EVALUATION OF THE QUALITY OF MUNICIPAL AND INDUSTRIAL WASTE-WATER SLUDGES FOR AGRICULTURAL PURPOSES

Sewage sludge was periodically sampled from one municipal and one indu strial wastewater treatment plant in Thessaloniki, N. Greece to determ ine quality parameters for potentially agricultural utilization. Both sludges were alkaline in nature and had similar nutrient content. At a n application rate of 10 tn ha(-1) y(-1), the P additions from sludge will be in excess of crop requirement, wherease supplemental N and K f ertilization will be needed to optimize crop yields. Both sludges had low heavy metal content thus meeting the requirements set by the Europ ean directive and the Greek law for agricultural use. An application r ate of 10 tn ha(-1) y(-1) of industrial sludge is in agreement with th e existing regulations, whereas lower application rates for the munici pal sludge should be considered.