Removal of Hazardous Organic Pollutants by Biomass Adsorption

FOCUS

Removal

of

hazardous

by biomass

organic

adsorption

John P. Bell, Marios

Tsezos

The fate of hazardous organic pollutants, such as pesticides, discharged into conventional biological wastewater treatment processes is not well understood. These compounds may be re moved from the wastewater stream by biod?gradation, volatil ization (air stripping), sorption by the biomass, or other processes. Of these processes, sorption would accumulate pollutants in the sludge and create potential environmental hazards associated with ultimate sludge disposal. This biological adsorption process, however,

may

a cost-effective

provide

treatment because

Also, pollutants. organic are present in discharges

biorefractory compounds

many

to municipal

for

method

been

reported.1"3

at the U.

Investigators

contamination

a 50-mesh

through

in the

accumulate

compounds

sludge.11

Adsorption

sponsible

for this

has

been

screen.

water

treatment

The

plant.

S. Environmental

onto

two

accumulation.5'910

of

types

biomass

type

inactive was

microbial

a pure

biomass

strain

was

of Rhizopus

examined. a

arrhizus,

fungus grown in the laboratory. The other biomass was amixed culture of activated sludge from the Hamilton, Ontario munic ipal wastewater

treatment

plant.

In addition,

tem

desorption,

perature effects, and the thermodynamics of the adsorption pro cess were

also

investigated.

several

repeated

and

times

and

then

iso-octane

and

The

R.

arrhizus,

an

hexane.

Water

solutions

were

made

water prepared in the laboratory. industrial

strain,

supernatant

the

sludge

was

recovered

and

a 50-mesh

to pass

pestle

demonstrated by pesticides to leach from land disposed sludges.

Adsorption

were

experiments

conducted

by

contacting

solutions of various concentrations with different quantities of biomass. Measured quantities of biomass were placed in 250 mL screw-top flasks towhich ameasured quantity (approximately 150mL) of solution was added. Solutions were prepared by dissolving the various chemicals in distilled/deion ized water. biomass

Controls

were

was

grown

in a

14-liter

bench top fermentor. Sterile techniques were used to prevent

run

that

same

the

contained

in each

but

solution

flasks were

The

experiment.

no

agitated

on an orbital shaker at 250 rpm for 3 days in a constant tem perature

room.

The

solutions

were

then

from

separated

the bio

mass by filtering through 0.45-/um membrane filters in a glass vacuum filtration apparatus. The filters were firstwashed with 300 mL of distilled water to remove any leachable materials. Approximately 50-75 mL of solution was first filtered to bring the filter to adsorption equilibrium with the solution. This por tion of the filtrate was discarded and the subsequent filtrate was then collected for analysis. Control solutions were filtered, using the

same

procedure.

To

for

compensate

adsorption

onto

the

apparatus, the concentration of the filtered control solution de by

by analysis the biomass

Desorption Organic chemicals used in the adsorption experiments were of +99% purity. Organic solvents used for extraction were pes grade

then

a mortar

with

ground

Adsorption reversibility indicate their potential

take

MATERIALS AND METHODS

ticide

the

screen.

termined

with distilled/deionized

and

chemical

This study and continuing research in this area is aimed at understanding adsorption in biological treatment processes and developing models for predicting the fate of hazardous organic pollutants entering biological wastewater treatment plants. The purpose of this study is to produce reliable, reproducible ad sorption data and to develop a better understanding of the mi crobial adsorption process. Removal of five toxic organic com pounds from water by adsorption on microbial biomass was investigated. Adsorption of organic chemicals (lindane, diazinon, malathion, pentachlorophenol, and the PCB 2-chlorobiphenyl) One

settled

sludge

water was decanted and replaced by fresh tap water. Washing by centrifugation. The sludge was dried in an oven at 115?C

and secondary primary as the mechanism re

proposed

was

arrhizus

The activated sludge biomass was obtained by collecting return activated sludge from the Hamilton, Ontario municipal waste

Protection Agency (EPA) have studied the fate of many organic priority pollutants discharged into an activated sludge pilot plant. Many

R.

