16. Reimagining Excreta as a Resource: Recovering Nitrogen from Urine in Nairobi, Kenya

Like many Development Engineering efforts, the process of defining our problem was iterative and time-consuming. Based on the team’s expertise, we approached the problem primarily from the motivation of increasing access to sanitation. We hypothesized that recovering valuable products from excreta could generate revenue for sanitation service providers. While we started with the technical aspects of designing recovery processes, we also had to consider the market viability of the recovered products, which involved another value chain, agricultural inputs, including fertilizers. Because our innovations could affect two dire needs in Kenya (access to sanitation and access to fertilizer), we spent considerable time talking with partners and subject matter experts to situate our project among the many stakeholders involved. We also constructed business model canvases and theories of change for both sanitation and fertilizer (see Sect. 3). As can be seen from our project timeline, we focused first on sanitation, then added agriculture, and then refined our vision at the nexus of both problems among partners in both sectors.

Our work on resource-oriented sanitation was motivated by two increasingly recognized theories: the circular economy and resource recovery from wastewater. For decades, fecal matter has been repurposed as compost, energy, and even irrigation water. Recently, efforts have intensified to recover additional valuable products from excreta, including microbial protein products (Calvert, 1979), building materials (Diener et al., 2014; Mohajerani et al., 2019), cooking charcoal (Ohm et al., 2013), and disinfectants (Huang et al., 2016). This resource recovery perspective aims to extract all possible value from waste before disposal. Most recently, a US National Academies of Engineering report identified one of the major twenty first-century environmental engineering challenges as “designing a future without pollution and waste” (Board and National Academies of Sciences 2019). Several of these extracted products intersect with other critical industries, including agriculture and energy storage. Another one of these five grand challenges is “sustainably supplying food, water, and energy”; resource recovery may play a major goal in realizing this vision over the next several decades.

More broadly, the circular economy re-envisions current linear, extract-and-emit chemical manufacturing as loops that use every molecule as many times as possible before disposal (Fig. 16.2). With this perspective, waste streams of all kinds, including excreta, should be maximally repurposed into useful products (Geissdoerfer et al., 2017). The circular economy perspective is a broader instantiation of resource recovery and can apply to gaseous carbon dioxide emissions (Amouroux et al., 2016), solid domestic waste (Tisserant et al., 2017), and consumer products (Singh & Ordoñez, 2016). The circular economy concept in sanitation is well-recognized and regularly discussed at conferences like the Fecal Sludge Management Conference and the International Water Association Conference on Resource-Oriented Sanitation. Recently, the concept has been synthesized as the Circular Sanitation Economy by the Toilet Board Coalition, a network of multinational industries in sanitation provision (Toilet Board Coalition, 2016).

While our academic focus on converting excreta into valuable products embodies resource recovery and a circular economy, our approach was also radically informed by observations in resource-constrained communities. By the ElectroSan team’s estimation in 2012–2013, resource recovery tended to focus on combined wastewater (urine and feces) most, followed by separately collected feces and urine as a distant third. From our informal review of resource-oriented toilet systems, the major motivation for separately collecting feces was to reduce water content by removing urine, which enhances composting and drying techniques. We observed that urine was underutilized, in part because of its large volume and high water content (Kvarnström et al., 2006), which would lead to high transport costs. Once we decided to concentrate our efforts on urine, we considered several possible recovered products. The most established product to recover from urine is struvite, or magnesium ammonium phosphate (MgNH₄PO₄∙6H₂O), a phosphate-rich fertilizer (NPK mass ratio 6:29:0). Urine contains the majority of macronutrients in excreta (80% N, 50% P, 60% K), making it an ideal stream from which fertilizer nutrients can be concentrated (Larsen & Gujer, 1996). At the time, we observed that urine efforts were more focused on phosphorus than nitrogen; thus, we concentrated our efforts on recovering nitrogen from urine. In addition to being understudied, nitrogen is the primary parameter by which fertilizer application rates are determined; furthermore, nitrogen recovery from excreta could benefit the global nitrogen cycle, which humans have severely imbalanced due to synthetic fertilizer production (Galloway et al., 2008). Ultimately, recovering nitrogen from urine was an untapped opportunity for recovery of valuable products from excreta.

