[USCC] USCC: Compost Definition

Wed Mar 23 17:16:30 CST 2005

Allison,
Good to hear back from you, and good luck on your current research.  I would
agree with your statements concerning plant pathogen reduction from compost
and vermicast, but see definite differences in the product use and for
process application.  The cost of vermiculture vs. large scale windrow or
static pile composting (two most common composting processes) is
considerably lower than the cost of producing the same quantity of worm
castings.  Vermiculture is best suited for small, and potentially
problematic waste streams such as food wastes, or other potentially odorous
feedstocks that require a timely processing.  I say this because the large
quantity of worms (and high cost of worms) necessary per ton of material
processed can be very high, and controlled environments are often necessary
for worms in many areas of the United States.  The other infrastructure and
supplies necessary for feeding, harvesting and packing of finished products
and worms can be costly, and the process is labor intensive for large scale
vermiculture operations.  

Vermiculture may be able to process some finely ground materials more
efficiently than composting because of the aeration action of worms and may
process materials faster than large scale composting (if a high ratio of
worms to feedstocks are used), but large scale composting can process a
wider variety of materials than vermiculture with less special processing
and over a wider range of environmental conditions.  

The land requirements for composting are greater than for vermiculture, but
the infrastructure and labor requirements can be considerably reduced.  Some
composting operations are quite elaborate and expensive to implement when
located in close proximity to urban areas, though most are not so.  Unless
composting operations bag compost, much of the product is sold in bulk.  The
labor for producing thermal compost may also be lower than required for
generating worm castings.  However, I presume that labor requirements for
vermiculture would undoubtedly be higher than for traditional composting as
well, with several processes required to occur simultaneously and requiring
more specialized attention.

The finished product of vermiculture, though similar in many respects to
traditional compost, is a more advanced degree of degradation and is more
closely related to humus and soil organic matter than compost.  If I were to
compare the two directly, particle size in vermicast is much smaller than
the bulk of compost particles.  As previously mentioned, the organic matter
compliment of clean compost (low mineral contamination) will usually be
higher than in the same materials processed through vermiculture.
Nutritional values of vericast may be higher than compost, especially N and
S, due to large losses that occur during heating of compost.  The end uses
and even the sales prices for the two materials are dramatically different,
with vermicast easily costing twice what compost is sold for, and only small
amounts of vermicast can be used in most planting situations due to the
extremely small particle size and high moisture holding capacity.  It is
true that compost and worm casting blend provide more value for plant growth
media than each used separately.  Teas generated from both worm castings and
composts are becoming popular for microbiological disease suppression and
beneficial microbiological applications to soils on agricultural and
landscaped land.   

You wrote:
"In my personal reference library there are 195 peer reviewed scientific 
journal articles from researchers all over the world that deal with 
vermicompost or vermicomposting that date back to the 1980's. Almost all of 
these scientific articles use the words "vermicompost" and 
"vermicomposting" to refer to their subject matter (about 5% of the 
articles use the terms "earthworm humus", "earthworm castings" or earthworm 
castings"). From a scientific perspective, "vermicompost" exists and is 
well established in the scientific literature as a type of composting 
system/compost end product.

Frank Teuton has pointed out literature prior to that period that discusses
worm composting, dating to the 1940s (though not in journal articles).
However, between the mid 1980s and early 1990s, waste management issues
including reduction in landfill capacity, bans on organic wastes in
landfills, landfill closures, and increased costs for landfill disposal
coupled with environmental issues of odors, gaseous emissions and fires in
landfills became common in many states.  Both composting and vermiculture
became waste management alternatives to landfill disposal of many organic
waste streams.  It is little wonder that the vermicompost and vermiculture
terminology took hold during this period.  The phrase "from trash to
treasure" was used to encourage beneficial use of organic wastes.  As
previously stated, people had heard of compost, but not many people knew the
benefits of worm castings at that time, and sales were dependent on product
recognition; hence the more scientific phrases of vermicomposting and
vermicompost to promote sale of worm castings.  I use the term vermiculture
because one of the initial objectives of the industry was propagation of
worms for sale, not the sale of castings.  Worm castings were generally a
byproduct of the worm propagation industry, were found to have benefit for
plant growth, and therefore were promoted for sale as well, to recapture
some of the expense for the process.  Prior to this time, most vermiculture
was performed by home based enterprises or by home garden entrepreneurs
either for worm production or castings for gardening.  

