Indicator bacteria reduction in sewage sludge by a metal bioleaching process

War. l~eJ. VO[.26, No. 4, pp. 487--495.1992 Printed in Great BriUun.All rights r~crved

0043-1354/92$5.00+ 0.00 Copyright~ 1992Petpmon Press pk:

INDICATOR BACTERIA REDUCTION IN SEWAGE SLUDGE BY A METAL BIOLEACHING PROCESS J. F. Bt,'as I ~ , R. D. TYAGII* ~), J. C. AUCt..~RL and M. C. Lxvon~: 'Institute National de la Recherche Scientiflque (INKS-EAU), Universit~ du Qu6bec, 2700 rue Einstein, Sainte-Foy, Quebec, Canada GIV 4C7 and 2D~rtement de Biochimie, Universit~ Laval, Quc~bec, Canada GIK 7P4 (First receit,ed October 1990; accepted in revised form September 1991)

AbsU'act--The presence of a potentially toxic concentration of metals and the ineffective destruction of pathogenic microorganisms by conventional sludge stabilization processes limit sewage sludge utilization in agriculture. Therefore, we evaluate the metals bioleaching process potential for the elimination of indicator bacteria (total coliforms, fecal coliform,, fecal streptococci). Physico-chemicalsludge characteristics (VS, VS$, soluble carbon and sulfate) as well as metals solubilization were also measured. The results obtained reveal that the high sulfuric acid production (pH < 2.5), as a result of sulfur oxidation by indigenous thiobacilli of sludge, allows a considerable reduction in bacterial indicators (3 log or under the limit detection of 103cfu/100ml) for all sludges examined over a 5 day period. Heavy metals were solubilized to levelscompatible with recommended norms for intensive sludge agricultural use. Moreover, this process allowed a VSS reduction, which varied according to the sludge used. These results indicate that this process can improve the stabilization of the digested sludge. Key words--metals, indicator bacteria, thiobaeilli, bioleaching, pathogenic bacteria, sulfur oxidation, sludge disposal, sludge stabilization

INTRODUCTION The treatment and final disposition of residual sludge often constitutes the most expensive stage in the treatment of municipal wastewaters (Couillard, 1988; Lester et al., 1983). Several approaches have been utilized: landfilling, incineration, oceanic dumping and as agricultural fertilizer. From an economic perspective, sludge use as fertilizer appears to be the most interesting alternative (Davis, 1987; US EPA, 1979), however the presence of pathogenic microorganisms and elevated concentration of toxic metals represent a serious constraint to implementation of this practice (Bruce and Davis, 1989; Mininni and Santori, 1987). Epidemiological studies conducted to determine disease transmission following the use of sludge as fertilizer have shown that risk of infection is associated with the presence of pathogenic bacteria and helminthic worms (AIderslade, 1981; Hays, 1977; Yeager, 1980). As well, trace metal assimilation by plants and subsequent bioaccumulation in the food chain can occur through the agricultural use of sludge (Lester et al., 1983; Tyler et al., 1989). Several chemical processes for metal removal have been proposed (Hays et al., 1980~ Jenkins et al., 1981; Scott and Horlings, 1979; Wozniak and Huang, 1982). In spite of high extraction efficiencies obtained with acid leaching, the elevated operational costs have led to the exploration of microbiological processes (Boulanger et al., 1992; Tyagi and Couillard, 1989; *Author to whom all correspondence should be addressed. 487

Wong and Henry, 1983). A joint process which concurrently removes metals and destroys pathogens to levels compatible with agricultural use would be desirable. The use of this technology could subsequently replace conventional sludge stabilization, in cases where a reduction of sludge volume is not indispensable for adequate operation of the wastewater treatment unit. Although bio-solubilization processes using Thiobacillus ferrooxidans and ferrous sulfate as substrate at pH 4.0 result in good extraction efficiencies of toxic metals (Tyagi and Couillard, 1989; Wong and Henry, 1983), their capacity to destroy indicator bacteria appears to be limited (Henry et aL, 1988). Our process utilizes metal bio-solubilization using adapted strains of Thiobacil/us isolated from sludge. The principal advantages of these adapted strains are: acid is not required to adjust the initial pH of the sewage sludge to 4.0 as they grow at the natural pH of sludge and growth rate is very fast so that the bioreaction time to leach metal is small as compared to T. ferrooxidans. Metal solubilization occurs through bacterial oxidation of added elemental sulfur and subsequent acidification (pH < 2.5) of the sludge media [equation (l)] 2S ° + 302 + 2H20--, 2H2SO4

(l)

MS + 202 --. MSO4.

