Elizabeth Tilley

Low-cost struvite production using source-separated urine in Nepal

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH(4)PO(4)·6H(2)O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160±50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.

Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH4PO4·6H2O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log-log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.

RECOVERY OF STRUVITE FROM STORED HUMAN URINE

Abstract In previous work, synthetic urine was used as a readily available proxy for real urine for determining the factors which affect the recovery of struvite from urine. Based on these findings with synthetic urine, we recovered struvite from real urine and, thus, showed that a) the synthetic urine served as an adequate model for determining the processes which affect struvite precipitation, and b) high quality struvite can be recovered from real human urine. For urine solutions diluted up to four times, an average of 23% of phosphorus and 80% of magnesium was precipitated naturally; the remaining supernatant was then dosed with magnesium to recover the phosphorus still in solution. The struvite recovered was approximately 99% pure regardless of storage conditions although full strength urine was best for struvite recovery since it contains the greatest mass of harvestable phosphorus. We conclude that synthetic urine can be used as a proxy for real urine when investigating struvite recovery provided the synthetic mixture is consistent with the expected composition in the specific context.

EFFECTS OF STORAGE ON PHOSPHORUS RECOVERY FROM URINE

Abstract In laboratory experiments using synthetic urine the effect of temperature, faecal contamination, dilution and headspace on urine to be used as a feedstock for struvite recovery were examined. The effects of adding different quantities of magnesium on the amount of phosphorus that could be removed from solution was also examined. An average of 62% of phosphorus could be removed in the form of struvite when magnesium was added to the urine solution after ureolysis had forced the precipitation of calcium and magnesium minerals. Dilution and the presence of faecal urease were found to affect the rate of ureolysis but not the purity of the struvite recovered. These results indicate that, by simply storing urine until it achieves a pH of 8 or greater, struvite can be recovered from source‐separated urine with only a magnesium addition.

A compatibility-based procedure designed to generate potential sanitation system alternatives

Regarding multi-criteria decision analysis (MCDA), the problem of generating alternatives has not received the attention it deserves. Most research is currently devoted to the problem of alternative selection, where it is assumed that a set of appropriate alternatives is already given. This paper addresses the generation of potential alternatives in the domain of sanitation systems planning and decision-making. A compatibility assessment procedure is proposed to determine the set of technically feasible or potential sanitation system alternatives. This is based on a clear definition of such an alternative containing sub-processes that include a user interface, storage, conveyance treatment and reuse/disposal. A newly developed compatibility matrix is applied to identify incompatibilities between the options of the sub-processes. A potential sanitation system alternative is therefore defined by the absence of two-by-two incompatibility between all its options. The compatibility assessment acts as a first filter on the set of sanitation system alternatives to eliminate those that are inoperable before the feasibility assessment. The objective of both steps is to obtain a set of alternatives that are of reasonable and manageable size from which the final solution may be selected.

Looking beyond technology: an integrated approach to water, sanitation and hygiene in low income countries

Reference EPFL-ARTICLE-202332doi:10.1021/es501645dView record in Web of Science Record created on 2014-10-23, modified on 2016-08-09

The Household-Centred Environmental Sanitation approach

Too often, standardized groupings of sanitation and treatment technologies are imposed in situations where they may not be appropriate. The Household-Centred Environmental Sanitation (HCES) approach instead emphasizes that the needs and means of households should be put first, and a collaborative process involving all stakeholders should steer the planning process.

The effects of urine storage conditions on struvite recovery

Phosphorus, like oil, is a non-renewable resource that must be harvested from finite resources in the earths crust. An essential element for life, phosphorus is becoming increasingly scarce, contaminated, and difficult to extract. Struvite, or magnesium ammonium phosphate (MgNFLPC^ 6H2O) is a white, crystalline phosphate mineral that can be used as a bioavailable fertilizer and can be recovered from aqueous solutions such as digestor supernant. In response to diminishing water resources, increasing nutrient pollution, and largely unaffordable centralized treatment, a paradigm of Ecological Sanitation (EcoSan) has emerged. A central tenant of EcoSan technology is nutrient recovery; by separating urine from feces in the absence of water, urine can be used as a clean, concentrated nutrient source. Urine harvested in this manner is used as a liquid fertilizer with varying degrees of success and acceptance. This research examines the potential of urine to be a feedstock for struvite recovery. By recovering a sustainable source of phosphorus from urine, the prospect of appropriate sanitation and closed-loop nutrient systems, may move closer to reality. In laboratory experiments using synthetic and real human urine, different methods of preparing urine to be used as a feedstock for struvite recovery, were examined. The effect of temperature, faecal contamination, dilution, and headspace on stored nutrient levels was examined. The effect of adding different quantities of magnesium, at different times, on the amount of phosphorus that could be removed from solution, was also examined. An average of 70% of phosphorus could be removed from real urine in the form of struvite when magnesium was added to the urine solution after ureolysis had forced the precipitation of calcium and magnesium minerals; magnesium added before ureolysis began retarded the process. Dilution and the presence of wastewater were found to affect the rate of ureolysis but not the purity of the struvite recovered; recovered struvite was approximately 99% pure regardless of dilution or contamination. Based on a comparison of the results, synthetic urine was found to be representative of the general behaviour of real urine during struvite formation.

The effect of giving respondents time to think in a choice experiment: a conditional cash transfer programme in South Africa

We conducted a choice experiment (CE) to estimate willingness to accept (WTA) values for a planned conditional cash transfer (CCT) programme designed to increase toilet use in South Africa. The payment is made conditional on using a toilet and bringing urine to a central collection point. In a split-sample approach, a segment of respondents were given time to think (TTT) (24 hours) about their responses, while the remaining respondents had to answer immediately. We found significant differences in the choice behaviour between the subsamples. To validate the stated preferences with actual behaviour, a CCT programme was implemented afterwards. The stated WTA estimates were far below those revealed by actual behaviour for both subsamples. Contrary to our expectations, the TTT group had underestimated their actual WTA values by an even larger margin. The preferences for various attributes were nevertheless useful in informing the design of the real intervention.