Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

  • Marijn Zandee
  • Marijn Zandee's Avatar
    Topic Author
  • Moderator
  • Student and part time Biogas and WASH consultant
  • Posts: 236
  • Karma: 21
  • Likes received: 105

Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

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

Marijn Zandee

Kathmandu, Nepal

E: This email address is being protected from spambots. You need JavaScript enabled to view it.
The following user(s) like this post: muench
You need to login to reply
  • JKMakowka
  • JKMakowka's Avatar
  • Long-term forum user
  • Just call me Kris :)
  • Posts: 805
  • Karma: 34
  • Likes received: 247

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

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.

Krischan Makowka
Microbiologist & emergency WASH specialist
The following user(s) like this post: muench, Marijn Zandee
You need to login to reply
  • Marijn Zandee
  • Marijn Zandee's Avatar
    Topic Author
  • Moderator
  • Student and part time Biogas and WASH consultant
  • Posts: 236
  • Karma: 21
  • Likes received: 105

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

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

Kathmandu, Nepal

E: This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • JKMakowka
  • JKMakowka's Avatar
  • Long-term forum user
  • Just call me Kris :)
  • Posts: 805
  • Karma: 34
  • Likes received: 247

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

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.

Krischan Makowka
Microbiologist & emergency WASH specialist
You need to login to reply
  • goeco
  • goeco's Avatar
  • Long-term forum user
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 148
  • Karma: 6
  • Likes received: 78

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

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

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
You need to login to reply
  • rcsindall
  • rcsindall's Avatar
  • Regular forum user
  • Posts: 5
  • Karma: 1
  • Likes received: 11

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Hello,

I think this is an interesting discussion. WHO defines sanitation as follows: "Sanitation generally refers to the provision of facilities and services for the safe disposal of human urine and faeces. ... The word 'sanitation' also refers to the maintenance of hygienic conditions, through services such as garbage collection and wastewater disposal." Therefore a sanitation system would be a system that provides for the safe disposal (or re-use) of human urine and faeces. The aim of sanitation is certainly one of removing causes of disease and having a positive impact on health at household and community level.

However, "safe" can only really be defined used a risk-based approach. As you quite rightly point out, water that is safe to put on the garden is not guaranteed to be safe to drink. That means that we need to understand the potential uses of the products that come from a sanitation system before we decide whether they are safe.

With liquid effluents, the suggestions that you make are sensible. You have accounted for the height of the water table (variations due to season should be considered here too), and the proximity of water systems. The proximity of other infiltration systems that you allude to with critical population density is very important and a way to look at this may be the minimum distance required between infiltration systems. If you cannot cater for a community whilst maintaining those minimum distances, a sanitation system that does not rely on infiltration is likely to be a safer option.

In terms of the secondary treatment of liquid effluents, I am not clear what you are referring to. Would this be something like a DEWATS? There is a lot of work going into the safety of irrigating crops for human consumption with DEWATS effluent here in Durban. The results look promising so far but there will always be some crops that are safer to irrigate with treated water than others. Back to the risk-based approach!

As for your comments on private sector operators, this is where policy is important. eThekwini Municipality are currently in the process of writing a policy for construction and operation of DEWATS. It will detail the stages that private operators need to go through in the design and construction of the systems and minimum staffing requirements and O&M capacity that must be in place. That helps to reduce the risk of private operators acting like cowboys.

For solids and sludge, emptying "fresh" faecal material using a vacuum tanker may not always be an option. In Durban, pits tend to be very dry and the rheology is not conducive to pumping out unless you add huge volumes of water first (not a popular option in a drought-prone area). The other challenge with pumping out pits is trash, which is where the other part of the WHO definition of sanitation is useful. If we had an effective trash collection service for all of Durban, we would remove a large chunk of our sanitation problems! Once again, we need to consider the risks. In Durban, pits are emptied manually so pit-emptiers are trained on the safest way to do the job and given the equipment and PPE to do the job in accordance with that training.

Finally, I think that limiting partially treated sludge to reuse for soil amendment is too simplistic. There are many options for solid products depending on the treatment process and extent of treatment, as well as the local market. Soil amendment is one option, bioenergy products or animals feeds are also being considered here in Durban and elsewhere. As Dean says, cost efficiency of a system is key and that may rely on selecting the right product for the local market.

Broad guidelines for sanitation are always going to be a challenge. There are too many variations in context for solutions to be straight-forward and easily copy-pasted from place to place. However, by moving away from these kind of broad guidelines to a risk-based approach we can improve existing systems and ensure the design of new systems are fit for purpose.

