Granular filtration of polydispersed aerosols

qULAR FILTRATION Granular f i l t r a t i o n o f p o l y d i s p e r s e d aerosols by Yongwon

Jung" and Chi Tien

Department of Chemical Engineering & Materials Science, Syracuse University, Syracuse, NY 13244, USA Present address: Environmental Engineering Laboratory, Korea Atomic Energy Research Institute, PO Box 7, Daeduk-Danji, Taejon 305-606, Korea This paper was presented at the Filtration Society meeting on 'Recent Advances in Gas Filtration' in London on 9 September 1992 A general discussion on the prediction of the dynamic behaviour of granular filtration of polydispersed aerosols is presented. Special emphasis is placed on the effect of the deposited particles on filtration rates. Experimental data demonstrating this effect are given, and a procedure for estimating this effect is developed.

r a n u l a r filtration is a p p li e d for the removal of suspended particles from gas streams, and is conG ducted by passing the stream to be treated through a bed packed with granular substances. As a fixed-bed operation, granular filtration is inherently a non-steady-state process. The accumulation of deposited particles within a granular filter implies that the medium's structure undergoes a continuing change, such that both the local collection efficiency and permeability vary with time. This situation is further complicated for the case of polydispersed aerosols. With polydispersed aerosols, t h e effect of d e p o s i t i o n depends on not only the extent of deposition, but also the size and size distribution of deposited particles. In this paper we present certain relevant experimental d a t a on g r a n u l a r filtration of polydispersed aerosols. Analysis of these results led to the establishment of a general method for estimating the effect of deposition on filtration rates, which may in turn be used for predicting the dynamic behaviour of granular filtration of polydispersed aerosols.

Dynamic behaviour of granular filtration For granular filtration of polydispersed aerosols under the constant throughput condition, the twin features of the dynamic behaviour are the history of the effluent concentration (namely, the effluent concentration of aerosols of each size, Ck, for k = 1, 2 , . . . , N, where N i s the total number of aerosol types), and the history of the pressure drop necessary to maintain the given flow rate. Mathematically, it is described by the following equation: O)

Macroscopic conservation equation: Ock , Oak

Uz~z +-~- = 0

k = 1,2,...,Y

(1)

Filtration rate equation: O0 = u~(~)kck

Filtration & Separation

May 1993

k = 1,2,..., N

(2)

(-AB) =

Ozz dz

(3)

with the following initial and boundary conditions: ck = (ck)~ Ck = (Ck)0

Ok = (~k)0

z = 0

0 > 0

Z> 0

0 < 0

(4a) (4b)

where us is the superficial velocity, ak is the specific deposit of the kth type of aerosol or the volume of the deposited aerosol of the kth type per unit filter volume, and (A)k is the filter coefficient of the kth type of aerosol. Here (ck)in is the influent value of Ck, and (ck)0 a n d (ok)O are the initial values of Ck and ak, respectively. The independent variables are the axial distance z (measured from filter inlet), and the corrected time 0, defined as:

O = t - f z~d-z Jo us

(5)

where t is the actual time. The solution of Equations 1 and 2 with the initial and boundary conditions of Equations 4 a and 4b gives the effluent history as well as the local deposition expressed in ak. The pressure drop can be found from the knowledge of the local pressure gradient, which is a function of the extent of deposition. To obtain the solution of Equations 1 and 2, the filter coefficient (A)k must be known. Generally speaking, the filter coefficient characterises a filter's ability to capture aerosols, and is directly related to the structure of the filter medium. Since the extent of deposition is a timedependent local function, (A)k can be expected to vary with both z and 0. It is therefore convenient to write (A)k as:

Ak = (Ao)kFk(al, a2,..., aN, a)

(6)

where (A0)k is the value of (A)k for a clean filter (namely, a filter w i t h o u t d e p o s i t e d a e r o s o l s ) . Here Fk may be considered as a correction factor which accounts for the effect of deposition; it is a function of the specific deposits of all types of aerosols, as well as the relevant operating 253

tNULARFILTRATION variables (which constitute the parameter vector, a ) . Alternatively, F~ may be regarded as a function of the total specific deposit and the composition of the deposit, or Fk ---- Fk(o', Wl, W2, ..., WN-1, 0:)

