Journal o f Scientific & Industri a l Research

Vol. 62, March 2003 , pp 193- 197

Toluene Degradation in Biofilter - Sequencing the Nutrient Addition Ajit Haridas, A S Baby and S Majumdar*

Regional Rescarch Laboratory(CS IR), Tri vandmm 695 0 19, Kerala

Reccivcd: 12 June 2002; acccptcd : 04 Octoher 2002

Biofi lt ration is a cheap and effec ti ve mct hod fo r purification of a ir stream with d ilute contami nat ion of vo latile organic compounds. To luenc is industrially important VOc. The biological degradation of to luene was studied in a bench scale biofilt e r where coir p it h was used as li lt er med ia. Nutrient s playa cm cial ro le in fac ilitati ng the degradati on efficiency. NUlri cnt level in the hio lil ter media is to he mainta ined at a parti cul ar level, below whi ch, the effic iency of the biolilter reduces. Under opt imized condit ion, depiction o f nutrients became s lower and in freq uent replacemen t o f nutr ient laden pith at the topmost layer of the hioli lter was cnough for main tain ing the good removal e ffi ciency. The pH of the media was maintained slightly aho ve neu tra l without any furt her addit ion of hulTer except during start-up.

Introduction

B io filtra ti on is an economica l method to contro l odorous and tox ic emi ss ions from va ri ous sources l

.

T he constructi on o f the bio filt e r is re lative ly s impl e compared to the a lternati ve techno logies ava il ab le2

. A bio filte r cons ists o f a conta ine r of o rgani c porous med ia popul ated w ith mic ro-organI sms through which odorous a ir is passed , usua ll y up ward1

. T he core of the biofilter syste m is the filte r med ia. O n the surface o f the filt e r medi a, growth o f the micro­organi sms takes pl ace. M ain func ti on of bi o filtrati on is to bring the po llutants conta ined in the a ir/ex haust gas streams in contac t w ith the mi cro-organi sms which are immobili sed on the surface of the biofilte r medi a4

.'. W ith the he lp o f ava il able mo isture the popul ati on cyc les of the mi cro-organi sms are mainta ined fo r degradati op of the po llutants. T he contaminated gas is d iffu sed in the bi o filte r and adsorbed into the bi o film . Mi cro-organi sms utili ze the pollu tant as ene rgy sources, with the final products being carbon di ox ide, wate r, mine ra l salts and heat. T he key phys ica l processes in vo lved in bi ofilt ra tion are convect ive transport o f a ir through the bed , di ffusion of the vo latil e compounds into the aqueous film on the bed , di ffu s ion of the compounds to the biofilm . Bi ofiltrati on is e ffecti ve to treat la rge vo lume of a ir conta ining vo latil e o rganic compound s in dilu te

* Correspondin g Author Phone: 91-47 1-490674; Fax: 9 1-47 1-49 17 12 em:li I: sW;lchchI1a @excitc .com, sm@csrritrd.rcn.n ic. in

concentrati on. A mmoni a, carbon monox ide, hydrogen sulph ide, styrene, acetone, benzene, a ldehydes, d iethy l amine, ke tones, me thano l, Ethano l, tri chl oroethane, pentane , and dime thy l sulphide are a few o f the compounds' w hich can be removed by bi ofi Itrat ion syste ms. G reater than 90 per cent re mova l of diff icult-to-degrade aromatic compou nds has been achi eved6 and in suc h cases the residence time required is greate r than 3 min .

To luene, C7HR, is a co lourless, mobile liquid with a di stincti ve aromatic odour somewhat mi lder than that of benzene. Toluene is produced mai nly from cata lytic reforming of refine ry streams. It is mainl y used as solvent and has got app lication in pa ints and coating industries, adhes ive indust ri es , pharmaceuticals, and fo rmul ated produc t industries . T o luene is quo ted as one o f the priority envi ronmenta l tox ic po llutants by US Environmenta l Protecti on Agency (EPA)R. T he odour th resho ld of to luene is 2.5 ppm. OS HA has stipul ated 200 ppm TWA as pe rmiss ible ex posure limit of to luene, 300 ppm ce ili ng fo r 10 min , 500 ppm peak. At an exposure limit o f 600 ppm, human be ings suffe r fro m s light nausea, w hereas at 800 ppm, rapid irritati on, nasa l secre tion, metall ic taste, drowsiness, and impaired ba lance will be observed .