Looking forward to further views or comments on this!

Thanks,

Becky
The following user(s) like this post: muench, eshaylor, Marijn Zandee, DianeKellogg
You need to login to reply
  • sdeshpande
  • sdeshpande's Avatar
  • Regular forum user
  • Posts: 5
  • Likes received: 1

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Hi Marjin;

In all my years of working in water and sanitation, I have far to often seen people not pay attention to sustainability when it comes to sanitation. By this I mean four things:

1. All domestic wastewater whether from toilets, bathrooms, kitchens or washing areas must be collected and treated. It makes no sense to focus only on toilets as that leaves dirty greywater with its own loads of health issues flowing down streets and streams potentially creating space for mosquitoes and other diseases to spread. Further putting toilet wastewater in the ground via soak pits is incredibly stupid as all it does is collect the solid and leave the untreated liquid to contaminate nearby water sources - remember it's not a case of just a couple of litres or less per use but that same water mixes with the larger amount of greywater soaking into the ground and then can affect a larger area. Also in the monsoons the solids can also liquify again, a fact often ignored, and create a even larger problem.

2. The beneficiaries must be able to operate the system installed both technically and financially. If this is not done we are looking at beneficiaries continuously forced to seek handouts whether via Corporate cCR or Government. Not an ideal solution by far.

3. The treated water must be reusable for at least agricultural field irrigation in rural areas as this can in essence augment available resources throughout the year. In urban areas, landscaping use is possibly the best option.

4. Finally the solution deployed must be a community based solution and not individual based. By this I mean while individuals can have their own toilets/bathrooms, the community must be responsible for the network and treatment solution used. this has a major advantage as it is much more difficult to revert to outdoor defecation if your community is watching you.

Do all this and I think the rest is easy...

I say this with confidence as we did just this side by side with the Nalanda Foundation (IL&FS) at a tribal village and you should see how happy the villagers are today. It is by the way 100% ODF as well and not by the government definition of just toilets build but 100% recycle and reuse of all domestic wastewater. By the way cases of Diarrhea have dropped to zero over the last year.

With regards,
Sanjay
www.clearford.com
You need to login to reply
  • Marijn Zandee
  • Marijn Zandee's Avatar
    Topic Author
  • Moderator
  • Student and part time Biogas and WASH consultant
  • Posts: 236
  • Karma: 21
  • Likes received: 105

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Dear Dean,

My focus on public health comes from answering the “what should sanitation achieve” question rather than “what is a sanitation system that is in all aspects sustainable”. Convenience and aesthetics are not a function of sanitation, though I fully agree that desirability is an important selling point.
Whether my thinking will fall or not, we will see. In many ways I hope so, as I also think that nutrient recovery is important and that we should very seriously work on getting rid of the need for all these expensive sewer pipes.

The reason I am not happy to prescribe re-use of liquid effluent for irrigation is that I have become convinced of the need for very simple (and somewhat conservative) rules regarding re-use. For any sanitation technology to make a real impact, it will have to be implemented at a massive scale. This means that it will be replicated by many not very well trained masons and entrepreneurs. In this context, we will have very little control over the sizing units, etc. Obviously, this also means that treatment efficiencies will vary. Perhaps, in a country where there is a government that can enforce building standards successfully one could promote re-use of the liquid effluents.
The distinction between “fresh” and “partially treated” sludge/solids is by no means there to suggest that partially treated sludge is safe. It is there to make a useful decision about how many protective measures are needed for those working with it. Yes, helminths will survive much longer than 6 months. This is why I think the slurry/sludge (in a low population context) should be used for tree planting or burial in a forest area (if available). I see this as a reasonable compromise between some re-use value for the organics and some nutrients, and the intention to separate the helminths from the population.

I am not at all convinced by your statement that urine is that much worse a fertilizer than effluent. Any fertilizer should be used together with a certain amount of organic material to keep soils healthy. Perhaps you can start trying to convince me by comparing the nutrient values of effluents (treated to a safe standard) with those of urine.

Regards

Marijn

Marijn Zandee

Kathmandu, Nepal

E: This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • Marijn Zandee
  • Marijn Zandee's Avatar
    Topic Author
  • Moderator
  • Student and part time Biogas and WASH consultant
  • Posts: 236
  • Karma: 21
  • Likes received: 105

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Dear Becky,

I agree with am lot of what you write. I think the idea of a minimum distance between systems that rely on filtration is an interesting one.