(7)

where

Ns,4y = [ A ( o 0 + 1-14N~/2( 1 - a)-3/2][Ns,/2]

cr : E aj

(8a)

j=l

w~ = rrk/a

(8b)

Similar to (A)k, the pressure gradient necessary to maintain a certain gas throughput, (OP/OZ) [see Equation 3] can be e x p e c t e d to be a time-dependent local function. Thus (Op/Oz) may be written as (Op/Oz) = (Op/Oz)oa(~7 , Wl,..., WN-1, ~)

(9)

where (OptOz)o is the value of (OptOz) when the filter is clean. Note that the local permeability of a filter is inversely proportional to (Op/Oz). Therefore G is the correction factor to account for the effect of deposition on permeability. The main purpose of the present work is to present relevant experimental data and analyses which can be used to predict F for specific conditions. For this purpose, we will first review some of the available correlations for estimating the clean filter coefficient, (A0)~.

Correlation for estimating (A0)} Interpretation of the filter coefficient in terms of the unit collector (or single collector) efficiency of granular media using the unit bed element concept has been reported previously.(L 2) Depending on the porous media model used for describing granular media, the following relationships are available.

(13c)

N st = (ppd~u~cs ) / (9 pdg )

(13d)

A = [6(1 - e)llr]'13(~ld9)

(10a)

F o r the sphere-in-cell m o d e l : = (3/2)(1 -- e)U3OT/dg)

(lOb)

where fl is the unit collector efficiency and dg is the filter grain diameter. Here A and fl refer to a specified aerosol size and the same filter medium state. The relationship between the unit collector efficiency and the single collector efficiency ~?s is ~/s = (1 - e)-2/3~?

(11)

There exist a n u m b e r of empirical correlations for the initial collector efficiencies (710or ~/s0) in the literature. A review of this subject can be found elsewhere. O' 3) For example, the recent correlation of Jung et al. 3 using the constricted-tube model for media description is given as:

~1o : n. . .2.~.n. N 1 . 3 4t3 7 N R0.23 1 3437

73

= 0.2589N~4~ 5 9R ~

a = 1- e

for for

M~

--~t < 1.2 Nst > 1.2

~_aj (12b)

where

"y = 1.4315N~tl}96s

(12c)

(13e) (13f)

where 7 is the adhesion probability, and accounts for the bouncing-off of impacting aerosols if the aerosol inertia is great. Here dp is the aerosol diameter, pf and pp are the fluid and particle densities, respectively, # is the fluid viscosity, and c~ denotes the Cunningham correction factor. Accordingly, for aerosols of a given size, the corresponding (A0)k can be found readily from Equation 10a, with Y0 estimated from Equation 12a or 12b.

Estimation of Fk The effect of deposition on filter coefficient depends on the e x t e n t of deposition, as well as the size distribution of deposited particles (in other words, either 41,42, ..., aN or a, wl, w2, ..., WY-1). For the simple case of monodispersed aerosols (namely, all aerosols are of the same size), F can be expressed as a power-law function of a : F - - - - 1 - F ~ I a~2

(14)

where a ] and 42 are constants. Several investigators in the past (4'5'6) have developed expressions relating the constants ~1 and ~2 for monodispersed aerosols with the operating variables. The results of Jung and Tien (6) are:

a~ = 0.4416Nst° 3649N°n"2397 41 = [ F - 1]~=10_3(103)"2 [F - 1]~=10_~ = O.09545N~t147SN~ °432~

For t h e c o n s t r i c t e d - t u b e m o d e l :

(13b)

Nn~ = dpPlU,/# A(a) = (6 - 645/3)/(6 - 941/3 + 9off/3 - 6~ 2)

N

254

(13a)

N . = d,,/d.

