Soil samples were treated with different rates of sewage sludge (10, 20, 40,
80 and 120 tons/fed). The lola I bacterial count and the count of microorganisms
adapted to different rates of sewage sludge were recorded after 1,2.4.8,12 and 14
weeks. Also, tolerance of some bacterial isolates to five heavy metals detected in
sewage sludge was studied. In addition, urease, phosphatase activities and C02
evolution were assayed during the incubation period. Results showed that when soil
was treated with sewage sludge. the total count was increased (rom 3.6 X10⁶ to 3.12X
10⁷ CFU s'' dry soil throughout the 14 days. Compared to the control treatment,
sewage sludge at the rate of 10 tons/fed proved to be toxic to the soil microbial
population. Moreover, addition of high rates of sewage (20, 4080 and 120 tons/fed).
the counts were less and ranged between 5.0 X 10² and 3.0 X10⁴ CFU s" dry soil. As
a result of adding different rates of sewage sludge, twenty seven bacterial isolates
were picked from the agar plates as resistant bacteria, These isolates were purified
and classified into four groups (G· cocci, O' spore former, G' short rods and G' short
rods). The data recorded about the enzymes activities (urease and phosphatase)
detected that urease and phosphatase activities were increased throughout the 14
days followed by a decrease in its activities until the end of the incubation period. The
same observation was recorded with C02 evolution, where its value was decreased
with the incubation period increased.