غلام خداکرمیان

Spreading of manure and sewage sludge on agricultural lands has been gaining attention in past decade as it improves soil nutrient status and enhances microbial activity. On the other hand, pathogens including bacteria, viruses, and protozoa have been found in these organic fertilizers. In many arid regions in developing countries the main source of drinking water is groundwater abstracted from drilled wells. Moreover, wastewater collection and treatment systems are uncommon in these countries and therefore there is a real risk for the abstracted water being contaminated with pathogens and pose a health risk through the food chain. Percolation through the vadose zone has been found to be a significant mechanism for removing microbial contaminants. Bacteria retention occurred mostly in the top layer of a soil (a few 10 cm). The main retention mechanisms are physical straining or filtration within the pores of the solid matrix. Depending on its physiological state a bacterial cell may attach to surfaces where it may grow or can be dislodged into the aqueous solution and transported to new regions. Soils as filtration media for percolating wastes carrying bacterial contaminants may allow their survival and 641 growth and thus serve as a temporary sink and a source for delayed leaching of bacteria into the subsurface. Several factors have been reported to affect the survival of fecal coliforms (FC) in soils. The two most significant abiotic parameters influencing the survival of bacteria in soil are temperature and water availability. Survival of bacteria decreases with increasing temperature. Survival of E. coli and P. fluorescens CHA0 under non-optimal temperature and nutrient deprivation has been studied. Survival of E. coli had an inverse relationship with temperature, whereas for P. fluorescens a direct relationship between temperature and T90 values was established in the range 5–15ºC, with an inverse relationship at higher temperatures. Animal and human waste-bor