The

stray microorganisms.

by

filtered through cheese cloth, washed repeatedly with tapwater, and autoclaved at 250?C for 30 minutes. The biomass was then vacuum-dried and ground with a mortar and pestle to pass

was

hazardous wastewater

treatment plants, a better understanding of the fate of these pol lutants is needed. Accumulation of some hazardous pollutants by selected live and dead microorganisms has been investigated by various workers.1"10Comprehensive reviews of the literature in this area have

pollutants

the biomass

was

the

was

computed

initial

solution by

concentration.

a mass

Up

balance.

experiments were conducted by first contacting with

ads?rbate

solutions

as

in the

adsorption

ex

periments. The biomass then settled in the adsorption flasks and the majority of the supernatant solution was decanted and re placed by distilled/deionized water. The flaskswere then sealed and put back on the shaker for 3 days. The decanted solutions were filtered and the quantities of biomass collected on the filters

191

April 1987

This content downloaded on Fri, 15 Feb 2013 04:17:01 AM All use subject to JSTOR Terms and Conditions

Bell & Tsezos_ were measured. The biomass quantity removed with the dec?n tate was subtracted from the original quantity of biomass to provide the biomass quantity basis for desorption. The filtrates were

and

analyzed

the adsorptive

were

values

uptake

calculated.

After desorption equilibrium was reached, the desorption so lutions were filtered and the filtrates analyzed. Equilibrium

and

samples,

initial

order

was

after desorption

loading duplicate

containing

solution

computed by a mass the same biomass

concentration,

of magnitude

concentration

were

balance.

Some

inert

The seals by

shaking

shaker atmaximum were

were

extractions

used

always

for

each

range.

analyzed

using

carried

out

the solvent/water

in septum

bottles

with

speed for 30minutes. The solvent solutions a gas Chromatograph

.,

t? o

an electron

with

t?

S o 10' o oCO CO -t? CL no

on a wrist-action

mixture

bo

^b 104t

concentration

All samples were prepared for analysis by extracting the solutes from the water solutions with pesticide grade hexane or iso octane.

10s

cap

'-z 102 CO

ture detector and a digital integrator. Standard solutions, ex in the same manner

tracted

as the samples,

were

analyzed

along

with the samples. Sample concentrations were determined by linear interpolation between adjacent standards. Precision of the analytical technique was generally within 2%. The overall ac of

curacy

the concentration

was

measurements

estimated

Figure

C0

equation was fit

Adsorptive uptake results. The Freundlich to the equilibrium data:

4=/W/n=^^

Where =

equilibrium

(i)

concentration

of

ads?rbate

concentration

of

ads?rbate

on

biomass,

Mg/g, = Ceq

Phase

Liquid

to be

RESULTS

q

10l

?10%.

approximately

equilibrium

in

B

= =

initial

Mg/L,

104

(ug/L) on R. arrhizus.

in solution,

of ads?rbate

concentration,

11 m

i_

103

of pentachlorophenol

concentration

biomass

102

Concentration

isotherm

2?Adsorption

/ug/L, and

g/L.

Typically, the Freundlich equation parameters are determined by applying linear regression to the logarithmic form of the equation, where log q is taken as the dependent variable and log Ceq as the independent variable. In the adsorption experiments, however, the true dependent variable is the equilibrium con centration, Ceq and the independent variables are the initial con centration,

solution,

i i 111mi

""'

10?

?0"1

The

C0,

and

parameters

the biomass

squares

routine.

Because

range,

a reduced

least

the data squares

not

line would

regression

the

using

variables, by a nonlinear

and independent

dependent

B.

concentration, 1/n were determined,

and

KF

favour

covers

a wide was

technique the higher

true

least

concentration so that

used

the

values.

concentration

In this case, the parameters which minimize }Wiel\

were determined:

(2)

^obs /

*

Where yobs ^modei

= =

observed values

values

of dependent

of dependent

and

variable,

variable

predicted

by

the model.

Selected adsorption isotherms at 20 ?C are shown in Figures 1-5 with the fitted Freundlich equation lines. Table 1 gives the Freundlich parameters for each isotherm where q is in /?g/g and is in /?g/L. In general, orders three or more mately Ceq

the

cover

data

adsorption

of magnitude

approxi

of concentration.

Ta

ble 2 gives the equilibrium adsorption capacity of the biomass at various

common

solution

concentrations,

at 20?C,

calculated

from the Freundlich equation. 10?

Figure

101 102 Liquid Phase Concentration

1?Adsorption

isotherm

of lindane

103

104

(pg/L)

on activated

sludge.

effects Temperature on adsorptive perature

on adsorptive uptake was

uptake. investigated

The for

effect

of tem

lindane,

dia

zinon, and malathion. The Freundlich equation parameters for the adsorption isotherms at the different temperatures are given in Table

1.

