Microbiological evaluation of sewage sludge in terms of possibilities of application in soil as a fertilizer

Abstract

Research was conducted of sewage sludge from wastewater treatment plant for the
existence of microorganisms of several major groups, containing pathogenic
representatives with epizootological significance (Gram-negative aerobic bacteria,
E. coli, Clostridium perfringens, the genera Pseudomonas, Staphylococcus,
Enterococcus, fungi, and the total number of microorganisms), in order to assess
the environmental safety of the final product. In parallel similar studies were made
of fresh and composted cattle manures. A comparison of the results was made with
the ready for manuring compost in order to assess the possibilities for the use of
sludge for fertilizing. The quantities of microorganisms were given in CFU per 1 g
of the investigated material, as well as per 1 g of dry substance for each of them. In
our opinion this new approach to the reporting of the results per unit of dry matter
of the investigated materials, allows for a more accurate comparison. It was found
that the examined sewage sludge from wastewater treatment plant were rich in
microorganisms from studied groups and their direct application in soils without
prior treatment by aerobic or anaerobic digestion may represent epidemiological
danger.