(15a) (15b) (15c)

where Nst and NR are defined as before. For polydispersed aerosols, the deposited particles are not of the same size. As a major part of our ongoing research of aerosol filtration at Syracuse, we have conducted experiments aimed at studying the effect of deposited particle size. These experiments were conducted using an apparatus similar to those used by Walata et al. (a~ To examine the effect of deposited particle size, the experimental filter (with a height less than 1.0 cm) was first conditioned by passing a monodispersed aerosol stream (or loading s t r e a m ) of d i a m e t e r d~ a n d relatively high concentrations for a specified period of time. Filtration measurements were then conducted using a monodispersed aerosol stream of another size (for example, dpk). This procedure was then repeated. Although both aerosols of diameters d~ and dpk were found in the deposit, the former kind was dominant, and the deposit could be considered as composed of aerosols of d~ only. Thus, by using aerosols of different sizes as the loading stream, the effect of deposited aerosol size may be examined experimentally. A typical set of such experiments is shown in Figure 1. Here the unit collector efficiency of aerosols with dp = 2.02 ~um of a filter with deposits composed of aerosols of dp = 1.1 pm, 2.02 pm and 3.09 pm as a function of the total deposit a are shown. The results shown in Figure 1 suggest that: [] The format used for describing the effect of deposition for monodispersed aerosols (i.e. Equation 14) can be extended to the case where the size of the deposited May 1993

Filtration & Separation

@ULAR FILTRATION ,

I

I

I

I

I

~

1

'-

' "1

'

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....

p

, J ,I

,

I

'

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, r ,)

,

, r

10 -~

I #

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,,

i A

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AAA

~

0

8

10-2

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o

A m

&

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1

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to" ~ 1

10 4

Specific deposit

T, I

,r} -s

10"

10 -s

a

10 "l

10 -3

10-2

Specific deposit o"

F i g u r e 1. E f f e c t of t h e size of p a r t i c l e s l o a d e d in t h e f i l t e r b e d s on ~ of 2 . 0 2 # m v e r s u s a .

© 3.09/~m • 1.1 #m /k 2.02/~m

Figure 3a. Comparison betwen experiments and prediction for rI of 1.1 ~ m partiole v e r s u s ~. Volume concentration ratio of particles in influent = 1:1.113, dp = 2.02, 1.1 .um. • Prediction /X Monodispersed 1.1 .um aerosols O Bidispersed aerosols (Exp. 90604)

I

i

I~

,

'

,'1

,

t I '1

1{')-I i-----

'

I

t '1

,

i

~

,

--

"6

•

10"2

•0,~10

• •

g

10 "3

-

:-

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i

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10 "e

10 ~

in ~ Specific deposit a

~0"3

10 .2

aerosols is different from t h a t of t h e aerosols u n d e r consideration, o r (16)

w h e r e ~l(k/i) d e n o t e s the u n i t collector efficiency of aerosols of d i a m e t e r dpk in a filter l o a d e d w i t h d e p o s i t e d aerosols of size d~; h e r e al(k/i) a n d a2(k/i) a r e t h e e m p i r i c a l constants. For k = i one has t h e m o n o d i s p e r s e d case, w i t h E q u a t i o n 16 b e c o m i n g t h e s a m e as E q u a t i o n 14. [] The r e l a t i o n s h i p b e t w e e n

7l(k/i ) and ~l(k/h) is

~(k/i) < ~?(k/k) ~?(k/i) > ~7(k/k)

dpi > dpk if dp, < dpk if

In a d d i t i o n to t h e e x p e r i m e n t s m e n t i o n e d above, filtration Filtration & Separation

May 1993

I 10 .6

F i g u r e 2. E x p e r i m e n t a l results of rl v e r s u s ~, s h o w i n g t h e e f f e c t o f c o n o e n t r a t i o n d i s t r i b u t i o n in b l d l s p e r s e d a e r o s o l s , w i t h d. = 2 . 0 2 / ~ n . Through filters loaded with 1.1 #m particles • Monodispersed 2.02 #m aerosols A Bidispersed aerosols (2.02 and 1.1 /~m, volume concentration ratio = 1:1.113) O • Bidispersed aerosols (2.02 and 1.1 gm, volume concentration ratio = 1:0.399)

