The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors Tuba H. Erg€ uder a ,EnginG€ uven b ,G€ oksel N. Demirer a, * a Department of Environmental Engineering, Middle East Technical University, In€ on€ u Bulvari, 06531 Ankara, Turkey b Department of Civil and Environmental Engineering, Marquette University, Milwaukee, Wisconsin 53201, USA Received 29 May 2002; received in revised form 23 December 2002; accepted 6 January 2003 Abstract Theinhibitoryeffectsandremovalefficiencyofdieldrin(DLD)inanaerobicreactorswereinvestigated.Anaerobictoxicityassay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed an- aerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactorsystemwhichwasfedwithethanolasthesolecarbonsource,indicatedthatanaerobicgranularculturescouldbesuccessfully acclimatedtoDLD.Chemicaloxygendemand(COD)removalefficiencieswere88–92%forthetwo-stagesystem.TheinfluentDLD concentration of 10 mg/l was removed by 44–86% and 86–94% in the second stage and overall UASB system, respectively. Bio- sorptionofDLDongranularanaerobicbiomasswasfoundtobeasignificantmechanismforDLDremovalintheUASBsystem. ThemaximumDLDloadingrateandminimumHRTachievableforthefirststageUASBreactorwere0.5mg/lday(76 lgDLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Acclimation; Anaerobic; ATA experiments; Dieldrin; UASB 1. Introduction Chlorinated insecticides (organochlorines) such as dieldrin (DLD), which is a chlorinated cyclodiene and canappearasaresultofmicrobialepoxidationofaldrin inareaswhereDLDitselfhasneverbeenused,received considerable attention in the 1940s and 1950s for the controlofdiseasevectorsandagriculturalpests(Rogers, 1996). Especially, DLD has been used to control mos- quitoes as vectors of malaria. The registration of DLD whichisacarcinogenicprioritypollutantwasbannedin 1975 by the United States Environmental Protection Agency. However, developing countries and even some developed countries still use this insecticide and manu- facture to export (Watts, 1998). Therefore, its entrance to natural waters and wastewater treatment plants handling a variety of wastewater sources, domestic and industrialinputs,stormwaterandagriculturalrunoffs,is possible. In the 1960s, little was known about degradation of DLD,thusitwasusuallyreportedthatmicro-organisms were incapable of degrading DLD. However, in subse- quentyears,itwasfoundthatDLDcouldbeconverted to aldrin diol by Aerobacter aerogenes under aerobic conditions (Wedemeyer, 1968) and the soil fungus Trichoderma koningi was capable of degrading DLD to CO 2 by degrading one or more of the carbons on the chlorinated ring of the DLD molecule (Bixby et al., 1971). Maule et al. (1987) achieved dechlorination of 96% of the initial DLD amount (10 mg/l) to syn- and anti-monodechloro DLD in anaerobic batch reactors with DLD-enriched mixed anaerobic cultures, which were more effective in transforming DLD than isolated cultures.Effectsofdifferentsubstratesondechlorination werealsoinvestigatedandformatewasfoundtobemost supportive of DLD dechlorination, while glucose and pyruvateinhibitedthetransformation.pHoftheculture was also as important as the carbon source in trans- formation of pesticides. Dechlorination of DLD was optimum at pH 8–9. Microbial-mediated reductive * Corresponding author. Present address: Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA. Tel.: +90-312-210-58-67; fax: +90- 312-210-12-60. E-mail address: goksel@metu.edu.tr (G.N. Demirer). 0960-8524/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0960-8524(03)00046-4 Bioresource Technology 89 (2003) 191–197