SURVIVAL OF ENTEROVIRUSES DURING
ANAEROBIC SLUDGE DIGESTION
A. PALFI
National Institute of Public Health, IX., Gyäli ut 4., Budapest, Hungary
INTRODUCTION
Facilities designed for the inactivation of sewage sludge are an essential and costly part
of waste water treatment plants, but insufficient interest is shown to sludge treatment
methods [1].
The most common method of sludge treatment is digestion, either aerobic or
anaerobic. Under .appropriate conditions most of the pathogens are destroyed. Their
complete elimination, however, can be carried out only by composting or heat treatment
of the digested sludge (10).
Only a few studies have been perfomed hitherto concerning virological efficiency of
sludge digestion [5, 6,7, 8 ] . Lund [9] has shown .that isolation of viruses is possible even
after digestion for 50-60 days at 50°C. She noted increased heat stability of polioviruses
during digestion as compared to other types of enteroviruses, Roediger [10] has drawn
attention to the high temperature resistance of T.B. bacteria and viruses; he found that
20-25 min. at 70°C was necessary to destroy them. The economical maximum
temperature attained in digesters is not enough for the elimination of pathogens. As
pointed out by Csanädy [4] the bacteriological picture of digested sludge might
materially change if a continuous-flow sludge digester is used. In this way, namely, the
digested sludge might always contain such particles that have been only retained for some
minutes.
In this study an effort is made to assess the virological efficiency of anaerobic
equipment operating at a waste water treatment plant in Budapest. For this purpose
qualitative virological examinations were carried out on 74 digested sludge samples in
1969. In 1970, following the modification of the digestion procedure, a further 82
samples were examined for their enterovirus density. The effects on virus survival of
various conditions of digestion (temperature, duration of treatment) were compared.
MATERIALS AND METHODS
In 1969 the retention period in the digesters was about 21 days at 30°C, with
continuous outflow and inflow of sludge and constant mixing. In 1970 the retention was
increased to 40 days, and consisted of three stages: in the two primary digesters the
detention time was 20 and 10 days respectively, with constant mixing. In the secondary
digester which constituted the third stage, sludge was detained for 10 days without
mixing. The temperature of the digester was raised to 33°C.
In 1969 sampling was conducted all year round, while in 1970 it was from March to
the beginning of October. In one instance 100 ml sludge was taken and concentrated to
1.5 ml by the means of a CaHP0 4 -gel adsorbent [2]. 0.1 ml quantities of this concentrate
99
ANAEROBIC SLUDGE DIGESTION
A. PALFI
National Institute of Public Health, IX., Gyäli ut 4., Budapest, Hungary
INTRODUCTION
Facilities designed for the inactivation of sewage sludge are an essential and costly part
of waste water treatment plants, but insufficient interest is shown to sludge treatment
methods [1].
The most common method of sludge treatment is digestion, either aerobic or
anaerobic. Under .appropriate conditions most of the pathogens are destroyed. Their
complete elimination, however, can be carried out only by composting or heat treatment
of the digested sludge (10).
Only a few studies have been perfomed hitherto concerning virological efficiency of
sludge digestion [5, 6,7, 8 ] . Lund [9] has shown .that isolation of viruses is possible even
after digestion for 50-60 days at 50°C. She noted increased heat stability of polioviruses
during digestion as compared to other types of enteroviruses, Roediger [10] has drawn
attention to the high temperature resistance of T.B. bacteria and viruses; he found that
20-25 min. at 70°C was necessary to destroy them. The economical maximum
temperature attained in digesters is not enough for the elimination of pathogens. As
pointed out by Csanädy [4] the bacteriological picture of digested sludge might
materially change if a continuous-flow sludge digester is used. In this way, namely, the
digested sludge might always contain such particles that have been only retained for some
minutes.
In this study an effort is made to assess the virological efficiency of anaerobic
equipment operating at a waste water treatment plant in Budapest. For this purpose
qualitative virological examinations were carried out on 74 digested sludge samples in
1969. In 1970, following the modification of the digestion procedure, a further 82
samples were examined for their enterovirus density. The effects on virus survival of
various conditions of digestion (temperature, duration of treatment) were compared.
MATERIALS AND METHODS
In 1969 the retention period in the digesters was about 21 days at 30°C, with
continuous outflow and inflow of sludge and constant mixing. In 1970 the retention was
increased to 40 days, and consisted of three stages: in the two primary digesters the
detention time was 20 and 10 days respectively, with constant mixing. In the secondary
digester which constituted the third stage, sludge was detained for 10 days without
mixing. The temperature of the digester was raised to 33°C.
In 1969 sampling was conducted all year round, while in 1970 it was from March to
the beginning of October. In one instance 100 ml sludge was taken and concentrated to
1.5 ml by the means of a CaHP0 4 -gel adsorbent [2]. 0.1 ml quantities of this concentrate
99