192

Journal WPCF,


Volume

59, Number

4

_Focus

on Adsorption

Processes

The enthalpy or heat of adsorption is given by the van't Hoff

?oV

equation:

a*=-*^

v;

d(i/r)

(6)

Where AH = heat of adsorption, kJ/mole, R T

= =

-

gas

constant,

absolute

?K,

kJ/mole

and

?K.

temperature,

Finally, assuming that AH is not a function of temperature, AH can be determined from equilibrium concentrations at constant adsorptive uptake at two different temperatures. Integrating Equation 6 and substituting for K, we obtain: -fllnKW/Ceo,2] (1/T2-1/TJ

AH

(7)

where

l=

C LO"

101 10' Liquid Phase Concentration

3?Adsorption

Figure

isotherm

of diazinon

10' (ug/L)

on activated

104

= Ceq2

T\

sludge.

Thermodynamic calculations. Assuming that the adsorption equilibrium is the result of a dynamic adsorption-desorption involving

the solute

and

solvent

(l)l + m(2)s^(l)s

in an exchange

of

concentration

equilibrium

solute

at temperature

1 2

at the same loading, iiq/L, T2

process

equilibrium concentration of solute at temperature at selected loading, ng/L,

reaction12

+ m(2)1

(3)

where (1) and (2) represent the solute and solvent, and super scripts s and / refer to the adsorbed (surface) phase and the so lution (liquid) phase, respectively, then the equilibrium constant for the exchange reaction is given by

(4)

= =

1, ?K,

temperature

2,

temperature

and

?K.

Using the fitted Freundlich equations to determine the equilib rium concentrations at different values of adsorptive uptake, the heats of adsorption in Table 3 were obtained from Equation 7. The free energy change of adsorption can be calculated using the following equation derived from theGibbs adsorption equa tion.13"15 AG'

=

r

-RT

Jo

N

?

da

(8)

a

Where AC = free energy change of adsorption, kJ, a = activity of adsorbed solute in solution, and N = number of moles of solute adsorbed.

Where K = equilibrium constant, = a\ activity of the solute in adsorbed phase, = ai activity of the solute in solution phase, = a2s activity of the solvent in adsorbed phase, and = a2l activity of the solvent in solution phase. In dilute solution it may be assumed that activities in the solution phase can be approximated by mole fractions and the mole fraction of the solvent remains essentially constant and approximately 1.Considering only conditions at constant surface coverage (such as constant loading or concentration of solute on the biomass) it can be assumed that the ratio of solute and solvent activities in the adsorbed phase are constant. Applying the assumptions, the following relationship can be written:

K*h*k

Where Xi

=

equilibrium mole

(5)

fraction of solute in solution phase,

101 103 102 Concentration Phase (ug/L) Liquid

10?

and

Ceq

=

equilibrium concentration of solute in solution phase, Aig/L.

Figure

4?Apparent

adsorption

isotherm

of malathion

on activated

104

sludge.

193

April 1987


Bell & Tsezos The entropy change associated with adsorption can be cal culated from the Gibbs-Helmholtz equation. AH-AG

(15)

AS=

Entropy changes at 20?C and a loading of 1000 /?g/g, computed from calculated values of AH and AG using Equation 15 are given in Table 3. Desorption equilibrium results. Desorption equilibrium iso therms for lindane, diazinon, and 2-chlorobiphenyl for both types of biomass were essentially identical to the adsorption isotherms, indicating complete reversibility. Desorption data are shown for lindane in Figure 6, superimposed on the respective adsorption isotherm.

Malathion

removal

was

reversible

at 5?C,

at

however

20?C, desorption did not occur. In fact, at 20?C, the malathion concentration in solution after desorption was less than predicted by accounting for dilution of the solution remaining after de canting the adsorption equilibrium solution. Rather than de sorption,

101 lO2 Phase Concentration (pig/L) Liquid Figure

To

isotherm

5?Adsorption

the free

compute

energy

per

change

unit mass

whereas

of adsorbent,

Ca ?da q

(9)

a

Jo

Where AG"

=

free

energy

of adsorption

change

per unit mass

removal

was

detected.

The experimental evidence indicates that removal of mala thion occurred primarily by amechanism other than adsorption,

we can rewrite Equation 8 in the form: AG" = -RT\

malathion

DISCUSSION

on R. arrhizus.

of 2-chlorobiphenyl

additional

103

the

other

compounds

were

removed

by

adsorption.