71(k/i) = 1 + al(k/i)a °2(klO

10 -a

I

I I] 10"5

I

I

I

ii

I

10 "~

I

I

I I 10 .3

I

I

I r 10 "2

Specific deposit cr

Figure 8a. Comparison betwen experiments and predioUon for r / o f 1.1 /~m partk:~le v e r s u s a. Volume concentration ratio of particles in influent = 1:1.113, dp = 2.02, 1.1 /Jm. • Prediction /k Monodispersed 1.1 #m aerosols O Bidispersed aerosols (Exp. 90604)

e x p e r i m e n t s using bidispersed and tridispersed aerosols w e r e a l s o c a r r i e d out, a n d t h e c o l l e c t o r efficiencies c o r r e s p o n d i n g to t h e two (or three) sizes of aerosols were d e t e r m i n e d . A typical set of such results is shown in Figure 2, which gives t h e collection efficiency of aerosols of 2.02 # m d i a m e t e r in t h e filtration of bidispersed aerosols of d i a m e t e r of 1.1 p m a n d 2.02/~m (i.e. two types of aerosol), as a function of a ( = al.1-I-a2.02)- Also included in t h e Figure are t h e collection efficiencies of a 2.02 # m - d i a m e t e r aerosol in t h e filtration of m o n o d i s p e r s e d aerosols of 2.02 #In, ~(2.02/2.02) as well as t h e ~/(2.02/1.1); namely, in t h e filtration of a 2.02 # m - d i a m e t e r aerosol in a filter w i t h 1.1 # m - d i a m e t e r d e p o s i t e d aerosols. The results of Figure 2 indicate that: [] For g r a n u l a r filtration of binary aerosols, the fraction collection efficiencies (~/)i and (~)j are governed by t h e 255

iULAR FILTRATION I

I

'll

= 1 + y ~ ~l(k/j)o°~(~/J)wj

'''1 ~

'

k

o.1 - -

l

0.0'I

i

I I I I 0.1

0.01

I

I

0.%?,)

l

I I I

I

I

f

1

10

....

Figure 4 a . [(F - 1),=t.0xl 0 4]limiting case 1 / [ ( F -- X)a=t.0xl0-']limiting case 2 versus 0.938(dp2/dpt)-x'~s.

I

I

1

I

[

I

I

I

I

(rf)

j=l

w h e r e (~0)k is the initial value of ~kThe above e x p r e s s i o n states t h a t for a polydispersed aerosol of N different sizes, t h e increase in the unit collector efficiency of the kth type of aerosol m a y be described as a linear c o m b i n a t i o n of contributions d u e to t h e p r e s e n c e of d e p o s i t s c o m p o s e d of aerosols of each of the N types with t h e i r v o l u m e fraction as t h e weighing factor. The e x p r e s s i o n holds t r u e in t h e limiting cases of ~?(k/j) and ~?(k/k). The validity of t h e above e x p r e s s i o n can be seen from c o m p a r i n g t h e e x p e r i m e n t a l l y d e t e r m i n e d values of (~)k a n d predictions based on E q u a t i o n 17, as shown in Figure 3. If one a s s u m e s t h a t E q u a t i o n 17 is valid in general, e s t i m a t i o n of Fk requires t h e knowledge of a ] ( k / j ) and c~2(k/j) k, for j = 1, 2, ..., N ; or, in o t h e r words, correlations for e s t i m a t i n g t h e s e c o n s t a n t s m u s t be available. A l t h o u g h t h e r e do not exist sufficient d a t a for establishing such correlations, s o m e possibilities do exist, as shown in F i g u r e 4. H e r e t h e v a l u e s of [~(k/i) - 1]/[7?(k/k) - 1] e v a l u a t e d at a = 10 -4 a n d 10 -~ a r e p l o t t e d a g a i n s t (dpk/dp~). Accordingly, ~?(k/i) given by E q u a t i o n 16 and ~?(k/k) m a y be e s t i m a t e d for E q u a t i o n 14; one can t h u s readily d e t e r m i n e a l ( k / j ) and ol2(k/i) from t h e relationships shown in Figure 4. With Fk known, one can readily d e t e r m i n e t h e effluent c o n c e n t r a t i o n at p r e s s u r e d r o p histories for t h e solution of E q u a t i o n s 1 - 4. This solution can be o b t a i n e d numerically by integrating E q u a t i o n s 1 and 2. Alternatively, one m a y view a filter to be a n u m b e r of u n i t bed e l e m e n t s c o n n e c t e d in series, with t h e rate of filtration given by E q u a t i o n 2 as discussed previously. (z) Conclusions

