Assessment of Airborne Microorganisms in a Swine Wastewater Treatment Plant

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1 Environ. Eng. Res Decemer,17(4) : Reserch Pper pissn eissn X Assessment of Airorne Microorgnisms in Swine Wstewter Tretment Plnt Ki-Youn Kim 1, Hn-Jong Ko 2, Dekeun Kim 3 1 Deprtment of Industril Helth, Ctholic University of Pusn, Pusn , Kore 2 Division of Livestock Policy, Jeju Specil Self-Governing Province, Jeju , Kore 3 Deprtment of Environmentl Engineering, Seoul Ntionl University of Science nd Technology, Seoul , Kore Astrct Quntifiction of the irorne microorgnisms (cteri nd fungi) t swine wstewter tretment plnt ws performed. Microil smples were collected t three different phses of the tretment process over 1-yr period. Cultivtion methods sed on the vile counts of mesophilic heterotrophic cteri nd fungi were performed. The concentrtions of irorne cteri rnged up to out colony-forming unit (CFU)/m 3, nd those of irorne fungi rnged up to out CFU/m 3. The primry tretment (e.g., screen, grit removl, nd primry sedimenttion) ws found to e the mjor source of irorne microorgnisms t the site studied, nd higher levels of irorne cteri nd fungi were oserved in summer. High levels of the respirle ioerosol (0.65 to 4.7 μm in size) were detected in the ertion phse. Among the environmentl fctors studied, temperture ws strongly ssocited with fungl erosol genertion (with Spermn correltion coefficient of 0.90 nd p-vlue <0.01). Occuptionl iorisks re discussed sed on the oserved field dt. Keywords: Bioerosol, Sesonl vrition, Size distriution, Swine wstewter 1. Introduction The rpid industriliztion of livestock production hs led to one of the world s most pressing environmentl prolems, including prolems cused y the lrge quntities of wstewter generted [1]. Collection nd tretment plnts for wstewter hve een used extensively to meet demnds for lower effluent concentrtions. Wstewters contin lrge mounts of pthogenic nd nonpthogenic microorgnisms, some of which my e potentil helth hzrds for workers [2]. Airorne relese from these sites my e criticl pthwy for pthogen movement off the sites [3]. Mny studies hve een crried out to evlute the iologicl risks of erosols emitted from municipl wstewter tretment plnts [4-10]. Teixeir et l. [4] reported tht in municipl wstewter tretment plnt, the indoor culturle ioerosol concentrtion vried up to colony-forming unit (CFU)/ m 3 for totl cteri, nd CFU/m 3 for totl fungi. The ioerosol emission lso vried ccording to the tretment stges [9, 11]. The exposure of workers to irorne microorgnisms my vry depending on the type nd cpcity of the fcility, the ctivities performed, nd the wether conditions. Livestock-relted fcilities re potentil source of pthogenic ioerosols [12], especilly Cmpylocter spp. (responsile for cmpylocteriosis), vin influenz virus, Newcstle disese virus, Escherichi coli (colicillosis), Slmonell spp., nd foot-nd-mouth disese virus. Ko et l. [3] investigted ioerosols relesed from twelve swine frms with different mnure tretment technologies, using liquid impinger for microiologicl ir smpling. They found tht the concentrtion of irorne culturle cteri rnged from 10 2 to 10 5 CFU/m 3, nd the irorne culturle fungl concentrtions rnged from 10 to 10 3 CFU/m 3. However, the liquid impinger hd 0.3 μm cut-off dimeter, which could result in lower collection efficiency for smller-sized ioerosols. The liquid impinger is less efficient for trditionl cultivtionsed detection compred to solid impctors, which re comprtively efficient for culturle cteril smpling sed on the results of moleculr microil nlysis [13]. Since treted wstes differ t the vrious sites, the initil numers nd concentrtions of microorgnisms could e site-specific. Hence, further studies re required to chrcterize the ioerosol emission in the swine wstewter tretment plnts. The environmentl effects on ioerosol