Assessing the quality of sewage sludge as an agricultural soil amendment in Mediterranean habitats

Abstract

Purpose Municipal sewage sludge generated from three operational wastewater treatment plants, located in the Bekaa valley of Lebanon, was assessed for its potential use as agricultural soil amendment. Methods Sludge samples were taken from three treatment plants located in the villages of Iaat, Ablah and Joub Jannine during the summer season of 2018, from June to September, on a monthly basis. The evaluation was based on characterizing the physicochemical parameters such as the metal content, the pathogenic microorganisms (Salmonella, E.Coli, Staphylococcus aureus, Helminth eggs, Ascaris, Acinetobacter) and the phytotoxicity–stability indicators of the sludge samples. Results The obtained results were compared to the Lebanese guidelines for sludge reuse in agriculture. For the physicochemical analysis, all the samples showed a possibility to be used in agriculture due to the high content of minerals and organic matter. Considering the metal content of sludge, Iaat and Ablah sludge were classifed as Class A according to the Lebanese guidelines; however, sludge from Joub Janine was classifed as B due to its high content of zinc that exceeded the limit of 700 ppm. Helminth eggs and Salmonella were absent in the sludge samples. Pathogenic organisms, mainly E. coli, were detected in Iaat dry sludge, Staphylococcus aureus was present in Joub Jannine sludge and Acinetobacter in Ablah station (>100 CFU/100 g). Conclusion It is recommended to submit the sludge which did not meet the required criteria, for further treatments, particularly the composting process to reduce the metal content and pathogenic microorganisms for a safer reuse in agriculture.