1 m

I

0.1

I

I

v I

,

'

'

'

We have p r e s e n t e d a m e t h o d for predicting t h e dynamic b e h a v i o u r of g r a n u l a r filtration of polydispersed aerosols, and give e x p e r i m e n t a l evidence of t h e i m p o r t a n c e of the effect of t h e size of d e p o s i t e d aerosols in e n h a n c i n g t h e r a t e of a e r o s o l d e p o s i t i o n . B a s e d on t h e analysis of t h e e x p e r i m e n t a l r e s u l t s , a p r o c e d u r e of . p r e d i c t i n g t h e v a r i a t i o n of (~)k w i t h a is established, which can be used directly in d e t e r m i n i n g the rate of filtration.

1

0.1

O.&.~ (~-~--~1)-L~

References

F i g u r e 4b. [ ( F - 1)a=l.0xl0-3]limiting case 1 / [ ( F -- 1).=t.o×to a]limiting case 2 versus 0 . 9 3 8 ( d p 2 / d p 1 )-1"'5'18.

1. Tien, C.: 'Granular filtration of aerosols and hydrosols' (Butterworths, Boston, USA, 1989). 2. Payatakes, A.C., Turian, R.M. and Tien, C.: AIChE J., 1974, 20, p.889. 3. Jung, Yongwon, Walata, S_A. and Tien, C.: Aerosol Sci. Technoi., 1989, 11, p. 168. 4. Walata, S~., Takahashi, T. and Tien, C.: Aerosol Sci. Technol., 1986, 5, p. 23. 5. Takahashi, T., Walata, S_4. and Tien, C.: AIChE J., 1986, 32, p. 684. 6. Jung, Yongwon and Tien, C.: J. Aerosol Sci., 1992, 23, p. 187.

following relationships:

v(i/j) < ~ < ~(i/i)

if

dp; > dpi

Nomenclature

A(~)

[ ] For a given t o t a l specific d e p o s i t a, t h e p r e s e n c e of a h i g h e r p e r c e n t a g e of s m a l l e r aerosol in the d e p o s i t t e n d s to e n h a n c e t h e increase in collection efficiency.

Ck (Ck)~n (ck)i

Based on t h e conclusions s t a t e d above, the u n i t collector efficiency of aerosols of d i a m e t e r dpk in t h e filtration of polydispersed aerosols of d i a m e t e r dpl, dp2 .... , dpN m a y be a s s u m e d to be given by t h e following c o m b i n a t i o n a l expression:

c~ dg dp d~ F

256

= P a r a m e t e r defined by E q u a t i o n 13e = C o n c e n t r a t i o n of aerosol particles of size dpk = Influent value of Ck = Initial value of Ck = C u n n i n g h a m correction factor = Grain d i a m e t e r = Aerosol d i a m e t e r = D i a m e t e r of ith aerosol = Correction factor of A May 1993

Filtration & Separation

ULAR FILTRATION Fk G NR

= = = = = = = = = = =

NRe

Nst Ystell P t Us

wi z

Correction factor of A of kth type aerosol Correction factor of pressure gradient Defined by Equation 13a Defined by Equation 13c Defined by Equation 13d Defined by Equation 13b Pressure Time Superficial velocity Defined as ai/a Axial distance

