Question of Day: Wastewater Combination vs. Segregation

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Question of Day: Wastewater Combination vs. Segregation
When is it better to combine or segregate industrial wastewater streams?

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6 Answers

  1. The chemistry of combination or segregation is what decides whether the streams should be combined. If the chemistry produces a stream that is harmful, then we should not combine. Whether it is combined or separated, National Pollutant Discharge Elimination Systems provides guidance on limits to the safe discharge of streams. If NPDES or TMDL does not yet have guidance on emerging pollutants, then we should conduct research to find chemistry (inorganic and organic) of the combined streams through analysis before we make a decision. Of course, compliance of relevant US EPA laws such as  SDWA,  Clean Water Act and any other pertinent laws must be followed. State EPA officials must be notified and appropriate permits obtained before an industry makes a decision.   

  3. It is totally depend on the characteristics of waste water. High strength waste, acidic & alkaline waste, toxic waste cane be segregated treated and allow to join the main stream. It reduces the treatment cost. If waste stream are of same characteristics then all can combine together. Some time acidic and alkaline waste can be combined to neutralize.

    Prof. Rajendrakumar V Saraf virajparyawaranprashala@gmail.com

  4. I like how the question is framed; as some have commented, we normally just look at all the streams and figure out which should be combined and which shouldn't be. The question points us to what should the principles be that would guide this activity.

    Let me give it a shot:

    Should combine when:

    1. It leads to better equalization and balancing e.g. one variable stream with another more constant stream or multiple batch streams with some continuous streams.

    2. It leads to reduced concentration where this may be required.

    3. There are much smaller streams that do not have much load and would be impractical to segregate and provide separate treatment.

    4. It is cheaper and more practical to build one large plant vs several smaller plants if segregated.

    Should segregate when:

    1. It is a highly polluted and high load stream requiring a pretreatment step before it can be safely combined with other streams

    2. The stream is relatively clean but having a large flowrate, which if combined will require a much larger, combined plant. I.e. it is cheaper or more practical to build smaller multiple plants.

    3. The stream has significant flow but different pollutants compared to others requiring different treatment technology.

  5. I would agree with Don's reply and the answer is often simple but complex.

    Here is an example of where separation is easy to determine.  A power plant had a consolidated wastewater stream that was treated and then concentrated by RO. Permeate was reused and reject went to evap ponds. Maximum reject TDS were 66,000ppm. Into the plant wastewater stream, they added demineralizer regenerant waste at a combined 90,000ppm. Removing the regenerant waste decreased a significant salt load to the RO. Further segregating the phases of the regenerant decreased the volume of total brine waste going to their evap ponds.

    This was easy because it was obvious, the combined plant waste stream to the evap ponds was 66,000 and the regenerant waste was 90,000 of nearly 1.5x.

  6. When you assess each individual stream.  The question is too general!  In the food industry it is better to separate human waste from process waste if the water is to be recycled.