Anaerobic digestion advantages and disadvantages are; flexibility, energy independence, land conservation, economic growth, food production, waste management, emissions reduction, bioremediation, job creation (advantages); cost, technical limitations, effectiveness challenges, time-consumption, and treatment inadequacy (disadvantages).
This article discusses the advantages and disadvantages of anaerobic digestion, as outlined below;
Advantages of Anaerobic Digestion
1). Anaerobic Digestion is Flexible and has a Wide Range of Applications
One of the main advantages of anaerobic digestion is its broad range of application.
The method has been used in various contexts, ranging from agriculture and soil amendment, to energy and waste management.
This is because of the flexibility of the anaerobic digestion process.
Studies have shown that the anaerobic bacteria which drive the digestion process, have a wide range of temperature tolerance.
This includes the psychrophillic microbes (10-25°C), mesophillic microbes (25-35°C), and thermophillic microbes (49-60°C) .
Anaerobic digesters may also be low-rate or high-rate digesters . This provides users with a variety of options when utilizing anaerobic digestion technologies.
Another reason why anaerobic digestion has a wide range of application, is the variety of byproducts of the process, which include solid biomass or digestate, ethanol, methane (biogas), and other gaseous products.
These byproducts are relevant in different industries.
2). Energy Production and Independence
This is because the raw materials or feedstock, used in anaerobic digestion, is biomass.
Biomass is itself a renewable natural resource, since plant and animal waste can be produced continually on Earth .
Biogas, which is a major byproduct of anaerobic digestion, is a renewable fuel which has found application in electricity generation within some sectors of industry.
It may be used in some combustion engines and cogeneration plants.
As a result of the fact that biogas can be produced in any region of the world, it can be said that anaerobic digestion technology has the potential to establish energy independence, by eliminating the dependence on fossil fuels for electricity.
However, whether this potential is actualized or not, depends on the level of advancement that is achieved in the field of anaerobic digestion technology, in the near future.
3). Anaerobic Digestion as a Means of Agricultural Land Conservation
Anaerobic digestion helps to conserve agricultural land in various ways.
These ways include removal of pathogenic agricultural waste, protection of water resources, and improvement and stabilization of soil.
When agricultural organic waste is treated using anaerobic digestion, open (aerobic) biodegradation of this waste is prevented.
By preventing open biodegradation, the agricultural soil is protected from harmful byproducts and influence of biodegradation.
In the same vein, water resources within the area, are protected from the harmful effects of runoff containing these byproducts of open biodegradation.
Anaerobic digestion contributes to agricultural land conservation by promoting healthy farming practices, managing soil and water resources, and minimizing pollution.
4). Anaerobic Digestion as a Tool for Economic Growth
Anaerobic digestion can contribute to economic growth in various ways.
The main reason for this is the fact that anaerobic digestion yields valuable byproducts like digestate, ethanol and biogas.
Two sectors of the economy which can be supported by anaerobic digestion are the agricultural and energy sectors.
This is because the products of the process can be used as fertilizer, and as renewable fuel for generating electricity.
Economic benefits of anaerobic digestion technology can be experienced both locally and beyond, in terms of human resources development, product utilization, incentives and tax revenue, among others.
5). Sustainable Food Production
Anaerobic digestion technology contributes to the global effort, to tackle food insecurity.
One of the main causes of low food production is low soil fertility in agricultural lands .
Anaerobic digestion provides a way to tackle this problem.
One of the products of anaerobic digestion; digestate, can be used as a fertilizer .
It occurs in a chemically less-complex form than other types of fertilizer, and is rich in nutrients, which can be easily accessed by plants from soil.
Anaerobic digestion can also be used to treat livestock manure before it is applied to soil . This approach can help to get rid of some pathogens which may be harmful to crops.
As a fertilizer, digestate (a product of anaerobic digestion) has the advantage of being cheaper to access, than industrially-produced fertilizers.
It also poses less risk of greenhouse gas production, since it is produced after most of the gaseous products of biodegradation have been removed.
Through anaerobic digestion, soil health is improved by the application of digestate to agricultural soil, as part of soil amendment measures. Such measures are capable of improving crop yield and food availability.
