[USCC] Re: Class A sludge

[Rufus Chaney]

Dear Caroline Snyder and USCC colleagues:

    The literature on regrowth of pathogens in biosolids materials seems =
pretty clear based on research done over 30 years on this issue. When our =
laboratory (Biological Waste Management Lab) at Beltsville was developing =
composting, Dr. Wylie D. Burge tested regrowth of Salmonella in relation =
to biosolids processing including composting. Their results were relevant =
to this discussion.
     If a heat dried or radiation sterilized biosolids product (even =
irradiated composted biosolids) is inoculated with Salmonella, the =
organism grows rapidly reaching high density. These types of products =
(like manure) are good media for growth of Salmonella.
     But when composted biosolids are inoculated, regrowth is small and/or =
numbers decline pretty rapidly. Properly composted biosolids or manures do =
not have Salmonella one can find using available methods. Hussong et al. =
(1985) (Burge's group) reported the factors in biosolids compost which =
contributed to suppression of Salmonella regrowth.


Hussong, D., W.D. Burge and N.K. Enkiri. 1985. Occurrence, growth, and =
suppression of salmonellae in composted sewage sludge. Appl. Environ. =
Microbial.  50(4):887-93.=20
	"Composted sewage sludge may be used to improve soil quality, but =
there remains some doubt concerning the microbiological safety of the =
product. Sewage sludge composts from 30 municipalities were sampled, and =
four samples (12%) contained salmonellae (two contained fewer than 0.3/g, =
and the other two had 21/g and 1.7 X 10(4)/g). All 30 composts were =
inoculated with salmonellae; the populations decreased at a specific death =
rate of about 0.15 h-1 over 24 h at 36  C. In irradiation-sterilized =
composts inoculated with salmonellae, the salmonellae grew at a rate of =
0.65 doublings per h for over 24 h. Growth and death rates were found to =
be moisture and flora associated. The growth or death rates for antibiotic-=
resistant salmonellae were not different from those of nonresistant =
strains. It was concluded that the active indigenous flora of compost =
establishes a homeostatic barrier to colonization by salmonellae, and in =
the absence of competing flora, reinoculated salmonellae may grow to =
potentially hazardous densities. The active microflora of moist composts =
eliminated contaminating salmonellae [10(5)/g] after 6 weeks." [available =
from the web at no charge]

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Others have reported similar results. The 2001 study of Sidhu et al. =
confirmed the findings of Hussong et al. (1985), and also showed that as =
the maturity of the compost increased, the rate of suppression of =
inoculated Salmonella increased.

All these results show that the diverse organisms and their use of =
nutrients present in the compost limit the growth of Salmonella. Thus =
sterilized biosolids products do not have this built in protection found =
in mature composts. Burge also examined irradiated biosolids or composted =
biosolids for Salmonella regrowth because DOE was evaluating irradiation =
as a pathogen reduction method. Irradiation, like heat sterilization, =
produces good media for Salmonella growth. I am not personally familar =
with the data on alkaline Class A processing, or on regrowth.

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Sidhu J, Gibbs RA, Ho GE, Unkovich I. 2001. The role of indigenous =
microorganisms in suppression of Salmonella regrowth in composted =
biosolids. Water Res. 35:913-920.=20
	"Composting is commonly used as an effective means of stabilizing =
wastewater biosolids and reducing pathogens to very low concentrations. =
However, it has been shown that under certain conditions Salmonella can =
regrow in previously composted biosolids. Growth of seeded Salmonella =
typhimurium in composted biosolids ranging from two weeks to two years =
maturity was monitored. Results from sterile and non-sterile composted =
biosolids were compared. Seeded S. typhimurium colonized rapidly in =
sterilized biosolids reaching a maximum population density of more than =
108 g-1. Growth of seeded S. typhimurium was suppressed in non-sterilized =
compost with a maximum population density of less than 103 g-1. There was =
a significant decline in the growth rate of seeded Salmonella in sterilized=
 compost when the compost was stored, suggesting that bio-available =
nutrients declined with storage. However, in non-sterilized compost this =
was not the case. This suggests that the indigenous microflora play a =
significant role in suppression of Salmonella regrowth in composted =
biosolids. There was a strong negative correlation (-0.85) between the =
Salmonella inactivation rate and the maturity of compost in non-sterilized =
compost. The Salmonella inactivation rate was seven times higher in =
biosolids composting for two weeks as compared to compost stored for two =
years. This suggests that the antagonistic effect of indigenous microorgani=
sms towards Salmonella declined with compost storage. It was concluded =
that all composted biosolids had a Salmonella regrowth potential. However, =
the indigenous microflora significantly reduced this regrowth potential. =
Long-term storage of compost is not recommended as this may increase the =
pathogen regrowth potential." [available from the web at no charge]