Therefore, the behavior of malathion will be discussed separately from the discussion of the other four compounds. Adsorption isotherm modelling. Of the commonly used ad sorption models the Freundlich equation provides the best fit of the data in our experiments. Adsorption in biological systems

of ad

sorbent, kJ/g, and = moles of solute adsorbed q per unit mass of adsorbent,

Table

1?Freundlich

for adsorption

parameters

iso

therms.

moles/g.

At low solute concentration, mole fraction may be substituted for activity to obtain: AG" = -RT\

Biomass

Compound

ft

Lindane

q?

"JAf

the Freundlich equation Pentachlorophenol

= q KFXi/n (11) then Equation

AG" =

KFXl/n'ldX

5.0

3.2

1.0

Activated

34.5

0.7

1.1

sludge

20.0

1.5

1.0

5.0

1.8

1.0

ft

arrhizus

R. arrhizus

(12)

20.0 20.0

-RTKFXl/n Malathion

*G=?(mr=-nRTq

28.8

0.9

10.1

0.8

1.9

0.8

(14)

Free energy changes of adsorption calculated from Equation at 20?C are given in Table 3.

14

1.3

20.0

0.4

1.0

sludge

5.0

0.1

1.2

20.0 5.0

2-Chlorobiphenyl

0.1

Activated

R. arrhizus

Equation 14 can be used to calculate the free energy change per mole of solute adsorbed AG" AG =-=-nRT Q

20.0 5.0

or _?

1.0 1.0

sludge Diazinon

-RT?

1.6 2.3

Activated

10 becomes

34.5

\/n

20.0

fraction of adsorbed solute in solution.

If q is related toXby

arrhizus

(10)

Where X = mole

Temperature, ?C

3.7

1.2

0.04

1.2

Activated

20.0

sludge

5.0

0.5

R. arrhizus

20.0

62.6

Activated

20.0

20.5

403.0

0.6 0.9 1.1

0.8

sludge

194

Journal WPCF,


Volume

59, Number

4

_Focus Table 2?Equilibrium

adsorption

at 20?C.

capacity

Adsorption capacity, stated concentration,

Lindane

ft

/ug/g

1000 M9/L

254 156

2 690 1570

231 69

1855 478

14 900 3 300

12 4

77 45

491 500

M9/L

arrhizus

24

Activated

15

2-chlorobiphenyl does show the highest uptake. Although pen tachlorophenol is slightlymore soluble than lindane it is adsorbed significantly more strongly. Water solubility, it appears, offers only a very rough prediction of adsorption by biomass. Accu mulation of pollutants by aquatic organisms has been positively correlated with the octanol/water partition coefficient of the ad

q, at

100 M9/L

10 Biomass

Compound

ft

arrhizus

Activated sludge ft

Diazinon

arrhizus

Activated

log Aow-

R. arrhizus Activated

57 1467

863 5 341

13 200 19 400

-


753 144

9 049 1012

108 800 7108

sludge

has frequently been represented by the Freundlich equation or by a linear relationship which the Freundlich equation reduces to when

the exponential

trations,

where

only

parameter a small

At

low concen

of the ultimate

adsorption

equals

fraction

one.1

capacity may be used, a nearly linear isotherm is expected. At higher concentrations, where a large proportion of the available adsorption

capacity

be used,

might

a nonlinear

is ex

isotherm

pected. In that case, the exponent in the Freundlich equation should be less than one. With compounds of low solubility, it may not be possible to attain high enough concentrations to observe

saturation

of

the

For

adsorbent.

most

of

the

systems

tested, the isotherms are close to linearity, indicating that sat uration

of

the

adsorption

capacity

of

the biomass

was

not

concentrations

fit the

same

3?Estimated

Thermodynamic

sludge.

reported.

Lindane

Diazinon

Malathion

between

relationship

uptake

and

the octanol/water

for R.

arrhizus

a correlation

with

of 0.956.

coefficient

reported

was

10.559

on Z.

/ig/g

ramigera

at a concen

Lindane

was

a mixture

onto

adsorbed

of

live and

dead

The

that observed

uptake

was

in these

about

an order The

experiments.

below

of magnitude exponential

parameter

in the Freundlich model was reported to equal 1.0. The uptake of lindane and diazinon by various soils and sed iment was investigated and approximate linear isotherms with

uptake,

500 M9/9

AG

k J/g-mole

1000 M9/9

k J/g-mole

AS ?K

J/g-mole

-12.5

-12.2

-2.4

-13.2

-10.1

-8.8

-2.4

+32.5

-0.7

-15.0

-3.0

-40.8

sludge

+15.5

+8.4

-2.3

+26.4

+165 +385

-2.1

sludge

+565 +1100


The

-13.4


the octanol/water

sludge


of

Parameters.

