Aplicacion De Sw Flujo En Lodos

Technical Publication

Liquid Level/Interface Monitoring in Flocculant/Sludge Control
By Steven Craig, Sr. Member Technical Staff Fluid Components International (FCI)

Visit FCI on the Worldwide Web g www.fluidcomponents.com Headquarters g 1755 La Costa Meadows Drive San Marcos, California 92078 USA Phone 760-744-6950 g Toll Free 800-854-1993 g Fax 760-736-6250 European Office gPersephonestraat 3-01 5047 TT Tilburg, The Netherlands Phone 31-13-5159989 g Fax 31-13-5799036 FCI is ISO 9001:2000 and AS9100 certified

Liquid Level / Interface Monitoring in Flocculant / Sludge Control
By Steven Craig, Sr. Member Technical Staff Fluid Components International (FCI)

Flocculants are used in both the treatment of municipal sewage and industrial wastewater. There are many differenttypes of flocculant chemicals and wastewater treatment systems. Flocculants cause the suspended solids in wastewater to float to the top or sink to the bottom where they can be removed. They also can be used in stormwater treatment systems and in drinking water filtration. In industrial applications, they efficiently remove oil, heavy metals, ink and other contaminants from water (Figure 1).

TheProblem
Precisely measuring and controlling the mixture of wastewater effluent, flocculants and sludge is essential to efficient water treatment. The level/interface instruments that support the process liquid measurements must be capable of distinguishing between liquids with varying properties in order to detect the levels where the different liquids interface in the pond or tank. With thisknowledge, the amount of air, effluent and flocculants is controlled to provide the optimum mix for treatment. Such wastewater treatment systems operate under variable conditions that change with system and plant demand. In addition, seasonal temperatures rise and fall along with humidity levels that affect bacterial growth and the quantity of air and effluent required for proper operation. Theinstruments in the process loop also must have a rugged design in order to survive in dirty harsh operation conditions where methane and hydrogen sulfide are likely to be present. A number of different liquid sensing technologies have been tried as level/interface sensors in wastewater treatment applications. Optical detectors, for example, have not been particularly successful because the sensors faildue to fouling in this dirty operating environment. When selecting a sensing a technology for liquid level/interface it is important to not only consider the process media and desired performance criteria, but the plant environment is important too.

I

n municipal and industrial wastewater treatment plants, sludge clarifiers are utilized to separate solids from the water treatment effluentsystem by introducing air and flocculants. This process results in the sludge rising to the top of the pond or tank and spilling over a weir into a separate collection area. The amount of air and flocculants are controlled by measuring the liquid level interface between the sludge and water.

The Solution
There are multiple technologies that can detect level/interface in liquids and foams. Each ofthem have their advantages and disadvantages. Thermal dispersion sensing is one example of a technology that works well in liquid level/interface switching applications. Thermal dispersion technology places two thermowell protected platinum RTD temperature sensors in the process

Fluid Components International LLC

g

www.fluidcomponents.com

g

Page 2

Liquid Level / InterfaceMonitoring in Flocculant / Sludge Control
By Steven Craig, Sr. Member Technical Staff Fluid Components International (FCI)

Figure 2. Thermal Mass Flow Sensing Theory of Operation

stream. One RTD is heated while the other senses the actual process temperature. The temperature difference between these two sensors is measured and is directly proportional to the flow rate of the liquid (Figure 2)....