National Activities - Finland Utilisation of anaerobic techniques in Finland

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Biological Conversion : National Activities - Finland

Utilisation of anaerobic techniques in Finland.

Introduction
In 1996 a decision was made to create a register of Finnish biogas (anaerobic digestion) plants as a result of which a comprehensive survey of these, other related installations and landfill gas utilisation schemes was carried out in 1997. The survey was based on direct interviews and inquiries. Finland was the first among the Nordic countries to adopt anaerobic techniques, when in the early 1930s the city of Helsinki began to process its sewage sludge by such means. The fuel value of biogas was discovered in Europe during WWII, but interest lagged after the war due to cheap oil. Interest in anaerobic processing increased again with the oil crisis in 1973.

Summary of results

There are 19 biogas plants in Finland: 14 for sewage sludge, 1 for municipal biowastes and sewage sludge, and 4 for industrial wastewaters and biosludges. Seventy per cent of all sewage sludge in Finland is stabilized, and 60% of the stabilized sewage sludge in the larger cities is stabilized anaerobically. Hence, about 50% of all sewage sludge is stabilized anaerobically. The total biogas energy production in 1996 was 189.5 GWh: from sewage sludge 115 GWh, from industrial wastes 15.2 GWh and from other installations 6.3 GWh. In addition about 53 GWh of landfill gas was collected.

Sludge digestion

The total accumulation of municipal sewage sludge is around 165,000 tonnes dry solids equivalent per annum. Most of Finland's anaerobic plants for treatment of municipal sewage sludge were built in the 1970's and 1980's. By the end of 1996 thirteen cities were operating a total of 15 treatment plants totalling 25 mesophilic anaerobic reactors, producing almost 23 million cubic metres of biogas with an average content of around 65% methane per annum from around 100,000 cum of reactor volume. However, there is no standardisation of municipal water treatment plants, all of which are unique. Only two localities (Helsinki and Vaasa) produce electricity, where as most produce processed heat.

Municipal solid waste

Estimates of the amount of MSW produced vary. The Ministry of Environment estimates at 693 000 tonnes per year. The accumulation of organic waste has been estimated at around 40 kg per capita per annum in Helsinki, but higher in some other towns. The realistic accumulation in Finland, with 5 million inhabitants, is probably in the order of 2 to 3 hundred thousand tonnes, or around 60,000 to 90,000 tonnes dry weight.

At present the organic fraction of MSW is treated anaerobically at only one locations (Stormossen, near the city of Vaasa) where about 22,000 tonnes of pre-sorted waste treated further to produce about 12,000 tonnes of refuse derived fuel (RDF) and an organic fraction of around 10,000 tonnes which goes to digestion. The thermophilic digester used generates around 140 cu.m. of biogas per tonne of such waste, which is about twice the average yield from sewage sludge. Hence, at around 50-75% collection efficiency, municipal solid waste could generate about twice as much biogas energy (230 GWh) as is presently generated from sewage sludge.

The basic and applied R & D work for the Vaasa biogas reactor represents the most intense effort in the area of anaerobic techniques to date. The process developed, the Waasal-Wabio process for solid municipal wastes, is being utilized not only at Stormossen but also in Germany and the United States. In addition to these countries, Finnish anaerobic techniques for large-scale plants (processing also sewage sludge and other matrices have been exported to Poland, England, Sweden, the Far-East, South Korea, China and India.

Anaerobic utilization of industrial wastewaters and wastewater sludges More research needs to be done on the use of anaerobic techniques in the pulp and paper industry. Today, biosludges and wastewaters are treated anaerobically only at two pulp and paper mills and two food industry plants, with a total of around 15,000 cu.m. giving around 3 million cu.m. gas per annum, but with a higher methane content at around 80%.
Anaerobic utilization of agricultural wastes The total amount of agricultural waste accumulated in Finland is around 20 million (wet) tonnes, of which cattle dung comprises 8 million (wet) tonnes. Agricultural waste is thus of great potential for energy utilization. However, only 2 farms currently digest such waste, although two projects for constructing plants under joint ownership are under discussion. One reason why anaerobic techniques are little used for the treatment of agricultural sludge of manure in Finland may be that they have been tried out in small self-made biogasification plants. Development has relied heavily on individual effort, and when no government funding was forthcoming the incentive was lost.

Landfill gas collection Five landfill schemes were operating in 1996: Domargard (Porvoo), Kiertokapula (Hyvinkaa), Seutula (Vantaa), Vuosaari (Helsinki) and Ammassuo (Espoo). Three further installations have since been constructed and one is under construction. In 1996 the biogas collection was 11.98 million cum, but of this 5.28 million cu.m. were burned to flare. The total biogas production capacity of Finnish landfills is estimated to be 300 million cu.m., but in 1996 only 4% of the capacity was being utilized.

Energy aspects The total fuel oil equivalent of the Finnish biogas reactor and landfill gas installations in 1996 was 24,800 tonnes. The amount burned to flare at landfill installations in 1996 corresponded to 3433 tonnes of light fuel oil. With so much gas wasted in flare burning, the utilization efficiency of the produced biogas energy is thus rather low. Effective utilization of the energy content of the biogas is only part of the net energy gain achievable with the process, however. As treatment techniques for wastes and wastewaters, anaerobic techniques could replace aerobic techniques, which consume energy.

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Contact

• Kari HANNINEN / University of Jyvaskyla Dpt of Biological & Environmental Sci / FINLAND