100 M9/9

Biomass

logarithm

bacteria.22 No difference in uptake by live and dead cells was

isotherm.

AH at stated

Compound

the

tration of 32 /Ltg/L which is approximately 7.5 times less than that of R. arrhizus and almost 5 times less than that of activated

The different compounds exhibit awide variation in adsorptive uptake. Adsorptive uptake is expected to be roughly inversely correlated with ads?rbate water solubility.1'7'9 Table 4 gives the water solubility of the compounds. The least soluble compound, Table

1.68

uptake

ap

proached. The equilibrium adsorptive uptake appears to be in dependent of initial concentration and adsorbent concentration because data obtained with different starting concentrations and biomass

lists

For activated sludge, the regression equation is log q = 0.671 0.396 with a correlation coefficient of 0.985. logK0w Comparison of present results to results of other investigators. Adsorption of lindane by yeast was investigated5 and itwas found that the adsorption isotherms for living and dead yeast followed the Freundlich equation with \/n equal to one, corresponding to results of this study. The dead yeast showed higher uptake than the live yeast although the reported uptake was approxi mately an order of magnitude below that observed in the present experiments. An isotherm for lindane adsorbed by live algae8 also fit the Freundlich equation but with a value of i/n greater than one. Uptake by the algae was approximately twice that of R. arrhizus at a concentration of 1000 /?g/L and approximately equal to that of R. arrhizus at 10 Mg/L In another study,4 lindane was adsorbed on microbial cells (a yeast, two bacteria, and an alga) fixed on magnetite. A bacterium, R. sphaeroides, had the highest uptake but was significantly lower than for R. arrhizus or activated sludge. The \/n value for the Freundlich model was reported to equal 0.80. Heat killed bacteria had a slightly greater uptake than live bacteria. The uptake of lindane by thirteen bacterial species was reported.7 The highest

sludge 2-Chlorobiphenyl

4

= 1.11 logK0w partition coefficient can be represented by log q

sludge Malathion

Table

s?rbate.1,9'1119

partition coefficients, logK0w, for the five compounds. The oc tanol/water partition coefficients for lindane and pentachloro phenol correctly predict that pentachlorophenol should be more strongly adsorbed than lindane. Ifmalathion is excluded, uptake iswell correlated with K0w as shown in Figure 7 where uptake at an equilibrium concentration of 100 /xg/L is plotted against

sludge Pentachlorophenol

on Adsorption Processes

+164 +339

+5.4

+164 +319

-4.3

-33.4 21.6

195

April 1987


Bell &

Tsezos_ 1 1 1 1 1 ? 11

1

10*,

adsorption process is exothermic, as is generally expected, and AH declines with increasing loading. Since the biomass materials

i 1 11

?1-1?1?i

we would

are nonhomogeneous

sites with

that adsorption

expect

bo

different adsorption energies would exist. The suggested decline in heat of adsorption with loading indicates that the higher energy

"bo

sites

Sorption

Isotherm

are

and

favoured

at

dominate

lower

loading.

The

change

in heat of adsorption is greater for activated sludge than for R. arrhizus indicating a greater degree of non-homogeneity which is to be expected. The low heats of adsorption estimated for diazinon suggest that a physical adsorption process is dominant. At this stage, and in view of the assumptions behind the cal

? o

ao 10' O oCO cd ?3 CU

of A H

culation

are

we

values,

not

certain

whether

adsorption

is endothermic at lower uptake values and changes to exothermic at higher loading as suggested by the data. The change in uptake with temperature is very small for diazinon, making it difficult to estimate AH precisely.

o 03

The

free energy

negative

are as expected

values

change

because

the solute is expected to be more concentrated on the surface of the biomass than in the bulk solution. The decrease in entropy

from activated

of lindane

6?Desorption

Figure

104

10* 10' Liquid Phase Concentration (ug/L)

"?01

on

were

experiments

Compared

reported.

to ac

tivated carbon, the adsorptive uptake of biomass was significantly less. Uptake

by activated

carbon

was

two

about

orders

of mag

nitude greater for lindane and about one order of magnitude greater for pentachlorophenol adsorbed onto R. arrhizus at 1000 Mg/L.24The higher uptake by activated carbon may be partly explained by its significantly greater specific surface area (on the order of 1000m2/g compared with 0.52 m2g for R. arrhizus and 1.1m2g for activated sludge25). It is interesting to note, however, that the uptake per unit surface area is greater for the biomass than for activated carbon. Lindane ismore strongly adsorbed by activated carbon than pentachlorophenol, as would be pre dicted by solubility considerations, in contrast to the opposite result for adsorption onto biomass as predicted by the octanol/ water

partition

coefficients.