In thi s study, ro le o f nutrie nt III biofilte r pe rformance is studied . De fi c ie ncy III organIc nutrients may cause unde rpe rformance fo r biofilte r applicati on. Several studies conclude that nutrient additi on IIlc reases the acti vit / · I I

. Low to luene

194 J SCI INO RES VOL 62 MARCIl 2003

re moval e ffi c iency in compost biofilte r is reported when le ve ls of ava il able N (NH4-N and NO,--N) dropped be low 200mg/kg of dry solids bed mate ri a l12

_

In another study in ves tigating hexane remova l in a compost bi ofilter, additi on of a concentrated po tass ium nitrate so lution caused a susta ined inc rease in re moval e ffi c iency from nearl y 50 to over 99 per cent l

' . Nutrient recycling occurs w hen initi a l additi on o f nutrients is carri ed out d uring sta rt up . But the recyc led nutrie nts may not be suffi c ient to mai nta in the microbia l activ it ies. A biorilte r wi th a mediu·m that uses organic nitrogen as the source of nitrogen may not meet the contaminati on load as compared to biorilter media that uses e ithe r ammoni a nitrogen or nitrate nitrogen as nutrient source l 4

. The issue of nutrient availability and nut rien t addi t ion is important ror biofilter operation. In another study, it was fo und that ni trogen limitation cou ld be cOLl nte racted by gaseous ammonia addition I ) . However, they

recommended that new strategy or addition must be implemented to reach a more even distribut ion throughout the biofilter. In this study, our objecti ve was to develop such strategy and to find out the e ffect of nutri ent addition on removal e ffi c iency o r to luene.

Materia ls and Methods

Filter mate rial consists or pith , a biostablc material , obtained afte r retting process o r coconut husk. Pith , inte rmitten tl y layered with dry co ir fibres, is rilled in to the bench sca le biorilter. The mo isture content and ash content cf pith (determined as pe r ASTM methods 0-2974-71), pH«determined as pe r ASTM methods), bulk volume and water holding capacity(determined as pe r ASTM methods 0 - 2978-7 1) of the pith (as rece ived from relting area) were rou nd to be Tl per cent, 1.46 per cent , 5.77, 187kg/m' and 738 per cents respectively. Magat

l 6 had

ex tens ive ly studied the characteristi cs o f the co ir pith .

Experimental Procedure

The laboratory sca le biofilter cons ists or a biofilter co lumn (acrylic, 50mm interna l diam, 1200mm height), toluene reeding and moisture reeding glass vessels , a constant temperature water bath , and a mass fl ow contro lle r with read out display, pe rista ltic pump, thermomete rs , and di gital mallomete r. The biofilter column has samp ling ports at each 200 mm interval a long its hei ght.

Toluene and moisture laden ai r are fed to the bottom of the column through leak proor 6 mm diam Teflon tube, wi th a sampling port for inl et sampling.

Two the rmo mete rs are provided at the top of the co lumn , one of whose bulb is wrapped in wet cotton swab to measure wet bulb temperature . The to luene feeding and mo isture feeding vesse ls a re kept in a constant te mperature wate r bath . A preca libra ted pe ri sta lti c pump (Auto contro l pu mp, Watson­Marl ow 505 u/R L) is connected to the to luene feeding vesse l and the air sucked by the pe ri stalti c pump is bu bbl ed th ro ugh the to luene feed ing vesse l, thus produc ing to luene vapour at 40°C. Compressed air is fed into a vesse l fill ed with wate r through mass fl ow cont ro ller (Model 5860i M ass F lowmeter, Brooks Instrument, USA), thus produc ing mo ist diluti on a ir (Figure I) . The a ir-to luene ratio can be a lte red by chang ing e ither the a ir flow rates or to lue ne feed rate or both . Samples fro m the sampling ports and open top of the co lu mn used to be take n by using

a 10 ilL syringe and then inj ec ted to GC (GC 8000 series, Fisons In struments SpA, Ita ly). The chromatograph is calibrated for to luene by injecting

known quantity o f to lue ne ( I ilL) into an ai r ti ght bottl e havi ng 609mL of ai r, then draw ing 0.1 mL of sample from the bott le and injecting into the column

