Study of sludge from the largest wastewater treatment plant in the Middle East (Southern Tehran, Iran) based on chemical and microbiological parameters for use in agriculture

Sludge (if not well-stabilized) used for improving the soil quality of agricultural lands might lead to soil contamination, and has caused many concerns in recent years. Therefore, the quality assessment of the sludge produced in wastewater treatment plants is essential prior to its application for the improvement of agricultural lands. This study is aimed to determine the quality of the sludge disposed from Southern Tehran Wastewater Treatment Plant. The microbial and physicochemical quality and concentration of sludge heavy metals resulting from anaerobic digesters and the sludge drying bed obtained from South Tehran Wastewater Treatment Plant were evaluated during spring and summer. The amount of volatile solids in sludge from digesters and sludge drying bed were between 62 and 68%, which showed the high level of organic matters in the sludge as well as poor anaerobic digestion and stabilization. Furthermore, the amount of heavy metals in the spring and summer in the sludge obtained from digestions and sludge drying bed was less than the EPA standard level. The present study showed that the sludge of South Tehran Wastewater Treatment Plant was often in class B, and the sludge should be used by taking into account certain considerations to improve the soil quality and to increase fertility, but it was in favorable conditions considering the concentration of heavy metals.