I see sustainability as a triangle with three corners, each an essential part of the whole:

1. hygiene (isolation of pathogens from humans)

2. convenience / aesthetics

3. nutrient recovery / reuse

I don't believe any of these elements should hold more importance than any other. Only if all are achieved can the system be truly "sustainable".


The two key factors that influence a system's success are:

• cost efficiency;
• reliability

I am very skeptical that any secondary treatment system operated in the developing world could consistently yield a water quality good enough to use for irrigating food crops. Therefore, infiltration or surface water disposal of treated water meeting minimum standards seems best to me.

In reply, my favourite quote:

Paradigms fall slowly, from the weight of repeated failure.

The paradigms above, if/as held by contemporary sanitation practitioners, will fall. Its one thing believing the statement, quite another being informed and aware of the available options to achieve sustainability... then shifting ones paradigm.

Unfortunately, methods for liquid effluent disposal continue to be perceived as arbitrary levels of treatment (primary, secondary etc, for either discharge to water or disposal by "infiltration"). Only once liquid effluents are regarded as a resource, conditional on quality levels that align with the product application, will re-use and sustainability be achieved. This means designing systems that generate the resource for the condition - e.g. for agriculture ...or aquaculture ...or energy etc. The WHO guidelines offer suitable definitions for wastewater quality according to end use suitable for different agricultural applications such as uncooked vegetables, cooked vegetables, tree crops, non-food trees etc.

So yes, I like the idea of defining "fresh" sludge and "rested" sludge, but helminths remain active for much longer than 6 months in sludge. This should not be specified as an arbitrary time "level" (6 months, one year etc) but as a time that meets the product quality requirements given the specific resting conditions.

Separating urine adds all sorts of problems and complexity, not the least being that urine is not a balanced fertiliser. In contrast wastewater is balanced because fecal nutrients (in particular P) are leached into the wastewater. So treatment of wastewater offers a product far more useful than separated urine, provided the product meets the pathogen limits.
cheers
Dean

Yes, I like that new definition better. For me the primary function is the public health function. But as I already mentioned, maybe that is not a commonly agreed primary function. In fact I would say that for many the primary function is to just get rid of the unpleasantness of having to deal with excreta.

Regarding the water reuse question: Yes maybe a simple guideline would be to not re-use water unless under severe water stress. And in the latter case everyone should be aware of the potential trade-offs in regards to safety.

Dear Kris,

Thanks for your reply. Below some clarifications and arguments from my side.

I think the separation is strictly speaking a secondary function. You could build a toilet that immediately disinfects the excreta and then you could let your children play with the faeces. The separation aspect is (while essential to some systems that only offer partial treatment) largely an aesthetic function, so far as people generally like living in a clean and smell free environment. However, similar to the "dignity" aspect of household toilet construction it can be vital for the acceptability of a sanitation system.

Then what would you consider the primary function of a sanitation system?

I am afraid I am not aware of a toilet that immediately sanitizes excreta to the point where kids can play with it. I see a sanitation system as: toilet (interface) + treatment + conveyance. Whether that is in one unit or in a complex chain. And I think that the primary aim of such a system is to block reinfection pathways for fecal-oral transmitted disease. Perhaps the definition should have been: "A sanitation system provides an effective barrier between a population and pathogens carried in its excreta, and therefore interrupts the re-infection cycle of excreta borne pathogens

I think this needs to be seen a bit more differentiated. Usually reuse of liquid effluent only make sense in water stressed areas. But user such conditions one has to weight different factors (often from outside the scope of the sanitation system) and therefore a compromise might be necessary. There are also plenty of non-food crops and or those used for animal fodder that could be irrigated quite safely. Last but not least,the risk of transfer of pathogens on the food-crop can be significantly reduced by the use of drip-irrigation or under-ground irrigation, both of which are very advisable technologies in water stressed areas

I think you are right that the risk equation will be shifted by water stress. However, these days, I am leaning towards simple and relatively strict guidelines. Partly this is informed by my recent work in healthcare waste management. We see in this field that our work is being copied (which is great in and of itself), and that we loose control over how well certain systems are implemented by those who follow. What I have learned from this is that if a technology may be widely copied, your safety standards should be very robust. They should not only be sufficient for the system in and of itself, but also maintain a healthy margin of error for design and use error by those who replicate without expert guidance (in the WASH sector much more so than in the health sector). I fully agree that the solutions you propose are safe in and of themselves. However, I think we should ask ourselves whether we work in a context where we can be assured that once a project is replicated locally our safety "barriers" will be replicated as well.

