A while ago, we posted the article on why food waste was a significant issue in greener living. Many of you applauded the context and were asked for a solution. The best way to manage food waste is certainly, anaerobic digestion.

Anaerobic digestion is a mechanism that has been around for a long time. It has a long history, dating back to the 1800s. 

However, as environmental concerns arise, the urge for renewable energy sources increases. As a result, developments in anaerobic digestion have significantly increased in recent years.

Waste-to-energy is viewed as one of the most critical future renewable energy sources, mainly because uninterrupted power production is attainable. 

The essential quality of such green technologies is their compatibility with the environment. Burning, gasification, decomposition, composting, and anaerobic digestion are some of the ways used to transform waste into energy. 

At present, anaerobic digestion has received more attention than others. Furthermore, the anaerobic technique has environmental, energy, and economic benefits.

Decomposers break down organic biodegradable substances in anaerobic digestion in an oxygen-free environment. 

Biogas is among the outcomes that provide power or convert it into renewable natural gas and automotive fuels when burned. Now, how does that sound for clean energy?

Table of Contents

Stages of Anaerobic Digestion

phases of anaerobic digestion
Phases of anaerobic digestion| Representation by Vimala Ebenezer

Hydrolysis, acidogenesis, acetogenesis, and methanogenesis are the four main phases of anaerobic digestion. 

The whole process can be classified as a chemical reaction in which anaerobic microbes biochemically consume organic matter such as glucose to produce carbon dioxide and methane.

I. Hydrolysis

Huge organic polymers make up the majority of biomass. The pre-existing complex linkages must primarily be subdivided into the simpler fundamental parts for the micro-organisms in anaerobic digesters to harness the energy potential. 

These fundamental parts, or monomers, such as sugars, are easily accessible for micro-organisms. The process of disintegrating these chains and dissolving the smaller molecules into a solution is called hydrolysis.

Therefore, hydrolysis of the high-molecular-mass polymeric elements is the inevitable first step in anaerobic digestion. 

Through hydrolysis, the complex organic units are broken down into simple sugars, amino acids, and fatty acids. Hydrolysis is the process of destroying these linkages and disintegrating the tiny molecules into solutions. 

As a result, the initial stage in anaerobic digestion is to hydrolyze the high-molecular-weight polymeric compounds. Complex organic compounds are converted into simple sugars, amino acids, and fatty acids during hydrolysis.

II. Acidogenesis

Acidogenesis is a biological process that causes acidogenic or fermentative bacteria to degrade and break down the remaining substances

VFAs, ammonia, carbon dioxide, hydrogen sulfide, and other byproducts are produced in this stage of anaerobic digestion. For instance, milk and dairy products spoil as they undergo acidogenesis.

III. Acetogenesis

Acetogenesis is the third phase of anaerobic digestion. In this stage, simple molecules produced during the acidogenesis are decomposed further by acetogens, resulting in acetic acid, carbon dioxide, and hydrogen.

IV. Methanogenesis

The biological mechanism of methanogenesis is the final phase of anaerobic digestion. Methanogens employ the intermediate components from the earlier stages to produce methane, carbon dioxide, and water. 

The majority of the biogas produced by the process are made up of these substances. Methanogenesis proceeds around pH 6.5 and 8 and is hypersensitive to high and low pHs. 

The digestate is made up of any undigested substance that the micro-organisms cannot digest, and dead bacterial remnants remain in the digestate.

What does anaerobic digestion give us?

process of anaerobic digestion
Process and uses of Anaerobic digestion| Infographics by KB bioenergy

1. Biogas

Methane, the chief element of natural gas, is present in biogas which accounts for 50 to 75 percent, along with other elements such as carbon dioxide (CO2), hydrogen sulfide (H2S), water vapor, and a small fraction of other gases. 

We can utilize biogas in the same way that natural gas produces heat, generates energy, operates cooling equipment, and many more. 

