Optimerad hygienisering vid kompostering av avloppsslam

Abstract: The aim of this study was to in laboratory experiments investigate how addition of urea, ECOX and structural materials can optimize sanitization during composting of sewage sludge. Today we strive for a sustainable society and the importance of closing the nutrient loop increases. It has therefore become even more important to safely reuse plant nutrients from human excreta to agricultural land. Partly because it increases the sustainability of society as the world's supply of many nutrients are finite, partly because it promotes human health, both by reducing disease transmission and by increasing Agricultural production. An untapped resource such as sewage sludge that is rich in nutrients and humus-forming materials could replace parts of the commercial fertilizers used in Sweden today. owever, sewage sludge contains undesirable substances such as heavy metals and drug residues, and pathogenic microorganisms. Sewage sludge must therefore be sanitized to ensure a safe reuse of the plant nutrients. The most common sanitizing treatments used today include pasteurization, composting and additions of lime. Since these methods may be difficult to implement because of economic or environmental reasons, new methods of sanitation are developing today. A relatively new method developed at the Swedish University of Agricultural Sciences is ammonia treatment. Previous studies have shown that an effective reduction of microorganisms was obtained with ammonia treatment and that the effect from the ammonia increases with an increased temperature. At higher pH the major part of the ammonia is in its uncharged form, NH3, which is harmful for most biological organisms. At a lower pH, in contrast, the ammonia is in its charged state, NH4+, which is readily available as plant nutrient. Urea is a common fertilizer and when it is added to the sludge it breaks down into ammonia and carbonates by means of the enzyme urease. The sewage sludge was composted in two periods in this study. Various combinations of ECOX, urea and structural material were added to the sewage sludge in an attempt to find an optimal sanitization method. Samples were analyzed on day 0,2,6,10,16 and 20. The most effective reduction of microorganisms was obtained for the treatments that included ECOX, urea and structural materials, where a reduction of 6 log10 for thermo tolerant coliform bacteria was obtained after 2 days. The study also shows that the highest composting temperatures were obtained for the combinations that included ECOX. The combination of ECOX and urea was also found to provide a high pH