Effluent Treatment with the Addition of another tank

[ChE51]

I am working on improving my plant's effluent treatment system. Currently we only control the pH before discharging. I am currently working on a new chiller project that will remove the addition of once thru cooling water to my effluent. First I am performing a study on the effluent minus the cooling water which I then think will lead to a better effluent treatment system. My first thoughts are to add another tank which when it becomes filled will be analysed and if deemed satisfactory will be discharged. I work for a chemical company that produces alot of polymers. Does anyone have any thoughts or suggestions?

 

[vintage70]

My first question is how did you get away with discharging cooling water to a wastewater treatment plant? So now you are going to reduce your flow but increase the concentration of pollutants. Is pH adjustment your only treatment. Adding a holding tank is only practical with batch or intermittent flows, but your are eliminating the cooling water and a low flow rate may work. If after testing the tank contents and the water can't be discharged are your going to have it hauled off site? The facility produces polymers, do you have a high BOD, COD, TSS? What other type of treatment besides pH are you applying?

 

[ChE51]

As far as the cooling water it is a very old plant. I know this is not allowed now when designing new plants. pH adjustment is the only treatment. When the effluent has been tested by the regional sewer representatives it is usually OK but this once through cooling water could make a big difference. The BOD, COD are fairly low and are TSS is like 40-70ppm. Once my test is completed I am going to determine problem pollutants and what products they come from. If there are large problems we are going to have to find other treatment methods but if a tank can't be discharged or preferably treated it will most likely be hauled off site. The main reason we want another tank is because if we have a spill and the pH is within the set points our effluent tank automatically discharges. Does this seem like the best option to explore at this time? Thanks for your input.

 

[waterexpert]

Your basic approach is good. First minimise water use, then look at treating the residual. Look at how you can reduce production, and recycle produced water at lower grade, or treat for reuse.

In order to do this, ask yourself: Is the main plant batch or continuous process? Batch processes suit themselves to batch effluent treatment, and continuous processes to continuous treatment, to some extent.

What requirements are there on the plant for water, and at what quality. Can water produced be recycled at lower quality without treatment? Can water produced be treated for reuse cheaper than buying new process water(don't forget to include disposal costs in this calculation)?

Your water seems pretty clean. Tankering away is likely to be costly compared with treatment for reuse.

 

[vintage70]

I'm a little confused. But that has been happening a lot lately.

OK

1. you currently have a holding tank
2. if pH is within acceptable range, it automatically discharges
3. so if you have a spill you don't want it discharged purely based on pH, you need further analysis
Correct?
4. so you want to add another holding tank to receive the discharge.
How am I doing so far?

If you size the tanks for worst case spills you should be alright as far as capacity.

But will spills always be directed to your treatment system?

An incompatable quantity could create a large volume of untreatable wastewater. That can be very expensive.

Can you direct spills to a holding tank upstream of the treatment plant?

If not, evaluate all possible spills. See which ones would be potential problems.

You may be able to isolate certain areas of the facility.

Some advice here, you should not have any open floor drains in production areas that would discharge incompatable chemicals to your treatment system.

 

[ChE51]

Waterexpert and Vintage,
Vintage you got it so far. Our water is not that clean. We produce wastewater treatment chemicals (including polymers and several other liquid flocculants/coagulants). I have since discovered some old info on effluent testing performed at our plant and depending on products we have cases of high sulphates, TKN (Total Kjedahl (or something) Nitrogen), zinc and TSS, BODS and Oils are sometimes above restrictions. I have already been performing a plant water usage study (for the past 3 months) to see where we use water and where we could possibly reuse water. Our plant is run entirely on batch processes but these batches can be quite large (16000kg). We have no direct requirement for water except for uses when contaminated water would be an issue. We have separated some of our trench systems to isolate problematic areas. The main reason we want to have twin tanks is to be able to contain a spill instead of automatically discharge which was a high cost to us recently when we discharged a large amount of zinc chloride (very very bad stuff). Thanks for all your help and any more suggestions would be great. This is my first plant effluent project and just wanted to make sure I was on the righ track.

Cheers
Che51

 

[waterexpert]

Your water is pretty cleam compared to domestic sewage, which have SS, BOD, COD in the low hundreds. Specific chemical compunds are likley to be a bigger problem than pH or simple SS/BOD/COD removal- for example,if you are making polyacrylamides, we have strict controls here in the UK on release of the monomer to watercourses-not sure if you do there.

Other than that, you can either have a second tank, and possibly do batch pH correction prior to discharge, possibly including sulphate removal by lime precipitation, or use one or two tanks to buffer flow prior to continuous pH adjustment plant.

BOD/COD/TKN/SS may then be removable with conventional biological treatment plant, or possibly membrane plant depending on their nature. treatability trials may be required to establish what is best. Organic polymers are removable by ultrafiltration, which will also stop any emulsified oils. If all of the COD/BOD/TKN is in this form, it will be cheaper and easier than biological treatment.

 

[bimr]

I have to believe that you are a small volume facility since a large facility would have to provide more wastewater treatment than what you are doing.

If you are eliminating the once through cooling water, you are in effect increasing the concentrations of the various pollutants that you are discharging. This may cause you to go out of compliance with the local sewer authority when you shut off the cooling water.

The addition of the cooling water probably has no effect on the pH of the effluent that you are discharging.

Assuming that your facility is small, it is probably not economical to try to treat the wastewater. That would mean shipping the wastewater offsite

Your idea of using twin tanks seems reasonable if you want to test the wastewater before allowing it to be discharged into the sewer. You might consider adding more than twin tanks. Additional tanks will allow more decision time, such as on weekends. It will also allow you time to arrange for shipping wastewater to an offsite waste disposal processor.

 

[chemo]

Hi to all.. I am involved in waste water treatment .My waste water ( 8 m3/hr )of COD 200 mg /l is geenrated. On analysis it was found a amide( CO- NH2 ) compound is causing the COD . Our COD specification to discharge the effluent is less than 100 mg /l.Since this is the only waster water generatied in the plant , presently we are diluting and discharging water. Is there any other method to reduce the COD..