The use of bacteriophage as tracers of aerosols liberated by sludge suction appliances

Three bacteriophage tracers were added to 600–1 containers of water and simulated latrine sludge to provide high titres of tracer in aqueous and semi-aqueous media. After a period of mixing and stabilization, media were removed from the containers with suction hoses coupled to the vacuum pump of one of two sludge suction tankers. Exhaust air from the appliances was sampled by cyclone sampler and assayed for the presence of tracer organisms carried over during the emptying process. In the experiments the appliances were operated at different vacuum pump speeds, drawing both aqueous and semi-aqueous (simulated sludge) media. Air around one tanker was also sampled during the emptying, under pressure, of the vacuum vessel. The degree of aerosolization and expulsion of tracer bacteriophage by the vacuum appliances was consistently low, regardless of medium and pump air flow. In contrast, the proportion of tracer retained within the appliances was very high, exceeding the proportion expelled by a minimum of 8log₁₀ orders of magnitude and a maximum of greater than 11log₁₀ orders. The highest total of tracer bacteriophage was recovered during the pressure emptying of the vacuum vessel of one tanker. The results may be used for assessing and comparing potential public health hazards associated with the handling of wastewater sludge by vacuum appliances.