Converting Biowaste into a Tax-Free Fuel

From late 2012, Swedish waste utility Västblekinge Miljö AB based in Mörrum, southern Sweden, will turn some 20,000 tons of regional biowaste per year into 1,500 tons of fuel. To make this possible, the company is converting its existing composting plant. The new facility, designed by Eisenmann (Germany) and combining a composter with a biogas plant, will enable all types of biowaste to be recycled.

Eisenmann tailored the plant to meet all of the customer’s needs while complying with local statutory requirements, particularly health and safety regulations. The turnkey plant’s design encompasses everything from pretreatment of the biowaste to final storage of the digestate. The biogas is produced by fermentation, then concentrated to biomethane in a biogas upgrading plant. The gas, compressed and filled in cylinders, is sold at filling stations as an eco-friendly alternative fuel for passenger cars and commercial vehicles.
Every component used in the facility was originally designed and engineered for industrial-scale plants, ensuring outstanding reliability and process stability. At the heart of the installation are two horizontal plug-flow digesters, each with a capacity of 800 cubic meters.

The heat-insulated digesters are made of precast reinforced concrete and equipped with specialised horizontal agitators. This means the facility is ideal for processing biowaste with a high solids content. At a temperature of 55 degrees Celsius, the system almost completely digests the feedstock within 25 to 30 days, destroying potentially harmful pathogens in the process.

The second process step is the separation of the digestate’s solid and liquid fractions in a separator. The dewatered solids are then processed in the composter. This approach leads to significantly lower emissions than composting untreated biowaste. The liquid digestates have proven to be an ecologically viable alternative to chemical fertilizers in agriculture.

In Sweden, fuel produced from biogas is tax-free. Biogas upgrading is also a worthwhile option for businesses based in Germany, where there are subsidies for injecting biomethane into the natural gas grid, and for the direct marketing of electricity generated from biogas or biomethane.

Eisenmann, an industrial solutions specialist with decades of experience, has constructed more than eighty biogas plants throughout Europe. Within this field, the Böblingen-based company specialises in anaerobic digestion technology for feedstocks with high solids content.