High TDS in Vegetable Processing Effluent

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We are running ​a vegetable ​processing ​industry and our ​process ​includes ​washing ​gherkins and ​vegetables. ​

The effluent with initial ​TDS of 3200 ppm ​is directed to ​an effluent ​treatment ​plant where it is aerated and passed through ​the sand filter. ​The TDS then drops ​to around ​2900 ppm which is very high.

How can ​we reduce ​the TDS to less ​than 1000 ppm?​

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22 Answers

  1. Changing your aeration technology to a fine and ultrafine bubble generator will provide a significantly better performance in coagulation and flocculation and thus improve filtration performance.

    However, I think your sand filter is failing if TDS is still high after tertiary treatment. I suspect that the filter bed has wormhole channeling due to the formation of biofilm. In this case, switching to Activated Filter Media would fix this problem because biofilm cannot form on the media bed. I have found this to be the most common reason why sand filters fail. I have experience in this process for food processing in Asia and Australia.

    If you would like to know more, please email me at andrew@waterandoilsolutions.com.au

  2. Bonjour 

    C’est un peu normal d’avoir autant de TDS. Peut être faudrait-il effectuer avant toute chose une filtration/décantation des solides flottants pour en  éliminer le maximum. Je ne voie pas très bien l’apport technique ou scientifique que l’aération peut apporter à un effluent tel que celui décrit. L’eau de lavage est brassée, aérée, elle s’écoule volontiers vers le site de traitement, il y a donc déjà pas mal d’oxygénation.

    Qui plus est en quoi l'aération a une efficacité scientifique sur un tel effluent. Le fait de filtrer cet effluent sur des filtres à sable devrait  lui enlever une grosse part de matière solide flottante, ce qui d’après votre post n’est pas le cas.

    Il faudrait donc choisir un dispositif de filtration plus efficace. Peut être que votre problématique tient du travail à effectuer en amont lors du lavage. Il faudrait que l’eau de lavage passe par plusieurs bassins avant d’aller rejoindre la STEP. L’eau circulerait uniquement par le trop plein des bassins qui retiendraient une grosse partie des TDS.

    Maintenant j’ai une autre proposition beaucoup plus intéressante. Mais à ce niveau on entre dans un environnement -biologique-. Si cet effluent n’est pas contaminé par des pesticides, des engrais chimiques et autres produits chimiques, il pourrait être recyclé immédiatement à l’arrosage d’une biodiversité quelconque. Ces TDS seraient un bon apport pour le sol.

    Hello this is somewhat normal to have as many TDS. May be should he perform a floating solids filtration/settling before anything else to remove the maximum. I see very well supply technical or scientific that aeration can bring to an effluent such as that described. The wash water is brewed, aerated, it flows to the treatment site, so there is already lot of oxygenation. In addition what aeration has an effective science on such effluent.

    Filter this effluent on sand filters should take away a big part of floating solid matter, which according to your post is not the case. You should therefore choose a more effective filtration device.

    Maybe your problem is the work to be done upstream during washing. It should be that the wash water through several ponds before going to join the STEP. The water would only circulate by the too full basins that would come a big part of the TDS. Now I have another much more interesting proposal.

    But at this level you enter an environment - biological-. If this effluent is not contaminated by pesticides, chemical fertilizers and other chemicals, it could be recycled immediately watering to a biodiversity any. These TDS would be a welcome addition to the ground.

     

  4. Dear Pramod,

     

    Sono-electrochemical water treatment could provide a solution.

     At Power & Water, we use Soneco(R) Technology which is a combination of electrolysis and assisted power ultrasound that is capable of scaling back TDS levels within an effluent but we also have an adapted system which is able to treat brackish water with high TDS levels and to reduce by around 2000 ppm is possible. 

     

    As below comment - further measurable parameters would be helful here. Presuming organic - if there was a need to break down or reduce contaminants, we also use AOP's. 

     

    Please let me know if you'd like to discuss further. Send me a message (or email) with some further details and I would be happy to send over some information and to chat through. 

     

    Thanks, 

    Zoe Matthews 

     

    Marketing & Sales Executive, Power & Water - UK 

    2 Comments

    1. We are also 12 months off full-scale, in country test validation of a low energy, low pressure and membrane-free desalination technology as well as our current capabilities for brackish/slightly saline water treatment. The desal is using a slightly different approach to clean water treatment which is also chemical free and utilises electricity. 

