ORGANIC MATTER, NITROGEN, AND PHOSPHORUS CONTENT IN SLUDGE DEWATERED BY NATURAL METHODS / Innehåll av organiskt material, kväve och fosfor i slam avvattnat med naturnära metoder
The objectives of this study were to investigate the possible effects of freeze/thaw-drying and drying as sludge dewatering methods on the organic matter, nitrogen, and phosphorus content in the sludge. The research work was carried out on three different levels. The effect of natural sludge dewatering on the overall status of the sludge was mainly investigated in a full-scale natural sludge dewatering pilot plant in northern Sweden. A pilot-scale sludge dewatering unit, consisting of bags in steel racks, was installed at the treatment plant and utilized for experiments for this evaluation. Laboratory experiments utilizing small boxes for sludge freezing and drying were also employed in the evaluation process. A significant degradation of organic matter was found to occur during the summer both in the full-scale unit and in the pilot-scale bags. The most important factors for a degradation of organic matter to occur seemed to be the complete freezing/thawing of the sludge, air contact, and time. Estimation of the loss of N and P through drainage water analyses from the full-scale pilot plant, and through laboratory experiments suggested that P losses would be negligible and N losses due to drainage would be 6-13 %.