(OY I, Supe lco, film thickness 0.25~1, length 30m, inte rna l d iameter 0 .32mm, co lumn mate ria l fu sed

s ili ca, fi lm thickness 0.2511 up to 350°C ). Toluene is de tected by Fro at 40°C (hel ium as carri e r gas at 50 Kpa, hydrogen and a ir at 50Kpa). Samples were taken by inse rting the needle into the g lass tubes attached to the corks in the samp le ports and by f lushing out samp le from the sy ri nge severa l t imes be fore taki ng fina l samp le . Ammonia nitrogen was analysed, using Orion Ion analyzer (mode l EA 940), using Ori on ammonia e lectrode. Samples were prepared M il li-Q water (Milli -Q mode l 185Q p lus). Standard addition

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HARIDAS e / al.: TOLUENE DEGRADATION IN BIOFILTER 195

techn ique was used for measuring ammonia nitrogen . pH measurement of the sample is carried out by putting I g sample into 100mL distilled water and measurement is carried out under stirred condition

using pH meter(mode l I1pH system 352, Systronics) .

Results and Discussions

The biofilter operation may be classified into 3 steps, name ly 'acc limati on period ', ' start up period ' and 'stab le period '. Durin g acclimation period , low feed rate (0.53 kg toluene/d/m.1) and hi gh EBCT ( 147s) wen.: maintained. 5.4 kg Urea/(m.1 of media) was added as nitrogen source. Then EBCT was reduced to I lOs. Poor degradation pattern was observed even after 15 days of acclimation period , as toluene sme ll could be detected from the top of the column . Then Bios ludge ( IS .35g/L YSS) from the effluent treatment plant of a petro leum refinery was used as seed mate ria l (source of mi croorganisms) for the media.

Considerable improvement in degradation (100 per cent removal) was achieved immediate ly after biosludge addition . EBCT was reduced to 27s , which resulted into s light reduction in the e limination capacity . A costant temperature wate r bath mainta ined at 40°C was introduced at this stage for maintaining isothermal conditions in and around feed vessels and 100 pe r cent removal of tolue ne was regained. With the enhanced toluene input of 1.76kg/d/m' , 83 per cent re mova l was observed . To check the stability of the bi ofilter, the EBCT was reduced furthe r to 18s. The percentage re mova l came down to 2 per cent within 72 h. The gradual increase in EBCT to 168s fa iled in rega ining the e ffi c iency in terms of per centage remova l (Figure 2). The loss of microbial activity is attributed to nutrient defic iency, since bios ludge could supply the microbial consortia , but consortia died due to lack of sufficient nutrients in the filter media. 2 .52kg/(m' of media) of nitrogen in the form of DAHP was added to the media in so lution form by spraying through atomizer, whereas to buffer the media against poss ible acidification, 12.6kg/(m.1 o f med ia) of calcium ca rbonate (CaCO.1) was added , fo llowed by thorough mixing. On an average, nitrogen le ve l in media was found to be 1.5mg/g of media (Table I).

Despite this , gas chromatography analysi s showed no improve ment in degradation . There fore, 8 1.611(m.1 of media) of biosludge was seeded into the med ia by atomizer spray. The combined effec t of add it ion of bios lndge and nutrient resulted into the

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DAHP add ition

Table 1- Removal effi ciency corresponding to ammonia nit rogen in ditTerent port in 2 d