      Not sure on your exact requirement but salts, dissolved particulates, organic and inorganic and ideally suited for removal via electro-chemical means. 

  5. Hi Pramod,

    To drop this TDS to 1000 ppm shouldn't be so difficult.

    do you have flow rate, COD or BOD and any additional analysis. assuming that the TDS is mostly organic I think that coagulation could help you or even electrocoagulation

    is the water turbid? could it be that you carrying over something like clay? fine clay may be stable an no settle readily and my bypass a sand filter.

    is there any reasons for this water to be loaded with ~3000ppm of dissolved salt? Inorganic matter?

    could you optimise the treatment plant (aeration process)

    feel free to contact me but we need to know a bit more before offering a solution.

    Gerald

  6. Hi Pramod,

    To drop this TDS to 1000 ppm shouldn't be so difficult.

    do you have flow rate, COD or BOD and any additional analysis. assuming that the TDS is mostly organic I think that coagulation could help you or even electrocoagulation

    is the water turbid? could it be that you carrying over something like clay? fine clay may be stable an no settle readily and my bypass a sand filter.

    is there any reasons for this water to be loaded with ~3000ppm of dissolved salt? Innorganic matter?

    could you optimise the treatment plant (aeration process)

    feel free to contact me but we need to know a bit more before offering a solution.

    Gerald

  7. Dear Mr. Kumar,

    I could see lot of suggestions on treatment etc. appreciate.  My suggestion is to start using Rain water and mix with your existing source of water in tanks. Rain is soft and fresh water, if you have large roofs as catchment then with roof top rainwater filters you can harvest huge volume of rain water which would bring down TDS to large extent due to dilution. 

  8. First: the question is about TDS and not TSS, so settling will not resolve much to reduce TDS.

    Second: sand filters don't treat, only concentrate the solids in the backwash water. They can be used for final polishing with the backwash to the biological treatment step (see further on).

    Wastewater from the vegetable industry can contain a high amount of solids from washing, these can be removed by settling (after a fine screen). Lamellae settlers are very effective and can be equipped with a surface scraper for floating solids, which also exist in the wash water! More TSS can be removed with a DAF system, with chemical dosing (PAC, polymer).

    Then the wastewater can contain quite some dissolved organic matter, which can be treated with aeration, but is only effective in the presence of dedicated bacteria (activated sludge as MLSS), final sludge settling and return. Excess sludge treated separately by dewatering, drying, composting etc.

  10. Dear Mr. Kumar,

    as first a reliable analysis and data addressing the volume to be treated should be transmitted.

    Beside all the valuable solutions offered, in order to reduce the TDS the last step needs to be a membrane based treatment. But if reverse osmosis is necessary or nanofiltration could achieve the limit value in the effluent needs to be assessed in detail. In any case for the successful processing of this kind of wastewater we strongly suggest to use membrane elements or membrane modules respectively based on the "open channel technology". 

    You may contact us via www.petersconsulting.eu.

    Best regards

    Dr. Thomas Peters 

  11. Dear Mr. Pramod, 

    The very fact that you have aerated the effluent & it reduced the TDS, keeping the balance at 2900ppm, indicates that you have destroyed BOD. Thus any additional treatment for BOD removal is not needed. 

    Now, kindly check the ash content of the same aerated effluent to verify, if all TDS is inorganic only or some non-biodegradable COD is remaining.

    If you find ash is equivalent to 2900ppm, then COD is not there & whatever balance is inorganic dissolved solids only.

    Then you are left with the option of mixing the same with incoming raw water, let it undergo usual treatment & reuse the same in process. The merit of this system is it does not leave any problem of residue.  

    Alternatively, if the above is not acceptable to management not for technical, but psychological reasons, then you will have to invest in RO to extract substantial portion of permeate at less than 50ppm TDS, which can reused, but balance must be sent to evaporation ponds to remove the dissolved unwanted salts to send them to waste disposal. 

    Please understand that washing removes many adhering soil components  adhering to vegetables. 

  12. Dear Pramod,

    Depending on the loading rate of TDS and volumes to be treated, you may either prefer a (sand) filtration system with automated backwashing (fairly cheap) or a percolation wetland system. If the loading rates are very high to start with, you may prefer to start with a primary settling tank to already clarify to a certain extent. The use of coagulants/flocculants will increase TDS removal yet at increased cost.

