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WASTE CONVERSION FOR
RESOURCE RECOVERY
An Examination of Terminology, Infrastructure, Regulation and
Standards
Michael
Theroux
June 2009
Toward
the New Hierarchy
It seems so
pointless to throw our National Resources into a hole and pay to keep them there, just to once again pay to put
virgin resources back into the one-way flow of our supply chain. Yet anyone who has been witness to indiscriminant
“trashing” of our environment understands that today’s best management practices are a grand improvement over past
calamities.
We can’t
(yet) stop throwing away at least a fraction of what we acquire. After consumer choice effects Reduction of
packaging (for example) and even after used items have indeed been Reused, utility eventually expires and the
remainder will be discarded by the owner. This release of a discarded item identifies it in law as a “waste”, and
passes ownership back to whatever means society at large has designated for waste management.
We
can maintain the socially and environmentally sound practice of extracting materials that can be
Recycled from the mixed municipal solid waste (MSW) stream. This process of segregating waste and returning
materials to the supply chain is not without cost, but the alternative of no recycling is far worse,
especially socially. We must break this self-destructive “throw-away” habit, and Recycling helps
retrain society in addition to the obvious reduction in disposal.
Once
Recycling has been accomplished, however, there remains a post-recycling residual. This residual is highly
heterogeneous, following as it does the nature of MSW, and must be assumed to occasionally contain every possible
form of contaminant that originally was a constituent of the initial discard.
If the only
goal is to reduce the volume and toxicity of that residual waste, sanitary disposal can be managed through
state-of-the art landfilling, or by incineration, where wastes are “rendered to ash”. But incineration is
still a form of disposal, and Disposal does not recover the resource, only places it permanently “out
of the way”. What a waste.
We have
means now to carefully “un-bake the cake” of that complex residual waste accumulation with a variety of methods we
might recognize collectively as reverse manufacturing. These processes disassemble waste components at the
molecular level, and prepare the foundation resources to be remanufactured into New Goods. When this ability is
properly used as a last-resort instead of disposal in an ordered Waste Management Hierarchy, molecular reclamation
can be called Recovery.
The European
Union recently modified their Waste Management Hierarchy. They have now officially added a fifth step of preference
in their overall schema for waste-management-by-choice: Reduce, Reuse, Recycle …
Recover … Dispose. Logic prevails; hopefully, our own national common sense will follow
suit.
The lines
are drawn, but the fine gradations between these Waste Management Hierarchy steps tend to represent a continuum,
instead of offering clear and discrete categories of action.
What
is “Recovery”, and how may this step be accomplished cleanly and economically? What must we do to
firmly establish this paradigm not just in institutionalized law, but also more broadly as a universal part of our
social and industrial infrastructure?
Conversion for Optimal Recovery
Conversion
of discarded waste materials at the molecular level for recovery of intrinsic resources requires two parts: (1) the
technology by design must allow access to intermediary products, such that those chars,
liquids and/or gases can be sampled, characterized, and modified as needed to result in ultra-clean final products;
and (2) this process of interception, characterization and modification must be accomplished by operational
mode, such that the information feed-back loop that intermediary sampling facilitates is actually acted
upon.
A decade
ago, requirements for real-time sensoring and computer analysis of the intricate changes occurring within the
explosive reactions of a thermal treatment unit were far too expensive, requiring massive data handling
capabilities not available outside universities and military facilities. Today, small and inexpensive computers can
assimilate those same data, the algorithms can be applied, and the resulting analyses become feed-back for
programmable logic controls (PLCs) directing the moment-by-moment operation of the equipment.
Energy is
the underlying requirement, when molecular bonds are to be separated. The surrounding molecules must be
sufficiently energized to overcome the strength of each bond to be disassembled, and the input amount varies
depending on that inherent bonding tenacity. That energy can be introduced in a number of ways, some better suited
to managing specific waste residuals than others. Some resources hold more molecular-level value than others in the
marketplace. The market will naturally promote cost-effective recovery. Those that believe an economy should
be solely market-based might argue that this guideline should be sufficient. Yet cheaper is not necessarily
better.
