MONITORING AND METERING
A sludge blanket level detector gives early warning of rising blankets and is greener too, says Michael Strahand, managing director, SludgeBlanket UK
Blanket benefits D
uring the wastewater treatment process it is necessary to identify and control levels of sludge in order to demonstrate compliance with legislation including consent to discharge. In order to confidently achieve compliance, wastewater treatment plants require reliable and effective sludge blanket level detectors. A sludge blanket level detector gives early warning of rising blankets and allows action to be taken to prevent environmentally damaging discharges. A further benefit of reliable level measurement is that good measurement provides confidence to rely on clarifier volume for temporary solids inventory storage, if needed. In all applications, continuous measurement with level trending provides more and better information to correlate with other process variables to improve process control.
Traditional detection techniques Sludge blankets can be detected using optical suspended solids monitors and both manual and fully automated systems are available. The portable devices are relatively low in cost and simple to use, as when a change in solids is detected an audible alarm is produced. Automated devices are more complex, as the sensor must be automatically lowered and raised into the tank and therefore control systems are needed to ensure that the sensor does not become entangled on any structures below the water. High and low sludge blanket alarms can be generated using fixed ultrasonic sensors. A transmitter and receiver are most commonly fitted in a ‘horseshoe’ arrangement. If sludge comes between the transmitter/receiver pair the ultrasonic signal is changed and an alarm is generated. These devices need regular cleaning to ensure reliable operation. Another ultrasonic technique is based on the detection of reflections of ultrasound from interfaces. In operation, ultrasound is transmitted vertically down into the tank. At interfaces ultrasound is reflected back to the receiver. Calculation of the transit times allows calculation of the distance to the interface. These devices measure the actual sludge interface .
New Advances SludgeBlanket UK supplies blanket detectors for all applications that provide faster and better digital processing. By locating the signal processing in the
Flow on show in U
S fluid sensing specialist Gems Sensors & Controls has introduced a RotorFlow Output (RFO) device
with a viewing window for flow rate monitoring or metering applications. RFO sensors provide a pulsed DC voltage output that is proportional to the rate of flow. Gems says that the 4.5 to 24VDC pulsed output is easily integrated into most digital logic units. However, users particularly like RotorFlow's highly visible paddlewheel that shows at a glance whether or not fluids are moving. Typical applications for the RFO sensors include water and treated wastewater. As liquid passes through the RotorFlow RFO body, a magnetic rotor spins at a rate proportional to flow. The magnetic fields turning with the
22 Water & Wastewater Treatment September 2010
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52