Investigation of Some Qualitative Characteristics of Sludge Produced in Hamadan Wastewater Treatment Plant and Its Application in Agricultural Lands

Sludge of municipal wastewater treatment plant contains considerable amounts of environmental pollutants and can be dangerous for humans and the environment if it cannot be managed properly. Therefore, the purpose of this study is to investigate the physical, chemical, biological characteristics and the levels of heavy metals in the sludge of municipal wastewater treatment plant and the feasibility of its use in agriculture in Hamadan city, Iran. In this study, the samples were collected from primary and secondary sludge in three seasons, i.e., fall, winter and summer. The results of this study have been compared with U.S.EPA standard (40 CFR Part 503) related to the application of sludge in agricultural lands. The results of this study showed that the ratio of VS / TS for raw sludge was 0.8, 0.55 and 0.55 in the fall, winter and summer, while this ratio for the secondary sludge was 0.65, 0.28, and 0.32 in the mentioned seasons, respectively. The average pH for the primary sludge was 5.73 and its value for secondary sludge was 5.82. The average concentration of parameters including COD, TKN, SOUR, Na, Ca in the primary sludge was measured to be 51283, 107, 0.50, 609, and 952 while these values for secondary sludge were 35595, 81, 4.90, 306, 493mg/L , respectively. The MPN value was determined to be 19.83 × 106 and 186 × 106 for primary and secondary sludge, respectively and the average number of parasite egg in primary and secondary sludge was 7.05 and 7.2 in 4 grams of dry solids. The highest number of eggs was found for Entamoeba coli (cysts). Evaluation of the results of this study shows that the highest concentration of heavy metals in the sludge is 21396 mg/kg and the lowest amount of cadmium is 4.5 mg/kg. The result of this study shows that if this sludge is used for farming and surface disposal, more efforts are needed to stabilize and improve the quality