BLOG, The Science Debates
By Yasha Husain, posted March 13, 2009
Debate #1: Biomass from Bacteria-induced, Hybrid Poplars
Biomass research of trees has been going on for years, the trees often studied include willow, poplar and cottonwood trees
Photos Courtesy of National Renewable Energy Laboratory
SUNY College of Environmental Science & Forestry biomass research farm in Tully, New York
Hybrid Cottonwood Tree Farm in Washington State
Willow biomass research plots at SUNY College of Environmental Science & Forestry genetics field station in Tully, New York
Moderator Question:
Can bacteria-induced, hybrid poplar tree farms located on Superfund Sites be used to produce energy from biomass safely, and more efficiently than if we were to continue using corn to produce ethanol?
Will the poplars be able to grow on the depleted and contaminated soils of Superfund Sites, simultaneously cleaning up contamination through phytoremediation?
Background:
Genetically modified poplar trees have been among the plant life studied for its capacity to be a fast growing, high yielding source of biomass. The very fact that the trees would be genetically modified makes them a less attractive choice for energy crops, especially for policy minded people aware of the ongoing controversy surrounding GMO crops and their ability to cross fertilize with other plants.
In this groundbreaking topic for debate we look at how bacteria strains, when induced into non-GMO poplar clippings, have been shown to accelerate the growth of trees, possibly making bacteria-induced poplars a valuable source of biomass. We'll look at whether this manner of cultivating poplar farms for biomass will be a balanced one.
What adds significantly to the reasoning behind the science is that the hybrid poplar tree farms would be situated on Superfund Sites, and through a process called phytoremediation would effectively clean toxins from the environment as they grow.
(The Science Debates are split into two sections. The first section, 'What Is Known', lays out important facts related to what we currently know about the science being debated, and the second section, 'The Unknowns', lists a number of the unknowns related to the proposed science. Inside of each section are 'the basics' and 'the specifics'. The basics offer broad explanations pertinent to the general science, and the specifics describe the applied science in more detail. Feel free to skip between sections and subsections using the hyperlinks below to find the information that is most relevant to you. Please also leave comments at the end that you think will contribute to a healthy debate. They will be posted in the next couple of days.)
SECTION ONE: WHAT IS KNOWN
THE BASICS (KNOWN):Cleaner environment = healthier population
Alternative energy = planetary health and strengthened global economy
Higher yields = more biomass to make energy
Tree farms at Superfund Sites = increased carbon sequestration
Nonedible plant parts = continued challenge to ethanol conversion process
Phytoremediation = less hazardous waste in local soils/waters
THE SPECIFICS (KNOWN):
Bacterium induced into poplar trees to accelerate growth = increased yields
Bacteria intended for use = possible antibiotic resistant strain
Growing poplar trees instead of corn = less greenhouse gasses
Tree growth at hazardous waste sites = cleanup of toxins and metals
Use of Superfund Sites = More food production for world population
Growing poplars instead of corn for fuel = less pesticides in the environment
Poplar harvests = rich soils for harvesting foods
SECTION TWO: THE UNKNOWNS
THE BASICS (UNKNOWNS):Compounds in parts per billion = potential cause of environmental toxicity
Grafting = means exploited to grow hybrid poplar trees, minus bacterium
Demand for biofuels = Relative supply of solar and electric vehicles
THE SPECIFICS (UNKNOWNS):Bacteria added to tree clippings = new questions
Diacetyl, dangerous when heated and inhaled = uncertain effects
The Biomass itself = contaminated?
