[USCC] Hutchinson and Haines Composting Projects

[Jim McNelly]

The City of Hutchinson, Minnesota composting project was initiated 
through my consulting efforts in 1993 beginning with a home 
composting bin distribution program. The city started containerized 
composing operations in 1995 and has evolved through several 
expansions since, currently functioning mostly as a windrow system 
for most of its volume.

A report on the project by Professor Ernie Diedrich at St. Johns 
University is available for download.

http://www.composter.com/rcm/Hutch-diedrich.pdf

Haines Sanitation, another of my projects, began in 2002 as a method 
of stabilizing municipal solid waste into inert material for 
landfilling with certain products suitable for landfill daily cover 
and final cover, not for unrestricted distribution.  Since it is a 
mixed waste composting project, I would not put it in the source 
separated organics category.

I think that the term "in-vessel" is a bit of a misnomer, as the 
definition from 1987 used by EPA in the promulgation of the 503 
biosolids rules was based on continuously agitated technologies that 
are no longer viable, never met the time and temperature standards or 
are now obsolete.  Most of the technologies that are commonly 
described as "in-vessel", including the NaturTech containerized 
composting system that I patented and market, are probably better 
referred to as "enclosed aerated static piles."

As to some of the reasons behind controlled batch composting, there 
are several I have noticed over the decades.  Aerated static piles 
require only 72 continuous hours over 55C to meet US EPA 503 pathogen 
reduction standards while windrows require 15 24-hour periods over 
55C at least once during each period with five agitations. It is 
possible to meet the US EPA vector attraction reduction (VAR) 
standard of 14 days over 40C averaging 45C in controlled batches, 
whereas windrows have to meet the VAR using other methods, if at 
all.  It is simply not possible to claim a temperature over 55C and 
average 45C at the same time.

Enclosures control mass in smaller batches, keeping fresh material 
from being commingled with older mass.  With temperature feedback, 
batch processing delivers more consistency and uniformity than less 
controlled processes, typically reaching higher value sales 
opportunities for compost.  Temperature control under 60C reduces the 
generation of volatile fatty acids, a common source of 
odors.  Mesophilic temperatures around 45C also have been shown to 
convert carbon to CO2 and heat than thermophilic temperatures, 
especially temperatures over 65C in most cases.  Optimum rate, often 
misstated as "faster composting" results in less retention time to 
achieve the same degree of compost stability and maturity, typically 
meaning less space required to bring the product to market.  Using 
air as a heat exchange system assists in optimizing the rate of 
decomposition as the mass balance of the composting process is 
measurable by the degree of heat removed more than the temperature retained.

Covers and enclosures restrict the infiltration of precipitation, 
reducing moisture management variables.  They also prevent 
commingling of leachate with stormwater, reducing the volume of water 
requiring treatment.  Enclosures enable the capture of process air, 
keeping it from being commingled with ambient air, reducing the 
volume of air to biofiltration, whereas windrows on hard surface are 
not capable of having air capture for biofiltration.  As such, 
windrows are typically used with high carbon feedstocks to generate 
soil amendments with less than .05% nitrogen.

Depending on design, enclosures can also retain more heat than open 
designs, as rectangles have less exposed surface area than triangles 
(windrows) and more mass achieves pathogen destruction temperatures 
during the heating cycle.  Cost is a relative issue and is driven by 
a wide degree of variables, depending on location, feedstocks and 
markets.  Most controlled, enclosed batch composting systems I am 
aware of are typically processing low carbon, high nitrogen 
feedstocks, up to 20-1 C/N ratio and relatively higher moisture 
percentages (65%) than windrows.  Some processes can produce compost 
consistently in the 2% nitrogen range, with some variations on the 
theme reaching 4% nitrogen and still being fully stabilized and 
mature using the TMECC testing methodologies.  Feedstocks with high 
volatile solids percentages such as raw, primary undigested 
wastewater solids, blood, grease, mortalities etc. that have high 
ammonia off-gassing characteristics are better suited for precision 
controlled composting if odors are a concern.  Aerated static piles 
failed miserably in tests in the 1970s with raw, primary wastewater 
treatment solids, even with one foot thick chip covers over the 
piles.  Enclosed batch composting can also process more material per 
hectare than windrows and are typically located in odor sensitive 
areas, such as industrial parks or urban areas.  If  any site is 
closed due to complaints, "low cost" is irrelevant.  If compost 
quality and consistency is a requirement of buyers, relatively higher 
nitrogen compost can command a premium price in the marketplace, 
further justifying supposedly higher costs.

If a controlled composting system can be substituted for conventional 
liquid digestion techniques at a wastewater treatment plant, then 
even $50,000 per process ton in capital costs can be a bargain over 
conventional treatment that can cost four times as much.  But the 
composting system has to meet public utility standards including zero 
odor events, certifiable pathogen destruction, controlled leachate, 
managed vector, no run-off, all climate functional and be monsoon and 
blizzard proof.  During the 1980s, as I evaluated the windrow methods 
and the emerging temperature controlled batch systems evolving out of 
the mushroom industry, it seemed clear to me that controlled batch 
composting was the superior technology for organics management.  The 
challenge was, and is related to bringing the approach to a cost 
justifiable basis that would cause its more widespread use.

I know of certain controlled composting approaches that are costing 
less than $10,000 per ton per day in capital cost, or 600 tons per 
day for around $6 million dollars.  In air quality sensitive areas 
such as Southern California where fugitive volatile organic compounds 
(VOCs) and ammonia are regulated due to smog rules, windrows are 
finding it increasingly difficult to document air emission control 
requirements.  Increasingly, it appears that fully oxygenated and 
temperature controlled composting reduces VOCs, particularly fugitive 
methane which will be regulated more and more in the years to come 
due to atmospheric warming impacts.

The USA is far behind Canada and the European Union when it comes to 
promoting putrescible organics composting and sadly, the list of 
sites in the US are too few.



Jim~ McNelly
Renewable Carbon Management LLC 320-253-5076
NaturTech, NaturSoil, CompostMan
jim at composter.com
www.composter.com