(2)

Metal solubilization from reduced sulfur compounds can also occur according to equation (2). This bacterial metabolic pathway has been demonstrated for several metals: NiS, ZnS, CoS, CuS (Hutchins et

J. F. BtJas et al.

488

a/., 1986). In the present study, we investigated the capacity of this process to reduce indicator bacteria through sulfur oxidation and modification of solids in sludges as well as metal solubilization for the improvement of sewage sludge stabilization. MATERIALS AND METHODS Source of samples The sludges were obtained from six wastewater treatment plants in the province of Qutbec, Canada: St-Georgesde-Beauce and Granby (secondary sludge from an activated sludge unit); Beauceviile, Cowansville and Ste Claire (secondary sludge from an activated sludge unit and aerobically digested sludge); and Black Lake (secondary sludge from a sequential biological reactor and aerobically digested sludge). Samples were collected in sterile polypropylene bottles, shipped cold and kept at 4°C before utilization. Bacteriological media Commercially available dehydrated media. Difco Laboratories were used in this study, except for thiobacilli media. Total coliforms were assayed on m-Endo agar LES, fecal coliforms were assayed on m-FC agar, fecal streptococci were determined on m-Enterococcus agar and total aerobic colonies on standard plate count agar. For the less acidophilic and acidophilic thiobaciili (Kelly and Harrison, 1988) the S~O~j- synthetic salts agar media described by Laishley et al. 0988) were used at pH4.0 and 7.0, respectively.

Bacterial sampling All bacterial populations in sludge were enumerated by direct plating on appropriate selective media according to the modified technique of Dudley et al. (1980). Samples were obtained after vortex mixing 5 ml of sludge at high speed for 2 rain with 15 ml of sterile phosphate-buffered saline (0.1 M, pH 7.2) containing (approx.) 1 g of sterile 4-5 nun diameter glass beads in a 50 ml centrifuge tube. Samples were diluted serially in sterile phosphate-buffered saline, and 0.1 ml samples were spread with sterile glass L-rods over each of three replicates plates. Incubation was carried out at 35°C for 24 h for total coliforms, 35°C for 48 h for fecal streptococci and total aerobic colonies and at 44.5°C for 24 h for fecal coliforms. Thiobacilli plates were incubated at 30°C for 2 weeks. Experimental The inoculum was prepared by growing indigenous sludge Thiobacillus strains in 500 ml Erlenmeyer flasks containing 150ml of the media sludge supplemented with 0.5% of tyndalized powdered sulfur. The flasks for inoculum preparation and for the experiments were agitated at 200rpm and 28°C using a gyrator), incubator shaker apparatus model 26 (New Brunswick Scientific Co.). A 5% volume of inoculum was used in all experiments. The ten sludge assays were carried out in triplicate; three 200 ml sludge aliquots were added to a 500 mi Erlenmeyer flask and supplemented with 1% (w/v) sulfur in the form of tablets 1.6cm in diameter by 0.6cm thick prepared in an aluminium mold according to Bryant et <11. (1984). The utilization of these tablets allowed a more precise measurement of sludge solids, since the tablets are removed prior to solids determinations, 30 ml samples were drawn from one of the three flasks at 12 h intervals for analysis. 250

8.5 e"

8.0

-r

¢3.

7.0

200 150

/

7.5

•

100

0 50

o 0 -50 I

6.5

I

I

I

-I00

1010 10 o ..J

E 0 0

108

[]

107

~

106 10 s

~ v ~.,.

v

D

~

D

~

10 4

10 3 0

E n

20

40

6O

80

100

TIME (hour=)

Fig. I. Variations of the microbial populations, pH and ORP during metal leaching with Black Lake control sludge. Symbols: O. pH; O, ORP; A, total aerobic colonies; A, total coliforms; I-1, fecal coliforms; I , fecal streptococci; V. acidophilic thiobacilli; V, less acidophilic thiobacilli.

Indicator bacteria and metals removal The experiment with Black Lake non-digested sludge (Figs 1.2 and 3) was carried out within 12 h after sludge sampling. In this experiment, 3 x 200 mi of sludge in 500 mi Erlenmeyer flasks was used. The control flask was neither inoculated nor supplemented with sulfur; a second flask was inoculated and supplemented with 0.5% of tyudalized sulfur, and a third containing 200 ml of concentrated sludge 07.41 g/l total solids) was also inoculated and supplemented with sulfur. 5 ml samples were drawn each day for chemical and microbiological analysis.

