Phytotoxicity Tests Applied on Sewage Sludge Resulted from Urban Wastewater Treatment Plants

Four types of urban sewage sludge were tested to estimate their effects on higher plants (Lepidium sativum - LES, Sinapis alba - SIA and Sorgum saccharatum - SOS) highlighting their reusable potential. Seeds germination and roots growth inhibition were used as parameters to measure the phytotoxic sensitivities. The tested samples were collected from three Romanian Waste Water Treatment Plants (WWTPs). The chemical investigations of samples revealed metal concentration values within accepted limits except Arsenic, Manganese, Calcium, Iron and Aluminium. The plants expressed different phytotoxic sensitivities related to the contamination level. The seeds germination was inhibited between20 to 100% for LES and SIA and between 25 and 75% for SOS. In case of roots growth, all the tested plants were significant inhibited (28 to 100%). The results indicated that all the samples were toxic for the tested plants, especially for the roots growth. The toxic effects of sludge could be reduced by adding more than 50% unpolluted soil that would allow to be reuse in agriculture as fertilizer. The study has proved that the phytotoxic microbiotests could be used as routine toxicity screening tests to provide rapid and relevant informations for sludge reuse and their environmental risk.