Generating Biogas

Wastewater must be treated such that when it is released back into the environment, it does not have any harmful effects on an ecosystem. Particularly in the food and agricultural sectors, carbohydrates and many other organic compounds are introduced from washing processes and various other processing steps. Releasing this nutrient-rich effluent without adequate treatment would result in abundant bacterial growth, deoxygenating the water and destroying aquatic life.

Effluent treatment can happen by either aerobic (oxygen-rich) or anaerobic (oxygen-deficient) digestion, or a combination of both, although anaerobic treatment is meant for higher concentrations of organics.

Industries processing bulk volumes of wastewater or other biomass with exceptional organic content can cut down costs and have a more positive environmental impact by generating renewable energy: biogas.

Waste is treated through anaerobic processes with activated bacterial sludge in digester tanks. Biogas can be processed and used as a utility or sold and fed back into the power grid. Use of a cogeneration plant (CHP) on-site maximizes energy efficiency by contributing heat to the digester(s), thus saving even more.

Process Opportunities

• Nutrient dosing to bacteria
• Influent to digesters
• Waste effluent compliance
• VOA/TAC in fermentation
• Moisture percentage in gas
• Trace ions in steam

Formation of Biogas from Waste Products

Biogas is produced when organic matters are broken down in a four-step anaerobic digestion process (acetogenesis, acidogenesis, hydrolysis and methanogenesis). Before it is processed, flammable biogas is a water-saturated gas mixture that is mainly composed of methane (CH₄) and carbon dioxide (CO₂). The CH₄ component is most essential in the use of biogas, as the oxidizable compound dissipates energy when burned.

Issues with High Organic Loads

Feeding the fermenter with excess organic load leads to an imbalance between the various kinds of bacteria, resulting in the formation of fatty acids and a lowered pH. The imbalance destroys the remaining bacteria in the tank and abruptly stops methanogenesis.

Metrohm Process Analytics provides different analytical approaches in many different analyzer configurations for any need, such as ion chromatography, photometry, NIR spectroscopy, titration, and ion-selective measurements. Metrohm’s online process analyzers and customized sample preconditioning systems are built in the Netherlands and maintained by Metrohm’s local service engineers globally.

Benefits of Online Monitoring

A shutdown, cleanup and replacement of the bacterial sludge is extremely costly, calculated in the hundreds of thousands of euros for even a small overloading event. However, process optimization can result in additional income from various areas in the plant, like the sale of excess sludge or produced heat as a utility. Hence, it is highly important to continuously monitor all processes related to biogas formation to minimize waste and increase profit in many areas.

Applications

Monitor Fermentation Efficiency Online with Ion Chromatograph (IC)

Fermentation produces short-chain fatty acids, alcohols and hydroxycarboxylic acids. The Process Ion Chromatograph can measure multiple organic acids (and more) in one, aqueous sample. This analyzer is available with either one or two measurement channels, with many optional inline sample preparation methods available to make online analysis simple in different areas. A single Process Ion Chromatograph can be configured to track up to 20 different sampling points with an extensive range of analyte concentrations (ng/L to %).

• Extensive organic acid analysis in one run
• Track fermentation process with acetic acid: propionic acid ratio
• Trend chart analysis and warning limits to mark fermentation inhibition or overfeeding episodes
• Trace corrosive ions in water-steam circuit (CHP)

Process Ion Chromatograph

Measuring Oxygen Demand and More in Influent

Various plants still use laboratory-based Chemical Oxygen Demand (COD) measurements to regulate methanogenesis in the fermenter(s), but the occasional analysis (sometimes once per day) easily misses peak concentrations in the influent to the fermenter. This can be avoided by online process analysis. Based on the predicted concentration range of COD, automated redox titration or photometric methods can be used. Various other fermentation-related uses can be carried out with the Process Analyzer ADI 2045TI like the permanganate number or the VOA/TAC (otherwise known as FOS/TAC) ratio.

• Methods conform to ISO 6060, ASTM D 1252, DIN 38409-41 and NEN 6633
• Divert or dilute highly concentrated influent before it reaches the fermenter
• Promote safety by moving COD analysis online

Process Analyzer ADI 2045TI

Reagent-Free Solutions for Biogas Production

Online near-infrared spectroscopy (NIRS) can improve upon different phases in the biogas production process. Being non-destructive, the reagent-free method enables real-time knowledge of dynamic processes. Process NIRS applications suitable for biofermentation comprise of:

• Monitoring the fermentation process (VOA/TAC) to increase production yield
• Optimization of the bacterial feeding process through quality control of incoming feedstock
• Inspection of fermentation residue (N, P, K)
• Moisture percentage in gas

NIRS XDS Process Analyzer

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.