emission in swine wstewter tretment plnt re not well known to the est of our knowledge. The size distriution of ioerosol emitted from plnt is importnt to study, ecuse the deposition of ioerosol prticles in the respirtory system depends on their erodynm- This is n Open Access rticle distriuted under the terms of the Cretive Commons Attriution Non-Commercil License ( org/licenses/y-nc/3.0/) which permits unrestricted non-commercil use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. Received July 23, 2012 Accepted Novemer 28, 2012 Corresponding Author E-mil: kimd@seoultech.c.kr Tel: Fx: Copyright The Koren Society of Environmentl Engineers 211

2 Ki-Youn Kim, Hn-Jong Ko, Dekeun Kim Woods Downwind 1 2 Primry tretment (indoor) Upwind Biologicl tretment Sludge tretment Fig. 1. Schemtic digrm of the swine wstewter tretment plnt nd smpling sites indicted with ( ): (1) primry tretment (indoor); (2) iologicl tretment; (3) post tretment (indoor). Upwind nd downwind externl control sites re indicted with ( ). ic dimeter, nd the effects on humn helth re relted to the sizes nd physicl properties of the prticles [14]. This study hs een conducted to exmine the genertion chrcteristics of irorne cteri nd fungi emitted from swine wstewter tretment plnt y using solid impct ir smpler. Cultivtion methods sed on the vile counts of mesophilic heterotrophic cteri nd fungi were performed. We chrcterized the sesonl chnge in irorne microorgnism concentrtion t different stges of the tretment process (primry tretment, iologicl tretment, post-tretment). We lso explored the distriution chrcteristics of irorne microorgnisms for ech prticle size in ech of the processes. The degree of correltion etween irorne microorgnisms nd environmentl conditions t the test sites ws lso determined. 2. Mterils nd Methods Office uilding 2.1. Plnt Description nd Smpling Loctions The study ws performed t the swine wstewter tretment plnt, with ctivted sludge iologicl tretment, locted in Hllym, Jeju Islnd, Kore. The selection of the study site ws sed on the structure of the plnt (indoor nd outdoor structures), nd the plnt ws lso locted wy from ny existing sources of nthropogenic ir pollution. A schemtic digrm of the plnt is presented in Fig. 1. The plnt receives 100 m 3 /dy of wstewter, trnsported y truck nd tnk triler, nd generted y swine frms scttered ll over Jeju Islnd. The plnt hs three seprte phses of tretment process, consisting of primry tretment, iologicl tretment, nd post tretment. Rw wstewter enters n indoor primry tretment process (herefter referred to s the inlet process ), with screen, n erted grit chmer, nd solid-liquid seprtion, ll of which re uncovered nd exposed to the indoor environment. The secondry tretment is sed on ctivted sludge (herefter referred to s the ertion process ), nd ertion 3 Post tretment (indoor) Rod is performed in opened ertion tnks with fine ule diffusers. The wstewter finlly moves to n indoor post-tretment process (herefter referred to s the outlet process ) with ozone oxidtion, cogultion, nd filtrtion. All processes except for the secondry tretment were performed inside uildings. Bioerosol smples were independently collected t ech processing site in the plnt to provide insight into ny differences in ioerosol genertion, nd to compre indoor nd outdoor environments in the plnt. The smpling loctions were selected ccording to wind directions nd ccess depending on the opertionl ctivities tking plce (see the smpling loctions in Fig. 1). Indoor smples were usully tken t distnce of 1 to 2 m from the potentil sources. Outdoor smples were tken 2 to 4 m downwind from the opertions. In ll cses, ckground smple ws tken t n upwind loction unffected y plnt opertions, usully 10 to 20 m upwind Air Smpling nd Anlysis Site visits for smpling were undertken once month from Octoer 2009 to Septemer Microil investigtions were crried out