A biogas digested (or biodigester) breaks down organic matter in an anaerobic biological process that not only decomposes plant and animal matter, but produces biogas (consisting of methane and carbon dioxide). Many types of organic waste products can be used in a biogas digester, including food waste, plant material, and manure from livestock. Anaerobic digestion processes occur naturally in any oxygen free environment, for example when organic matter is buried under the soil, muddy substrates of lakes and dams, or under ocean sediments. They can also occur under more controlled conditions such as those found in a specially designed biodigester or biogas plant. In the latter, organic waste material, such as manure from livestock, is placed into an airtight biodigester together with various kinds of anaerobic bacteria -- bacteria that flourish in an oxygen-free environment. The anaerobic bacteria then start to feed on the organic matter, breaking it down in three phases: 1.
Decomposition: the first phase of the anaerobic digestion process consists of the decomposition (or hydrolysis) process. In this process organic plant and animal matter is broken down into smaller molecules (i.e. sugars). 2.
Organic Acids: in the second phase, the decomposed material is converted into organic acids. 3.
Methane Gas: in the third, and final phase of the anaerobic digestion phase, the organic acids are converted into methane gas. Depending on the biogas systems design, and the type of waste used in the biodigester, biogas typically tends to consist of between 55-75% pure methane. Highly sophisticated biodigester systems can produce biogas that contains more than 95% pure methane. Aerobic digestors are now commercially available and can be used with agricultural organic waste, or to treat industrial and municipal wastewater. In many of these cases unprocessed waste material would typically result in odors and water contamination, whereas anaerobic digestion minimizes odors and problems associated with the disposal of liquid waste, producing biogas that can be used as a fuel for heating or to generate electricity.
Monitoring the Flow Rate of Biogas Produced
The anaerobic digestion process takes place in a sealed airtight environment -- either under the soil, underwater, or in a specially designed airtight container. The biogas produced is collected and channeled through piping to fire up a gas engine, which powers a generator that produces electricity. But how does one monitor and control the flow of biogas collected from a sealed biodigestor system?
The Accu-Flo thermal mass flow meter lets an operator do precisely that -- it uses the constant temperature difference method to measure the Gas Mass Flow Rate of the biogas passing through the pipes, allowing the operator to make adjustments to control the flow with extreme accuracy. The
Landtec Accu-Flo meter is equipped with a zero calibration self-check, which is a unique feature that enables a user to verify that the equipment has not deviated from the original factory calibration setting, and comes in very handy when used to monitor gas-to-energy projects. The Accu-Flo Meter comes with a display fitted into the meter head, a 1/2 inch diameter probe and isolation valve assembly with a 3/4 inch MNPT mounting connection, but adapters are available for other pipe diameters.
Image Credit: "Haase anaerobic digester" by Vortexrealm at en.wikipedia. Licensed under CC BY 3.0 via Wikimedia Commons
