Characterisation of pit latrine sludge from shackleton, a peri-urban residential area of Zimbabwe

Theobjectiveof this studywas to characterise thephysical and chemical properties of human faecal sludge from various pit latrines in relation to the differences in usage andmanagement practices of each pit over time. Physico-chemical parameters were measured from the sludge collected from the top layers of six different pit latrines that were sampled six times at an interval of 40 days. Data were also collected on pit user habits andmanagement practices. Multivariate statistical analyses were carried out to determine the variations in sludge physico-chemical characteristics among the pits and the associations between these anduser habits andmanagement practices. The results showed that the sludge characteristics from the six pits were significantly different from each other (global test sample statistic (R): 0.862 and p< 0.002). This study also indicated that user habits were important determinants of pit sludge characteristics. This study scientifically contributes to knowledge on how pit management and usage practices determine the potential value and quality of pit latrine sludge for various anaerobic digestion applications for resource recovery. The findings also contribute the knowledge required for the management and treatment of pit latrine sludge, adoption and adaptation of new treatment technologies for local use. 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.2018.041 om http://iwaponline.com/washdev/article-pdf/8/3/568/484319/washdev0080568.pdf er 2021 M. C. Changara (corresponding author) Department of Environmental Science and Technology, Chinhoyi University of Technology, P.O. Box 7724, Chinhoyi, Zimbabwe E-mail: chrischangara@gmail.com C. Bangira Department of Agricultural Engineering, Chinhoyi University of Technology, P.O. Box 7724, Chinhoyi, Zimbabwe W. T. Sanyika Department of Biotechnology, Chinhoyi University of Technology, P.O. Box 7724, Chinhoyi, Zimbabwe S. N. Misi Department of Civil Engineering, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe

INTRODUCTION different sites which can be costly and, subsequently, the need for disposal of pit latrine contents once full.
One typical area that uses pit latrines in Zimbabwe is Shackleton in Chinhoyi, Mashonaland West Province, which was once a mining and smelting settlement for gold and copper.
During the mining era, workers used centralised sanitation facilities which are now derelict due to lack of maintenance.
The mine was closed due to operational challenges leading to loss of jobs for the majority of people. Former workers' houses were abandoned. When there was an outbreak of cholera in the Tombstone and Bere peri-urban areas of Chinhoyi in the year 2000, families were relocated to Shackleton by the government to occupy the former mine workers' houses.
Currently, Shackleton is a low income community with an average of eight adults (above 16 years) per household. Most residents do not have formal employment but depend on part-time work at nearby farms for survival. There is also another group which depends on illegal mining in areas around Shackleton.
In order to improve sanitation in Shackleton, the current residents have constructed different types of pit latrines ( Figure 1).
Periodically, pits fill up and due to the limited sizes of the residential dwellings (<200 m 2 ) residents often find it challenging to look for an alternative space to construct new ones. There are also no provisions for a pit-emptying system in Shackleton.
Given that pit latrines will at some stage fill up and become a hazard to human health and the environment, a management system is required for the collection, transport, treatment, end use, and disposal of the faecal sludge from onsite systems (Bassan et al. ). The design, collection, transportation, treatment, end use and disposal of the faecal sludge from onsite systems requires accurate data on faecal sludge characteristics to properly size and select treatment technologies and operational parameters (Bassan et al. ). A number of previous studies have been done to characterise the physical and chemical characteristics of sludge from various pit latrines over space (Bakare et al. ; Gudda et al. ) and time (Bassan et al. ). These studies indicated that the characterisation of pit latrine sludge varies according to site and depth, characterisation over time showed that the characteristics were highly variable during both the dry or rainy seasons, and this high variability resulted in similar characteristics for faecal sludge collected during the dry and rainy seasons.
The characteristics of faecal sludge also depend on the design and construction of the sanitation technology and how the technology is used. All of these variables may result in significant differences in faecal sludge characteristics (Niwagaba et al. ). Due to this variability, it is important to consider the effect of local pit management practices, construction and user habits on the characteristics of pit latrine sludge.
Despite being the main onsite faecal management technology in rural and peri-urban settlements in Zimbabwe, there is limited detailed information on the characteristics of pit latrine sludge, which is important for making decisions on the design or adoption of a technology for local use in management of pit latrine sludge. The relationships between user habits and some physico-chemical properties of pit latrine sludge can also help in the management and treatment of pit latrine sludge. This research was conducted to determine the physical and chemical characteristics of sludge in selected pit latrines and to establish the relationships between those characteristics, user habits and pit latrine management over time.

Study site
The study site is Shackelton (30.03 E and 17.30 S), which is located in Chinhoyi, Zimbabwe at an altitude of about 1,160 m ( Figure 2). Shackleton was selected because most of the residents in this area use pit latrines as sanitation facilities. The average annual temperature and rainfall for Shackleton are 20 C and 800 mm, respectively. The geology of the area consists of dolomitic limestone which overlies light brown clayey soils.

