Design of a Constructed Wetland for Grey Water

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Hi all,

I am designing a wetland for treatment of grey water from showers at a charcoal factory in central Namibia where 200 people shower per day.

The design loading is 10 m3 per day and using the Kickuth equation I have a surface area of about 65 m2.

I have selected a horizontal flow SSFCW wetland with an existing septic tank as preliminary treatment.

Has anyone in Southern Africa done a similar design with a cost projection for the materials required? 

Thanks in advance 

Megan 

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16 Answers

  1. Hello Megan

    Note:-This is a shower for 200 people whose half will urinate at the same time.
    -as it comes to sanitary, where are the toilets? What are they connected to?

    Detail:-Waste water from showers will contain: urine, charcoal dust, dead bacteria, living bacteria.
    -these same wastewaters contain dispenser: shampoo, body care products. 
    -These wastewaters are grey and will therefore be very polluting for the environment because the septic tank upstream has no purification efficiency since it is only a storage tank of the suspended matter. The grey waters are very liquid with little suspended matter. The upstream pit is not going to hold anything back.
    -to this it is necessary to add all the household cleaning products of these showers which will drain on the humid zone.
    Very soon the pollution will kill all traces of life of this humid area and the middle will rot with a release of odors pestilential

  2. Hi. Megan. You may 1stly resort to bio soaps with less chemical content. Have the process in 3 phases.. having 2 Nos stage of 10sqm 2m deep to be anaerobic septic tank type. 3rd one 15sqm on say 5 beds with native plants with flowers for aeasthetic.. At the end have a 2 day collection tank of 20cbm.. say 5m Lx 2m Wx 2m Deep to consolidate final collection of effluent. This recycled water can be used for secondary purposes viz. flushing. irrigation to farms.parks.lawns etc ... w wshs .. Prof Ajit Seshadri. Vels University. Chennai. India .. 

    1 Comment

  3. Dear Megan,

    I read some comments to your quetsion and I want to clarify some concepts for you and for the readers, on the basis of my expertise. From my point of view, horizontal flow CWs is fine for your purposes. Firstly, it's not true that HF are more prone to clogging,  if you properly design the transversal inlet area (see Treatment Wetlands 2nd edition - Kadlec and Wallace, for more details) the risk of clogging is lower than VF, since you use coarser material (gravel) instead of the sand used in the VF. Secondly, it's not true that HF are used only for denitrification; HF provides some benefits in comparison to VF, especially in terms of simpler functioning (no needs of pumps or syphons if you have good horographic), this also means that you need less O&M activities and costs.  Moreover, HF works in more or less "plug-flow", with higher hydraulic retention time in comparison to VF, therefore you have more time to create contact within roots and greywater, helping to let me say find  carbon or nitrogen (in greywater you can have excess of both C and N, depending from which sources you take the grey water and if people pee in the shower) "somewhere" to have proper balance of C:N for biofilm, issue often encountered in compact activated sludge reactor used for grey water, and possible also for VF. The drawbacks of HF in comparison to VF are mainly 2: i) the less TSS removal, which you can tackle with a second VF stage, depending of the type of reuse you want (for simple irrigation is enough HF, for reuse in toilet flush it could be advisable to use also a VF) and the size of your system; ii) environmental, since HFs are mainly anoxic/anaerobic, and produce higher amount of methane (a greenhouse gas) in comparison to VF.

    Cheers

    1 Comment

  4. Clogging could be a problem,unlike for vertical flow constructed wetlands,though for simple greywaters from showers,horizontal flow SSFCW should theoretically suffice,in combo with a septic tank,as u indicated.

    But with 65m2 area,as per your calculations,it is fairly large,making it more prone to frequent clogging.

    Hair should mineralize without problems in vertical flow systems,I feel.

    Moreover,expert maintenance may be required,unless u use proven systems,as may be possible,to have,readily.

    Moreover suspended solids are not well removed in septic tank,which is more suited to higher denitrification requirements,which is not so much the case with grey water alone,with the organics.

    If organic load is higher multi stage,higher surface area vertical flow constructed wetlands can be considered with subfilters.

  5. Hello Megan,

    The main risk concerning the process you choose is clogging, due to biofilms and/or unsufficient SS settling in the septic tank (decantation of hair is fairly difficult).

    Did you consider designing a vertical flow constructed wetland, directly fed with raw water?

    It requires a higher water head than HFCW, but SS are trapped on the surface of the filter and mineralize rapidly. Together with alternate feeding of 2-3 subfilters, this totally prevents clogging.

    Depending on the organic load and outlet spec, total surface area could be between 50 and 90 m², in 1 or 2 stage VFCW.

    Good luck for your project!

    François (France)

    1 Comment

  6. It looks a really interesting project. Are they just showers or are toilets involved?  It may be advantageous to put some form of separation prior to the wetlands to remove some of the carbon.  If it is just showers, then wetlands would be suitable and relatively low maintenance and would clean up the water.  The carbon particles would become incorporated into the soil.

    1 Comment

    1. Hi Don, yes its very interesting! 

      The current situation is as follows: 200 employees working in shifts, 7 mobile long drop toilets, 10 showers with grey water draining to a 5m3 Clarus Fusion activated sludge package plant (PP),1 kitchen/butchery where blood and fat is trapped and then drained to PP 

      As the PP only receives grey water, there is insufficient COD for microbial growth and digestion. Futhermore, as the staff work in a charcoal factory, their bodies are covered in charcoal dust which makes its way into the plant via the shower water. 