>>> cgsnyder@post.harvard.edu 01/16/04 12:02PM >>>
Response to GKuter with regard to the National Academy of Scienes comments =
on Class A sludge:

     "Issues of concern (about Class A processes) included regrowth of =
pathogens with short-term stabilized biosolids and odors. Other (issues) =
were specification of treatment process versus product control and the =
appropriate organism to predict pathogen survival and recontamination.  =
However the major problem discussed ( at the EPA workshop) was the Class A =
process criteria that do not take into account the potentials for =
regrowth.  Regrowth of pathogens can occur in Class A biosolids . . . To =
prevent pathogen regrowth, a fairly stable background population of =
microorganisms are needed.  Class A disinfection processes generally =
eliminate these competing  microorganisms, REQUIRING RETESTING  OF CLASS A =
BIOSOLIDS IF USED  IN BULK QUANTITIES MORE THAN 3 WEEKS OR SO AFTER =
PRODUCTION." (page 60  NRC report  Pre publication edition)

------------------------------
Snyder:
     A member of the panel also expressed the need for metal tracking if =
Class A is used repeatedly on food crops.  I am not sure that recommendatio=
n was incorporated in the NRC report.

Chaney response:=20
     You need to cite the source of that claim, which I believe is the =
Cornell group. However, research has clearly shown that the Zn inhibition =
of plant uptake of Cd and bioavailability of crop Cd to animals provide =
protection against Cd in Class A biosolids used on soils where food crops =
will be grown. Those were the feeding tests I noted earlier, several of =
which were done in cooperation with Cornell scientists. Other elements are =
regulated to protect gardeners for their lifetime exposure to such foods, =
assuming that we start with 1000 t/ha, not that we start with 0 t/ha and =
use appropriate annual applications limited by N or P. As I noted, Pb =
uptake is reduced by application of biosolids, so I don't know any element =
which is most limited thru risk from the garden foods pathway that has not =
been clearly shown to not comprise risk to humans who consume large =
amounts of home grown foods produced on biosolids or compost amended =
soils.

------------------------------
Snyder:
     One flaw in the current federal  rules is that there are no site =
restrictions or label requirements for the use of Class A sludge. A =
lowering of pH , moisture, soil property, application rates, and many =
other interacting factors can mobilize some of the pollutants in this =
product.  Dry weather and wind can move bioaerosols off site.  There =
has=20
also been concern that some of the methods used to produce Class A sludge =
do not reliably reduce pathogen levels.