Reduced greenhouse gasses from energy conversion = so far, theory
Nonnative species = possible disadvantages over native species
______________________________________
SECTION ONE: WHAT IS KNOWNTHE BASICS (KNOWN):
Cleaner environment = healthier population
Efforts to clean, detoxify, and improve environmental conditions generally result in a healthier population.(Top)Alternative energy = planetary health and strengthened global economy
Alternative energies, such as biofuels, produced efficiently so to significantly reduce the carbon footprint, and the footprint of greenhouse gases, including methane and nitrous oxide, will help create greater global security in terms of job creation, stable markets, and, as anticipated by global warming scientists, normalized weather conditions.(Top)Higher yields = more biomass to make energy
The higher a crop’s yield, that is, the more that can be harvested from a single crop, that is then multiplied over many farm fields, the more biomass or raw energy in the form of plant sugars that can be converted to a usable energy form of energy such as biofuel.(Top)Tree farms at Superfund Sites = increased carbon sequestration
Most plant life absorbs carbon dioxide (CO2) from the atmosphere and uses energy from the sun to convert an equal amount of water and CO2 to make sugars, which in turn promote plant growth. The process is known as photosynthesis, and the sugars the plant makes can later be used to produce biofuels. This ability of plants to absorb and store carbon underlies why it’s so important great swaths of rainforests aren’t lost; the forests are natural carbon sequesters. Tree harvests for biomass on Superfund Sites become another means of sequestering carbon; however, the energy created through photosynthesis would later be converted to biofuel, or another manmade energy source.(Top)
Nonedible plant parts = continued challenge to ethanol conversion process
Sugars in edible parts of plants (e.g. corn) have so far been most easily converted to ethanol at ethanol refineries; they have in relative terms also provided the most cost-efficient means of producing ethanol, however, arguably not the most environmentally friendly means. The more cumbersome to extract and manipulate sugars in the walls of nonedible plant parts (e.g. corn stalks), continue to pose a challenge to the ethanol refining process, which it is hoped will be overcome so that the cost to produce what is referred to as cellulosic ethanol becomes more competitive. Advanced technologies are being crafted to assist in the affordable conversion of lignocellulosic, or nonedible, plants and fibers.
(Top)Phytoremediation = less hazardous waste in local soils/waters
Phytoremediation describes how plants through natural processes are able to absorb unwanted heavy metals and toxic contaminants from marginal soils and ground waters as they grow. It’s a tool for environmental cleanup used at locations with hazardous waste, like abandoned manufacturing centers, nuclear sites, and mines, designated Superfund Sites by the Environmental Protection Agency. Poplar trees have been used for phytoremediation purposes.(Top)THE SPECIFICS (KNOWN):
Bacterium induced into poplar trees to accelerate growth = increased yields
A particular strain of bacteria, Enterobacter sp. strain 638, that otherwise naturally occurs in soil, and in poplar roots, and to a lesser degree their stems and leaves, when induced or added by scientists to hybrid tree clippings (Populus deltoids x Populus nigra DN-34), in parts per billion, increases the growth rate of the poplar trees growing in marginal soils.(Top)The location of the test site from which this science was produced was a greenhouse at the University of Georgia’s Savannah River Ecology Lab (SREL), at the Savannah River Site (SRS). SRS, a large Superfund Site, has been on the EPA’s National Priorities List since 1989. Today, there is an ongoing clean-up effort to undo all of the environmental damage done on the 192,000 acre site since refining of nuclear weapons began there in 1951, and nuclear spent fuel began to be stored there. Also at SRS, a controversial nuclear reprocessing facility, known as a mixed oxide (MOX) fuel fabrication plant, is currently under construction, it would be the first operational MOX plant of its kind in the United States.
Adam Hoffman, a University of South Carolina graduate student, conducted the study involving Enterobacter s sp. 638, as well as other bacteria strains, at SREL, under the supervision of Dr. Lee Newman, who is now at Brookhaven National Laboratory in Upton, New York.Hoffman found that by adding certain strains of endophytic (naturally occurring) bacteria, particularly Enterobacter s sp. 638, hybrid poplar clippings grew rapidly compared with clippings not induced with the bacteria, presumably spawning greater amounts of biomass to be used to produce energy more efficiently than methods for producing, for example, corn ethanol. He thought of how it might make sense to grow these poplars on tree farms at Superfund Sites and use them for biomass.(Top)
Bacteria intended for use = possible antibiotic resistant strain
Enterobacter s sp. 638 was first discovered by another member of Hoffman's team at the University of South Carolina's microbiology lab to have promising growth promoting properties when added to trees growing atop trichloroethylene contaminated groundwater. The trees used for this portion of the study are known hyperaccumulators. That is, they are able to absorb large amounts of toxins from the environment. In this case, what was absorbed was trichloroethylene, a very common and volatile hazardous waste found at Superfund Sites.