Biogas can also be processed to provide sustainable natural gas by eliminating inert or low-value ingredients such as carbon dioxide, precipitation, hydrogen sulfides, etc. 

The produced biogas can be marketed and pumped into the gas pipeline network, pressed and utilized as transportation fuels, or further be processed to produce various transportation fuels, liquid fuels, etc.

2. Digestate

The remnant matter left over from the digestion process is known as digestate. It is made up of both solid and liquid components. 

Because each has a great significance achievable with different extents of post-processing, these semi-solid and liquid are frequently isolated and extracted separately.

And, we can utilize both solid and liquid components of digestate in a variety of favorable application domains with proper processing, including livestock bedding, plant fertilizer, etc. 

The residue can also be used as foundation matter for bio-based merchandise (such as bioplastics), organic manure, or simply as soil remediation, including farm spreading for enhanced productivity.

Advantages of Anaerobic Digestion

  • A net energy-producing method generates biogas, a renewable energy source.
  • It disinfects the livestock waste products with the help of high temperatures.
  • Decreases stench to a great extent compared to organic wastes left untreated at dumping sites. 
  • Far less prone to pollute the environment than dumping raw organic waste on land.
  • Anaerobic digestion enables improved resource restoration and non-renewable energy consumption reduction. 
  • Anaerobic digestion produces less sludge mass when preferred as a primary water treatment method than an aerobic system.
  • The effectiveness of manure is much better than that of unprocessed organic waste.
  • It can be converted to “biomethane,” with numerous benefits over raw biogas.
  • The mechanism creates carbon dioxide that can be refined and marketed as a profitable commodity.
biogas generation by anaerobic digestion
Anaerobic digestion on biofuel and biogas process| Infographics by gcesystems

According to the United States Department of Agriculture, 30-40% of food in the United States is discarded. 

Nearly 41 million tons of food scraps were created in 2017, with just 6.3 percent of the material redirected from dumping sites to composting units.

Food waste accounts for around 8% of total global greenhouse gas emissions. All of the wastage that winds up in dumping sites produces methane, which is about four times more harmful than carbon dioxide.

At present, anaerobic digestion has surfaced as the most popular organic municipal solid waste management solution. 

Digestate management plans are created to ensure safe dumping and maximize the potential and commercial viability of the waste.

Norms and guidelines for digestate administration are being developed to tackle environmental problems, protect vulnerable regions, combat infectious diseases, and inform the public about digestate management and applications.

The significant factors for improving digestate through preprocessing and post-digestion treatment approaches for solid and liquid components of digestate are legislation and intended end applications.

The most comprehensive existing management approach uses digestate as manure or soil improver to increase crop productivity. 

Alternative uses, such as microalgal cultivation, biofuel, and bioethanol synthesis, render a promising prospect.

Currently, the priority of anaerobic digestion process efficiency and optimization is solely on increasing biogas generation, with the grade of digestate generated being overlooked. 

To Wrap Up

The burden of solid waste management and treatment has now been turned into an income opportunity using biogas plants. 

Transforming garbage into power, heat, or car fuel is a sustainable energy source that can significantly alleviate reliance on foreign oil shipments, cut greenhouse emissions, enhance ecological integrity, and create new employment opportunities in the area. 

Biogas systems such as anaerobic digestion also allow minerals in food production to be recycled, lowering the requirement for both chemical and inorganic nutrients.

Anaerobic digestion is a waste recycling solution that can help with various issues and provide a mixture of benefits to both humans and the environment.

(Last Updated on January 26, 2022 by Sadrish Dabadi)

Shradha Bhatta holds a Bachelors’s Degree in Social Work along with a Post-graduate degree in Project Management from Georgian College in Canada. Shradha enjoys writing on a variety of topics and takes pleasure in discovering new ideas. She likes traveling and spending time with nature. She is a very people-person who loves talking about climate change and alerting people to go green!