Water Environment Federation (WEF) Discussion Forums / Biosolids & Residuals / WEF Discussion Forums / sludge drying / Latest Posts

RE: sludge drying

Pellet — Tue, 26 Feb 2008 09:15:08 GMT

I thought the thermal drying pathogen reduction required a certain time above a certain temperature. We've got an Andritz going in and I think in order to meet 503 we have to maintain 200F at the discharge end of the drum.

RE: sludge drying

Grant H — Fri, 08 Feb 2008 04:59:36 GMT

There is a company called Flo-dry in New Zealand that makes dryers. They use a complex system of blending dried, partdried and feed sludge and separate fines from the pellets and reblend.

But are such dryers Greenhouse Gas monsters? I guess if you are a big plant > 10 mgd, or cold climate then the economies of scale justify.

For smaller plants what about solar driers. Has the technology survived its brief entry onto the scene? We looked at solar driers for a temperate climate and were looking at a drying area based on 4 kgH2O/m2.day. The driers cost about $880 000 per 1000m2.

Solar drying manages to disinfect both E.coli and Salmonella. The sludge typically gets up to 40 or 50 degC.

We were drying liquid sludge from a lagoon - up to a soil like consistency. In this configuration you dont need any polymer. You can load them with belt press sludge if you want faster drying - the economies probably favour this.

RE: sludge drying

01667602 — Thu, 17 Jan 2008 11:31:25 GMT

We have a dryer that we use for WAS that is thickenend and then dried. Our biggest problem is not with the dryer but the dewatering. Can't get much above 9% with the unit we have. I have operated this unit for about 18 months and it works well considering. We are changing our dewatering unit to improve performance with the dryer and save money. The dried product looks like dirt and doesn't have much of an odor unless it gets burnt. Coliform results have been ND.

RE: sludge drying

D Shulmister — Mon, 14 Jan 2008 13:36:15 GMT

Not a long list of references -- apparently only one sewage works. I cannot tell whether this technology produces an EQ quality of product or not. And I don't think I'll be buying a product from Hungary anytime soon.

RE: sludge drying

FarkasPeter — Sat, 12 Jan 2008 08:11:59 GMT

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RE: sludge drying

MR_HOLMES — Fri, 26 Oct 2007 12:32:12 GMT

wsclifton (4/20/2007)

Jeff,

I am interested in all types of sludges, but have had sticking problems with a straight waste activated that is dewatered (prior to drying) to about 22% solids using about 25 pounds per dry ton of polymer conditioning.

One comment I heard was that an anaerobically digested sludge drys the best, with waste activated second and raw primary/waste blend third. Not sure about this and was hoping for some feedback.

steve

I wouldn't worry to much about how the differences between anaerobic vs. waste activated sludge unless you are designing a new facility. Most of us are stuck with what we got. Both anaerobic and aerobic digested sludge are suitable for sludge dryers. Neither works great if the digestion is incomplete.

Indicator organisms may not be destroyed if incomplete digestion occurs. There are some interesting papers floating around that discuss regrowth and reactivation, etc. I don't think anybody tests for pathogens. We only test for indicator organisms.

Is the sticky sludge causing an issue? How ofter is the unit cleaned? Is it run continuously or batch?

RE: sludge drying

MJB — Wed, 17 Oct 2007 10:47:02 GMT

I have found that non digested solids pose some operational problems. Primary sludge in general could cause various issues with sticking, clogging, etc. (not fun). If you receive biosolids from more than one source operators will be faced with constant changes in operational parameters. It is a definite challenge when your plant is receiving sludge from different plants.

RE: sludge drying

MJB — Wed, 17 Oct 2007 10:32:37 GMT

What David is refering to is the final product (Dried biosloids). 90% solids or better is the goal for most "Class A" drying facilities. Meaning that there is 10% or less residual moisture remaining in the final product.

RE: sludge drying

D Shulmister — Wed, 25 Apr 2007 13:14:00 GMT

Sure -- When you sample the dried sludge and put in a drying oven for a sufficient time. the dried weight should be at least 90% of the original sample weight (i.e., 10% or less moisture.)

RE: sludge drying

Vassilis Karmiris — Wed, 25 Apr 2007 02:30:46 GMT

could you please explain when you say "dried pellet in the 90% solids range"?

Thanks

RE: sludge drying

D Shulmister — Tue, 24 Apr 2007 13:23:57 GMT

The pathogens in such dried sludges should essentially be eliminated. I presume you have a dried pellet in the 90% solids range. The main question becomes what testing frequency your regulatory agency requires.

RE: sludge drying

Vassilis Karmiris — Tue, 24 Apr 2007 06:29:51 GMT

[quote]Jeff Naumann (4/20/2007)

What type of sludge are you talking about? (raw primary, digested anaerobic, digested aerobic, un-digested aerobic, etc.)
The City of Los Angeles is currently using very large rotary gas-fired dryers for (I think) digested/dewatered anaerobic sludge. The rotary dryers replaced their ill-conceived Carver-Greenfield system. Strangely enough, the same plant (Hyperion) had rotary dryers in the early 1950's, which were abandoned when the plant commenced ocean discharge of digested sludge into Santa Monica Bay via their 7-mile outfall.
I would think that pathogens would be almost (if not totally) eliminated with this type of dryer in that the sludge is subjected to a temperature of at least 200 deg. F for several minutes.
There are other types of drying equipment, of course, that might have been tried somewhere.
http://www.lasewers.org/treatment_plants/hyperion/index.htm[/quote]

I am talking about dewatered sludge, which has been digested anaerobicaly (approx. at 35 degrees C) and will be further treated in a rotaty dryer. The temperature ranges from 400 degrees C at the beginning of the dryer to 100 degrees C at the end. I suppose that, as you mentioned, pathogens would be almost eliminated at such temperatures, so the question is how often should this dried sludge be tested for pathogens and in general what is the purpose of performing microbiological analysis in that kind of sludge

RE: sludge drying

D Shulmister — Mon, 23 Apr 2007 12:47:21 GMT

If it was well digested ANAEROBICALLY, you wouldn't have that problem either.

RE: sludge drying

Jerry — Fri, 20 Apr 2007 17:11:24 GMT

If it was well digested AEROBICALLY, you wouldn't have that problem.

RE: sludge drying

D Shulmister — Fri, 20 Apr 2007 12:45:31 GMT

One detail you may be interested in: If you're using the dried sludge as a fertilizer AND the original sludge has not been digested, the comment is that the product when wetted smells like sludge. I don't think the neighbors will like that.

RE: sludge drying

wsclifton — Fri, 20 Apr 2007 12:09:55 GMT

Jeff,

I am interested in all types of sludges, but have had sticking problems with a straight waste activated that is dewatered (prior to drying) to about 22% solids using about 25 pounds per dry ton of polymer conditioning.

One comment I heard was that an anerobically digested sludge drys the best, with waste activated second and raw primary/waste blend third. Not sure about this and was hoping for some feedback.

steve

RE: sludge drying

Jeff Naumann — Fri, 20 Apr 2007 10:22:44 GMT

RE: sludge drying

Vassilis Karmiris — Fri, 20 Apr 2007 07:18:59 GMT

I would like to add one more question to the above mentioned:

What is the effect of this dying process on the pathogens contained in dewatered sludge?

thank you in advance

sludge drying

wsclifton — Fri, 02 Mar 2007 11:57:33 GMT

Any operators out there that have sludge dryers?

How are they working, how do you operate them, any trouble with sludge sticking on the inside, polymer causing drying problems, time and temperature settings changing frequently.....?

Just interested in your experience operating sludge dryers

thanks

steve