The data Hoffman's lab partner found from several strains of bacteria, including Enterobacter s sp.638, was shared with Dr. Newman, who instructed Hoffman, her graduate student, to conduct the next stage study at SREL, which involved studying the effect the bacterium has on the growth rate of trees in marginal soils, including varieties of hybrid poplars.Enterobacter proved to be the bacteria that consistently caused hybrid poplars to grow most rapidly, over several other chosen bacteria strains that also showed growth promoting properties.
However, though this particular strain of Enterobacter, s sp. 638, is not pathogenic to humans or plants, meaning it will not harm humans or plants, many of the 637 other Enterobacter strains, in high enough doses, will make people sick, and be antibiotic resistant.(Top)Growing poplar trees instead of corn = less greenhouse gasses
Corn ethanol, while it once held great promise, now appears to be a less efficient form of alternative fuel than previously believed. It currently requires large amounts of fossil fuels in order to be produced, and therefore releases considerable amounts of carbon and nitrogen into the air before it hits the roadways. And its production requires valuable farmland, and water resources.*
Biomass from bacteria-induced poplar trees would be considered a cellulosic feedstock, or energy crop, used to make cellulosic ethanol, or potentially, an advanced biodiesel. This form of biomass shouldn’t require as much energy input up front, particularly since it likely won’t require fertilizer, and definitely not pesticides, to grow the trees, and irrigation methods will differ from those used to irrigate crops. Conceivably, according to Hoffman, in the conversion process there would also be less nitrogen emitted from the trees than is emitted from corn. There again would be the added benefit of carbon sequestration from poplar tree farms on plots of land that otherwise might not see the same amount of plant growth, given the barrenness and state of abandon of many Superfund Sites.
*Cogeneration (or combined heat and power (CHP) that recycles ‘byproduct heat’ from plants to produce an efficient local energy source), and pending plant infrastructure changes that would require the input of biofuels versus fossil fuels to operate, may help alter the dynamics once again, but until then, cellulosic ethanol from forms of biomass other than corn (e.g. switchgrass, corn stover, and wood products) has become an important point of focus, as have biodiesels (derived from oils and fats) and second generation biofuels (e.g. Amyris Advanced Renewable Fuels; which involve the bioengineering of microorganisms, or synthetic biology).
A remarkable discovery by James Dumesic, a biological engineering professor at University of Wisconsin-Madison, has turned up a means of converting the plant sugars in nonedible plants, a.k.a. lignocellulose, to molecules of ‘acids, alcohols, ketones, and cyclics,’ that can be directly upgraded to gasoline, diesel and jet fuels, by maintaining 90% of the energy in the original sugars. The science is brand new, but if applied the gas and diesel produced from plants could be used in the existing infrastructure for fuels, and become a popular alternative to cellulosic ethanol production.(Top)Tree growth at hazardous waste sites = cleanup of toxins and metals
Part of the brilliance behind this scheme to create alternative energy is that the trees are to be grown on Superfund Sites where they can be used for phytoremediation, which involves the plant’s biochemistry taking up or absorbing heavy metals and contaminants, like trichloroethylene, toluene, benzene, and ethylbenzene, from the soils and ground waters in which they grow.
