How to select correct parameters for designing an industrial wastewater treatment work?

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Hi everybody, 

I am working on my master thesis about designing a wastewater treatment system for a pulp and paper mill using waste paper as raw materials. All of the streams are mixed into only one stream to be treated. The influent profile is shown as follows: 

-Design flow rate: 167 m3/h, maximum flow rate at the collection pits: 334 m3/h

-BOD5: 2600-7000 mg/L

-COD: 5000-12000 mg/L

-TSS: 300-4200 mg/L 

-Color: 3000 Pt-Co

-AOX: 20 mg/L

-Dioxin: 12 pgTEQ/L 

I have some questions as follows:

1. Large variations in flow rate: 

I am planning to have an equalization basin to equalize the flow rate. As my understanding, I should use Qmax for the units before the equalization basin (such as primary sedimentation) and Q average for units after the equalization basin. However, as I know, the flow record for at least 24h is needed to calculate the volume for the equalization basin. The company only gives me the maximum and average flow. Are there any simple approaches  to calculate the equalization basin? 

2. Large variations in contaminants concentration (BOD, COD, TSS):

Should I use the average concentrations or the maximum ones for design and calculation? 

 

3. Are there anything else I should take into account? 

Any practical experience shares are appreciated. 

 

Thank you very much for your time! 

 

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6 Answers

  1. Hi Hung,  in response to your first question, you do need to calculate the volume of your peak flow, not just the peak flow rate itself.  this means the integration of the above average flow vs time as this is then the volume of your equalization basin (plus allow additional for non average days as well as possible maintenance shut downs on the treatment plant).

    Regarding the contaminants, others have responded better than I can.

  2. Thank you guys for answering me and sorry for any missing/confusing information. I have updated my post. Basically, there are two questions: 

    1. Are only the average flow and maximum flow adequate for calculating the equalization basin ( as I know from an exercise, 24-h flow record is needed). 

    2.  Should I pick the average or the maximum contaminants concentration for calculation? 

  3. First have to ask what kind of pulp mill, paper, dissolving sulfide...What processes are in the mill are there evaporators for red liquor, then you will have acid condensate. Is it a caustic extraction process, then you will have Black liquor which can be toxic if concentration is too high but can be diluted with acid condensate.

    Both mills I worked added ammonia and phosphoric acid. One used aerobic for most streams and anaerobic processes, anaerobic for the black liquor. The other had a very large aeration basin. Solids were processed through screw presses and burnt in the power boilers.

    I would map out all the waste streams, determine what treatment is fits and see which streams can be combined. Most mills have systems to recover and recycle from waste streams to reduce wastewater.

     

    1 Comment

    1. Thank you Mark for your answer. Actually this paper mill uses wastepaper as raw materials (not wood), so I suppose the Black liquor is not present? Yes I also think separating the streams for individual treatment is more proper. But for the mill in my case study, they mix all of wastewater fractions into only one stream. 

  4. I concur with my colleagues -- tackle the organics first -- and don't design for the average -- or your process will  be running efficiently and economically only 50% of the time. 

    1 Comment

  5. Having worked at paper mills in the past, I would now add fiber recovery to the wastewater process before the EQ tank or primary clarifier, using hydrocyclones or vortex screening systems, they will remove fiber, add DO, lower BOD and COD and enhance settling in the primary clarifier making it more efficient. Recovered fiber can be diverted back to sluice box of fordrinier or cylinder whichever process is used. This will helps in equalization basin and level out influent flow characteristics.

    1 Comment

    1. John Salonich Thank you very much for your answer. For the primary treatment before the equalization basin, I am planning to have coarse screen followed by microstrainer for fiber recovery, and then primary sedimentation. I believe they will significantly reduce suspended solids and BOD5 before going to the equalization basin. 

      1 Comment reply

  6. Hi Hung Bui, you should register the water consumption over 24 hours of all water sources and take samples every 2 hours and analyze them not only BOD, but also COD because the COD:BOD ratio shows you the biodegradability of the pollutants. Check also if the mill uses chlorination for pulp bleaching, which will result toxic chloroorganic pollutants. In any case you should run continuous degradation tests for the determination of process parameters.

    1 Comment

    1. Thank you Imre for your answer. I am very sorry because I have not given all the data. I will edit my post now. The COD is 5000-12000 mg/L. Yes I believe the sampling approach you suggested is very essential. But the company only gave me the data which  I have mentioned all in my post.