Nevertheless, the amount of biogas plants and wastewater treatment plants continues to grow, and
therefore, this problem urgentl7y needs to be solved. Also, to find solutions to the organic waste handling
is usually crucial for the biogas and wastewater treatment plants and significant parts of the total
economic profit may rely on sales of the organic waste product. At the same time, due to reduced animal
stocks, most farmers need organic fertilizers for their agricultural soils in order to compensate for lack of
farm manure.
Studies of long-term effects of organic wastes are still lacking in research publications. Hence, the
objective of this study was to fill a gap in knowledge regarding long-term effects of amending soil with
residue from biogas production and waste water treatment. In this paper, the results from a 16-year long
field experiment are presented. A field experiment was established in central Sweden where agricultural
soil was continuously fertilized with biogas residues and sewage sludge for a period of total 16 years. The
effects on soil and crop quality (positive as well as adverse) was evaluated.