Sludge Dryers for Concentrating Plating Wastes

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.

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.

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%.

That I like, Rick!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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.

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 °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!

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, P.E.
Striving to live Aloha
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.

A. Mr. Cooper,

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

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.

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 topic. 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.

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.

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.

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-