TiO2-photocatalytic-biological treatment for the elimination of benzalconium chloride from water

FIOL P.; MEICHTRY J.M.; CANDAL R.J.; CURUTCHET G.; GAUTIER E.; LITTER M.

Pittsburg, PA, EE.UU

Congreso; 11th Internacional Conference on TiO2 Photocatalysis: Fundamentals and Aplications; 2006

Benzalconium chloride (BKC) is a widely used surfactant and bactericide, due to its low toxicity and high activity at low concentrations. Because of its bio-recalcitrant characteristics, it cannot be degraded by biological processes, becoming a persistent pollutant in industrial wastewaters. Recently, it was shown that the coupling of TiO2-photocatalysis with a biological process is an interesting alternative for the treatment of bio-recalcitrant compounds (S. Parra, S. Malato, C. Pulgarin; Appl. Catal. B: Environ. 36 (2002) 131-144 and G.B. Tabrizi, M. Mehrvar, J. Environ. Sci. Part A. 39 (2004) 3029-3081). In this work we present a preliminary study on the treatment of BKC with a coupled UV/TiO2-photocatalytic-biological treatment based on active sludge. TiO2-Photocatalytic degradation of BKC at different treatment times was studied with an annular reactor with internal UV illumination (photonic flux: 4 ´ 10-6 einstein s-1 dm-3). An aerated TiO2 slurry (1g dm-3) containing 50-300 ppm of BKC was circulated through the reactor and samples were taken at different irradiation times. The concentration of BKC and the remaining amount of carbon were determined by HPLC and TOC respectively. For biological experiments, a microbial consortium from an active sludge was used. BKC biodegradation experiments were made adding 10 cm3 of the inoculum to erlenmeyer flasks containing 25 cm3 of sterile mineral media and pure BKC at several concentrations or photocatalyzed samples taken at different irradiation times. Remaining TOC was measured in all cases. More than 80% of the initial amount of BKC is degraded during the first 100 minutes of photocatalytic treatment, although the TOC content decreases only slightly. In separate experiments, it was determined that BKC concentrations lower than 50 ppm were not toxic for the microorganisms of the activated sludge. Based on the previous information, a 350 ppm BKC sample was submitted to photocatalytic treatment, and samples were taken from the photoreactor in such a way that the remaining BKC concentrations were close to 0, 50 and 100 ppm. Samples were introduced into the biological reactor and, for comparison, pure BKC solutions (50, 100 and 350 ppm) were also bio-treated. The degradation fraction of BKC after several days of bio-treatment was calculated as remaining TOC with respect to the TOC content of a sterile control. The biodegraded fraction of the 50 ppm BKC solution reaches 100 % in the first 7 days, but in systems with 100 and 350 ppm the biodegradation is very poor. These results are in agreement with the toxicity of BKC on the activated sludge previously reported. By the contrary, the degradation fraction of BKC in the pre-treated solutions is c.a.5 times higher than in the untreated ones. These results indicate that some intermediates produced by oxidative photocatalysis are less bio-recalcitrant than pure BKC. Presentación Oral