Environmentlnternational, Vol. 10, pp. 251-258, 1984 0160-4120/84 $3.00 + .00 Printed in the USA. All rights reserved. Copyright © 1984 Pergamon Press Ltd.

BACTERIAL REMOVAL BY ANAEROBIC DIGESTION

Mohamed M. EI-Abagy and Helmy T. EI-Zanfaly Water Pollution Control Laboratory, National Research Centre, Dokki, Cairo, Egypt

(Received 29 November 1983; Accepted 17 July 1984)

The impact of anaerobic digestion and post composting of the digested slurry on total bacterial counts, total coliform, fecal coliform, and fecal streptococci was investigated. Anaerobic digestion removed up to 99% of the bacterial parameters; however, the residual numbers present in the digested slurry were still high. The residuals ranged from 105/g to 10"/g for total bacterial counts, 102/g to 108/g for total co- liform, 104/g to 108/g for fecal coliform, and 102/g to 10S/g for fecal streptococci. The digested slurry was mixed with soil for one week and then for two months, but the density of bacterial parameters was not reduced. There was an increase in numbers during the two composting steps.

Introduction

The published data on the removal of pathogenic microorganisms during the anaerobic digestion have a wide range of values. Burtucci et al. (1977) reported that poliovirus type I was reduced by 90°/0/day when sub- jected to anaerobic digestion at 35 °C. E1-Gohary et al. (1980) studied the effect of anaerobic digestion on the removal of bacterial parameters on a bench scale. They found that there was a high percentage of removal of total bacterial counts, total coliform, and fecal strep- tococci densities; however, the residual number of bacterial parameters in the digested slurry was still high. This may lead to pollution of soil, vegetables, root vegetables, and underground water. Hence, EI-Abagy et al. (1981) and EI-Hawary et al. (1981) recommended that, before land application, the digested slurry must be subjected to further treatment such as post corn- posting or addition of lime.

The main objective of this study was to investigate the effect of anaerobic digestion and post composting on the bacterial viability.

Material and Methods

Sampl ing Samples were delivered to the Water Pollution Con-

trol Laboratory from biogas production demonstration units located in three Egyptian villages: Omar Makram, EI-Manawat, and Shobra-Kas. In Omar Makram there are two family-size digestors. The first digestor is the

Indian-type Khadi and Village Industries Commission (KVIC) floating gas holder design (Singh, 1971; Prakasam, 1979). The second digestor is the fixed dome Chinese design (Ru-Chen and Zhi-Ping, 1979). In E1- Manawat, the family size digestor is constructed accord- ing to the Indian design. The digestor in Shobra-Kas is used to treat poultry wastes and has a capacity of 50 m 3.

Bacteriological examinat ion One gram of the sample was added to 100 mL of

sterile distilled water and mixed well. Tenfold dilutions were prepared, after which the following tests were per- formed:

1. Total bacterial counts: Poured plate technique was employed according to APHA (1980). Temperatures of incubation were 22 and 37 °C.

2. Enumeration of total coliform group: The multi- ple tube fermentation technique according to APHA (1980), with MacConkey broth as a selective medium, was used.

3. Enumeration of fecal coliform: From the positive total coliform tubes showing acid and gas, subculture into MacConkey broth tubes was performed. The tubes were immediately placed into a well-controlled sensitive water bath set at 44.5 °C ±0.2 °C. After an incuba- tion period of 24 h, the tubes showing acid and gas were detected and the relative most probable number-index was computed using Swaroop's table (Swaroop's, 1951).

4. Enumeration of fecal streptococci group: For measurement of fecal streptococci density, a presump-

251

rive test was employed, using Azide dextrose broth, fol- lowed by ethyl violet azide broth as a confirmation test (Saleh and E1-Abagy, 1976).

Results and Discussion

The results of bacteriological examination of the feed and the digested slurry from the two digestors in Omar Makram are presented in Figs. 1 and 2.

The total bacterial counts of the outlet samples ranged between 105/g and 10'3/g during the period October 1982 to August, 1983 (Fig. 1). The lowest count was recorded during October 1982 and highest counts was observed during April 1983. The results also indicated that there are no obvious differences between the Chinese or Indian digestor types at Omar Makram.