Date

25/11/99 ,Bcfore sludge addition

3/1 2/99, 7 ds aner sludge add ition

Port

PI

P2 P3

P4

Top

P2

P3

P4

Top

Ammonia nitrogen Per cent (mg/g wet pith ) removal

1.1 2 X.5

1.5 6.9 1.59 3 1.45 11.6

1.5X 10.7 0.1 4 41.6

0.2 93 .6 I.I X 94.6

1.63 97 .3

100 per cent re mova l of to luene from the system. The res idence time was decreased by slowl y increas ing the dilution air flow rate, as the accl imation period was now phased into start-up phase. After 4 d of the bios ludge additi on, the EBCT was reduced to 78s to maintain constant loading rate and after 7 d of continuous operation , slight reduction in re moval efficiency was observed. Samples from different sampling ports , inlet and top were estimated for ammonia-nitrogen. It wa s found that the degradation took place when both nutrients and biosludge were added . Microorganisms spec ific to the compound starts mUltiplying in the presence of the sufficient nutrients.

It is also found that the concentration of ammonia-nitroge n depletes faste r from the lower ports where ex posure to hi gher concentration of

196 J SCI IND RES VOL 62 MARCH 200]

toluene in air stream result into higher microbia l growth. Another reason cou ld be the upward transportation of nutrients by air flow (Table 2).

The concentration of ammonia nitrogen at the upper ports depl etes at a s lower rate. Just after the nutrient addition, loss of some nutrients is observed as ammonia sme ll was detected from the top of the reactor. But it is soon stabilized at gas liquid interface and further loss of nutrient does not occur. Due to decrease in remova l e ffici ency, after 15 d of previous addition, another addition of DAHP of 2. 1 kg/em' of media) was added to the media in the same manner as carried out earlier and the biofilter column was refilled for restarting the operations. After 25 d of second nutrient addition, it was found that percentage removal has decreased to 75 per cent. Therefore nutrient addition for the third time was carried out by adding 6 .5kg/(m' of medi a) of DAHP (based on mass balance to make ammoni a nitrogen level at roughly 1.5mglg of wet pith) and the removal observed after this additi on was 100 pe r cent in the biofilter and same removal effic ie ncy was mainta ined for further 15 d . At thi s stage, th ough removal was 100 per cent , it was found that level of ammonia nitrogen reduces sharpl y at the lOp of the reactor (Figure 3). Therefore, instead of mixing nutrient to the whole medi a, it was decided to supple ment the nutrient onl y at the top porti on of the biofilter co lumn. Since some of the medi a was regu larl y be ing taken for analys is, to

Table 2 - Remova l cfllciency corrcspondi ng to ammoni a nitrogen in d iffcrcnt port before and aft cr nutricnt addition

Date Port Ammoni a Pcr ccnt nitrogcn remova l

(mg/g wct pith)

8/ 12199,one day before PI 0.08 0 nutrient addit ion

P2 0 .019 38.4

P3 0 .0]6 47

P4 0.033 18.5

Top 1.23 1 79

1011 2199. one day aftcr PI 0.404 89.7 nutricnt addi tion

P2 0 .442 100

P3 0.426 100

P4 0 .377 100

Top 0.445 100

1 Duc [ 0 addi tion of fibrc

maintain the bed height, it was necessary to add fresh pith at the top of the bi ofilt er co lumn. Therefore, instead of adding only pith , DAHP, calculated by mass balance, was added in the fresh pi th, and known we ight of fresh pith was added at the top of the co lumn . Hereafter, each addition of fresh pith , whenever was required, was carried out and eac h time corresponding amount of DAHP was added to maintain the nutri ent level at the top of th e reactor. It was found that unde r such operati ona l condition, the removal of to luene was cons istentl y main ta ined at 95 per cent or above.