during ordinry work time (1:00 PM to 4:00 PM) t height of out 1.5 m ove the floor of the site eing investigted. Cultivtion-sed detection in selective medi fter impction ws pplied to detect nd chrcterize the vile components of ioerosol. Mesophilic heterotrophic cteri were chosen to e nlyzed, ecuse they re prevlent in the environment [9]. Air smples of irorne cteri nd fungi were collected using two ir smplers; single-stge impctor smpler (Buck Bio-Culture Pump model B30120; A. P. Buck Inc., Orlndo, FL, USA), nd six-stge vile prticulte cscde impctor (Model ; Andersen Inc., Smyrn, GA, USA). The cscde impctor ws selected to identify the distriution chrcteristics of the prticulr ioerosol y the erodynmic prticle size, for which the rnges in stges 1 to 6 re >7.0 μm, μm, μm, μm, μm, nd μm, respectively. The sum of the colonies counted etween stges 3 nd 6 corresponds to the respirle frction. The impction flow rte for oth smplers ws set to 28.3 L/min. The durtion of ir smpling ws initilly set to 5 min, nd then vried ccording to the environmentl conditions t the mesurement loctions. Bcteri nd fungi smples were smpled in sequence. Trypticse Soy Agr (TSA) (Lot ; BD, Frnklin Lkes, NJ, USA), with 500 mg of cycloheximide dded to suppress fungl growth, ws used s the cteril culture medium. Airorne fungi were cultured in Sournd Dextrose Agr (SDA) (Lot ; BD) with 100 mg of chlormphenicol to inhiit the prolifertion of cteri. The culture medi were immeditely trnsported to the lortory fter every collection cycle, nd cultured in n incutor for 1 2 dys t 37 C for cteri, nd for 3 5 dys t 25 C for fungi. The colonies were counted, nd the mesurement ws expressed s CFU/m 3. Environmentl fctors were lso mesured to nlyze ny correltion with ioerosol genertion. Temperture nd reltive humidity were mesured with digitl thermohygrometer (Model 608 H-1; Testo, Lenzkirch, Germny). Odor intensity ws nlyzed with hndheld odor meter (Model OMX-SR; Shinyei, Koe, Jpn). Airorne prticulte mtter (TSP, PM10, PM2.5, PM1.0) ws nlyzed using portle dust monitor (Dustmte; TurnKey Instruments Ltd., Cheshire, UK). 212

3 Bioerosol emission from swine wstewter tretment plnt c Fig. 2. Sesonl vrition in ioerosol concentrtions t the inlet process (), the ertion process (), nd the outlet process in the wstewter tretment plnt (c). The ox plots show geometric mens nd geometric stndrd devitions. Numer of smples for seson is 9 ech smpling site. F: fll, W: winter, G: spring, S: summer Dt Anlysis The microil contmintion ws nlyzed y seson nd seprtely for ech step of the tretment process. The sttisticl significnce of the correltion etween environmentl fctors nd irorne microorgnisms ws verified y Person nd Spermn correltion nlysis tests using the SAS/Stt 9.1 (SAS Institute Inc., Cry, NC, USA). The nlysis of vrince (ANOVA) nlysis method ws used to verify the sttisticl significnce of the differences etween the vlues of mesurements tken for two indoor processes nd n outdoor process. 3. Results nd Discussion 3.1. Totl Culturle Bcteri nd Fungi in Air Smples Culturle cteri nd fungi were detected in ll ir smples collected t ll sites t the scheduled times. The results re summrized in Fig. 2, which presents sesonl vritions in ioerosol concentrtions for ech step of the tretment process. Concentrtions of irorne culturle cteri generlly rnged from to CFU/m 3, nd those of culturle fungi rnged from to CFU/m 3. In the previous study, the levels of ioerosol relesed from twelve swine frms were slightly higher thn those of our oservtion [3]. However, s demonstrted in tht study, the difference in overll ioerosol concentrtions ws not sttisticlly different. In municipl wste tretment plnts, site workers should not e exposed to levels higher thn CFU/m 3 over n 8-hr working dy [15], nd the threshold limit in occuptionl tmospheres is 10 4 CFU/m 3 for the totl cteri concentrtion [16]. The oserved levels in