To address the shortcomings of modern wastewater treatment, Ecological Sanitation (EcoSan) has been advocated as a sustainable approach to promote closed-loop flows of resources and nutrients from sanitation to agriculture. In this study, we discuss the rationale behind its conception and provide a state-of-the-art review on the subject. Through an exhaustive literature analysis of EcoSan systems, its historical developments and programs implemented worldwide we (i) validate the potential applicability and feasibility of decentralized, source-based sanitation and (ii) depict fundamental problems in EcoSan systems design that have stalled its adoption and proliferation. Specifically, we focus on urine diversion to demonstrate its potential to elegantly separate, collect and concentrate products that we require (nutrients) and those that we wish to regulate (pathogens and micropollutants). Since recent research efforts have been devoted to the technological recovery of nutrients from human urine, we believe that we are witnessing a paradigm shift within a paradigm shift as it represents a change in emphasis from ‘split-stream collection and reuse’ to ‘split-stream collection, resource recovery and safe reuse’. Our analysis of various nutrient recovery technologies for human urine indicates that provisioning of urine-diverting toilets tends to reduce sanitary risks; however, to contain and completely eliminate these risks continued research effort is needed to envision and implement integrated technological pathways that ensure simultaneous nutrient recovery, pathogen inactivation and reduction of pharmaceuticals and active substances

Source-separating sanitation systems offer the possibility of recycling nutrients present in wastewater as crop fertilisers. Thereby, they can reduce agriculture's impacts on global sources, sinks, and cycles for nitrogen and phosphorous, as well as their associated environmental costs. However, it has been broadly assumed that people would be reluctant to perform the new sanitation behaviours that are necessary for implementing such systems in practice. Yet, few studies have tried to systematically gather evidence in support of this assumption. To address this gap, we surveyed 3763 people at 20 universities in 16 countries using a standardised questionnaire. We identified and systematically assessed cross-cultural and country-level explanatory factors that were strongly associated with people's willingness to consume food grown using human urine as fertiliser. Overall, 68% of the respondents favoured recycling human urine, 59% stated a willingness to eat urine-fertilised food, and only 11% believed that urine posed health risks that could not be mitigated by treatment. Most people did not expect to pay less for urine-fertilised food, but only 15% were willing to pay a price premium. Consumer perceptions were found to differ greatly by country and the strongest predictive factors for acceptance overall were cognitive factors (perceptions of risks and benefits) and social norms. Increasing awareness and building trust among consumers about the effectiveness of new sanitation systems via cognitive and normative messaging can help increase acceptance. Based on our findings, we believe that in many countries, acceptance by food consumers will not be the major social barrier to closing the loop on human urine. That a potential market exists for urine-fertilised food, however, needs to be communicated to other stakeholders in the sanitation service chain.

For sanitation systems aiming at recycling nutrients, separately collecting urine at source is desirable as urine contains most of the nutrients in wastewater. However, reducing the volume of the collected urine and recovering majority of its nutrients is necessary, as this improves the transportability and the end-application of urine-based fertilisers. In this study, we present an innovative method, alkaline dehydration, for treating fresh human urine into a nutrient-rich dry solid. Our aim was to investigate whether fresh urine (pH < 7) added to five different alkaline media (pH > 11) could be dehydrated at elevated temperatures (50 and 60 °C) with minimal loss of urea, urine's principal nitrogen compound. We found that it was possible to concentrate urine 48 times, yielding dry end-products with high fertiliser value: approximately, 10% N, 1% P, and 4% K. We monitored the physicochemical properties and the composition of various dehydration media to provide useful insights into their suitability for dehydrating urine. We demonstrated that it is possible to recover >90% nitrogen when treating fresh urine by alkaline dehydration by inhibiting the enzymatic hydrolysis of urea at elevated pH and minimising the chemical hydrolysis of urea with high urine dehydration rates.

In urine-separating sanitation systems, bacterial urease enzymes can hydrolyse urea to ammonia during the pipe transport and storage of urine. The present study investigated whether it was possible to reduce the urine volume without losing the nitrogen as ammonia. A method for stabilising the urine prior to dehydration was developed. Briefly, fresh human urine was stabilised by passage through an anion-exchanger, added to an alkaline media (wood ash or alkalised biochar), and dehydrated. Urine dehydration was investigated at three temperatures: 40, 45 and 50 °C. The influence of various factors affecting the dehydration process was modelled and the rate of urine dehydration was optimised. Results indicated that 75% (v/v) of the urine has to pass through the ion-exchanger for alkaline stabilisation of urine to occur. At all investigated temperatures, the dehydrator accomplished >90% volume reduction of ion-exchanged urine, > 70% N retention and 100% recovery of P and K. To realise high degree of nutrient valorisation, this study proposes combining source-separation of human urine with alkaline dehydration.