= D e f i n e d a s (1 - e) = Empirical constants of Equation

~l(k/j), ~2(kli) a,~

zxp £

~7 rls

,7(k/i) 0

(,~)~ ( ,~o) ~ # Pl

14

= Empirical constants of Equation 10b = P a r a m e t e r v e c t o r s i n E q n s . 6 a n d 9, r e s p e c t i v e l y

Pp ak ~r

= = = = = = = = = = = = = = =

Adhesion probability Pressure drop Filter porosity Unit collector efficiency Single collector efficiency I n i t i a l v a l u e o f r/ U n i t c o l l e c t o r e f f i c i e n c y o f a e r o s o l s o f k t h s i z e in filter loaded with ith type of aerosol Corrected time Filter coefficient of the kth aerosol I n i t i a l v a l u e o f (A)k Viscosity of gas Gas density Aerosol density Specific deposit of the kth type aerosol Total specific deposit

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OIffRACTSOFREFEREED PAPERS Operating Line Analysis of Pump and Filtration Systems Arbeltskurvenanalyse yon Pump- und Filtrationsanlagen van G. G. Chase Es glbt mehrere Altemativen zur GroBenbemessung von Pumpen, die zum Einsatz in einem bestimmten chemischen Verfahren bestimmt sind. Zahlreiche Ingenieure verlassen sich bei der Festlegung der ungef~hren GrSBe einer benStigten Pumpe auf eine Mischung von Erfahrung und Instinkt. Dem Uneingeweihten oder Unerfahrenen kann die GrSBenbemessung einer Pumpe jedoch ein Greuel sein. Einfach Pumpen kaufen, um sie auszuprobieren, ware eine kostspielige Ldsung. Das Referat beschreibt einen LSsungsvorschlag, der eine Arbeitskurve beinhaltet, mit deren

Hilfe die Leistung von Kreiselpumpe, Fiiterkuchen und Rohrleitungsnetz bestimmt werden soft. Kriterien wie Filtrationszeit kbnnen zur Auewahl der geeigneten Pumpengr6Be dienen. Dutch diesen Ansatz I~Bt sich der Erfahrungsschatz erg~nzen; er kOnnte sich auch ale nOtzlicher Ausgangspunkt erweisen, wenn man es mit einem neuen Verfahren zu tun hat oder wenn es einfach an Erfahrung mangelt. (6 sn., 8 abb., 1 tab., 10 teL)

Analyse de la Ilgne op6ralolre d'un syst6me pompe/flltre p a r G. G. Chase II y a plusieurs fa.cons pour choisir la taille des pompes pour un precede donne. Pour bea uco up d'ingenieurs, I'experience et I'intuition peuvent ~tre utilisees pour determiner la taille approximative de la pompe requise. Pour les novices, la chose est epouvantable. De plus, simplement acheter des pompes pour les essayer est une solution coOteuse. Dans cet article, on decrit une approche par figne operatrice pour

determiner los performances d'un systeme avec pompe centrifuge, filtre a g~teau et tuya uterie. Des criteres tels que le temps de filtration peuvent ~tre utilises pour choisir la bonne taille de pompe. Cette approche peut s'ejouter a I'experience et peut eervir de point de depart lors d'un nouveau procede ou quand l'experience fait defaut. (6page., 8 figs., 1 tab., 10 refs.)

Anillsls de funclonamlenfo a lines de slstemas de bombs an flltracl6n p o r G. G. Chase Hay varies metodos de calcular el tamale necesario de bombas en procesos quimicos determinados. Muchos ingenieros emplean experiencia e intuici6n para determinar el tamale aproximado que requieren. Calcular el tamale de una bomba consterne a los inexpertos o no iniciados. Ademas comprar bombas para probarlas es mucho pedir. En este articulo se discute un enfoquende funcionamiento a finea para

determinar el rendimiento de una bomba centrifuga, torta de fiitro y red de tuberia etcetera. Se puede emplear criterios tales come tiempo de fiitraci6n para elegir los tamahos correctos de bombe. Este enfoque complementa experiencia y sierve de puntos de partida cuando se plantean nuevos procesoe, o cuando hay falta de experiencia. (6 page., 8 figs., 1 tab., 10 refs.)

