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Help with wastewater treatment from soda-can factory

2003

Dear all,

I have a problem with my wastewater system and would like to ask somebody who has experiences to settle it. My factory has produced the can for beverages of all kinds (Coca-cola, Pepsi) and uses much metal cleaning chemicals. Therefore, the COD and mineral oil content in wastewater is very high. Before, about 4 years ago, a Singapore company designed and built a wastewater treatment system for us at high price and the treated wastewater quality was quite good. However, from the beginning of this year, we do not know why the COD and the mineral oil found in effluent (treated wastewater) are increasing. The COD before is about 70 ppm to 80 ppm but now, it is approximately 300 ppm to 450 ppm and even 500 ppm. The mineral oil content is also increasing, from 10 ppm before to around 7000 ppm as now. I do not understand since my factory capacity in production is nearly unchanged and all chemicals used in treatment system are also normal. Let me tell briefly about the treatment system: wastewater is mixed with Aluminum sulphate, lime and Polymer then is led to a flotation tank. The "clear" water then is pumped to a weir tank for sedimentation, after that it goes into final tank where addition of HCl is made for pH adjustment before discharging to water body. The sludge goes into a sludge thickening tank, then it is pumped to a filter press for de-watering. What I do not understand is why the treatment system is poorer in treatment capability. We already contacted with the former supplier in Singapore but now they refused to come back to our factory to work. Please, somebody who has experiences in treatment of wastewater from a can factory can tell me the possible cause of problem and if possible, give me some advice on that. What should we do if we want to do further treatment in order to decrease the COD from 400 ppm as now to 50 ppm and mineral oil from around several thousands to 5 ppm as requirement. Any advice is still very useful for us now. Thank you very much.

Good luck for all,

VO HONG THI
Can factory - HO CHI MINH, VIETNAM

Has your cleaning process been changed by switching cleaning products? Sometimes increasing detergent level or switching surfactant types can overcome the treatment chemicals. Your cleaners are dispersants and emulsifiers and your treatment chemicals are coagulants and demulsifiers.

James Chunn
- Theodore, Alabama
2003

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You would need to investigate the reason why the oil does not mostly come out in the flotation cell, and if the oil has mostly come out of solution. I assume you are using dissolved air flotation, with lamella plates. Check the pH. To further reduce the COD, biological treatment would be needed, whether anaerobic or aerobic, depending on the biodegradability of the oil and detergents.

I work for a company which specializes in solids and oil/water separators, so my boss is very knowledgeable in dissolved air flotation.WE are the market leader in DAF equipment and oil/water separator.

I DO NOT HAVE much experience in your type of waste. I have very considerable experience in biological treatment.

Good-luck.

Vincent Lim
- Sydney, Australia
2004

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2004

The increasing COD and mineral oil content in effluent may be caused by some reason as following

- COD and mineral oil content increase in the influent of wastewater treatment plant. Therefore it is over the loading designed;

- The detergent used in washing stage of manufacturing process has been change; this results in mineral oil change in form. So that it can not separated by this wastewater treatment; (change the mineral oil also generate the same problem;)

- The operation conditions are not optimizing.

To solve this problem, a lot of procedures have to take in. But in general, some work is suggested

- Check the COD and mineral oil content in influent wastewater treatment. Investigation why COD and oil content increase? (low oil separating in pre-treat process, washing chemical changed is suggestion). And also check a loading design (may be now the COD and mineral oil content overload the design) - Optimize the operation conditions

To reduce the COD and mineral oil content, two options can be choose

- using adsorption to reduce oil and then biological treatment [in case the wastewater have high biodegradability (BOD/COD >=0.4); and your company have a large space for build up]

- using adsorption to reduce oil and then oxidation [in case your company do not have a large space for build up]

Good-luck

NGUYEN NGOC CHAU
- Hochiminh City, Vietnam

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My understanding is that the feed to your plant has not significantly changed, but the composition of your effluent has progressively become similar to that of the feed. This could be an indication that the plant is clogged with solids, or with compacted mud, so that the effective residence time is smaller than designed, so that separation cannot take place. I would look for a plug in the pack of lamellae or in the coagulation-flocculation spiral. And if you find the plug, remove it.
It would also be worthwhile to consider a change of your recipe. Indeed, instead of Alum and Lime (or caustic soda [affil links] ), we have systematically found that the combination Sodium Aluminate and Alum performs better, is cheaper and leaves less dissolved salts in the effluent.

Samuel Wajc
- Haifa, Israel
June 1, 2011