In the composting industry everybody wants to promote their product as being
better than somebody else's in order to promote sales.  But, we know that
every compost product is different, even those suitable for the same end
use.  The same is true for worm castings.  And, we do know that worm
castings do not have the same properties of compost and that worm castings
made from different feedstocks are also different. I don't mean to sound as
if I am putting down worm castings at this point, or the vermiculture
industry, but as a whole, the vermiculture industry has taken on an
adversarial role in the organic waste recycling family.  The high price of
the worm castings, and reduced price for composts, has benefited the
composting industry for sales of end products.  In order to promote the worm
castings product as a unique material, not to be confused with conventional
composting products, much of the industry literature for vermiculture
promotes worm castings as "better than" thermally composted organic
materials, and list a multitude of reasons (some true, some false).  If the
vermiculture industry truly believes that worm castings should be considered
compost, why degrade the traditional compost products to promote worm
castings? If the vermiculture industry truly believes that worm castings are
better than compost, vermiculture needs to separate itself from the
composting industry, or the worm castings (viewed as a compost product)
sales may be hurt do to association with the lower priced compost.         

You are somewhat mistaken about the dynamics of microbiological populations
in thermal composting processes.  All composting piles or windrows have
stratified temperatures from the center to the outer layers and from top to
bottom.  There are always mesophilic temperatures and microbiological
activity occurring in the same thermal composting materials.  There are
never only thermophilic activities occurring in the composting materials,
except possibly in continuously turned invessel systems.  Stratified
temperature regimes create far greater diversity in microbiological
populations.  When organics are redistributed during turning, so too is
microbiological diversity.  

Finally, I truly believe that you think of vermiculture as a means to cure
composted materials, but that may not be the case.  Some of the phytotoxic
chemicals produced during the initial heating periods of composting are
degraded rather quickly during curing, assuming that the compost is truly
stable. After an initial period of self heating, the composting materials
cool to mesophilic temperatures, giving the appearance of stability.
Usually within a month, a second wave of mesophilic microbiological activity
takes place, though not as pronounced as the first.  Temperatures rise to
near or above thermophilic conditions due to microbiological enzyme activity
on alternative organic C sources.  We have observed as many as three self
heating periods during composting.  However, the finished compost has too
little readily available organic C to support high levels of microbiological
activity, and less for worm nutritional demands.  The materials used in
vermiculture are probably not a finished compost product, but are only
partially degraded. The particle size reduction from initial composting
process enhances the worm's ability to consume the feedstocks.  In my
opinion, feeding worms partially degraded organic feedstocks is an
accelerated natural attenuation process, not a curing process as you
suggest.   

Dave Schellinger   
W. A. Callegari Environmental Center
Phone: (225)765-5155 

-----Original Message-----
From: compost-bounces at compostingcouncil.org
[mailto:compost-bounces at compostingcouncil.org] On Behalf Of Allison Hornor
Sent: Tuesday, March 22, 2005 2:14 AM
To: compost at compostingcouncil.org
Subject: [USCC] USCC: Compost Definition

Celebrate International Compost Awareness Week - May 1, 2005 to May 7, 2005
The Possibilities are Endless ... Compost!

Hello everyone (and thanks to Dave Schellinger for his comments on my 
previous posting),

Just a few more brief thoughts to weigh in on the "is vermicompost 
compost?" debate.