Organic Stablllsaflon and Nitrogen Removal in a Membrane Separation Bloreactor for Domestic Wastewater Treatment Organische Stabilisierung und Stickstoflbeseltigung in einem Membransbscheidungs-Bloreskfor zur Haushsltsabwasserbehendlung yon C. Chiemchaisri, Y.K. Wong, T Urase u n d K Yamamoto Die organische Stabilisierung und Stickstoffbeseifigung wurden anhand eines Bioreaktors mit Hohlfasermembran-Abscheidung mit einem Volumen yon 62 I untersucht. Das Verfahren bestand in Fest-FlOssig-Abscheidung mittels Hohlfasermembran in einem Belebtschlamm-BeliJftungstank. Dutch Wirbelung im Abscheidungsbereich und Aufnahme einer DOsenbeliJftungseinrichtung in den Membranbausatz laBt sich die Schlammansammlung an der Membranoberfl~che sowie innerhalb des Membranbausatzes verringern. Nach 330 Betriebstagen lag der PermeatfluB 0,2 m/Tag unter dem bei stoBweiser Saugwirkung beobachteten Weft. Abgesehen von Probenahmen wurde in dem System ein hohes Ausma8 an organischer Stabifisierung ohne Schlammverlust ermittelt. Es wurden kontinuierliche und stoBweiser BelOftungsarten untersucht. Es wurden durchschnittliche Abwasser-

CSB-Konzentrationswerte von 20,8 bzw. 16,5 mg/I bei kontinuierlicher bzw. stoBweiser BelOftung beobachtet. Der Nitdfikationegrad richtete sich nach der Konzentration des gelSsten Sauerstoffs im Abwasser-Belebtschlamm-Gemisch w~hrend dee Beli)ftungszeitraums. Dutch die EinfOhrung stoBweiser BelOftung wurde die totale Stickstoffbeseitigung aufgrund von gleichzeitiger Nitrifikation und Denitrifikation auf bie zu 80% oder mehr verbessert, so dab sich ein Durchschnittswert yon 4,9 mg/I Totalstickstoff im Abwasser ergab. Dutch ErhShung des gelSsten Sauerstoffgehalts im BelOftungszek traum yon 1,5--2 mg/I auf 4--5 mg/I stieg die Stickstoffbeseitigung auf Ober 90%. Sperrung einer 4 - 6 log Viruskonzentration dutch eine an der Membranoberfl~che gebildete Gelschicht wurde ebenfalls beobachtet. (6 sn., 5 abb., 2 tab., 10 teL)

Stablllsatlon organlque ef ellmlnaUon de I'azote dens un blor~acfeur i membrane pour le traitement d'eau r~sldualre domesUque p a r C. Chiemchaisri, Y.K. Wong, T Urase et K Yamamoto On a etudie la stabilisation organique et I'elimination de razote dane un bioreacteur fibres creuses de 62 L Le proced~ utilise etait une separation sollde-liquide directe par des membranes a fibres creuses a I'interieur d'une cuve a boues activees. En realisant des conditions de grande turbulence dane la zone de separation et en incorporant un jet d'aeration a I'interieur du module membranaire, on a pu reduire I'accumulation de boue sur la surface de la membrane e t a I'interieur du module. Les flux de permeat obtenus apres 330 ]ours d'operation etaient de 0.2 mid sous succion intermittente. Un haut degre de stabilisation organique rut obtenu dane le systeme sans perte de boues saul pour prises d'echantillons. On a etudie des aerations continues et intermittentes. On a observe des valeurs moyennes de COD de I'effiuent de 20.8 et de 16.5 mg/I

respecfivement pour des aerations continues et intermittentes. Le degre de nitrification d~pendait de la concentration DO de la liqueur mixte pendant la p(~riode d'aeration. L'introduction d'une aeration intermittente a am~liore relimination de I'azote total de 80% ou plus par une nitrification et une d~nitrification simultanee, ce qui a conduit une valeur moyenne de 4.9 mg/I d'azote total dans I'effluent. Une augmentation de DO pendant la periode d'aeration de 1.5--2 mg/1 lusqu'a 4--5 mg/I a augment~ relimination d'azote de plus de 90%. On a aussi observe un relet de 4 - 6 log de la concentration en virus suite a la formation d'un gel sur la surface membranaire. (6 pags., 5 figs., 2 tabs., 10 refs.)

