Sewage Farming in Iraq: A Potential Hazard for Pollution

A number of surface and subsurface soil and sewage samples were collected from a sewage-irrigated farm near Baghdad. A bacteriological examination of the samples included the determination of the total counts of bacteria, coliforms, streptococci, staphylococci, and the detection of salmonellae. Changes in the population density of coliforms, faecal streptococci, and salmonellae in surface soils incubated at 10 and 37°C were followed over 5 weeks. Samples of lettuce (Lactuca saliva) grown in this farm were tested for coliforms as an indicator for microbial pollution. Total bacterial counts were 4 × 10⁶ cell/g for surface and subsurface soils, and 45 × 10⁹ cell/ml for sewage samples. The average number of coliforms was 4 × 10⁵ cell/ml for surface and subsurface soils, and 34 × 10⁵ cell/ml for sewage. The percentages of Escherichia coli type I in surface soil, subsurface soil, and sewage samples were 60, 44, and 39%, respectively. The densities of faecal streptococci in the surface soil, subsurface soil, and sewage samples were 6 × 10³ cell/g, 4 × 10³ cell/g, and 17 × 10³ cell/ml, respectively. Coagulase positive staphylococci were 26 × 10³ cell/g, 6 × 10³ cell/g, and 3 × 10³ cell/ml, in the surface soil, subsurface soil, and sewage samples, respectively. Salmonellae were detected in most of the soil and sewage samples. Estimates of coliforms in lettuce indicated the presence of these organisms in all parts of the plant, which indicates the probability of the presence of intestinal pathogens. The population of different bacteria progressively declined with time, but the reduction in numbers was relatively greater in samples incubated at 37°C, than in those incubated at 10°C. Salmonellae were detected after 1 week, but disappeared thereafter. The potential hazard for pollution caused by sewage farming, as it is practiced, threatens vegetables grown on the farms as well as ground and surface waters of the nearby area. Sewage farming may seriously affect the consumers. It is recommended that the conventional methods of treating the sewage effluents be adopted.