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Shock Effects of Copper Ion onActivated Sludge Unacclimated and ItsRecovery TechniqueBing Xie a & Eiko Nakamura ba Department of Environmental Science and Technology , EastChina Normal University , Shanghai, 200062, Chinab Department of Education and Human Science , YokohamaNational University , Yokohama, 240-8501, JapanPublished online: 29 Oct 2010.

To cite this article: Bing Xie & Eiko Nakamura (2002) Shock Effects of Copper Ion on ActivatedSludge Unacclimated and Its Recovery Technique, Toxicological & Environmental Chemistry,83:1-4, 55-67, DOI: 10.1080/716067230

To link to this article: http://dx.doi.org/10.1080/716067230

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Toxicological and Environmental Chemistry, Vol. 83, pp. 55–67 � 2001 OPA (Overseas Publishers Association) N.V.

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a member of the Taylor & Francis Group.

SHOCK EFFECTS OF COPPER ION ON

ACTIVATED SLUDGE UNACCLIMATED

AND ITS RECOVERY TECHNIQUE

BING XIEa,* and EIKO NAKAMURAb

aDepartment of Environmental Science and Technology, East China NormalUniversity, Shanghai 200062, China; bDepartment of Education and Human Science,

Yokohama National University, Yokohama, 240-8501, Japan

(Received 5 February 2002; Revised 26 February 2002; In final form 3 December 2002)

To study the effects of heavy metals on the pilot-scale activated sludge process, the uptakeof heavy metals and the removal rate of CODMn by activated sludge were investigated in vari-ous conditions. When 20mg/L of copper ion was added to the sequence batch reactor (SBR) ofthe unacclimated activated sludge, copper ion was rapidly adsorbed by the activated sludgeflocs at first and then released from them after aeration. The copper ion concentrationof mixed liquor in the reactor increased until the removal rate of CODMn became constant.When three kinds of the additives including special nutrients (as CODMn 45mg/L),powdered activated carbon (PAC, 50mg/L) and condensed sludge (as MLSS less than300mg/L), which are possible candidates for the recovery techniques, were added to theactivated sludge, different bio-kinetic constants were obtained, indicating different inhibitionrates of treatment efficiency. In the case of special nutrients, the removal rate of CODMn wasthe highest among all three additives, showing that they stimulated microorganisms in theactivated sludge to absorb organic substances. Addition of PAC and condensed sludge alsoimproved the removal rates of CODMn and copper ion. Especially when the organic loadwas light, the addition of PAC could efficiently remove organic substances and copperion from the mixed liquor. However, the addition of the condensed sludge increased the turbid-ity of the mixed liquor. And some long time aeration was found leading to the deflocculationof activated sludge.

Keywords: Heavy metal; Copper ion; SBR; Unacclimated activated sludge; Wastewatertreatment; Recover technique

*Corresponding author. Fax: þ86-21-62233670. E-mail: wswz@public2.sta.net.cn

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INTRODUCTION

Heavy metals are toxic to microorganisms, although some trace amounts of

heavy metals are beneficial to microbes for their growth [1,2]. When heavy

metals are loaded in the acclimated activated sludge, there is little effect on

the treatment efficiency. Usually, the state of acclimation will maintain high

treatment efficiency of sludge if it has been exposed to high concentration

of heavy metals [3–5]. On the contrary, a load of heavy metals to the unac-

climated activated sludge causes serious problems on the process, the

treatment efficiency becomes unsteady, the structure and diversity of the

microorganism community of the activated sludge will be affected and

that will take a long time to recover [6]. The time period required for

recovery increased when the metal concentration went up [7]. Therefore, it

is important to study how to recover the activated sludge process that has

been damaged by heavy metals and to improve the treatment efficiency

quickly. The practical method of removing heavy metals from the mixed

liquor is one of the most important technology in wastewater treatment

[8]. Study on the recovery technique of the process is required not only to

reduce the effects of heavy metals in the activated sludge process, but also

to recover the treatment efficiency in a shorter term.