489

coliforms and fecal streptococci decreased. Autotrophic populations of less-acidophilic thiobacilli were initially undetectable and increased to 2 x 10Scfu/100ml after 4 days. The increase in population probably occurred through the oxidation of reduced sulfur compounds already present in the sludge. Over a 2 day period the pH increase diminished the indigenous acidophilic thiobacilli to below 103 cfu/100 ml. The addition of a 5% inoculum of microbiologically acidified sludge and 0.5% of sulfur (powder) to the non-digested Black Lake sludge (Fig. 2) reduced the pH to 2.0 in 48 h accompanied by a large increase in ORP. The concentration of the total aerobic microorganisms is only slightly decreased after a 4 day solubilization period. However, the initially diverse microflora is replaced by 2 types of dominant colonies (yeast and fungi). The disappearance of indicator bacteria occurs during the first 2 days at pHs above 2.0. The reduction in the pH occurs through the growth (sulfur oxidation to sulfuric acid) of the less-acidophilic thiobacilli (pH 7-8 to 4-5) followed by the acidophilic thiobacilli (pH 4-5 to I-2). The reduction in pH below 2.0 during the last 2 days results in the elimination of the less-acidophilic thiobacilli. The initial pH reduction is slower in the concentrated sludge (17.4 g/I total solids) (Fig. 3) than in the

Analytical The pH and oxido-reduction potential (ORP) were monitored by using a Fisher Acumet model 805 MP pH meter, The solids determinations (TS, VS, VSS) were as recommended by Standard Metho~ for the Examination of Water and Wastewater (APHA, 1989). For chemical analysis, samples were centrifuged at 20,000g for 15 min and elements (metals, total carbon and sulfur) in the liquid and solid fractions were determined by Plasma Emission Spectroscopy (ICP) with a Thermo Jarrell Ash Corporation, Atom Scan 25 apparatus, according to APHA (1989). RESULTS

Modification of microbial population For the control sludge (without sulfur or an inoculum, Fig. I), incubation at 28'~C with agitation resulted in a slight increase of pH and ORP and few changes in the heterotrophic population. The concentration of total aerobic microorganisms and total coliforms were slightly increased, while fecal

450 7.0

40O e

6.0 (

~

e

35O 300

5.0 .1es

4.0

250

~" E

200

"-"

150 3.0

100

o

2.0 1.0 1

50

°

0

--O I

I

-50

I

I

~7

._/

E O

.P

10 7 10 6

10 4 10 3

0

,

,

20

40

-

,

60

_-

-_ 80

100

TIME (hours) Fig. 2. Variations of the microbial populations, pH and ORP during metal leaching with Black Lake non-concentrated sludge. Symbols: O, pH; O, ORP; A , total aerobic colonies; A , total coliforms; l"l, fecal coliforms; II, fecal streptococci; V , acidophilic thiobacilli; V , less acidophilic thiobacilli.

o_

J. F. Bum et of.

490

450 400 350 300 250

7.0 ~

0

6.0 (: 5.0

200

O.

4.0

>

E

150

100 50 0 -50 -100

3.0

~0~0

2.0

•

/

1.0!

~

1

I

|

,o,o : _ _

,

I

o

I

.J

E

O O

LL lOS

.

104

~

~

Y

103 . 0

, 40

20 -

m

, 60

~

m 80

100

TIME ( h o u r s )

Fig. 3. Variations of the microbial populations, pH and ORP during metal leaching with Black Lake concentrated sludge. Symbols: O, pH; O, ORP; A, total aerobic colonies; &, total coliforms; O, fecal coliforms; I , fecal streptococci; ~7, acidophilic thiobacilli; V, less acidophilic thiobacilli.

non-concentrated sludge (6.84g/I total solids) (Fig. 2); after 48 h, the pH is 2.7 rather than 2.1 (Fig. 3). However, after 3 days the pH of both sludges is similar. It therefore appears that the solids concentration is not an important factor for the growth of the thiobacilli. Indeed, the lowest pH encountered occurred during the bio-solubilization of metals of the digested Ste-Ciaire sludge (Table l) which had the Table I. Variations of indicator bacteria in the sludges after 5 days

of microbial leaching Sludge

pH

ORP (rnV)

Total coliforms (cfu/100 ml)

SI-Georges

Initial

6.14

17

(non-digested) Beauceville (non-digested) Ikauceville

Final Initial Final Initial

2.20 6.34 1.85 6.82

362 - 152 370 - 116

(digested) Black Lake (non-digested)

