Assessment of the influence of intrinsic environmental and geographical factors on the bacterial ecology of pit latrines

Funding Information: This research received financial support from the Bill and Melinda Gates Foundation (grant number OPP52641). AWW and JP were supported by the Wellcome Trust [grant number 098051]. AWW and the Rowett Institute of Nutrition and Health, University of Aberdeen, receive core funding support from the Scottish Government Rural and Environmental Science and Analysis Service (RESAS). UZ is funded by Natural Environment Research Council (NERC) Independent Research Fellowship (NE/L011956/1). CQ is funded through an Medical Research Council fellowship (MR/M50161X/1) as part of the MRC Cloud Infrastructure for Microbial Bioinformatics consortium (MR/L015080/1).Peer reviewedPublisher PD

Figure 1

<p><b>Drop-hole modification and trap placement.</b></p

Modelling the fill rate of pit latrines in Ifakara, Tanzania

A model of the rate at which pit latrines fill was developed and compared with actual fill rates measured in latrines in Ifakara, Tanzania. Model parameters were derived primarily from data collected during the field study in Tanzania, with one fitted parameter. Although the model did not accurately simulate the fill rate of individual pits, it provided a good simulation of the average fill rate of the pits and aided the identification of pits that were performing poorly. Laboratory experiments conducted on samples of sludge from the pits were used to identify the average hydrolysis constant for biodegradation of the organic material. The average hydrolysis constant (0.046 day−1) was higher than that identified in another modelling study (0.0015 day−1), conducted in South Africa. The higher hydrolysis constant provided a simulation of the profile of volatile solids with lower root mean square error in 17/24 of the pits, however, for the other pits a lower hydrolysis constant was more appropriate. A sensitivity study of the model indicated that the pit fill rates were particularly sensitive to the parameter that quantified water accumulation in the pit, as such quantifying water flow through the pit is a priority for future research.</jats:p

Characteristics of latrines in central Tanzania and their relation to fly catches.

The disposal of human excreta in latrines is an important step in reducing the transmission of diarrhoeal diseases. However, in latrines, flies can access the latrine contents and serve as a mechanical transmitter of diarrhoeal pathogens. Furthermore, the latrine contents can be used as a breeding site for flies, which may further contribute to disease transmission. Latrines do not all produce flies, and there are some which produce only a few, while others can produce thousands. In order to understand the role of the latrine in determining this productivity, a pilot study was conducted, in which fifty latrines were observed in and around Ifakara, Tanzania. The characteristics of the latrine superstructure, use of the latrine, and chemical characteristics of pit latrine contents were compared to the numbers of flies collected in an exit trap placed over the drop hole in the latrine. Absence of a roof was found to have a significant positive association (t=3.17, p=0.003) with the total number of flies collected, and temporary superstructures, particularly as opposed to brick superstructures (z=4.26, p<0.001), and increased total solids in pit latrines (z=2.57, p=0.01) were significantly associated with increased numbers of blowflies leaving the latrine. The number of larvae per gram was significantly associated with the village from which samples were taken, with the largest difference between two villages outside Ifakara (z=2.12, p=0.03). The effect of latrine superstructure (roof, walls) on fly production may indicate that improvements in latrine construction could result in decreases in fly populations in areas where they transmit diarrhoeal pathogens