Pit latrine fill-up rates: variation determinants and public health implications in informal settlements, Nakuru-Kenya

Table 1 and Table 2 present a summary of the findings. Table 1 describes the demographic characteristics of all the study respondents. Most of the respondents (63%) were female, because they were at home during the field visits. In addition, the highest proportion of the sampled age group ranged from 51 to 60 years, composition of the group was mainly the property owners. Only 1% of the respondents were uneducated and the highest proportion (37%) had primary level (basic) education. The majority (33%) of the respondents had an income ranging between 101 and 300 USD as illustrated in Table 1.

Table 2 describes the structural design of the pit latrines with a focus on factors that determine sharing (compartments) and cleanliness maintenance (slabs). All the pit latrines had iron sheet roofs and superstructure for privacy. It also describes the extent of sharing by individuals and across families.

The majority of the pit latrines (31%) had two doors leading into two compartments. The median use period was 15 years. However, it was noticed that 17% have been in operation for over 26 years without getting full. All the pit latrines were shared and the largest proportion (47%), were being shared by 6 to 15 families. The number of individuals sharing a pit latrine ranged from 4 to 56 people with a median of 23 individuals.

Anal cleansing materials varied with the largest proportion of households (47%) using tissue paper. As the study progressed, it was observed that household’s use of tissue paper increased with almost double proportions from 34 to 65% (Table 3). The type of anal cleansing materials does not only determine personal hygiene, but also affect sludge accumulation rates as some are slow degrading and others are non-degradable. Families provide the highest proportion of slab cleaning services (51%). Table 3 shows an increase in slab cleaning operation with every sampling episode. Observation of the vault and slab showed that 61% of the facilities had visible solid wastes (Fig. 2a and b). The materials included; polythene, papers, cardboard, diapers, clothes, plant leaves, plastic and glass bottles. Materials such as sanitary pads and diapers are purposefully disposed into the vaults whereas regular household wastes like papers and food remains are randomly disposed into the vaults.

Sanitation awareness is defined as the state of having been provided with information on the importance of pit latrine maintenance and the need for proper faecal matter disposal. The question was to document whether at any duration since they started using the facility, they had received any related information. The household survey showed that 45% of the residents had not received any form of sanitation maintenance awareness. Awareness creation varied and the government was cited as the most common awareness provider (21%) especially when inspecting facilities and during disease outbreaks. Other stakeholders who intermittently, provided sanitation related information included public health officials (15%), community based organizations and non-governmental organizations (8%), property owners (9%), volunteers and residents both accounted for 1%. The main facility cleanliness maintenance activity was slab washing or sweeping. Sixty-four percent of the respondents had regular unit cleaning schedules, whereas 36% did not have such programs. Regular unit cleaning schedules meant that users of a facility had personnel responsible for offering facility cleaning services within planned intervals of execution. The largest (51%) proportion of facility floor cleaning services was offered by families and the least (2%) proportion offered by workers.

Sludge accumulation for the study period ranged from − 98 to 10,320 l and mean accumulation for all the pit latrines was 870 l. Accumulation varied within and across the study locations with Kaptembwo having highest and Njokerio recording the lowest rates (Table 4 & Fig. 3). Fill-up rates differed across the latrines with some recording accumulation increase while others had volume decreases as shown in Fig. 3.

The accumulation contribution per person ranged from 11.69 to 135.51 l per person per year, with a mean of 41.82 l per person annually (l/p/yr.). Noticeable is the high individual contributions reported in Kaptembwo (Table 4). The rates are relatively higher and could be explained by the documented disposal of wastes into the pit latrines within the area. The survey reported that solid waste and grey-water are disposed into the pit vaults. Figure 4 shows the mean and standard error bars of accumulation per location.

Longitudinal analysis on pooled data for the sites in each location indicated significant variability in the annual mean fill-up rates (m³ year^− 1) across the five locations over the five sampling episodes (1-way ANOVA, F_4,1089 = 14.80; p = 0.000). Confirmatory post-hoc Fisher’s exact test isolated Kaptembwo to record the highest annual fill-up rate 2.16 (±2.71) m³ year^− 1. Hilton was significantly lower than Kaptembwo but higher than Free Area and Jewadhu in the fill-up rate per year. The lowest rate was observed in Njokerio with a mean rate of 0.01 (±0.64) m³ year^− 1. The area which documented significantly higher fill-up rates had the highest rate of solid waste (70.83%) and grey-water (50%) disposal into the pit latrines. Therefore, the variations in user activities as documented by the survey justify the differences in fill-up rates of pit latrine within and across the study locations.

Sludge accumulation trends within and across locations varied with each of the 5 sampling episodes. All the sampled pit latrines within a location showed erratic individual sludge contribution trends. Figure 5 shows the mean analysis of accumulation contribution per person over the study duration and the average sludge accumulation per site across the 5 sampling areas.