our study cn therefore pose occuptionl iorisks in n occuptionl tmosphere. Fig. 2 shows tht the cteril concentrtions t the inlet process were the highest mong ll sites (ANOVA, p < 0.01), s were the fungl levels t the inlet process (ANOVA, p < 0.01). It hs een shown in other studies tht the pretretment process nd primry clrifier generte the highest concentrtions of irorne microorgnisms, including cteri nd fungi, mong the tretment stges of the wstewter tretment plnts [2, 7-9]. The ertion chmer hs een recognized s presenting the highest risk for exposure to iologicl erosol ecuse of the mount of microiologicl pollution generted [11]. Hence, the oserved results indicte tht potentil ioerosol sources, such s the undnt microorgnisms in the rw wstewter, my e suject to mechnicl gittion during pretretment, such s in the grit removl tnk, ertion sin, nd primry clrifier. Fig. 2 lso shows the sesonl vritions in culturle microorgnisms in ir smples. The mximum exposure ws found to occur during the summer t the following men levels: 4,141 ± 1,386 CFU/m 3 for culturle irorne cteri nd 765 ± 171 CFU/m 3 for culturle irorne fungi, oth of which were oserved t the inlet process. For indoor sites (inlet nd outlet processes), cteril nd fungl levels in ir smples were oserved in the following descending order: summer > spring > winter > fll, while for the outdoor site, the cteril level in the summer ws not the highest. Krr nd Ktsivel [9] oserved tht the heterotrophic cteril concentrtion in ir decresed during summer dy in the sunshine, ccompnied y incresing solr rdition nd temperture, while fungl concentrtion incresed slightly. High temperture nd solr rdition in the summer could ffect the survivl of the irorne microorgnisms or dectivte them. Correspondence of the ioerosol level to sesonl chnges ws significnt (ANOVA, p < 0.01) for ll smpling sites. The sesonl vrition in ioerosols with meteorologicl conditions such s temperture, humidity, wind speed nd direction, solr rdition, nd pollutnts, hs een investigted in previous studies, where it ws speculted tht these fctors should ffect the genertion levels of ioerosols outdoors rther thn indoors [2, 9]. The reltionship etween ioerosol genertion nd environmentl conditions will e discussed in Section

4 Ki-Youn Kim, Hn-Jong Ko, Dekeun Kim Fig. 3. Summry of ioerosol concentrtions during the field study. The ox plots show medins, 5th nd 95th percentiles, nd outliers. The dotted line indictes ckground levels of ioerosols (300 CFU/m 3 for irorne cteri; 220 CFU/m 3 for irorne fungi; oth re verge vlues over the period of study) t ech loction. The ckground dt were otined t distnce of 10 to 20 m from the plnt nd ginst the wind direction. Fig. 4. Size distriutions of irorne cteri () nd irorne fungi () t the smpling loctions t the wstewter tretment plnt. The erodynmic dimeter rnges for the vile prticle sizing smpler were >7.0 μm (stge 1), μm (stge 2), μm (stge 3), μm (stge 4), μm (stge 5), nd μm (stge 6). Fig. 3 presents the overll ioerosol concentrtions t the smpling sites during 1 yr of study. A grdul decrese in the concentrtions of cteri nd fungi in the ir smples ws oserved fter n erly step of the tretment process (i.e., inlet process). The men concentrtions of culturle cteri in ir smples were 1,753 ± 1,693 CFU/m 3 t the inlet process, 735 ± 461 CFU/ m 3 t the ertion process, nd 327 ± 234 CFU/m 3 t the outlet process. In comprison, the men concentrtions of culturle fungi were 345 ± 264 CFU/m 3 t the inlet process, 238 ± 203 CFU/ m 3 t the ertion process, nd 199 ± 128 CFU/m 3 t the outlet process. In totl, the concentrtion of culturle cteri in the ir smples decresed y more thn 80% fter post-tretment, ut those of culturle fungi did so only y round 40%, regrdless of sesonl vrition. The culturle cteril concentrtion in the ir smples ws, t lest, 5 times the culturle fungl concentrtion t the inlet process; further, the