Transactions on Ecology and the Environment vol 1, 1993 WIT Press, ISSN

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1 Deodorization of industrial waste air by a biofilter J.L. Fanlo, J.R. Degorce-Dumas, P. Le Cloirec Laboratoire Genie de VEnvironnement, Centre de VEnvironnement Industrie^ Ecole des Mines d'ales, 6, avenue de Clavieres, Ales Cedex, France ABSTRACT : The objective of this study is to show the possibilities to deodorize malodorous air using a biological filter packed with dry activated sludge. The experiments were performed on pilot units fed with air loaded by H2S. The packing material was humidified activated sludge mixed with calcium carbonate. This support was colonized by bacteria which oxidized the odorous molecules in S, SiO]^ and SO^-. The performances of the process were found in terms of HiS removal versus the volumic load. The influences of different operating conditions were studied : moisture of the packing material, ph and the calcium carbonate concentration which buffered the activated sludge. The head losses were measured. These experiments allow us to design the industrial biofilter used to purify air loaded by malodorou^ molecules.

2 728 Air Pollution INTRODUCTION : Odors from industries or even waste treatment plants cause serious problems. The malodorous gases contain a large number of compounds : ammoniac, amines, hydrogen sulfide, mercaptans, aldehydes, ketones or organic acids [1] [2]. Among these odorous compounds H%S is often found in different industrial or agricultural activity sources : refineries, chemical or pharmaceutical industries, wood or paper activities, animal dropping and manure, household wastes... [3] [4]. Several processes are available to remove these substances from air. Then, processes using a physical transfert and/or chemical reaction operate : washing with bases, acids, water, heavy solvents... or with oxydants like chlorine, ozone, hydrogen peroxyde... [1] [2]. More recently, biological processes were used in deodorization [5] [6] [7] washing with bacteria suspensions, bioscrubber or biofiltration [8] [9]. For this last system, biomass, degradating odorous molecules, is fixed on a packing material : peat, clays, compost, soils... [2]. In this case, to obtain good performances of the biofilter,, nutrients in the water of humidification are required. To avoid the utilization of nutrients, it would be interesting to use a packing material which would be also substrate. Therefore, dry activated sludge seems to be a useful support and substrate for the biomass. This by-product of wastewater treatment plant is very cheap and has interesting qualities. The main objective of this paper is to show the performances of dry activated sludge as packing material of biofilter used in deosodorization. An approach of the quality and quantity of bacteria is also developped.

3 MATERIAL AND METHODS Activated sludge characteristics Air Pollution 729 The characteristics of the dry activated sludge used in this study had been described in a previous paper [8]. Table 1 summarizes some data. c H 0 N S inorganics bacteria UFC/g Table 1 : Characteristics of the dry activated sludge (in % of dry material weight) Pilot unit and procedure Figure 1 gives the shematic representation of the pilot unit which is 5 cm in diameter and 40 cm in height. The influent together with the humidification water penetrate into the top of the bioreactor. The moisture of the packing material was in a range between 20 to 50 %. The polluted air flow was from 901/h to 450 1/h i.e a velocity from 16 m/h to 90 m/h. This air velocity is low because of the high concentration of H]S between 500 and 2500 vpm. These operating conditions allow the sweep of a large range of volumic load (Cv).

4 730 Air Pollution Water Flowmeter Figure 1 : The pilot unit Analytical methods H2S was measured using a chromatography apparatus HNU model GC 311. The analytical conditions are the following : injector temperature : 120 C oven temperature : 80 C carrier gas : N? column : Hay's - N 1,20m, Mesh detector : photoionisation (10.2 ev)

5 Air Pollution 731 The retention time of H2S in the column is found to be 42 s. The concentration range is between 0.1 vpm and 3500 vpm. The bacteria were counted with petri box cultures [11]. RESULTS AND DISCUSSION Performances of the bioprocess The performances of the biofilter are approached by the determination of the removed H]S amount as a function of the volumic load. Figure 2 presents these results. QP (kg/m3) 45. r 6 ^ 8» * * U Oil* :, n 4 n!3 " 15 - ; i i i i i Cv (kg/m3.d) Figure 2 : Removed H%S vs volumic load 1-5 Dry activated sludge 6-11 Dry activated sludge with ph control with calcium carbonate grains in the column (10%) Dry activated sludge column fed with poor O2 (6%) influent Good performances are found. The ph control allows us to obtain better results. Previous studies [8] have shown an acidification of the packing material due to the production of sulfuric acid by bio-oxydation of the substrate H?S. Then, the

6 732 Air Pollution addition of calcium carbonate grains in the column buffers the medium to ph close to 7 and gives a better degradation velocity. The head loss as a function of the gas velocity and the moisture of the packing material is given in the figure 3. Approach of mechanisms Analyses in the packing material [10] allow to propose mechanisms of the biodegradation of H%S on the material (Figure 4). Different biomass quantifications show the presence of 50% autotrophic and 50 % heterotrophic bacteria. Among the bacteria we have to note the presence of Thiobacillus and Pseudomonas, Bacillus and Aspergillus species. Ah/L (mm H2O/m) 120 T -0% a-10% 20% 50% U (m/h) Figure 3 : Head loss in the column vs the gas velocity and the moisture of the activated sludge.

7 Air Pollution 733 x,o Figure 4 : Evolution of H]S and sulfur oxydized forms CONCLUSIONS This study produces the following conclusions: The biodegradation of H]S is possible using a biofilter packed with dry activated sludge and calcium carbonate grains. Good performances are obtained for the removal of H2S with acceptable operating conditions. An approach of mechanisms is proposed. REFERENCES [1] Le Cloirec P., Fanlo J.L., Degorce-Dumas J.R, Odeurs et Desorisation Industrielles, Innovation 128 et CPE Eds, Paris, [2] Martin G., Laffort P., Odeurs et Desodorisation dans I'Environnement, Tech & Doc, Lavoisier, Paris, [3] Bouscaren R., "Les odeurs et la desodorisation", Tech Sci. Mun.,6, , [4] Le Cloirec P., Lemasle M., Martin G., "Les odeurs, analyses et concentrations dans diverses situations", Pollut., 119, , 1988.

8 734 Air Pollution [5] Pomeroy R.D, "Biological treatment of odorous air", J. Wat. Pollut. Control Fed., 54, , [6] Martin G., Le Cloirec P., Lemasle M., Gabon J., "Retention de Produits odorants sur tourbe", Proceeding 8th World Air Clean Congress, The Hague, The Netherlands, 4, , [7] Jol A., Dragt A.J., "Biological elimination of ammoniac in ventilation air from livestock production, Proceeding 8*h World Air Clean Congress, The Hague, The Netherlands, 2, , [8] Kowal S., Fanlo J.L., Degorce-Dumas J.R., Le Cloirec P., "Removal of H2S by a biofilter with dry activated sludge, an approach of mechanisms", Proceeding Intern. Symposium Environmental Biotechnology, Ostende, Belgique, , [9] Diks R.M., Ottengraf S.P., "Process Engineering aspects of Biological waste gas purification", Proceeding Intern. Symposium Environmental Biotechnology, Ostende, Belgique, , [10] Kowal S., "Elimination d'hzs par biofiltre", These Universite d'aix Marseille, France, [11] Kowal S., Fanlo J.L., Degorce-Dumas J.R., Le Cloirec P., "Desodorisation sur biofiltre a support consommable : exemple du precede BSE", Pollut. Atm., 1, 34-41, 1992.