Sludge Liming Decreases the Growth of Keratinolytic and Keratinophilic Fungi

Due to the content of pathogenic organisms, including fungi, sewage sludge land application poses risks to both human health and the environment. One of the ways for reducing pathogens in sludge is liming. This study aims to determine the effect of sludge liming on the composition of keratinolytic and keratinophilic fungi in model experiments. The fungi were examined using the hair baiting method and the dilution method with incubation on a Wiegand medium supplemented with chloramphenicol (100 mg/L) and actidione (500 mg/L). The sludge liming considerably decreased the number of actidione-resistant fungi propagules and eliminated many fungal species, including Pseudallescheria boydii. The influence of this process on hair-baited fungi was that the liming eliminated keratinolytic and keratinophilic fungi at 37oC. In the range of 23-33oC, the liming considerably restricted the growth of keratinolytic fungi, including Microsporum gypseum, but only slightly affected keratinophilic fungi, including Pseudallescheria boydii. The sludge liming decreases the risk posed by geophilic dermatophytes and other keratinolytic fungi, as well as by keratinophilic fungi to humans and the environment. The process affected more keratinolytic fungi than keratinophilic ones.