Coagulation–flocculation pretreatment of sanitary landfill leachates A.A. Tatsi a , A.I. Zouboulis a, * , K.A. Matis a , P. Samaras b a Department of Chemistry, Division of Chemical Technology, Aristotle University of Thessaloniki, Thessaloniki GR-541 24, Greece b Chemical Process Engineering Research Institute, 6th km Charilaou-Thermi Street, Thermi-Thessaloniki GR-57001, Greece Received 29 August 2002; received in revised form 25 April 2003; accepted 25 April 2003 Abstract Sanitary landfill leachates are considered as heavily polluted industrial wastewaters, presenting significant time and spatial variations of their physical–chemical parameters. Special care is required for their efficient treatment and dis- posal. The main aim of this work was to examine the application of coagulation–flocculation for the treatment of raw and partially stabilized leachates. Jar-test experiments were employed in order to determine the optimum conditions for the removal of organic matter and color, i.e. coagulant–flocculant combination, effective dosage and pH control. Ferric chloride, aluminium sulphate and lime were tested as conventional coagulants, whereas four commercial polyelectro- lytes were co-examined: one anionic, two cationic and a non-ionic polymer. High chemical oxygen demand (COD) removal capacities (about 80%) were obtained during the addition of ferric chloride to the partially stabilized leachates, whereas low COD reductions (i.e. lower than 35%) were measured during the addition of coagulants in the raw samples. The addition of polyelectrolytes and pH adjustment in the alkaline region were found to affect slightly the removal of pollutants. The physico-chemical process may be used as a useful pretreatment step, especially for fresh leachates, prior to biological treatment, or as a post-treatment (polishing) step for partially stabilized leachates. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Landfill; Leachate; Treatment; Coagulation; Flocculation 1. Introduction Leachates from municipal solid waste landfill sites are often defined as hazardous and heavily polluted wastewaters. Leachates may contain large amounts of organic matter (biodegradable, but also refractory to biodegradation), where humic-type constituents consist an important group (Kang et al., 2002), as well as ammonia-nitrogen, heavy metals, chlorinated organic and inorganic salts (Wang et al., 2002). Landfill leach- ates have been identified as potential sources of ground and surface waters contamination, as they may perco- late through soils and subsoils, causing extensive pol- lution of streams, creeks and water wells, if they are not properly collected, treated and safely disposed (Mott et al., 1987). Leachates present considerable variations in both volumetric flow and chemical composition (Tatsi and Zouboulis, 2002). The composition and concentration of contaminants are influenced by the type of deposited wastes, the quality of refuse, hydrogeological factors and mainly by the age of landfill (Ehrig, 1984; Crawford and Smith, 1985). As a landfill becomes older, there is a shift from a relatively shorter initial aerobic period to a longer-time anaerobic decomposition period, which has two distinct sub-phases: an acidic phase, followed by a methanogenic one. Chemosphere 53 (2003) 737–744 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +30-310-997794; fax: +003- 2310-997794/30-310-99-7795. E-mail address: zoubouli@chem.auth.gr (A.I. Zouboulis). 0045-6535/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00513-7