Final Initial Final

2.10 6.06 1.70

400 -80 384

< 1.00 x 10J 1.27 x 106 < 1.00 x 10j

Black Lake (digested) Cowansville

Initial Final Initial

6.16 1.76 6.33

12 384 - 169

7.30 x 104 < 1.00 x 103 3.23 x l0 s

(non-digested) Cowansvi/Ic

Final Initial

1.76 6.55

391 - 190

< 1.00 x I0 ) 1.40 x I0e

(digested) Granby (non-digested) Sic-Claire (non-digested) Sic-Claire (digested)

Final Initial Final Initial Final Initial Final

2.14 6.52 1.95 6.23 1.72 6.48 1.40

307 - 172 361 - 134 394

4.00 x 1.56 x < 1,00 x 7.20 x 2.93 x 2.96 x < 1,00 x

-187 370

5.07 x 10) 5.73 1.20 < 1.00 5.33

x x x x

104 10' I0 ) I04

10) I0e I0 ) 10) 104 10' I0 j

highest concentration of volatile solids (Table 2). Similarly, a 4 day solubilization period with the concentrated Black Lake sludge allowed the complete elimination (103cfu/100 ml), of the indicator bacteria. The disappearance of the fecal streptococci occurred in 2 days (pH > 2.7), while the destruction of the coliforms required a pH reduction below 2.7. Irrespective of the sludge origin (Table 1), the elimination of the total coliforms occurs with a large mortality (3 log or under the detection limit of 105cfu/100 ml) of the indicator bacteria. Modifications of solids in the sludges

The production of sulfuric acid due to the oxidation of sulfur (Table 3) results in an important increase in the volatile solids (VS) (Table 2). However, this VS increase is inferior to the contribution in solids as a result of sulfuric acid production, because of decrease in the volatile suspended solids (VSS) (Table 2). In addition to the reduction in the VSS. the concentration of the soluble organic matter as determined from dissolved carbon measurements in the supernatant is also reduced (Table 3), except for two digested sludges (Black Lake, Ste-Claire). The greatest decrease occurred prior to the pH decrease (600-250mg/I, Fig. 4; 350-180mg/I, Fig. 5) and remained stable at pH values less than 4.0. Afterwards, a slight increase in dissolved carbon produced

Indicator bacteria and metals removal Table 2. Solids variations in the dudles after 5 days of microbial leaching Volatile Volatile solids suspended solids Sludge

St-Georses (non-digested) Beauceville (non-digested) Beauceville (digested) Black Lake (non-digested) Black Lake (digested)

Initial Final % Removal Initial Final % Removal Initial Final % Removal Initial Final % Removal Initial Final % Removal

Cowansville (non-digested) Cowansville (digested) Granby (non-digested) Ste-Claire (non-digested) Ste-Claire (digested)

Initial Final % Removal Initial Final % Removal Initial Final % Removal Initial Final % Removal Initial Final % Removal

(ml~l)

(mg,q)

4462 6247 -40.0 8566 11688 -36,4 2158 4956 - 129.7 3205 5870 -83.2 12477 14291 - 14.5 9227 13091 -41.9 19354 24027 -24.1 8784

4070 3370 17.2 8327 5680 31.8 1547 413 73.3 2847 1013 64.4 12087 9413 22.1 8893 6393 28.1 19150 18873 1.4 8353 4947

13203 --50.3

1042 1878 -80.2 22257 29727 -33.6

40.8

993 250 74.8 22240 17707

20.4

by organic matter hydrolysis and cellular lysis, was observed in very acidic sludge (pH < 2.5).

Microbial sulfur oxidation in the sludges Sulfur oxidation and sulfate production, which varied considerably a m o n g sludge types, are summarized in Table 3. Oxidized sulfur ranged from 4. I % in the non-digested to 33.7% in the digested and concentrated Sic-Claire sludge. The sulfate production kinetics appeared to follow two distinct patterns. In

49[

most cases, two stages could be identified corresponding to the consecutive growth of the less-acidophilic and acidophilic thiobacilli (Fig. 4). In other cases (Fig. 5), sulfate production occurred in a single step, strongly suggesting that the growth of the two thiobacilli occurred simultaneously. Close inspection of Figs 2 and 5 shows that sulfur utilization in powder form (Fig. 2) allows a more rapid reduction in pH than the use o f sulfur tablets (Fig. 5); a consequence of the greater surface area and colonization of the former substrate.