culturle cteril concentrtion in the ir smples ws 3 times tht t the ertion process nd 1.6 times tht t the outlet process. It is importnt to note tht the ckground levels of ioerosols were greter thn those oserved t the outlet process, lthough fr less thn those t the inlet process. The exct microil concentrtion cnnot e determined using cultivtion-sed detection due to the fct tht there is methodologicl limittion of culturing ll the individul microorgnism colonies existing in n environmentl smple [9, 17], leding to underestimtion of the irorne living microorgnisms s well s underestimtion of the risks from toxic or immunopthogenic effects on the workers t site. Li et l. [10] reported tht y polymerse chin rection nd denturing grdient gel electrophoresis (PCR-DGGE) nlysis, pthogenic species such s Morxell nonliquefciens nd Flvocterium odortum, were detected from the ioersol t municipl wstewter tretment plnt. Pscul et l. [7] found Pseudomons erugino- s t pretretment nd primry clrifiers t municipl wstewter tretment plnt y PCR methods. It is therefore necessry to conduct qulittive evlution of irorne microorgnisms y identifiction, which would provide informtion out contriutions from internl genertion Distriution of Microorgnisms y Bioerosol Prticle Size Fig. 4 shows digrm of the distriution of irorne cteri nd fungi ccording to ioerosol size t ech step of the wstewter tretment plnt. At the inlet process, the highest distriution ppers in stge 2 (85 CFU/m 3 for culturle cteri nd 35 CFU/m 3 for culturle fungi), with ioerosol size is in the rnge of μm. The lowest distriutions were in stges 3 nd 4 (7 CFU/m 3 for culturle cteri in oth stges nd culturle fungi were undetectle). The ioerosol sizes re in the rnges μm nd μm, respectively. At the outlet process, the highest distriution ppered in stge 2 (57 CFU/m 3 for culturle cteri), where ioerosol size is in the rnge of μm, ut differences in the distriutions of other size rnges were not significnt. At this site, culturle fungi show n even distriution in stges 2, 3, 4, nd 6. At the inlet process, the rtios of respirle concentrtion to totl concentrtion (corresponding to ioerosol sizes of 0.65 to 4.7 μm) were 0.37 nd 0.30 for culturle cteri nd fungi, 0.54 nd 0.69 t the ertion process, nd 0.27 nd 0.75 t the outlet process, respectively. In full-scle composting fcility, size distriutions of the totl irorne microorgnisms were evenly distriuted in the six stges, nd the concentrtions t ech stge were over 10 4 CFU/m 3 [18]. In feedstuff-mnufcturing fctories, over 70% of irorne cteri were concentrted in respirle ir nd more thn 60% of irorne fungi consisted of respirle irorne fungi [17]. It hs 214

5 Bioerosol emission from swine wstewter tretment plnt No. Tle 1. Correltion coefficients for geometric mens of ioerosol concentrtions compred with environmentl prmeters Person correltion Spermn correltion Person correltion Spermn correltion Airorne cteri Airorne fungi r p-vlue r p-vlue r p-vlue r p-vlue Temperture < < <0.01 Reltive humidity < < TSP < < PM < < PM < < PM < < Odor intensity < RH: reltive humidity, TSP: totl suspended prticle. For Person correltion coefficient (r) nd Spermn correltion coefficient (r), old-fce: strong ssocition (r 0.6); underlined: moderte ssocition (0.4 r < 0.6). For p-vlue, significntly correlted (p < 0.01); mrginlly significntly correlted (0.01 p < 0.05). Numer of pired dt set: non-pired dt sets were removed for correltion nlysis. een reported y others [19, 20] tht ioerosols with erodynmic dimeters of 5 μm hve greter effect on the lveolus thn those with lrger dimeters, nd result in llergic rections nd other serious illnesses. In this study, the outdoor ertion process showed the highest rtio of respirle to totl ioeorsol concentrtion. It is speculted tht the secondry genertion of microorgnisms due to iologicl mechnism in the ertion process could contriute to