104
A. Pälfi
CONCLUSIONS
The modification of digestion technology (length of treatment, higher temperature,
unmixed secondary digester) unfavourably influenced the survival of enteroviruses in the
sludge. Comparisons with the results of the previous year show that the virus density of
digested sludge decreased by 60 per cent and compared with the raw sludge samples by
about 80 per cent.
The number of virus strains isolated in one sample was also lower, and the number of
virus types also fell from eight to three. As quantitative determinations show, the virus
concentration of digested sludge is 0.85 virus unit per 100 ml (MPNCU) while that of raw
sludge is 17.9 MPNCU. This is equivalent to a reduction of about 95 per cent. It follows
that due to modified conditions of digestion 85 per cent of the samples did not yield
virus isolates and virus density of positive samples decreased. In spite of these findings,
however, it should not be overlooked that digested sludge treated by the modified technology remains a potential source of infection and as such should be handled as an
infectious material.
REFERENCES
1 BENEDEK, P. and NEMETH, A (ed.), Treatment of sewage sludge in Hungary. VITUKI,
Monographs, Budapest (1968).
2 PALFI, A., SIMON, M., and SCHULEK, E., Virological examination of urban sewage from
Budapest. II Virus isolation experiments. Egeszsegtudomany, 14, 127-132 (1970).
3 CHANG, S.L., BERG, G., BUSCH, K.A., STEVENSON, R.E., CLARKE, N.A. and KABLER, P.W.,
Application of the "most probable number" method for estimating concentrations of animal
viruses by the tissue culture technique. Virology 6, 27-42 (1958).
4 CSANADY, M., Investigations into the aerobic decomposition of sewage sludge. Egeszsegtudomany
11,378-392(1967).
5 GEAR, J.H.S., The virus of poliomyelitis: its distribution and methods of spread. J. Roy. San. Inst.
(Brit) 69, 149(1949).
6 GRIGORIEVA, L.V., KORCHAK, G.I., BONDARENKO, V.l., and BEI, T.V., Sanitary virological
and bacteriological features of the sewage and soil in the suburbs of Kiew. Gig. i Sank. 33, 44-48
(1968).
7 KELLY, S.M. and SANDERSON, W.W., The effect of sewage treatment on viruses. Sew. ind. Wast.
31,683-689(1959).
8 KNORR, M., Aktuelle Fragen der Müllbeseitigung, Müllaufbereitung und Müllverwertung. Wasser,
Abwasser 5, 56 (1957).
9 LUND, E., Observations on the virus binding capacity of sludge. 5th Int. Wat. Poll. Res. Conf.
1970. Pergamon Press 1-24 (1971).
10 ROEDIGER, H., Die anaerobe alkalische Schlammfaulung. München (1967).
A. Pälfi
CONCLUSIONS
The modification of digestion technology (length of treatment, higher temperature,
unmixed secondary digester) unfavourably influenced the survival of enteroviruses in the
sludge. Comparisons with the results of the previous year show that the virus density of
digested sludge decreased by 60 per cent and compared with the raw sludge samples by
about 80 per cent.
The number of virus strains isolated in one sample was also lower, and the number of
virus types also fell from eight to three. As quantitative determinations show, the virus
concentration of digested sludge is 0.85 virus unit per 100 ml (MPNCU) while that of raw
sludge is 17.9 MPNCU. This is equivalent to a reduction of about 95 per cent. It follows
that due to modified conditions of digestion 85 per cent of the samples did not yield
virus isolates and virus density of positive samples decreased. In spite of these findings,
however, it should not be overlooked that digested sludge treated by the modified technology remains a potential source of infection and as such should be handled as an
infectious material.
REFERENCES
1 BENEDEK, P. and NEMETH, A (ed.), Treatment of sewage sludge in Hungary. VITUKI,
Monographs, Budapest (1968).
2 PALFI, A., SIMON, M., and SCHULEK, E., Virological examination of urban sewage from
Budapest. II Virus isolation experiments. Egeszsegtudomany, 14, 127-132 (1970).
3 CHANG, S.L., BERG, G., BUSCH, K.A., STEVENSON, R.E., CLARKE, N.A. and KABLER, P.W.,
Application of the "most probable number" method for estimating concentrations of animal
viruses by the tissue culture technique. Virology 6, 27-42 (1958).
4 CSANADY, M., Investigations into the aerobic decomposition of sewage sludge. Egeszsegtudomany
11,378-392(1967).
5 GEAR, J.H.S., The virus of poliomyelitis: its distribution and methods of spread. J. Roy. San. Inst.
(Brit) 69, 149(1949).
6 GRIGORIEVA, L.V., KORCHAK, G.I., BONDARENKO, V.l., and BEI, T.V., Sanitary virological
and bacteriological features of the sewage and soil in the suburbs of Kiew. Gig. i Sank. 33, 44-48
(1968).
7 KELLY, S.M. and SANDERSON, W.W., The effect of sewage treatment on viruses. Sew. ind. Wast.
31,683-689(1959).
8 KNORR, M., Aktuelle Fragen der Müllbeseitigung, Müllaufbereitung und Müllverwertung. Wasser,
Abwasser 5, 56 (1957).
9 LUND, E., Observations on the virus binding capacity of sludge. 5th Int. Wat. Poll. Res. Conf.
1970. Pergamon Press 1-24 (1971).
10 ROEDIGER, H., Die anaerobe alkalische Schlammfaulung. München (1967).