Some methods
for energizing and breaking molecular bonds are more costly than others. Technical designs and modes of operation
that can effectively recovery resources from homogenous waste types may not be sufficiently robust for highly
heterogeneous feedstock. Technical specifications become important, defining “envelopes” of design and operation
according to the input, and the intended end-product. Permitting processes guide proper usage, and implement
restrictions on use of the wrong tool for the job at hand. These checks on the market forces need to be constructed
only where optimization for cleanliness and percentage recovery trumps the underlying
economics.
As the
molecular diversity of the feedstock increases, the nature of bonds requiring deconstruction also varies. Some of
the most toxic residuals are also the most difficult to devolve; to maximize environmental cleanliness, the
conversion process must be optimized to effectively reduce these most reticent fractions to their non-toxic
constituents. Environmental concern must drive Conversion Technology design and operation toward both maximum
recovery of resources AND maximum reduction of toxicity; these responses to appropriate environmental concern
become performance standards.
Many of the
technologies available for conversion of waste into recoverable resources have been around for half a century or
more. Our industrial ability to design, operate, monitor and modify the process “on the fly” is only now able to
meet our modern and ever-tightening standards of environmental cleanliness. Design and operational control advances
allow conversion operations to be scaled to fit within our communities. Conversion of wastes at the
source (rather than regionally) can dramatically reduce shipped volume and weight, thus minimizing both
cost and impact of transport. Community-scaled, ultra-clean conversion of post-recycling municipal solid waste
residual for cost-effective recovery of our natural resources: this is new. And because it is new, much
remains to be developed to define, and to ensure, proper integration within this shifting paradigm that now informs
our Waste Management Hierarchy.
The
Integrated Conversion Platform
What are the
tools of this new Recovery trade? What do these systems look like; where can they be located? How “clean” is
clean?
First: there
is no “silver bullet”, no single system or method of operation that can handle every molecular recovery challenge.
Our waste stream is simply too complex. Our best hope is to carefully select “best of class”, in a number of
classes, each tuned to manage a breadth of materials as feedstock. We may then combine a suite of these selected
modules into one integrated process flow, capable of optimally receiving, processing and recovering the greatest
degree of resources available for conversion, in any particular region. The optimal conversion platform,
therefore, would be an integration of subsystems, custom designed to effectively process the region’s materials
requiring conversion and recovery.
One basic
waste conversion guideline for conversion process selection has been offered by the Environmental Protection
Agency, as part of their AgStar program: if the waste is wet, keep it wet; if dry, keep it dry.
Of course,
“waste” comes in all degrees of moisture as well as molecular diversity, and conversion processes have developed
over time to meet these widely disparate characteristics. Three basic categories of Conversion Platform, or
integrated mechanisms: thermal, microbial and chemical / kinetic. Each category contains
technical complements proficient at conversion across the range of the moisture and molecular
profile.
Thermal
Conversion. Technologies based upon Pyrolysis,
Gasification and Plasma effect carbon molecule breakdown to create a molecularly rich selection of solid, liquid
and/or gas, depending on the feedstock, the system and its various modes of operation.
Optimal
Operation - Our goal is to create enough thermal
energy in the retort chamber to break molecular bonds, while retaining as much of the value as possible. There are
three controls we can adjust over our mode of operation, given any specific technology: (1) feedstock, the still-bound molecular resources we which to take apart and reconfigure;
(2) retention, the time the feedstock remains in the chamber; and (3) the amount of oxygen (or similar
bond-filling elemental) allowed to interact with that feedstock during its time in the retort. Three “legs” of
control provide flexibility and resilience.
Again, the
degree of heterogeneity of molecular structure enters the equation: the system’s sensoring, data analysis and PLC
feedback control needs to constantly provide for conversion of the greatest challenge presented - the highest
contaminant spike, the most explosive heat value. Wood chips vary little molecularly as a feedstock; MSW residuals
vary dramatically.
Molecular
dissociation and instability is the condition that allows us to direct molecular recombination to
reform to desired foundation chemicals and fuels. It is also the condition that if not properly
controlled, can create some of the most extreme toxins. Accessing hot char, oil and/or producer gas for purposes of
characterization, separation, and reforming is a difficult, often dangerous exercise. Once the molecular “cake” of
waste is unbaked, much of the real work of Recovery has just started.