Metal solubilization Sludge metal concentrations and recommended levels for agricultural use (Flynn et al., 1984) are shown in Table 4. It is necessary to note that all sludges tested exceeded these levels for at least one metal. The amount of solubilized metals expressed as a percentage of metals initially associated with the solid sludge phase are shown in Table 3. The degree o f copper and manganese solubilizations are indicated in Table 3, since these metals are most often above the recommended limits, 8 out of l0 times in the case of copper, and 7 out of 10 times in the case of manganese. The degree of Cd solubilization obtained are also indicated since this metal is considered to be potentially more toxic for humans (Coker and Matthews, 1983; Mininni and Santori, 1987). DISCUSSION Bio-solubilization of metals results in the efficient elimination of indicator bacteria and by extrapolation of most bacterial pathogens. The elimination o f indicator bacteria by our process is clearly superior than the results obtained by Henry et al. (1988). Their process used Thiobacillus ferrooxidans and ferrous sulfate as substrate for the treatment of anaerobically

Table 3. Variations of total carbon and sulfate in supernatant fractions and metal solubilizationin dudges after 5 days of microbial leaching Metals solubilized (% of initial) Carbon Sulfate 5° oxidized Sludge (mlffl) (miffl) (% of initial) Cd Cu Mn St-Georges Initial 789 29I (non-digested) Final 279 2328 6.8 76.7 58.9 62.0 Beau~.ville Initial 599 243 (non-digested) Final 348 3410 10.6 79.3 63.0 80.8 Bcauceville Initial 518 201 (digested) Final 241 2025 6.1 59.7 62.9 84.6 Black Lake Initial 352 138 (non-diaened) Final 243 2903 9.2 58.2 75.6 59.5 Black Lake Initial 297 336 (dis~ted) Final 304 4327 13.3 67. I 95.8 58. I Cowansville Initial 340 378 (non-disested) Final 313 4237 12.9 49.5 81.5 95.9 Cowansville Initial 852 548 (dil;ested) Final 504 5342 16.0 60.5 46.7 94.7 Granby Initial 1060 342 (non-digested) Final 367 4755 14.7 63.7 87.2 95.0 Sic-Claire Initial 465 354 (non-diaeuted) Final 125 1576 4.1 88.2 65.8 94.8 Ste..Cialm Initial 498 312 (digested) Final 621 10409 33.7 86.5 77.5 94.5

492

J.F. Bt,ALSet al. 7.5

/

6.5

0 ~

o

5.5 -r" e-,

4.5

/,,"

2.5

/ A

600,

0 I--

~°~o f A

A ~

3500 3000

A

2500 2000

I A "

_1

O ~ i

E

v LO

1500

A""

1000

i

0--"~ O ~ i

0______0

i

i

(/1

500 0

'\

500

0

v

< (.3 ...J

/

j A

1.5

Z 0 m

\ 0

3.5

E

/

A

400

\

°~°/o/°

300 ~ 0 ~ . 0 ~ 0 200 100 0 0

i

I

I

I

I

i

20

- 40 -

60

80

100

120

TIME (hours) Fig. 4. Total carbon and sulfate changes in the soluble fraction of the non-digested Beaucevillesludge during bacterial leaching. Symbols: O, pH; @, carbon; A, sulfate.

digested sludge which was adjusted to pH 4.0. The concentrations in sludges after leaching (Table !, metal leaching over a l0 day period, with a sludge Figs 2 and 3) and the total coliform concentrations containing 12g/I of total suspended solids (TSS) obtained after conventional aerobic and anaerobic reduced the fecal streptococci by 3 orders of magni- sludge digestion (107-108bacteria/100 ml; US EPA, tude, but the total and fecal coliform populations 1979), it appears that thiobacilli-mediated acid prowere slightly raised (Henry et al., 1988). Moreover, duction could be more efficient at indicator bacterial the indicator bacteria destruction in the process of removal than the aerobic digestion of sludge. Henry et al. is strongly inhibited by high concen- Although, parasitic egg destruction was not tration of suspended solids. According to these evaluated, this process is probably not efficient, due authors concentration of 10g/I of TSS appears to to the acid resistance of Ascaris eggs which is almost be critical for a significant reduction of bacterial legendary (Schmidt and Roberts, 1989). The substitution of the indigenous microflora by yeast and fungi indicators. Our process permits the reduction of indicator is not surprising; their capacity for growth in highly bacteria to levels compatible with the agricultural use acidic media has been amply demonstrated of sludge, since the coliform concentrations encoun- (Harrison, 1978; Rossi and Arst, 1990; Silverman and tered (<10Jcfu/100ml) are similar or lower than Munoz, 1971). concentrations normally found in agricultural soils The reduction in volatile suspended solids (VSS) (Ibiebele and Inyang, 1986). The reduction of can be attributed to the endogenous metabolism of indicator bacteria is largely due to the production of sludge biomass before sludge is acidified to a level acid. The acid injury of indicator bacteria is well which does not permit further growth of indigenous known (Roth and Keenan, 1971; Wortman et al., heterotrophic microflora. However, the exopolymeric 1986). The concentrations of metal ions in solution matrix disaggregation of the biological floc during are comparable to those encountered through the sludge acidification may also be a cause of the VSS bio-solubilization by Thiobacillusferrooxidans 0Vong reduction observed. This phenomenon could explain and Henry, 1983; Tyagi and Couillard, 1989), that the VSS reduction is not completely reported in however, the latter is inefficient in the removal of VS variation because the extracellular polymer will be indicator bacteria. Comparing the indicator bacteria transferred to the soluble fraction during filtration. (total coliforms, fecal coliforms, fecal streptococci) The exopolymers liberated by the acidification will

