Suggestions for re-treatment method for water mixed with solids and mud after coagulation and sedimentation process?

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We have a problem in a drinking water station here in Egypt for which I would appreciate suggestions about how to solve. The station treats about 70,000 cubic meter a day. After the coagulation and sedimentation processes, a lot of sludge remains in the sedimentation pool. To clean this sludge the station pumps back the sludge to a tank which is 500 meters away from  the incoming source, where about 5000 cubic meters of water is mixed with sludge every day.

We are therefore losing every day about 5000 cubic meters of water and bearing a high cost for this. I am trying to find a solution to re-treat this 5000 cubic meter water a day .

I am working with this water treatment plant and looking out for some equipment for treating water mixed with solids and mud after coagulation and sedimentation process. We need to retreat about 5000cu/m per day

Best Regards 

Mahmoud Zedan 

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17 Answers

  1. Perhaps I am missing something.  You mention this is sedimentation from a DRINKING water system, correct?  This is not a waste water treatment system, correct?  So, the sludge is not biological in nature.  There seems to be a lot of advice regarding aerobic and anaerobic which I don't think applies here.

    Can you tell me what you do with this sludge after the Sludge Tank?  What is the percent solids of the sludge by weight when it is pumped to the sludge tank?  Why do you mix the 5000 cubic meters of water with the sludge?

    Regards

    Dave

  2. If you are using polyelectrolyte, you have to take into account that polyelectrolyte used has already loosed its coagulation properties. In order to clarify and filter the rejected water you have to proceed a new coagulation (chemical addition and polyelectrolyte) and filtration.

    You have to estimate (after laboratory coagulation tests) the additional chemicals you will need to use, which should be maybe equal or more from what you are using now for the main treatment per day. I suppose it will not be an economical treatment conserning the water quantity you will recover.

  4. Screening to remove solids sand filtration to remove mud etc, coagulation with alum to settle colloid particles ,activated carbon to remove foul odour, and chlorination to kill micro organisms and for gaining potability. Dr MP Sukumaran Nair

  5. Mr. J. Seamus Boylson

    I see many good, practical & efficient/cost-effective potential solutions already offered, & don't wish to either complicate or confuse the basic issue(s) for the party seeking this group's technical assistance.

      However, the respondent that suggested the plant move its process from "aerobic" to "anaerobic" has quite possibly offered an overall solution that could both streamline the entire process, as well as convert a potentially valuable "waste" by-product into a renewable resource. [Plus: Recall that ALL Pathogenic forms are "aerobic"; & can't survive in anaerobic environments. Thus, an added "natural purification" process is introduced to you "value added" check-list!]

    A couple of major/positive "secondary/side-effect" results could also help improve the treatment station's "bottom line", while doing much good for local agriculturists.  My more comprehensive approach is a bit more extensive & detailed than these short retort formats can accommodate; so offer an invitation to contact me - either directly or via my LinkedIn Network connections - for added specifics.

    But in short: 1) Natural process elimination of much suspended effluvia can be pre-removed, simply via use of "ponding" raw water & allowing it to filter through Water Hyacinth ponds. [NB: A major So. CA water district I worked with employed this method, & reported a savings of $10K/Monthly on their treatment costs. The aquatic plant mass grows RAPIDLY, & without other care, simply from digestion of the effluvia; so replacement cost is NOT a factor: In fact, harvested it in turn has great value as a composting/mulching material; & also usable for animal fodder when mixed with other natural grasses/feeds.  2) In addition, we've found that adding very low cost/non-toxic Aluminum Sulfate to water greatly hastens the final clarification process; by promptly sending ALL suspended matter to the bottom for ease of removal, (sans costly filters, et al).

     But the idea of using all that effluvia as a new income source/profit center is ideal: I've worked on experiments here in the deserts of CA & Southwest USA, where we used treated food-waste converted to sludge, to turn total desert lands into fertile growing fields. A final example: While working in E. Africa in the '60's>80's, it was learned that Malawi's growing lands/soils were left so depleted (via Colonial farming excesses), they couldn't grow enough to feed themselves, let alone have any produce for sale/export. That condition was corrected, simply by having "TA" stop using costly methods to destroy a valuable renewable resource growing on their important lake & rivers, & instead use it as a "No Cost" renewable resource, to quickly/easily revitalize their depleted soils via composting/mulching. I mention this latter example, as while your water "pollution" dilemma is now a costly problem to your organization, LACK of fertile/water-retaining soils is the same to agriculturists in your area! Hence the old saying: "One man's Trash is another man's Treasure" comes into play; and what could otherwise be costly "solutions", are readily converted to valuable new income, if handled with care, thought & cost-effectiveness. Bottom Line: DON'T IGNORE APPROPRIATE TECHNOLOGY &/or LET "SKEPTICISM" BLIND YOU TO BROADEST OPTIONS IN PROBLEM RESOLUTIONS!

  6. Agreed with Andrew Fletcher ! Dear it seems like this system needs operational changes, however much more details and plant survey is required for a complete remedial action plan. Please find below some points and apply them if possible: 1) Increase the RAS (Return Activated Sludge) flow to aeration basin OR biological reactor (If available) to increase the age of bacteria. For example: Increase 10% flow in first step and observe for five days then 15 % to 30% gradually. 2) If any nutrient is dosed i-e DAP or UREA..check the NH4-Nitrogen and PO4 results....they should not exceed more than 1 ppm. Reduce dosing if results are higher than 1 ppm. 3) Coagulant should be dosed at outlet of aeration basin, however rapid mixing is required. If there is a degaser b/w aeration tank and secondary clarifier, dose the coagulant just before degaser for better mixing and retention time. 5) If tertiary clarification is available, dose floculant (Polymer) just before tertiary clarifier @ tertiary upstream. 6) If you have centrifuges or belt press for dewatering, conduct Sludge Volume Index SVI 30 test. Also adjust the dosing of polymer at belt press. 7) Temperature adjustment of effluent is one of the most critical points among treatment. Keep it in consideration. I wish, if I could have the complete data. Best regards.

