WWT REUSE and mixing with rainwater

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the need for water becomes more and more intense. So for real recovery, even see a total recovery of treated wastewater, such as Tunisia, which has around 300 million m3 / year and which suffers from a water shortage and whose call for unconventional resources, such as treated wastewater, are there methods or sectors that can reuse all of this resource?


can mixing treated wastewater with rainwater be a good solution for significant reuse? are there any experiences in the world?

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14 Answers

  1. Rain water harvesting and re-use is common, the question you need to ask is if you need to mix the typically higher quality rain water with a lower grade wastewater effluent - you may have specific needs without mixing the two and can optimise the distribution and re-use thereof accordingly. If not, yes it can be blended, bear in mind final water use quality requirements, this will drive what upstream treatment processes need to be applied

    It is generally not recommended or acceptable to allow stormwater into the sewer for combined treatment, the treatment capacity is greatly increased when rain water is discharged into the sewer, requiring more capital as more infrastructure will be required.

  2. to reuse the rainwater should  consider the level of groundwater, and check the sea water will not follow while we pump the rainwater. the Cl- of  rainwater with little sea water will rise rapidly, and the will affect the benefit of reuse.

  4. Why not if the final quality is within required quality norms?

  6. The way question is presented is rather misleading .

    At first , talking about reusing rainwater whereas rainfall is not consistent is tricky .  Of course rainwater in areas as Tunisia is considered rather clean and therefore minimal treatment is required .

    On the other hand , use of treated wastewater after tertiary treatment mainly for agricultural use is already widely used in GCC countries with different degree and complexity (with subsequent varying cost) .

    I have been deeply involved in three cases of water re-use in Creta Island , Greece , in Jabel Ali Plant , Dubai , UAE and Sulaibiya Plant in Kuwait .

    The last one is designed for water reuse at potable level treatment so after conventional biological treatment , water passes through 60μ. disk filters , followed by UF and finally two or three stage RO treatment.

    The last Plant produces clean chemically water H2O , which i have tried it myself with BOD @ 0  , TDSS below 100 , zero micro organisms etc.

    Of course a cost of around  $0.7 USD is involved . This water is used for agriculture .

    Therefore one should consider all available technologies and combine costs involved .

    So for waste water effluent i gave above an indication , whilst for rainwater one should consider cost of collection in open reservoirs (small storage dams) , piping network to distribution areas or pumping stations for enriching water wells and so on .

    For sure it is a MUST for those countries that they already face water shortage and hence water handling and management is of utmost importance .

     

  7. Endorsing MM 's notings, wish to further add that wwt effluent is not consistent, may become deficient if there is a lapse or mal function Etc.

    Hence the two are left separately. If you are very sure and all parameters are compliant, then after phyto remediaton and extended aeration theceffluent more than compliant, may be taken for rechrge aquifers Etc..

    Well wishes.

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  9. While I wouldn't combine the two, wastewater reuse is a good option in arid areas. What you do with the reuse water will determine the level of treatment needed. Watering animal fodder crops has a lesser treatment requirement and can benefit from left over nutrients, same with consumption crops that the edible portion isn't in contact with the water. Irrigation technique and site access need to be considered. 

    Potable reuse requires a high level of treatment. I have seen a system where the wastewater plant effluent treated to a good level (20mg/l max BOD, TSS) is then run through a up flow clarifier and sand filter, 24 hours of contact time with a free chlorine residual of 0.2 mg/l and then used to recharge the aquifer.  The nearest potable well was several miles away.

    We have been looking at a similar system, but using micro filtration for the wastewater plant. The aquifer in our area has been declining. We currently produce water to be stored in the aquifer through the drinking water plant during seasonal high water flows. This has slowed the aquifer decline. We may be able to stop the decline if we do the same with the wastewater plant.  

  10. Rainwater in most cases is far cleaner than treated wastewater. I strongly recommend that you do not mix them. With a well designed rainwater catchment system you should have much cleaner water. Test a prototype of the proposed system design in the location you intend to collect, to confirm this (use potable materials). You reduce your exposure to a plethora of emerging contaminants including fire retardants, pharmaceuticals etc. that many wastewater treatment systems struggle to completely remove. A well designed rainwater catchment system can catch and safely store large volumes of rainwater if you protect it from heat. "Treated" wastewater can continue to be problematic and may not store for extended periods of time without serious complications. Rainwater alone should  be much more cost effective.

  11. hi

    IT is better to separate the rain water from sewage, 

    even good effluents need special care and it is not worth to put the rain water there

    Ilan

    Answered on by

  14. In Jordan, By Law for Wastewater Reuse for Agriculture: It is not allowed to mix clean water with WWTP effluents inorder to satisfy and compliant with standards.

    Be note that mixing wastewater with clean water not favor from microbiological point of view. Be careful.

    Now, after the effluent discharge to the river or lakes, nature will take care for self purification through sunlight, oxygen mixing will enhance the quality of water if the process and the ecosystem nutrient unloaded.

    Jordan has the best experience  in this sector.

    Best regards 

    1 Comment

    1. Rain water is already aesthetically and bacteriologically acceptable and its independent harnessing  is widely undertaken and accepted. Methods of optimizing rain water usage should in my opinion be limited to its direct use without introduction of another role as a ''contamination dilution agent'' for waste waters. The economic benefits of such role are not apparent and I have no experience in my 40 years of work where such practice has been made. One has to treat the entire practice on a case by case basis to establish the practicality and economic sense this would make.