Dear all,

My contract in Raipur came to an end recently. My output was part of a feasibility study of three sanitation concepts proposed by our local partner to the municipality who need to decide with advisory of the local partner and GIZ, and apply for funding at the different national programs (e.g. JNNURM):

• On-site disposal of blackwater trough subsurface infiltration and off-site treatment by a decentralized greywater treatment system.
• Combined discharge of black- and greywater through a low-cost sewerage network and off-site treatment by a decentralized wastewater treatment system.
• Connection to the existing and/or proposed conventional centralised sewer network.

I am thankful to all of you for your contribution. The Susana platform proved to be a very helpful tool for me.

I will try to share my diploma thesis which summarize my findings in the Susana library by the beginning of 2013.

Best regards,

Moritz

Thanks a lot Florian. I agree, in the case of a simplified sewer I definitely have to stress the desludging of septic tanks.

The topic of phosphorus removal was mostly to get all technologic options on the table, same for nitrification and denitrification, as effluent guidelines for phosphporus and nitrogen are rather high, anyway.

Development has to go step by step. If required an iron-rich sand filter for p-removal can be upgrated at a later stage.

Hi Moritz,

The question to "where to draw the line" is always an important one.

And it is very often the case that the line is drawn at the wrong place: Almost all failed water and sanitation projects have their roots in the assumption that O&M just will be done, and later it turned out that it hasn't been done.

In your example a likely scenario could be: You build a solids free simplified sewer system and a constructed wetland for effluent treatment. Septic tanks continue to be without maintenance, thus the effluent will not be solids free. Frequent blockings of the sewers will occur and the constructed wetlands will be colmated after a couple of years.

Of course it is difficult to provide good advice to your situation, but generally speaking I would say that it is better to aim for lower objectives but for a more complete approach. E.g. forget about phosphorous elimination and put a simple but robust treatment plant in place and reserve a good part of the capacity to develop a plan jointly with the local operator for the O&M of your system, including slude management.

Best, Florian

Thank for you comments and suggestions. I totally agree.

Sorry Florian, there was an "n" missing: At the moment the city seems not even to have the technical equipment to supply this service to the residents.

We are not building septic tanks. As 80 % of the residents use septics (as it might be in whole Raipur and many other Indian cities) we have to find way to integrate them into our treatment concept e.g. as settlers before a solid free simplified sewer. This is a big task in whole India.

The questions is, where to we draw the line? My task is: Elimination of untreated wastewater inflow into an urban water body, elimination of pathogenic blackwater in the surface drains while using the existing on-site treatment infrastructure. This touches sludge managament, solid waste managment,education/awareness, water supply etc. However I can not plan a landfill and introduce a sludge management system (including drying beds) as part of a treatment project for 1000 pe.

Interesting point though, e.g. if an international consultant is assigned to plan a sewer system in a city without a sufficient treatment capacity, is it their duty to plan it as part of their project? I guess no, they rather have to "assume" it gets implemented at some stage. (maybe the consultant will not take the job)

I quite agree with what Christoph says, just one more comment on this:

Moritz wrote: At the moment the city seem to even to have the technical equipment to supply this service to the residents.

That is quite typical, many municipal utlities offer desludging services to the residents, thus normally operate a couple of vacuum trucks. This service usually responds to the demand of the residents, who call call for emptying when something in their septic tank is blocked or other problems occur. These problems only occur once the tank is entierly full with sludge, which means that the treatment efficincy as per design was lost years ago. As the service is normally charged, and not cheaply, obviously the people only call this service when they really have problems.

Implementing a good sludge management faces two main challenges:
- Providing a sludge treatment plant (not so easy, because not yet too much experience available)
- Increase the emptying frequency of the septic tanks, so that they are emptied early enough to maintain their treatment efficiency. This is almost entirely an management issue, which requires good planning, regulation and enforcement, intelligent tariff systems, etc.

Hi Moritz, I do think to say

“we must assume and plan that they get maintained according to the technical regulations”

.is a wrong approach.
You simply cannot build septic tanks and “assume” they are maintained and emptied right. That leads a worse situation than it is now.
The situation you describe does not differ very much from what you see in many larger cities. So the problem to solve is somewhat similar as well. When you do have septic tanks you have to achieve that an ORGANIZED fecal sludge management is introduced. When you are not sure that the fecal sludge is treated, you probably got nothing better for your water body and even the health situation is still in danger as dumping can easily be critical for people who use a water body below the dumping point.
Getting organized a fecal sludge management is a demanding task, but highly necessary.
Yours
Christoph

Thanks Elisabeth. Great case studies about constructed wetlands including design and construction considerations.

Thanks Florian for your contribution and the clarification of the expression "septage". Some literatures are not clear about the definition.

About the subsurface infiltration: To sum it up, there is no way around a proper soil and groundwater study to decide whether subsurfce infiltration is a suitable option or not. I am pretty that it is not an option in our case due to the proximity to water sources (public health) and at the end the lack of knowledge about groundwater dynamics (which are highly complex and way harder to identify that issues related to water above ground) and soil conditions (which can also be very heterogeneous) (technical feasability), however a clear guideline or legal basis would make it easier to sell the decision to stakeholders.

I will look in experiences from the states who seem to have done some bigger infiltration trenches.

The survey in our catchment revealed that around 15 % of the septic tanks got desluged at some stage while 65 % never had any maintenance (and no information about the other 20 %), while 50 % of the septic tanks are between 6 and 20 years old. So there is a significant gap of maintenance. The sludge gets dumpened on a landfill (with no kind of seepage cleaning). Anyway, at some kind stage we have to recomment steps and assume that the local bodies and local consultants are enforcing them respectivly, at some stage e.g. if we intend to use the septic tanks in any way in our treatment concept (pre-treatment - interceptor) we must assume and plan that they get maintained according to the technical regulations. At the moment the city seem not even to have the technical equipment to supply this service to the residents.