Indicator bacteria and metals removal

493

8.0

/0"~--0~0 ~

7.0

/

6.0 -r

3000

/ A

o

5.0

/

A

2500 2000

A

1500

i-i

v

E

4.0 1000

3.0

t~

0~0------0----_ 0 500

~____~__~_~/

2.0

..I

_...-- A

1.0 "D

I

E

i

I

!

I

0

400

U.

Z

I

\

300

0 rn n~ .< 0

200

0k--

100

•

0 0

•.

I

|

20

40

.•.___..•/•/•

-•~•

I

-60

I

I

I

80

100

120

TIME (hours) Fig. 5. Total carbon and sulfate changes in the soluble fraction of the non-digested Black Lake sludge during bacterial leaching. Symbols: O, pH; @, carbon; A, sulfate.

not be included in the dissolved carbon measurement because the high speed ccntrifugation (20,000g) would precipitate this matter in the pellet portion (Brown and Lester, 1980; Pavoni et al., 1972). The pH reduction kinetics in this process depends largely on the length of the lag phase and growth of the less acidophilic thiobacilli. During this lag period, an important part of the soluble carbon is incorporated into the heterotrophic microflora or perhaps into the thiobaciUi cellular material as has been demonstrated by Matin (1978). Since the oxidation of elemental sulfur to sulfate by thiobacilli takes place with no soluble intermediates accumulation (Kelly, 1985; Lundren et al., 1986; Parker and Prisk, 1953),

the soluble sulfur measured corresponds to sulfate. The kinetics of sulfate production as revealed in Fig. 5 demonstrates that in certain sludges, the growth of less acidophilic and acidophilic thiobacilli occurs simultaneously, which indicates that the latter begin their lag phase and growth at pH levels where growth is not observed in synthetic media (Kelly and Harrison, 1988). The pH reduction obtained with the 10 sludges allowed the metal solubilization levels to be compatible with the recommended values. The large increases of the oxido-reduction potential (ORP) during the bacterial leaching (Figs 2 and 3, Table I) is essential for metal solubilization. In fact, the

Table 4. Metal compositions in the sludges and their recommended levels Composition (mg/kg dry sludge) Sludge St-Georges (non-digested) Ikauceville (non-digested) Bcauceville (digested) Black Lake (non-digested) Black Lake (digested) Cowansvine (non-digested) Cowansville (digested) Granby (non-digested) Ste-Claire (non-digested) Ste-aaire (digested) Recommended levels

Cd

Cr

Cu

Mn

Ni

Pb

Zn

4.4 5.0 2.6 9.2 10.0 4.5 4.0 2.3 2.2 10.7 10

91 87 66 401 1719 124 87 99 256 515 ~0

712 215 200 1070 1827 737 625 1211 611 627 600

393 933 1053 445 395 4613 5696 2914 986 933 500

69 28 42 141 177 30 26 142 50 55 100

209 110 234 278 336 177 129 266 43 201 300

869 419 392 413 596 379 343 181 1430 1514 1750

494

J.F. BL~s eta/.