After reviewing existing methods for nitrogen recovery from wastewater in practice and in academic literature, ElectroSan developed two technological solutions to achieve selective separations: ion exchange and electrochemical stripping. Ion exchange and electrochemistry were first identified as methods with untapped potential for selective nitrogen recovery; within those two areas, we iterated ideas over several months. Throughout this chapter, we focus primarily on ion exchange, as we chose to do during technology development in Kenya, because it was the more mature technology. The relative maturity of ion exchange eased communication with partners and integration with existing treatment processes.

Ion exchange leverages solid adsorbents in a fixed-bed column, where liquid flows over stationary adsorbent beads. For nitrogen recovery, positive ammonium ions are passed over a negatively charged ion exchange resin and trade places with protons (Fig. 16.6). After all adsorption sites are filled with ammonium, an acid (proton-rich) solution is passed over the resin to regenerate the resin and produce concentrated ammonia solution. To produce ammonium sulfate fertilizer, we used sulfuric acid as an eluent. Previously, adsorbents were primarily used for nitrogen removal rather than recovery and rarely used in hydrolyzed urine with the aim of producing high-purity ammonia concentrate. In our first study, we compared the behavior of clinoptilolite, wood husk biochar, and two industrial ion exchange resins for ammonium adsorption and fertilizer production (Tarpeh et al., 2017). In addition to characterizing adsorption mechanisms in ideal solutions and real urine, we examined several performance criteria: maximum adsorption density (mg ammonia/g resin), regeneration efficiency (ratio of ammonia eluted to ammonia adsorbed), and cost per mass of nitrogen recovered.

Electrochemical nitrogen stripping was still in development as we concentrated our efforts on ion exchange in Nairobi. As electrons are removed from solution via the circuit, ammonium (NH₄ ⁺) ions and protons cross the cation exchange membrane (CEM) to the cathode (Fig. 16.7). Both diffusion due to concentration gradients and migration due to applied current contribute to transmembrane flux. Protons are produced from the oxidation of water, which decreases the pH of the anode, making it strongly acidic. Once ammonium reaches the cathode, it is transformed into aqueous ammonia (NH₃) due to high pH resulting from the production of hydroxide ions. Aqueous ammonia is selectively transported to the trap chamber, which conserves the driving force for ammonia flux from cathode to trap by consuming the ammonia with dilute acid and producing ammonium concentrate, a key ingredient for fertilizer. The liquid can be further processed by distillation or freeze-drying to produce concentrated liquid and solid fertilizer. The cathodic reduction of oxygen produces hydroxide ions that raise pH, facilitating the production of ammonia from ammonium (Tarpeh et al. 2018a, b).

We regularly benchmarked the energy consumption, nitrogen recovery efficiency, and selectivity of electrochemical stripping with ion exchange and the other existing nitrogen treatment technologies. Even during our field study of ion exchange, we operated preliminary tests on electrochemical stripping on the same influent that accelerated development back in the laboratory. Ultimately, electrochemical stripping excels in its low chemical and energy input requirements, as well as its much higher selectivity than ion exchange. On the other hand, ion exchange requires less technical maintenance and exhibits potentially longer lifetime due to its relative simplicity compared to electrochemical stripping.

Designing with the user in mind, and even more specifically operators within Sanergy, drove design decisions like combining columns in series for easy operation. Working closely with Sanergy treatment operators helped the ElectroSan team understand their schedules, incentives, and challenges (e.g., intermittent electricity). These users were kept in mind when developing technologies and provided informal and formal feedback on the technologies during our field visits. Based on discussion with Sanergy, we have since aimed to reduce chemical inputs due to limited and potentially volatile supply chains to informal settlements.

There are two main direct beneficiaries of ElectroSan innovations: fertilizer consumers and sanitation collection services. Within fertilizer consumers, we characterized smallholder farmers who would benefit from access to locally produced affordable fertilizers to improve their crop yield and increase income. Currently, almost all fertilizer is produced outside of Kenya and distributed by either the national government or private wholesalers. Utilizing local distribution networks and incorporating education with product distribution, ElectroSan targeted farmers who need agricultural innovation the most. Sanitation collection services like Sanergy would benefit by avoiding transport of collected urine for disposal and by increasing revenue due to sales of urine-derived products. As such, we developed two theories of change: one for agriculture and one for sanitation (Fig. 16.8).

