Mini biodigesters are seeing a rise in popularity on dairy farms across Europe and North America, offering a comprehensive look at the benefits and options available.

Achieving a reduction in carbon emissions on dairy farms is a pressing objective, particularly to demonstrate to consumers the efforts made by dairy producers to mitigate global warming and ensure the sustainability of dairy products.

Biodigesters have emerged as the most efficient method for reducing methane emissions from cow manure, a significant contributor to atmospheric warming. (Another methane source from cattle is their burping.)

Not only do biodigesters significantly cut down methane emissions from manure, but they also produce heat for warming farm buildings and generate electricity by burning the cleaned methane (resulting in CO2 emissions from the farm’s manure, which is far less potent as a greenhouse gas compared to methane). Consequently, the farm saves on electricity expenses, aiding the digester’s cost recovery. Moreover, in some areas, it’s possible to sell surplus electricity back to the local power grid, creating an additional income source for farmers.

Due to the high costs and impracticality of traditional biodigesters for smaller farms, agricultural technology companies have developed smaller, more affordable versions called mini-digesters. These smaller systems are a cost-effective alternative, offering numerous benefits. Typically, they only necessitate a straightforward permit from local authorities, bypassing the extensive impact assessments required for their larger counterparts. Mini-digesters come fully assembled and can be installed rapidly, consisting of the digester unit and an integrated control system.

Unlike the full-sized biodigesters that may need additional off-farm feedstocks to support bacterial activity, mini-digesters operate solely on manure. This simplifies operations, with farmers typically spending around 10 minutes daily monitoring the system through an online control system interface.

Biolectric, a Belgian company, has successfully deployed 300 mini biodigesters, with the vast majority, 295, being installed across Europe and a few, 5, in North America. These installations predominantly serve dairy farms (285), while the remaining are utilized on pig farms and at select wastewater treatment facilities and small-scale food processing plants.

Klaas Vanhee, the commercial director at Biolectric, notes that five dairy farmers, who made purchases from 2011 to 2013, have invested in a second unit. Furthermore, over 15 farmers have upgraded their systems to accommodate the expansion of their farming operations. Biolectric also provides a leasing option for those uncertain about purchasing, along with maintenance contracts ensuring operational downtime remains below 10%.

HoSt, a Dutch company, has also ventured into the mini biodigester market. To date, 20 of their Microferm units are operational, with additional installations underway in the Netherlands and France, and one in Germany.

Mini biodigesters have found applications in developing countries as well, integrated into carbon credit initiatives. For instance, Biolectric’s systems are capable of preventing the release of 45 to 940 tonnes of CO2 annually, depending on the size of the mini biodigester.

For example, the international energy corporation Total Energies has committed to a decade-long carbon offset initiative in collaboration with the GoodPlanet Foundation, a leading CO2 offset organization globally. This commitment includes supporting the implementation of compact manure biodigesters in Telangana, India’s rural areas. Similarly, the worldwide energy company BP is sponsoring the BIRU manure biodigester initiative in Indonesia, which has already allowed over 100,000 individuals in 10 rural provinces to utilize biogas for cooking, heating, and generating electricity.

Furthermore, Sistema.bio, a biodigester company based in Mexico, predicts that 400 million small-scale farmers around the globe could leverage small-scale biodigesters to satisfy their household energy needs and produce biofertilizer. This approach not only fosters savings but also enhances crop yields and incomes.

Sistema.bio has documtented a case where a dairy farmer in India, owning approximately 200 cows, adopted a Sistema.bio biodigester (35 cubic meters) about two years ago. The biodigester supplies sufficient biogas for the farmer’s household needs, cooking in eight farm labourer homes, and for cattle feed processing as well as sporadic electricity production. The use of digestate as ‘biofertilizer’ from the system has led to reduced fertilizer expenses and improved crop yields for the farmer, who is now also engaged in selling the biofertilizer.

Biolectric presents a lineup of seven mini biodigester models, ranging in capacity from 9.7 kW to 74 kW. The smallest model requires a minimum of 1,500 cubic meters of slurry annually (equivalent to the output from 80 cows) and around 200 square meters of installation space. This system is designed to transfer a consistent volume of manure from the reactor to the digestate storage daily, while also incorporating fresh manure from the livestock pens. Through the MyBiolectric application, farmers can monitor the amount of electricity generated in real-time and receive suggestions for enhancing the efficiency of their biodigester.