Most of the respondents had attained primary education, an indication that they had basic education. The economic income of most of the respondents was relatively low (<USD300), given the extent of dependants within the households in the settlement. The findings are in congruence with results documented in 2013 by the Kenya Institute of Public Policy and Research Analysis (KIPPRA), explaining that low-income settlements are characterised by poor people who are likely to have low levels of education [24]. The majority of the inhabitants having a primary level of education are associated with low paying jobs, hence contributing to higher poverty levels. These characteristics would result in people constructing or using low-cost on-site sanitation services.

The studied units were simple pit latrines. Design and construction of the facilities had no plans regarding the numbers of use years and post fill-up management programs. Large proportions of the latrines are in locations that are inaccessible to emptying trucks. This necessitates emptying through manual methods (shovels, buckets, and spades) posing a health risk to emptying personnel, environment, and creating public health nuisance [17, 25‐27]. Emptying would be faster and relatively cheaper as compared to abandoning a facility once full and constructing a new one. Such decisions have lower cost benefits in terms of resource allocation and encouraging open defaecation. According Eawag, an emptying cycle in Nairobi costs up to $130 [28], whereas construction of a new facility is approximately $430 [29]. Almost similar findings were reported in Dar es salaam that the cost of emptying was about $35 whereas constructing a new facility would be up-to 5 times higher [30]. Therefore, the cost-benefit of emptying contents is higher than the construction of new facilities [31, 32]. However, the scenarios within the study areas show that upon fill-up, pit latrines were either abandoned or decommissioned. Policies on the minimum acceptable shared pit latrine standards and operational management would provide significant impetus towards achieving the SDGs goals on sanitation and meeting the JMP standards [31, 33]. Highly-variable simple pit latrine designs are a major feature observed in many developing countries such as Kampala [34]. Provision of pit latrines without consideration of social, cultural, behavioural and gender aspects of sanitation facilities contribute to non-satisfactory services [35‐37]. Generally, post fill-up emptying and management is not factored at design stages.

Single compartment latrines shared by more than one family do not only put pressure on facility use, but also limit basic sanitation maintenance. Such facilities significantly negate privacy and dignity of users, as people have to queue or wait outside as others use. Culturally, defaecation is viewed as a private affair; therefore, cases where one has to wait for his turn to use a facility greatly infringes on individuals psychosocial wellbeing. Building single compartment latrines could be attributed to the limited space and economic constraints within peri-urban low-income settlements [14, 33]. However, housing pressure associated with large population prioritizes housing settlements without factoring sanitation facilities. Nonstandard structural design and construction materials significantly affect hygiene and cleanliness of facilities, hence reduce sanitation quality. The case in Kenya is contrary to other countries in Africa with a minimum acceptable standard for a sanitation facility; South Africa (VIP latrine), Malawi (Blair VIP latrine) and Botswana (Double Vaulted VIP latrine). Kenya has no infrastructure designs on acceptable basic pit latrine standards [38]. It adopted a WHO task force recommendation of VIP latrine standards which have not been publicised leading to limited stakeholder awareness [34]. Therefore, the owners’ socioeconomic status widely determines the design of the facilities, a fact that resonates with other findings in most urban settlements of developing countries [39]. There is a need to actualize the designs of the latrines, create awareness programs supporting their development and support the minimum acceptable shared pit latrine designs.

The median number of people sharing a latrine was 23. It is higher compared to the numbers (10 people) reported in Kampala [40]. However, it is lower compared to those reported in Kibera, Kenya as 150 people per pit latrine according to the UN-World Bank report in 1997. When more families are sharing then it could influence people to resort to open defecation especially when there are long queues during peak periods of facility use (early morning and night). The JMP (2015) defined unimproved sanitation as a pit latrine without a slab, flush or pour flush to elsewhere, bucket, hanging latrine, shared sanitation or no facility [41]. None of the studied facilities met the WHO standards on improved sanitation. Case studies conducted in Kibera and informal settlements of Kisumu, Kenya have confirmed that shared facilities are appropriate sanitation provision options in high population settlements [38, 39]. The findings of this study suggest that shared facilities play an important role in sanitation service delivery to residents of low-income settlements [22, 26, 34]. This information concurs with a study in Kampala, which reported that informal settlements populations far exceed the sanitation infrastructure capacity hence communally shared facilities are common [42].

High urbanization rates in the low-income settlements lead to increased waste generation [43]. Solid and liquid waste handling services are relatively insufficient, because local authorities do not provide the services, but have contracted refuse collection to private handlers. These have associated costs; hence residents opt for disposal into pit latrine vaults or the environment. Grey-water disposal facilities are not provided and end up being discarded in the environment with a large proportion poured into the pit latrines. Water disposal affects sludge moisture content and gaseous balance, therefore, interfering with aerobic and anaerobic degradation processes [44]. Pit latrines and the environment form part of the alternative point of waste disposal in these areas. Similar inefficient wastes handling in similar settlements have been reported in many regions of the world, including Blantyre [45], Kolkata [46] and EThekwini Municipality [47].