I a t 3 7 " C

Geldreich and Bordner (1971) reported that the use of bacterial indicators is more logical for detecting and measuring fecal pollution from all warm-blooded animals than the search for pathogens which requires a variety of complex, time-consuming, and often tentative procedures for each sample analyzed. In the present in- vestigation, total coliform, fecal coliform, and fecal streptococci seemed to survive better than fecal coliform (Fig. 2). In addition, the density of the three indicators decreased significantly during October 1982. On the other hand, there was an increase in the density of bac- terial indices of pollution during June 1983. This may be due to one or more factors prevailing under natural con- ditions (Reitter and Seligmann, 1957, Carlucci et al., 1961; Mitchell et al., 1967; Saleh and E1-Abagy, 1976).

The bacterial density of inlet and outlet samples of

I n d i a n T y p e 13

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252 M.M. EI-Abagy and H. T. E1-Zanfaly

I I I I ' ' ' ' ' ' '

T i m e ( m o n t h )

Fig. 1. The density of total bacterial counts (Omar Makram).

Bacterial removal by anaerobic digestion 253

the Indian digestor at EI-Manawat are represented in Fig. 3. The results show the same pattern observed for the samples taken from the Omar Makram digestor. The total bacterial counts were decreased and the per- centage of removal ranged between 38°7o and 99°70. The highest removal was recorded during November 1982. With regard to bacterial indices of pollution, fecal strep- tococci increased in number during April and May 1983.

The study was continued to follow up the inlet and outlet discharge of Shobra-Kas digestor. The results are presented in Fig. 4 for the density of bacterial param- eters during May and August 1983. Fecal coliform seems to be more sensitive than fecal streptococci. The percentage removals were 62°70 and 100°7o during August and May 1983, respectively.

In general, the digestion process is effective in the

reduction of bacterial parameters. However, the bacte- rial level in the digested slurry may be considered to be hazardous because of the remaining pathogenic organ- isms (Rankin and Taylor, 1969).

The digested slurry was mixed with soil and stored for 1 week near the digestor (composting a). Then, this mix- ture was transferred to the field and left there for about 2 months (composting b).

The results of total viable bacterial counts for outlet, from the composted (a) and composted (b) samples of Omar Makram and EI-Manawat, are recorded in Fig. 5. An examination of the data in Fig. 5 shows that the composting treatment had no effect on the removal of total bacterial counts. Moreover, there was an increase in bacterial density during April 1983.

Removal of total coliform, fecal coliform, and fecal

lOEb.. II~li~ Type I Chinese Type [

Faecal streptococci _ o o Inlet | - I = Ouletl

I

IoK~ ~ . - - . , - - - - ~ Faecal coliform I

Time (month)

Fig. 2. The density of bacterial indices of pollution (Omar Makram).

254 M.M. E1-Abagy and H. T. EI-Zanfaly

" ~41 Faecal streptococci ii 2 Total counts at 37 C I

,'o°J -o °r 8 1

.~ ,/2 Total counts at 2 2 C l o t Q ~ Total coliform

m° I0 ~ 0 0 Inlet

: t ° '

I ° r i i i i i i i i i I0 = i , , I = = = I

Time (month) Fig. 3. The density of bacterial parameters (EI-Manawat).

streptococci in both Omar Makram and E1-Manawat samples are shown in Fig. 6. The increase in total co- l iform density is expected, due to the additions of co- l iform soil types (Medreck and Litsky, 1960). On the other hand, the increase of fecal coliform and / o r fecal streptococci may be due to an additional contaminat ion by fecal wastes or to simple reproduction of organisms originally present. As recommended by several investi- gators, fecal streptococci is superior to fecal coliform as an indicator of fecal pollution (Saleh and E1-Abagy,

1976; E1-Abagy et al., 1981; E1-Hawary et ak, 1981). Thus the results shown in Fig. 6, emphasize that there was a possibility of additional contamination during the two composting steps.

The composting process used in this investigation did not show the expected results of additional removal of the fecal bacterial parameters. Therefore, by using this process, the care in transportat ion of the digested slurry, as well as the increase in time of composting, must be taken into consideration.

Bacterial removal by anaerobic digestion 255

8 I0

,o"

,o

8 o, I0

,@-

Q 10

"" 4 ¢Ji o I0 OB

2 I0

8 I0

6 I0

4 I0

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I I i I

Foeca I coliform

, s D

\ / / /

I E l I I I

Faecal streptococci

I I I I May June July Aug. 1983

12 I 0 -

I0 I 0 -

8 I 0 -

6 I 0 -

4 I 0 -

2 I 0 -

I

I0 I 0 -

8 I 0 -

6 I 0 _

4 I 0 -

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I

May 1983

Time (month)

Total counts at 22°C

l - - - - I Ou t l e t

o o Camp. (a)

I I

0

Total counts at :37 C

o . ~ - ~ r ~ - -

......LD

-0

I i I June July Aug.