Heavy metals have inhibitory or toxic effects on activated sludge

microorganisms and upset the operation of the activated sludge [9,10].

The removal rate of organic substances depends on the area of binding

sites for the substances of the activated sludge. The rate will decrease if

the binding sites are not sufficient since heavy metals compete with organic

substances for the binding sites [11,12].

Copper was selected for this study because of its high toxicity, ubiquitous

presence in wastewater and chemically well-known of its solution. The

effect of copper depends on its chemical species and concentration.

Copper has little effect on the viability of the microorganisms and removal

rate of BOD when its concentration is below 10 mg/L [3,7,12], and can

stimulate the biomass yield at 10 mg/L [13]. However, copper ion affects

the process seriously at a concentration above 30 mg/L [14]. The

copper ion concentration of influent was adjusted to 20 mg/L in this

experiment, since there are few researches about the effect of copper ion

at 10–30 mg/L.

However, addition of powdered activated carbon (PAC) will help the

adsorption of toxic substances and the stability against heavy metal shock

loads and toxic upset [15–17]. In this experiment PAC was tested as a

recovery agent. The adjustment of sludge age or a rapid increase of

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suspended solid concentration (MLSS) in the reactor is an easy approach

in activated sludge treatment plant [18,19]. Condensed activated sludge

was studied as another recovery method, because it would increase the

biomass and reduce the toxicity of heavy metals. Furthermore, addition

of special nutrients is helpful for the recovery of the process because some

nutrients can reduce the effects of heavy metals and stimulate the growth

of microorganisms. For example, peptone and cystine are useful in uptaking

the metals because they have an ability to form complexes with sludge

flocs [20]. Glycerophosphate (BGP) may meet the increasing demand

for Adenosine triphosphate (ATP) and enhance the culture viability of

microorganisms [21,22]. Addition of the mixture of these nutrients was

tested as the third possible recovery technique.

Other methods, including a longer aeration period, were also studied.

The treatment efficiency and economic evaluation of each method were

compared.

MATERIALS AND METHODS

Activated Sludge Simulation

The activated sludge process was simulated in a laboratory unit as shown in

Fig. 1. The unit was constructed with four plastic bottles (labeled 1,2,3,4) as

reaction tanks (reactors). A mixture composed of activated sludge (2 g/L),

synthetic wastewater and copper ion (20 mg/L) was added to each reactor.

Bottle 1 (control reactor) was used for control test. Bottle 2 (PAC reactor)

FIGURE 1 The experimental device: 1. Control reactor; 2. PAC reactor, supplied with pow-dered activated carbon; 3. Sludge reactor, supplied with condensed sludge; 4. Nutrients reactor,supplied with special nutrients (pepton, systine and BGP).

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was supplied with mixed solution and PAC at 50 mg/L. Condensed

sludge was added to Bottle 3 (sludge reactor) at 120 mg/L or 300 mg/L

in order to increase MLSS. Bottle 4 (nutrients reactor) was supplied

with mixed solution and special nutrients (Peptone 40 mg/L, BGP 50 mg/L

and cystine 20 mg/L; CODMn is 45 mg/L) [22]. The composition of the

synthetic wastewater is shown in Table I. The initial CODMn value of the

mixed liquor was adjusted to 180 mg/L (low organic load) or 328 mg/L

(high organic load) by adding aliquots of the synthetic wastewater.

The temperature of the unit was maintained at 20�C by a temperature

controller. The mixed liquor in the reactor was aerated for 30–40 h.

CODMn and the concentration of copper ion were measured at regular

time intervals.

The activated sludge was collected from the municipal wastewater

treatment plant (Yokohama central wastewater treatment center,

Yokohama, Japan). The sludge was washed five times with distilled water

to remove the original ions. The sludge was 10 days old and SVI was

100 mL/g prior to experiment. The concentration of the heavy metals in

the dry sludge of wastewater treatment plant is shown in Table II.