high levels of respirle ioerosols detected. Although these ioerosol distriutions re ffected y environmentl fctors, meteorologicl conditions, nd genertion sources, the results oserved in this study my e site specific. The rtio of respirle ioerosol ws significnt, nd this poses potentil iologicl risk, which could e hzrdous to workers Effect of Environmentl Fctors on Bioerosol Genertion The degree of correltion etween irorne microorgnisms nd environmentl conditions t the test sites is summrized in Tle 1, which ws otined y pplying Person correltion nlysis nd Spermn correltion nlysis. Among the environmentl fctors investigted, ir temperture showed sttisticlly significnt correspondence with irorne fungi (p < 0.01) for oth Person nd Spermn correltion nlyses. In generl, Person correction is most pproprite for dt with liner reltionship, while Spermn correltion is more pproprite for non-liner cses. Hence, Spermn correltion is quite suitle for iologicl prmeters. For the Spermn correltion nlysis, the correltion coefficient for temperture ws found to e 0.90, while tht for reltive humidity ws In our previous study, the correltion etween reltive humidity nd irorne fungi ws much more significnt thn temperture in feedstuffmnufcturing fctories [17]. In sewge tretment plnt, oth ir temperture nd humidity were strongly correlted with irorne fungi ccording to the sttisticl estimtion y Spermn correltion [11]. The growth of irorne fungi is mximized when the reltive humidity is greter thn 70% [21]. In our field dt, the tempertures mesured vried from 2.3 o C to 33.0 o C, nd reltive humidity vried from 25% to 68%. The reltive humidity fluctuted less due to the smpling site eing wter sed. Fungi re especilly verstile, nd cn utilize different sustrtes for their growth, nd temperture nd wter vilility re the most importnt fctors for fungl growth [22]. For odor intensity, significnt ssocitions were found with the genertion of oth irorne cteri nd irorne fungi. Even odor intensity is not meningful s n environmentl fctor in iologicl development, ut it my e useful indictor of irorne iologicl issues. There hve een no similr reports on the distriutions of irorne microorgnisms in swine wstewter tretment plnts. However, compred with other studies on municipl wstewter tretment plnts [2, 7, 9, 23] nd other working sites [16-18, 24], the distriution of irorne microorgnisms ws found to hve similr pttern. There is no officil stndrd for the exposure to ioerosols in the indoor re of the studied site. The Americn Conference of Government Industril Hygienists (ACGIH) recommends indoor concentrtions of cteri nd fungi to e less thn 1,000 CFU/m 3 [25]. From the results of this study, the indoor pre-tretment process should e of concern to workers, nd thus, it is impertive tht pproprite institutionl stndrds nd mintennce guidnce e mde ville s soon s possile. 4. Conclusions The concentrtions of ioerosol (mesophilic heterotrophic cteri nd fungi) emitted from the swine wstewter tretment plnt vried depending on the step of the process eing considered, nd y seson. The pretretment process ws found to e the mjor source of ioerosol. For the ertion process, portion of the respirle ioerosol concentrtion ws significnt. Our study is the first report on the size distriution of cteri nd fungi erosolized from swine wstewter tretment plnt using solid impct ir smpler. A significnt correspondence etween temperture nd irorne fungi ioctivity ws found, nd the odor intensity could e used for detecting high levels of oth irorne cteri nd fungi. Our field dt should e tken into considertion in the design nd mintennce of the swine wstewter tretment plnts with respect to occuptionl sfety nd helth