Sampling procedures
Samples were collected from six pit latrines: three covered with thatching grass and the other three covered with tents in Shackleton during the period February to October 2016. Sampling was conducted six times on each pit at 40-day intervals and each sample was collected in triplicate from the topmost contents of the pit. Purposive sampling was used in this study whereby pits that were almost full (about 40-60 cm pit to contents depth), with at least eight users and of similar age (in terms of period of start use) and depth were targeted (1.2-1.7 m).
Shackleton is divided into three sections: A, B and C. Section A ( Figure 2) is relatively highly populated with at least ten people per household who use pit latrines only as sanitation facilities. Sections B and C use a mixture of pit latrines and other types of toilets. Out of the 170 households in area A, 130 use pit latrines and of these 130, 60 met the selection criteria and 10% of these 60 were randomly selected and used as a sample. Sampling was conducted using a modified auger ( Figure 3) which was graduated to show sampling depth.
Sampling in the pit was through a squat hole (Figure 4(a)) and the sludge was collected in a plastic bucket (Figure 4(b)) before being placed in polythene bottles. Only pit latrine users who were willing to take part in the research were considered, after seeking informed consent. Data were collected on number of pit latrine users, diet, material added to pit latrines, anal cleansing material and pit management practices using a template (Table A1,  available with the online version of this paper) at each stage of sampling. In addition, information was collected on the details of pit construction. The data on diets taken by users and user habits were coded into numerical categories using presence/absence data for data analysis.  The SIMPER analysis was used to identify the variables that characterised each cluster (based on similarities) and also those variables that discriminated between each pair of clusters (based on major differences). The variables TS, VS, COD, K and Ca contributed the most to within cluster similarity in all clusters while pH, P, Mg and Na contributed the most to the within cluster variability. COD, TS, VS, N and P were the important contributors to the between group dissimilarity.

Sources of variability in the pit latrine sludge
Using PCA analysis, the first, second and third principal components accounted for 31.5%, 22.3% (Figures 7 and 8) and 15.3% of the variation in the data set, respectively. The sludge from pit 4 (cluster 3) was characterised by high levels of TS, COD, VS and BOD and pits 1 and 2 (cluster 1) had high levels of P, Na and N. The sludge from pits 3, 5 and 6 (clusters 2 and 4) had high levels of Ca, K and Mg (Figures 7 and 8).
Association between user habits, pit management and sludge characteristics CCA was used to determine the relationships between the physicochemical characteristics of the pit latrine sludge and user habits. The high COD, BOD, TS and VS in pit 4 was associated with the use of newspapers and shelled maize cobs for anal cleansing. This pit also had a tent covering around the pit. The high levels of N and P in pits 1 and 2 were associated with the use of extraneous material such as kitchen waste. These pits were covered with thatching grass with some of the thatching grass falling in the pit. The high concentrations of Mg, Ca and K in pits 5 and 6 were associated with the addition of ash in the pits (Figure 9). Wood ash   has been reported to be a major source of alkalinity, and is composed of macronutrients Ca, K, Mg and P.

Relationship between diet and environmental characteristics
According to Rose et al. (), human diet is also a factor that can impact the composition of faeces. In this study, we could not establish conclusive associations between diet and sludge characteristics.
Our analysis when considering descriptive data of the physico-chemical properties showed that the sludge from all the pit latrines (1-6) had high strength properties (Table A2, available with the online version of this paper) according to standard classification of sludge samples (Strauss et al. ). This property could be explained by the fact that samples were from pit latrines without connection to water sources, thus resulting in high strength sludge.
Biodegradability potential of the pit latrine sludge is relatively high in half of the pits (pits 4-6) and relatively low in pits 1 to 3 as indicated by a BOD:COD ratio closer to 3 and greater than 3, respectively (Table A2). The pit latrine sludge of pits 4 to 6 was highly biodegradable, indicating potential treatment and resource recovery from the pit latrine sludge through processes such as anaerobic digestion. The low biodegradability of pits 1 to 3 could be because of the addition of other solid waste, such as kitchen waste, which is shown to be added by the pit latrine users of pits 1 to 3 ( Figure 9). Gudda et al. () stated that household disposal of solid waste into the pit latrine vaults lowers biodegradability of faecal sludge by increasing organic load.
The BOD values of the sludge characterised from pits 1 to 6 (Table A2)   In recent years, pit latrine faecal sludge has been gaining recognition as an important resource for bioenergy generation by poor communities and the by-product has been found to have potential use as a fertiliser and soil conditioner. The assessment carried out in this study contributes to the assessment of the sludge quality for such applications because it enables comparison and standardisation of the data on sludge from different regions. Such knowledge can be useful for informing technology development including supplementation of substrates for optimisation of sludge treatment.

CONCLUSIONS
In this study we have shown that within a given site every pit latrine is unique in its physico-chemical properties and maintains specific characteristics that distinguish it from other pits over time due to the consistency in user habits and pit management practices. The values of the sludge physico-chemical characteristics (N, P, COD, VS and BOD) reported in this study were generally high as compared to those reported in other geographic regions. The pit latrine faecal sludge showed potential biodegradability with processes such as anaerobic digestion and contains nutrients that can potentially be useful for crop production. However, there is a need to explore appropriate onsite treatment technologies prior to resource recovery for agricultural reuse and disposal into the environment to reduce potential for pollution.