In support of the Millennium Development Goals to provide improved sanitation to the world, a sustainability-inspired composting latrine design based on work in rural Panama, but also applicable to similar situations, is offered here. The design is based on the three aspects of sustainability namely economic, social, and technical. The new design will allow for improved health for current and future generations. The design is less costly (economic), is based on concepts to improve the likelihood of use based on interviews with potential users (social), and provides better quality compost through ammonia-based treatment (technical). The design consists of two ferrocement compost vaults to save money over conventional vaults, urine storage tanks to improve ammonia conditions in the compost, urine control valves for urine control, a water-washing bidet for personal washing (as preferred by the users), and a handwashing station within the latrine superstructure for convenience.

According to the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF), 842,000 deaths could be prevented annually by improving water, sanitation, and hygiene (WASH). This is despite the final progress report on the Millennium Development Goals (MDGs) by the WHO/UNICEF Joint Monitoring Programme (JMP) stating that 91% of the world's population has access to an improved water source. This disparity stems from the sanitation situation that 2.4 billion people who have no access to improved sanitation facilities (ISFs).

An ISF is defined by the WHO as (a) not being shared among households and (b) able to ‘hygienically separate human excreta from human contact’ (WHO 2014; Exley et al. 2015). This is in contrast to unimproved sanitation facilities, which include the absence of any facility at all, as is the case for 946 million people who practice open defecation worldwide (JMP 2015). Current ISFs include pit latrines, pour-flush latrines, and the focus of this work, composting latrines (CLs) (Exley et al. 2015). The JMP has developed the ‘sanitation ladder’ hierarchy for sanitation technologies that include open defecation on the bottom ‘rung’ and ISFs like flush toilets connected to sewerage on the top rung (Kvarnström et al. 2011).

### Latrine cost

Cost of the compost vaults slab can be reduced by using ferrocement. Ferrocement is common in developing countries and uses light-gage wire as reinforcement instead of steel rebar and is, therefore, less expensive than reinforced concrete. The cement portion refers to the 1:2 or 1:3 cement-to-sand mortar that is plastered over the reinforcing steel. These ratios must be prescribed by weight rather than volume for optimal performance and differ depending on cement origin and fabricator. Ferrocement calls for a workable mortar consistency for application, yet the water-to-cement ratio must be as low as possible for the best strength conditions. Although not the focus of the current study, thicker walls for insulation or applying a dark material to the outside of the ferrocement could improve the mechanisms described for pathogen inactivation in CLs and in ammonia-based sanitation (ABS). Ferrocement construction can be less expensive than masonry block walls due to the ease of construction not requiring skilled labor.

### Latrine user acceptability

Despite the proposed benefits gained through improved sanitation interventions – including those involving CLs – there still exist sizeable issues aside from the aforementioned technical ones. Latrine use has much more to do with other barriers like convenience, comfort, privacy and safety (Jenkins & Scott 2007). The governments of developing countries may have some moral obligation to aid in the elimination of open defecation through pit latrines and other methods as well (Mara 2017). Odor control is also of concern (Hashemi & Han 2017).

### Ammonia-based sanitation in composting latrines

ABS consists of the addition of ammonia (in the form of urine) to the feces in the latrine pit to help in the biodegradation and feces sanitation process. As of yet, ABS has not been applied to large-scale sanitation interventions and has only been studied in laboratory studies (Nordin et al. 2009; Fidjeland 2015). ABS depends on the presence of uncharged or un-ionized molecules, NH3, to create a toxic environment for microorganisms or, for these purposes, pathogens through the disintegration of the protein membrane of the cell wall. The NH3 molecule has the freedom to travel between this membrane and alkaline properties might raise the internal pH and cause this cell disintegration. This has an added benefit to biosolids or compost in that the process does not consume ammonia, but rather increases its nutrient potential (Nordin et al. 2009; Fidjeland 2015).

### Goals of the research

The goal of this research is to find a sustainability-inspired CL design through ‘economic’ (the use of less expensive ferrocement instead of block vaults), ‘technical’ (the use of ABS through the addition of urine and ash), and ‘social’ (the incorporation of users’ preferences for washing) aspects. The combination of economic, technical, and social aspects are the definition of sustainability used here.

### Compost degradation testing using ammonia-based treatment

Data showing the biweekly temperature, pH, ash%, moisture content, un-ionized and total ammonia and calculated inactivation time calculated from Fidjeland (2015) were collected (Kierys 2016). Certain findings were consistent with the literature, such as the fact that the groups that received more alkaline amendment (ash) produced more basic (pH <7) readings. An unforeseen outcome was that the group receiving the most ash by volume of compost only slightly outperformed the other less-alkaline groups, especially the control group that was un-amended. This group averaged a pH of 9.77, the highest of all the groups, but had an average uncharged ammonia concentration of 348 mg-NH3-N/L, not far from the intrinsic uncharged ammonia found in the control group. Uncharged ammonia concentration is positively correlated with Ascaris ova inactivation (Trimmer 2015).

