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Heat inactivation of enteric viruses in dewatered wastewater sludge
Abstract:
The effect of moisture content on the rates of heat inactivation of enteric viruses in wastewater sludge was determined. The protective effect of raw sludge on poliovirus previously observed (R. L. Ward, C. S. Ashley, and R. H. Moseley, Appl. Environ. Microbiol. 32:339--346, 1976) was found to be greatly enhanced in sludge dewatered by evaporation. Other enteroviruses responded in a similar fashion. This effect did not appear to be due merely to the state of dryness of the sludge samples because in humus-deficient soil, a relatively inert material, the rate of poliovirus inactivation by heat was not significantly altered through dewatering. Instead, this effect appeared to have been caused by protective substances in the sludge, such as detergents, which are concentrated through dewatering. As reported previously (R. L. Ward and C. S. Ashley, Appl. Environ. Microbiol. 34:681-688, 1977; R. L. Ward and C. S. Ashley, Appl. Environ. Microbiol 36:889--897, 1978) raw sludge is not protective of reovirus, but, instead, the ionic detergents in sludge cause the rate of heat inactivation of this virus to be accelerated. Dewatering of sludge, however, was found to partially reverse this virucidal effect. Evidence is presented indicating that this reversal is caused by an unidentified protective substance in sludge also concentrated through dewatering. Finally, it was shown that the effects of raw sludge on heat inactivation of poliovirus and reovirus are greatly reduced by composting, a result that correlated with the degradation of detergents.
Insights
Dewatering wastewater sludge enhances protection of poliovirus from heat inactivation due to concentrated protective substances. Composting reduces these effects by degrading detergents, impacting viral inactivation rates.
Area of Science:
- Environmental Microbiology
- Virology
- Wastewater Treatment
Background:
- Wastewater sludge treatment aims to reduce pathogen load, including enteric viruses.
- Moisture content is a critical factor influencing the efficacy of heat inactivation processes.
- Previous studies indicated a protective effect of raw sludge on poliovirus.
Purpose of the Study:
- To determine the effect of moisture content on heat inactivation rates of enteric viruses in wastewater sludge.
- To investigate the role of sludge dewatering and its components in viral heat inactivation.
- To assess the impact of composting on the protective or virucidal effects of sludge.
Main Methods:
- Experiments involved heating wastewater sludge samples with varying moisture content.
- Polio virus and reovirus were used as model enteric viruses.
- Sludge dewatering by evaporation and composting were employed to alter sludge properties.
Main Results:
- Dewatering sludge significantly enhanced its protective effect against poliovirus heat inactivation.
- Protective substances, like detergents, concentrated during dewatering, were implicated.
- Composting reduced the protective effect on poliovirus and the virucidal effect on reovirus, correlating with detergent degradation.
Conclusions:
- Sludge dewatering can alter the heat inactivation rates of enteric viruses, primarily through the concentration of protective or virucidal substances.
- Detergents play a dual role, protecting poliovirus but accelerating reovirus inactivation in raw sludge.
- Composting effectively mitigates these effects, suggesting a method for improving viral inactivation during sludge treatment.