Reducing Dissolved COD 1

[illhp]

Can anybody help me find some options for treating wastewater with a high level of dissovled COD (as high as 2000 mg/l). Is ultrafiltration capable of removing dissolved COD? System requirement: 20000 gpd of wastewater. Also could somebody provide me with ballpark figures on possible options such as DAF.

Thanks

 

[Muggle]

DAF applications are not good dissolved oil/grease removers, protein skimmers work better, though use of catalytic enzymes improve the performance of such by several logs whether you use a skimmer or not. Though you do not mention what particular compound the soluble COD is, I would hasten to guess oils/fats/grease as compare to surfactants - but they are each treated differently, and to my knowldge, DAF has no effect on the surfactants found in cleaning solutions.

Electrolytically, hydrocarbon solubles - such as from motor oils and other gasoline/diesel/oil derivitives are easily oxidized - the same is true of animal fats and grease. Dosing at a rate of 2-3 ounces per 10,000 gallons of a specific enzyme formulation will speed the cleaving of the hydrogen-carbon bonds, enhancing both electrolytic and biological oxidation/removal of the COD - speeding the process by several hundred times normal.

2000mg/l (ppm) is not a high COD for industrial effluents, and 20,000gpd is not much, so your not looking at a large investment here. If possible, I would look at enzyme addition as far "upstream" of the effluent coming into the plant as possible first - as this may alone solve your problem. You may want to increase the aeration - or look at electrolytic with O2 injection to produce sufficient oxy-radical species to ensure total COD reduction. Electrolytic with O2 injection would mean using a simple oxygen concentrator at 10-15 lpm rate to raise DO and oxy-radical species to well over 150-200% saturation. This provides sufficient oxidative species to ensure complete enzyme action, plus oxidation of the fats/oils/grease, without any reduction of the DO for the wastewater plant. This is not an unheard of application - we normally maintain 116-254% saturation at altitude over 5,280' and water temperatures over 84-degrees F.in 86,000 gallons. Lower the altitude, lower the water temprature - the higher DO saturation and the oxy-radical species available in the water. This is not ozone use/creation - so don't get confused.

Anyway, let me know if you want to try enzyme addition (yes, it's approved for sewage agency use and is not detrimental to anaerobic or aerobic bacteria - won't harm fish, etc.) and I will get you in contact with the manufacturer who can send out a couple gallons at no charge for you to play with.
Rgds,,
Dave Orlebeke/Aquatic Technologies

 

[illhp]

Muggle,

I appreciate your response and have found it to be very helpful. However, I have further questions regarding protein skimmers and aerobic bacteria.

You were correct in assuming that the cause of the high levels of COD were due to fogs. Secondly, to clarify, the dissolved COD is as high as 2000 mg/l. The total COD can be as high as 150000 mg/l.

Would wastewater treatment using protein skimmers have to be done in batches? If so, how many gallons can be done simaltaneously and how long would it take?

Would aerobic bacteria be possible for waste water with high pH levels and chlorine concentrations?

Thanks for the help
illhp

 

[Muggle]

Ok - protein skimmers work on continuous flows - think of DAF filters, but at finer levels, with enzyme dosing creating very fine bubbles to capture the soluable fats/grease/oils and remove from suspension - this should drop total COD by 50-60% (same principal as off-shore oil platform crude/oil reduction) - the skimmer dumps the foam to a waste tank, either for secondary treatment or dumping. Most protein skimmers work at flow rates of 100-600gpm. If a higher flow rate - split the water into several protein skimmers.

High chlorine levels in the wastewater will kill anaerobic and aerobic bacteria, even .5-1.0ppm will shock them and stop/slow microbial oxidation by 60-90%.

If using electro-catalytic (ECP) process with protein skimmer - then looking at batch treatment. Batch treatment time depends on how many electrodes are used and the rotational rate. We figure on 400gpm flow, 14hrs a day, to drop COD from well cleaning on off-shore oil rig, that rotational rate to lower COD from 20-30,000 to less then 5, would require rotational rate of 2400gpm - but that is broken down by 4-separate tanks each rotating at 600gpm with constant in-flow. If a true batch treatment - where you don't add additional influent during the treatment - figure you have to rotate the entire batch (so figure the coefficient of purity ratio if using a round tank as compared to a rectangular baffle tank) 9-10x to reduce COD by 60-80% where protein skimmers are used - or micro-fine DAF.

Since total COD is (I'm making an assumption here) insoluble or "solid" fog - then that is easily removed. If you can't remove it, for whatever reason, then you first bring it to a aeration tank where enzyme dosing occurs to emulsify and turn all the fog to dissolved COD - then batch treat - though helps to use electrolytic action on the areation tank too- as this just reduced batch treatment time.

Hope that answers the question.
DAve

 

[bimr]

Some people on this site must be doing 420's.

A level of 2,000 mg/l of dissolved COD is quite high. The classical approach to remove dissolved COD is to use biological treatment, also known as the activated sludge treatment process.

You need to find out if this COD is organic and biodegradeable.

Forget about enzymes, protein skimmers, and DAF. They will not work on dissolved COD. DAF will work if you are trying to remove suspended matter and oil. Ultrafilters will also not work on dissolved material, it will go right through.

 

[Muggle]

First, enzymes are amino acids - they cleave chemical bonds, such as hydrolases - which break apart carbon-hydrogen bonds. In a human stomach, lactase is the enzyme secreted that breaks down milk fats and milk based alkaloids - so enzymes wil work on "dissolved" COD - cause guess what -it's a chemical compound!

Most oils that are described as "dissolved" are actually microfine molecules and are held in suspension - that's the design criteria around microfine DAF - the smaller the air bubble, the greater the oil removal as the smller bubbles grab te smaller oil molecules and lift them to be skimmed off - so in 90% of the cases - again, we don't know what is being termed "dissolved COD" here, microfine DAF or protein skimming works to reduce the oil/fats load in the waste stream.

Before anyone makes a decision - the definition of what "dissolved COD" is for this discussion should be determined, or any answer is "shooting from the hip".

 

[bimr]

Illhp,

If you would like to receive a useful response, you need to provide some minimum basic information as to type of waste, industry, receiving stream, as well as a characterization of the wastewater. Like muggle says, "any answer is "shooting from the hip" unless you provide this minimum information.

 

[illhp]

It seems as if the source of the high levels of COD is vegetable processing (baking and frying) and the cleaning of the equipment. Lab tests show that the dissolved COD increases during the cleaning process.

 

[Muggle]

The COD is therefore detergents, some surfactants, with micro-molecule oil/grease in all likelyhood. Micro-DAF or protein skimming can remove much of the oil/grease and surfactant if good polymer is used. You'll have some sludge, but probably not much. Dosing with and enzyme inconjunction with polymer will help reduce the "dissolved" BOD - but the key is capturing the micro-fine globs/molecules of the oil/grease and surfactant.

 

[bimr]

The traditional wastewater treatment system for the food industry is DAF. DAF will remove almost all of the fats and oils as well as the suspended matter and the BOD/COD associated with these paratmeters. Normally, the effluent from a DAF unit is acceptable for discharge into a municipal wastewater system.

On the other hand, if you are a direct discharger, then you will also have to install an activated sludge wastewater system (in addition to the DAF) to reduce the BOD/COD to an acceptable discharge level.

If you are just having problems with the high COD, then you should investigate to determine the source of the COD and find an alternative cleaning agent.