BACTERIA REGROWTH - REACTIVATION
Also see current list of Studies
Bacterial regrowth or reactivation in sludge biosolids has been a known fact since it was reported in the 1973
Proceedings of the Joint Conference on Recycling Municipal Sludges and Effluent On Land
Yet, the experts claim they just discovered the fact in 2006?
Organizations Respond Quickly to Evidence of Coliform Reactivation (bacterial regrowth)
December 2006, Vol. 18, No. 12
Water Environment & Technology (WE&T)
“There was a lot of concern that once [WERF’s] report was released there could be some backlash in the biosolids community from a
lot of the opponents of biosolids,” said Rhonda Bowen, recycling manager at Hampton Roads Sanitation District (Virginia Beach, Va.)
and a co-chair of the WEF subcommittee that compiled the TPU.
Even though it might open a big can of worms, asking these tough questions is the only way to ensure that land application remains a
viable option, said Chris Hornback, senior director for regulatory affairs at the National Association of Clean Water Agencies (NACWA;
A few facts to keep in mind before your blinded by the lies. Coliform are some deadly bacteria
The above agencies are funded by taxpayers. Therefore, they should not be lying to the public or putting the public health at risk!
Although WEF Director, Albert Grey, assured millions of viewers on CNN's 1997 "Hazardous Harvest" that sludge was: 1) a
material (sludge) that is carefully processed, and 2) tightly regulated, 3) carefully monitored, and 4) fully controlled precisely for the
purpose of protecting public health,--- the opposite is true.
EPA's 2006, Biosolids Technology Fact Sheet, Use of Composting for Biosolids Management, based on Yanko's
1988 study states, "Under some conditions, explosive regrowth of pathogenic microorganisms is possible." "Composting
is not a sterilization process and a properly composted product maintains an active population of beneficial
microorganisms that compete against the pathogenic members."
[Note: EPA and partners have assured the public that composting distroys pathogenic disease causing
According to the preamble to the final part 503, there is a problem, "The vector attraction reduction requirement
concerning incorporation of sewage sludge into the soil also requires that sewage sludge that is Class A with respect to
pathogens be applied to or placed on the land within eight hours after being discharged from the pathogen treatment
process. After that, the sewage sludge must be incorporated into the soil within six hours after being applied (beneficial
use) or placed (disposed of) on the land. The purpose of this requirement is to ensure that regrowth of Salmonelle sp.
bacteria do not occur between the time the sewage sludge is discharged from the pathogen process and the time the
sewage sludge is applied or placed on the land." (FR. 58, p. 9353, 9401
In 1973, EPA was warned by USDA's John Walker that in the field, it takes about 30 days for the bacterial spores to
dissolve and the germs become active again. There is no way to keep this toxic soup spread on crops out of our food
chain. Even if corn was the only crop grown and it was used for ethanol production-- gluten is a byproduct of ethanol
used in animal feed and human food.
Walker made it clear in Proceedings of the Joint Conference on Recycling Municipal Sludges and Effluent on Land, July
9-13-1973, pp. 39-47. Sponsored by EPA, USDA, and National Association of State Universities and Land Grant
Colleges, that there would be serious prblems with the EPA's beneficial sludge use program.
In the discussion section of the proceedings, John Walker of the USDA Research Station at Beltsville, Maryland, (now
with EPA) discovered that EPA actually knew very little about the nature of limed treatment destroying disease
organisms in sludge or making the metals less available to plants. (USDA didn't either, Beltsville Research Station was
declared a Superfund site in the 80's.
In 1994, Constantine Skanavis and William Yanko conducted a study of composted sewage sludge based soil
amendments for potential risks of salmonellosis.The authors conclude that "compost-based products could, in specific
situations, represent a source of Salmonella infection. This study, therefore, points to the need for intensive study of
the factors associated with Salmonella spp. regrowth." (p. 9)
December 2006, Vol. 18, No. 12
Water Environment & Technology (WE&T)
Organizations Respond Quickly to Evidence of Coliform Reactivation
According to a recent Water Environment Research Foundation (WERF; Alexandria, Va.) study, fecal coliform counts
can increase dramatically in anaerobically digested biosolids, but the reason is unclear.
Utility managers, microbiologists, design engineers, policy analysts, and regulators came together to discuss this
unexpected phenomenon at a special technical session at WEFTEC®.06 in October.
“Basically, what happens is when you come out of digestion and go into a dewatering device, you have one density of
fecal coliform and then, immediately after dewatering, that level increases by one, two, three, or four orders of
magnitude,” said Matthew Higgins, associate professor in the Department of Civil and Environmental Engineering at
Bucknell University (Lewisburg, Pa.), and a principal investigator for the WERF study.
Because the bacteria cannot reproduce that quickly, researchers have concluded that this phenomenon is due to the
reactivation of bacteria. That is, the fecal coliforms were always present in the samples but were invisible to standard
culturing methods until dewatering somehow spurred them to function fully.
Higgins described several mechanisms that could account for this nonculturable state. The first theory is that the
bacteria could have been injured but not destroyed during digestion and that dewatering enabled them to repair
themselves and become active again. The second theory points to the bacteria entering a viable but nonculturable
state; this state would be a defense mechanism to the conditions of the digestion process. The third theory, Higgins
explained, is that an inhibitor present in the digested solids is removed by the dewatering process.
