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topic 6632

Sludge Dryers for Concentrating Plating Wastes


(2000)

Q. Although I have been involved in engineering for many years, I am brand new to the area of waste water treatment and the like. My company has asked me to look into a replacement for our old sludge dryer. We currently use a dryer that uses gas heat to evaporate the moisture and a scrubber to scrub the exhaust; its capacity is approximately 50 pounds of water removed per hour. It is 12 years old and seems to require constant attention. Perhaps because of its age and maintenance requirements, many here seem to be in favor of finding a "better way."

What options/technologies are available to me?

David W. Cooper
- Hastings, Nebraska


(2000)

A. I can't resist this. What are you trying to accomplish? Just trying to reduce sludge volume? Cut costs? Or what? In my humble opinion, what you should do is get into pollution prevention, which will decrease the sludge volume at the root cause. Describe the situation, and, you will get more useful information.

James Totter
James Totter, CEF
- Tallahassee, Florida


(2000)

A. I agree, James. I have personally never liked the concept of thermal sludge dryers. Richard is not the only one to complain of a maintenance headache. And at the cost of huge amounts of energy, and with the risk of contaminating the premises with toxic dust, all they remove is the innocuous water from the waste, while doing nothing to ameliorate the harmful.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. Last year we purchased a mechanical dewatering press. It uses hydraulic pressure to reduce the water in our pressed sludge by as much as 25%.

Rick Alexander
- Gaffney, South Carolina


(2000)

thumbs up signThat I like, Rick!

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

Q. To further clarify our operation and what I am trying to do:

We have a waste water treatment system on our zinc plating line (zinc chloride). Before returning the cleaned water to the city system, we use a filter press to remove the solids. To reduce volume, we then use a sludge dryer to remove excess moisture prior to shipping.

Reducing the pollutants at the source is a good and desirable goal, but can they truly be eliminated, or will I always want a sludge dryer to minimize the moisture content?

David W. Cooper
- Hastings, NE


(2000)

A. I think Mr. Totter's point was that if your company is committing resources of time, effort, and capital, that you might be better off applying those resources where they'll do more good.

Viewed in that light, although you'll probably never get to zero sludge, your best decision might still be to look elsewhere.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. David,

First I would ask of these persons who chose to respond to your question "have they ever managed a plating operation" and secondly you asked for help as I see the responses offer opinions but not much substance in true help!

With that aside there are several ways to approach sludge drying.

First I do agree that all chemistries used in your wastewater process that generate solids should be reduced or looked for replacements. The first step in sludge management is volume reduction.

There are several types of sludge dryers. The preferred unit uses a dehumidifier process. Where as it takes air at 140 degrees F and recirculates it through the sludge hopper. The unit removes the moisture from the air via condensing coils.

I would also say there are some used electric units available. I much prefer the electric over the gas for safety reasons.

Good luck!

Bill Paul
- Olathe, KS USA


(2000)

A. Bill,

Please continue offer your own advice as you did. Thanks! But please visit the sci.chem newsgroups to see how quickly a once-priceless resource plummeted to complete worthlessness when people started challenging each others' qualifications.

In response to David's statement that he is "brand new to the area of waste treatment" and looking for guidance, myself and Mssrs. Totter & Alexander read his question and offered our best good-faith responses, based on our decades of broad experience in the plating industry.

My own experience includes setting up and maintaining sludge dryers, plus every other type of centrifuge, vacuum filter, filter press, pressure filter, automatic filter, sludge thickener, drying pond, rotary filter, and sludge drying approach you can imagine -- going back to Department of Interior days before the EPA even existed or anybody heard the name Rachel Carson. I feel it is perfectly legitimate to warn a self-proclaimed newbie that the way he is framing his question may not be optimal.

You are perfectly welcome to disagree with my responses and opinions as strenuously as you like, Bill! But you are absolutely unwelcome to challenge my, or any other responders, qualifications.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. What I am suggesting here is that people look at methods of reducing sludge volume at the source. What is truly desirable is to take the metals and return them to the tank. This not only reduces the sludge volume, it reduces the amount of anode metal purchases. In the world of pollution prevention, this sort of thing snowballs and reduces pollution, costs, inventory, and effort.

For example, you could investigate wastewater evaporation, ion exchange, reverse osmosis, or dialysis to recover the zinc as opposed to creating sludge. Given the MP&M rules coming down (and I take pride in the fact that I was one of the people who made the prepublication copy available to the industry) such steps make more sense than at any time heretofore.

And, just to let Mr. Paul know, I have been a process engineer in the industry for 18 years, and am now working on projects for pollution prevention for metal finishers.

James Totter
James Totter, CEF
- Tallahassee, Florida

(2000)

thumbs up signI appreciate the time and energy that the various participants have put into their responses. As I was seeking recommendations on specific equipment, I especially appreciate the advice of Mr. Bill Paul; if he has the time, I would be willing to talk with him further on the subject.