(According to the data of Yokohama Wastewater Bureau.) All inorganic

salts were of analytical reagent grade. Water was double distilled. Plastic

ware and glassware were soaked in 1mol/L HNO3 and rinsed with distilled

water before use.

Analytical Procedures

Samples were centrifuged and filtrated with 0.45 membrane filter. Heavy

metals in the mixed liquor were determined using a Shimadzu AA-660

flame atomic absorption spectrophotometer. Samples were also filtered

with quantitative filters and dried to constant weight at 105�C, and the

final weights were measured to determine the biomass concentration

of MLSS. However, an hourly monitoring of MLSS was carried out

TABLE I Composition of the synthetic wastewater

Constituents Concentration (mg/L)

C6H12O6 320KH2PO4 14.1Na2HPO4 � 12H2O 44NH4Cl 108CaCl2 <0.3MgSO4 � 7H2O <5

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turbidimetrically with spectrophotometer. SVI and SS of the mixed liquor

were determined by standard methods [23] respectively, and CODMn was

determined by JIS methods [24].

Data Analysis

The treatment efficiencies (COD removal rate) were calculated from the

following equation (Eq. (1)).

E ¼ ðS � S0Þ100=S0 ð1Þ

Substance removal in biological treatment processes could be described

by Monod equation (Eq. (2)).

Vs ¼ �maxXSðKm þ SÞ ð2Þ

At low substrate concentration (Km�S), Eq. (2) will reduce to a first-order

formulation. For sequence batch reactor (SBR) process, a mass balance on

substrate in the reactor during the reaction period can be shown as:

�dS=dt ¼ �maxXS=Km ¼ KS ð3Þ

where in this experiment, S¼COD concentration of the mixed liquor

(mg/L); S0¼ initial COD concentration of the mixed liquor (mg/L);

Vs¼COD removal rate (mg COD/ l h); Km¼ half-velocity constants (mg

COD/L); X¼microorganism concentration (MLSS) in the mixed liquor at

steady state (mg COD/L); mmax¼maximum specific growth rate constant

(h�1); K¼ (mmaxX /Km) pseudo first order rate constant; the value of K

can be determined from a linear plot of ln S versus time.

TABLE II The concentration of the heavy metals in the drysludge of wastewater treatment plant (1999)

Heavy metals May (mg/kg) October (mg/kg)

Cu 190 140Zn 810 310Total Cr 43 21Ni 450 290Mn 25 9.8

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RESULTS AND DISCUSSION

Analyses on Bio-kinetics Constants

The CODMn concentration of the mixed liquor measured was plotted with

time as shown in Fig. 2(a) and (b), in which initial CODMn concentrations

were 180 mg L�1 and 328 mg L�1 respectively. Linear relationships between

lnCOD and time were obtained with a relatively good fit (R2 > 0.93) in

all cases. The linear relationships indicate that the first-order formulation

Eq. (3) can be applied in describing metal inhibition of COD removal.

FIGURE 2 Plots of lnCOD vs time for first-order kinetic constant determination for: (a) atlow strength organic load (initial COD concentration of the mixed liquor: 180mg/L); (b) at highstrength organic load (initial COD concentration of the mixed liquor: 328mg/L). � Nutrientsreactor, œ PAC reactor, 4 Sludge reactor, Control reactor.

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The values of K calculated from the slopes of these linear plots are

summarized in Table III. K values obtained at low strength organic load

were larger than those obtained at high strength organic load.

The lowest K value is obtained from the control reactor, while the K

values obtained from the nutrients and PAC reactors are higher than that

from the control reactor regardless of the initial CODMn. These results

indicate that copper ion has a serious impact on microorganisms in control

reactor than those in other reactors. The highest K value is obtained from

the nutrient reactor at high organic load. This shows that the addition of

nutrients is the best way to stimulate the growth of microorganisms. In

the case of adding PAC, its K value is the highest among the four reactors

at low organic load. Two processes are probably involved, namely adsorp-

tion and biodegradation in the removal of organic substances during

the course of aeration. The contribution of PAC is to adsorb copper ion,

thus minimize its effects on activated sludge [16,25].