We characterized user needs by incorporating feedback from multiple stakeholders with experience in Kenya including agricultural experts, farmers, and sanitation and fertilizer distribution companies. Based on our team’s expertise, we primarily focused on the sanitation theory of change but were informed by our agriculture theory of change. We engaged several potential agriculture partners, both with Sanergy and on our own. With Sanergy, we engaged potential organic fertilizer users, such as Lipton and horticulture farms. In parallel, the ElectroSan team consulted with businesses focused on farming inputs (e.g., One Acre Fund, Mavuuno). These did not lead to formal partnerships but informed our technology design and instilled confidence that these activities could be carried out once the fertilizer product was more firmly characterized.

Several versions of both business model and social impact canvases have been iterated within ElectroSan (one example in Fig. 16.9). A key part of our business model is partnering with fertilizer distributors so that ElectroSan can focus on fertilizer production. Ongoing work focuses on characterizing the market for liquid fertilizers in Nairobi, as well as the potential for producing solid fertilizer by freeze-drying or other similar methods. Anecdotally, most fertilizer is distributed in solid form, so we would need to identify submarkets open to liquid fertilizer (e.g., horticulture) or show that liquid fertilizer has marked advantages over solid fertilizer to elicit behavior change. Another key aspect related to behavior change is demonstrating the efficacy of our fertilizer product, which we have considered piloting during exhibitions, landscaping projects, or cooperative farms to double as research and demonstration sites.

In parallel with our laboratory development, we catalogued cost and forecasted costs at scale. Initially, we used experimentally determined adsorption densities to estimate operating costs of ion exchange adsorbents. Naturally derived adsorbents (clinoptilolite and biochar) were cheaper than conventional nitrogen removal via nitrification-denitrification but exhibited suboptimal recovery efficiencies. Of the synthetic resins tested, Dowex Mac 3, a weak cation exchange resin, exhibited the lowest cost because of its high nitrogen adsorption density and high regeneration efficiency (99%) (Tarpeh et al. 2017). Our preliminary cost estimates showed that just ten uses of Dowex Mac 3 would make it more cost-effective than conventional nitrogen removal, which we demonstrated during our pilot study in Nairobi. Urine-derived ammonium sulfate fertilizer was also produced at lower cost than urea and diammonium phosphate (Tarpeh et al., 2018a, b). We used local fertilizer prices in Nairobi, which reflect the costs of importing fertilizer and markups associated with transport from the port of Mombasa to inland Nairobi. Through this market analysis, we determined the major value of urine-derived fertilizer: its local and steady production. An ongoing challenge is to communicate the most fitting comparison for nitrogen fertilizer recovery to the sum of fertilizer production and nitrogen removal. Wastewater treatment experts tend to compare nitrogen recovery to only nitrogen removal, and fertilizer producers tend to compare nitrogen recovery to only Haber-Bosch nitrogen fixation. However, nitrogen recovery meets both value propositions: curtailing nitrogen wastewater discharges and producing usable fertilizer.

A market analysis for positioning human urine and derivatives as fertilizers was conducted by Sanergy and ElectroSan in 2014. Synthetic nitrogen fertilizers use the Haber-Bosch process, which requires million-dollar capital investments and large quantities of natural gas that limit the number of installations in sub-Saharan Africa (Buluswar et al., 2014). According to stakeholder interviews, urine is commonly viewed as a means to achieve increased crop yield as well as an effective insecticide (Sanergy, 2014). ElectroSan aims to leverage this market opportunity for our urine-derived fertilizer product. Based on interviews, farmers value low-risk, repeatable yield increases and return on investment. We identified several competitors and existing options for fertilizer, including synthetic fertilizers. Both solid synthetic fertilizers (e.g., calcium ammonium nitrate) and liquid synthetic fertilizers (e.g., solubilized diammonium phosphate) are commonly used across Kenya but are often cost prohibitive for low-income farmers. Import tariffs, a 30% markup due to transportation costs, and few importers contribute to high price points (Sanergy, 2014). Solid fertilizers tend to be easier to transport, but each formulation requires different production mechanisms. Liquid fertilizers may be more difficult to transport but can be easily combined with irrigation. ElectroSan exhibits several competitive advantages: local production, regular supply, customization to various chemical compositions, and application by fertigation.