6 Ki-Youn Kim, Hn-Jong Ko, Dekeun Kim Acknowledgments This study ws supported y the Bsic Science Reserch Progrm through the Ntionl Reserch Foundtion of Kore (NRF), funded y the Ministry of Eduction, Science, nd Technology (No ) nd y the Kore Ministry of Environment nd humn resource development project for energy from wste recycling. References 1. Melse RW, Timmermn M. Sustinle intensive livestock production demnds mnure nd exhust ir tretment technologies. Bioresour. Technol. 2009;100: Frcchi L, Pietronve S, Rinldi M, Giovnn Mrtinotti M. Site-relted irorne iologicl hzrd nd sesonl vritions in two wstewter tretment plnts. Wter Res. 2006;40: Ko G, Simmons OD 3rd, Likirdopulos CA, Worley-Dvis L, Willims M, Sosey MD. Investigtion of ioerosols relesed from swine frms using conventionl nd lterntive wste tretment nd mngement technologies. Environ. Sci. Technol. 2008;42: Teixeir JV, Mirnd S, Monteiro RA, et l. Assessment of indoor irorne contmintion in wstewter tretment plnt. Environ. Monit. Assess Fe 10 [Epu]. dx.doi.org/ /s Fischer G, Alrecht A, Jckel U, Kmpfer P. Anlysis of irorne microorgnisms, MVOC nd odour in the surrounding of composting fcilities nd implictions for future investigtions. Int. J. Hyg. Environ. Helth 2008;211: Grisoli P, Rodolfi M, Villni S, et l. Assessment of irorne microorgnism contmintion in n industril re chrcterized y n open composting fcility nd wstewter tretment plnt. Environ. Res. 2009;109: Pscul L, Perez-Luz S, Ynez MA, et l. Bioerosol emission from wstewter tretment plnts. Aeroiologi 2003;19: Snchez-Monedero MA, Aguilr MI, Fenoll R, Roig A. Effect of the ertion system on the levels of irorne microorgnisms generted t wstewter tretment plnts. Wter Res. 2008;42: Krr S, Ktsivel E. Microorgnisms in ioerosol emissions from wstewter tretment plnts during summer t Mediterrnen site. Wter Res. 2007;41: Li L, Hn Y, Liu J. Assessing genetic structure, diversity of cteril erosol from ertion system in n oxidtion ditch wstewter tretment plnt y culture methods nd iomoleculr tools. Environ. Monit. Assess Mr 10 [Epu] Korzeniewsk E, Filipkowsk Z, Gotkowsk-Plcht A, Jnczukowicz W, Dixon B, Czulowsk M. Determintion of emitted irorne microorgnisms from BIO-PAK wstewter tretment plnt. Wter Res. 2009;43: Cmr-Lopez M, Arnink AJ, Zho Y, Clvet S, Torres AG. Airorne prticulte mtter from livestock production systems: review of n ir pollution prolem. Environ. Pollut. 2010;158: Li K. Moleculr comprison of the smpling efficiency of four types of irorne cteril smplers. Sci. Totl Environ. 2011;409: Reponen T, Lehtonen M, Runem T. Effect of indoor sources on fungl spore concentrtions nd size distriutions. J. Aerosol Sci. 1992;23: Sigsgrd T, Bch B, Mlmros P. Respirtory impirment mong workers in grge-hndling plnt. Am. J. Ind. Med. 1990;17: Domingo JL, Ndl M. Domestic wste composting fcilities: review of humn helth risks. Environ. Int. 2009;35: Kim KY, Kim HT, Kim D, Nkjim J, Higuchi T. Distriution chrcteristics of irorne cteri nd fungi in the feedstuffmnufcturing fctories. J. Hzrd. Mter. 2009;169: Byeon JH, Prk CW, Yoon KY, Prk JH, Hwng J. Size distriutions of totl irorne prticles nd ioerosols in municipl composting fcility. Bioresour. Technol. 2008;99: Reponen T, Hyvrinen A, Ruusknen J, Runem T, Nevlinen A. Comprison of concentrtions nd size distriutions of fungl spores in uildings with nd without mould prolem. J. Aerosol Sci. 1994;25: Pstuszk JS, Pw UK Lis DO, Wlzlo A, Ulfig K. Bcteril nd fungl erosol in indoor environment in Upper Silesi, Polnd. Atmos. Environ. 2000;34: Wlter MV, Mrthi B, Fielnd VP, Gnio LM. Effect of erosoliztion on susequent cteril survivl. Appl. Environ. Microiol. 1990;56: Burge HA. Bioerosols. Boc Rton: Lewis Pulishers; Orsini M, Lurenti P, Boninti F, Arzni D, Lnni A, Romno- Spic V. A moleculr typing pproch for evluting ioerosol exposure in wstewter tretment plnt workers. Wter Res. 2002;36: Millner PD. Bioerosols ssocited with niml production opertions. Bioresour. Technol. 2009;100: Mcher J. Bioerosols: ssessment nd control. Cincinnti: Americn Conference of Governmentl Industril Hygienists;