Effect of Different Additives on The Removal Rate of CODMn and Copper

The copper ion concentration of the mixed liquor measured was plotted

with time as shown in Fig. 3 (low strength organic load) and Fig. 5 (high

strength organic load). The CODMn removal rate of each reactor was

shown in Fig. 4 (low strength organic load) and Fig. 6 (high strength organic

load). The copper ion concentration in the mixed liquor was very low in

the beginning for several minutes, and then started to increase. The removal

rate of CODMn increased in about 10 h aeration at low strength organic load

and about 20 h aeration at high strength organic load (see Figs. 4 and 6).

Most of the uptake of copper ion was achieved within several minutes

after aeration [19,26]. The increase of copper ion in the mixed liquor

suggests that organic substances compete with copper ion at the binding

site of the activated sludge. After the removal rate of CODMn attained a

constant, the concentration of copper ion in mixture began to decrease.

These results were in agreement with previous studies [9,27]. A longer

time period was required for a constant removal rate of CODMn at high

TABLE III Comparisons of pseudo first order kinetic constants (h�1)

Group Controlreactor

PACreactor

Sludgereactor

Nutrientsreactor

COD 180mg/L 0.0451 0.0657 0.048 0.0616COD 328mg/L 0.0268 0.0378 0.0276 0.0399

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FIGURE 3 Change of copper ion concentration in the mixed liquor with time at low strengthorganic load.

FIGURE 5 Change of copper ion concentration in mixed liquor with time at high strengthorganic load.

FIGURE 4 CODMn removal rate with time at low strength organic load.

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strength organic load. This indicated that the reduction of the organic load

was helpful for a good quality of effluent when the activated sludge

was shocked with heavy metal.

The lowest concentration of copper ion in the mixed liquor was obtained

in PAC reactor at low organic load. Although the removal rate of CODMn

in PAC reactor was lower than that in the nutrients reactor within the

first 10 h of aeration, the removal rates of both reactors were getting

close after 20 h of aeration. PAC supplied great surface to adsorb copper

ions. The addition of PAC led to a low copper ion concentration in the

mixed liquor. It was good for the growth of microorganism and would

enhance the removal efficiency of CODMn. The result was consistent with

Sublette’s review [15]. However, at high strength organic load on the PAC

reactor is less than that on the nutrients one. It seems that the addition

of PAC (at 50 mg/L) is a good method to remove copper when organic

load is low. In case of nutrients reactor, no matter how low or high organic

load was, the removal rates of CODMn and copper ion in the mixed liquor

increase quickly in the first 10 h. This result indicated that the nutrients

could enhance the absorption of organic substance. These results were

different from Chang’s results [4]. Chang’s study showed that nutrients

could stimulate the uptake of heavy metals of acclimated activated sludge

for 25 h. The unacclimated activated sludge in our experiment had different

characters from the acclimated activated sludge on the uptake of heavy

metal. Our result showed that if in a sufficiently long period, the addition

of nutrients could enhance copper uptake of the activated sludge. Also,

the concentration of copper ion in the nutrient reactor was the lowest

among the reactors using different recovery techniques after 20 h at high

strength organic load.

FIGURE 6 CODMn removal rate with time at high strength organic load.

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The removal rates of CODMn and copper in the sludge reactor is shown in

Fig. 7. The removal rates of copper were calculated by Eq. (1). They

increased in line with the increasing amount of the condensed sludge

(with 6 and 15% MLSS up respectively), and at the same time, the turbidity

of the effluent increased. The addition of the condensed sludge increased the

biomass and undoubtedly enhanced efficiency of the treatment and uptake.

