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Biodiesel Wastewater
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I am looking for typical dissolved BOD numbers in biodiesel wastewater for various biodiesel processes. There does not appear to be much data available.
 
Registered: August 09, 2007Reply With QuoteReport This Post
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I'd like to discuss this with you.

Sending a PM.

Bob in Denton


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Location: Moncure, North Carolina | Registered: April 21, 2001Reply With QuoteReport This Post
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We'd all like to discuss it!!!

I've been wondering about the BOD... I have farmers who are spreading the stuff back onto their fields.


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Registered: March 09, 2006Reply With QuoteReport This Post
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It sure would be nice to come up with a system that would render waste water completely inert, so you could irrigate a garden or a lawn with wash water, and a test to be sure your wash water is harmless.
 
Location: West Michigan | Registered: April 26, 2006Reply With QuoteReport This Post
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Bob, If you can discuss it on the forum, we'd all be interested!
 
Location: Cowboy Country | Registered: December 06, 2004Reply With QuoteReport This Post
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Which test would be most meaningful to us? There's CBOD, BOD5 and BOD30 (i think), and there may be some others.
 
Location: Cowboy Country | Registered: December 06, 2004Reply With QuoteReport This Post



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Originally posted by RickDaTech:
Bob, If you can discuss it on the forum, we'd all be interested!


Hi Rick,

There's not much to discuss here at this point.

The poster is asking for 3rd party lab results from biodiesel washwater, if there's any out there that can be openly shared, it would be helpful.

I don't have any data that meets this criteria - not yet anyway.

Like many commercial biodiesel producers, we are seeking ways to minimize (or eliminate) water use in our processes. This will likely include characterization tests for wash water, wash-down water, and storm water.

As testing can be expensive, I want to try to get the sampling and testing understood prior to committing money.

When I feel like I've learned something that can be shared here on the forum, I'll mention it to Graydon.

Ha Ha Ha! (I really couldn't pass that one up. Smile )

Seriously, I'll be happy to share any significant insights when I've witnessed them with my own two eyes.

Best regards,

Bob in Denton


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Location: Moncure, North Carolina | Registered: April 21, 2001Reply With QuoteReport This Post
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Bob,

I've been wanting to test some wash water for BOD, Is there a specific test the regulators are most interested in seeing?
 
Location: Cowboy Country | Registered: December 06, 2004Reply With QuoteReport This Post
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The contaminants that are most likely to be in biodiesel washwater that are of most interest to regulators are:

BOD - Biological Oxygen Demand - regulators are getting savvy and now want to see weight of BOD over time (like pounds per day) so that dilution will not be a solution.

TSS - Total Suspended Solids

Phosphorus content

pH of waste water

VOC - Volatile Organic Compounds - i.e. methanol, (which also contributes to BOD)

Oil content - oil water separators are required at commercial facilities.

Getting your hands on municipal wastewater discharge regulations in your location can be as easy as contacting the waste water folks in your town - or one near you - and requesting the spec.
They will outline allowable limits for potential contaminants.

Regulations for discharge of wastewater are different for different areas and different proposed discharge systems - i.e. down the municipal wastewater system vs. discharge into a lagoon on your property - many different possibilities are permitable based on local conditions - water supply availability, geology of local groundwater system, etc, etc, etc.

Talking to local regulators is the place to start, at least for us commercial guys. We need to do this prior to breaking ground on a new plant in order to determine the process design that will be most appropriate for a given location.

FWIW, the BOD of biodiesel washwater is typically very high (10,000 to 500,000 mg/l). This can make discharge down the sewer a cost prohibitive option for commercial producers.

Hope this helps...

Bob in Denton


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Location: Moncure, North Carolina | Registered: April 21, 2001Reply With QuoteReport This Post
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If it is any interest to anyone,

While I am not a chemist by any means, I have extensive experience dealing with city water departments on the subject of waste water discharge and the permits required. I am very familiar with the testing procedures of a waste water stream but not so much with the chemical analysis.

Most industrial places have individual limits imposed on them that are dictated by the category of business activities.
For instance, while you may be able to discharge 1ppm of one substance, your next door neighbor, running a different kind of operation, may have a limit of 5ppm imposed on them.


As for the BOD of wash water, would I be correct in saying that its due to the soap?

How to remove soap from water? can it be coagulated and flocked out like dissolved metals? (i'm guessing no)

I'm thinking distillation would do it but that could be really expensive.


