Wastewater Equalization vs. Segregation

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Wastewater Equalization vs. Segregation
In wastewater treatment, when does it make sense to combine all the waste streams into one equalization tank versus segregating the waste streams for treatment?

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10 Answers

  1. Equalization tank is used only when there is variation in Flow and strength of waste water.  Segregation of of high strength waste water stream and slowly releasing it to the ETP will be a better option. one can also treat high strength waste separately and then release it to ETP.  For example in Pickle making industry the brine is separately collected & treated.

    Rajendrakumar V Saraf

  2. The concept of equalization is very clear: to feed the wastewater treatment plant with as much possible constant flow and pollutants concentration. There are in literature the methods to calculate and to design the equalization basin. In my opinion in many industrial discharge one well designed equalization basin is the basis of the success of the wastewater treatment plant.

    The concept of segregation for me isn’t very clear. If I have an industrial discharge to treat and the production is only 10 hours/d or 5 days/week and I store the water to feed 24h/24 or 7 days/week is this segregation?

    I suppose that segregation can be applied for toxic or overload discharge to have the possibility to treat it separately or to dilute this water dosing it in the normal effluent up to remain under critical condition.

    The problem is to apply segregation in the plant. To make an example if the discharge is related with one desultory and scheduled production it’s very easy but if come from accidents or not scheduled activity it’s very difficult because you can detect the negative effects on the wastewater treatment plant too late. I know that there are some on-line instrument based on oxygen uptake rate able to protect the plant but I don’t have experience on this kind of instrument.

     

  4. In general, equalization makes sense when blending all waste streams into one blend makes treatment easier and more consistent. I have recommended equalization in the food industry with very good success.

  5. In general, you should know the average constituents of all contributing streams of the source water. Once that is relatively certain, mixing some or all of the streams may add some consistency to the overall end product being treated. This may result in the dilution of some of the more concentrated waste streams and may also assist in adding certain catalyzing components to other stream that could help the chemistry work more effectively.

  6. Predictive software is available to assess the probable characteristics of the blended streams (qualitative and quantitative) which would allow selection of streams to blend and or reject. It mat be more economic to consider two or more separate blends of several streams  rather than a one pot catch all

  7. Sometimes the only direct benefit is homogenization if the waste stream, which can be very helpful in treating many waste streams. Sometimes mixing waste streams can make overall treatment easier in that the characteristics of the water are synergistic for the purpose of treatment. For example, mixing a high TSS waste stream with a metal waste stream may help with solids development upon flocculation. When it is detrimental is when chemical consumption is unnecessarily increased from mixing the streams. If only 10% of a plant’s wastewater contains hex chrome, mixing it with the rest of the waste can result in an excessive use of chrome reduction chemistry. 

  8. My thought is, when treating the total is cheaper and easier than treating the parts

  9. Generally I would say yes, equalization does make sense.  Like most things, there will always be exceptions to the rule (e.g. items toxic to bacteria should be treated separately from things that are biodegradable).  Equalization often levels out issues that would otherwise make wastewater treatment more difficult.  For example, streams that are low in BOD can be blended with streams that are high in BOD providing a more uniform food source for a treatment system.  Also, temperature extremes, pH extremes, etc. may also be normalized making life for a biological system more viable.

  10. I would suggest that when this wastewater arises from ion exchange equipment regeneration involving acid and caustic soda, then the various pH sources can partially neutralize against each other, depending on how the various steps are controlled.  

    If the sources come from say, wafer fabrication, it might not entirely make sense to combine these various streams from different aspects of the process, as some of them may require only minimal treatment prior to re-use, while others will need special treatment to remove toxic metals or fluoride.