Regulatory Dysfunction - The California Public Resources Code currently includes a prescriptive
standard that stipulates mode of operation where there is to be no added (or excess) oxygen, other than as
needed for temperature control. Change in temperature is in affect a symptom, not a
controlling cause; it is one of the physical conditions we can monitor as an indicator of the results
of the three-part conversion reaction control. An operator can raise or lower temperature by altering any one or
more of the input factors of feedstock, retention time and/or oxygenation. Constraints applied to only one control
simply shift the operational emphasis to the other two.
The law does
not stipulate that minimum temperatures be maintained, nor is there a direct correlation with maximum
contaminant control. The language only provides that an excess of oxygen not be used, beyond whatever
thermal set-point is established. If higher temperature regimes are to be achieved and maintained, greater
through-put rates and/or introduction of less reticent feedstock must become the compensating control factor(s),
rather than introduction of more oxygen. Beyond being terribly confusing, this “two-legged stool” approach
restricts process optimalization, especially when conversion must respond in an instant to the vagaries of
constantly-varying feedstock such as our target, post-recycling MSW residual.
Microbial
Conversion. Molecular breakdown is a
natural, for bacteria, fungus and a few other very small, simple-celled organisms. Some work best wet, some
effectively convert high-solids slurries, others can “digest” dry feedstock. There are high-temperature microbes,
and there are those that function in extreme cold. Some microbes do their best work in near or complete absence of
oxygen (anaerobic processing; fermentation); other demand a constant high level of oxygen to function (aerobic
processing; composting). Still others (yeast strains, for example), can operate with varying levels, and often the
products of their molecular breakdown can be adjusted by varying the oxygen percentage as one of the available
control factors. All the myriad microbial processes offer keys to Recovery, when properly harnessed in a controlled
process flow: whatever they eat, they break down and recombine into simpler molecular structures. Ours is the task
of selection and husbandry.
Optimal
Operation – Any population of microbes will act
according to their genetic make-up, in concert with (1) feedstock, the resource to be reconfigured; (2)
retention, the time the feedstock remains in the chamber; and (3) the amount of oxygen (or similar
bond-filling elemental) interacting with that microbial population as it consumes and converts the feedstock during
its time in the retort. Again, we have the three “legs” of control that provide operational flexibility and
resilience.
Again, we
can vary one, two or all of these controls to optimize for a specific desired outcome, and change this “on the fly”
with the critical aid of real-time sensoring, computerized analysis and system operations
feedback.
Regulatory Dysfunction – For microbial conversion, the regulatory language is less specific
and perhaps more forgiving, if thoroughly inaccurate to the point of absurdity. Conflicting permitting standards
prescriptively restrict an operator’s ability to select an optimal feedstock blend specific to the requirements of
the technology and the desired products of the conversion. Those that would convert animal manure microbially to
recovery fuel gases and liquids cannot add necessary nutrients found in available post-consumer food waste, even
when management of this municipal waste fraction is problematic at best, for the existing waste management
regime.
Perhaps a
more basic error, if less objectionable, is the technically inaccurate depiction of
all microbially-driven conversion as “composting”. Our federal law provides definitions for and
conditions appropriate to a group of related processes referred to as composting; these are primarily
designed to protect the public health by reducing the pathogenicity of the feedstock. The far more complex issue of
molecular decomposition and resource recovery involved in Conversion is ill-suited to being lumped in with
composting, per se. There are more exceptions than fitting examples; new terms and standards are
needed.
Chemical
/ Kinetic Conversion. Molecular bond energy
certainly can be broken using various combinations of chemicals, positive and negative pressures, and motion. Our
bodies rely on these principles as much or more than upon enteric microbiota … the “bugs” in our guts … and every
transfer of energy from our food through our blood to our nervous system is conferred by breaking down a complex
molecular structure specifically to harness the energy released.
Optimal
Operation - This energetic decomposition and
conversion in our bodies usually occurs via enzymes. Our understanding of what enzymes are, how they
function, and how they can be controlled has transferred in part to the field of resource recovery: the science of
enzymatic hydrolysis is one of the most promising for controlled conversion of reticent large-chain woody
fiber molecules into biofuels.