      Thus I decided to change the system to the following:

      Install 8 low flush toilets (Eaziflush from Envirosan with 2l per flush), Urine, Faeces and kitchen drains to existing PP for AS treatment, effluent used on tree orchard at the factory, Showers drain to new constructed wetland or alternative treatment (capacity = 5m3 per day, BOD 269 mg/l). 

       

      So to answer your question, yes it is just grey water- and a constructed wetland should provide adequate treatment. 

       

      Regards

  7. We have just commissioned and started upa  wetland system for sewage but it is vertical sub superficial and use also a septic tank upwards. One interesting point in this system is that feed is intermitent. I also agree with Hamadi. Good luck in your project.

  8. Hi Megan,

    I would discuss firstly why you choosed the scheme Septic tank+Horizontal Flow CW for grey water (shower and kitchen waters?). HSSF-CW is used for denitrification but I guess that your total Nitrogen is not high in your wastewater (it would be great if you inform us about WW characteristics). I would suggest rather a Vertical SSF-CW for more removal of suspended solids.

    Hamadi

    Tunisia 

    1 Comment

    1. Hi Hamadi 

      Thanks for your feedback! I'm actually going to do a small pilot study with VF and HF to ascertain which is best. I have attached the water quality results - yes I would actually prefer to have less N-removal as the water will used for agriculture. Thanks for your advice, regards Megan 

  9. Hello Megan. Great to see that you are taking on work of this nature. We were colleagues in a previous consulting company.  I know of someone who can assist you with cost projections, however you treatment facility is specific to its use, and this means adjusting for the particular needs. 

    I would be willing to share the information.

    Regards

    Lynesha

    lynesha_pillai@yahoo.com

     

     

    1 Comment

  10. Hi Megan, good to see some application for grey water treatment, the Water Research Commission through the WADER programme are doing work on grey water systems in South Africa.

    I'm based in Joburg and will happily point you in the right direction, if required.

    A thought, it may be cheaper to purchase a system rather than to construct a wetland, my experience with constructed wetlands, subsurface is that it is critical to select the right size media, and equally critical to ensure laminar flow across the wetland basin, so the inlet arrangement, slope, media etc is key.

    Over time, wetlands require maintenance on vegetative growth, this can be a daunting task for the unprepared.

    You are welcome to contact me on gary@dikubu.co.za

    Regards

    1 Comment

    1. Hi Gary, thanks for your valuable insight. I haven't found any systems that are affordable in Namibia and as the site is isolated on a farm we have the luxury of trail and error. Do you have any examples of a working system or contacts who could advise me? Thanks again, my email address is galloway.mg@gmail.com. 

  11. Hello Megan,

    I would suggest using a lined pond with a passive filter system based on your affordability cost, to remove hair and other larger particles. In our constructed, and our floating treatment wetlands we use Vetiver grass  http://www.vetiver.org/TVN_VS_GAL_PUB/VS_Effluent_o.pdf  great for phyotoremediation and many other uses. It can withstand high nutrient loads and salinity. Check out vetiver.org for info. I would sell you some but we service the USA.

    DeAna Vitela-Hayashi

    AquaBio Environmental Technologies, Inc.

    deana@aquabio.us 

    1 Comment

  13. I design 100% closed eco systems for high tech industry. There is a way to do what you ask and make a profit doing it while at the same time cleaning the community, conserving potable drinking water and increase crop production.  I believe there is a water crisis in all of Africa. The solution starts with one drop at a time. When you begin nature will jump in and do some very unexpected things to accelerate the recovery process.  I have this type of project in many countries.

  14. Hi Megan,

    65 sqm is a bit over size but its ok

    Is you do it right, good construction and liner, proper gravel and piping and mature plants the cost per sqm will be round 100us$

     

    good luck

    Eli 

  15. Megan,

    We have developed and supply a product for commercial Grey Water reuse. We use it in the U.S. for large dormitories. The reason I am showing  you this is because I would strongly suggest some time of effective pre-screening. We use the WFF 150 and WFF 300 Wisy Vortex filters to filter out the hair and lent. The biggest thing that I have noticed with Grey Water reuse is that you need to use the water fairly quickly. Within a day or two or else the water quality breaks down rapidly. Let me know if you need pricing on any of these materials we use and or the complete package system I have attached in this email. 

     

    Shawn Crawford

    1 Comment

  16. Hi Megan, 

    By my calculations using Kenyan prices this comes out at about 1,600usd for materials only. This has no labour or transport cost, nor any pipework or chamber cost before or after the HF bed. Do contact me if you need anything further. 

    If you are able to add a stage to aerate the effluent before the HF bed this would be beneficial. 

    Best regards, Sarah

    2 Comments

    1. Dear Megan,

      Kindly take straight advantages of FRESH (O2 rich) grey water, therefore take out of your system the septic tank. Have an easy exchangeable rough coarse filter for hairs and other objects in greywater. Use vertical flow CW not HF as HF have a stagnant water and becomes anaerobic system and later clogging by anaerobic biofilm. Use gravity flow to CW for equal distribution to bed. Under tropical condition 1-2 m2 per p.e. should be enough. The founder of CW is not Prof. Kikut, it is late MS Dr. Käthe SEIDEL, see her now open patent in German language at my web page: http://www.aqua-verde.de/Orts-PKA/patente-von-dr-kaethe-seidel/

      and

      Beautiful Bulrushes, Remarkable Reeds:
      The Water Reclamation Miracles of Kaethe Seidel

      1990 by

      Elisabet Sahtouris, PhD

      evolution biologist and futurist 

      Gaia’s Dance (Kindle)  www.sahtouris.com

       

       

      Good luck

      Detlef

    2. Hi Sarah, thanks very much for your help and advice! I plan on doing a small pilot study and will definately contact you. Your company looks very interesting! Best regards Megan