BOD reduction 1

[antonevi]

Hi,

we are now testing a phisico-chemical sewage treatment plant.
The system is working pretty well on most of pollutants.
The biggest problem we are facing is dissolved BOD reduction. Obtained effluent is at 170 mg/l, while limit is set on 30 mg/l. The BOD reduction along the treatment is 90% as mean.
Problem is mostly connected to the total absence of solids in water (TSS < 7 mg/l).
possible options we are evaluation is:
-Increasement in chlorine injection (problem on the effluent limit for total chlorine)
-Use of hydrogen perhoxide (quantity seems eccessive.

Does anybody have soem suggestion?

Thanks in advance!

 

[Muggle]

Morning Antonevi -

Need more information - like total flow per day, lagoon sizing,e tc. - but electrolytically, you can remove the BOD down below 10 and further depending on batch treatment time. We've taken veneer plant water from 1000mg/l to 6.29mg/l in a few hours - again, time is dependent on flow rate and your holding time before discharge to ground or stream.

Would also need analysis of the water. ECP International out of connecticut can help you - contact them at infoecp@yahoo.com.

No chemical additons for this - and your chlorine dosage won't need adjustment.

 

[antonevi]

Hi Muggle,

Thanks for your interest!
Regarding the additional data you required, please find them here below.

The daily flow rate of WWTP is 100 tons/day.
The water we are treating is a mixusture of wastewaters similar to municipality wastewaters: black, sanitary, laundry, food waste percolate, disch washers discharges.

The pollutants values of the influent water are:
COD = 4311 mg/l
BOD = 1250 mg/l
TSS = 1770 mg/l
FOG = 29,8 mg/l
Ntot = 106 mg/l
Ptot = 32,8 mg/l
Faecal Coliforms = 34000000 MPN/100ml
Total Coliforms = 48000000 MPN/100ml
Copper = 0,038 mg/l

In efffluent we have:

COD = 208 mg/l
BOD = 170 mg/l
TSS = 7 mg/l
FOG = 2,2 mg/l
Ntot = 42,3 mg/l
Ptot = 0,47 mg/l
Faecal Coliforms = 0 MPN/100ml
Total Coliforms = 0 MPN/100ml
Copper < 0,016 mg/l

We remove solids by flotation, with relevant pollutant quote, and we abate the main part of remaining by chlorine injection.
For contact time we have:
Feeding tank + Flotation unit + 2 contact tanks = 8,5 m3 about.

As you see by the results we get, the system is weel working on most of required parameters, but we have hard problems for BOD abatement.
We already tried to increase contact time by adding an additional tank with 2 m3 of volume, but there was no change in BOD level.

I hope that the data I am giving can help you in having a sharper idea.

Thanks againg for the help!

Ciao

 

[bimr]

What you need is an activated sludge biological treatment system. That is the system that is most economical for removing BOD. In a biological treatment system, the microorganism consume the dissolved BOD

The system that you installed is not going to economically remove the BOD. Do you have a consultant that recommended the process that you installed? If so, you should go back to him and request that he fix the problem.

If you don't have a consultant, you should get one.

 

[antonevi]

the main problem we are facing is that it is impossoble to use a biological step due to chlorine contamination in influent water.
We already tried with bio-membrane treatment, but was impossible to have the bio stage well working.
In addition to this, there is also an high amount of emulsified oil (both mineral from engines and vegatal from kitchen) that cannot be retaind by grease traps. This oil build up big yellow balls in the aeration stage, capable to clog transfer pumps (we had an impeller broken by the stress!!).
All this serie of troubles make bio-stage a problem with influent water, and almost impossible as finalò refining of the effluent.
Regarding consultant, unfortunately we have....
In addition to this we have enourmous problems in space, and as you know, for a well working bio-step you need at least 8 hours retention time, even if is enhanced by enzime addition.
These are the reasons that pushed us in trying a phisico chemical treatment.