Protecting environments for future generations is a major motivation of ElectroSan’s vision of reimagining waste. Worldwide, 80% of wastewater is discharged without treatment (Larsen et al., 2016); re-envisioning toilets as collection centers for raw materials could incentivize collection and treatment. Reimagining waste as a resource is particularly beneficial for global nitrogen use, because the global nitrogen cycle is severely unbalanced due to anthropogenic interferences. Industrial ammonia production, large-scale agriculture, and fossil fuel combustion have added unprecedented amounts of reactive nitrogen (e.g., NO₃ ⁻, NH₄ ⁺, N₂O) to the biosphere from the atmosphere, outpacing denitrification that converts reactive nitrogen back to dinitrogen gas (N₂). Because of the widespread untreated wastewater discharge, much of the world’s synthetic reactive nitrogen contributes to eutrophication and threatens aquatic ecosystems. Recovering nitrogen directly from wastewater could reduce the demand for atmospheric N₂ extraction and incentivizes restoration of polluted aqueous environments.

Even while we were still developing our ion exchange technology, we evaluated the environmental impacts of its potential implementation using life cycle assessment (LCA) and techno-economic assessment (TEA). LCA considers embedded energy and emissions associated with engineered processes from raw materials to disposal; TEA considers process modeling, engineering design, and cost estimation. These system-level assessments of new technologies can serve two major goals: (1) comparing to existing approaches and (2) prioritizing opportunities for optimization (Corominas et al., 2013a,b). We considered ion exchange cartridges or ammonia recovery from urine for both purposes and using both TEA and LCA, along with geospatial modeling for a citywide collection scheme (Kavvada et al., 2017). Our analysis demonstrated that ion exchange was not only less environmentally harmful than conventional nitrogen removal but net-negative for greenhouse gas emissions and energy input considering the avoided Haber-Bosch production. Within ion exchange-based ammonia recovery, we expected transport (collection of cartridges from households) to be the major emitter and energy consumer; however, the sulfuric acid for regenerating the resin represented 70% of greenhouse gas emissions and energy input (deriving from the manufacturing process). Although the city used for the environmental impact analysis (San Francisco, CA) differs in important ways from Nairobi, the finding that the sulfuric acid contributed such a large footprint would likely apply in both contexts. This insight inspired another laboratory iteration focused on alternative regenerants including acids (hydrochloric, nitric) and brine (sodium chloride). We found that the acids were similar in performance but the brine exhibited a trade-off: lower environmental impacts but also lower regeneration efficiency. Ongoing efforts focus on alternative regeneration schemes to further reduce the emissions and energy input required for nitrogen recovery from urine.

The team returned to UC Berkeley to plan the next trip to Nairobi, with the major objective of identifying effects of the Safe Sludge process on compost in small-scale containers. We also explored the impact of lime addition as a cover material during toilet use on the thermophilic composting process at Sanergy’s collection depot. Both the 2012 and 2013 field visits built a relationship with Sanergy and familiarized the UC Berkeley team with their operations by visiting toilets, meeting operations and collection team members, and working alongside treatment operators. In January 2014, two ElectroSan team members (Tarpeh and MBA student Ryan Jung) visited Sanergy to conduct focus groups with Fresh Life Toilet users. The major goals were to survey existing business resources in Nairobi, examine the price and cost needs for a successful business model to sell Fresh Life toilets to homeowners, and obtain feedback from users on prototyped treatment options.

These early trips also identified several challenges and opportunities for Safe Sludge. A major challenge was conducting experiments without a fully functional laboratory, which incentivized both partners to accelerate laboratory installation. Experiments during the 2012 trip were conducted some 15 km from Mukuru, the center of operations. During the 2013 trip, experiments were conducted at the composting treatment site; however, intermittent electricity required largely battery-operated experiments (e.g., pH meters, mass balances).

From January 2014 to December 2015, the ElectroSan team dedicated its efforts to developing ion exchange and electrochemical stripping in the laboratory. A major goal of laboratory efforts was to establish an experimental dataset and descriptive model that could be used to predict adsorption density for a given urine composition. We also successfully identified mechanisms of adsorption and the influence of composition by comparing simplified solution, synthetic urine, and real urine for both ion exchange and electrochemical stripping. During this focused time in the laboratory, the ElectroSan team still engaged with Sanergy through conference calls, meeting at conferences (e.g., Fecal Sludge Management Conference), and Sanergy visits to Berkeley. During this time, Sanergy grew rapidly in staff, number of toilets, and volume of excreta collected daily. We originally planned to visit Nairobi in Summer 2015 but decided to delay for a year to better characterize adsorption in realistic continuous operation and achieve publication-quality results during the field trial.

