Removal of pesticides from aqueous solutions by combined physicochemical processesÐthe behaviour of lindane A. Kouras, A. Zouboulis*, C. Samara, Th. Kouimtzis Department of Chemistry, Aristotle University, GR-54006 Thessaloniki, Greece Received 8 November 1997; accepted 18 June 1998 Abstract The adsorption of the insecticide lindane on powdered activated carbon (PAC) from aqueous solutions with and without the simultaneous presence of coagulants has been studied. Ferric chloride and basic polyaluminium chlorosulfate were examined as coagulants, in laboratory experiments aided in certain cases by polyacrylamide (a common polyelectrolyte) addition, in order to evaluate and optimize the various process parameters, such as coagulant and carbon concentrations, solution pH and position of coagulant addition (before or after PAC). The obtained results indicated that PAC adsorption eciency was not highly aected by solution pH, while PAC doses greater than 20 mg/L were found to be necessary in order to reduce lindane from initial concentra- tion of 10 mg/L down to 0.1 mg/L within 1 h contact time. However, when coagulants have been added after the addition of PAC, a certain decrease of adsorbent eciency was observed and, therefore, double PAC concentration (40 mg/L) was necessary for the aforementioned removal. In order to evaluate the eect of position of coagulant addition on the removal eciency of PAC, the respective adsorption isotherms were calculated and rate studies were performed. # 1998 Published by Elsevier Science Ltd. All rights reserved. Keywords: Lindane; Water treatment; Coagulation; Adsorption; Powdered activate carbon (PAC) 1. Introduction Many human-made organic chemical compounds are currently possible to be detected in drinking water sources, hence, they are of increasing interest, because of their potential toxicity, carcinogenicity and muta- genicity eects. Among them, pesticides constitute a pollutant class of particular importance and priority; they can enter drinking water supplies, either from point (such as industrial waste discharges, accidental spills) or from non-point sources (e.g. agricultural run-o). The fate of pesticides during drinking water treatment has been already examined using bench, pilot, as well as full-scale, experiments (Robeck et al., 1965; Miltner et al., 1989; Pirbazari et al., 1991), The conventionally applied water treatment processes, such as chemical coagulation, sedimentation, ®ltration and disinfection, appear to remove eectively only selected (i.e. the less water-soluble) pesticides, such as DDT (Robeck et al., 1965; Thebault et al., 1981; Miltner et al., 1989), or the easily degradable ones, such as carbamates (Mason et al., 1990). On the other hand, advanced water treatment pro- cesses, and mainly the adsorption onto activated car- bon, have proved to be the most ecient and reliable method for the removal of aqueous-dissolved organic pesticides (Pirbazari et al., 1991). Both activated carbon types, i.e. granular (denoted hereafter as GAC) and powdered (PAC), can be used eectively for this pur- pose. GAC is mainly used in ®xed-bed column adsor- bers, presenting the advantages of relatively lower carbon application rates, easier handling, as well as the possibility for regeneration process to be applied. A number of studies have been published, concerning the eciency of GAC for the adsorption of pesticides for example (El-Dib et al., 1975). Based on pilot experi- ments it has been also reported that GAC ®lters work- ing with empty bed contact times between 6 and 30 min, can remove triazine, uron and chlorophenoxy types of pesticides below the detection limit at operation times between 29 and 222 days (Smetham et al., 1994). How- ever, the GAC ®xed beds require an appreciable invest- ment in equipment, as well as high cost for operation and maintenance. Regarding the application of PAC, little attention has been given to its use for the adsorption of pesticides. 0269-7491/98/$Ðsee front matter # 1998 Published by Elsevier Science Ltd. All rights reserved. PII: S0269-7491(98)00124-9 ENVIRONMENTAL POLLUTION Environmental Pollution 103 (1998) 193±202 * Corresponding author.