Chaney response:
     States do the actual regulation of marketing of biosolids Class A =
products. States specify the nature of labels required on bags of the =
product. Normal crop production practices (keep pH high enough to prevent =
toxicity of soil Al and Mn, hence 5.5 or above) prevent significant =
mobilization of soil metals accumulated from application of biosolids, =
manures, composts, etc. Only the Cornell group claims important metal =
leaching from biosolids amended soils. Many other studies confirm the =
retention of biosolids metals within the depth of incorporation or small =
movement into the soil layer immediately below the depth of incorporation. =
Questions about windblown amended soils need to consider the rapid death =
of organisms after application to soils, and that Class A composts did not =
have significant numbers of pathogenic microbes, virus, or parasite ova in =
the first place. Regarding concerns about effectiveness of pathogen =
reductions, I refer all to the review paper of Gerba et al. (2002). Yes, =
EPA is working to improve the assurance that process to make Class A =
pathogen reduction biosolids products, and to evaluate alternative methods =
under the Pathogen Equivalence Committee. If EPA or others find a need to =
change the minimum practices required for any Class A process, they will =
propose the change for public comment. And the letter from EPA regarding a =
petition to cease use of biosolids on land clearly summarized EPA's =
official position on the quality of the evidence claimed to show risks to =
humans from pathogens in soils amended with biosolids.=20
     As I have previously agreed, it is clear that EPA does not have =
Federal enforcement staff needed to make sure 503 is enforced appropriately=
. But that is hardly relevant because States and/or local government have =
their own version of 503 regulations and provide the enforcement expected =
by the public. Malodor does occur and regulatory agencies keep working to =
minimize malodor situations. As always, composting is the one management =
technology which can clearly process biosolids to achieve nutrient =
stabilization, malodor generation potential, and pathogen reduction and =
suppression.


Gerba, C.P., I.L Pepper and L.F. Whitehead, 3rd. 2002. A risk assessment =
of emerging pathogens of concern in the land application of biosolids. =
Water Sci. Technol. 46(10):225-30.=20
	Since the development of the United States Environmental Protection=
 Agency's 503 biosolids Rule, which includes treatment requirements to =
reduce the threat of pathogen transmission, many new pathogens have been =
recognized which could be transmitted by biosolids. A risk analysis was =
performed assess which emerging pathogens would be most likely to survive =
treatments required for Class B biosolids before land application. The =
literature was reviewed on the resistance of emerging pathogens to =
temperature and other environmental factors to assess their probability of =
surviving various biosolids treatment processes. In addition existing =
information on occurrence in biosolids and dose response models for each =
pathogen was reviewed. It was concluded that adenoviruses and hepatitis A =
virus are the most thermally resistant viruses and can survive for =
prolonged periods in the environment. The protozoan parasites microsporidia=
 and Cyclospora were unlikely to survive the temperatures achieved in =
anaerobic digestion and do not survive well under low moisture conditions. =
A risk model was used to assess the risk of infection and illness from =
enteric viruses after application of class B biosolids." [available from =
the web at no charge]


-----------------------------
Snyder:
     Also, several scientists and compost specialists believe that the US =
metal standards for sludge compost are not protective.  The US permits =
much higher metal levels  in sludge compost than most industrialized =
countries that have compost standards.

Chaney response:=20
     There will always be someone who believes that the standards are not =
protective. The question is "Are there field data coupled with dietary =
exposure models which predict risk from elements applied in Class A =
biosolids products marketed in the US today?" All evidence indicates that =
when bioavailability is also taken into consideration, there is no such =
evidence. The Cornell claims address the 503 calculations which did not =
include a factor for bioavailability of elements in crops grown on =
biosolids amended soils. It is a "paper tiger" with no real teeth -- when =
you look at the feeding tests with biosolids products which comply with =
503, there are no reports of element risks to animals consuming a high =
fraction of their diets from crops grown on biosolids amended soils.
     European standards are "don't increase soils above background" or not =
above some set low addition (3 mg Cd/kg soil), not risk based limits based =
on field data with crops grown on biosolids amended soils and especially =
not on such crops fed to livestock or test animals. Both the Congressional =
Law, EPA regulation development, and normal practice in the US is to base =
regulations on field results with real biosolids products where information=
 is available. Such data are available, both from US and European =
research. Limiting quality of products which may be marketed is the best =
way to limit potential worst case exposures to highly exposed individuals.
     One additional benefit of composting is the alleviation of most of =
the potential acidification from oxidation of N and S present in biosolids.=
 If the stabilization occurs in a compost curing pile, and the product is =
still near neutral pH, the compost will have little ability to cause pH =
lowering after application. Most non-composted biosolids products are =
richer in organic N and S and generate more acidity per ton applied than =
do composts.

----------------
Caroline

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Rufus Chaney
USDA-ARS
Beltsville, MD