Ac. Soares et al., EFFECT OF ANAEROBIC-DIGESTION ON THE OCCURRENCE OF ENTEROVIRUSES AND GIARDIA CYSTS IN SEWAGE-SLUDGE, Journal of environmental science and health. Part A: Environmental science and engineering, 29(9), 1994, pp. 1887-1897
The disposal of anaerobically digested sewage sludge onto farmland has
created the necessity to evaluate the fate of pathogens which are oft
en present. The occurrence of enteroviruses and Giardia cysts in mesop
hilic anaerobically digested sludge before and after treatment, was mo
nitored for a period of 14 months. The concentration of enteroviruses
in sludge determined by Most Probable Number (MPN) ranged from 4.36 x
10(3) to 7.00 x 10(5) MPN/Kg before anaerobic digestion and from < 6.2
5 to 2.52 x 10(5) MPN/Kg after treatment. The concentration of Giardia
cysts as determined by immunofluorescence ranged from 7.33 x 10(4) to
3.30 x 10(6) cysts/Kg of undigested sludge and 1.00 x 10(5) to 4.14 x
10(6) cysts/Kg of anaerobically digested sludge. The percentage virus
removal after anaerobic digestion varied from 68 % to > 99.94 %. The
levels of intact Giardia cysts did not show any significant removal af
ter sludge treatment. However, cyst viability could not be assessed by
the method used for detection. Results of this study suggest that sig
nificant concentrations of both groups of pathogens can be present in
anaerobically digested sludge.