The Advantages and Disadvantages of the Anaerobic Digestion Process
Anaerobic digestion (AD) is an important process in waste treatment where anaerobic bacteria (those that thrive in the absence of oxygen) are used to breakdown organic matter. As with any process, there are many benefits to using it but there are also drawbacks too.
In this article, we look at the most common advantages of anaerobic digestion and how industries that use this process can optimise it.
What Is Anaerobic Digestion?
In AD, anaerobic bacteria are used to break down bio-solids into digestate and biogases and reduce contaminants of pathogens such as viruses, bacteria and parasites.
The feedstock ‘waste’ depends on the industry and local sources, such as food waste, animal litter and dung, crop residues, or sewage sludge.
The digestate produced in AD can be used to create fertilisers while biogases can be used to produce energy or heat. As the process requires sealing off in a tightly controlled environment, it is an alternative to open air landfill, that allows for the capture and conversion of pollutants.
The Advantages of Anaerobic Digestion
1. Environmentally Beneficial
One of the key advantages of AD is its positive environmental impact. It produces biogas, primarily composed of methane, nitrogen and carbon dioxide. Methane can be used to generate electricity or heat or it can be upgraded to biomethane for use as fuel or injection into the natural gas grid. Additionally, the capture of methane and carbon dioxide during the process prevents its atmospheric release and mitigates its contribution to greenhouse gases.
AD also results in the reduction of organic waste which can include food waste, agricultural residues and sewage sludge, which would otherwise end up in landfill or require incineration or chemical treatment.
The resulting digestate can be recycled into fertiliser, reducing the need for synthetic fertilisers which are energy-intensive to produce. Digestate can also be added to soil to add back nutrients and improve quality.
2. Highly Efficient and Space Saving
The most compact and simplest AD plants are to be found processing waste from individual homes. Their reliance on naturally occurring bacteria means that once in operation, they are very cost-effective to run and can even be kept going by manual or low-energy mixing.
Medium-sized AD facilities are used on farms and eco-housing developments.
In densely populated areas, centralised AD treatment plants can handle large volumes of organic waste from multiple sources. This allows for efficiencies of scale not available to multiple smaller facilities. An AD system can also be designed in a modular fashion to ensure scalability.
Moreover, AD systems can be integrated into existing treatment systems, reducing the need for additional construction of facilities. Unlike aerobic bacteria systems which require extensive aeration and large basins or tanks, AD requires less land for its components such as digesters and storage units.
Additionally, as the AD process is closed to the outside air, odours and emissions are contained.
Disadvantages of Anaerobic Digestion
While AD is an important part of waste treatment and the industry's drive towards carbon neutrality and sustainability, it does have three drawbacks.
1. Capital Expenditure
Some of the elements used in the process are expensive so it does require significant capital investment to install the correct equipment. Low capital-cost facilities and poor equipment choices can cost more in the long run, reducing financial viability and environmental benefits. For example, the right type of pump for the application, will save energy and generate more before it has to be replaced. To achieve the best efficiency and maximum lifetime, each process needs to be optimised: wastewater transfer, grit removal, and gas handling equipment.
For example, wastewater sludge typically has high solids and high wear components which require the use of specialist pumps. General pumps for clean water or single-source crop pulp, whether Centrifugal or Progressive screw pumps, can fail quickly in the wrong situation and can be expensive to repair. Due to the unpredictability of mixed waste streams, recycling and waste companies favour equipment built for their niche, such as LSM industrial peristaltic pumps, SlurryPro centrifugal or Toro progressive cavity pumps which are better able to handle abrasive, high solids bearing fluids.
2. Health and Safety Regulations
Health and safety must be taken into consideration – not only does AD require specialist knowledge, but it also involves ensuring the safe handling of explosive gases. It’s important that anyone who installs or works on AD systems is appropriately trained and complies with regulations.
Digesters need periodic cleaning out to remove the buildup of non-organic solids such as grit and to service or repair internal mixers and pumps. Methods that remove the need for workers to enter these confined spaces are preferred.
3. Storage Capacity and Maintenance
AD can take weeks to months depending on the system and design which means substantial storage capacity may be required. The bacteria involved also need to be kept in specific temperature ranges which can be harder to maintain in colder climates.
Measuring probes connected to remote data analysis and control software such as Senteos are important in maximising throughput and the beneficial returns of energy and nutrients.
Here at Atlantic Pumps, we are specialists in pumping abrasive and aggressive fluids, get in touch with us today for more information.
