Toxicity and benefits of urban stabilized sludge intended for agriculture use

Sludge reuse is one of the main challenges of waste management and an action with environmentally consequences that must be kept under control. The progress of civilization leaded to the globally increase of sludge production. WWTPs treatment technologies, sludge disposal/recovery and also quality control and toxicological involvements became parts of strategical actions at international level. The main disposal strategies for sludge management include agriculture or landscaping purposes, or final disposal. The accepted international policy is sludge application as organic fertilizer in agriculture. In this context, the research paper presents laboratory data used in decisional actions for the sludge land disposal. The study covers physical and chemical characterization of sludge resulted from Focsani WWTP, agriculture soil collected from around of Focsani WWTP and their leachates in compliance with national norms. In addition, the toxic effects on soil organisms (plants) were evaluated. Generally, soil and sludge quality meet the normed criteria for minimizing the potential impact on the environment. The leachate experiments showed the non-hazardous character on the soil properties of groundwater, the predicted impact being insignificant for the tested sludge / soil chemical composition. Ecotoxicological assessment of stabilized sludge showed inhibitory effects in the range of 25% to 100% on seed germination and root growth of plants Sorghum sacharatum, Sinapis alba and Lepidium sativum. In the range of 1% or 5% no significant inhibitory effect of sludge on plants growth was observed. Sorghum sacharatum showed the best growth, but there were no relevant differences between species. A saftey dose of 5% sludge mixed with agriculture soil (250 tonnes per hectare) was established. A monitoring program of sludge / soil quality and also ecotoxic evaluation was recomanded for the saftey of crops growth and health of living organisms including humans.