 

[antonevi]

the main problem we are facing is that it is impossoble to use a biological step due to chlorine contamination in influent water.
We already tried with bio-membrane treatment, but was impossible to have the bio stage well working.
In addition to this, there is also an high amount of emulsified oil (both mineral from engines and vegatal from kitchen) that cannot be retaind by grease traps. This oil build up big yellow balls in the aeration stage, capable to clog transfer pumps (we had an impeller broken by the stress!!).
All this serie of troubles make bio-stage a problem with influent water, and almost impossible as finalò refining of the effluent.
In addition to this we have enourmous problems in space, and as you know, for a well working bio-step you need at least 8 hours retention time, even if is enhanced by enzime addition.
These are the reasons that pushed us in trying a phisico chemical treatment.

Regarding consultant, unfortunately we have....

 

[bimr]

From my experience, chlorine is relatively easy to remove. All that you need is bisulfite for that.

Oil & grease removal is not difficult either, but oil & grease removal will have to done in a separate pretreatment step.

I appreciate your space issues, but physical chemical treatment is not going to be economical.

You can try an UV/oxidation system, but the operating cost is going to be high because of the high organic loading.

 

[antonevi]

thanks for your suggestion Bimr,

The space problem we have is so high that pushed economic troubles in second sight. Anyhow the cost of fines will be higher on the long term.

If I understood right, you suggestion is to make a mixuture of air/ozone and water and make it pas thruogh the UV lamp.
The reduction we need is not so high, because we got new results from the plant and effluent BOD has been reduced to 65 mg/l as steady figure.
Reduction we need is of 35-40 mg/l to be withon limits.
I will investigate with possible suppliers about the technology you suggested.
We are in this moment checking the possibility to abate BOD by the use of electrolisys. First result we got is emulsion breaking, and it is anyhow a good result. We are waiting from lab tests result to have an idea on BOD values.

Thank you for your help!

 

[Muggle]

Antonevi -

Sorry have not replied back sooner - been buried addressing issues on wastewater for Scotland and Romania.

I agree that your system is doing well - it appears to be more of a last stage &quot;clean-up/polishing issue&quot;. I will review your flows and such this weekend and get back to you - but this looks pretty simple and nothing that can't be adapted to your existing system. Your COD and BOD is just not that high.

Do me a favor - I'm going to print this off and run calculations, but give me a some other information. Reply to aquaticonsult@yahoo.com--

Questions:
Do you have 3-phase power available?
What is the size of the 2 contact tanks?
What is retention time of the tanks, or do they receive a constant flow - if so, what is that constant flow rate?

Thanks -
Dave

 

[Muggle]

Antonevi -

Ok - looked it over. Are there one or two contact tanks of 8.5cm each (roughly 2,000 gallons each)? If so - any aeration in them?

I gather from the post that you've got 25,000 gallons a day coming in, figuring a steady flow rate, that's approximately 1041 gallons per minute. If both tanks are 2000 gallons working volume, you've got about an hour plus in each on for treatment - so, we want to rotate each tank at 400gpm through electrolytic cell at the right voltage/amperage output, plus inject about 2oz. per 1000 gallons of a catalytic enzyme at the receiving tank (ECP International has the one we use - inexpensive and works well on motor oils, refinery oils, animal fats, etc) - simple injection tank handles that- to increase emulsification of oils/fats/grease - whole set-up would require an area 6'x6'x6' give or take a foot. Got that space available? Power consumption would be 100amps 230v/single phase, about 50amps 208-220v/3-phase.

Treatment should reduce BOD to less then 5mg/l, COD to 10mg/l and total N to 5 or less - that's figuring your treatment levels can rise 10-15% at any time. FOG is going to be less then .5. Daily maintenace is going to be 5 minutes tops, if that.

I would not recommend UV/peroxide. Oils and fats are going to cause problem with quartz sleeve of the UV - occluding the light and diminishing UV breakdown of the hydrogen peroxide to OH - plus you ahve to use 35-50% hydrogen peroxide solution that is highly caustic and a real OSHA hazard. Electrolytic treatment makes OH from the wastewater itself, as well as other oxy-radical ions without creating health/saftey hazard. Besides, oxidation not the only issue here or your chlorine would solve the problem.

Aeration of the 2 2000gallon tanks would help. 8&quot; diffuser plates at 3-5cfm each would be sufficient. No ozone required - just air. Wifley Weber has good 8&quot; membrane diffuser plates. One or two per tank is sufficient. Won't need cleaning like aeration stones - good medium size bubble formation.

Let me know the layout - and confirm my &quot;assumptions&quot; on tnak sizing and flow rate.
DAve