If applied on a large scale, anaerobic digestion may be a significant step to address world hunger.
It is also a means by which the impact of food waste on the environment can be reduced.
This is because anaerobic digestion helps to recycle nutrients, water and bioenergy resources from food waste, thereby returning these natural resources to the environment.
6). Anaerobic Digestion and Waste Management
Anaerobic digestion is a method of municipal waste management .
Other types of waste such as agricultural waste, biodegradable industrial waste, and forest residue can also be treated using anaerobic digestion.
Anaerobic digestion is especially important for managing organic waste, which is a major problem in landfills  and other waste disposal sites.
The biodegradation of organic waste is unfavorable for the environment, because it produces unpleasant odors, aesthetic pollution, and greenhouse gases that affect the climate.
In addition to providing a beneficial method to treat organic waste, anaerobic digestion (AD) is means by which the sustainability of the ecosystem is ensured. It recycles nutrients effectively, preventing them from being lost from the environment.
7). Anaerobic Digestion as a means to Reduce Methane Emissions
It is estimated that methane is over 25 times more potent than carbon dioxide, as a greenhouse gas.
This greenhouse gas is released when biomass decomposes, and has been identified as a major contributor to global warming.
During anaerobic digestion, methane (or biogas) is usually captured and stored for use. This measure helps to reduce the rate and volume of emissions of greenhouse gases into the atmosphere.
It also ensures that methane is made useful as a renewable fuel.
Anaerobic digestion can also act as an avenue for carbon capture and storage, when the carbon dioxide (CO2) which is produced in the process, is captured, rather than being released directly into the atmosphere.
In general, anaerobic digestion technology is an aspect of environmental and economic decarbonization .
8). Anaerobic Digestion as a Method of Bioremediation
Because anaerobic digestion converts organic matter to simpler end-products, it can be used as a method of environmental remediation.
Specifically, anaerobic digestion is a bioremediation technique, because it depends on microorganisms and biological/biochemical processes.
The use of anaerobic digestion for environment remediation is mostly possible and effective, when the contaminants to be removed, are organic or biodegradable. Such contaminants include petroleum, pesticides and heavy metals.
Some areas of environmental remediation where anaerobic digestion can be applied, include soil treatment, contaminated water remediation, and control of eutrophication.
In these applications, it has the advantage of being an environment-friendly option, because it does not involve the use of chemicals that may have negative effects on soil, air or water.
Anaerobic digestion can be used to address air pollution in terms of unpleasant odors  due to gases like hydrogen sulfide, which are released from decomposing organic matter.
9). Job Creation
Anaerobic digestion plants require skilled labor for their maintenance and operation.
This creates an avenue for job creation, which is a source of economic growth.
Jobs in the anaerobic digestion field include electrical engineering, construction, plumbing, process engineering, plant operation, and other forms of labor.
Disadvantages of Anaerobic Digestion
1). High Cost of Anaerobic Digestion
The capital cost required for anaerobic digestion is generally high.
This is especially as a result of the need for digesters to be used.
Anaerobic digesters have high purchase and installation costs , which prevents many potential users from carrying out anaerobic digestion.
There are also high operation and maintenance costs.
In the agricultural sector, this is a problem. especially because it prevents relatively-small farms from being able to utilize anaerobic digestion.
Estimates have placed the cost of anaerobic digesters between $400,000 and $5 million.
Similarly, the production of bioenergy and electricity from anaerobic digestion plants, is associated with significant expenses for equipment and labor.
2). Land-use Limitations
Although anaerobic digestion is a method of waste management, soil amendment and environment remediation, it is also associated with some problems of land use.
Anaerobic digestion is strongly dependent on scale. This implies that the level of productivity of an anaerobic digestion plant is proportional to the size of the plant.
For example, in waste-to-energy applications, the amount of biogas and bioenergy produced from anaerobic digestion, depends on the size of the farm or land within which it is being conducted.
This dependence of productivity on scale, implies that anaerobic digestion is a land-intensive technology. The demand for large areas of land, makes it difficult for anaerobic digestion to be conducted in the absence of sufficient land resources.
In addition to the issue of scale, anaerobic digestion also affects land resources by causing some forms of degradation. This may be in the form of unpleasant odors from the digester , pathogen-breeding, and other occurrences.