Households in the study area showed little attention and emphasis to provision of anal cleansing materials inside a facility. Similar findings indicating significantly low emphasis and high ignorance on the importance of anal cleansing materials in the WASH provision have been reported in previous studies [48‐51]. Lack of anal cleansing materials affects personal hygiene and has a strong association with faecal contamination and disease spread [52]. In addition, use of solids and slow degrading solids for anal cleansing contributes to high organic load and encourage faster accumulation [4]. When on-site facilities fill-up faster, they lead to the management burden of either emptying or building a new pit latrine, health risks, and occupational hazards associated with sludge disposal [53]. In addition, menstrual products adversely affect fill-up rates in cases where sanitary pads are disposed in the pit latrines [54].

To achieve maximum performance of sanitation facilities, there is a need of linking hardware (structural design and technology) and software (hygiene practices, policy, and education) components [52, 55]. However, in this case there is limited provision of the necessary information, yet education and awareness are important in the primary health provision. Although knowledge and awareness should be provided to the design and construction personnel on most appropriate facilities and to users on management and operations of the facilities, there is no such evidence. Awareness would provide an informed decision, hence better services and enhanced facility performance. A large proportion of household had not yet received sanitation awareness and this could explain the reported low levels of facility cleanliness maintenance and cases of solid waste disposal into the vaults [56]. The willingness to pay for sanitation maintenance services may present constraints due to the general low-income [18, 23].

Results from this study indicate that if economically sustainable services and public health protection is to be attained, then these issues which directly affect user operations must form the basis of policy recommendations. Further noted in this study is that the designs must factor the extent of sharing and operational management. Other activities such as waste disposal and the inconsistent number of users would not support long term and safe delivery. However, when the users’ operational characteristics are factored at design stage, then decisions linking information and structural components would lead to improved sanitation delivery.

The mean sludge accumulation rates of 41.84 l/p/yr. were relatively moderate compared to the WHO recommendation of 40 to 60 l/p/yr. and up to 90 l/p/yr. where dry cleansing materials are used. The accumulation was within the range reported by WHO in the 1950s indicating a mean annual fill-up of 40 l in dry pit latrines characterised by solid materials and other waste disposals [57]. However, they are lower than data from Brazil [58] and Besters camp South Africa that documented an average of 90 and 69.4 l/p/yr. [25]. On the contrary, studies in South Africa reported relatively lower accumulation rates of 24 l/p/yr., but indicated a 50% increase in cases where solid wastes are thrown into the vault [59]. The fill-up rate documented in this study indicates that a pit latrine of 2.5 m³ would serve up to five people for 12 years. These rates can be used for designing vault sizes applicable for specific populations. Further, modelling of such ratios would inform programs of vault emptying cycles. The survey data showing individual contribution can be used alongside modelled accumulation rates to design specific use period.

Significant differences in fill-up rates can be attributed to the differences in the user practices and management activities as presented in the survey. User practices account for the characteristics and make up of faeces that determine degradation of the faecal sludge [9]. Varying geographical locations and socioeconomic incomes may have contributed to the variations. In addition, solid and liquid wastes have a potential of suppressing content degradation and encouraging vault content accumulation. The varying household practices across the study areas as reported in the survey justify the differences in fill-up and performance of the pit latrines. The variations in fill-up of pit latrines across these study areas are consistent with previous studies [40].

The findings of this research give evidence of the importance of both user operational management and structural components of pit latrines in determining pit latrine service duration. To increase pit latrine performance and efficiency, then the design of vault sizes must be justified by the intended number of users and use duration [60‐63]. Moreover, all the stakeholders have to be educated and provided with appropriate information supporting various stages of sanitation service delivery from facility design, operational phase and post fill-up management. If the stages are handled in isolation, then the sanitation outcome may not be beneficial to users, property owners and the environment. Linking information and awareness regarding appropriate facility development and operations would contribute the progress in sanitation ladder [56, 64, 65]. Such measures would ensure efficient, economically viable and sustainable pit latrines hence protection of public health and the environment.

This study was designed to factor variation in seasons. However, the country experienced a drought hence there were no significant variation in rainfall volumes across the months of the study. However, it would be possible to have different fill-up rates in the rainy and dry seasons. The findings of the study are applicable within the context of Kenya and other low-income settlements within the sub-Saharan Africa. Moreover, these findings can form a basis for comparison studies in other low-income settlements. Facility physical environment was not investigated hence future studies ought to establish soil permeability around each pit latrine and possible sinking of true bottom.