Data from the regular monitoring of a full-scale biofilter at a municipal solid waste treatment facility for the integral treatment of domestic residues was analyzed in order to assess potential operational problems and to evaluate reactor’s performance in terms of ammonia removal, the target odorous compound
at the facility. Performance was assessed based on ammonia removal efficiency and elimination capacity. Average elimination capacities up to 1,6 g NH3 m-3 h-1 at average inlet loads of 2,1 g NH3 m-3 h-1 were found, which correspond to a low-loaded biofilter type. Year-round data collected and packing material
analysis revealed a marked effect of water content in the packed bed of the biofilter which lead to reduced removal efficiencies.Peer ReviewedPostprint (published version

Diaz, O

Gabriel Buguña, David

Gamisans Noguera, Javier

Lafuente Sancho, Francisco Javier

English

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PERFORMANCE CHARACTERIZATION OF A FULL-SCALEBIOFILTER AT AN ORGANIC WASTE TREATMENT PLANTO. Díaz1, X. Gamisans2, D. Gabriel1, J. Lafuente11Department of Chemical Engineering, Universitat Autònoma de Barcelona, Edifici C, 08193 Bellaterra, Barcelona, Spain. david.gabriel@uab.es2Department of Mining Engineering and Natural Resources, Universitat Politècnica deCatalunya, Bases de Manresa 61-73, 08240 Manresa, SpainABSTRACTData from the regular monitoring of a full-scale biofilter at a municipal solid waste treatment facilityfor the integral treatment of domestic residues was analyzed in order to assess potential operational pro-blems and to evaluate reactor’s performance in terms of ammonia removal, the target odorous compoundat the facility. Performance was assessed based on ammonia removal efficiency and elimination capacity.Average elimination capacities up to 1,6 g NH3 m-3 h-1 at average inlet loads of 2,1 g NH3 m-3 h-1 werefound, which correspond to a low-loaded biofilter type. Year-round data collected and packing materialanalysis revealed a marked effect of water content in the packed bed of the biofilter which lead to reducedremoval efficiencies.INTRODUCTIONMunicipal solid waste composting facilities (MSWCFs) are facilities for the integral treat-ment of domestic residues. Since people is not very concerned about selective collection, acti-vities at these facilities include separation of received material and composting of the organicfraction from domestic waste, which are known as odour emitting activities. Odour compoundsin MSWCFs mainly originate from decomposition of organic waste since the arrival of the wasteto the facility until its separation and aerobic decomposition of composting. Amongst others,volatile organic compounds (VOCs), ammonia and hydrogen sulfide are produced during thecomposting process, which are noticed as annoying odours. Biofiltration is an inexpensive and effective gaseous waste treatment method based on theability of some microorganisms to degrade mainly malodorant compounds, under aerobic con-ditions, into biomass and mineral end-products (Dicks and Ottengraf, 1991). In a biological fil-ter, the waste gas is forced through a layer of biologically active packing with a relatively highspecific area. A water phase is then entrapped in the packing material (Devinny et al., 1999). The aim of this research was to assess the performance of a full-scale biofilter designed totreat 345000 m3/h of foul air from different areas of a completely covered municipal solid wastetreatment facility. Performance parameters such as removal efficiency and elimination capacityover more than a year of operation are discussed coupled with some findings such as packingbed drying and probable nitrogen accumulation in the biofilter.MATERIALS AND METHODSFull-scale biofilter characteristics and biofilter monitoring planAs shown in Figure 1, the MSWCF where the biofilter is located is divided in areas for rawmaterials processing, areas for organic waste treatment such as composting tunnels and anaero-bic digesters, and areas for by-products treatment in a wastewater treatment plant and a biofil-317Gaseous Emissions and Odourster. It should be noted that foul air from a total of 38 composting tunnels is first passed throughan acidic chemical scrubber for ammonia absorption and then mixed with the air coming fromall covered areas of the facility before entering the biofilter. Before the biofilter a humidifier rai-ses air humidity up to 95-100% RH.The biofilter is compartmentalized in four identical modules (Figure 1 callout) with a surfa-ce area of 625 m2 each and a 21 m long and 30 m wide