Regarding the idea of a risk based approach. Who would asses the risks? Sanitation entrepreneurs, the local government involved in planning approval or the government level that sets standards. It is great to hear that so much research and quality/capacity improvement is going on around Durban. I think in your context it should be feasible to use a more detailed risk based approach. However, most of the people that urgently need sanitation live in areas with much weaker government and private sector capacity. (Or in places where the incentives to look the other way are stronger than those to enforce the rules :( ). How do we balance safety, affordability and re-use in a very weak governance context dominated by "cowboys"?

For fecal slurry/sludge. I think my proposals for burial are only valid for low density rural areas. For (peri) urban area's some form of (semi) centralized treatment will be needed.

Finally, regarding solid waste management. Establishing markets for recyclables (and local recycling capacity) should become a matter of priority in my view.

Regards

Marijn

Marijn Zandee

Kathmandu, Nepal

E: This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • goeco
  • goeco's Avatar
  • Long-term forum user
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 148
  • Karma: 6
  • Likes received: 78

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Hi Marijn,
By "convenience/aesthetics" I mean the desirability of the toilet for the user. If it stinks or is not clean then people would be far more likely to avoid using it. This is a perception thing and I see it as an important function of the sanitation system and more than just a selling point.

My interest is in onsite systems, not sewer pipes. Clearly reuse is not always an option, depending on the site. However, I just can't see that strict rules should be only around reuse and not also around discharge/disposal. I heard recently that even India is implementing stringent rules around effluent disposal, as strict as here in NZ.

If the treatment technology is simple and inexpensive and resilient (to varying loads) then provided the principle is adhered to (for example settling for removal of helminth eggs or even residence time for pathogen reduction) then risk is significantly reduced for reuse. Compare that with the current situation in many developing countries - high levels of reuse with no treatment at all... people will continue to ignore strict rules if raw or partially treated sewage is what is available.

Sure, some knowledge of system design is required for any system. A bit like some knowledge of diet is required to be healthy. Not insurmountable. Simple rules of thumb like a capacity of x litres per person.

There is also "fully treated" solids. Resting time can determine that and design can ensure it. For example twin vermi-digesters that rotate every 5 years when one side fills. Wait for it to fill before removing fully treated solids from the other side. Simple, reliable and safe as a soil amendment for food crops.

Soil fertility is not so much about what the soil contains, but what it is lacking - the so-called "limiting" nutrients. In most cases phosphate is the limiting nutrient for plant growth (see " peak phosphorous "), whereby it doesn't matter how much nitrogen or potassium you throw at the plants - they do not grow unless you also add phosphorous. Urine is useful only where phosphorous is not the limiting nutrient because the phosphorous in our food ends up in our feces. Feces + urine = balanced plant nutrients. The phosphate in feces is dissolved into the wastewater as treatment takes place. This is not the same issue as adding organic matter as a soil amendment.

cheers
Dean

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
You need to login to reply
  • rcsindall
  • rcsindall's Avatar
  • Regular forum user
  • Posts: 5
  • Karma: 1
  • Likes received: 11

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Hello,

I agree that Durban is a relatively unique environment in terms of governance but the risk-based approach still has a value elsewhere. I believe that there is a need to identify and involve government players wherever possible if they are to be involved in the long-term solution. However, in terms of applying risk-based approaches, this can be something that is done at a number of levels. In a slightly different field (flood risk), I am involved with an organisation that facilitates communities to carry out drowning risk assessments. This requires facilitation and some expert guidance to dispel myths (e.g. the river steals our children because of the spirits that live there) but the ultimate aim is for the community to identify the risks that they face and then select ways to mitigate those risks that are within their ability to implement. This sort of approach is not uncommon in disaster risk reduction and I think that similar approaches could be trialed as an extension to CLTS. It's not a perfect solution as we know that CSOs have different levels of power in different regions and even from village to village, the success of these approaches can vary based on who is involved and their level of interest. However, that is true of any project that is repeated in many locations.

I like the idea of adopting recycling to deal with MSW and would suggest that more needs to be done to consider this (both informal and formal sectors) when we talk about sanitation!

Becky
The following user(s) like this post: Marijn Zandee
You need to login to reply
  • Marijn Zandee
  • Marijn Zandee's Avatar
    Topic Author
  • Moderator
  • Student and part time Biogas and WASH consultant
  • Posts: 236
  • Karma: 21
  • Likes received: 105

Re: Sanitation systems, what should they acomplish and what does it mean for re-use and disposal

Dear Dean,

By "convenience/aesthetics" I mean the desirability of the toilet for the user. If it stinks or is not clean then people would be far more likely to avoid using it. This is a perception thing and I see it as an important function of the sanitation system and more than just a selling point.


