The human body is only capable to take care of a fraction of the pharmaceutical compounds a person eats and the rest is excreted, mainly by urine. When the sewage water reaches the wastewater treatment plant it is treated mechanically, chemically and biologically but the wastewater treatment plants are not designed to take care of pharmaceutical residues or organic compounds from detergents, paint, etc. Based on the chemical and physical properties of the compound it will either leave the plant with the discharge water or end up in the sewage sludge. The sludge is stabilized through anaerobic digestion, dewatered and may then be used as agricultural fertilizer.
This study examines if composting of sewage sludge together with other organic matter can improve the sludge by resulting in less odor, high nutrient content and reduced incidence of pharmaceutical residues and undesired organic compounds.
Three different kinds of organic matter were tested; horse manure, deep litter manure from cattle and garden compost. Also, three different methods for oxygenation were used and evaluated. In the first method drainage tubes buried in the compost was attached to a fan. The second method also included the drainage tubes but instead of using a fan the air flowed through the tubes by natural ventilation. In the third method the compost was mixed by an excavator.
From regular measurement of the temperature in the composts it was decided which method that generated the highest microbial activity. Before, half-way through and after composting, analyses were performed regarding nutrients and metals to see how the composition of the matter changed during the process of composting and to decide whether the products could be considered as good fertilizers.
In the compost with the highest microbial activity analyses of pharmaceutical residues and undesired organic compounds were performed as well and compared with a reference consisting only sewage sludge that had not been treated in any way to increase oxygenation.
Interviews with farmers and project staff showed that the mixed product was not odor-free but it did not smell as bad and strong as pure sludge that had been stored for an equal amount of time.
Analyses of nutrients and metals showed that the mixed products are good fertilizers and their content of metals are below the limit for metals in fertilizers. Horse manure and deep litter manure from cattle gave the best results.
Mixing of the compost with an excavator generated highest temperatures and was the method preferred by the farmers since it was easier to handle the compost when it did not have tubes in it and also the choice of location is free when the operation doesn't depend on access to electricity.
Analyses of undesired organic compounds showed that the degradation of phtalates, LAS, organophosphates, triclosan and alkyphenol/alkylphenoletoxylate were bigger in the compost consisting a mix of sludge and deep litter manure from cattle and which was oxygenated by mixing of the matter compared with the reference compost. To verify the result the examination has to be repeated multiple times.
Further investigations must be performed on the degradation of pharmaceutical residues. The degradation was bigger in the mixed compost for a majority of the analyzed substances but in several cases the result was the opposite and in some cases the total amount of the substance increased during composting. The latter is due to the fact that only the primary form of the substances were analyzed and not their metabolites. If a large part of the substance was in the form of a metabolite before composting and transformed back to the primary form during composting it may have looked like there was an increase in the total amount of that substance. For the same reason it is impossible to decide whether a decrease is due to decomposition of the substance or if it is due to formation of metabolites.