In the present work, 10 packing materials commonly used as support media in biofiltration are analyzed and compared to evaluate their suitability according to physical characteristics. The nature of the packing material in biofilters is an important factor for the success in their construction and operation. Different packing materials have been used in biofiltration without a global agreement about which ones are the most adequate for biofiltration success. The materials studied were chosen according to previous works in the field of biofiltration including both organic and inorganic (or synthetic) materials. A set of nine different parameters were selected to cope with well-established factors such as material specific surface area, pressure drop, nutrients supply, water retentivity, sorption capacity and purchase cost. One ranking of packing materials was established per each parameter studied to define a relative suitability degree. Since biofiltration success generally depends on a combination of the ranked parameters, a procedure was defined to compare packing materials suitability under common situations in biofiltration. Selected scenarios such as biofiltration of intermittent loads of pollutant and biofiltration of waste gases with low relative humidity were investigated. The results indicate that, out of the packing materials studied, activated carbons were ranked on top of several parameter rankings and showed as a significantly better packing material when parameters were combined to assess such selected scenarios. Keywords: packing materials; biofiltration; Physical properties; Economical assessment IntroductionBiological treatments have become an effective and economical alternative to traditional gas treatment systems.The correct selection of the packing material employed in a biofilter or a biotrickling filter is an important decision to achieve high removal efficiencies and to maintain an optimal performance in the long-term run [1]. Despite the widely recognized importance of the support media role, several packing materials have been used in biofiltration under a wide range of operating conditions without a global agreement about which one is the most adequate.Previous works studying packing materials are mostly based on a sole packing material case study [2][3][4] or on the comparison of the removal efficiency achieved by different packed biofilters under the same operating conditions [5,6]. In general, these studies concluded that high removal efficiencies in biofilters are strongly related to packing material properties although physical and chemical properties of the materials were not evaluated thoroughly. The nature of the carrier material, which may be organic, natural inorganic or entirely synthetic, is a crucial factor for the successful application of biofilters and biotrickling filters because it affects the frequency at which the medium is replaced and other key factors such as bacterial activity and pressure drop across the bioreactor [7,8].Among the natural carriers reported, com...

Oleic acid has been reported as a good inducer of lipase production by Candida rugosa. In order to know if this enzyme is induced by oleic acid itself or by a metabolite, different short chain fatty acids were tested. Butyric acid was the best carbon source to growth microorganism but it did not induce lipase production. Although caprylic and capric acid were the best inducers of lipase production, at concentrations up 1 g/1 they have toxic effect in Candida rugosa growth. Thus, from the point of view of industrial production oleic acid could be considered as the best substrate tested.

The temperature effect on denitrification rate of a two-sludge system has been studied. An industrial high-strength wastewater and an industrial by-product containing mainly methanol, as external carbon source, were used in this study. The maximum denitrification rate (MDR) was determined at six different temperatures: 6, 8, 10, 15, 20 and 25ºC in batch mode. The temperature coefficient was found to be 1.10 ± 0.01 at temperatures between 10 to 25ºC and 1.37 ± 0.01 at temperatures between 6 to 10ºC. The MDR obtained in the two-sludge system (0.28 mg N•mg VSS-1 •d-1 at 25ºC) was higher than the one obtained in a single-sludge system with a similar external carbon source. The COD/N ratio required for complete denitrification in the two-sludge system was approximately stoichiometric, which is 3.7 ± 0.9 mg COD•mg N-1 .

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