It seems we are simply confused about what we mean with the word function. For me (as a non-native speaker) function means “What should it achieve”. In that sense I stand by my idea that lowering pathogen levels to a point where re-infection can be easily controlled with occasional use of medicine is the primary function of sanitation systems. (Note, with sanitation systems, I mean the whole system including conveyance and treatment).

When it comes to sustainability, I think there are a few different takes that all need attention.

- Social sustainability (I am not sure that is the correct term). This would cover convenience/aesthetics, but also whether the system fits with local cultural practice and whether it is aspirational enough (i.e. does it fit with people’s sense of progress and modernity).

- Economic sustainability (especially for conveyance and treatment, but also for user O&M for stand-alone systems).

- Technical sustainability. This includes durability of construction materials, availability of skilled repair workers in case something goes wrong, robustness to environmental shocks to the treatment process, etc.

-Ecological sustainability. Prevention of pollution, and recovery of nutrients, water or energy.

My interest is in onsite systems, not sewer pipes. Clearly reuse is not always an option, depending on the site. However, I just can't see that strict rules should be only around reuse and not also around discharge/disposal.


I am not saying there should not be any rules on discharge or disposal. See the discussion above on when population density is so high that simple (pit) or improved (septic tank) systems that rely on infiltration are not feasible without causing pollution. However, when water is re-used in agriculture there are higher re-infection risk then when it is soaked away. This should be reflected in how strict you make the rules.
By the way, I think the work you are doing is very good. Just to add another little pet argument of mine. In developing nations, consumers, engineers and planners tend (on majority) to want to emulate the lifestyle of OECD countries. This means that if we want non-sewer and re-use oriented technologies to become widely used in developing countries they first need to become widely used in developed nations.

If the treatment technology is simple and inexpensive and resilient (to varying loads) then provided the principle is adhered to (for example settling for removal of helminth eggs or even residence time for pathogen reduction) then risk is significantly reduced for reuse. Compare that with the current situation in many developing countries - high levels of reuse with no treatment at all... people will continue to ignore strict rules if raw or partially treated sewage is what is available.


No-one suggested that the disposal or re-use of untreated sewage was acceptable. My concern is whether we can safely assume that decentralized (or semi-centralized) solutions can reliably generate a waste water quality that is sufficient for re-use. I am not convinced we can, but I will admit that there are locations where water is a scarce enough commodity that re-use should be considered. However, for me, the default would be not to promote re-use of effluents from a better safe than sorry perspective.

There is also "fully treated" solids. Resting time can determine that and design can ensure it. For example twin vermi-digesters that rotate every 5 years when one side fills. Wait for it to fill before removing fully treated solids from the other side. Simple, reliable and safe as a soil amendment for food crops.


Yes, however, is the added cost justified for a developing world consumer considering the very small amount of soil amendment?

Soil fertility is not so much about what the soil contains, but what it is lacking - the so-called "limiting" nutrients. In most cases phosphate is the limiting nutrient for plant growth (see " peak phosphorous "), whereby it doesn't matter how much nitrogen or potassium you throw at the plants - they do not grow unless you also add phosphorous. Urine is useful only where phosphorous is not the limiting nutrient because the phosphorous in our food ends up in our feces. Feces + urine = balanced plant nutrients. The phosphate in feces is dissolved into the wastewater as treatment takes place. This is not the same issue as adding organic matter as a soil amendment.


I am aware of basic plant nutrition theory. In my experience, it is quite rare to see signs of phosphate deficiency in plants in Nepal. This indicates that phosphate is not the only nutrient that is limiting plant growth. However, I understand the risk of nitrogen only fertilization. Your comment implies that phosphate is not excreted in urine which is not true. P is both found in urine and feces. In the table attached, the properties of urine stored under field condtions in Nepal are given.
This table can be found in the following report: www.susana.org/_resources/documents/defa...thdripirrigation.pdf . It would be interseting to see the composition of the effluent of the vermi based systems to see how much closer to a “perfectly” balanced fertilizer it is.

Note, my suggestion to bury partially treated sludge and plant trees on top (for rural areas) is specifically so because it will allow the tree to use the phosphates and other remaining nutrients.

Regards

Marijn

Marijn Zandee

Kathmandu, Nepal

E: This email address is being protected from spambots. You need JavaScript enabled to view it.
Attachments:
You need to login to reply
Share this thread:
Time to create page: 0.736 seconds