[USCC] Would PFRP need to be done twice

Matt Cotton mattcotton@mindspring.com
Mon Mar 20 11:54:43 2000

Martine and Lauren:

Got your post and have the following response:

> Situation: Food waste from restaurants (contains meat, dairy products,
> grease and bones) is accepted at a transfer station for reload to go to a
> distant compost site. The food waste is run through the Process For Reducing
> Pathogens (PFRP) at the transfer station, then loaded into trucks to go to a
> distant compost site that compost yard debri and may not reach PFRP in that
> process.
> Issue: Oregon Department of Environmental Quality is trying to determine if
> it would be necessary to do PFRP again after hauling the pathogen-reduced
> unstable compost to the distant compost site?

May not be necessary, but may be desirable. Similar to what Craig said about
North Carolina, here in California, one is encouraged to conduct PFRP
documentation (time/temperature) as close to the end of the process as
possible, the back up being that the finished (for sale) compost must be
sampled for either Salmonella or e. coli every 5000 cubic yards. Some of the
literature on this topic talks about the high potential for pathogen "bloom"
after adding "fresh" feedstocks to already PFRP'd material (bacteria are
bacteria, give them nutrients under the right conditions, they will grow).
So if you wanted to ensure compliance with PFRP you would require both the
time temperature relationship (presumably of the mixed feedstocks) and also
documentation via sampling and analytical data of the final (mixed),
finished compost.

> Concerns: Human pathogen transmission: reinfecting of unstable compost
> material after it leaves the transfer center and goes into compost pile,
> pathogen regrowth in the compost pile, pathogen movement from compost site
> into surface and ground water.
> Questions: 
> *    Do you know of documented information concerning the potential for
> human pathogen regrowth in unstable compost made from meat products?

There is lots of documentation of pathogen regrowth (see BioCycle June 1995,
June 1996, and June 1996 for some excellent discussions). Most of this work
was conducted with biosolids, but work I have done here in California shows
that regrowth is possible post-pfrp even in yard waste only composts. Some
have argued that the PFRP temperatures (designed to kill human pathogens in
sludge) tend to kill off all beneficial bacteria allowing for potential
regrowth of which ever species gets there first, or thrives best.

I have not seen any research about pathogen movement from compost to surface
and/or groundwater, though my guess is that manure folks have grappled with
this issue. 

> *    Could the low level of pathogens still remaining after PFRP blossom
> in the material during composting?

Yes. As I mentioned above you could either have regrowth (or bloom) from
existing spores or from something reintroduced.

> *    Could human pathogens be reintroduced into the unstable compost via
> the vehicle transporting the unstable compost to the compost site, human
> contact, via flies, rats, seagulls at the compost site?

Yes. One of the findings of some early research was that a really good way
to re-grow pathogens was to introduce "fresh" material to composted sludge.
I also believe that a relatively "sterilized" medium (post PFRP compost) is
ripe for re-introduction of pathogens. The real question is whether or not
high e. coli numbers which you may find (and we have found in post PFRP
compost) truly indicate a problem with "human pathogens" and/or if this is a
water quality threat. Unfortunately though moist composters in CA test their
stormwater, I don't know of any who are required to test for potential
pathogens there.

> *    Is it possible to achieve the 55 degrees C necessary for PFRP for 3
> days in the unstable compost (can the composter get it to reheat readily)?

Given my understanding (partially composted, PFRP'd food waste being added
to yard trimmings to compost), there should be no problem getting the
material to re-heat and achieve PFRP time/temperature relationships (though
my guess is that you'd use the 15 day standard unless they're using an
in-vessel system). 

> *    Do you know of a sampling/testing protocol that would ensure no
> human pathogen regrowth potential in the unstable compost once it reaches
> the compost site?

There are several management practices which might limit potential for
re-introducing pathogens, but my guess is that even if you had the yard
trimmings go through PFRP before mixing the two feedstocks, in the end you
could still get relatively high e coli numbers.

> This has become a "hot topic" around here. Your input is appreciated. We'd
> especially appreciate documented sources concerning the potential for
> regrowth of human pathogens in feedstocks containing meat. Thank you.
Hope this is useful.

Matthew Cotton
Integrated Waste Management Consulting
19375 Lake City Road
Nevada City, CA  95959
phone: 530-265-4560
fax: 530-265-4547