Biogas biorefineries are an innovative concept in the field of process engineering. As a process engineer, this is my first experience working with biogas biorefineries, and I am eager to explore and understand this subject in depth. This section will help us get acquainted with the basics and significance of biogas biorefineries within the industry.
Definition of Biogas Biorefineries
Biogas biorefineries use sophisticated, combined processes to convert organic waste, energy crops, and agricultural leftovers into biogas, biomethane, and valuable bio-based products through anaerobic digestion.
Biorefineries of biogas may include the following type:
- Biogas biorefineries focusing on the production of biogas and fertilizers using energy crops or waste substrates like food waste or food production waste
- Sugar crop biorefineries based on sugar beet, sugar cane, etc.
- Starch crop biorefineries based on cereals, maize, potato, etc.
- Green biorefineries based on wet biomass like grass, clover, etc.
- Biorefineries that process all kinds of organic waste, including municipal, food industry, restaurant, and grocery store waste.
Typical Process of Biogas Biorefineries
Typical process of biogas biorefineries is shown below.
The process of biogas biorefineries consists of three processes:
- Substrate reception, pretreatment, and feeding equipment.
When substrates are more complex or contain higher amounts of inorganic impurities, additional pretreatment steps are required. For instance, food waste facilities often use hammer mills or centrifugal separators to remove packaging and other impurities from the organic material.
- The digestion unit comprises one or more gas-tight, heated anaerobic tanks, which are integrated with a biogas collection system.
For the digestion of solid substrates and high-strength liquids, fully mixed tank reactors are typically preferred. During anaerobic digestion, organic material is decomposed into an oxygen-free atmosphere by bacteria that produce a gas, called biogas, and usually containing methane and carbon dioxide plus components of minor importance
- Digestate storage and posttreatment units
After digestion, the remaining digestate is typically stored on site and directly applied as fertilizer to nearby farmland. Digestate from plants using agricultural byproducts, energy crops, or food wastes is chemically suitable for immediate land use.
Key Differences Between Aerobic and Anaerobic Treatment of Liquid Organic Wastewater
The figures compare anaerobic and aerobic treatment of organic residues or industrial wastewater. Anaerobic treatment is more efficient for nonlignocellulose substrates, converting 70–90% of their chemical energy into biogas. This process results in minimal heat loss and low bacterial biomass production. Anaerobic digestion is preferred when recycling of valuable substances is not feasible, and biogas generation is a common feature in most biorefinery processes due to the inevitable production of organic-rich waste streams.
Typical Characteristics of Biogas
Table below shows typical composition of biogas. Biogas mainly consists of methane and carbon dioxide.
Table below shows energy characteristic of biogas. The energy value of biogas is primarily determined by its methane and hydrogen concentrations. In typical biogas systems, methane accounts for approximately 99% of the overall energy content.
References:
- Pandey, Ashok et al. Industrial Biorefineries & White Biotechnology. 2015. Elsevier