Establllzacl6n org,~nica y ellmlnacl6n de nlfr6geno en un bloreactor con membrsns de uparscl6n pars el trstamienfo de ague duechada domestics p o r C. Chiemchaisri, Y.K. Wong, T Urase y K. Yamamoto Se ha estudiado estabilizaci6n organica y el quitar de nitr6geno empleando un bioreactor de 62 I capacidad, con membranas de separaci6n de libra hueca. Es un proceso de separaci6n directa s61ido/liquido, con la membrana de libra hueca dentro de un tanque de aireaci6n de lode active. Con la provisi6n de alta turbulencia dentro de la zona de separaci6n y el empleo de una instalaci6n de aireaci6n a chorro dentro del m6dulo membrana se puede reducir la acumulaci6n de lode sobre el superficie de la membrana y dentro del m6dulo. Se ha obtenido flUlO de filtrado despues de 330 dias, de 0.2 m/d, bajo succiOn intermitente. Se ha realizado un alto nivel de estabilizaci6n org~nica sin perdir lode, a la excepci6n de muestreo. Se han estudiado modes de aireaci6n continues e intermitentes. Se han hallado concentraciones COD medias de

~

efluente de 20.8 y 16.5 mg/ I durante aireaci6n continua e intermitente, respectivamente. El grade de nivel de nitrogeno depende de la concentraci6n DO (oxigeno disuelto) del licor mezclado durante el periodo de aireaci6n. Introducci6n de aireaci6n intermitente ha aumentado el quitar del nitr6geno total fiasta mas de 80% per un mecanismo de nitrogenaci6n y eliminaci6n, con el resuitado de un valor de 4.9 mgll de nitr6geno de todas formas en el efluente. Aumento de DO desde 1.5--2 mg/I hasta 4 - 5 mg/I durante aireaci6n ha eliminado nitr6geno hacia mas de 90%. Se ha observado tambien el quitar de una concentraci6n virica per una capa de gel en el superficie de la membrana. (6 pags., 5 figs., 2 tabs., 10 refs.)

Granular Fillration of Polydlspersed Aerosols Granularflltration yon polydisparsen Aerosole yon Yongwon ,lung u n d Chi Tien

Das Referat beinhaltet eine allgemeine Er~)rterung der Vorhersage des dynamischen Verhaltens von Granularfiltration polydisperser Aerosole. Die Auswirkungen abgelagetter Parfikel auf Filtrafionsraten werden besonders hervorgehoben. Es werden

experimentelle Daten zur Darlegung dieser Auswirkungen und ein Verfahren zur Absch~tzung dieser Auswirkungen vorgelegt. (5 sn., 4 abb., 6 ref.)

Filtration granulalre d'aerosols polydlspers6s p a r Yongwon J ung et Chi Tien On presente une discussion generale sur la prediction du comportement dynamique d'une filtration granulaire d'ae'rosols polydisperses. Une mention speciale est accordee I'effet des particules depos6es sur lee vitesses de filtration. Des resultats

experimentaux demontrant cet effet sent donnes et I'on developpe une procedure pour estimer cet effet. (5 pags., 4 figs., 6 r~fs.)

FIItracl6n granular de aerosoles polldlspersados par Yongwon J ung y Chi Tien Se presenta una discusi6n general sobre el pron6stico del comportamiento dinamico de filtraci6n granular de aerosoles polidispersados. Se concede mucha importancia al efecto de particulas depositadas en velocidad de filtraci6n. Se dan dates

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experimentales que demueetran este efecto y se desarrolla metodo de calcularle. (5 pags., 4 figs., 6 refs.)

May 1993

Filtration & Separation