However, the formation of highly stable pinpoint flocs resulted from the

unacclimatised activated sludge shocked by heavy metals [28]. Of the

condensed sludge concentration studied, the removal rates of CODMn

and copper were lower than that of the other additives, and only slightly

better than that of the control. According to Lamb and Tollefson [18], 20

times MLSS could reduce metal toxicity from 80 to 3%. Perhaps more acti-

vated sludge should be added to make sure that the total MLSS contents is

high enough to increase the treatment efficiency significantly.

Above all, the conclusion could be drawn that the addition of nutrients

was the best method in this study for the removal rates of CODMn and

copper after 20 h of aeration. The nutrients used in this experiment were

expensive and could be replaced by less expensive ones such as starch.

The PAC and condensed sludge can also reduce the toxicity of heavy

metals and increase the treatment efficiency. Higher efficiency might

be achieved if sufficient amount of additive would be provided. Mostly,

the increment of the sludge concentration is the easiest operation for the

sewage treatment plant.

The Effect of The Aeration Period on The Removal

Rate of CODMn and Copper

In heavy metal shock load system, a long aeration period can increase the

removal rate of CODMn and the absorption of copper by the activated

FIGURE 7 The removal rate of CODMn and copper ion and effluent turbidity (MLSS) atdifferent sludge adding amount. H: 0.4 g/L MLSS adding; L: 0.14 g/L MLSS adding.

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sludge after CODMn removal rate becomes constant. Also, it led to the

deflocculation of activated sludge and deterioration of the effluent quality

(as shown in Fig. 8), the variation of sludge volume in 30 min (SV30), and

SS in the effluent with time. Although PAC and nutrients bring forth

better effluent, both SV30 and effluent turbidity were on the increase from

a long aeration period. It indicates that prolonged aeration in the activated

sludge shocked by metals will damage the structure of activated sludge and

bring about the biomass loss.

CONCLUSIONS

. The load of copper ion to the non-acclimated activated sludge system

affected the bio-kinetics constant K. The addition of PAC, nutrients

and condensed sludge could reduce the inhibitory effect of copper ion

on microorganisms in the activated sludge and accelerate the recovery

of the system. The addition of nutrients and PAC showed the highest K

values at low and high strength organic load respectively.

. The addition of nutrients could stimulate the removal rate of CODMn and

enhance metal-complexing capacity of copper ion when the removal rate

of CODMn reached a certain level. Therefore, it may be a good recovery

method for the process shocked with heavy metals in sufficient time

period. However, the cost is high. Less expensive nutrients are suggested.

. The addition of PAC (50 mg/L) has a result of better removal rates of

CODMn and copper than adding of condensed sludge. At relatively low

strength organic load, the addition of PAC and continuing aeration

could enhance the removal rate of copper and CODMn. It is a good

FIGURE 8 Change of SV30 and effluent turbidity (MLSS) with time — SV30 (%);line - - - - effluent turbidity (mg/L).

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way to recover the process shocked by heavy metals if the organic load is

light.

. The addition of unacclimated condensed sludge could be effective to

increase the removal rates of CODMn and copper. However, the effluent

quality will be poor. It may be the easiest and most inexpensive recovery

method when sufficient amount of activated sludge is provided.

. The absorption of copper ion in SBR unacclimated activated sludge

process is characterized as follows:

The copper ion was rapidly adsorbed by the activated sludge flocs at

first and then released from it during the aeration period. The concentra-

tion of copper ion in the mixed liquor increased till the removal rate of

CODMn reached a constant. It is suggested that the copper ion has

more affinity for binding sites on the activated sludge flocs at first, but

the organic substance becomes a stronger competitor with long time

aeration; lower organic load was good for the effluent.

. A long aeration period could increase the removal rate of CODMn and

reduce the concentration of copper ion in the mixed liquor. However, it

would result in deflocculation of activated sludge and higher turbidity

of effluent.

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