Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres A new mathematical model to evaluate simazine removal in three different immobilized-biomass reactors M. Martin a,Ã , L. Casasus b , C. Garbi a , M. Nande a , R. Vargas a , J.I. Robla c , M. Sanchez a , J.L. Allende d a Departamento de Bioquimica y Biologia Molecular IV, Facultad de Veterinaria, Universidad Complutense de Madrid (UCM), Avda. Puerta de Hierro s/n, 28040 Madrid, Spain b Departamento de Matematica Aplicada, E.T.S.I. Industriales, Universidad Politecnica de Madrid (UPM), C/Jose ´ Gutie ´rrez Abascal, 2, 28006 Madrid, Spain c Centro Nacional Investigaciones Metalurgicas (CENIM), Consejo Superior de Investigaciones Cientificas (CSIC), Avda. Gregorio del Amo, s/n. 28040 Madrid, Spain d Departamento de Fisica Aplicada, Facultad de Veterinaria, Universidad Complutense de Madrid (UCM), Avda. Puerta de Hierro s/n, 28040 Madrid, Spain article info Article history: Received 21 December 2006 Received in revised form 18 July 2007 Accepted 26 September 2007 Available online 4 October 2007 Keywords: Simazine Biomass-reactor Mathematical model Biofilm abstract A new mathematical model based on the cinetical Langmuir equation is developed to interpret and predict the effectiveness of simazine (SZ) removal in immobilized-biomass reactor (IBR), to consider herbicide-support affinity (Cx), and herbicide-cell affinity (Cy). Three solid supports: sepiolite monolith, granular sepiolite, and alginate were used in pilot- scale reactors that were inoculated with Klebsiella planticola DSZ. The abiotic process was analysed by measuring the SZ sorption capacity of the reactor supports. Sepiolite monolith showed the maximum value for herbicide-support affinity (28.0270.9%). The effectiveness of the biotic process was estimated considering the formation of biomass and SZ biodegradation. Granular sepiolite showed either higher affinity with SZ and viability rate (0.90) throughout the process, and SZ removal rate was 3.3970.06 mg/h. The mathematical model presented in this paper provides useful insights into the interpretation of experimental data as well as prediction for the implementation of biological reactors. & 2007 Elsevier Ltd. All rights reserved. 1. Introduction s-Triazine herbicides have been used in a variety of weed- control programs with major crops, but herbicides containing an s-triazine ring are relatively persistent in the environment. Simazine (SZ) is a synthetic chemical that is widely used as a selective triazine herbicide to control the growth of broad- leaved weeds and annual grasses in field, berry fruit, nuts, vegetable and ornamental crops, turfgrass, orchards, and vineyards. At higher concentrations, it is used for non- selective weed control in industrial areas, and before 1992, it was used to control submerged weeds and algae in large aquariums, farm ponds, fish hatcheries, swimming pools, ornamental ponds, and cooling towers. The increasing awareness of the harmful effects of environmental pollution has led to a notable increase in research on various strategies that may be employed to clean up the environment (Vande- casteele et al., 2000; Wackett et al., 2002). It is now accepted ARTICLE IN PRESS 0043-1354/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2007.09.026 Ã Corresponding author. Tel.: +34 913943911; fax: +34 913943886. E-mail addresses: margamar@vet.ucm.es (M. Martin), lcasasus@etsii.upm.es (L. Casasus), cgarbi@vet.ucm.es (C. Garbi), mnande@naturalbiotec.com (M. Nande), rvargasl@vet.ucm.es (R. Vargas), jrobla@cenim.csic.es (J.I. Robla), jlallende@vet.ucm.es (J.L. Allende). WATER RESEARCH 42 (2008) 1035– 1042