Sensing transmitter devices for measuring leachate level and converting it to a 4-20mA current output signal to send to other instrumentation on a landfill site used to bury waste material.
Due to the decomposition of buried waste material over time, a landfill site presents a potential hazard to the environment unless precautions are taken to contain pollutants and prevent contamination.
Decomposing waste will produce a mixture of flammable and greenhouse house gases that can escape into the local atmosphere. In a landfill site extraction wells are used to collect the landfill gas (LFG) from surround waste at multiple locations around the site. This LFG is then treated and typically used to fuel power generators to provide electricity.
A wide range of harmful liquids are released from waste material as part of the decomposition process, which then mix with rainwater which percolates through the waste. The resulting liquid poses a major contamination risk to the surrounding environment. This polluted water, which is called Leachate, has to be contained within the confines of the landfill site, otherwise it could reach the water table and contaminate water supplies. To prevent leachate escaping a landfill, a membrane lining is buried in the landfill site during construction to create a tank to contain the leachate. Various measurement devices are installed around the landfill site to monitor the leachate and provide feedback to control systems which ensure the integrity of containment.
A leachate level transmitter is an instrument for measuring the height of leachate in a landfill site and converting it to a 4 to 20 milliamp current loop output, which is sent to other instrumentation to display, monitor, log or control the leachate level.
There are many different types of technology used to measure leachate level, there are transmitters that can be mounted above the leachate such as ultrasonic or radar which bounce a sound or electromagnetic wave off the surface of the leachate and use the travel time to determine the distance from the leachate surface.
For leachate filled tanks there are level transmitters which can be attached externally, such as floats running up and down a leachate filled tube connected at the bottom of the tank, or a pressure transmitter installed in a hole in the bottom of the tank which measures the pressure generated by gravity acting on the leachate.
Another method is to lower a probe into a tank, borehole or collection pit and immerse it in the leachate. A capacitive probe can be used which detects the changing capacitance charge as the length of the probe is exposed to varying proportions of leachate and air, or a pressure transmitter which will measure the pressure generated by gravity acting on the surrounding leachate.