solubility of metals in sludge is a function of pH, ORP, the concentration of metals and ligands and the chemical equilibria between the constituents (Tyagi and CouiUard, 1989). The use of the thiobacilli for the solubilization of toxic metals from municipal sludges is advantageous since they are not natural pathogens toward animals and man. However, environmental use requires that the concentrations of sulfur also be minimized, to avoid excessive acidification of soils (Bryant et ai., 1983; Karavaiko et al., 1981; Laishley et al., 1988). For this reason, the use of sulfur pellets or immobilized sulfur with recycling would be very advantageous, given that most of the biomass would be recycled on the pellet surface (Takakuwa et ai., 1979). An important point is that all sewage sludge types can be utilized, since the thiobaciili strains can be isolated and adapted to the different sludges. The present bioleaching process solubilizes metals to recommended levels for the utilization of municipal sludge on agricultural land. In addition, the efficient destruction of indicator bacteria and the possibility of decreasing volatile suspended solids in certain sludges (two most important parameters to assess municipal sludge digestion) suggests that this technology might replace the conventional sludge digestion process. Acknowledgements--We thank the Natural Sciences and Engineering Research Council of Canada (Grant A4984), and the Education Ministry of the Province of Qutbcc (Grant FCAR 90-AS-9713) for supporting this research. Thanks are also due to A. Gravel and N. Meunier for their technical and experimental assistance.

REFERENCES

Alderslade R. (1981) The problems of assessing possible hazards to the public health associated with the disposal of sewage sludge to land; recent experience in the United Kingdom. In Characterization, Treatment and Use of Sewage Sludge (Edited by L'Hermite P. and Ott H.). Proc. 2nd Eur. Syrup., Vienna, 21-23 October 1980. APHA (1989) Standards Methods for Examination of Water and Wastewaters, 17th edition. American Public Health Association, Washington, D.C. Boulanger B., Tyagi R. D. and Campbell P. G. C. (1992) Effects of process parameters o n bacterial leaching of heavy metals from municipal sludge with hyperactive microbial strains. Biotechnol. Bioengng. In press. Brown M. J. and Lcster J. N. (1980) Comparison of bacterial extracellular polymer extraction methods. Appl. envir. Microbiol. 40, 179-185. Bruce A. M. and Davis R. D. (1989) Sewage sludge disposal: current and future options. Wat. Sci. Technol. 21, !113-1128. Bryant R. D., Costerton J. W. and Laishley E. J. (1984) The role of Thiobaciilus aibertis giycocalyx in the adhesion of cells to elemental sulfur. Can. J. Microbiol. 30, 81-90. Bryant R. D., McGroarty K. M., Costerton J. W. and Laishley E. J. (1983) Isolation and characterization of a new acidophilic Thiobacillu.¢ species (7". albert~ ). Can. J. Microbiol. 29, 1159-1170. Coker E. G. and Matthews P. J. (1983) Metals in sewage sludge and their potential effects in agriculture. War. Sci. Technol. 15, 209-225. Couillard D. (1988) Rtude de quelques indices de croissance

du Lar/x/at/c/ha fert/lis~ par des boues anatrobies. Envir. Technol. Lett. 9, 191-206.

