Cleaner Technology Projects in Denmark 1997
Processing of Waste Products from Biological Gas Plants
Forædling af restprodukter fra biogasanlæg
Arbejdsrapport nr. 63, 1997, Miljøstyrelsen
With reference to an evaluation of the possibilities for establishing a biological gas plant in Copenhagen the report includes quality demands with regards to the bio-products that result from the treatment of organic household waste in the biological gas plant. The demands are set with reference to work report no. 32 from the Environment Agency "Depositing of compost and biological gas in refuse collection. A preliminary study of the market conditions."
Further focus is put on the possibilities of adjusting the bio-products according to potential receivers wishes and needs. Environmental and economical evaluations are also made of the conditions surrounding production and depositing of processed bio-products.
The primary products from the biological gas plant, as predicted they will be in Copenhagen are:
 | Degassed biomass |
| Liquid manure |
| Scrubber liquid |
These products are preferably deposited either directly or as processed products. The products are evaluated on their chemical and the physical properties and can be compared with products on the market.
The chemical composition of degassed biomass can be compared to a mixture of pig slurry and cattle dung. The potassium contents are though only a fourth of that in slurry.
Liquid manure is best comparable with diluted pig manure.
With regards to the scrubber liquid the highest nutritional value is in the nitrogen that is bound as nitrate and the product is best comparable to Chilean nitrate.
The bio-products are subject to certain legal demands that are described in the Ministry of Environment’s departmental order on the use of waste products in farming. Besides the legal demands the purchaser of the products also has quality demands. The products are meant to be used as fertilisers, soil improvement or growth media so they can replace or supplement the use of imported fertilisers and sphagnum.
Based on a questionnaire amongst 100 potential purchasers – gardeners, municipalities, farms, garden centres and forestry – the estimated use of different types of natural manure is calculated at almost 20.000 tons per annum. In order to receive the bio-products the receivers demand a possibility to assess the properties and the manorial value. This can be solved by making a targeted declaration of the products, which in general must describe whether the product is user-friendly, well convertible and competitive with regards to price, heavy metal contents and contents of human infection seeds. The demands are again dependent on where the products are going to be used. As a common demand it is demanded that the bio-products observe the limits on harmful substances as decided in the Environmental Control’s departmental order nr. 823 of the 16th of September 1996.
The bio-products are not at first suitable for what they are needed for, therefore it can in certain circumstances be advantageous to treat the end products so they are adjusted to the user’s needs. Amongst other things it might be necessary to dry the solid fraction since many users demand that the product must be user friendly (i.e. dry). With regards to the liquid manure it might be necessary to add further nutrients in order to obtain a positive market value.
In order to fulfil the consumers’ demands it will be necessary to establish some kind of own-control combined with a tightened industry control. This could lead to the establishment of an Industry Secretariat that could be built up according to the already existing rules from the State. An important part of this solution would be determining parameters, analysis methods and testing frequency as success criteria.
The bio-products are covered by three departmental orders: the manure order, slurry order and the Plant Directorate’s supervision order. The former demands that the products are reported to the Plant Directorate for approval and whether the labelling is in agreement with the order. The slurry order makes demands on the frequency of testing and analysis. In addition, demands are given for what information must be included in the labelling of a product.
Calculations show that post-treatment of the bio-products can increase earnings by 170-180 DKr. Per ton waste compared to the prices that are calculated in the original proposal for the biogas plant in Copenhagen. This income increase corresponds to approx. 11%. The calculations are based on a model where the depositing of the different bio-products is estimated in relation to the expectations of a future market.
The calculations further show that there is the largest economical advantage in the production and sales of processed waste products if these can be disposed of. Whether it is possible to dispose of processed waste products form a biogas plant cannot be determined before the products are on the market.
It is therefore still an open question whether processed surplus products from waste treatment can be disposed of on the market at the same prices as can be obtained for equivalent products produced by new raw materials.
Author/ institution
Biogas Copenhagen
This report is subsidised by the National Council for Recycling and Cleaner Technology
ISSN no. 0908-9195
ISBN no. 87-7810-877-2