  7. There seem to be many mechanical suggestions to resolve this issue. All are practical and solid. The waste treatment facility IS the problem. Chemicals are expensive. Water is a resource. Pathogens are a reality. The waste and or sludge/slur are valuable nutrients. Your farmers are in desperate need of this . Please do not use water to make the problem worse. Do use oxygenation cycle but stop any chlorine, DO use Archaea microbes to reduce waster (organic compounds) then refit waste nutrient rich water for agricultural use. No smell, no pathogens, agricultural land or reforest. Change desert back into ag or forest. Simple solution for a hard problem. Good luck.

  8. Clearly, Egypt needs to move away from aerobic treatment to anaerobic digestion where most of the solids are converted into methane gas, which could then be used to run desalination plants to convert brackish and sea water into potable water. The waste from this process would be pathogen free and contain all of the nutrients required to convert desert soil into fertile arable soil. If forests could be grown along the coastline, it is feasible that localised climate could be modified to induce additional rainfall. Egypt has planted forests and now exports timber from what was once desert, using solids and waste water for irrigation. Egypt as far as I am aware has not planted a coastal forest yet. This would need to be established along the shoreline for maximum benefits. I also believe that deserts are formed when coastal vegetation was removed by earlier civilisations, who grew grain to fuel manpower, which in turn impoverished the soils and eventually led to prolonged drought and deluge cycles. Over the years I have corresponded with the Egyptian Embassy and other governments affected by an inherent lack of rainfall, but alas no one has taken on board these self evident truths. Andrew PS The video is a presentation I did at the House of Commons. http://youtu.be/KHhXqzk7LhE

  9. The sludge treatment is realy issue if i am not wrong. Read this apper which is sort of case study describing different ways about waste treatment fro the drinking water treatment plant WASTES FROM WATER TREATMENT PLANTS: LITERATURE REVIEW, RESULTS OF AN ILLINOIS SURVEY AND EFFECTS OF ALUM SLUDGE APPLICATION TO CROPLAND - http://www.isws.illinois.edu/pubdoc/cr/iswscr-429.pdf

  10. membranes to treat sludge from water treatment sedimentation tanks

    Why do you mix the sludge with water?? And what do you do afterwards with this mixture? Anyway, you should thicken/dehydrate this sludge WITHOUT mixing it with water. There are a lot of methods for this, but on my opinion the best is to use RO membranes. Installing them may be a little more expensive that the rest of the classical methods, but you won't have to worry ever again about chemicals' expenses, or a whole sludge treatment plant maintenance etc

  11. I think the sludge pumped into the holding tank needs to be dosed with a polymer to aid its thickening, and the supernatant can be decanted and pumped back to the head of the works at 10% of the plant flow rate. The thickened sludge can be spread over drying beds and the subnatant recycled together with the supernatant as well. A jar test can be carried out to determine a suitable polymer for the thickening process. This is a common industry practice. Hope this helps. Good Luck

  12. Hello, you have several options to solve the problem, no sludge turbines you move the mud with very little water, if need be can be used as fertilizer in cultivation, on the other hand, you should try to separate it from oxygenation or by decantation, or with self-cleaning filters either by gravity or by pressure, separating the solid particles depending on their size in microns, recovering the water at the end of simply add it to the main processing process, or tratala with filters in the same area, if the also add to the main process will help to dilute the sludge part, but this is all speculation, to make a good diagnosis and a good solution would need more imformation, or see the plant, we produce drinking water plants, and discard with our system this problem, because the water and produce directly without solid, but still you can help solve the problem if you give me more imformation can study the case and talk to you about some more concrete thing. Yours truly. Xavier Dolo xdolo@dologroup.com

  13. Dr Raman Saravanane

    One of the exercise would be to optimise the dosage of coagulant plus optimum process factors pH etc., to reduce volume of the sludge  produced as low as possible or if that been fine tuned, next option would be to place a pre-sedimentation tank  before the coagulation which would help reduce dosage of chemicals and save running cost,  and eventually reduce the final sludge resulting out of coagulation. If all been done and the concentration is only for the sludge ,  solid thickener facilities are ok, however, sludge reuse schemes can be suggested to avoid addition water for cleaning. The posted clarrification needs some detailed data on the source of supply and layout etc. without which its quite difficult to visualise the solution.

    Thank you, Raman

  14. Be aware of the risk of creating a pathogen loop

    Whatever you do, be careful with the recovered water.  Sending it straight to the head of the works without further treatment could create a pathogen loop and increase the probability of pathogen breakthrough in your treated water.

  17. Suggestions for re-treatment method for water mixed with solids and mud after coagulation and sedimentation process?

    In case that your questions is how to get more water out and reduce volume of the sludge, try sludge thickening methods starting from the bottom going up. First test flocculents to make sludge more dense, follow by the gravity thickening, lamella/tube clarifier and so on. You may consider membrane thickening, which may be more costly, while it may be more effective.

    Regards,

     

    Val S. Frenkel