Critical considerations for anaerobic digestion projects
In the field of industrial wastewater treatment, anaerobic digestion is a powerful process that transforms waste into valuable by-products. Most notably, it produces renewable energy in the form of biogas, which can be used to fuel operations, cogenerate electricity, or even be sold. Another valuable by-product of the process is digestate, which can be used in agricultural and horticultural applications, as well as a foundation for bioplastics and other products.
However, several common assumptions about waste-to-energy processes can lead to misunderstandings and inefficiencies. Before investing in an anaerobic digester, it’s important to explore and debunk some of these assumptions, both pro and con.
Assumption #1: All Digesters Are Huge
One misconception is that all digesters are large and require a lot of space. In reality, digesters come in various sizes and configurations. There are compact models designed for small-scale operations, urban settings, or even individual industrial facilities. The size of the digester should be matched to the specific waste type, treatment needs, and constraints of the project.
Assumption #2: All Digesters Are Expensive
There’s a common belief that all digesters are prohibitively expensive. While some systems can be costly, there are options available that cater to a wide range of scales and budgets. Small-scale digesters can be quite affordable and still provide significant benefits, making anaerobic digestion accessible to a wider range of projects. Most point-source digesters for industrial operations carry lower ROI than larger regional digesters-cogenerators with larger infrastructure.
Assumption #3: Project Infrastructure Can Be Copy-Pasted
The idea that project infrastructure can be replicated exactly from one site to another is a misconception. Rarely are two projects the same. Site conditions, regulations, and other factors almost always result in process differences. These can include tank designs and hydraulic retention times, as well as variations in dewatering processes and pollutant-removal methods. While previous projects can serve as valuable starting points, they cannot be replicated exactly. Customizing infrastructure to suit these variables is essential for the success of a project.
Assumption #4: Costs Are Linear With Volume
It’s often assumed that costs scale linearly with the volume of digestate produced. However, economies of scale, operational efficiencies, and logistical considerations can all impact the cost structure, with both very small and very large facilities skewing the numbers. Additionally, the strength of the digestate can drive costs, as h3er digestate may require more intensive treatment. Larger volumes may reduce per-unit costs, but they can also introduce complexities that must be managed carefully.
Assumption #5: Digestate Quality Is the Same Within Industries
Another common assumption is that all digestate is of uniform quality. In reality, digestate quality can vary significantly, even within the same industry. Factors such as feedstock combinations, logistics, regulations, and process configuration can lead to differences. Another factor is location: Some facilities are located in remote areas, while others operate under different regulatory standards. Quality control is crucial to ensure that the digestate meets the standards required for its intended use, whether as a fertilizer, soil conditioner, or for other applications.
Assumption #6: Digestate Can Be Sold or Given Away
Many believe that digestate, whether from point-source industrial operations or post-consumer/cogeneration regional facilities, can easily be sold or given away. While this is true in some cases, it may require significant effort to find buyers or recipients who can use it effectively. The market for digestate may be limited, and regulatory requirements may restrict its distribution. Additionally, the physical movement of liquid or solid digestate fractions can be costly, and raw digestate often cannot be discharged directly. It typically requires a solid and liquid separation phase, such as dewatering or a more complex treatment, to make it suitable for use or disposal. It’s essential to have a clear plan for digestate management from the outset of a project.
Assumption #7: Digestate Can Be Sent to POTW
Because hauling digestate off-site can be very expensive, sending digestate to a publicly owned treatment works (POTW) is sometimes seen as a preferable disposal method. However, most municipalities don’t allow the release of digestate into sewers because of the risk of clogging the system. Per gallon, digestate can carry 10 to 50 times the load of municipal wastewater. In other words, adding digestate to an existing POTW will overwhelm most municipal treatment works. When municipalities do accept the load, there will likely be a substantial surcharge. It’s important to verify the capabilities and requirements of the local POTW before planning to use this option.
Experts in Waste-to-Energy
Anaerobic digestion projects can be both beneficial and complicated. Fluence is a top provider of waste-to-energy solutions. Before embarking on a project, contact Fluence to learn how we can deliver up-to-date solutions tailored to your exact requirements.