Davis R. D. (1987) Use of sewage sludge on land in the United Kingdom. War. Sci. Technol. 19, I-8. Dudley D. J., Guentzel M. N., Ibarra M. J., Moore B. E. and Sagik B. P. (1980) Enumeration of potentially pathogenic bacteria from sewage sludges. Appl. en~ir. Microbiol. 39, 118-126. Flynn F., Jalbert J. M., Robert J., St-Yves A., Terrault A. and Trudel G. (1984) Rapport sur |a qualit6 des hours des stations d'tpuration et autres hours. Gouvernemcnt du Qutbec, Ministtre de l'Environment, aofit. Harrison A. P. Jr (1978) Microbial succession and mineral leaching in an artificial coal spoil. Appl. envir. Microbiol. 36, 861-869. Hayes T. D., Jewell W. J. and Kabrick R. M. (1980) Heavy metals removal from sludges using combined biological/chemical treatment. In Proc. 34th Ind. Waste Conf., Purdue Unit,., West Lafayette, Ind., pp. 529-543. Hays B. D. (1977) Potential for parasitic disease transmission with land application of sewage plant effluents and sludges. Wat. Res. 1i, 583-595. Henry G., Prasad D. and Lohaza W. (1988) Survival of indicator bacteria during leaching. In ASCE Natn. Conf. envir. Engng, 13-15 July Vancouver, Canada, pp. 369-376. Hutchins S. R., Davidson M. S., Brierley J. A. and Brierley C. L. (1986) Microorganisms in reclamation of metals. A. Rev. Microbiol. 40, 311-336. lbiebcle D. D. and lnyang A. D. (1986) Environmental movement of indicator bacteria from soil amended with undigested sewage sludge. Envir. Pollut. (Ser. A) 40, 53-62. Jenkins R. L., Benjamin J. S., Marvin L. S., Rodger B., Lo M. P. and Huang R. T. (1981) Metal removal and recovery from municipal sludge. J. Wat. Pollut. Control Fed. $3, 25-32. Karavalko G. I., Abakumov V. V., Krasheninnikova S. A., Mikhailova T. L., Piskunov V. P. and Khalezov B. D. (1981) Ecology and activity of microorganisms during metal dump leaching. Appl. Biochem. Microbiol. 17, 58-64. Kelly D. P. (1985) Physiology of the thiobaciUi: elucidating the sulphur oxidation pathway. Microbioi. ScL 2, 105-109. Kelly D. P. and Harrison A. P. (1988) Genus Thiobacillus. In Bergey 'a Manual of Determinative Bacteriology (Edited by Holt J. G., Staley J. T., Bryant M. P. and Pfennig N.), pp. 1842-1858. Williams & Wilkins, Baltimore, Md. Laishley E. J., Rae K., Dillman A. M. and Bryant R. D. (1988) Characterization of a new less-acidophilic Thiobacillas isolate (Thiobacillas capsulatus). Can. J. Microbiol. 34, 960-966. I,ester J. N.0 Sterrit R. M. and Kirk P. W. W. (1983) Significance and behaviour of heavy metals in waste water treatment process. It. Sludge treatment and disposal. Sci. Total £nvir. 30, 45-83. Lundren D. G., Valkova-Valchanova M. and Reed R. (1986) Chemicals reactions important in bioicaching and bioaceumulation. Biotechnol. Bioengng 16, 7-22. Matin A. (1978) Organic nutrition of chemolithotrophic bacteria. A. Rev. Microbiol. 32, 433-468. Mininni G. and Santori M. (1987) Problems and perspectives of sludge utilization in agriculture. Ecosystem Envir. 18, 291-31 I. Parker C. D. and Prisk J. (1953) The oxidation of inorganic compounds of sulphur bacteria. J. gen. Microbiol. 8, 344-364. Pavoni J. L., Tenney M. W. and Echelbcrger W. F. (1972) Bacterial exocellular polymers and biological flocculation. J. War. Pollut. Control Fed. 71, 583-604. Rossi A. and Arst H. N. Jr 0990) Mutants of Aspergillas nidulans able to grow at extremely acidic pH acidify the

Indicator bacteria and metals removal medium less than wild type when grown at more moderate pH. Microbiol. Left. 66, 51-54. Roth L. A. and Kcenan D. (1971) Acid injury of F~cherichia coil Can. J. MicrobioL 17, 1005-1008. Schmidt G. D. and Roberts L. S. (1989) Order Ascaridata: large intestinal roundworms. In Foundations of Parasitology, Chap. 27. Times Mirror/Mosby College, St Louis, Mo. Scott D. S. and Horlings H. (1979) Removal of phosphates and metals from sewage sludges. Era,it. Sci. Technoi. 9, 849-855. Silverman M. P. and Munoz E. F. (1971) Fungal leaching of titanium from rock. Appl. Microbiol. l ] , 923--924. Takakuwa S., Fujimori T. and lwasaki H. (1979) Some properties of cell-sulfur adhesion in Thiobacillus thiooxidarts. J. gen. appl. Microbiol. 25, 21-29. Tyagi R. D. and Couillard D. (1989) Bacterial leaching of metals from sludge. In Wastewater Treatment Technology (Edited by Chermirnoff P. N.), pp. 557-590. Library of Environmental Pollution Control Technology, Gulf.

WR 26/4,--H

495

Tyler G., Balsberg Paklsson A. M., Bengtsson G., Baath E. and Tranvuk L. (1989) Heavy metal ecology of terrestrial plants, microorganisms and invertebrates. A review. Wat. Air Soil Poilut. 47, 189-215. US EPA (1979) Sludge Treatment and Disposal. Process design manual. Center for Environmental Research Infor. mation, Cincinnati, Ohio, EPA-625/I.79-O01. Wong L. and Henry J. G. (1983) Bacterial leaching of heavy metals from anaerobically digested sewage sludge. Wat. Pollut. Res. J. Can. I& 151-162. Wortman A. T., Voelz H., Lantz g. C. and Bissonnette G. K. (1986) Effect of acid mine water on Escherichia coil: structural damage. Curr. Microbial. 14, I-5. Wozniak D. J. and Huang J. Y. C. (1982) Variables affecting metal removal from sludge. J. Wat. Pollut. Control. Fed. 54, 1574-1580. Yeager J. G. (1980) Risk to animal health from pathogens in municipal sludge. In Sludge-health Risks of Land Application (Edited by Bitton G., Damron B. L., Edds G. T. and Davidson J. M.), pp. 173-199. Ann Arbor Science, Ann Arbor, Mich.