easier with the concentrated collection of these contaminants in the filter systems. Moreover, the disposable of the cleaned rainwater in the infiltration systems is environmentally friendly, thus considerably saving associated costs.
About KROHNE Messtechnik
KROHNE is a world-leading manufacturer and supplier of solutions in industrial process instrumentation.
KROHNE offers supporting products and services for one-stop-shopping and in industries as widespread as oil & gas, water & wastewater, chemical & petrochemical, food & beverage, power, minerals & mining and marine.
This information has been sourced, reviewed and adapted from materials provided by KROHNE Messtechnik GmbH.
For more information on this source, please visit KROHNE Messtechnik GmbH.