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Registered: March 09, 2006Reply With QuoteReport This Post
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Murphy,

Think you could centrifuge the soap out of the water?
 
Location: Cowboy Country | Registered: December 06, 2004Reply With QuoteReport This Post
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Murphy,

quote:
As for the BOD of wash water, would I be correct in saying that its due to the soap?


While I too am not a chemist, here is what I understand about BOD.

Biological O2 Demand is a measure of how much O2 is required in the decomposition process of a given material.

In our case, it will be a combination of FAME, and mono & diglycerides which are entrained by the soap, along with the soaps themselves which contain the FFA chain.

This is on reason, at least in theory, to wash gently, as the soaps may, again, in theory, pick up less of the other components in the fuel and carry them into the water.

When high FFA oil causes lower yeilds, I believe (no tests) that it is in part do to high levels of soap which in turn carries into the water a higher amount of actual fuel.


Andrew

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Location: Northern California | Registered: February 27, 2006Reply With QuoteReport This Post



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Originally posted by RickDaTech:
Murphy,

Think you could centrifuge the soap out of the water?


That is a good question, it surely seems feasible, and you could go for a long time between cleanings.
 
Location: West Michigan | Registered: April 26, 2006Reply With QuoteReport This Post
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I thought about a septic system just for wash water, but I do not believe all soaps are consumed by the bacteria that make a septic tank work.
 
Location: West Michigan | Registered: April 26, 2006Reply With QuoteReport This Post
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i thought i read something a few years ago about reed beds being able to "filter" wash water. like raised cascading ponds (with liners on the bottom) that would have much cleaner water at the end of the loop.
 
Registered: February 16, 2006Reply With QuoteReport This Post
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The first thing that regulators will look for in wastewater is FOG (fat, oil and grease), total BOD and TSS.
We expect biodiesel wastewater to originate from: crude oil washwater, biodiesel washwater (via centrifuges), pressure leaf filters, vacuum drier system, spillage and washdown.
Total BOD will result from FOG, TSS, and dissolved material. We can deal with the BOD related to FOG and TSS. The question is, what is the source of the dissolved BOD. This would probably be starches, sugars and to some extent, methanol. If the dissolved BOD is too high for discharge, then some form of evaporation may be required. If such a step is required, then a total water recycle system may be in order.
 
Registered: August 09, 2007Reply With QuoteReport This Post
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Its been a while since I even read most of these acronyms, so I could be WAY off. But....

I dont expect that the use of water to wash biodiesel does anything to change the BOD. Biological Oxygen Demand. Bio meaning life form. Usually Bacteria/Algae/Animals/Plants that might be consuming Oxygen. I can only imagine that most Biodiesel wash tanks do not contain any of these. Of course if you had some REALLY nasty oil with creatures that managed to survive 2 hours at 130F, then, ok, yes, you might have some BOD increases as a result of using water to wash.

BOD is a measure of how fast biological organisms use up oxygen in a body of water

I can however see LOTS of reasons to the COD ( Chemical Oxygen Demand ) to go way up as a result of washing. COD is a measure the amount of organic compounds in water.

Waterwater quality indicators from Wikipedia
 
Location: Mechanicsville, VA | Registered: May 30, 2006Reply With QuoteReport This Post
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COD and BOD will usually be relative to each other.
 
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mrti --

Or are you concerned about commercial scale facilities where this might be a valid concern? I would expect each facility to be different because of different processes.

Awfully technical question for someone with only 4 posts. Who are you?

C
 
Location: Mechanicsville, VA | Registered: May 30, 2006Reply With QuoteReport This Post
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mrti,

The only substances worth reporting in wash water are 1) methanol, at most about 2% v/v and contributes to BOD, 2)soap, content depends on feedstock oil, and 3) oils/methyl esters or FOG.

Using an ION exchange on the soaps to convert them to an insoluble soap releases the FOG for easy grease trap removal. Soaps are skimmed and disposed of as a solid waste. This treatment leaves some salt (type of salt depends on several factors) in the water, so salinity may be an issue.

Acid treatment also works to break up the soaps into fatty acids, but the resulting oil is hygroscopic and will trap water. Grease traps are not nearly as effective with this treatment.

Untreated wash water also has an elevated pH due mostly to the presence of soap and a high BOD as described above.
 
Location: Cowboy Country | Registered: December 06, 2004Reply With QuoteReport This Post
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