Practical Paper Characterization of pit latrines to support the design and selection of emptying tools in peri-urban Mzuzu, Malawi

The urban areas of many low-income countries must balance a rising demand for pit latrines for household sanitation provision against limitations in space, resulting in a need for pit latrine emptying services. This study was undertaken in the peri-urban neighborhood of Area 1B in the city of Mzuzu, Malawi, to examine the characteristics of household pit latrines for designing and selecting pit latrine emptying tools. We used 150 structured household surveys and field observations. From this, a subset was selected and 30 manual cone penetrometer tests were conducted at full latrines. Chemical oxygen demand analysis was also performed for 14 pit latrines. The results indicated that in addition to serving as a disposal for fecal matter, 90% of households also used pit latrines for domestic waste. Only 10% of the studied pit latrines were lined. The filling rate in the study area is calculated to be about three years, and no respondents reported previous emptying. It is suggested pit latrine emptying technology development focuses on a maximum tool diameter of 10 cm to fit through the keyhole (squat hole) and height of 146 cm to fit inside the superstructure, as well as supporting unlined pits and the ability to pump trash. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/washdev.2017.096 s://iwaponline.com/washdev/article-pdf/7/1/151/386195/washdev0070151.pdf Rashid Chiposa Rochelle H. Holm (corresponding author) Centre of Excellence in Water and Sanitation, Mzuzu University, Private Bag 201, Mzuzu 2, Malawi E-mail: rochelle@rochelleholm.com Chimuleke Munthali Forestry Department, Mzuzu University, Private Bag 201, Mzuzu 2, Malawi Russel C. G. Chidya Department of Water Resources Management and Development, Mzuzu University, Private Bag 201, Mzuzu 2, Malawi Francis L. de los Reyes III Department of Civil, Construction and Environmental Engineering, North Carolina State University, Campus Box 7908, Raleigh, NC 27695, USA


INTRODUCTION
Many developing countries assumed they would follow the western example of sanitation (i.e., networked and waterbased), and it is only recently that on-site sanitation and fecal sludge management (FSM) are being considered as national approaches (Strande et al. ). Pit latrines are the most common on-site household sanitation facility used in many low-and middle-income countries, but managing accumulated fecal sludge (FS) from pit latrines requires plans for emptying, transportation, treatment, and safe enduse or disposal (Strande et al. ).
Many variables can affect pit latrine sludge, including environmental conditions and household practices, which impact the ability to pump the sludge during emptying operations. For example, household anal cleansing methods that are dominantly 'washing' versus 'wiping' would result in more water entering the pit latrine and impact the shear strength for pumping (Still & Foxon a, b). Additionally, tools for emptying must be able to physically access the pit latrine. While synthetic pit latrine sludge has been developed to assist in classifying emptying tool performance, there is limited in-situ work (Radford & Fenner  Pit latrine emptying tools must consider the latrine substructure and superstructure, environmental factors, household practices on use, and characteristics of FS. This study was undertaken in the city of Mzuzu, Malawi, to examine the characteristics of household pit latrines that must be considered when designing and selecting pit latrine emptying tools.

MATERIALS AND METHODS
This study was carried out in Area 1B, a peri-urban neighborhood in the city of Mzuzu, which is characterized by the Mzuzu City Council as a high density permanent residential area with no major industrial activities. There is an open-air market serving daily consumer demands, and several primary and secondary schools. All roads are earthen, characterized by potholes and gullies. The altitude ranges from 1,200 m to 1,370 m above sea level. Sandy clay soils are prevalent in the area. Piped municipal water supply is provided via in-home connections or community kiosks by the Northern Region Water Board, although there are also many shallow wells in the area (Mzuzu City Council ).
A total of 150 households, representing 30% of the neighborhood population, were purposively selected for this work in Area 1B based on the presence and usage of a household pit latrine. Purposive sampling was used due to the poor road network and general lack of maps for the area. A structured questionnaire was administered on household sanitation practices to the household head, including: religion, frequency of pit latrine use and type of domestic waste (greywater and trash) deposited in the pit latrine.
Field observations were also made of the surrounding area and of the pit latrine characteristics using a structured checklist, including keyhole (squat hole) and superstructure dimensions plus water table at nearby shallow wells (where available). Key informant interviews were also conducted.