While I agree in general, I think one should also take a sort of dilution factor in mind. If the raw faeces make up only a very small percentage or come from a low risk population (such as one that had a well running sanitation system for a long time and has very low levels of pathogen prevalence), even sludge with "fresh" faeces mixed in can be handled reasonably safe. I am mainly thinking of septic tank sludge emptying, which also due to the easiness of pumping poses a quite low risk of infection to the workers in most cases.

I think here we are mostly in agreement. In my view, septic tank emptiers should be professionals using vacuum trucks. I agree they will be at low risk, but I think they should still use PPE (personal protection equipment) and be vaccinated. This type of "fresh" sludge (despite its dilution factor) should still undergo secondary treatment in my view.

Regards

Marijn

Marijn Zandee wrote: What is a sanitation system?
As a working definition, I would suggest: “A sanitation system separates a population effectively from its excreta, and therefore interrupts the re-infection cycle of excreta borne pathogens.”

I think the separation is strictly speaking a secondary function. You could build a toilet that immediately disinfects the excreta and then you could let your children play with the faeces. The separation aspect is (while essential to some systems that only offer partial treatment) largely an aesthetic function, so far as people generally like living in a clean and smell free environment. However, similar to the "dignity" aspect of household toilet construction it can be vital for the acceptability of a sanitation system.

Marijn Zandee wrote: Liquid effluents
[...] Finally, I am very skeptical that any secondary treatment system operated in the developing world could consistently yield a water quality good enough to use for irrigating food crops. Therefore, infiltration or surface water disposal of treated water meeting minimum standards seems best to me.

I think this needs to be seen a bit more differentiated. Usually reuse of liquid effluent only make sense in water stressed areas. But user such conditions one has to weight different factors (often from outside the scope of the sanitation system) and therefore a compromise might be necessary. There are also plenty of non-food crops and or those used for animal fodder that could be irrigated quite safely. Last but not least,the risk of transfer of pathogens on the food-crop can be significantly reduced by the use of drip-irrigation or under-ground irrigation, both of which are very advisable technologies in water stressed areas.

Marijn Zandee wrote: Solids and sludge
The first distinction I would like to make is between “fresh” and “partially treated” solids or sludge. As a rule of thumb, I would suggest that any sludge that had raw feces added in the last 6 months should be considered “fresh”. This fresh sludge (or solid) should be treated with care. Essentially by emptying professionals using tools such as vacuum trucks and compete personal protection gear who are vaccinated against those pathogens we can vaccinate against. (This is obviously not the case, but it would have to be for a sanitation system to fulfill the definition above). The partially treated solids will have much lower levels of pathogens (helminthes may be the main survivors). As such, the emptying and handling of such solids can be done by laborers using hand tools and somewhat limited personal protection (gum boots, long sleeves and trouser legs, and gloves). Special care should be taken to instruct people handling such solids to wash very thoroughly with soap!

While I agree in general, I think one should also take a sort of dilution factor in mind. If the raw faeces make up only a very small percentage or come from a low risk population (such as one that had a well running sanitation system for a long time and has very low levels of pathogen prevalence), even sludge with "fresh" faeces mixed in can be handled reasonably safe. I am mainly thinking of septic tank sludge emptying, which also due to the easiness of pumping poses a quite low risk of infection to the workers in most cases.

Dear all,

This long and winding post is partly inspired by this discussion on vermifiltration: forum.susana.org/205-vermifilters-or-ver...ermifilters?start=12 and also includes a number of assorted thoughts I have had in the last years. I will try to take a wider look at what sanitation should achieve (as a minimum) with a focus on the developing world where the need is greatest. Further, I will use “my” definition of sanitation to look a bit more at re-use and further treatment/disposal of effluents.

Since below is more or less an opinion piece, I am sure you will not agree with all of it. Please comment so we can have a discussion.

Obviously, the post depends on the work of many others I apologize for not referencing.

What is a sanitation system?
As a working definition, I would suggest: “A sanitation system separates a population effectively from its excreta, and therefore interrupts the re-infection cycle of excreta borne pathogens.”