    Following are the cheap method for removing TDS
    1.  Biochar

    2. Advanced biological treatment

    3. Sand filtration with automatic backwash

    4. RO (Costly)

    Knowing that TDS = total dissolved solids, the first step is to remove all non-mineral dissolved solids by advanced biological treatment (without adding any chemicals other than nutrients if/as required). This results in ultra-low TOC, COD, BOD, TSS, turbidity (NTU) and SDI (silt density index) which minimizes irreversible fouling and power consumption of NF/RO membranes and doubles their economic lifetime. In the second step, some of the minerals could be removed by precipitation and/or air stripping. Finally after UF/cartridge pre-filtration and conditioning, the remaining TDS is retained by partial or full RO filtration as needed. I would like to add that some minerals such as sulfates, nitrates, ammonia, ... can also be removed in the first step by advanced biological treatment. In this way, we develop, design and realize tailored high grade water reuse systems with over 90% overall water recovery = less than 10% water loss at the lowest operating and lifecycle cost. Depending on the scale/capacity and on the quality of the source water the treatment steps 1 and 2 could be skipped as to minimize investment cost.

    RO is the only commonly used domestic filtration system that removes even the dissolved impurities. RO is required if the Total Dissolved Solids (TDS) exceeds a certain value. (what is the upper limit ? Look for discussion on that elsewhere in IWP). RO is also suggested if you have reasons to believe that your water may be contaminated with sewage/ pesticides/ heavy metals/ industrial effluents.

    A problem with RO is, it needs a lot of water. It divides the input water in two parts, and forces the dissolved solids out from one part in to other. Thus, the output comprises two streams of water – a “clean” stream with low TDS and cleaned of other impurities too. And a “reject” stream that is even more dirty than the input water. Typically, an input of 3 liters will give 1 liter of clean water and 2 liters of “reject”. Theoretically, the “reject” water can be used for mopping the floor etc. but few have the discipline to do that.

    regards,

    Prem baboo

  14. I am pretty sure all the answers above properly addressed the pre-screening and sedimentation by clarification which will reduce TSS (Total suspended solid) to the appropriate level for required effluent stream or possibly to the reuse/outfall requirements. MBR (Membrane bio reactor) is also good candidate for removing TSS for next process if the plant has not enough space and the energy can be compensated somehow. Even though some chemical process involved in clarification and bio-process (coagulation & flocculation including chemical injection for COD and BOD control) can be beneficial for reducing some of TDS, it won’t drastically reduce the TDS (Total dissolved solid). To reduce TDS you probably want to use membrane based approach after you reduced TSS drastically down to to the level of SDI 5 or less. Hope I addressed what you need. Thanks.   

  16. Have you determined the identity of the TDS yet? That will dictate the treatment.

  18. Dear Mr Kumar

    for wastewater from vegetable washing process it is necessary to have following treatment units prior to aeration such as:

    - screening

    - grit removal

    -  primary sedimentation tank

    In general, TSS should be significantly reduced and then you  could use existing aeration process and adjust air quantity.

    If necessary secondary  sedimentation unit could be applied before sand filters.

     

     

     

  19. I think even though your TDS is very high (and there are ways to drop it).... What is your BOD level as that will override most, if not regulations and therefore determine what treatment I would recommend. Quite honestly, the fastest way to drop TDS especially highly organic TDS is to discharge the permeate from the sand filter to a settling tank for at least 90-120 minute and then through carbon filters.  The settling tank should remove at least half the TDS and if not, a coagulant and possibly a polymer may need to be added and mixed into the sand permeate  (in a separate tank) prior to entering the settling tank.  This would be the cheapest option by far but as with anything I do I would always run bench scale tests to make sure the performance fits your needs.  If this initial option fails then we need to jump to a whole other level of treatment which I won't even start talking about here as it will take pages to write.  I always start with basics before going further.  And no the polymer will not wreck your GAC filters just in case you are wondering... We do it all the time. 

     

    Kurt

  20. Dear

    The normal treatment can not be effective,  to reduce tns you have to membrane system like uf depending on the end using of water.

  21. Kindly go through this article. complete replacement for Primary Clarifier. Poly Disc Filter, DAF, Sedimentation Systems, Sedicell... others! 

    Hydraulic time: 30~45 minutes max
    BOD / COD Reduction: 40%
    TSS Reduction: 95%
    Power Consumption:

  22.  Catatonic or anionic polymer selection  an use could help. Happy to discuss further if needed. Where are you based?