ARTICLE

Don't mix  - a paradigm in practice

Introduction

Urine is a powerful fertilizer. If you still don't believe it, here's a way to prove it:

• Buy a few young tomato plants (preferably in spring).
• Collect a urine sample, most suitably, your own.
• Dilute it 1:10 and fertilize the plants with it 2-3 times in the course of two weeks.
• The growth-promoting effect of your home-made urine fertilizer will be visible within a few weeks.

Urine is also a potential source of irritation for many. It contains substances our body wants to get rid of. Some of them act as microcontaminants in nature and are suspected to, e.g., disrupt endocrine regulation of water organisms. If you invite your best friends to a tomato salad made from your urine-fertilized tomatoes, some of these irritations may become visible and it could be the start of an interesting discussion on the concrete effects of recycling nutrients in modern society.

Separating urine from the wastewater stream in the toilet. Storing, processing the urine  and producing fertilizer from it. Identifying and tackling all obstacles along the way, both technically and socially. This is, in brief, what the Swiss Novaquatis project tried to accomplish with its nine work packages (summarized Fig. 1).

After 7 years with considerable progress in some areas, the project has come to an end. On March 7, 2007 the project was presented at the EAWAG info day in Zurich. The final report is available online (see [1]).

What was accomplished by Novaquatis?

Since the project results have been documented very well by EAWAG (see [1], [2]), it is futile to just repeat what's been published there. This article tries to summarize the main outcomes of Novaquatis - as they were presented at the info day - from my subjective view. I also had the chance to ask Dr. Tove Larsen a few questions, who was the driving force behind Novaquatis in all these years.

1. Citizen feedback

As Dr. Judit Lienert, project co-manager, reported, more than 1'000 citizens gave their feedback and expressed their opinion about urine recycling after having used a NoMix toilet at one of the four pilot sites of Novaquatis. It is quite clear now what Swiss people think about NoMix toilets and about recycling urine for plant production.

A majority of users found NoMix toilets acceptable in public buildings, as long as they are maintained properly. The support for the use of urine fertilizer in agriculture was encouraging. 78% even supported the idea of using it in organic agriculture (given some constraints described further down). Regarding private appartments, the results were more biased. Useability of NoMix toilets for kids were rated as not satisfying - a result that coincides with another survey at SolarCity, Linz (see report in Newsletter No. 12, 2006). It seems to be harder to clean and maintain NoMix toilets. Comfort of use was regarded as lower than in ordinary flush toilets. All this must be seen in a Swiss context, where citizens are used to a rather high standard.

These results are a valuable resource for further development of NoMix toilets.

2. Urine collection

Urine collection brings a number of tricky problems with it, as Dr. Kai Udert reported [6]. As soon as the urine leaves the human body, rapid hydrolysis (by dissolved enzymes and microorganisms) takes part.

In less than a day, 100% of the urea is hydrolized to ammonium (NH4+) and the pH rises from 6.2 to 9.1 . Due to the rise in pH, precipitates start falling out. In waterless urinals these precipitates consist of hydroxyl-apatite and struvite. If not maintained properly, a waterless urinal will clog within 3-6 months.

Use of flush water helps to slow down this clogging process. However, for storage and treatment, the increased volume is unwanted. On the other hand, precipitation could also be used as a means to recover nutrients, says Udert.

3. Urine processing

In the Swiss situation, is not advisable to just store urine and spread it on the fields directly as it is done, e.g. in some Swedish projects on urine separation. According to Dr. Max Maurer [4], the goal of Novaquatis was to produce a product that can be used in organic farming and that complies with Swiss standards for a safe fertilizer. In particular, it needs to be free from pharmaceutical products, hormones, prions, pathogens and other contaminations.

In the Novaquatis project, a procedure for processing human urine was developed that now works on a pilot-scale. The procedure is based on electrodialysis and ozonation. As any engineer will notice right away, this procedure consumes energy: about "45 to 55 kWh per m³ of urine", according to Wouter Pronk of EAWAG (personal communication). With this amount of energy one could heat the same 1 m³ from 20°C about 59 to 67°C. This is a lot of energy and means that the grey energy in any kg of reclaimed nitrogen would be up to one third of that needed in the Haber-Bosch process. Provided that the energy demand can't be reduced.

4. Urevit - a certified urine-based fertilizer

A brief interview with Dr. Tove Larsen

During the Novaquatis project quite some progress was made towards developing NoMix technology. My impression is that pilot phase is coming to an end and large-scale technical application of NoMix technology comes closer. Does Dr. Tove Larsen, the main project manager of Novaquatis, agree with this perception?