Fig. 4. The density of bacterial parameters (Shobra-Kas).

256 M.M. EI-Abagy and H. T. EI-Zanfaly

1012

i0 I0

10 8

10 6

~, id z

,do

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14 I0

1012

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EI-Manowat ( Indian type )

_ at 22 *C at 5 7 *C

o ~ e-- - - - e Outlet / ~ . \ o-----o Comp. (a)

• ,\NN%~ :¢-- - - -x Comp (b) • ,~ X-- - - -x Comp (b)

\ -

I I I , I I I I i

Omor Makrqm ( Indian type)

I• at 22 *C

I I I

at 37 *C

I I 1

Chinese type at 22 "C

\

I I I I April May June July 1 9 8 5

April 1983

nese type at 3 7 "C

U" I I I I

May dune July

Time (month)

Fig. 5. Effect of composting on total bacterial counts.

Bacterial removal by anaerobic digestion 257

i0 I0

I0 8

,o 6

10 4

,o z

Total coliform

\ . J ; x j z

~-Manawat ( Indian type )

Faecal coliform

\ /

I 11 , I

Faecal streptococci

, .

I I I I

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6

0

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D

V I I I I

April May dune July 1 9 8 3

_ B. (Chinese type)

- ~ , , , //I)

I April May dune July 1 9 8 3

Time ( month )

\\ D

I f I I April May June July 1 9 8 3

Fig. 6. Effect of compost ing on bacterial indices of pollution.

258 M.M. EI-Abagy and H. T. E1-Zanfaly

Acknowledgements--This study was supported in part by funds p~o- vided by the Development and Application of Biogas Technology in Rural Areas of Egypt, a research project sponsored by the Egyptian National Research Centre (Dokki, Cairo, Egypt) and United States AID. The authors express their deep thanks to Prof. Fatma El- Gohary, for her valuable advice and keen interest during the present investigation.

References

American Public Health Association (1980) Standard Methods for Ex- amination o f Water and Wastewater, 15th. ed. APHA, Washington, DC.

Bertucci, J., Lue-Hing, C., Zenz, D., and Sedita, S. J. (1977) Inac- tivation of viruses during anaerobic sludge digestion, J. Water Pollut. Control Fed. 49, 1642.

EI-Abagy, M. M., E1-Hawary, S., and Abou-EI-Azm, M. (1981) Sur- vival of bacterial indicators and Salmonella typhimurium during methanogenesis, Bull. NRC (Cairo, Egypt), in press.

E1-Hawary, S., E1-Abagy, M. M., and E1-Newigy, A. (1981) Effect of biogas on the survival of fecal indicators and Salmonella typhimurium. Research Bulletin of Faculty of Agriculture, Ain Shams Univ., October.

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Geldreich, E. E. and Bordner, R. H. (1971) Faecal contamination of fruits and vegetables during cultivation and processing for market. A review, J. Milk Food Technol. 34, 184.

Medrek, T. F. and Litsky, W. (1960) Comparative incidence of co- liform bacteria and enterococci in undisturbed soil, J. Appl. MicrobioL 8, 60.

Mitchell, R., Yankafsky, S., and Jannash, H. W. (1976) Lysis of E. coli by marine microorganisms, Nature, 215, 891.

Prakasam, T. B. S. (1979) Application of biogas technology in India. Biogas and Alcohol Seminar, Chicago, IL.

Rankin, J. D. and Taylor, E. W. (1969) A study of some disease haz- ards which could be associated with the system applying cattle slurry to pasture, Veterinary Rec. 85, 578.

Reittler, R. and Seligmann, R. (1957) Pseudomonas aeruginosa in drinking water, J. Appl. Bact. 20, 145.

Ru-Chen, C. and Zhi-Ping, X. (1975) Digestors for Developing countries-water Pressure Digestors. Chinese Academy of Sciences, 1975.

Saleh, F. A. and EI-Abagy, M. M. (1976) The density of coliform and faecal streptococci in Nile water prior to impoundment. Symposium on Nile Water and Lake Dam Project, Cairo, Egypt, Session 2, p. 102.

Singh, R. B. (1971) Biogas plant generation methane from organic wastes. Gobas Gas Research Station, Ajitmal, Etawan, 1971.

Swaroop's ( 1951) The range of variation of the most probable number of organisms estimated by the dilution method, lndian J. Med. Res. 39, 107.