Kind regards,

Moritz

Moritz wrote: Is anyone of you familiar with legal regulation or recommendations regarding the subsurface infiltration of septage (septic tank effluent), as 29 % of the Indian population are using septic tanks. The literature I reviewed mostly recommended no subsurface infiltration in urban areas and in proximity less that 20 meters of any water source. It is clear that it is highly depending on the groundwater and soil conditions and the facility of infiltration. The US might have some as they using a high percentage of septic tanks.

Hi Moritz!
First, to avoid confusion: "septage" is normally used for the sludge accumulated and removed by pumping from septic tanks, not for the clarified effluent.

I do not know the Indian regulations for infiltrating effluents from septic tanks, but this is of course the most important reference to consider.

Other than this, you'd need to assess the technical feasibility (which depends on soil permeability and ground water level), and the risk to public health (which further depends on density of settlements and if ground water is used locally or not).

The main problem with septic tanks is very often that they are not properly managed, which means sludge (septage) is not removed often enough (thus reducing the treatment efficiency of the septic tanks) and removed sludge is dumped just somewhere. So any solution building on individual septic tanks needs to address these problems by providing a solution for enforcing slduge removal according to the designed frequency and septage treatment facility.

Best regards,
Florian

Dear all,

Thank you for your helfpul responses and shared ressources.

Our project partner is CDD an Indian NGO established by BORDA, so I am familiar with the DEWATS approach. However it is (almost) neglecting phoshorus removal, ecological integration etc. so I am trying to complement their approach with low-tech approaches for removal of nutrients and other features, which as you pointed out is a rather tough undertaking.

Thank you very much for you responses which keep me on the right track.

Is anyone of you familiar with legal regulation or recommendations regarding the subsurface infiltration of septage (septic tank effluent), as 29 % of the Indian population are using septic tanks. The literature I reviewed mostly recommended no subsurface infiltration in urban areas and in proximity less that 20 meters of any water source. It is clear that it is highly depending on the groundwater and soil conditions and the facility of infiltration. The US might have some as they using a high percentage of septic tanks.

Thanks a lot.

Greetings

Dear Moritz,

With regards to constructed wetlands in developing countries (if you choose constructed wetlands), see also this brandnew publication which could have useful information for you:

Muellegger, E., Langergraber, G., Lechner, M., EcoSan Club (eds.) (2012). Treatment wetlands. Sustainable Sanitation Practice (SSP), Issue 12. EcoSan Club, Austria.

www.susana.org/lang-en/library/library?v...eitem&type=2&id=1572

Articles:

‘Treatment wetlands in Austria: Practical experiences in planning, construction and maintenance’. Author: Mitterer-Reichmann, G.

‘Constructed Wetlands for the Treatment of raw Wastewater: the French Experience’. Authors: Troesch, S., Esser, D.

‘Comparing the treatment efficiency of different wastewater treatment technologies in Uganda’. Authors: Muellegger, E., Lechner, M.

‘A Hybrid Wetland for Small Community Wastewater Treatment in Morocco’. Authors: El Hamouri, B., Kinsley, C., Crolla, A.

‘Constructed Wetlands for Urban Wastewater Treatment in Egypt’. Authors: Abdel-Shafy, H.I., Dewedar, A.

‘Sludge Treatment in Reed Beds Systems – Development, design, experiences’. Author: Nielsen, S.


One minor thing I don't like about this publication is that they use a new abbreviation: TW (for "treatment wetland"), whereas the abbreviation CW (for "constructed wetland") is perfectly fine.

Anyhow, nice compilation of experiences with constructed wetlands in various countries.

Elisabeth

Dear Moritz, a little bit more to the useful contributions of Florian and JKMakowka. I agree with JKMakowka that a constructed wetland is better for P removal than just soil absorption. In the wetland situation the adsorbed P is then utilised by the plants, making provision for additional adsorption capacity (provided the plants are harvested from time to time) Your idea that you could then remove the soil and use it for agriculture may have merit, but it is a small unit so why not grow a useful crop in the wetland. It also sounds as if the community will gradually develop such that all households can be connected to the treatment system, which should then aim to provide a good quality effluent from all aspects (COD removal, N and P removal, pathogen removal) which will generally require additional steps such as an oxidation pond before the constructed wetland. However if malaria is a problem other alternatives may need to be considered.

Eutrophication of the pond used for bathing (and perhaps water for other purposes if the tap water fails) should not be taken lightly. I eutrophication leads to growth of blue-green algae (cyanobacter) this can lead to the release of toxins into the water if they experience stress (e.g. scum formation in thick surface layers, exposure to treatment chemicals such as chlorine). these toxins can lead to liver damage and other ailments in vulnerable populations.

Options for partial removal of phosphates which can also be integrated into an environmental education programme include the establishment of floating wetlands on the pond/lake, harvesting of floating plants and even algae and used for vermiculture and subsequent soil fertizer.

A recomemnded COD effluent value is less than 50 to a maximum of 75 mg/l, but you should check the Indian standards. Orthophosphate should be less than 10mg/l, but preferably less than 1 mg/l is discharging into a eutrophic water body (check Indian standards). Nitrates should be less than 10 mg/l.

You would certainly provide a great asset to the community if a communal clothes washing place (and perhaps cubicles for personal bathing) be constructed away from the pond. The wash-off from this could then be handles separately and as far as possible prevented from re-entering the pond.

I have attached an article on management options for a eutrophied lake in South Africa - it is not an urban pond but receives effluents and run-off from the city of Johannesburg and has experienced fairly severe eutrophication. Research into ways of managing the lake is ongoing.