Coupled TiO2-photocatalysis-biological treatment for the elimination of benzalkonium chloride in water

ELSA LÓPEZ LOVEIRA; ALEJANDRO SENN; GUSTAVO CURUTCHET; CANDAL ROBERTO; MARTA I. LITTER

San Diego, CA

Conferencia; 15th International Conference on TiO2 Photocatalysis: Fundamentals and Applications; 2010

Redox technologies

Biological treatment is the cheapest way to eliminate contaminants from water. However, some recalcitrant organic compounds cannot be effectively biodegraded, and may be toxic for the biomass. Benzalkonium chloride (BKC) is a bactericide widely used in pharmaceutical and cosmetic formulations and, being risky for the biota, should be removed before discharge. Because BKC cannot be easily degraded in biological water treatment plants (BWPTs), its elimination would require other more expensive technologies. TiO2-photocatalysis is a low-cost technology that can be used either as a pretreatment to improve the biodegradability of wastewaters or as a polishing decontamination step after a biological treatment. In this work, results obtained with both ways of coupling TiO2-photocatalysis with biological treatments are presented. TiO2-photocatalysis: preliminary results indicated that BKC is rapidly degraded by TiO2-photocatalysis, but with a low mineralization degree. Photocatalytic tests were performed in a 1 L thermostatted (25 ºC) recirculation batch system, composed of a cylindrical photoreactor (15 W black light lamp, 8 meinstein s-1 L-1) and a reservoir. The TiO2 suspension (Degussa P-25, 1 g/L) containing BKC was recirculated (1 L/min) from the reservoir through the photoreactor. Air was bubbled at 0.2 L/min all throughout the irradiation time. Samples were periodically taken to monitor BKC concentration (HPLC), TOC and COD. Biological reactors: a packed-bed aerobic biological system, consisting of a flooded reactor connected in series with a tricking filter reactor, was used. A microbiological consortium taken from a BWTP was grown on glass beads contained in cylindrical glass reactors. Air was blown through the reactors at 2.5 L/min. The consortium was adapted to BKC by incorporating 50 mg/L of the compound to the culture medium, the maximum supported by the bacterial consortium, as proved in preliminary tests. Two different coupling configurations were adopted: i) Photocatalysis + biological treatment: a 220 mg/L BKC solution was photocatalytically treated until 60% elimination (210 min). Almost no COD reduction was observed in this period. After 0.22 mm filtration, the resulting solution was mixed with an equal volume of a culture medium solution and introduced into the bioreactor at 50 mL/h; the inlet composition was 2050 mg/L COD and 48 mg/L BKC. The outlet solution presented rather low COD (500 mg/L) and BKC (30 mg/L) contents. These results indicate that an effluent containing high BKC concentration can be treated by a first photocatalytic step until a concentration able to be introduced in a BWTP and then, combined with another effluent with enough COD to feed the microorganisms, can be biologically treated.ii) Biological treatment + TiO2-photocatalysis: the biological reactor was feed with a 100 mg/L BKC + 2500 mg/L COD culture medium. This COD value, as determined in previous experiments, allows concentrations as high as 100 mg/L of BKC in the BKC-adapted bioreactor without lost of biomass metabolic activity. The outlet effluent had 500 mg/L COD and 40 mg/L BKC. Introduction of this solution into a TiO2-photocatalytic reactor yielded complete BKC conversion after 120 min. This strategy is an appropriate combination for the treatment of water containing high level of nutrients and low to medium BKC concentration.