This would ‘kill two birds with one stone’, Hoffman likes to say. On the one hand, poplar tree farms would do the dirty work of cleaning up toxic and abandoned Superfund Sites. On the other, the tree farms being situated on Superfund Sites could free up farmland for growing food crops versus biomass, for corn and cellulosic ethanol.(Top)Use of Superfund Sites = More food production for world population
Switching to biomass production via poplar tree farming at hazardous waste sites could free up farmlands for food harvests that might otherwise be used to grow corn to produce ethanol, which in the face of food and hunger protests around the world couldn’t be timelier.(Top)Growing poplars instead of corn for fuel = less pesticides in the environment
An objective of big agrochemical businesses, the United States Department of Energy, and farmers alike, in recent years, when the price of crops used for biofuels was driven upwards, and the push for alternative fuels reached a new high, was to increase yields of crops like corn, soybeans and sugar cane. The ongoing effort to improve yields globally includes the heavy use of pesticides.Using naturally-occurring bacterium as opposed to pesticides to grow hybrid poplar trees for biomass could reduce the amount of controversial pesticides in the environment.(Top)
Poplar harvests = rich soils for harvesting foods
Farming poplars for biomass could also spell more nutrient-rich and stable soils for farmlands. That is, the corn stover intended for use in cellulosic ethanol production has traditionally been allowed to breakdown in corn fields and re-supply the soil with the nutrients it initially took up in order to grow. It also serves as a protective covering that locks in moisture and keeps dryer earth from blowing away in the wind. Corn stover is sometimes referred to as cellulosic waste, and is comprised of leftover corn stalks that remain on the field after corn has been harvested. Using a percentage of it to make ethanol, a proposed solution to the corn ethanol conundrum, could arguably deplete or worsen the quality of soils if the percentage used was too high, making alternative biomass options like poplar tree farms seem attractive, at least initially.(Top)
SECTION TWO: THE UNKNOWNSTHE BASICS (UNKNOWNS):
Compounds in parts per billion = potential cause of environmental toxicity
In the last 10 years of environmental science the use of increasingly sensitive equipment for making measurements has resulted in an impressive number of studies showing that certain organic compounds, down to parts per billion, can and do adversely affect different species’ biological growth patterns, sexual behavior, and healthy functioning. Much of the science regarding bioaccumulation and convergence of compounds, for instance, in municipal water systems, is still unfolding.(Top)Grafting = means exploited to grow hybrid poplar trees, minus bacterium
Grafting was once described to me as the splicing of genes, and is a means by which one creates hybrid plants and trees. It is not a controversial practice, such as the engineering of genetically modified organisms. GMOs involve manipulating the DNA of an organism in a laboratory to create a variation of it that becomes a manmade good. Scientists insert portions of genetic code that alter so far untouched code, or create cross-sections of code, with a specific intent in mind. Opponents of GMO crops believe altering nature in such a way will negatively effect the natural functioning of environment and species, as the crops are planted outdoors, opposite non-GMO fields, where cross-pollination can occur; there are too many unknowns.
Grafting, in its simplicity, is a means of asexual plant propagation, or the practice of joining clippings of two or more plants (usually trees, fruit trees, or shrubs) so they will grow in unison forming a plant anew. Poplars are frequently grafted since they are very fast growing trees used for making wood products and plywood, and restoring the environment through phytoremediation. According to the Segal Ranch Hybrid Poplars web site, poplars can grow 60 feet in six years and produce four to 10 dry tones of wood per acre per year.Though grafting is commonly used in agriculture and horticulture, it is not normally practiced on a large-scale using bacterium to accelerate plant growth. Only further studies or experiments would lead to greater knowledge about this particular means of promoting grafting.(Top)
Demand for biofuels = Relative supply of solar and electric vehicles
Regardless of the decline in oil and gas prices toward the end of 2008, the demand for alternative energy remains high around the globe. Solar-powered and lightweight vehicles and farm equipment offer still more alternatives to vehicles powered with biofuels. Solar-powered transportation could also create additional jobs as the demand for domestic sources of solar panels, advanced lightweight materials like carbon fiber, and green lithium or nickel metal hydride batteries, rises. Solar electrolysis for running cars; hydrogen fuel cell technology; maglev trains; and simply learning to use public transportation, walk or take the bike to work, could all be additional means for meeting the demand for alternative, clean, energy. The potential gains from all of these options continue to need to be figured into whatever projections of future demands for biofuels look like.(Top)
THE SPECIFICS (UNKNOWNS):Bacteria added to tree clippings = new questions
Unfortunately, we don’t know what amount of Enterobacter s sp. 638 bacteria added to trees can potentially cause environmental toxicity down the road, or the degree to which accumulated amounts of this bacterium may be deposited into plant roots, soils, surface waters and ground water, nearby tree farms. However, based on initial findings, the scientists responsible for the study believe the added bacterium will have an insignificant affect on the environment.As well, while Enterobacter s sp. 638, when compared with other bacteria strains in the study, causes poplar clippings (Populus deltoids x Populus nigra DN-34) to grow the fastest, it appears to not be as strong of a cleaning agent as a less popular choice of bacteria, nor does it have the same built-in controls that prevent inhibition of plant growth, as does still another choice.
