Application of a novel respirometric methodology to characterize mass transfer and activity of H2S-oxidizing biofilms in biotrickling filter beds, Biochemical Engineering Journal http://dx.doi.org/10.1016/j.bej. 2015.02.030 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. • A novel respirometer design characterized the kinetics in H 2 S-oxidizing biofilms 3• H 2 S biofiltration properties were evaluated from a sample of biotrickling filter bed 4• Short-term respirometric assays (< 20 min) were performed 5• A mathematical model of the biotrickling filter bed respirometry was developed 6• The non-wetted biofilm fraction contributed 65% to the overall removal of H 2 S by the experimental evaluation of the oxygen uptake rate (OUR

BACKGROUND: Biological oxidation in biotrickling filters of high H 2 S loads contained in biogas streams still requires further study to reduce elemental sulfur accumulation due to limited gas-liquid oxygen mass transfer inside biotrickling filter beds.Reduction of elemental sulfur accumulation may be improved by regulating the main manipulated variables related to oxygen mass transfer efficiency during biological hydrogen sulfide removal in biotrickling filters. RESULTS: Trickling liquid velocity and co-current flow were selected as the most appropriate manipulated variable and flow pattern configuration compared with manipulating the air supply flow rate and a counter-current flow pattern in order to improve gas-liquid oxygen mass transfer in abiotic conditions. The influence of trickling liquid velocity on the performance of a lab-scale biotrickling filter treating high loads of H 2 S in a biogas mimic and operating in co-current flow at neutral pH and packed with plastic pall rings was investigated.CONCLUSIONS: The effect of trickling liquid velocity modulation between 4.4 and 18.9 m h −1 in biotrickling filter performance was compared with operation without trickling liquid velocity regulation. Velocity regulation resulted in an improvement of 10% in the elimination capacity and, most importantly, a 9% increase in product selectivity to sulfate at a loading rate of 283.8 g S-H 2 S m −3 h −1 . Concentration profiles along the biotrickling filter height evidenced that trickling liquid velocity regulation progressively led to better dissolved oxygen distribution and, thus, enhanced overall biotrickling filter performance.

The behavior of E. coli O157:H7 strains during the storage of plain live yogurt at 4, 8, 17, and 22 ºC was investigated. Lactic acid bacteria and pH were also studied. Linear regression analysis was carried out to obtain the specific death rate, the death rate and time of death. During the 1st 24 h, the pathogenic strains decreased slightly at 4 and 8 ºC. This decrease was greater at 17 ºC, and even greater at 22 ºC. E. coli O157:H7 was not detected after 312, 168, 28, and 16 h at 4, 8, 17, and 22 ºC, respectively. Counts of Lactobacillus and Streptococcus were about 9 log CFU/g during the study. An increase was detected in the values for time of death from refrigeration to room temperatures. A decrease in the values of both the specific death rate and the death rate related with the increase of temperature was observed. Counts of E. coli O157:H7 were higher than those of nonpathogenic E. coli during the storage period at 4 and 8 ºC, showing a better and a higher adaptation capacity to acid pH environments at refrigeration temperatures. This behavior was not observed at room temperatures.

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