In 2016, the ElectroSan team had collected enough experimental data to plan for a field study of ion exchange. We met approximately monthly with Sanergy staff, particularly the laboratory manager and personnel. Pictures and supply lists were shared between the Berkeley and Sanergy laboratories to ensure compatibility. In 6 weeks during June to August 2016, Tarpeh, Nelson, and MS student Ileana Wald collected data on repeatable column performance using Dowex Mac 3 and Sanergy urine, surveyed urine composition across a representative set of Sanergy toilets, and monitored composition changes during collection. We also fabricated and operated columns at ten times the size of lab scale, which could then treat ten toilets’ daily production of waste based on Sanergy’s average across all toilets. Key performance metrics, including adsorption density and regeneration efficiency, were conserved over ten cycles at 6.5 L/d (one average Sanergy toilet) and for two cycles at 65 L/d (ten average Sanergy toilets). We continued analyzing the data collected in Nairobi over the 2016–2017 academic year that resulted in a publication in the new Development Engineering Journal in (Tarpeh et al., 2018b) (https://​www.​sciencedirect.​com/​science/​article/​pii/​S235272851730074​X).

Based on the encouraging results from our work in Nairobi, the ElectroSan team continued to develop larger-scale setups in Berkeley, as well as relax some of the assumptions that accelerated previous laboratory experiments. A master’s student from ETH Zurich (Maja Wiprächtiger) explored urea hydrolysis and combining nitrogen recovery with phosphate recovery. We explored several options of combined nitrogen and phosphorus recovery: struvite precipitation followed by cation exchange, anion exchange followed by cation exchange, and simultaneous anion and cation exchange. We hypothesized that phosphate recovery could be conducted before nitrogen recovery with minimal effects on nitrogen recovery. In 2017 and 2018, we published several articles on our findings and presented our work at several conferences.

Dr. Kevin Orner, a postdoctoral researcher at UC Berkeley, conducted the most recent visit to Sanergy in September 2019. The objectives of the visit included (1) evaluating the economic feasibility of producing and selling urine-derived fertilizer, (2) exploring the technical feasibility of toilet-level nutrient recovery, and (3) determining if pit latrine waste could be used to produce liquid fertilizer via ion exchange. ElectroSan and Sanergy explored selling to Unilever, the owner of Lipton, which makes teas that require liquid fertilizer. Although Lipton could pay a premium for organic liquid fertilizer for their organic teas, we later learned that urine-derived fertilizer could not be classified as organic under current regulations. Another strategy for economically treating urine is to recover nutrients via ion exchange and locally dispose the treated urine effluent, which avoids transportation and disposal costs. Ion exchange can be used to recover ammonium and phosphate but will require additional treatment steps to meet effluent discharge requirements (e.g., pathogens, organic contaminants). This need motivates current research at UC Berkeley on urea hydrolysis, ion exchange, and media filtration that can take place underneath the Sanergy source-separating toilets. Liquid from fecal sludge could also be an influent to ElectroSan processes, which Orner explored with Sanergy and Sanivation, another sanitation company in Kenya.

ElectroSan came of age with the Development Engineering program at Berkeley and benefited richly from interacting with the DevEng ecosystem of students, faculty, and collaborators. This enabling ecosystem also included the Blum Center for Developing Economies and the Development Impact Lab, supported by the US Agency of International Development through the Higher Education Solutions Network (HESN).

In Spring 2013, Tarpeh led a team of students in a Design for Sustainable Communities course to design an in-home toilet with Sanergy. This assessment validated the existing business model of shared public toilets being more profitable and user-friendly than in-home toilets. After pivoting away from in-home toilets, the ElectroSan team applied for class funds for the Summer 2013 field visit. The project continued during Fall 2013 as part of Cooperative Innovation, a new course focused on designing with low-income communities. The team designed and evaluated business models for excreta-derived products in Nairobi. Students traveled to Nairobi for several weeks in January 2014, supported by a Development Impact Lab Explore Grant ($5000) to seed new projects or pivots.

