Suitable biological conversion processes of biomass in a circular economy

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April 19, 2023


RECOMMENDED / Synthetic Biology


Suitable biological conversion processes of biomass in a circular economy

Suitable biological conversion processes of biomass in a circular economy

Biomass must be processed to be used as chemicals, energy, or materials. There are several conversion and separation technologies available. Microorganisms or enzyme-related activities carry out the biological conversion processes. The most important recognised biological conversion process mechanisms are covered in this article.


Fermentation processes 

Fermentation is a biological conversion process where microorganisms such as molds, yeasts, and bacteria use anaerobic conditions to make alcohols, acids, or hydrogen from organic matter. The chemical and energy sectors use a fermenter containing a liquid that typically includes carbohydrates, but sometimes organic acids, even though fermentation can be conducted under anaerobic conditions. The definition is sometimes expanded to include processes that necessitate oxygen (aerobic conditions). Pure cultures are produced by sterilizing the substrate and fermenter each time they are used with a single type of microorganism.

Monosaccharides (such as glucose) and disaccharides (such as sugar crystalline or sucrose) comprise the most critical raw material in fermentation science. Biomasses such as carbonated cane sugar, beet sugar, and molasses are suitable raw materials similar to lignocellulose, cellulose, or starch from which fermentable sugars can be manufactured. Biomasses like wood, leaves, grass, straw, corn and wheat are all acceptable raw materials for fermentation because they contain a lot of sugar. Raw materials such as glycerol, fats, alcohols, amino acids, proteins, and organic acids, may also be utilized in the fermentation process, thus creating a range of different products.

Applications and Importance of Fermentation in Industrial Processes


Producing high product concentrations in fermentation can lead to economic benefits, and there may be no need to dilute the raw material with water. Fruits, juices, and wastewater are the least suitable because they have high dry matter content, more than 25%.

Fermentation products such as hydrogen, isobutanol, butanol, and ethanol are important products in the energy carrier category. Lactic acid, an ingredient for bioplastic polylactic acid. It is also important in addition to polyhydroxyalkanoate (PHA), a bioplastic that forms granules in bacterial cells. Fermentation products like itaconic acid, succinic acid, and other dicarboxylic acids have become increasingly important. This due to their bioplastic production suitability. One uses fermentation in the production of amino acids, enzymes, citric acid, and other products, such as baker’s yeast, bread, wine, and beer.

Anaerobic digestion – Biological Conversion Process

Anaerobic digestion refers to the breakdown of organic material into methane by microorganisms in an anaerobic environment. One commonly uses it to refer to methane fermentation. It produces biogas as the end product, a mixture of methane and carbon dioxide. Large reactors with a volume of over 1,000 cubic meters stir and heat solid biomass for anaerobic digestion into biogas.The process can take up to one month to complete. 

Suitable biomass for anaerobic digestion may include industrial wastewater, sewage treatment plant sludge, fruit and vegetable wastes, etc. In a co-fermentation process, one can process manure with grass, corn, or other co-substrates to increase biogas yield without altering the reactor’s volume.

Various Uses of Biogas and Digestate in Agriculture and Energy Production

One can upgrade biogas to a quality comparable to natural gas. It inject the purified biogas, also known as green gas, into the natural gas grid. One can use biogas as a transport fuel after liquefying it to Bio-LNG. Alternatively, one can utilize biogas in a combined heat and power plant (CHP) that generates both heat and electricity.. The byproduct of anaerobic digestion is digestate. It still contains composted manure, minerals (including phosphate and ammonia), water, and unfermented organic materials. One can use these materials to fertilize agricultural land.


Composting is a micro biological conversion process. It oxidizes and breaks down organic material into compost. In a system that passes air through a heap of pore-filled, solid material. It can occur naturally in the field. One performs controlled composting by using a forced ventilation system via a ventilator in an open-air environment, a hall, or a container to ensure composting occurs. Composting generates heat through a biological combustion process that one can harness for other purposes.

The high temperature (70°C) causes water to evaporate, resulting in the material becoming drier, and it destroys many weed seeds and pathogens. The composting process usually takes a few weeks to complete. The material must be suitable biomass such as pruning and mowing material (grass, leaves), SSO, dry manure, straw, and digestate produced in digesters. The biomass materials must be moderately wet but porous, excluding slurry and liquids. 

The compost produced during composting contains minerals and organic materials that are difficult to break down, such as humic acids and wood fragments. One can use compost to enhance soil fertility, and some types of compost can serve as a substrate source for cultivating mushrooms. Upcycling Gemert is a well-known example of a composting business. 

Future research direction

Although different regions of the world have significantly developed the conversion processes discussed above, future research can focus on utilizing other methods such as ensilage and bokashi, enzymes, and vermiculture as biomass biological conversion processes. Ensilage and bokashi are methods for fermenting solid biomass under anaerobic conditions to produce organic acids, which acidify the biomass, eliminating the need for further biological conversion process. This process preserves biomass materials like grass, enabling them to be stored for months.

Vermiculture uses worms for processing biomaterials. When worms consume biomass in an oxygen-rich environment, they generate compost. Enzymes (made from organisms) can convert a set of substances into other substances through the use of catalysts. The conversion of starch into glucose by the enzyme amylase is a good example of the use of enzymes. As such, enzymes find application in multiple areas, for example in the hydrolysis of natural biopolymers like proteins and cellulose.

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