3). Suitability Limitations for Biogas
A major byproduct of anaerobic digestion is biogas, which comprises of 50-75% methane, 25-50% carbon dioxide, and 2-8% nitrogen .
This byproduct is considered valuable because of its relevance in energy production.
However, there are some limitations to the suitability of biogas produced from anaerobic digestion, in terms if its usage to produce energy.
One of these limitations is the actual purity of biogas. Most anaerobic processes produce biogas which is contaminated with impurities . These impurities affect the efficiency of the gas as a fuel.
The production of biogas is relatively inefficient, due to technological limitations of anaerobic digestion.
For example, biogas production is affected by temperature , because digester systems are not yet capable of controlling the temperature of the anaerobic digestion process.
Biogas dependence is also not suitable for dense urban areas, because anaerobic digestion thrives when feedstock (organic waste) can be sourced locally in a sustainable manner.
The absence of farms in urban areas limits the versatility of anaerobic digestion.
Lastly, the energy density of biogas is not as high as that of fossil fuels like diesel . This means that most technologies cannot rely effectively on biogas, since it is unlikely to meet the energy demand.
4). Anaerobic Digestion may be Ineffective for Pathogen Destruction
Anaerobic digestion is known to be a means by which biomass can be stabilized, and viable pathogens like virus, antibiotic-resistant microbes, and viruses, can be largely and efficiently deactivated .
However, studies have shown that there are significant limitations to the effectiveness with which anaerobic digestion can deactivate these pathogens.
Firstly, anaerobic digestion is unlikely to reduce the level of pathogens by 90-99% . Rather, there is a possibility that pathogens may multiply in anaerobic digesters.
Also, due to variability of temperature in the anaerobic digestion process, pathogen deactivation may vary.
For example, anaerobic digestion which is conducted under mesophilic temperature conditions, is less effective to destroy pathogens, than that which is conducted at higher thermophilic temperatures .
This inefficiency of pathogen removal is a disadvantage, because it implies that organic matter can still be harmful after it has undergone anaerobic digestion, and may therefore need further treatment before it can be safely released to the environment.
Such conditions increase the complexity and cost of anaerobic digestion as a method of organic waste treatment and bioremediation.
5). Anaerobic Digestion is Time-Consuming
One of the reasons why anaerobic digestion may be time-consuming, is the fact that anaerobic digesters require continuous maintenance, to ensure that they run efficiently.
Also, the complexity of the anaerobic digestion process itself, in terms of the presence of various stages and reactions, implies that a significant amount of time may be expended.
The retention time of organic matter in a digester, affects how long the overall process of anaerobic digestion will take .
This retention time may range from hours to days, and depends on factors like the type and size of digester, physicochemical conditions, nature of organic matter, and rate of loading.
In some AD plants, the intermediate products like acetic acids, ammonia and hydrogen sulfide which are produced before the final stage of anaerobic digestion, are collected. This can further increase the overall time spent.
6). Water Treatment Inadequacy
Studies suggest that aerobic treatment is a better method of nutrient removal for contaminated water, than anaerobic digestion .
When anaerobic digestion is used for water remediation, it is often necessary for post-treatment measures to be carried out before the water can be safely discharged.
This makes the method unreliable in some cases, especially where there is a high concentration of pathogens and contaminants in the water.
Advantages of anaerobic digestion are;
- Anaerobic Digestion is Flexible and has a Wide Range of Applications
- Energy Production and Independence
- Anaerobic Digestion as a Means of Agricultural Land Conservation
- Anaerobic Digestion as a Tool for Economic Growth
- Sustainable Food Production
- Anaerobic Digestion and Waste Management
- Anaerobic Digestion as a means to Reduce Methane Emissions
- Anaerobic Digestion as a Method of Bioremediation
- Job Creation
Disadvantages of anaerobic digestion are;
- High Cost of Anaerobic Digestion
- Land-use Limitations
- Suitability Limitations for Biogas
- Anaerobic Digestion may be Ineffective for Pathogen Destruction
- Anaerobic Digestion is Time-Consuming
- Water Treatment Inadequacy
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