Toxicity assessment of sewage sludge from municipal sewage treatment plants

Abstract

The aim of this study was to assess the toxicity of sewage sludge from the municipal sewage treatment plant in Bialystok. Raw sewage, sewage sludge from the primary settling tank, activated sludge, sludge before the fermentation chamber, recirculated sludge and sewage sludge after fermentation and dehydration on press were tested. The Microtox Model 500 kit using Aliivibrio fischeri luminescent bacteria was used for the toxicity analyzes. The EC50 index (indicating the concentration of toxic substances resulting in a 50% reduction in the intensity of luminescence of the bacterial strains used) converted into the TUa toxicity units was adopted as the value describing the toxicity of the tested media. The obtained results showed high and very high ecotoxicity of raw sewage and sewage sludge from the primary settling tank, sludge in front of the fermentation chamber and after fermentation and dehydration in the press. The use of tests determining the toxicity of sewage flowing into the sewage treatment plant and sewage sludge generated at various stages of the treatment process allows to detect the danger associated with the uncontrolled discharge of toxic substances into the sewage system.