footprint. Each level is divided in twomodules with independent waste air and clean air plenums. Design and recommended operatio-nal parameters are shown in Table 1. A set of 20 sprinklers per module placed on the biofilter roof are used for humidification ofthe packing material. Watering is performed once a day for a period of 30 minutes at a flow rateof around 33 m3/d per module. The packed bed has a first layer of around 25-30 cm height madeof roots for proper air distribution and a second layer of 80-85 cm height made of coconut fiberas biological packing support. Notice in Table 1 that the design volume corresponded to a totalheight of 1,5 m but the height of the packed bed at the time of the study was noticeably lowerprobably due to coconut fiber compression. A regular monitoring plan and operational testing was carried out in the biofilter in order toassess operation. Monitoring of the biofilter operation focused on NH3 as the target pollutant.The lower right module in Figure 1, namely module 4, was chosen as representative of the wholebiofilter for monitoring biofilter performance. Leacheate data was collected from a leacheatecollection pipe. Measurements were performed once a week for inlet and outlet gas samples,while leacheate measurements were performed on a monthly basis. Foul airflow rate was perio-dically measured using a Pitot tube into the inlet duct of the biofilter. Ammonia and H2S mea-surements were made with a portable Dräger MiniWarn meter. RH and temperature were mea-sured with a Testo 400 portable hygrometer. Ammonium, nitrite, nitrate in samples collected inthe leacheate were analyzed by an outside certified lab. pH was determined in the facility lab318Sustainable Organic Waste Management for Enviromental Protection and Food SafetyFigure 1. Front view of the biofilter and schematic of the overall facility: waste material reception and selection area (¡), anaerobic digesters (S), composting tunnels (), biofilter (z), compost storage area (¢), wastewater treatment plant (¥) Design Parameters Operational ParametersSurface (m2)  2700  Air Relative Humidity (%)  95-100Packed bed volume (m3)  4050  Packing material humidity (%)  50-70 Gas velocity (m/h)  128  Temperature (ºC)  15-40 Gas flow rate (m3/h) 345000  Pressure drop (Pa) 350-1000 Watering flow rate (m3/d) 100-160 pH 6-9Table 1. Design parameters for the biofilter and maximum and minimum operational parametersrecommended by the biofilter maker. with a CRISON 507 pH meter.RESULTS AND DISCUSSIONThe full-scale biofilter was monitored for more than a year, starting January 2003, in orderto fully cover seasonal effects such as temperature. In order to this, three clear periods wereencountered along the monitored period (Figure 2). Firstly, a 150 days period (period I) with alow temperature of the inlet waste gas and marked fluctuations in the inlet and outlet RH.Secondly, period II showed a progressive raise in the off-gases temperature fed to the biofilter,which took place around day 150 until day 310 coincident with the hottest months of the year.In spite of some RH fluctuations until day 180, inlet airflow was maintained close to water satu-ration thereafter. Thirdly, named period III, the temperature of the inlet gas progressively decre-ased to a value of around 20ºC, a similar value on average to the corresponding to period I.Notice in Figure 2 that the outlet relative humidity (RH) was markedly below the inlet RH afterday 180, consistent with a lower temperature measured at the outlet of the biofilter, thus indica-ting higher water requirements in the packing material during periods II and III. Inlet NH3 concentration fluctuated during normal operation in the range of 13 to 80 ppmv.On average, inlet ammonia concentration was 41±17 ppmv for the monitored period. Outlet NH3concentration followed the same inlet pattern with average outlet ammonia discharge of 10±7ppmv. Although the discharge limit is not regulated, a value of 20 ppmv averaged for 8 hours wasestablished by the facility for ammonia concentration exiting the biofilter. H2S levels found weremarkedly low, with an average inlet concentration along the monitored period of 2 ppmv.Consequently, local acidification of the media by H2S degradation is not probable. No controlsystem was used to maintain the pH to c.a. 8.It should be noted that measured outlet NH3 concentrations in period III were notably hig-her compared to those in periods I and II even though the inlet loads were similar. Higher remo-val efficiencies were found in period II (89% on average) compared to period I (74% on