The price for these systems varies between €125,000 and €500,000. According to Vanhee, the timeframe for investment recovery ranges from three to ten years, depending on the specific requirements and additional investments of the farm, as well as the country of operation. He notes that many European countries offer investment grants covering up to 40% of the expenses, along with ‘feed-in-tariff’ programs for the generated electricity and heat, with similar incentives available in North America.

Tamarah Swensen, the marketing communications manager at HoSt, recommends the Microferm model for dairy operations with a minimum of 250 cows, producing at least 7,500 cubic meters of manure. She highlights the Microferm+, an enhanced version capable of handling a broader range of feedstock beyond just manure. This model can process between 5,000 and 10,000 tonnes of various materials annually, including manure, maize silage, grass clippings, and organic waste, generating enough biogas to meet the cooking and heating needs of approximately 360 European households each year.

Regarding alternative mini biodigesters available, PlanET Biogas, a company based in Germany, produces the Valentin model, which ranges from 75 to 150 kW depending on the type of material processed. Another German firm, ATT, offers a compact digester suitable for herds of 100 to 400 cows. In the UK, SEaB Energy has developed the Muckbuster, a system that arrives in several standard-sized shipping containers and can be up and running in approximately two weeks.

Qube Renewables, also from the UK, provides the BioQUBE, a versatile mini biodigester that can be customized for individual sites, supporting the operation of multiple digesters from a single feed system. This includes capabilities for biogas storage, energy production, and the pasteurization of digestate. Additionally, it can work alongside the company’s LagoonQUBE, a floating digester designed for manure lagoons, with each modular, hexagonal unit spanning 94 square meters.

In 2020, the Microferm model was installed in Blokzijl, located in the eastern Netherlands, as a component of the third cooperative Jumpstart initiative, with HoSt’s involvement dating back to 2018. Jumpstart, an effort by the dairy cooperative FrieslandCampina, aims to promote the use of manure digesters among farmers.

SEaB Energy, the company behind Muckbuster, collaborates with the Berkeley – Andhra Smart Village project, a joint venture between the Andhra Pradesh government in India and the University of California, Berkeley.

The BioQUBE, designed to pair with the company’s LagoonQUBE — a floating digester in manure lagoons, showcases the versatility of these technologies in enhancing farm sustainability.

Biolectric partners with major agricultural cooperatives, including ALCCP, Sodiaal, and FrieslandCampina, reflecting its commitment to sustainability. The University of Cambridge selected Biolectric to outfit their Park Farm, which houses approximately 200 dairy cows. In September 2021, Park Farm was the venue for the Farming for Clean Air event, featuring the T6.180 Methane Power tractor from New Holland, powered by methane produced from the farm’s biodigester.

Furthermore, in 2018, Biolectric expanded its product line to include the Nitrogen Stripping Unit. This additional module allows farmers to extract nitrogen from the digestate to create an on-site fertilizer, offering an alternative to the highly energy-intensive synthetic fertilizers. Priced at €150,000, this innovation presents a sustainable fertilization solution.

How Biodigesters Operate:

·        A biodigester consists of an airtight, well-insulated container equipped with a stirring mechanism.

·        This container is continuously fed with fresh, liquid manure.

·        Automatic mixing ensures the temperature is maintained at around 40°C, keeping the anaerobic bacteria within active and effective.

·        Throughout the digestion process, these bacteria not only break down the manure but also neutralize any seeds of weeds present.

·        Methane gas, a byproduct of this bacterial activity, is captured, cleaned of sulfur impurities, and then directed to a generator.

·        This methane is combusted to generate electricity. This electricity is utilized on the farm, and surplus power may be sold to the local power network in certain areas.

·        Additionally, the warmth generated by the digester can be harnessed to provide heating for farm buildings and other needs.

·        The liquid byproduct of digestion, known as digestate, can be systematically removed and applied to agricultural fields as a nutrient-rich fertilizer and soil enhancer.

·        When dried, this digestate serves as an economical bedding material for cattle, further reducing farm expenses.