Organic material refers to carbon-based compounds formed by living organisms (e.g., animal manure, food waste, and wastewater biosolids). It can be turned into more usable compounds (i.e., biogas and digestate) through a process known as anaerobic digestion.
The anaerobic digestion process utilizes microorganisms to break down organic material in the absence of oxygen. It occurs within a sealed vessel called a reactor or digester, which contains microbes that process (i.e., digest) the material and produce biogas and digestate. These end products are then discharged from the vessel so they can be collected and used.
What Does an Anaerobic Digester Produce?
The process of anaerobic digestion produces two key products: biogas and digestate.
Biogas consists of methane, carbon dioxide, hydrogen sulfide, water vapor, and trace amounts of other gaseous compounds. Several types of bacteria are involved in producing it. First, first-stage bacteria break down the carbohydrates present in the material into soluble compounds (e.g., sugars and amino acids. Next, acidogenic bacteria consume these compounds and convert them into ammonia, carbon dioxide, hydrogen, and organic acids. Then, these compounds are turned into acetic acid, which is converted into biogas by anaerobic methanogenic archaea bacteria. Finally, the biogas can be purified to generate renewable natural gas (RNG). This final product can be used as a power source for various equipment.
Digestate is the material remaining after anaerobic digestion. It consists of solid and liquid components, which are generally separated and handled individually since they can be valuable with proper post-processing. Applications include animal bedding, bioplastics, compost, fertilizer, and soil additives.
Types of Anaerobic Digesters
There are many types of anaerobic digesters available. They can be classified into four general categories:
Covered anaerobic lagoon digesters: These systems are sealed with a flexible cover. They are designed to recover and pipe methane to the combustion chamber.
Plug flow digesters: These systems feature a low, narrow concrete tank with a rigid or flexible cover. They are designed to be partially or fully below grade, which limits the demand for supplemental heat.
Complete mix digester: These systems have an enclosed and heated tank with a mechanical, hydraulic, or pneumatic mixing mechanism.
Dry digesters: These systems have an upright, silo-style design. They are made from concrete and steel and feature a rigid cover.
Anaerobic Digesters From Nova Analytical Systems
Anaerobic digestion primarily produces carbon dioxide and methane. However, trace amounts of other gases, such as hydrogen sulfide, nitrogen, and oxygen, are also generated. While these compounds can be valuable when properly handled, they can also present some problems, especially methane. Methane greenhouse gas is 20 times more potent than CO2. That’s why many countries require gas levels to be monitored at biogas and landfill sites. Facilities may also integrate an analyzer system between the gas supply line’s output and the receiving process’s input to determine the specific makeup of the gas, which is essential to attaining and maintaining efficient and safe operating conditions. Different gas readings can be used for different purposes. For example, oxygen readings can be used to detect inbound air leaks in the collection system, while carbon monoxide readings can be used to detect subsurface fires.
Need gas analyzers for your biogas or landfill facility? Nova Analytical has got you covered! We offer a variety of gas analyzers systems to suit different customer applications. To learn more about our product offerings and how they can benefit your facility, contact us or request a quote today.
Electrochemical gas sensors—also sometimes referred to as electrochemical analyzers or electrochemical toxic gas detectors—are designed to measure the concentration of a specific gas (e.g., oxygen or carbon monoxide) within an external circuit. In the following article, we outline how they work and what gases they can detect.
Operating Principles of Electrochemical Gas Sensors
An electrochemical gas sensor generally consists of a working (i.e., sensing), counter, and reference electrode, all of which are contained within a housing with a gas-permeable membrane. During sensing operations, it is submerged in an electrolytic liquid. Combined, these components allow it to perform its function.
The housing membrane allows gas—but not the liquid—to pass into the sensor. An electrochemical reaction—either oxidation or reduction, depending on the type of gas—occurs when the gas reaches the working electrode. This reaction initiates a flow of electrons (i.e., current) between the working electrode and counter electrode. An oxidation reaction moves electrons from the working electrode to the counter electrode, while a reduction reaction causes electrons to move from the counter electrode to the working electrode. In either case, the electrical current generated is proportional to the concentration of the target gas. This current is then amplified and processed according to the calibration to give the user a reading in either parts per million (PPM) or percentage volume. If no target gas is detected, most electrochemical sensors indicate a reading of zero. However, unlike catalytic bead sensors, the sensor does require a balance or zero adjustment.
While electrochemical sensors are designed to identify a specific gas, most demonstrate some degree of cross-sensitivity. This phenomenon refers to the response of the sensor to gases other than the target gas, generally as a result of greater chemical reactivity in the non-target gas than the target gas. In some cases, the non-target gas can mask the presence of the target gas. For these reasons, it is important to employ the use of filters and bias voltage during operations to minimize the effect of cross-sensitivity on the accuracy of readings.
The rates of the chemical processes on which electrochemical sensors rely are proportional to temperature. As such, variations in temperature can affect sensing performance. For greater reading accuracy across a broader range of environmental conditions, some form of temperature compensation is recommended.
What Gases Do Electrochemical Sensors Detect and Measure?
Electrochemical sensors can detect and measure a variety of gases—ranging from toxic to explosive to air quality—depending on the needs of the application, including the following:
Electrochemical Gas Sensor Solutions From Nova Analytical Systems
Electrochemical gas sensors find use in a wide range of industrial, commercial, and residential applications. In addition to detecting the presence of toxic gases in occupied spaces, they are used to ensure gas employed in sensitive operations remain at optimal levels. For customers in need of quality gas analyzers that utilize electrochemical gas sensors, Nova Analytical Systems is the ideal supplier.
The Next Generation for Portable Gas Analysis is NovaNOW
Continuing on a 40 year tradition of quality and reliability, Nova Analytical Systems is pleased to announce our new family of portable gas analyzers, NovaNOW.
This analyzer family is built upon proven technologies and techniques that carry the same rugged reliability, but configured into half the size and weight. Also, incorporated into NovaNOW are many new features that complement our tried and true original features that have made Nova Analytical a chosen choice for portable analysis.
Our portables are suitable for a wide range of industries such as flue gas and engine exhaust measurement, heat treating atmosphere and ambient air monitoring. as well as for commercial, industrial and residential settings.
Designed for accuracy, inquire about your NovaNOW today! Learn more by watching our video.
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Have additional questions about process gas monitoring or how to improve your process efficiency using off-gas analysis? Please feel free to contact us.
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