In recent times, biodigesters have surged in popularity. Take Germany, for example, where it’s commonplace to find multiple biodigesters operating on farms. Traditional biogas facilities are quite large, necessitating significant investment and space. As such, smaller-scale biodigesters present a viable alternative.
These devices are heralded as the most efficient method for reducing methane emissions from pig farming operations, addressing methane’s role as a potent greenhouse gas. Within these systems, methane produced by bacteria breaking down manure is captured. This methane is then purified and combusted to produce heat for buildings on the farm and generate electricity. While this process does release carbon dioxide—a less potent greenhouse gas compared to methane—it represents a net environmental benefit. Furthermore, certain regions permit farmers to sell surplus electricity back to the grid, thereby generating additional income. Utilizing biodigesters for manure management also significantly diminishes the odour compared to traditional methods such as manure lagoons or direct field application.
However, the cost and space requirements of conventional biodigesters limit their feasibility for smaller farms. To address this, companies like Biolectric and HoSt have introduced compact models. These “mini” digesters are much more affordable and offer several benefits, such as simplified permitting processes, pre-assembly for quick installation, and operation solely on manure without the need for additional feedstock.
The design incorporates a digester linked to an automated control system that manages the daily transfer of manure from the reactor to storage, while also integrating fresh manure.
Adoption and impact
Biolectric, based in Belgium, appears to lead in the deployment of mini biodigesters on pig farms, with over 300 units primarily in Europe and some in North America—mostly on dairy farms. According to Jules Dobbels of Biolectric, a small number are installed on pig farms, utilizing either exclusively pig manure or a mix of pig and dairy manure. Plans are underway for additional pig manure-only installations.
The MyBiolectric app allows farmers to monitor electricity production and make adjustments for improved efficiency, requiring minimal daily management time.
Operational insights
In Poland, Biolectric’s distributor Naturalna Energia has installed 45 minis, with a portion on pig farms. The challenge of African Swine Fever outbreaks has impeded further installations. Pig slurry presents specific challenges for the digestion process, which Biolectric addresses through additional mixing and, sometimes, the introduction of micro-elements to boost bacterial activity. Adjustments to accommodate the lower dry matter content of pig manure include larger silos, ensuring adequate daily processing volumes.
The 44kW mini model requires a significant amount of slurry, with specific requirements based on the type of farm. Successful installations in Poland demonstrate the system’s viability, with a return on investment achievable within eight years without subsidies. Adam Orzech (Naturalna’s technical marketing leader) notes that the 44kW size mini needs a minimum of 30 m3/day porker slurry or a minimum of 40m3/day of slurry from sows and gilts. Orzech says, “Based on this feeding, the first mini-installation on a Polish pig farm produced 355 000kWhe/year and the second 312 000kWhe/year.”
Required livestock numbers
Collaboration with university extension services has helped define the livestock numbers necessary to support a 44kW mini biodigester:
Finisher pig farms: between 4,000 and 5,600 pigs;
Sow farms: 700 to 900; and
Closed cycle farms: 400 to 500 cows.
Prospective investors undergo a preliminary slurry test to estimate the potential biogas yield and system size. Beyond energy production and financial returns, converting slurry to digestate benefits soil health and reduces the need for chemical fertilizers. Despite the small number of pig farm installations, Biolectric is optimistic about future potential and plans to increase efforts in this sector.