Dave Schellinger wrote:

"Additionally, compost itself has been documented to produce the many of 
the same benefits you list for vermiculture products, "worm castings" 
(sorry I don't have the specific articles here).  Does this mean that the 
pre-composted feedstock used to feeds the worms provide the benefits you 
speak of, or do the worms in some way impart the beneficial aspects to the 
worm castings?  Aeration itself can reduce some non-spore-forming anaerobic 
pathogenic microorganisms to some degree, so do worms reduce pathogens, or 
the aeration of the feedstocks?"

My thoughts:

I totally agree that plant growth promoting and plant disease suppression 
characteristics have been associated with thermophilic compost as well as 
vermicompost. This is actually one of the reasons that I think they should 
be considered together under the larger umbrella of "compost" because they 
have similar positive effects on plants (when made properly of course). The 
feedstock issue is a really good point. I think (and the literature 
supports) that both the feedstock and the composting process will affect 
the characteristics of the end product. For example vermicompsot made from 
sewage sludge was not suppressive against a plant pathogen while 
vermicompost made from cow manure was (Szczech 2001). There have been very 
few comparisons of the two composting processes with the same feedstock in 
order to make a well supported direct comparison...I'm working on that in 
my research right now. And the last question you raise is a good one 
too...the mechanism of pathogen suppression (both for human and plant 
pathogens) by vermicompost is currently unknown. I'll be working on the 
plant pathogen suppression issue for my PhD research and will get back to 
you on that one :-).

Szczech, M. and U. Smolinska 2001. Comparison of suppressiveness of 
vermicompost produced from animal manures and sewage sludge against 
Phytopthora nicotinae Breda de Haan var. nicotinae. Journal of 
Phytopathology 149: 77-82.

Dave Schellinger wrote:

In many cases worms can be fed organic matter such as processed high 
moisture food wastes and will process it just fine.  Paul Olivier' black 
soldier fly larvae perform a similar process to degrade food wastes.  Would 
you compare this vermiculture?

My thoughts:

As for black soldier fly larvae, and whether or not I would consider that 
compost, I haven't seen any literature about this system so I really can't 
say either way. My instinct would be that since earthworms form such an 
integral part of the soil ecosystem, and I have yet to see an arable soil 
teeming with fly larvae, that this would be best considered an entirely 
separate type of organic waste processing. I am curious to learn more about 
it, however.

Dave Schellinger wrote:

"The process and end products of vermiculture vs. thermal composting are 
not the same.  The thermal composting process is typically a 
microbiological process that does not rely on macroorganism 
degradation.  The end product of vermiculture is typically lower in organic 
matter, higher in mineral matter, and contains a higher fraction of organic 
matter as humus than composted materials.  In my opinion, vermiculture is 
an alternative end use for lower compost products but should not be 
compared with the thermal composting process."

(and in another posting:)

"Worm castings are generated under mesophlic (sic) conditions by 
macroorganisms whereas compost is generated under thermophilic conditions 
by microorganisms."

My thoughts:

I totally agree with you that the processes and end products are different, 
but I don't see why that precludes them from being considered two different 
types of compost since they are also similar in many ways.

Also, the macroorganism/microorganism idea is a gross over-simplification 
of both composting processes. Thermophilic compost starts with mesophilic 
organisms that generate enough heat to create thermophilic conditions, from 
which point the thermophilic microorganisms take over. When the pile begins 
to cool down, mesophilic microorganisms recolonize the pile and carry out 
the curing process (final stabilization of the organic matter).

