Sludge Watch ==> Kansas Plant Centrifuged Sludge - what about repathogenation?

[Maureen Reilly]

Sludgewatch Admin:

For those of you who are as curious as I am, this story illustrates a 
situation that is taking place
across North America, as even smaller sewage treatment plants move to 
centrifuge dewatering of sewage sludge.

The problem is pathogens.  Recent tests demonstrate a massive re-emergence 
of pathogens in many anaerobically digested and centrifuged sludges.  This 
suggests that the pathogens are not eliminated just temporarily difficult to 
detect.

For some reason the centrifuge stress makes the pathogens 'reactivate'.  
There have been no follow up reports from WERF, WEF, or the EPA since this 
phenomena was 'discovered' last year.

The question is whether the 'disinfection' of sludge is taking place.  As it 
is, with digested sludges, the number of Ecoli or fecal coliform and viruses 
is as high or higher in the sludge than it is in the raw sewage...on a 
bacteria per gram basis.

The research suggests that the sludge digestion may be increasing, no 
decreasing the pathogens (and pathogen indicators) in sludge that is headed 
to for farm communities.

..........................................




Sludge report: Plant seeks a solution


Centrifuge implemented to make waste byproduct transportation easier, more 
efficient

By John Green

The Hutchinson News




jgreen at hutchnews.com

Improvements made last year at Hutchinson's wastewater treatment plant are 
working so well, they've created an unexpected consequence.


The amount of waste sludge hauled from the plant in large tanker trucks and 
sprayed on area cropland each week has more than doubled.

That's prompted officials to hire a contractor to explore the methods the 
city uses to process and handle sludge in the future.

The contract began last week with a demonstration of the latest in sewer 
plant technology - a sludge centrifuge.

Local officials were impressed, but they will wait for recommendations from 
the project contractor, environmental engineering firm Camp Dresser & McKee, 
before developing a plan. The company has four months to complete a master 
plan.



A centrifuge separates the 2 percent of solids from the digester at the Reno 
County Wastewater Treatment facility. Photo by Travis Morisse.

Increase in sludge

In 2004, responding to concerns about the levels of ammonia and nitrates in 
the treated water being discharged from the wastewater plant, the city added 
more aeration basins, Public Work Director Reg Jones said.

In the several 400,000-gallon tanks, bacteria consume the waste solids 
suspended in the water and drop to the bottom of the tank, creating the 
waste sludge at the bottom. Adding more basins allows the microbes to work 
in the water longer, removing more waste, but also creating more sludge.

In 2004, the city paid a contractor to haul 10.2 million gallons of liquid 
sludge from the plant and spread it on cropland, said Millie Reed, 
wastewater plant superintendent. In 2005, because it was a dryer year, 
sludge production dropped slightly to 9.2 million gallons.

So far for 2006, however, the amount of sludge being hauled away has 
increased approximately 59 percent, Reed said. The 8.5 million gallons 
disposed of through July equates to a projected 14.6 million gallons for the 
year.

At 3,500 to 4,500 gallons per tanker load, that's a lot of trucks in and out 
of the treatment plant each week. Of even greater concern, however, Jones 
said, is that sometimes weather prevents the sludge from being hauled out 
and applied on land, meaning it has to be held at the treatment plant, which 
has a limited holding capacity.

"If the digesters get full, we don't have anywhere to pump the things we 
need to move," Reed said. "We have to keep the sludge down enough that the 
digesters operate the way they're supposed to."

Cutting the volume

Part of the project the city has contracted with CDM for is to clean 
accumulating sludge from the bottom of the massive tanks. The 
trailer-mounted sludge centrifuge was used to process the water being 
removed from the first of the tanks.

The centrifuge spins the contents so the water is pressed out by gravity, 
leaving dewatered sludge.

"Liquid sludge usually runs about 3 to 4 percent solids," Reed said. "The 
product out of the centrifuge was 30 percent solid. It was a like a crumbly 
potting soil. It looks like dirt."

Instead of 100 tanker trucks of liquid waste being hauled away from the 
digester, they ended up with about 200 cubic yards of dewatered sludge in a 
pile at the plant, Reed said.

"The nice thing about it, it can be stored in this form until we're ready to 
haul," she said. "It makes it a lot easier to handle."

The dewatered sludge will also be placed on cropland, but in a different 
manner than the liquid sludge, Jones said. Thought it is concentrated, the 
amount of nitrogen in the dewatered sludge is lower because a lot of it 
stays in the water that is removed.

Worth the cost

Neither Reed nor Jones knew the cost of the centrifuge, but they estimated 
it at $150,000 to $200,000. If one were installed there would also be costs 
for piping the removed water back into the treatment process, chemicals that 
must be added to make the sludge clump together, and a storage building for 
the sludge.

The cost of hauling away sludge in 2005 was $268,000. Based just on the 
probable cost of the centrifuge, it could pay for itself quickly in reduced 
hauling, Reed said.

"The contract has worked well over the past years," Reed said. "But it's 
time to go back and look at what we're doing. The study may say what we're 
doing is fine, it may say to look at something else."

Besides a centrifuge, some plants use belt filter presses, which remove the 
sludge using filters, then press and heat the sludge to remove the water 
along a conveyer belt. The dryers, however, are very high temperature, 
resulting in higher energy costs, Reed said.

Jones said any major changes in the sludge processing system likely wouldn't 
occur until the current sludge-hauling contract is close to expiration, 
which is in 2010.


10/10/2006; 08:47:43 AM
http://www.hutchnews.com/news/regional/stories/sludge101006.shtml