The discrepancy between the pH and corresponding NH3 values in the group with 75% ash could be explained by the lack of mixing and the resulting moisture content upon ash amendment. Perhaps the combination of a lowered moisture content and heterogeneous distribution of aqueous NH3 produced a highly volatile concentration and inhibited movement of hydroxide ions (Nordin et al. 2009). The ammonia production performance of the group consisting of compost and urine was the highest after 12 weeks.

These findings suggest that for ABS treatment a lack of a desiccant or cover material is not inhibitory as is the case for both composting and alkaline desiccation – two widely used EcoSan methods. Sawdust availability is dependent on the success of sawyers and on an optimistic rate of deforestation. Ash is less widely found due to the change towards the use of propane and improved cooking stoves in light of the correlated effects open fires have on pulmonary disease and also the former phenomenon of deforestation that causes families to search for wood further and further away. If neither process can explicitly improve health outcomes or even be found to eliminate pathogens or the vector from human excreta then more commonly-available and practical dry materials such as grass should be promoted to diminish smells and create a biological barrier to fend off vectors.

Testing was performed using microscopy at a local clinic laboratory. The clinic performs routine stool sample analysis and for this reason, viability or log reduction determination was not possible. Thus, the initial samples showed either the presence or absence of Ascaris ova. Samples taken at the end of the 12-week experimental period showed that only five of the 12 treatment matrices had no presence of viable Ascaris ova.

As the data imply, there is not an obvious correlation that could be drawn between ammonia concentration and pathogen inactivation. There are several matrices that outperformed or were in line with their more successful counterparts, only to yield a positive reading. Most notably, Matrix B5, which had readings near the absolute bottom of the groups, yet was still able to provide inactivation. Matrix temperature was found to correlate to ambient temperature and result in the highest uncharged ammonia concentration at approximately 30.5 °C (Kierys 2016).

### Ethnographic research

The answers to the survey questions generally revealed a positive opinion of CLs (Table 1). More details are given in Kierys (2016).

Table 1

Ethnographic survey summary of CL design-affecting responses (Kierys 2016)

QuestionResponse summary
Why don't others have CLs? High expense
Problems? Lack of sawdust as a desiccant
Inaccessibility of toilet paper
Want water washing bidet
Feelings towards urine use for ABS Willing to do more to operate urine valves if the compost was degraded faster
QuestionResponse summary
Why don't others have CLs? High expense
Problems? Lack of sawdust as a desiccant
Inaccessibility of toilet paper
Want water washing bidet
Feelings towards urine use for ABS Willing to do more to operate urine valves if the compost was degraded faster

### Applicability to other cultures

While this ABS design should be applicable to most developing-world cultures, estimating building costs and surveying the potential users as to their preferences will increase the likelihood of successful use.

### Sustainability-inspired CL design

The objectives of the study were accomplished since a sustainability-based CL was realized. Based on the results of the cost (less-expensive ferrocement), technical (ABS experiments showing successful contaminant removal), and social (ethnographic survey giving washing preferences) noted above, the sustainability-based CL should be employed (Figure 1). The design consists of two ferrocement compost vaults to save money over conventional vaults, urine storage tanks to improve ammonia conditions in the compost, urine control valves for urine control, a water-washing bidet for personal washing (as preferred by the users), and a hand-washing station within the latrine superstructure for convenience.
Figure 1

Conceptual model of ABS latrine design (the ABS is fully enclosed even though the walls and door are not shown here).

Figure 1

Conceptual model of ABS latrine design (the ABS is fully enclosed even though the walls and door are not shown here).

Close modal

The operation of the latrine would be identical to that of a traditional CL in terms of urine diversion, avoiding the entry of water, and proper desiccant use. However, every three months, the tank would have to be sealed and become a reactor for the ABS process to begin. Two valves control the influent urine from entering the vault, but once urine does enter the urease in the compost will begin ureolysis and the second vault would have to be primed with desiccant and begin being used. Once another three months has passed, another valve controlling the effluent of the reactor would have to be opened to drain and release the leachate, preferably into a soak pit. The disposal of this nitrogen-rich effluent is key to not making ABS another contributor to eutrophication and other environmentally-detrimental anthropogenic actions. Next, the false floor would be raised and the tank unsealed after several hours to allow the residual ammonia gas to disperse before the compost is shoveled off for agricultural use. Also, 3.81 cm PVC pipes were used to avoid clogging. There must be a gap between the house superstructure and the top of the ferrocement compost vaults to avoid any vault collapse. Urine diverting cups are used inside the toilet. Both toilets drain into a common urine storage tank located in between the two toilets. Only one urine storage tank is needed since only one toilet is used at a time. The feces go into the ferrocement compost vault. The urine should drain out through the effluent release, after which the compost would be harvested by shovel from the top of the vault for use as fertilizer. The ferrocement compost vaults were each designed for the collection of six months' worth of feces for the number of users desired, or approximately 1,136 L. Other CL details are given in Mihelcic et al. (2009). Urine scale formation is not a problem on the smooth walls of the PVC pipe specified here, but could be in the ferrocement compost vaults. Therefore, periodic clearing of any deposits is recommended. The durability and robustness of the proposed design is comparable to the traditional CL. In addition, the ABS odor was deemed by the authors and villagers to be no worse than the traditional CL.

This research was carried out as part of the Peace Corps Masters International Program.

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