Feasibility of Using the Dried Sludge by Municipal Wastewater Treatment with Activated Sludge Process

Using the sludge as fertilizer on farms is one of the options to dispose it, which due to its variety of pathogenic microorganisms, it may cause a wide range of bacterial and parasitic diseases in human and livestock. The purpose of this study is to investigate the feasibility of using dried sludge produced in municipal wastewater treatment processes to fertilize agricultural lands in accordance to the health and environmental standards.

In this analytical-descriptive study, three sewage treatment plants of Chahar Mahal and bakhtiary province were selected as the sample plant, including Shahrekord, Farsan and Borujen due to their similarity in the weather condition and the treatment process. In order to investigate the sludge in its lowest and the highest rate of evaporation, in the freezing cold winter and burning hot summer respectively, two winters and two summers were selected as the timeframe. In this study, faecal coliform and total coliform were determined as the sludge microbial indexes and examined in accordance to the EPA standards.

The findings of this study indicated that the mean value of faecal coliform for the three treatment plants in winter were 1.63 × 106, 1.93 × 106 and 1.98 × 106 respectively. Also in summer they were 4.51 × 106, 5.75 × 106 and 9.23 × 106 respectively.

The evaluations of this study indicated that the biological sludge generated from the three treatment plants in the winter after drying off naturally were located in class B of the EPA standards. Thus, based on recommendations of the organization, such sludge can be used with regards to standard restrictions for agricultural purposes. However, the microbiological quality of the sludge in summer was lower than the U.S. EPA standards for Class B sludge, and thus is not applicable in agricultural use.