Acidity of a
substrate tends to control solubility: basic pH keeps molecules stabile and insoluble, while acidic conditions rip
the molecular structures apart and make them more like to dissolve into other fluids. Acid
Hydrolysis (with greatly varying strengths of the acidic condition) is an “old standard”, a naturally
occurring process that breaks down and puts into solution both organic and inorganic materials. When used for
conversion, acid hydrolysis can “grind” and homogenize the larger molecules into smaller, more easily
managed fragments.
Curious
changes take place, in extremes of size, temperature and pressure: Super-Critical Water Oxidation” (or SCWO) is a
field that has been shown effective for decomposition of feedstock containing highly toxic contaminants and/or
explosive tendencies; the military finds SCWO quite useful for decommissioning munitions and drugs. The concept of
using SCWO for recovery is only recently following its use for disposal. Similarly obtuse and
astounding are the changes that take place at the sub-molecular scale: aspects of
nano-technology impart control over molecular structure surface tension, facilitating access to and
decomposition of those structures in new and dramatic ways.
Regulatory Dysfunction – If these processes are no less necessary for integrated conversion of waste
and recovery of resources than are thermal and microbial methods, they are also new to the regulations erected. The
steps necessary to reverse and “decommission” what our elite manufacturing processes have so carefully built will
naturally include all of the methods used to build those molecular constructs. Manufacturing is innately understood
to live or die by the performance if the products created. Yet these methods entering our industrial
tool-box to take those materials apart, separate them, and ready them for re-manufacturing are somehow held to a
different and most often, prescriptive, standard.
Conclusions
Science
must lead this field of Conversion for Recovery, both in the necessary research and development, and in
the design and operation of integrated platforms of Conversion Technologies. The guidelines developed as an
environmental safety net need to be based upon tested and proven performance, certainly not upon
arbitrarily assigned prescriptive standards. The construct for environmental control during full
operation that is implemented through permitting and licensing must also facilitate a constant process of data
gathering and analysis, upon which this Science can remain current with the products of the
exploration.
If
Conversion for Recovery requires that both design and operational parameters be met, it is this second step that is
usually skipped, or only minimally employed. This is perhaps most clearly seen in the thermal conversion
complement. It is both costly and dangerous to do anything with hot, explosive liquids and gases. Yet
there is a difference we can establish between raw "producer" gas and carefully designed "syngas", just as there is
a difference between raw biofuel and to-specification "biodiesel".
If
technologic design allows, but operations do not stand ready to act on occasionally spiking conditions, then all
that is left is to "clean up the mess" after the fact, and this is no different than can be done with a world class
incinerator. Any system can be operated in a range from clean, to dirty. It is the
human factor that we keep ignoring, and in general, it costs more to run clean than it does to operate
dirty.
If a
Conversion Technology can be operated without intrusively taking samples, by doing nothing more than taking sensor
readings and being ready to act as necessary, then both points are covered, and the system is a
conversion technology being operated for conversion, not destruction or disposal. This is usually the case where
electricity and / heat are the desired products of the conversion. No molecular recovery occurs, when conversion
only results in capture of the energy released by the breaking molecular bonds. The electric and thermal energy
thus harvested may be renewable, but this does not constitute Conversion for Molecular
Recovery.
But when
Molecular Recovery is the target, the difficult and dangerous industrial step of sampling, segregating and
sequestering fractions of the intermediary process products must almost always be considered a
necessity.
To reach
this most sustainable goal of Conversion for Molecular Resource Recovery, all factors have to come into
play:
·
The Technology must by design allow access to and modification of intermediary products;
·
The operational mode employed collects real-time sensored data of the process. The computerized system performs the
necessary analyses, and instantaneously and constantly acts to correct the operations of the
process.
·
Both the Conversion Technology and the Operational Mode are selected to optimize for Recovery of the molecular
resources present in the feedstock, including as needed separation and characterization of the constantly changing
intermediary products.
In this way,
our fledgling industrial efforts can integrate whatever Conversion Technology modules might be required to address
the diversity of feedstock presented, and to perform optimal resource recovery, at the molecular
level.
© Teru Talk by JDMT, Inc 2011. All rights
reserved.
You are free to reprint and use this article as long as no
changes are made to its content or references and credit is given to the author, Michael Theroux.
http://www.terutalk.com
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