Drying sewage sludge is a major aspect of biosolids management. Several investigations were performed in a pilot-scale solar dryer for the subsequent development of design rules for solar dryers. The pilot dryer was operated outside simultaneously with a full-scale dryer and, later, in a building. Total solids in the sludge and climate data were analyzed and logged regularly during drying. The fecal coliform and ammonium content was measured as well. Operation next to the full-scale plant was intended to enable comparison of their evaporation rates. The pilot plant was operated in a building in order to assess the influence of external heat input on the drying process. The results showed constant drying progress and that drying was feasible. Although differences in evaporation rates arising from operation, aeration and scaling existed, evaporation rates comparable to full-scale dryers were observed. Under floor heating improved evaporation rates by 25%. More than 50% of total Kjeldahl nitrogen was degraded, and this could be detected as NH3 in the discharged air. Reduction in fecal coliforms could be achieved without reaching secure disinfection, as required by USEPA standard 503 (USEPA 2007).

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