Note that no (viable) sanitation system completely eliminates the transmission of excreta borne pathogens. The goal should be to reduce the transmission of pathogens to a level where disease can be (close to) eliminated with basic medical services. Once safe and functional sanitation is available, fewer pathogens will escape into the environment. This should mean less people are infected, which in turn lowers the pathogen levels that the sanitation system has to be a barrier against. Similar positive spirals should exist when hand washing (with soap) is made common and de-worming campaigns are done at the same time sanitation technologies are introduced. In some communities, animal husbandry practices may be an enduring source of infection.

This perhaps narrow definition (for me) helps to bring some of the issues and non-issues around re-use or the disposal of effluents and solids in focus.

Liquid effluents
For systems that rely on infiltration of liquid effluents (e.g. septic tank, tigerworm toilet, twin-pit), I see two main limitations: ground and surface water proximity, and population density. Regarding ground and surface water proximity, I would support a rule of thumb to stay away at least 30 meters from surface water and water points. And to have a wet-season ground water table at least 2 meters below the bottom of the soaking system. However, if the population density gets too high, such rules will not suffice and some form of secondary treatment of effluents will be required. (This is essentially when the local soil cannot break-down organic and inorganic pollutants sufficiently and deeper aquifers get contaminated.) Unfortunately I have no idea what the “critical population density” is at which secondary treatment is needed. If secondary treatment is required, some form of (semi)centralized treatment for multiple houses or a larger area is likely to be effective. Finally, I am very skeptical that any secondary treatment system operated in the developing world could consistently yield a water quality good enough to use for irrigating food crops. Therefore, infiltration or surface water disposal of treated water meeting minimum standards seems best to me.

To elaborate on the last bit a little. For sure, it is technically possible to build systems that can deliver the required effluent quality. However, I am talking about environments where you have little control over operation and maintenance and over whether extra buildings/families will be connected to the system in the future. Another difference, in my view, is whether you design a system for a specific location, or whether you are trying to popularize a concept which can be built by local private sector operators. In the latter case, you will have very little control over design parameters used.

Solids and sludge
The first distinction I would like to make is between “fresh” and “partially treated” solids or sludge. As a rule of thumb, I would suggest that any sludge that had raw feces added in the last 6 months should be considered “fresh”. This fresh sludge (or solid) should be treated with care. Essentially by emptying professionals using tools such as vacuum trucks and compete personal protection gear who are vaccinated against those pathogens we can vaccinate against. (This is obviously not the case, but it would have to be for a sanitation system to fulfill the definition above). The partially treated solids will have much lower levels of pathogens (helminthes may be the main survivors). As such, the emptying and handling of such solids can be done by laborers using hand tools and somewhat limited personal protection (gum boots, long sleeves and trouser legs, and gloves). Special care should be taken to instruct people handling such solids to wash very thoroughly with soap!

Fresh sludge, should be collected and treated in a (semi)centralized plant. Partially treated solids and sludge, in my view, can be used with some care. To keep instructions simple, I would suggest that they only be used for trees. Preferably, they are put into a pit (with added lime?) with a young tree planted on top. Alternatively, burial in trenches in a forest seems a good solution. Considering potential risks, and the relatively small quantities that need to be dealt with (in a rural setting), I don’t think it is worth promoting another solution. Sludge from a (semi) centralized treatment facility is a different matter.

Urine use
First of all, it works as a fertilizer. I have done enough experiments and seen enough in the field to be convinced of this. The main issue with the multi barrier approach www.ecosanres.org/pdf_files/ESR2010-1-Pr...InCropProduction.pdf that I see is that storage times of the urine cannot be controlled and are not followed (assuming re-use at level of individual farmers). Rules about how to apply and the withholding time can be successful if a long-term training and support program is available. Considering that the multi-barrier approach has some kinks in its armor I would suggest that urine should not be collected with separating toilets/toilet pans. If farmers are convinced urine use is a good idea, it is better to encourage them to only collect when they are urinating, but not when they are using “the long toilet”. If no urine is collected when defecating, you still collect the other 90%. In this way, cross-contamination is very unlikely to occur, which greatly reduces the potential pathogens in the urine. One problem is that with UDDT (urine diverting dry toilets) this approach is not possible. Perhaps the urine could be infiltrated (sub surface) into a fruit tree grove, as suggested on this forum forum.susana.org/forum/categories/175-ur...n-in-school-uddt#123 if a separating toilet is used. If urine is collected at scale, a more high tech approach (such as developed by VUNA - www.eawag.ch/fileadmin/Domain1/Abteilung..._Urine_Treatment.pdf) can be used, but this type of technology should probably be scaled first in a developed country setting.

Looking forward to your comments

Marijn