Washers and wipers
All respondents (100%, n ¼ 150) in the study were reported to be Christians. Based on the prevailing custom in the area, it is likely that those who self-identified as Christians are wipers and do not use water for anal cleansing. These results

Sanitation projects
No households (n ¼ 150) reported that sanitation projects or education had previously been undertaken in the study area.
Further, no respondents (n ¼ 150) had ever had their pit latrine emptied.
In the study area, and other similar peri-urban areas of Mzuzu, manual pit emptiers are charging MK20,000/pit (USD$30) to shovel full pit latrines by hand and with illegal disposal. However, there are only two or three active manual pit emptiers in Mzuzu City. In addition, vacuum tankers, which can not access all roads in the neighborhood studied, for emptying FS in Mzuzu focus on septic tanks.
Alternatively, the cost for a household to hire a local sanitation business to install an improved, lined, pit latrine (inclusive of substructure, superstructure, labor, and materials) is MK335,000 (USD$500).

Pit latrine structure
Only basic pit latrines (with and without a cement slab) were found. There were no ventilated improved pits, composting, or pour flush latrines. All pit latrines in the study area had immovable superstructures, and none had an access hatch to the pit specifically for emptying operations external to the superstructure.
In the study area, pit emptying tools must enter through the keyhole, or the broken slab, but must also be able to fit within the footprint of the pit latrine superstructure. There was a general lack of standardization of the pit latrine Out of the 150 studied pit latrines, 15 were found to be lined. Pit depth ranged from 118 to 198 cm (mean 159 cm).
The pit diameter ranged from 51 to 110 cm (mean 80 cm).
As pit emptying is often limited to lined latrines due to the potential for collapse, only 10% of the latrines in the study area would be able to utilize most of the pit emptying tools currently available on the global market (Thye et al.

Environmental factors
The minimum water table in Area 1B was 15 m below ground surface (n ¼ 30 wells), which is below the depth of all studied pit latrines. Combined with the soil type and field observations in the study area, it is assumed that water content from the pit latrine is infiltrating into the surrounding soils.

Physical and chemical characteristics of FS
Our study is complementary to the penetrometer tests on 109 pit latrines in Kibera, Nairobi, Kenya, that investigated how FS varies with depth (Seal et al. ).
For our study, at 30 full pit latrines, penetrometer measurements were taken in advance of emptying operations. The manual penetrometer proved to be a useful tool to show variability in the FS with depth ( Figure 1).
However, penetrometer results did not cluster to show trends in FS characteristics that may be easier to empty, as anticipated, unemptiable pits were seen at all levels.
Although many factors can affect whether pit emptying operations are successful, in this study, sludge with similar penetrometer profiles did not necessarily perform equally.
As an example, some pits were not able to be emptied due to the high trash volume. Sludge in all cases would generally be classified as dry, and no watery layer was found at any depth. The technical challenge of emptying dry pit latrines is that technology such as the screw auger tool

CONCLUSIONS
Gathering household-specific data combined with environmental and chemical data provides a snapshot of the current situation of pit latrines in Mzuzu, Malawi, and the data can be used to optimize the selection of pit latrine emptying technologies. The pit latrine contents in the study area were characterized as dry, despite greywater being added by many households. It is also surprising that none of the pits had been emptied before, indicating there is both degradation and leaching occurring in the pit. It is suggested that pit latrine emptying technology development focuses on a maximum tool diameter of 10 cm to fit through the keyhole (squat hole) and height of 146 cm to fit inside the superstructure, as well as supporting unlined pits and the ability to pump trash. The following areas have been identified for further research: 1) understanding of pit latrine layers of varying resistance using a penetrometer; 2) in-situ FS laboratory analysis for total nitrogen (mg/L) and total suspended solids (mg/L); and 3) assessment of pit latrine characteristics in other areas of Malawi.