Dear Euiso and dear Ajit & other experts in the field,

May you and others kindly add as experts in the field your second or probably third practical opinion/advice/know-how to the advantages of Agas's future project + others & my self could learn from this constructive "Open Source" exchange too, by not having a competition on the subject.  Keep in mind Agas and many others are not practical experts in the field, so you may use therefore "plain" English .

All the Best

Detlef Schwager
Dipl.-Ing.(FH) & MSc. Tropical Water-Engineering

Dear Researcher Agas:
Can ideally go for Dewats type design to remedy Sewage water and take for reuse also.
Both processed water, sludge and plant foliage from CWs can be reused by communities  for monetary good.

With best wishes, do well
Prof Ajit Seshadri 
The Vigyan Vijay Foundation 

Dear Professor Choi,
Thank you for the advice. We will take this into consideration as we plan our project.
best regards,
Agas

Dear Agas,

Thanks for the details.

My very practical approach towards CW-WWTP design is always very conservative, not trying to “save” every little m2, m3 and $...

Your ~30 m3/d for ~250 p.e. is at a “communal level” for a CW-WWTP!
 
By all means, your main emphasis should be the protection of your drinking water sources, the boreholes against this large amount of WWTP effluent.  Kindly add the locations of the boreholes to your map.

Keep away this later punctual distributed high amount of effluent from your boreholes, please far as possible! Do not take this "stuff" too lightly in the longer term, I mean e.g. pathogenic E-coli (Escherichia coli)! Do you have any treatment in place for the raw borehole water? Do you have any information about the hydrogeological underground condition of your boreholes and your general area? Groundwater flow direction?  Groundwater flow direction do not always following the surface water flow direction...

Seeing the contour lines and location of your future CW-WWTP, unfortunately it will be very unlikely to fed your future CW-WWTP by gravity.  A simple gravity approach with less technical components is very unlikely. You will need at least 2 submerged wastewater lifting pumps, who are running alternating automatically.  

Having pumps enables you to use the more efficient vertical flow CW (good aerobic conditions), them horizontal flow CW (more anaerobic & only partly aerobic condition) to have an CW-WWTP effluent with a good max. 100 mg/l COD or 25 mg/l BOD.

“My” vertical flow CW’s make 10-40 mg/l COD under much colder climatic condition by quality planning and construction with permanent and hard quality controls, using 4 m2/p.e..

2 parallel installed vertical flow CW beds with total very conservative ~3 m2/ p.e. should be installed. Total ~750 m2, each bed ~ 380 m2. The beds should be fed by alternation every 7 days. This means always one bed should stay dry 7 days.  This bed alternation is typical for a communal level CW-WWTP.  Following my experiences the bed "in charge" should get only small ~5 mm for pre-treated effluent (by septic tank and others) distribution not heavy 20 mm distribution as stated in standards. (mm = l/m2). In practical terms ~380 m2 x 5 l/m2 = ~1,900 l (~2 m3) per distribution of pre-treated effluent to one bed.   Any permanent effluent distribution to a CW bed is ok for small private level (scale) CW's only.  For a communal WWTP scale you have to use industrial approaches and equipment quality. NO DIY-standard!!!

Probably you need a receiving tank for the treated effluent too, to be able to pump your final effluent to every direction in need and far away from your boreholes.

I was in hope south of your boundary the waste land is yours too. Is there any possibility to make probably use for fire wood production or just percolating there the effluent of the CW-WWTP?

I hope it is not too disappointing for you, as you where in hope for a much simpler gravity fed horizontal flow CW?!

Waiting for your reply to take it further.

Detlef


PS: What are the general conditions around this ~30 septic tank with soak pits or pipe drainage? Any messy puddles? Any disturbance by this septic tanks towards any borehole? Are you forced by authority to take your waste water treatment to a much higher level or is it "just your hobby" ?

Dear Detlef,

Thanks for your post with some detailed questions.
I will try to answer them as best I can.

- I am just guessing, you have ~30 already existing septic tanks, right?
Yes, they are all existing, many quite old.

