[USCC] Maturity vs Stability

[Matthew Cotton]

Jim -

At risk of exposing my ignorance on the subject and with deference to 
individuals with much more experience than I on this topic (Frank S., 
Wayne T., David S. , Will B., Rufus, to name but a few)...I wanted to 
offer a partial thought on your post:

The examination of compost is a complex subject fraught with some of 
the difficulties you mention (feedstock variations, fluctuating 
moisture content, etc). And while it is attractive to think that there 
is one single test  to measure a given property (like "stability"), it 
would seem that the complex bioprocess of composting lends itself to 
using more than one test. Even the (sometimes frustratingly unclear) 
PFRP process relies on more than one test (you've got to document 
time/temperature and pass the pathogen test), not to mention VAR.

The CCQC Compost Maturity Index developed by Marc Buchanan (with input 
from Frank Shields, Will Brinton, Wayne Thompson and Jim West among 
others) recognized this aspect of compost testing. The Maturity Index 
(described at great length in the TMECC) uses three indicators to give 
a general three tier rating (immature, mature, very mature) of compost 
maturity based on the results of C:N, a stability test (you can choose 
which one) and a maturity test (again, you can choose). By using a 
minimum of these three parameters (C:N, stability, and maturity) you 
can with some confidence make a judgment about compost maturity. I 
think it is easy to come up with one or more examples of materials that 
might be composted but might frustrate any one test (especially if the 
method isn't followed correctly). For example you mention that a 
self-heating test might be fooled by low moisture content. But the 
proper lab method for a self heating test (using a Dewar flask for 
example) requires that you have an adequately moist sample. I believe 
the same would be true of carbon dioxide evolution/respiration or 
oxygen consumption, if you dry out the sample, the test will not 
accurately reflect the stability condition of the material, but the 
specific lab methods require adequate moisture to be present.

So I guess what I'm saying is as long as you follow the lab methods 
properly, any of the traditional stability tests should provide you 
with an adequate result. But I will be happy to be 
corrected/enlightened by you or others out there.

Matthew Cotton
Integrated Waste Management Consulting, LLC
19375 Lake City Road
Nevada City, CA  95959
(530) 265-4560
Fax (530) 265-4547
mattcotton at mindspring.com

On Aug 31, 2006, at 10:07 AM, Jim McNelly wrote:

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> Fellow Composters,
>
> I am being asked in one of my projects to propose
> a standard of compost stability that a certain
> composting process should meet other than the EPA
> time and temperature requirements for pathogens
> and vectors.  This standard would be for a
> maximum of 21 days of composting and should not
> be a maturity standard for the suitability for
> plant growth, but an indicator of how well a
> particular composting system is performing.
>
> Regarding the definition of compost maturity, in
> the past ten years, great progress has been made
> using testing methodologies developed in the
> USCC's laboratory handbook, "Test Methods for the
> Examination of Composting and Compost
> (TMECC).  More information can be found at
> www.tmecc.org . Compost maturity largely deals
> with the suitability of a bionutrient or compost
> product to facilitate growth a particular plant
> under controlled conditions.  Stability, as I
> understand it, deals more with regulatory
> compliance parameters dealing with nuisances
> while protecting public health and the
> environment.  Heated garbage, for example, may be
> pathogen free but it is not "stable".
>
> I am wondering how the issue of stability is
> being addressed in actual composting facilities
> in operation today.  Specifically, I am looking
> for indicators of stability required by various
> states or used by operators.  In wastewater
> treatment solids evaluation, volatile solids
> reduction is typically used for determining the
> change in raw and digested solids, but VSR does
> not work as well as a standard for composting as
> bulking materials that do not decompose or are
> not a part of the putrescible material being
> evaluated.  Specifically wood chips have a high
> level of volatile solids but show little volatile
> solids reduction in composting whereas food
> products or biosolids show a greater volatile
> solids reduction.  The two materials commingled
> make the VSR analysis usable perhaps for an
> operator in evaluating their own process compared
> to other time periods in their operation, but are
> not reliable when evaluated against other
> technologies, other blends or other facilities.
>
> Regarding time and temperature, the basics of
> stability begin with the EPA's 503 rules for
> pathogens and vectors.  While there are many ways
> of meeting these rules, composting operations
> typically use the time and temperature standards.
>
> PFRP, the Process to Further Reduce Pathogens
> Using either the within-vessel composting method
> or the static aerated pile composting method, the
> temperature of the biosolids is maintained at
> 55°C or higher for 72 hours.  For windrow
> composting, the requirement is 15 days over 55°C with a minimum of 5 
> turnings.
>
> For Vector Attraction Reduction (VAR), one of the
> options is aerobically treating the biosolids for
> 14 days or longer, during which time the
> temperature always must be over 40°C and the
> average temperature must be maintained at
> 45°C.  This time and temperature standard applies
> to windrow and in-vessel systems both.  I am not
> aware of how a windrow system can document
> meeting VAR as it appears to me that there is a
> conflict between temperatures exceeding 55C for a
> total of 15  24 hour time periods and being
> "maintained" at 45C during the same time.
>
> Most windrow systems I am aware of use conduct
> quarterly pathogen testing.  If testing is used
> as alternative, these are the EPA standards:
>
> This alternative states that biosolids are
> considered to meet the Class A standards if:
>
> *  the density of fecal coliform in the biosolids
> must be less than 1,000 MPN per gram total solids (dry-weight)
>                                      or
> *  the density of Salmonella sp. Bacteria in the
> biosolids must be less than 3 MPN per 4 grams of total solids 
> (dry-weight).
>
>
> Regarding the pathogen tests, have seen
> composting systems meet PFRP and VAR, only to
> become reinoculated with fecal coliforms due to
> cross contamination with unprocessed materials,
> either from the loader bucket or commingling in
> curing piles.  Should the ability of a compost
> product to resist reinoculation be considered as an indicator of 
> stability?
>
> Forced aeration systems can meet PFRP in three
> days and then VAR in an additional 14 days,
> suggesting to me that regulatory compliance using
> time and temperature requires at least 17 days
> plus the time it takes for the composting mass to
> reach PFRP temperatures, meaning a minimum of 18
> days. Forced aeration alone is typically unable
> to bring the temperature of the composting mass
> down to 45C and maintain it there without
> temperature feedback and heat exchange.  In
> addition, I have never received an authoritative
> answer to the question as to whether the 14 days
> of VAR can include the 3 days of PFRP.  I would
> assume not, based on the term "maintained",
> suggesting that three days over 55C is not the
> same as "maintaining" the temperature at 45C.
>
> The PFRP and VAR rules tell us little about how
> many BTUs are actually oxidized in the composting
> process, as a mass retaining heat tells us little
> about how much heat is being removed.  PFRP and
> VAR are at least, in my opinion, minimum
> standards to meet, but I think that there should
> be additional indicators and standards of stability.
>
> Which brings us back to my original question,
> which is concerning alternative standards or
> measurements of stability other than the EPA time and temperature 
> standards.
>
> Seed germination rates are commonly used in
> determining compost maturity, but can we use them
> as indicators of stability as well?  If so, which
> seeds and under what conditions and compost
> sampling protocol?  Some compost feedstocks high
> in carbon, meaning mostly woody materials, can
> have respectable seed germination results in only
> three weeks, whereas high nitrogen mixes can take
> longer.  Seed germination rates are largely
> indicative of stability or maturity of a
> particular mass being composting relative to its
> initial characteristics.  I can see this test
> having value in certain cases, like the VSR test,
> relative to starting parameters, but I question
> this approach as an "across the board" indicator of stability.
>
> What about ammonia off-gassing?  I have seen its
> value in determining maturity, but can it be a
> good indicator of stability as well?  Measuring
> ammonia might be problematic, however, other than
> the general observation of whether the mass
> stinks or not.  I am not aware of a reliable low
> cost ammonia indicator test other than the change
> in color of pH litmus paper, which is a good
> general indicator, but to me, not a sufficient
> specific indicator, given the subjectivity of
> color change in the paper.  Again, if the
> feedstock is high in carbon, there is low ammonia
> off gassing in the first place.
>
> I suggest that compost mass re-heating is not a
> reliable indicator as, like VSR, it is indicative
> of the original feedstock more than the process
> being used.  It can also be affected by reduced
> moisture.  Mass dried under 35% can often avoid
> reheating as there is insufficient moisture for significant microbial 
> activity.
>
> The fusarium suppression test is a good
> indicator, but again only of maturity, not stability.
>
> I was leaning toward 02 consumption and CO2
> production indicators, but I ran across a
> decomposition system that effectively sterilized
> the decomposing mass.  Their media showed zero 02
> consumption unless it was re-inoculated with
> microbes.  I think that 02 consumption and or CO2
> production values could work if the microbial
> population is intact, there were sufficiently
> available volatile solids to begin with and there
> is adequate moisture.  O2 consumption is an
> indicator of volatile solids reduction, which can
> be measured by heat removal.  Has anyone ever
> used heat being removed as an indicator of
> stability?  I think that it might be a good
> measurement for temperature feedback - forced
> aeration systems where temperature can be
> measured in the exhaust pipe related to the
> volume of air indicating the degree of decomposition activity going on.
>
> An alternative suggestion for forced aeration
> systems might be (VOCs) Volatile Organic
> Compounds or methane, CH4 production.  Tests from
> the South Coast Air Quality Management District
> in Southern California showed what appear to he
> high levels of VOCs, presumably CH4 released from
> windrows.  Low VOCs might serve as an indicator
> that the aerobic process was working to keep 02
> levels up.  Perhaps an easier method might be
> oxygen sampling within the composting mass to
> show levels of 02 over 10% or 15%.  But that
> would show viability of the aeration process,
> perhaps, but is it an indicator of stability?  If
> windrow technology is actually anaerobic system
> with aerobic edges, heated with intermittent
> oxygenation after turning, this does not mean
> that the process is an inadequate decomposition
> process?  I don't think so. Windrows achieve
> stability and maturity, just in a different way
> than forced aeration or at a different
> rate.  That would be a question more for air
> quality officials or the role of composting in
> mitigating fugitive methane in the atmospheric warming debate.
>
> Perhaps something about nitrogen conversion and
> the relative concentrations of the form of
> nitrogen in the composting process.  Any suggestions?
>
> I am wondering if there ever can be a standard
> compost stability indicator other than time and
> temperature given the differences in
> decomposition methods and the wide range of
> materials to be composted. My thought at the
> moment is that we need to define the parameters
> of a compost feedstock related to a particular
> management strategy and then define a stability
> method for that particular set of variables and
> then measure how well the particular
> decomposition process is working against its baseline standard.
>
> Thanks in advance for any feedback,
>
>
>
> Jim~ McNelly
> Renewable Carbon Management LLC 320-253-5076
> NaturTech, NaturSoil, CompostMan
> jim at composter.com
> www.composter.com
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