Among these alternate bacteria strains, which are expected to be used on future tree farms in addition to Enterobacter, one was shown to develop external colonies on the surface of tree roots, while Enterobacter only formed internal colonies. What this all means for the science exactly, well, is not entirely known.(Top)
Diacetyl, dangerous when heated and inhaled = uncertain effects
To promote the growth of trees, Enterobacter s sp. 638, produces acetoin, which converts to 2,3-butanediol, also known as, diacetyl.While diacetyl’s exact role in helping poplars grow, and the degree to which it is present in mature trees, are not known, the compound has been in the news in recent years. When heated and inhaled for long periods of time, it is known to cause an incurable lung disease, bronchiolitis obliterans. The only answer for those stricken by the disease is to have a lung transplant.
Diacetyl is a common addition to microwave popcorn, butter, margarine and chardonnay, and in 2004 and 2005 two workers at popcorn factories in Missouri were found to have the terrible lung disease. At butter flavoring factories in California, a number of male workers who didn’t smoke and were young and healthy when they became ill, were also diagnosed with the disease. Reports and studies have also circulated indicating workers and consumers exposed to lesser amounts of diacetyl are still at risk of becoming sick with asthma, pneumonia, fibrosis and other health impairments.
By 2007, the United States House of Representatives passed a bill requiring the Occupational Safety and Health Administration to put in place an emergency standard that would limit workers’ exposure to the dangerous compound. And in September 2007, a letter from Senators Edward Kennedy and Pat Murray was sent to the Department of Labor, Centers for Disease Control and the Food and Drug Administration, suggesting that in light of surfacing reports about risks to workers, their families, and consumers, from the food additive diacetyl, the agencies look into what steps should be taken to mitigate public health concerns, and report back to the Senators within a 90 day timeframe. By the time the letter was sent, 80 percent of microwave popcorn manufacturers had stated their intention to abandon the use of diacetyl.(Top)
The Biomass itself = contaminated?
The health promoting properties of biomass coming from poplar trees grown in contaminated soils is also in question. Since the trees would be grown on Superfund Sites and part of their job would involve the uptake or absorption of toxins, depending on the amount of pollutants that are taken up by the trees, they could be considered contaminated. Later converting the trees to biomass for biofuel, or to produce steam to make electricity, might allow otherwise contained, hazardous substances to travel. Further experiments, such as volatility studies that the Oak Ridge National Laboratory conducts, are likely needed to provide more conclusive answers regarding the ultimate safety of tree farms grown on Superfund Sites.(Top)
Reduced greenhouse gasses from energy conversion = so far, theory
While biomass from bacteria-induced hybrid poplar farms converted to energy would theoretically not create as many greenhouse gas emissions in the form of carbon and nitrogen during the production process than growing corn and converting it to ethanol currently does, only more experiments will make this argument absolute.(Top)
Nonnative species = possible disadvantages over native species
Last but not least, scientists debate whether it is better for the environment, and more cost-efficient, to grow a variety of native species on Superfund Sites, if they are also good at phytoremediation and can grow in marginal soils. The alternative is to grow nonnative species known to take up, or hyperaccumulate, organic compounds such as toluene and benzene, compounds considered hazardous to health when present at levels above the standard set by the Environmental Protection Agency.In the case of hybrid poplars, since the roots of the trees can literally reach down to the ground water and absorb liberal amounts of liquid, the trees could potentially draw down the water table. At the same time, by reaching and absorbing groundwater contaminated with a common pollutant such as trichloroethylene, the trees should be able to reduce a pre-existing public health concern.
While poplars make sense on a number of levels for phytoremediation at Superfund Sites, they are not the only means of achieving it using basic photosynthesis and plant biochemistry. Holistic studies may be required at the outset to help determine the best route to take in varying climatic regions.(Top)
Revisions posted on March 17th by Yasha Husain
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