avera-ge) and III (64% on average) probably due to the higher temperature in the biofilter which incre-ased biological activity in the packing material. A significant decrease in RE and EC were found in period III even when the volumetric loadto the reactor, was kept almost constant along the monitored period. According to the results and319Gaseous Emissions and OdoursFigure 2. Evolution of inlet andoutlet relative humidity, tempera-ture, pH and ammonia concentra-tion along the monitored periodplant personnel observations around days 150-180 in Figure 2, it was found that some parts ofthe surface of the packing material were not completely wetted because of a reduced pressureavailable in the spraying system, which caused a decrease in the area showed by the sprinklers.This is consistent with the increased water demand in period III according to RH data (Figure2). Dried zones in biofilters have been reported to cause short-circuiting and in consequencereduced elimination efficiencies (Devinny et al., 1999). In consequence, three samples of packing material were withdrawn from two zones of modu-le 4 of the biofilter and analyzed for water content and water holding capacity according to TestMethods for the Examination of Composting and Compost (1995). One sample was withdrawnfrom the surface of a dry area that was not well sprinkled. Two other samples were withdrawnfrom a wet zone, one from the surface of the packing material and the other from a depth ofabout 50 cm. Results in figure 3 certify dry out of the packing material in the sampled area andthat the drier the coconut fibre is the less water holding capacity has. In consequence, it is cru-cial to avoid dry out of the material, mainly because the lack of humidity implies a decrease ofthe microbiological activity and possible short-circuiting The results discussed herein demonstrate the performance and capabilities of a biofilter interms of ammonia removal. Full-scale biofilter monitoring revealed that proper watering of thepacked bed is essential to preserve biofilter activity; otherwise reduced efficiencies and elimi-nation capacities are likely to occur. According to the data, main parameters that influencedammonia removal were temperature and, in special, watering and water content in the packingmaterial. Activities towards maintenance and appropriate functioning of watering systems mustbe warranted.REFERENCESAPHA. 1995. Standard Methods for the Examination of Water and Wastewater. 19th edition, AmericanPublic Health Association, Washington DC (US). Chung Y., Huang C., Tseng C., Pan, J.R.v. 2000. Biotreatment of H2S- and NH3- containing waste gasesby co-immobilized cells biofilter. Chemosphere., 41: 329-336.Devinny, J. S., Deshusses, M. A., Webster, T. S. 1999. Biofiltration for Air Pollution Control. Lewis, BocaRaton, FL (US). Dicks, R.M., Ottengraf, S.P.P. 1991. Process Engineering Aspects of  Biological Waste Gas Purification.Proceedings of the. International Symposium on Enviromental Biotechnology, Ostende (B), 1991, pp353-368.U.S. Composting Council. 1995. In P.B. Leege and W.H. Thompson (ed.) Test methods for the examina-tion of composting and compost. USCC, Bethesda, MD (US). 320Sustainable Organic Waste Management for Enviromental Protection and Food Safety Sample locationDry zone Upper wet zone Lower wet zoneWaterContent(%)0102030405060708090100 Sample LocationDry zone Upper wet zone Lower wet zoneWaterHoldingCapacity(gwater/gdrymaterial)02468Figure 3. Water content and water holding capacity of packing material samples. 

Performance characterization of a full-scale biofilter at an organic waste treatment plant

Data from the regular monitoring of a full-scale biofilter at a municipal solid waste treatment facility for the integral treatment of domestic residues was analyzed in order to assess potential operational problems and to evaluate reactor’s performance in terms of ammonia removal, the target odorous compound

at the facility. Performance was assessed based on ammonia removal efficiency and elimination capacity. Average elimination capacities up to 1,6 g NH3 m-3 h-1 at average inlet loads of 2,1 g NH3 m-3 h-1 were found, which correspond to a low-loaded biofilter type. Year-round data collected and packing material

analysis revealed a marked effect of water content in the packed bed of the biofilter which lead to reduced removal efficiencies.Peer Reviewe

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Performance characterization of a full-scale biofilter at an organic waste treatment plant

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