Anaerobic fluidized bed reactor applied to the removal of linear alkylbenzene sulfonate (LAS) present in laundry wastewater J. K. Braga*, F. Moterani*, T. Z. Macedo*, E. L. Silva**, M. B. A. Varesche* * Department of Hydraulics and Sanitation, School of Engineering of São Carlos, University of São Paulo, Ave. Trabalhador São carlense, 400, 13566-590 São Carlos, SP, Brazil (E-mail: jukawanishi@gmail.com; fabricio_moterani@yahoo.com.br; thazmacedo@gmail.com ; varesche@sc.usp.br) ** Department of Chemistry Engineering, Federal University of São Carlos, Rod. Washington Luis, km 235 - Monjolinho13.565-905 - São Carlos, SP, Brazil (E-mail:edsilva@ufscar.br) Abstract The commercial laundry is an important service sector and surfactants are the major active ingredients of laundry detergents. So, special attention should be given to the treatment and disposal of these wastewaters. The purpose of this study was to evaluate the fluidized bed reactor performance treating laundry wastewater. It was performed the wastewater characterization and reactor operation for 225 days. Constant characteristic was not observed through the physical- chemical analysis. The values of LAS ranged from 16.9 to 1,023.7 mg L -1 with an average of 162.3 ± 243.7 mg L -1 and the values of COD ranged from 415 to 3698 mg L -1 with a mean value of 1414 ± 934 mg L -1 . The reactor was operated in three stages: inoculation (480±135 mg L -1 of COD), stage I (adaptation of biomass with 598±49 mg L -1 of COD), stage II (10 mg L -1 of LAS and 637±80 mg L -1 of COD) and stage III (30 mg L -1 of LAS and 723± 82 mg L -1 of COD). The organic matter and LAS removal efficiencies were 84±9% and 74±14%, respectively, in stage II. In stage III was obtained, respectively, 91±4% and 68±17%. Thus, it was found that the laundry wastewater did not affect the organic matter removal and that this reactor is satisfactory for the surfactant removal. Keywords Characterization; sand; organic matter; anionic surfactant. INTRODUCTION Detergents are an important source of industrial, commercial and domestic pollution. They are widely used in household cleaning detergents, personal care products and industries like textiles, paints, polymers, pesticide formulations, pharmaceuticals, mining, oil recovery and pulp and paper (Ying, 2006). Linear alkybenzene sulfonate (LAS) is the synthetic surfactant most produced worldwide. Thus, developing technologies that allow not only the removal but the anaerobic surfactants mineralization in commercial laundry wastewater treatment justifies the relevance of this research. Alternatives should be investigated, since studies in this research line are still scarce, though growing. MATERIAL AND METHODS Characterization of commercial laundry wastewater was done through physical-chemical analysis (APHA, 2005). The fluidized bed reactor was made of acrylic, 100 cm in length (L) and 4 cm internal diameter (D) and a total volume of 1256 mL. This reactor was filled with 306 g of sand where the microorganisms were immobilized. The hydraulic detention time (HDT) was 18 hours for 225 days and maintained at 30°C. The reactor was inoculated with sludge from a UASB reactor treating swine culture wastes. The reactor was fed with synthetic substrate containing sucrose, yeast extract, sodium bicarbonate and salt solution (Duarte, 2006) plus laundry wastewater for concentrations of LAS in the range of 10 mg L -1 and 30 mg L -1 . Duran flasks (5.0 L) were utilized to storage the substrate during the feeding of the reactors. The flasks were kept on 4°C. The reactor behavior was accomplished by the following analyses: chemical oxygen demand (COD), linear alkylbenzene sulfonate (LAS), pH, alkalinity, solids, sulfate, sulfide, phosphate (APHA, 2005). Bicarbonate alkalinity were carried out as described by Dillalo and Albertson (1961) and adapted by Ripley et al. (1986). Volatile acids concentrations were determined by Liquid Chromatograph according to Moraes et al. (2000). LAS determinations were carried out according to methodology developed and validated by Duarte et al. (2006). The reactor was operated in three stages: inoculation (480±135 mg L -1 of COD), stage I (adaptation of biomass with 598±49 mg L -1 of