ElectroSan was first identified as an independent project through the Big Ideas at Berkeley grant competition, in which the team placed first in the Global Poverty Alleviation Category. As a Big Ideas recipient, the team benefited from mentoring from sanitation experts, funders, and impact investors. The work in progress was also presented at several conferences, which provided professional development to ElectroSan students, including Tarpeh.

In Fall 2014, the Development Engineering core course was offered for the first time at UC Berkeley. ElectroSan was pitched as a project and benefited from contributions from a multidisciplinary team (environmental/sustainability engineering, social work, business) that developed business models and surveyed potential users. This was a major step in articulating ElectroSan’s relationship with Sanergy and role at the food-energy-water nexus: producing an agricultural input from wastewater at reduced energy. ElectroSan benefited from a free supply of urine to test its technologies, and Sanergy benefited from research and development that could expand the product portfolio of excreta-derived products by valorizing urine rather than paying for its disposal. A major output of this class was a Development Innovation Ventures Proposal, which is a USAID competition. ElectroSan did not actually submit the proposal, but articulating the ideas in a concise way guided both technology development and planning for future implementation.

ElectroSan continued to conduct research, funded in part by Big Ideas, NSF fellowship support, and the VentureWell business competition, which we won based on a presentation at the HESN annual meeting in 2016. VentureWell funds supported planning for installing a pilot source-separating toilet on the UC Berkeley campus to supply urine for research and attract visitors. ElectroSan successfully applied for the Scaling Up Big Ideas Program in 2018, which helped fund the next iteration of technology development. We also extended preliminary results on accelerating urea hydrolysis to facilitate toilet-level recovery. This iteration was again the subject of a Development Engineering course project that informed the most recent visit to Nairobi in Fall 2019. Several students have benefited from the ElectroSan project at UC Berkeley and Stanford, including undergraduates, MS students, PhD students, and postdoctoral researchers.

Reaching meaningful scale for nitrogen recovery from urine could involve numerous small installations or a few large ones. We aim to identify optimal scale by combined experimental and modeling efforts. On the modeling side, we identified Pareto-efficient scales that minimize energy consumption and emissions in San Francisco. We will conduct similar analyses with Nairobi data to identify optimal scales for environmental impacts and costs. Experimentally, we have expanded our focus from larger-scale pilot installations to toilet-level treatment, which requires engineered urea hydrolysis.

Sanergy’s rapidly scaled toilet collection inspired rapid scaling of feces and urine treatment. Several iterations of feces treatment have been considered, including thermophilic composting, anaerobic digestion, and, most recently, black soldier fly larvae. Sanergy now has a profitable full-scale plant for treating feces but transports and disposes urine without cost recovery due to no economically viable options. Thus, ElectroSan efforts were generally dedicated to developing pilot- and full-scale treatment options to recover nitrogen fertilizer from urine.

More recently, we have considered toilet-level urine treatment to recover nutrients and discharge treated effluent. Accordingly, ElectroSan researchers at UC Berkeley are currently investigating media filtration for removal of carbon and pathogens prior to local discharge (Fig. 16.11). This option would achieve scale by thousands of installations (one per Fresh Life Toilet). The real optimum may be a hybrid of toilet-level and centralized urine treatment, but further characterization of toilet-level nitrogen recovery is needed. Regardless, a practical, effective urine treatment solution could reach hundreds of thousands of users in Nairobi alone.

A challenge in recovering ammonium on-site from source-separated urine via ion exchange is accelerating the hydrolysis of urea. When urine exits the body, nitrogen is in the form of urea. The urea-N must be hydrolyzed into ammonium-N prior to nutrient recovery via ion exchange; however, the urea hydrolysis process can last multiple days. Accelerating urea hydrolysis by varying biofilm carriers or the bacterial inoculum could reduce reactor size to be feasible for individual source-separating toilets in informal settlements (Deleu 2020). Urine will be collected from a LAUFEN Save! urine-separating toilet installed in a bathroom on campus at UC Berkeley and used as an influent to the pilot treatment system that integrates urea hydrolysis, ion exchange, and media filtration.

