Technologies for the treatment of source-separated urine in the eThekwini Municipality

Abstract

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.

Inactivation kinetics and mechanisms of viral and bacterial pathogen surrogates during urine nitrification

“…16 MBBRs are currently used for urine nitrification in Durban and Dübendorf. 13 The use of several MBBRs in this study allowed evaluation of several bacteriophages and bacteria under field-relevant as well as varied experimental conditions. Inactivation was evaluated using gram negative and gram positive bacteria (Salmonella typhimurium and Enterococcus spp., respectively) as well as three bacteriophages (MS2, Qβ, and ΦX174) that served as surrogates for human enteric viruses.…”

“…Alternative urine treatment and nutrient stabilization technologies are now available to produce marketable fertilizers. 12,13 A promising nutrient recovery process that yields a chemically stable solution from stored urine is nitrification. 14 In configurations where nitrification is applied in combination with evaporation, a concentrated solution that preserves nearly all nutrients in the urine can be produced.…”

“…15 Pilot reactors for combined nitrification/distillation systems are operated at eThekwini Water and Sanitation in Durban, South Africa and at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) in Dübendorf, Switzerland as part of the Valorisation of Urine Nutrients in Africa (VUNA) project. 13 Nitrification of urine, i.e., the oxidation of ammonia (NH 3 ) to nitrate IJNO 3 − ), prevents ammonia volatilization, enhancing the recovery of nitrogen in urine. Two groups of nitrifying bacteria are involved in this process: ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB).…”

Bacteria Inactivation during the Drying of Struvite Fertilizers Produced from Stored Urine

“…This could be achieved, for example, through the application of flat cotton filters in an automated pilot-scale struvite reactor developed in eThekwini. 46 Such a reactor yields a thinner struvite cake relative to the cloth filter bags and likely more consistent moisture across the retained struvite during treatment. Conversely, increased homogeneity of the struvite cake may affect the accumulation of bacteria from urine into struvite via modified straining of bacteria in the struvite cake during its formation.…”

The Impact of Conditional Cash Transfer on Toilet Use in eThekwini, South Africa

“…EWS had already installed urine tanks on 300 UDDTs and was collecting urine in three communities, so these became the control areas. The urine was being collected for related research on nutrient recovery [34,35] within an interdisciplinary sanitation project (see www.vuna.ch). The 300 households in the control sample represented about 10% of the total households who had a UDDT (complete lists of all UDDTs installed in the areas were not available when the experiment started).…”