Thermodynamic adsorption

are probably

not

accurate

the estimated heats of

because

of the assumptions

involved in their calculation, they are considered the correct order of magnitude. Others26,27 compared heats of adsorption for solutions obtained from calorimetric experiments to those calculated from thermodynamic considerations similar to those used in this study and found order of magnitude agreement. To test the assumption that AH is independent of temperature, the logarithm of equilibrium concentration versus reciprocal tem perature was plotted for lindane at a loading of 500 /*g/g (Figure 8). These plots should yield a straight line if AH is independent of temperature.

Linear

regression

of the data

for both

R.

arrhizus

and activated sludge yielded correlation coefficients greater than 0.95 for a linear relationship, therefore the assumption of the temperature independence of Ai/ is reasonable for the experi mental

temperature

range

of

the present

on R.

diazinon

is con

arrhizus

of the solute molecules

arrangement

work.

The estimated heats of adsorption for lindane adsorption on both types of biomass are low and in the range where physical adsorption is expected to be the dominant mechanism.10 The

were

in entropy

of aromatic

for adsorption

reported29

carboxylic acids on carbon blacks. They concluded that for large molecules, the simplified view of themore ordered arrangement on

of molecules

the

surface

not

may

be

that

and

appropriate,

nonspecific interaction energy between the ads?rbate and the surface, coupled with configurational changes in the ads?rbate on

account

could

adsorption,

for

the positive

entropy

changes.

isotherms for lindane, Desorption equilibrium. Desorption diazinon, and 2-chlorobiphenyl indicate complete reversibility within the 3 day contact time. This is further evidence that an adsorption process is responsible for removal of these compounds from solution. The ease of reversibility also suggests that physical adsorption is the dominant mechanism for these compounds. The reversibility of the microbial adsorption process leads to a concern for the possible leaching of adsorbed chemicals from wastewater

land-disposed

treatment

plant

sludges.

If the pollut

ants remain adsorbed through the sludge digestion process they may

considerations. While

and

ordered

on the biomass surface than in solution.28However, the diazinon/ activated sludge system appears to exhibit an increase in entropy.

sludge.

uptake values several to several hundred times less than those in these

a more

with

Increases

observed

lindane

for

adsorption

sistent

be desorbed

into

surface

of malathion

Mechanism

or groundwater Malathion

removal.

after

disposal.

is the most

water

soluble of the five compounds investigated and also has the lowest octanol/water partition coefficient. Itwould therefore be expected to exhibit the least adsorptive uptake of all the compounds. On

water Table 4?Approximate ter partition coefficients. Solubility, Compound

mg/L

solubilities

log Reference

Lindane

K0w

16 10 1417

Pentachlorophenol

Diazinon Malathion 2-Chlorobiphenyl

150

16 40 16 18 6

a Average of values reported in reference b Estimated by fragment method.20

196

Journal WPCF,


and octanol/wa

Reference

3.72

20

4.65a

20

3.14 2.89 4.87b

21 20 20

20.

Volume

59, Number

4

_Focus

on Adsorption

Processes

within the experimental contact time used in the present work. Our data suggest that the biomass acts as a catalyst for the de composition of malathion. Perhaps the reaction is catalyzed by on

adsorption

the biomass

A

surface.

was

mechanism

similar

proposed30 where rapid decomposition of malathion in the pres ence of sterile soil was observed. Preliminary experiments on the rate of malathion removal indicate that given enough time, the

3.0

reaction

to completion

proceeds

and

that

the

rate

reaction

is significantly reduced by decreasing the temperature. No de composition products have been identified, thus far, and the experimental data currently available are insufficient to deter mine the nature of the chemical reaction.

er bo o 2.5 r

CONCLUSIONS The results of these experiments indicate that adsorption by microbial biomass is an important process in the removal of

2.0 OR. arrhizus D Set sludge

hazardous

2.5

5.0

logKo? 7?Adosorptive

Figure

uptake

against

coefficient

partition

octanol/water

at 100 Mg/L for lindane (LND), pentachlorophenol (PCP), diazinon (DZN), malathion (MTH), and 2-chlorobiphenyl (PCB).

