Abstract
Background: Little is known about occupational exposures that occur along fecal sludge collection and resource recovery processes. This study characterizes inhaled endotoxin exposure to workers of a municipal scale fecal sludge-to-fuel processes in Kigali, Rwanda. Methods: Forty-two task-based air samples were collected from workers in five tasks along the fecal sludge collection and resource recovery process. Samples were processed for endotoxin using the limulus amebocyte lysate (LAL) test. To account for exposure variability and compare measured concentrations to established exposure limits, we used Monte Carlo modeling methods to construct distributions representing full eight-hour (8-h) exposures to endotoxin across eight exposure scenarios. Results: Geometric mean (GM) endotoxin concentrations in task-based samples ranged from 11–3700 EU/m3 with exposure concentrations increasing as the dryness of the fecal sludge increased through processing. The thermal dryer task had the highest endotoxin concentrations (GM = 3700 EU/m3) and the inlet task had the lowest (GM = 11 EU/m3). The geometric means (GM) of modeled 8-h exposure concentrations were between 6.7–960 EU/m3 and highest for scenarios which included the thermal dryer task in the exposure scenario. Conclusions: Our data suggest the importance of including worker exposure considerations in the design of nascent fecal sludge management processes. The methods used in this study combine workplace sampling with stochastic modeling and are useful for exposure assessment in resource constrained contexts.
Highlights
Onsite sanitation systems such as pit latrines or septic tanks currently serve more than 2.7 billion people globally and this number is expected to be as high as 4.9 billion by 2030 [1]
On days in which a large number of trucks dumped fecal sludge at the plant, the individual tasks were performed for longer durations of time compared to days in which the plant was operating under capacity because of the fewer trucks delivering fecal sludge
Our findings are consistent with a significant body of literature which shows that exposure varies significantly with task and type of waste handled [22,37].Unsurprisingly, the solar dehydration task and the thermal drying task, which exhibited the highest endotoxin concentrations, were the tasks in which workers were handling drier material with a lower percentage of total solids
Summary
Onsite sanitation systems such as pit latrines or septic tanks currently serve more than 2.7 billion people globally and this number is expected to be as high as 4.9 billion by 2030 [1]. Given the high concentration of solids and contaminants in fecal sludge waste streams, conventional wastewater treatment processes are neither effective or affordable for treating fecal sludge in resource strapped contexts [3]. As it stands, wastewater treatment systems which are built in low-resource contexts are. Methods: Forty-two task-based air samples were collected from workers in five tasks along the fecal sludge collection and resource recovery process. Results: Geometric mean (GM) endotoxin concentrations in task-based samples ranged from 11–3700 EU/m3 with exposure concentrations increasing as the dryness of the fecal sludge increased through processing. The methods used in this study combine workplace sampling with stochastic modeling and are useful for exposure assessment in resource constrained contexts
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