Determination of Fungi Species Variety in Thermal Phases of Compost Production and Related Operational Parameters

Compost is a self-heating process in which organic matters are stabilized by microorganisms. Fungi are one of the suitable indicators of compost stabilization, but many parameters affect their growth. The aim of this paper was to determine the correlation between fungal density and some operational parameters during the composting process. We quantified taxonomic composition of the fungi in the compost. Compost mass was divided into four thermal phases and sampled over 100 days. Sabouraud dextrose agar medium was used for growth colonies. The samples were incubated at 37°C (thermotolerant) and 45°C (thermophilic) for 3–7 days. The colonies were counted and identified by slide culture methods. Then, the correlation between fungal communities and physicochemical parameters was determined by Pearson’s test. Data were analyzed with Excel 2007 and SPSS 19. The density of thermotolerant and thermophilic fungi were $0.5\times {10}^6$ and $0.25\times {10}^6$ colony-forming unit/gram (CFU/g), respectively. However, there was an adequate linear correlation between the thermophilic fungal density and temperature ($r=0.456$, $p<0.001$) and thermophilic fungal density and pH ($r=-0.5$, $p<0.001$), and there was not a significant correlation between thermophilic fungal density and moisture ($r=0.2$, $p=0.12$) or fungal density and heavy metals ($p>0.05$). Moreover, the strength of correlation between pH or moisture with fungal density was lower than that of temperature. Although there was no significant correlation between the density of fungi and concentration of heavy metals, only species resistant to heavy metals (i.e., A. fumigatus and Paecilomyces) were isolated. With regard to the results of this paper, thermophilic fungal communities were correlated to operational parameters such as temperature and pH. Only the effects of temperature and pH were significant.