Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

  • groverhmc
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Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear ladies and gentleman,

First of all let me introduce myself, I am Grover Mamani from Bolivia, currently enrolled in the Urban Water and Sanitation MSc programme offered by UNESCO-IHE (The Netherlands) and UNIVALLE (Colombia). At the moment I am working on my research project titled: "Pathogen removal in household-size sludge treatment wetland. A study case in Gujarat, India"

As you know, the anaerobic digestion process has several advantages such as: low production of solids, low energy consumption, low land requirement, production of methane, generation of digested bio-solids and versatility to apply in small and large scale, yet conversely some of its main disadvantages are the unsatisfactory removal of nitrogen, phosphorus and pathogens.

In the rural area of South Gujarat (India), the anaerobic digester at household-size level has been implemented successfully since 1990's, not only generating biogas utilized to cook but also bio-solids applied as soil conditioner. Additionally, conventional cistern-flush and pour-flush toilets had been linked to a biogas unit as an alternative to collect and treat domestic wastewater. Currently, this system known as toilet linked biogas plant (TLBP) is working successfully as it produces enough biogas to cook meals for a family of five members. However, regarding to the residual sludge (slurry) preliminary results of an ongoing project in India by WASTE (2013) found high concentration of pathogen indicators (E. Coli = 210 most probable number (MPN)/g in a wet sample). Consequently, for safe reuse of the slurry, post-treatment is required to enhance the microbiology quality of this residue.



This research aims to: i) characterize the slurry and ii) evaluate the feasibility of STW (also known as sludge drying reed beds), applied as a post-treatment for anaerobic digested sludge to obtain a final product sufficiently safe from a health perspective.

To characterize the slurry, both: pathogen indicators like faecal coliforms, E. Coli, and Salmonella; and physico-chemical parameters such as: TSS, VSS, Nutrients (nitrate, nitrite, ammonia), pH, temperature, and dissolved oxygen will be tested.

To evaluate the feasibility of STW, six pilot-scale sludge treatment wetland units are already implemented. Each unit is a plastic cylindrical tank of height 0.7m and diameter 0.75m. The units contain from the bottom to the top four substrate layers: at the bottom a 10 cm thick drainage layer of crushed rock gravel (range 25 to 55mm), in the middle a 10 cm thick layer of medium gravel (range 4-25mm) and a 10 cm of fine gravel (range 1-8mm) at the top a 15 cm thick layer of fine sand. Additionally, two perforated PVC tubes are installed to enhance aeration. See Figure 2.


Figure 2. Experimental units

Each unit was planted with three Phragmites australis (common reeds), separated 30 cm from each other.
The next step in the research is to start the feeding and resting period. The feeding will be carried out manually during 7 days in daily equal portions, followed by a resting period of 1 week. Based in previous studies three different sludge loading rates will be applied: low, medium and high (30, 60 and 75 kg dry matter/m2 * year). Sampling and testing are going to be carried during the two coming months.
To finalize, at the end of the research the expected results are: i) characterization of slurry, ii) determination of pathogen removal efficiency in STW and iii) determination of the optimal design parameters according to local conditions.

Any question, suggestion or recommendation will be most welcome, especially those of you who are related with Faecal Sludge Treatment and Constructed Wetlands.

Kind regards

Grover

Grover H. Mamani C.
MSc. Urban Water and Sanitation
The Netherlands
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Mobile: +919428621967(India), +31628476049(Netherlands), +59173006364(Bolivia)
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  • christoph
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Re: Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear Grover,
nice to hear from a Bolivian!
I think this layout is too expensive and not necessary.
You have

The units contain from the bottom to the top four substrate layers: at the bottom a 10 cm thick drainage layer of crushed rock gravel (range 25 to 55mm), in the middle a 10 cm thick layer of medium gravel (range 4-25mm) and a 10 cm of fine gravel (range 1-8mm) at the top a 15 cm thick layer of fine sand. Additionally, two perforated PVC tubes are installed to enhance aeration.

45 cm of material, this is expensive especially if you think in large scale. How do you implant a system with 4 layers 10 cm each? That is a lot of work and not necessariy. From my experiences just two layers are enough. The “secret” is to have the upper layer in a size that is does not enter the drainage layer. The most critical aspect to me is the fine sand…, but as you did not specify the sand it might just be a case of not writing exactly. It should be a coarse sand.

The loading should be ok, although with your temperatures I would be interested in higher loadings, as I think none of the three gets to the limit. You should do a layout where the highest trial leads to failure, in order to determine the best solution.
Personally I think a weeks rest is to short.
Take care of not doing just a 3 month trial, that is not enough.

Yours
Christoph
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  • groverhmc
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Re: Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear Christoph,

I agree with your comments; about four substrate layers, initially it was proposed three layers however we decided to apply four due to the availability of materials in the project area. Regarding to the loading rates you are right and probably I will increase the loading rates based on achieved removal efficiencies. And finally related with the time of study is totally true that 3 months are not enough to evaluate the system completely, but unfortunately I can't spend more than 3 months doing my research, hopefully we will find another student from a local university who could continue with the evaluation of the system.

I will continue updating the progress of this research.

Thank you very much for your comments, I appreciate it.

Best regards

Grover

Grover H. Mamani C.
MSc. Urban Water and Sanitation
The Netherlands
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Mobile: +919428621967(India), +31628476049(Netherlands), +59173006364(Bolivia)
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  • Madhu
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Re: Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear Grover,
I am curious as to what your research threw up.
I am grappling with this problem in New Delhi and studying alternative approaches.
Thanks
Madhu Thakar
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  • groverhmc
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Re: Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear Madhu,

Long time ago I didn't follow the discussion on my post, thanks for asking. Please you will find attached the final report regarding to post-treatment of Toilet Liked Biogas effluent. In summary I should say that the results are very good, practical and applicable in the rural area of countries with tropical climate like India. Using sludge treatment wetland not only the quality of effluent is improved in terms of nutrient concentration but also the pathogen reduction is very significant. Additionally, the recovered water can be used for agriculture and harvested plants can be used to feed the animals.
Please have a look the attached report and let me know if you have questions.

Also I will kindly request Elisabeth to post the complete thesis in right location at SUSANA webpage.

Best regards

Grover

Grover H. Mamani C.
MSc. Urban Water and Sanitation
The Netherlands
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Mobile: +919428621967(India), +31628476049(Netherlands), +59173006364(Bolivia)

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Re: Sludge Treatment Wetland (STW) for anaerobic digested slurry. A study case in Gujarat, India

Dear Grover and all,


Thanks for providing the latest results.

You can find the case study (MSc thesis) in the SuSanA Library now:
www.susana.org/en/resources/library/details/2435


Kind Regards
Jasmin (on behalf of the SuSanA Secretariat)

Posted by a member of the SuSanA secretariat held by the GIZ Sustainable sanitation sector program
Located at Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, Germany
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