Our company has been and continues to be interested in environmental issues and quality. While I am new to this area of expertise, others have been and continue to be involved in seeking ways minimize our environmental impact. Even though our plating waste is considered to be non-hazardous, we are very careful in how we dispose of it and are always interested in ways to minimize it. As I become more knowledgeable about the zinc plating process, I too, may be able to find ways to reduce it even further.

While the above is an ongoing long term goal, I feel our short term goal is to search for a new sludge dryer as our current one is at the point of needing to be replaced. That is why I felt this might be a good forum for me to learn more about the prevailing and emerging technologies in sludge dryer equipment. If this forum is not intended for that purpose, I am sorry for the time I have wasted.

David W. Cooper
- Hastings, Nebraska


(2000)

A. Mr. Cooper,

We try to make this the right forum for ANY metal-finishing-related purposesmiley

Nobody is trying to discourage you from seeking the information you are seeking--and hopefully Mr. Paul and others can expound further.

But suppose I were to say: "Folks, I'm brand new to the area of watching my health and I've decided I should eat more protein. Which candy bar do you guys recommend?" Some people will offer their evaluation of which candy bar has the most protein, but some will suggest that I eat more meat and less candy. I'm not wrong to ask such a question, and the people who recommend particular candy bars wouldn't be wrong, but neither are those who suggest I would be better off eating meat.

This is a public forum so there are going to be people (like me) who are utterly opposed to the whole idea of sludge dryers. I've been to shops that dry cadmium sludges, and have seen the dust in the air, and I find the idea that people are breathing this cadmium dust terrifying. I am not going to quietly whisper it just once; rather I am going to be persistent enough that people are left with no doubt that there are some of us who think that thermal sludge dryers are a bad enough idea that they should be immediately decommissioned, not upgraded.

Thanks in anticipation for your understanding.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. I inherited the operation of a sludge dryer (gas, hopper, conveyor chain, cyclone scrubber) of the type which you describe, for dewatering sludge from the pretreatment of steel and galvalum coil (alkaline cleaner, and scotch brite brushing).

I would not want to use one again, because of the fugitive emissions of dust from every orifice of the machine, of which there were many. It was a maintenance and ecological nightmare; that may be why the emotions are particularly strong around this letter. It did reduce the volume of our sludge, but it was not a safe machine to work around because of the exposure to dried, powdered hazardous sludge.

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 


(2000)

A. Mr. Cooper,

As an equipment manufacturer and engineering company, the multitude of options, gadgets, and technologies can be blinding. These gentlemen are steering you in the right direction: Minimize your waste - in all forms.

I would look at methods of reducing your dragouts first, then look at alternative chemistries that will produce 70-85% or less sludge, then go shopping for your equipment. Your budget will be happy, your compliance will be happy, and your WWT operators will be happy.

tom baker
Tom Baker
   wastewater treatment specialist
Warminster, Pennsylvania



(2003)

A. There are a lot of sludge drying system: heat pump drying system, paddle dryer, rotary dryer, etc. For the small treatment, I think you should use heat pump drying system. It can dry up to 2 tons per day of wet sludge. One KWH of power can evaporate 4 kg of water.

Long Huang
manufacturing - Gainesville, Florida


(2003)

A. Regarding sludge drying, we have several successful installations in the US. Our sludge and slurry driers are typically applied to drying metal hydroxide sludge and brines from evaporators, RO etc.

Regards-

Rob Sheldon
waste minimization - Saunderstown, Rhode Island


July 22, 2009

Q. Looking to install a drying system. Any background on the J Vap process?
My system is industrial waste water, using lime to process zinc and nickel.

C. Martin
Manuf. Eng. - Kentucky

Ed. note -- Readers: To the extent possible, please keep responses generic. Discussion of the technologies employed in this drying system would be great, but the internet is too anonymous for testimonials to, or slams of, particular brands of equipment.


January 14, 2011

Q. Well, I am working in wastewater treatment plant, we have concluded to terminate our sludge dryer due to huge cost related to operational and maintenance and at the same time poor working environment for the staff. Instead someone suggested to replace the sludge dryer with heat pump and heat exchangers. Could anyone who has experience with this technology help me how this technology works.

Rashid Kofi
Manager - Sweden


September 24, 2013

Q. I have taken over the Waste Water treatment facility at our Chrome Plating facility. We also generate filter cake sludge. Our system used to have a dryer a few years back, but the unit died a slow and terrible death according to those who were here at the time.

I am looking into a way to dry my filter cake,(or raise the percentage of solids as much as possible) as we send it out for metals reclamation, and with our current process we are lucky to get 20% solids from the cake. I am working with my operators to try and improve this through procedure, but I don't see much of an increase from this approach.

I am completely new to the plating industry, and do not know what options I would have in reducing the metals I am receiving from our plating operation, so I need to look at ways to increase my solids in our Waste Water Treatment. If I can raise the % solids, it translates into much higher return on the metals recycled.

Any guidance on this would be greatly appreciated.

Gary Reed
Chrome Plating Facility Environmental Manager - Urbana, Illinois, USA



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