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Rapport2004Öppen tillgång

Kompostering av avloppsslam för produktion av anläggningsjord

Fahlander, Denise


Composting could be an environmentally acceptable alternative to take care of the sewage sludge that is generated at Swedish sewage treatment works. The sludge contains metais, pathogens and more or less known chemicals from the society. There are no weIl developed methods to take care of the residual sewage sludge. Earlier landfilling was an alternative to take care of the problem, but after the year 2004 it will not be allowed to deposit organic compounds. This study comprises three practical parts to evaluate the composting of sewage sludge performed by Gästrike Avfallshantering at the site Forsbacka Avfallsanläggning. Experimental composts were made to evaluate the method used by the company (Experiment 1), the compost residue was analyzed for heavy metals and degree of maturity (Experiment 2), the third experiment (Experiment 3) was a greenhouse experiment were the compost residue of Gästrike Avfallshantering made up the organic fraction of two different plant substrates. The degradation of the organic material was slow in the experimental composts, primarily because of the bad proportions of the starting feedstocks, which led to poor carbon content and weak structure of the compost mixtures (Experiment 1). The disadvantageous mixtures resulted in low microbiai activity (ineffective composting). The low temperatures in the experimental composts made one wonder if there were any actual composting processes going on. The low temperatures partly depended on the small sizes of the experimental composts (ca 6 tons) which were cooled off from the ambient air. Tough one of the experimental composts consisted of the same feedstock proportion as the mixture of Gästrike Avfallshantering, the results indicate that more carbon rich substrate and more bulk material, to improve the structure of the composts, should be added. To increase the oxygen content in the large piles at Forsbacka Avfallsanläggning the size of the compost piles should be reduced. Proposed alterations would be needed to achieve a good composting process, which involves e.g. sanitation, odor reduction and a faster turnover by the substrates. A good alternative feedstock is the fibrous material residue (from a carton mill) used in the experimental composts. The fibrous material probably contains lots of easily accessible carbon, and may weIl be used during the winter season to achieve effective composting. The compost residue of Gästrike Avfallshantering achieved the metal and maturity demand of certification "SPCR 120", although this certification does not include compost residue based on sewage sludge, but SPCR 120 was used because it was the regulation obtainable to compost residue (Experiment 2). The compost residue was similar to other compost residues irrespective of it being based on sewage sludge or other organic materials. The compost residue was rich in phosphorus and nitrogen. Nutrient content varied a lot between different places. The greenhouse experiment showed that mixed with mineral soil the compost residue was a very good growth substrate (Experiment 3). The plant growth was good and the metal content was acceptable, though copper and zinc content were relative1y high. During the greenhouse experiment, with two other plant soils, one of those soils had higher zinc content. The experiment indicated fairly well that the metal uptake in the crop depended on the metal content in the soil. The plants used in the experiment were red elover and rye grass. The zinc and copper contents in both species were evidently within normal values


avloppsslam; kompostering; tungmetaller; anläggningsjord

Publicerad i

Avdelningsmeddelande / Sveriges lantbruksuniversitet, Institutionen för markvetenskap, Avdelningen för lantbrukets hydroteknik
2004, nummer: 04:1Utgivare: Institutionen för markvetenskap, Avdelningen för lantbrukets hydroteknik, Sveriges lantbruksuniversitet

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    Miljö- och naturvårdsvetenskap

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