For most large scale vermicomposting operations, initial thermophilic 
composting is carried out and vermicomposting is used as part of the curing 
process (not unlike the mesophilic curing process in "thermophilic" 
systems). The composting earthworms carry out many functions, it's not as 
simple as eating and pooping. The earthworms aerate the pile with their 
constant movement (think very small windrow turner). They ingest 
decomposing organic matter with the associated microorganisms. There is a 
small but growing body of scientific literature on the details of earthworm 
digestion. One of the current theories is that earthworms have a 
mutualistic relationship with microorganisms (Brown 2000). Upon ingestion, 
the earthworm internally secretes digestive mucus that stimulates the 
microbes that have been ingested. The microbes in turn digest the ingested 
organic matter. The earthworm then grinds everything up in their crop and 
absorbs the available nutrients. The cast that is then deposited is coated 
in a mucus layer (the peritrophic membrane) with serves as a carbon source 
for soil (or in this case compost) microorganisms. This mucus layer 
stimulates the microbial community that is present and gives them the 
energy source they need to further break down the decomposing organic 
matter. There is some evidence that the composting earthworm has species of 
microbes that live exclusively in their guts, but this has not been well 
established (Toyota 2000). The way I conceptualize vermicompost is that the 
earthworms are "priming" the microbial communities that are already present 
in the decomposing organic matter through the addition of polysaccharides 
(intestinal mucus). I would have to agree with Frank Teuton that you can't 
really separate the earthworm from the microorganisms...they need to be 
considered together when attempting to understand the complex ecological 
interactions that occur during the vermicomposting process.

Brown, G. G., I. Barois and P. Lavelle 2000. Regulation of soil organic 
matter dynamics and microbial activity in the drilosphere and the role of 
interactions with other edaphic functional domains. European Journal of 
Soil Biology 36(3-4): 177-198

Toyota, K. and M. Kimura 2000. Microbial community indigenous to the 
earthworm Eisenia foetida. Biology and Fertility of Soils 31(3-4): 187-190.

Dave Schellinger wrote:

"The term vermicompost was created as a marketing ploy to aid in the sale 
of worm castings.  Most people knew what compost was, but worm castings 
were relatively unknown until recent years.  The name doesn't really define 
the product in this case, so you can call worm castings and vermiculture 
what you want, but the name does not make the product any less worm 
castings or worm poop.  My point is that your vermiculture digestion of 
organic matter does not fit in my definition of composting, and therefore 
the end product is not compost in my opinion."

My thoughts:

In my personal reference library there are 195 peer reviewed scientific 
journal articles from researchers all over the world that deal with 
vermicompost or vermicomposting that date back to the 1980's. Almost all of 
these scientific articles use the words "vermicompost" and 
"vermicomposting" to refer to their subject matter (about 5% of the 
articles use the terms "earthworm humus", "earthworm castings" or earthworm 
castings"). From a scientific perspective, "vermicompost" exists and is 
well established in the scientific literature as a type of composting 
system/compost end product.

And part of the Dave Schellinger/ Frank Teuton exchange:

The issue of mesophilic bacteria being present even during the thermophilic 
stages of composting, there is evidence in the scientific literature of 
this as well:

Droffner, M. L., W. F. Brinton and E. Evans 1995. Evidence for the 
prominence of well characterized mesophilic bacteria in thermophilic 
(50-70-Degrees-C) composting environments. Biomass & Bioenergy 8(3):
191-195.

OK, one last paper...more solid evidence that vermicomposting can meet both 
Mexican and USEPA regulations for pathogens in biosolids (even though we 
don't know exactly how it works) (Vigueros 2002). Dave is right, it would 
be great to have a direct comparison of the two processes on the same 
biosolids feedstocked and spiked with the same amount of pathogens to 
really see what is going on. That was one weakness in the Eastman 
paper...although the pathogen reduction they documented was below allowable 
limits (if I remember correctly) and it was really a pilot project to show 
that was possible.

Vigueros, L. C. and E. R. Camperos 2002. Vermicomposting of sewage sludge: 
a new technology for Mexico. Water Science and Technology 46(10): 153-158.

Eastman, B. R., P. N. Kane, C. A. Edwards, L. Trytek, B. Gunadi, A. L. 
Stermer and J. R. Mobley 2001. The effectiveness of vermiculture in human 
pathogen reduction for USEPA biosolids stabilization. Compost Science & 
Utilization 9(1): 38-49.

That's all for me for a while...
-Allison

****************************************************************************
*****************************************************
Allison L. Hornor
Graduate Student
335 Plant Science
Department of Plant Pathology
Cornell University
Ithaca, NY 14853

(607) 273-5762
alh54 at cornell.edu

****************************************************************************
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