the contrary, malathion shows the highest apparent uptake for activated sludge and higher uptake than all but 2-chlorobiphenyl forR. arrhizus. The malathion data are highly scattered (Figure 4) and do not seem to consistently fit a single adsorption iso therm. The data also do not appear to be independent of biomass concentration and initial malathion concentration. The high positive values of AH calculated for malathion are not typical of adsorption phenomena but suggest a chemical reacton. The fact that desorption of malathion was not observed at 20?C pro vides further evidence that at this temperature removal of mal athion is the result of a mechanism other than adsorption. The desorption observed at 5?C suggests that at higher temperatures (for example, 20?C) adsorption also takes place but is over shadowed by another removal mechanism that is significantly affected

by

temperature

in biological

pollutants

organic

treatment

systems.

For compounds that are not readily degraded, the dominant removal mechanism appears to be physical adsorption; uptake is rapid and the process appears to be completely reversible. The octanol/water partition coefficient is a better indicator of the relative extent of adsorption by microoganisms for the physically adsorbed

than

compounds

is water

Lindane,

solubility.

penta

chlorophenol, diazinon, and 2-chlorobiphenyl, are in this cat egory of compounds. At 20?C, malathion is removed primarily by a chemical decomposition reaction catalyzed by the inactive biomass. The mechanism of this reaction and the decomposition products are as yet unknown. One implication of this work is that

the

removal

of biorefractory

can

compounds

organic

be

accomplished in biological treatment systems by adsorption onto Because

biomass.

the

adsorption

is reversible,

there

however,

must be concern for the potential desorption of the pollutants in the

reactor

as for

as well

environment

the ultimate

disposal

change.

It seems most likely that at 20 ?C the disappearance of mal athion isprimarily a consequence of a chemical reaction inwhich malathion

is decomposed.

cannot

data

be treated

adsorption

Consequently, as adsorption data,

removal

plus

by decomposition

the malathion

uptake

but

represent actually after a 3-day contact

period using various biomass and initial solution concentrations. In this light, the scatter of the data is explicable. Furthermore, the large increase in the observed malathion removal with in action

can

temperature

creasing

hypothesis.

is greater

and

At

also

be

the higher

the observed

removal

explained

re

the chemical

by

temperature, after a given

the

rate

reaction

contact

period

is thus greater. The fact that additional removal rather than de sorption took place during the desorption experiments can also be

accounted

position

process

for by which

the

of

continuation takes

place

upon

the

chemical

the

contact

decom of

the

3.20

3.25

3.30

3.35

3.40

3.45

3.50

3.55

3.CO

3.65

so

lution with the biomass. The desorption observed at 5?C suggests that at this temperature the reaction rate is probably reduced to the point where adsorption is the dominant removal mechanism

T-lCK-1) Figure loading

8?Liquid

phase

against

reciprocal

lindane

equilibrium

concentration

at 500 Mg/g

temperature.

197

April 1987


Bell &

Tsezos_

of waste sludges to prevent the return of hazardous pollutants to the environment.

12. Everett, D. H., "Thermodynamics of Adsorption from Non-aqueous Solutions." and Polymer Sei., 65, 103 (1978). Progr. Colloid on Metal Surfaces of Long Chain 13. Daniel, S. G., "The Adsorption from Hydrocarbon

Polar Compounds

ACKNOWLEDGMENTS The

Credits.

present

work

was

supported

by

a grant

to

the

second author from the Natural Sciences and Engineering Re search Council of Canada. didate

and

Hamilton,

P. Bell

John

Authors.

professor,

and Marios respectively,

Canada.

Ontario,

Tsezos

are

at McMaster

University, be

should

Correspondence

can

doctoral

ad

dressed toMarios Tsezos, Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada, L8S 4L7.

Serum of Bovine "Adsorption Biophys. Acta, 19, 464 (1956). 15. Chattoraj, D. K., and Birdi, K. S., "Adsorption Excess." Plenum Press, New York (1984). 14. Bull, H. Biochim.

R. N.,

Canada,

Ottawa,

Crit.

Ph.D. Pollutants." J. P., "Biosorption of Hazardous Organic Canada McMaster Hamilton, Ontario, (1986). University, inWater by Microbial Cells 4. McRae, "Removal I.C, of Pesticides to Magnetite." Water Res. (G. B.), 19, 825 (1985). Adsorbed 3. Bell,

Thesis,

and Desorption P. M. L., "Adsorption S., and Tammes, and Dieldrin Toxic, 4, by Yeast." Bull Envir. Contam.