- Are you in a sloppy area? I found your x,y-geolocation, so I could determine your existing slope by my self. I made a contour line map with   contourmapcreator.urgr8.ch/
Yes, as you see the slope is from NW to SE and about perfect for gravity flow.
The treatment works will be located in the SE corner of our plot. 

- Please mark your ~30 septic tanks, kitchen and your original plan on the provided "map" and send it back. Your CW's will be in the southern part of your large property by gravity fed?
I have attached a sketch plan showing the pipelines to collect the effluent and the location of the CWs.

- Any wells for human consumption in the South? 
We have five boreholes, the nearest is approx. 30m from the location for the CWs. The Static Water Level is approx. 20-30m below ground level.

- "using two horizontal flow reed beds" in line or parallel? 
In parallel. The intention is that when they need cleaning, one can continue to be used while one is cleaned.

- How many people you like to serve with the project? Always 100% during the year? Average water consumption per day and per year?
see attached file
  These are the design figures. Actual are considerably lower, but allowing for increase in numbers. The number of people living on site is much less during holidays which are approx. one month, three times a year.

- Any kitchen or other difficult effluents included?
No, grey water is mostly disposed of in mulch basins (based on OasisDesign.net)

- Do you like to make any use of the treated effluent? Keep in mind planted CW in your hot dry climate "loose" via plants evaporation nearly all the water, the effluent output is very small or even nil.
Yes, we will use it to irrigate citrus orchards, but it will supplement borehole water, so losses are not critical.

- How you or your suppliers could make sure the gravel and sand are very clean washed and have the right grain sizes (good grading curve)?
We can probably mix purchased sieved gravel with river sand to achieve the required grading.

Many thanks,
Agas

 

Dear Agas,

Easter-Greetings from Zanzibar.

Let me give you just my practical experiences without starting a deep theoretical discussions.  Please provide some basic technical information about your project, in order to do so.

- I am just guessing, you have ~30 already existing septic tanks, right?

- Are you in a sloppy area? I found your x,y-geolocation, so I could determine your existing slope by my self. I made a contour line map with  contourmapcreator.urgr8.ch/

- Please mark your ~30 septic tanks, kitchen and your original plan on the provided "map" and send it back. Your CW's will be in the southern part of your large property by gravity fed?

- Any wells for human consumption in the South? 

- "using two horizontal flow reed beds" in line or parallel? 

- How many people you like to serve with the project? Always 100% during the year? Average water consumption per day and per year?

- Any kitchen or other difficult effluents included?

- Do you like to make any use of the treated effluent? Keep in mind planted CW in your hot dry climate "loose" via plants evaporation nearly all the water, the effluent output is very small or even nil.

- How you or your suppliers could make sure the gravel and sand are very clean washed and have the right grain sizes (good grading curve)?  

Until I receive your answers please see in the meantime at www.aqua-verde.de many pictures about CW, ABR and ponds constructions and design considerations (use auto translation for the German language texts). "Pictures say more them 1,000 words"...

Keep all as simple as possible and with some economical long term benefit!

See you again.

All the Best

Detlef
 

PS: Do not become a "slave" of your future system...

Dear Agas,
Hope my experience in Cambodia would help your wetland problem.
We applied vertical flow wetland for septic tank effluent for school with a loading rate of 20 to 40 gCOD/m2/d.
If you want to treat it with horizontal flow, then you need to apply with lower loading rates than vertical flow.
The drain in vertical flow must be free flow to allow easier oxygen penetration through drain and ventilation tubes.
The O & M aspects; You can grow reeds but also corn. The reed may help som oxygen supply, but it is difficult to find how to use after harvest.
The corn can be a feed for animals. There would be some residues on the sand surface, and you can remove them by hands after every harvest.
Hope this would help you how to design the V-flow CW with O&M.

Euiso Choi
Professor Emeritus
Korea University
This email address is being protected from spambots. You need JavaScript enabled to view it.

We are preparing to construct a system to treat septic tank effluent from about 30 septic tanks using two horizontal flow reed beds. 
We are located in Botswana, with a generally hot, dry climate. 
I would be glad to hear of experiences with similar projects, including design recommendations, operation and maintenance requirements and lessons learned. 
Many thanks,
Agas