In parallel with toilet-level efforts to recover urine, ElectroSan researchers at Stanford are investigating more selective adsorbents to improve the lifetime, cost-effectiveness, and purity of the process (Clark & Tarpeh, 2020; Clark et al., 2022). Electrochemical stripping has also been further developed with predictive models for removal and recovery and energy estimations that show that electrochemical stripping is on par with other nitrogen removal technologies (Liu et al., 2020). We have also demonstrated high recovery efficiencies in various wastewaters, which may expand the applications of electrochemical nitrogen stripping (Fig. 16.12). This line of research was first inspired by ElectroSan’s 2016 visit to Sanergy, in which ion exchange was tested on anaerobic digester effluent because of potential scale-up of anaerobic digestion at the time.

As is typical for Development Engineering, research questions have evolved over time from fundamental and proof-of-concept to applied, practical questions. Now that we have demonstrated that high-purity ammonium sulfate can be recovered from various wastewaters, including urine, several questions remain to reach scale. Establishing a regular supply chain for adsorbents is one such practical question. Making infrequent bulk purchases could be possible, but the overall lifetime of the adsorbent needs to be characterized to inform purchasing decisions. We have explored several alternative methods for regeneration in the laboratory but look forward to contextualizing this regeneration decision based on cost and available supply chains for various acids and brine solutions. During a 2018 field trial in the United States, we encountered the practical challenge of how to apply an acidic ammonium sulfate fertilizer. Fertigation seems to be the best option, but dilution ratios must be devised and adapted from conventional ammonium sulfate application. Another question to reach scale is how to automate the continuous nitrogen recovery process, which we can adapt from other industrial ion exchange processes, such as water softening. Building on our cost analysis of ion exchange, we aim to identify marginal costs at scale. We expect economies of scale to exist, especially for resin purchasing and potential regenerant reuse, but aim to do a more long-term pilot study to further establish both technical and economic feasibilities. This was the aim of our pilot scale study with Lipton, but classifying urine-derived fertilizers as organic may be a prerequisite to running such a pilot study with fertilizer consumer interest.

Throughout its development, ElectroSan reported its results in scientific and gray literature, ranging from academic articles to reports and general media. Research collaborations have also played a critical role in disseminating our results, including with the University of Michigan where Tarpeh conducted postdoctoral research with Professors Nancy Love and Krista Wigginton. Ion exchange columns were constructed and operated at the University of Michigan to create ammonium sulfate fertilizer and applied to fields in Vermont. A growing community of urine-focused researchers now gathers annually at the Urine Summit, sponsored by the Rich Earth Institute in Vermont and most recently by the University of Michigan. Professor Tarpeh’s research group at Stanford also led a recent short course in Senegal with master’s students from Cheikh Anta Diop University in Dakar. Additional installations of urine-diverting dry toilets have led to informal communication among urine researchers, especially at conference symposia at several conferences, including the American Chemical Society and the Association of Environmental Engineering and Science Professors.

Another major challenge is reaching scale beyond Sanergy to other sanitation service providers (SSPs). To date, we have depended on building relationships with SSPs through our networks, including Sanivation and Delvic Sanitation Initiatives. The Container-Based Sanitation Alliance (CBSA) brings together several of these entities, some of whom have encountered ElectroSan at conferences and other meetings. To reach the needed scale of billions, we will need to leverage this increasingly robust network and develop regional models that cities can learn from and adapt.

Since 2018, ElectroSan team members have explored electrochemical nitrogen stripping in partnership with Delvic Sanitation Initiatives (DSI), an SSP in Dakar, Senegal. This context differs considerably from Nairobi along several dimensions. In Dakar, the majority of the population is served by septic tanks that are exhausted by private trucks. DSI works with L’Office National de l’Assainissement de Senegal (ONAS), the national sanitation agency, to operate fecal sludge treatment plants in Dakar and recover valuable products. We have recently demonstrated high recovery efficiency from fecal sludge collected from anaerobic digesters at one such fecal sludge treatment plant and can produce both fertilizer and disinfectant from influents of varying composition. DSI benefits from strong collaborations with ONAS and Cheikh Anta Diop University (UCAD), from where its founders graduated. This enabling environment has accelerated field visits, funding, and student exchanges from 2018 to 2020. Most recently, a field visit in December 2019 included demonstration of electrochemical stripping, tours of fecal sludge treatment plants, meetings with ONAS and UCAD collaborators, and a short course on resource recovery for UCAD master’s students. Diversifying ElectroSan’s product portfolio will help identify additional markets and customers to incentivize urine collection and treatment.