271 (1969). D. M., et al, "Sorption of Organics by Selenastrum Water Res. (G. B.), 17, 1591 (1983). pricornutum" 7. Grimes, D. J., and Morrison, S. M., "Bacterial Bioconcentration

6. Casserly,

Hydrocarbon

Insecticides

from

Aqueous

Ca~ of

Systems,"

2,43(1975).

on the Accumulation of Lindana (7 P-D., "Experiments spec, and Chlorella pyr BHC) by the Primary Producers Chlorella enoidosa." Arch. Environ. Contam. Toxicol, 8, 721 (1979). Chloroethanes 9. Tsezos, M., and Seto, W., "The Adsorption by Mi 8. Hansen,

crobial 10. Herbes, Between

and the Gibbs

Environment

Sourcebook." Data York

Surface

on Organic (1977).

of PCB's." CRC Press, Boca 18. Hutzinger, O., et al, "The Chemistry Raton, Fla. (1974). of Bioconcentration Factors." Environ. 19. Mackay, D., "Correlation

Water Res., 20, 851 (1986). Aromatic S. E., "Partitioning of Polycyclic Hydrocarbons Phases in Natural Waters." Water and Paniculate Dissolved

Biomass."

21. Zaroogian, G., et al, with Structure-Activity Freshwater 22. 23.

Fish."

"Estimation Models

Aquatic

to Marine of Toxicity Species to to Estimate Toxicity

Developed Toxicol, 6, 251

Sugiura, K., et al, "Adsorption-Diffusion idues." Chemosphere, 4, 189 (1975). of Sharom, M. S., et al, "Behaviour Aqueous

Suspensions

(1985). Mechanism

12 Insecticides

of Soil and Sediment."

Water

of BHC-Res in Soil Res.

and

(G. B.),

14, 1095(1980). Isotherms for J.M., "Carbon Adsorption 24. Dobbs, R. A., and Cohen, D.C. U. S. EPA. Washington, Toxic Organics." EPA-600/18-80-123

(1980). 25. Tsezos, M., "Determination of Specific BET Method," Personal communication.

Surface Area

of Biomass

by

and Phenols from Non 26. Crisp, D. J., "The Adsorption of Alcohols on to /. Alumina." Colloid Solvents Sei., 11, 356 polar Interface

(1956). of Chain Molecules 27. Kern, H. E., et al, "Adsorption from Solution onto Graphite: in Ordered Mono Evidence for Lateral Interactions layers." Progr. Colloid and Polymer Sei., 65, 118 (1978). 28. Wright, E. H. M., libria for Aromatic

and Powell, Molecules

A. V., "Solid-Solution Interface Equi from Non-Aromatic Media."

Adsorbed

/. Chem. Soc. Faraday Trans., 168, 1908 (1972). E. H. M., and Pratt, N. C, "Solid/Solution Interface Equi 29. Wright, Media." libria for Aromatic Molecules Adsorbed from Non-Aromatic Soc. Faraday Trans., 170, 1461 (1974). a Phospho et al, "Soil Degradation of Malathion, Soil Sei. Soc. Am. Proc, 33, 259 (1969). Insecticide." rodithioate

J. Chem.

Res.,

11,493(1977). 11. Petrasek, A. C, et al, "Fate of toxic organic compounds treatment plants." J. Water Pollut. Control Fed., 55,

16,274(1982). for Correlation Constants and Leo, A., "Substituent C, and Biology." John Wiley & Sons, New York, in Chemistry

Analysis N.Y. (1979).

46,95(1982).

Ecol,

et al, "Water Quality Canada (1979).

on Glass."

Albumin

of Environmental K., "Handbook Reinhold Van Nostrand Co., New

17. Verschueren, Chemicals."

of

and Effects 2. Lai, R, and Saxena, D. M., "Accumulation, Metabolism, Microbiol of Organochlorine Insecticides on Microorganisms," Rev.,

Chlorinated

B.,

16. McNeely,

20. Hansch,

1. Baughman, G. L., and Paris, D. F., "Microbial Bioconcentration Critical Review." Organic Pollutants from Aquatic Systems?A Rev. Microbiol, 8, 205 (1981).

Microb.

Faraday

Sei. Technol,

REFERENCES

5. Voerman, of Lindane

Trans.

Solutions."

Soc, 47, 1345(1951).

inwastewater 1286

(1983).

30. Konrad,

J. G.,

198

Journal WPCF,


Volume

59, Number

4