Whichever of these mechanisms is at play, dewatering, frequently centrifuge dewatering, often triggers the bacteria to
Fecal coliform concentrations are an integral part of the U.S. Environmental Protection Agency (EPA) Part 503
regulations that govern biosolids treatment and use. Class B and A biosolids must contain fewer than 2 million colony
forming units of fecal coliform per gram of dry solids and less than 1000 CFU/g dry solids, respectively, at the time of
use or disposal to comply with the pathogen criteria of the Part 503 regulations.
However, the regulations also include process-based equivalents for Class A and B that require no subsequent testing.
In these cases, the observed reactivation and regrowth could push the fecal coliform concentrations above the allowed
levels unbeknownst to utilities.
To find out how many nonculturable fecal coliform bacteria are present in digested solids, the researchers used
polymerase chain reaction (PCR) testing to count Escherichia coli cells. PCR enumerates bacteria based on copies of
DNA present, and E. coli is one of the main fecal coliform detected in culturing methods, Higgins said.
The testing showed that anaerobic thermophilic digestion followed by centrifuge dewatering led to reactivation most
consistently and with the greatest magnitude of increase, Higgins said. About 87% of samples dewatered by centrifuge
However, substantial increases in fecal coliform and E. coli density can occur after any type of dewatering of
anaerobically digested biosolids. Such reactivation occurs about 70% of the time, according to WERF’s findings.
At the technical session, Mark Meckes, an EPA microbiologist, stated that much more work needed to be done before
any actions were taken. “We still feel that the 503 [regulations] are appropriate and protective,” Meckes said. “There’s a
lot more research necessary in this area if we are to discern the public health impacts.” However, he added, that as
data comes to light, EPA will make changes to the part 503 rules as needed.
Meckes emphasized that reactivation and regrowth have only been seen in bacterial indicator organisms, not
pathogens. Moreover, he said that this issue is strictly a bacterial one. Viruses, protozoa, and other monitored
organisms require a living host to multiply. Meckes said the chances of those pathogens reactivating or regrowing after
digestion are “slim to none.”
He also noted that reactivation has not been found at every plant using anaerobic thermophilic digestion with centrifuge
dewatering. “Don’t jump the gun and assume you have a problem because you have that digestion process,” Meckes
To provide a level basis for seeking answers, the Water Environment Federation (WEF; Alexandria, Va.) in September
issued a technical practice update (TPU) on reactivation and regrowth issues. The TPU includes an overview of related
regulatory issues for biosolids stabilization and testing protocols, recommendations for communication strategies, and a
description of known methods to address reactivation and regrowth.
“There was a lot of concern that once [WERF’s] report was released there could be some backlash in the biosolids
community from a lot of the opponents of biosolids,” said Rhonda Bowen, recycling manager at Hampton Roads
Sanitation District (Virginia Beach, Va.) and a co-chair of the WEF subcommittee that compiled the TPU.
Even though it might open a big can of worms, asking these tough questions is the only way to ensure that land
application remains a viable option, said Chris Hornback, senior director for regulatory affairs at the National
Association of Clean Water Agencies (NACWA; Washington, D.C.).
“The court of public opinion rules the day, and that’s ultimately where we will be judged on our response to this
situation,” Hornback said.
To that end, the speed and extent with which the initial data was shared with stakeholders and the ongoing commitment
toward research and communication are almost as important as the research results itself, Hornback added.
Hornback applauded WEF, WERF, and NACWA for moving so quickly and disbursing the information so widely.
“In fact, this project and our industry’s response, I think, have highlighted what we can accomplish when we all work
together,” he said.
There are steps that treatment facilities can take to either avoid the reactivation or mitigate it. John Willis, vice president
of Brown and Caldwell (Walnut Creek, Calif.), suggested four options for Class B systems. The first is land application
of liquid biosolids, as there has been no documented reactivation or regrowth without dewatering, he said. Second, he
suggested switching to a different dewatering technology, such as belt filter presses. Third, some form of post-
dewatering treatment, such as lime addition, can be used to keep coliform levels in the acceptable range. Last, he
suggested simply storing the dewatered solids until the fecal coliform reactivate and regrow and then die off.
To prevent reactivation and regrowth for Class A systems, he suggested keeping the solids hot from digestion through
land application, using liquid land application, switching dewatering technologies, dosing dewatered biosolids with lime,
and exploring multistage Class A thermophilic digestion. To date, systems with multistage anaerobic thermophilic
digestion and centrifuge dewatering have shown no reactivation and regrowth, he said.
At press time, the second phase of research was expected to be completed by the end of the year, with a report on the
findings due in spring 2007.
The objectives of the second phase are to verify and to better understand reactivation and regrowth and to develop
mitigation strategies by answering the following questions:
What combinations of wastewater process technologies lead to this observed increase in fecal coliforms?
What specific process designs and operating conditions contribute to this increase in fecal coliforms?
What are the mechanisms for reactivation?
What conditions contribute to regrowth?
The study report, Examination of Reactivation and Regrowth of Fecal Coliforms in Centrifuge Dewatered, Anaerobically
Digested Sludges (03-CTS-13T), was published in June. It can be obtained by searching WERF’s publication database
at www.werf.org. The WEF TPU can be obtained through the WEF online bookstore at www.wef.org/marketplace. The
TPU, free to WEF members, costs $55 for nonmembers.
— Steve Spicer, WE&T