Dear Agas,

 "What is the grading of the sand / gravel in the CW?"

The grading of the sand / gravel in the CW is your "engine" of your upcoming CW-system, therefore use only thoroughly washed "natural" sand and gravel (not crashed material!) with a mixture of ~60% 0...2 mm sand and ~40% 2...8 (6) mm gravel = 0...8 mm.  Permeability value K_f = 5.5 x 10^-4 m/s (this is the filter flow velocity)

See attached my two PDF, you can do your self a machine translation.

Good luck

Detlef

Dear Prof. Seshadri,

If your interest is to use the effluent after planted CW for irrigation, how is your average outlet flow by using planted CW?

"Planted constructed wetlands have higher water loss through evaporation and evapotranspiration than unplanted constructed wetlands and overall percentage of inflow lost was found to be highest in non-aerated wetlands, due to the lower hydraulic load that they received compared to identical but aerated systems (Nivala et al., 2022). "

In cold Europe in hot midsummer, it only drips in average out at the outlet of the CW's, due to evaporation and plant evapotranspiration. If your interest is to use the effluent after CW for irrigation, as a possible ‘remedy’: CW's are just aerobe biofilm systems, which means that CW's do not need/must have plants, if so only small ground cover and small flowers to make it look nicer. 

‘The eye helps to clarify’  = just by beautification!... 

The discharge values of a customer's CW without plants were identical to those of the customer's CWs with plants - are very GOOD =  10-50 mg/l COD...

What are your valuable practical experiences in this regard?

Best Regards,
Detlef Schwager

Dear Prof Ajit Seshadri,

Thank you for sharing the information about your experience using a constructed wetland as the final stage of the treatment process.
I am interested that you are using elephant grass sp as the reeds. Do you think that would work well in our climate in south east Botswana, with hot summers (typical temp range 20-35 degC) and cool dry winters (typical temp range 0-25 degC)?

Could you share some more details, e.g.:
What is the water quality before and after treatment?
What is the flowrate?
What size and geometry is the CW?
What is the grading of the sand / gravel in the CW?

This would be very helpful as we begin the detailed design of our system.

best regards,
Agas

Dear Detlef,

We are still waiting for the EIA consultant to complete the EIA.
We will then go ahead with the detailed design. 

Thanks for your continued interest in the project.

regards,
Agas

Dear Researcher Dr Agas
Greetings. 
Have been a Dewats practitioner and in the last stages of treatment process use CW constructed wetlands using Elephant grass sp

This has given us good bio Remediation and results.
On noting rhe treated water is well compliant and user ready.
Have used the recycled water ie output for others site uses viz flushing toilets,  veg farm irrigation Etc.
While doing CW Constructed wetlands plants, we used Floating Bed techniques 
While using FBs Floating Beds we get advantage of doing cropping in a convenient location. FBs are kept ready in nursery and we exchange them depending on our needs Etc
Above info details given to SuSanA Members as information Etc.
Pl arrange propagate info ..

Thanking you
Prof Ajit Seshadri 
Vels University Chennai India 

Dear Agas,

What is the outcome of your CW project?

Best Regards,

Detlef

Dear Detlef and others who have contributed to this thread.
Sorry for the long silence and thanks for the suggestions and advice.
The project requires an EIA (Environmental Impact Assessment) before we can proceed with the next step which is detailed design.
The EIA has been underway since August last year and we hope it will be completed in the next 4-6 weeks. However, it is hard to predict, and they can drag on for a long time. We have an environmental engineer who is helping us with the design, and we are considering the different suggestions that were raised here. I hope that we can respond with more details soon.

best regards,
Agas

Dear Agas,

What is your progress on your communal wwtp (CW)?

Best Regards,

Detlef

Dear JF and LetLef,
Nice info on CWs and Dewats - indeed an apt combo.
For all physical remedials settlers- anaerobic tanks with or without filters are used.
Can be followed by more ultra- fine filtration done.
We used next CWs in float form in 3 phases
Initial process in CWs done till fairly compliant effluent is reached say BOD5 @ 30ppm
In Final stage, CWs in Floats use Elphnt grass sp. grown, cropped for fodder use Etc
All P, C and micro-bio parameters in limit and compliant per PB standard s Then recycled water taken for secondary water uses in complex- flush water for toilets, garden irrigation Etc.
As all are NbSs, no handles, just visit once 6mths Etc

Well wishes for prospects 
Prof AjitSeshadri, 
Vels University
Chennai India 
 

Dear Letlef.

In my experience implementing CW  (20 years) the sludge quantity for schools,restaurants or hauseholds are always different!!.. So I only use literature standards as reference.

 I really recommend   to measure the flow and the waste water quality ( Q= ?? L/d, COD =  ? = mg/L , BOD5 = mg/L) ... 


For your reference I make fast calculations for your Settler/ septic tank using the DEWATS spreadsheet..

Best regardsJFrancisco

Dear Juan,

Thanks for your suggestion.

Just to have a better understanding about the sludge volumes involved in this possible septic tank-sludge reuse example:

I would start with ~50 ml (settled dry matter) per p.e. and day (50 ml/p.e./d) = ~250 p.e. x ~50 ml/p.e./d = ~12,500 ml/d (~12.5 l/d) x 365 days/a = ~4,562 l/d (~4.5 m3/a for ~250 p.e.). 

Experiences and University studies (BSc, MSc. & PhD-work) found out: After resting/settling sludge more them ~5-6 years in septic tanks ~1/3 of settled sludge volumes "disappears" by internal anaerobic processes over the years = ~3 m3/a remain under "could" climatic condition. Maybe less under "warm" climatic condition!?

If all septic tanks gets dislodged every ~6 years by ~2/3 (~2 m3) of settled sludge (keeping ~1/3 (~1 m3) sludge volume in order to keep biological processes in septic tank in takt).

 ~6 years x ~2 m3/a = ~12 m3 settled (dry) sludge could be processed in a humification plant every ~6 years.

Just guessing, pumped out with water content (steering the settled sludge with water to be able to pump out) , we might talk about ~25 m3 watery sludge every ~6 years , or more.

Would you follow this simple sludge calculation?

All the Best
Detlef 

I have taken note of the valuable points raised by my colleagues regarding to the constructed wetlands, and I concur with their perspectives. However, I would like to draw attention to an aspect that seems to have been overlooked: the collection and treatment system for the Fecal Sludge in all 30 septic tanks. In light of this, my contribution to the ongoing discussion is the suggestion that you take it into consideration.In areas with arid weather conditions, I recommend employing a Sludge drying bed in conjunction with co-composting of the kitchen biowaste. Conversely, in tropical environments, I propose considering the utilization of Sludge drying reed beds while recirculating the lixiviate back into the first CW.


Please accept my best regards.JFrancisco