Tove Larsen: No, not quite, or at least that depends where you are. You are probably right, when you speak of the countryside in China, for example, where already today dry NoMix toilets are installed in large numbers. For the urban situation, however, there are still a number of problems that must be solved before we can speak of a mature, mainstream technology.

We can treat urine centrally, but we do not have a suitable transport method. This means that we can either try to solve the transport problem; or adapt the treatment methods to the demands of decentral treatments. At Eawag we pursue the latter issue at the moment, but this is a very challenging task and  it will take some time before we are there.

Where do you currently see the greatest chances for a full-scale implemetation of NoMix technology?

Tove Larsen: It is obvious that it is much easier to implement NoMix in areas without sewers. Especially in coastal  regions  where nitrogen is of primary concern, even NoMix alone  - i.e. only to treat the urine -  could solve a large part of the problems.  This  is attractive as compared to the immense investments in sewers and advanced treatment plants. For reducing the nitrogen flows to the oceans, I would set my money on NoMix technology.

Where do you currently see the biggest obstacles that still slow down the implementation of NoMix technology in Switzerland (as an example for a Western industrialized county) and, compared to this, in China?

Tove Larsen: The biggest obstacle is the existing wastewater management system with its high level of comfort and good results for water pollution control. In China, we have seen that NoMix technology can be well applied in the countryside - as I said before, we are already well beyond the pilot phase in this setting.

But also in urban settings, China probably has better chances for innovation due to the  fast expansion of the cities. In new residential areas, it is much easier to install new technology. As we have seen in Kunming, the problems are also larger in China. With high population densities as compared to the fresh water resources available, it becomes increasingly difficult to achieve the necessary removal efficiencies with conventional technology.

It is important to see that we need the large markets with pressing problems in order to develop cost-efficient technology that will then eventually be able to compete with the existing system here. Only mass production can lead to such financial advantages.

In concrete, will you continue to work with NoMix technology?

Tove Larsen: We will probably work on different topics, which are more or less related to the NoMix idea. An important project will start beginning of  September where we will look into the stability of biological nitrogen transformation processes when we apply them very decentrally.

Finally: If you'd have to make a guess about where NoMix technology will be in 10 years from now, what would you say?

Tove Larsen: I think that in 10 years time, interesting NoMix technologies will have emerged. Interest has been steadily growing over the last 5 years and there are signs that this process will now accelerate.

Conclusion

The biggest drawback in  the concept in my view is, that the high safety standards followed in Novaquatis lead to a considerable energy demand. It remains an open question to me whether this fact may hamper the spread of the concept in the future. It poses the threat that in the end the elaborate treatment procedure of urine obliterates the advantages recycling of urine may actually bring, particularly in developing countries.

Yet, promoting urine reuse without strict safety standards may eventually lead to the same result. In the European community (and also in Switzerland), spreading sewage sludge on agricultural lands is no longer allowed, mostly due to its contamination with heavy metals. We certainly don't want urine reuse to go the same way.

In general I was very impressed how far the NoMix concept has developed in the past 7 years. In seems to become a realistic and promising alternative for urban water management.

References:

[1] Novaquatis - A new Approach to Urban Water Management (2007), Final report, http://www.novaquatis.eawag.ch/publikationen/final_report_E (20.8.07)

[2] Eawag News 63e, March 2007: Mix or NoMix? A closer look at urine source separation. http://www.novaquatis.eawag.ch/publikationen/index (20.8.07)

[3] BAFU press release, July 9, 2007: Abwasser: Pilotversuch zur Beseitigung von Mikroverunreinigungen, http://www.bafu.admin.ch/aktuell/medieninformation/00004/index.html?lang=de&msg-id=13588 (20.8.07)

[4] Max Maurer, personal communication during his presentation at EAWAG Infotag, March 7, 2007

[5] Markus Boller, personal communication during his presentation at EAWAG Infotag, March 7, 2007

[6] Judit Lienert, personal communication during her presentation at EAWAG Infotag, March 7, 2007

[7] http://en.wikipedia.org/wiki/Hydroxylapatite (20.8.07)

[8] http://en.wikipedia.org/wiki/Struvite (20.8.07)

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Apatite: a naturally occurring form of calcium apatite with the formula Ca₅(PO₄)₃(OH), that is usually written Ca₁₀(PO₄)₆(OH)₂ to denote that the crystal unit cell comprises two molecules [source: 7]

Struvite: An ammonium magnesium phosphate mineral with the formula: (NH₄)MgPO₄ * 6H₂O [source: 8]