Determination of the effect of stabilized treatment sludge on counts of some soil microorganisms

In this study, the effect of addition of different percentages (10, 20 and 30%) of stabilized treatment sludge on some soil microorganisms (total bacteria, actinomycetes, anaerobic bacteria, proteolytic bacteria, fungi-yeast) were determined under laboratory conditions. The stabilized treatment sludge was added to the soils taken from different depths (0-10 cm and 10-20 cm). pH and electrical conductivity determinations were also made in the samples. Soils without treatment sludge were used as controls. For the detection of microorganisms suitable culture media for development of them were used. Petri dishes were incubated at 20 0C for proteolytic bacteria, 27 0C for actinomycetes and fungi-yeast, 37 0C for total bacteria and anaerobic bacteria and experiments were repeated three times.The total numbers of bacteria in controls were lower than that observed in treatments during incubation. In general, during incubation, the total numbers of bacteria in the depth of 0-10 cm were higher than the numbers of total bacteria in 10-20 cm depth. In the soil sample taken from the depth of 0-10 cm, the lowest number of Actinomycetes was in control throughout the incubation. Actinomycetes numbers in the soil sample taken at the beginning were lower than the numbers in soil sample from 10-20 cm. Increase in the number of anaerobic bacteria in all soil samples from the depth of 0-10 cm which treated with sludge was observed during the first 14 days of incubation. The number of anaerobic bacteria in soil sample taken from the depth of 10-20 cm which treated with sludge at a percentage of 30% was suddenly increased at day 7 and after this increase, the number of anaerobic bacteria rapidly decreased until day 14. The number of proteolytic bacteria in the soil taken from 0-10 cm depth was lower than the numbers in the soil taken from the depth of 10-20 cm, at the beginning of the incubation period. During incubation the fungus-yeast counts were lowest in controls. In the soil sample taken from the depth of 0-10 cm, especially in the first 21 days of incubation, the highest numbers of fungus-yeast were seen in the treatment with highest sludge.The total number of bacteria in the controls taken from 0-10 cm was increased and decreased depending on pH until day 21. In the treatments, the total number of bacteria increased when pH decreased and the number decreased when pH increased until day 14. The number of Actinomycetes as well as the total number of total bacteria was increased and decreased depending on pH until day 21. When sludge addition in the soil sample taken from 0-10 cm depth increased, the dependence of the actynomycetes number to pH decreased. The numbers of microorganisms in the other controls and treatments changed independently from pH and electrical conductivity.Key Words: Proteolytic bacteria, Actinomycetes, Fungi-yeast, Total bacteria, Anaerobic bacteria, Soil, Treatment sludge