7 th International Conference on Environmental Science and Technology Ermoupolis, Syros island, Greece – Sept. 2001 THE USE OF JAR TESTS FOR THE DETERMINATION OF COAGULATION CONDITIONS OF A SECONDARY EFFLUENT M. PETALA 1 , T. ALBANIS 1 , P. SAMARAS 2 , A. KUNGOLOS 3 and G. P. SAKELLAROPOULOS 1, 2 1 Chemical Process Engineering Laboratory, Department of Chemical Engineering, Aristotle University of Thessaloniki, PO Box 1520, 54006 Thessaloniki, Greece 2 Laboratory of Solid Fuels and Environmental Processes, Chemical Process Engineering Research Institute, 6 th km Harilaou Thermi Road, 57001, Thermi, Thessaloniki, Greece 3 Department of Planning and Regional Development, University of Thessaly, 38334, Volos, Greece. ABSTRACT The objectives of this study were the examination of chemical coagulation of a secondary effluent from a municipal wastewater treatment plant by using pre-hydrolyzed metal salts of aluminum and iron in the form of AlCl 3 and FeCl 3 respectively, and the determination of optimum experimental conditions resulting in efficient removal of organic loading, phosphorous and nitrogen for the production of high quality reclaimed wastewater. For both coagulants, organic loading removal increased with the coagulant dosage, and ferric ions gave the highest COD removal efficiency reaching up to 80 %. However, pre-hydrolysis of metal salts did not affect organic matter removal capacity. Phosphorous removal decreased with the degree of pre-hydrolysis, due to the competing action of phosphate and hydroxyl ions to occupy active sites on the polymeric complex species formed during pre-hydrolysis. In addition, ammonia nitrogen removal lower than 50% was observed for both coagulants. 1. INTRODUCTION Wastewater reclamation and reuse has become an attractive option for conserving and extending available water supplies, as many communities throughout the world are reaching the limits of their available water supplies (Mujeriego and Asano, 1999; Tchobanoglous and Angelakis, 1996). Reclaimed wastewater may have different applications such as industrial uses, irrigation and groundwater recharge. However, the presence of toxic substances and pathogenic micro-organisms in untreated wastewater may have adverse health effects. Secondary treatment of municipal wastewater may be acceptable for reuse applications where the risk of public exposure to reclaimed water is low, such as in irrigation of non-food crops. However, additional wastewater treatment processes are necessary when a high quality reclaimed wastewater is desired, such as for contact recreation uses, groundwater replenishment and irrigation of urban landscaping and food crops (eaten raw). Coagulation of a secondary effluent is usually the first step in the wastewater reclamation process, for the removal of suspended solids, heavy metals, trace substances, phosphorous and turbidity and for the enhancement of wastewater settling characteristics (USEPA, 1992; 419