Conclusion

It may be conc luded that the nutrien t nitrogen at the rate of 0.06kg/(kg dry media) is required for stable operation of a co ir pith biofilter remov lllg

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nitrogen Icvcl at thc top of the biolilter du ring 70 d of opcration from start up

Tablc 3 - Removal e flicicncy corrcspond ing to d iffcrcnt parametcrs ovcr the pcriod of opcration

Air Ilow Supcrti cial Retenti on Loading Percentage ratc gas velocity Time ratc rcmoval

(m.1/d ) (m/h ) (min ) (g/m3/h)

1.008 2 1.39 2.8 1 100

4.32 9 1.67 0.66 100

4.32 9 1.67 0.66 55.94 85.66

1.152 24.45 2.45 66.21 98.6

1.728 36.67 1. 64 20.59 98 .63

2.16 45.84 1. 3 1 76.82 100

2.736 58.06 un 86.37 100

2.74 58.06 1.0] 92.56 99. 18

y-

HARIDAS et af.: TOLUENE DEGRADATION IN BIOFILTER 197

toluene with 95 per cent or above remova l effi ciency. In se veral cases of biofiltration studies the sorption effect could be mistakenl y considered as biodegradation leading to overestimat ion of biofilter performance l7

, but in thi s study, the sorption effect was found to be neg li gibl e. A summary of the operati on of the biofilter is given in Table 3.

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research forum fi eld study on bio iliters for control o f vo latil e hydrocarbo ns,./ Environ Eng, (June 1997) 556-562.

2 McNevin Denni s & Barford John . Bioflltrati on as an odour abatemcnt strategy. Biochelll En g ./, 5 (2000) 23 1-242.

3 Swanso n J. Warren & Loehr C Raymond, Biofiltrati on: fundamentals, dcsign and opcrat ions principl cs, and app li cation , .1 En viron Eng, (Junc 1997) 538-546.

4 Schwa rz C E. Dcvinny S Joseph . Tsots is T & Thcodo rc A. ' Biofi lt cr nctwork model - Importance of thc pore structure and othcr large-sca le hetcrogcneiti cs, Choll Lng Sci. 56 (2001) 475-4X3.

5 Jori o Hasnn a. Ki ared Karim , Brzczinski Ryszard . Lcrou x, Vi cl Guy & Heitz Michele, Treat ment of air polluted wit h hi gh conccntrati on of tolu cne and xylenc in pilot-sca le bioil itcr, .I Chelll Techno! Biotechn o!, 73 ( 1998) 183- 196.

6 Ergas S J. Schrocder E D, Chang D P Y & Morton R L, Contro l of vo latil c organ ic compound emiss ions usi ng a co mpost biolliter, Water I:;nviron Res, 67 (5) ( 1995) 8 16-82 1.

7 Zilli Mario . Palazzi Emilio. Senc Lu ciane, Co nven i Allili o & Borghi Del Marco , Toluene and styrene remova l from ai r in bioiliters, Process Biochelll , 37 (200 1) 423-429.

8 Hyder De B. Ovcrmcire A, Van Langenhovc H & Verstraete W, Eth ane remova l from a syntheti c waste gas usin g a dry hiobed, Biotcc//I /O ! niaeng , 44 ( 1994) 642-64X.

<) Wec khu ysen B, Vriens L & Verachtert H. The effect of nutri cnt supp lemen tati on on th e bioflitration removal o f

butanol in contaminated air. Ap!)! MicroiJio! Biotl'c//lw!, 39 ( 1993) 395-399.

10 Ergas S J, Schroeder E D, Chang D P Y. Scow K M, Spati al di stributi on of mi crob ial populations in biofllters. 94-RPIlSn.OI ( 1994), Pmc Air Wast e Mana ge AssaI'. 87'" AnI/II Meet, Cincinnati OH.

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14 Morales Marcia. Revah Sergio &Au ri a Ri chard. Stan-up anti effect of gaseous ammonia additi ons on a hi oiliter for the eliminati on of toluene vapo rs, Biotl'chno! Biol'ng , 6()(4 ) ( 1998) 483-49 1.

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Abbreviations and Notations

PI - Sampling port <l tthe 20cm height from inl et

P2 - Sampling port at th e 40cm height from inl et

P3 - Samplin g port <l tthe 60cm height from inl et

P4 - Sampling pon at the 80cm height from inl et top- bioliiter exi t

DAHP - Di - ammo nium hydrogen phosphate

EBCT -Empt y bed cont ac t time

VSS - Volat il e suspended so lids

OSHA - Occupati onal safety and health ad mini strati on

TWA - Time weighted average