by Mark Edwards
arbon, (often CO2 or CH4) garners the most press as the villain of global warming and the resulting climate chaos. Pollutive C contributes to life-threatening air pollution such as smog that triggers asthma attacks, heart attacks and reduces crop production. As the earth approaches a 1.5oC temperature raise, decarbonizing our economy has become paramount.
Successful decarbonization requires a change in the way carbon is used and a focus on preserving the carbon budget for essential uses. Carbon pollution can be found in abundance in all the wrong places. Agriculture discharges carbon plumes, as do power plants that also release black smoke carbon particulates that pollute cities. Industry currently recycles metals, plastics and paper. The next logical step, recycling carbon, makes sense using the principles of the circular economy to convert it into useful bioproducts.
Algae have evolved to be the most important CO2 fixers in aquatic ecosystems and the major biomass constituent in marine and freshwater environments. Scientists can achieve significant carbon capture by taking advantage of algae’s unusual gift; to capture and fix CO2.
Algae offer the most promising solution for industrial capture of emitted CO2. Algae’s ability to convert CO2 into carbon-rich lipids and protein greatly exceeds food crops and does not compete for arable land or fresh water. Each ton of algae absorb 1.8 tons of CO2. This exchange is possible because the atomic weight of C is 12, while the atomic weight of O is 16. Algae releases enormous amounts of O2, 200 tons per hectare per year, while assimilating the C in its biomass.
David Dah-Wei Tsai and team at the Feng Chia University in Taiwan published a study where they compared the efficiency of several algae cultivation systems with terrestrial plants for carbon uptake. Carbon capture in the algae biosystems were close to 100%. The scientists found that trees and shrubs tested in 16 countries captured less than 20% of the available carbon.
Carbon smart companies will capture waste emissions from power, cement plants and factories and repurpose the carbon into chemicals to make biofertilizer, biofeed and biofuel. Others will make bioplastic as fibers for running shoes, green chemicals or high value medicines.
Several power plant flue gas systems are under development. Michigan State University and PHYCO2 has built a test carbon capture to algae process. The University of Kentucky project with Duke Energy offers a good video. Global Algae Innovations in Hawaii has also posted a video of their robust carbon capture to algae production system. Power Plant CCS provides a brief history on algae carbon capture and storage.
Heavy metals are natural constituents of the environment, but substantial use for human purposes has altered their geochemical cycles and biochemical balance. Human overuse allows release of heavy metal poisons such as arsenic, cadmium, copper, lead, nickel, mercury and zinc into the soil and aquatic environments.
The cost of fertilizers to farmers and the environment is terrible, since only about 40% of the nutrients are absorbed by the crop and the rest pollute ecosystems. The cost of pesticides to farmers and the environment is catastrophic because less than 1% of pesticides are absorbed by the crop, while the residue poisons air, water and soil.
The economic toll of pesticides residuals in fields, on food and food packaging is astonishing. Pesticides create an urgent public threat posed by endocrine disrupting chemicals, especially to our children. Pesticide residuals disrupt the body’s hormones and are linked to myriad severe health problems, such as impaired brain development, lower IQs, behavior problems, infertility, birth defects, obesity and diabetes and all the follow-on diseases.
Toxic heavy metals attach to major organs and interrupt normal organ functions. Lead poisoning in Flint Michigan focused world attention on the effects of heavy metals poisoning. The Flint lead problem affected 100,000 people. Persistent pesticide residue exposure affects at least 10 times more people nationally and 100 times more people globally.
A recent study led by Pete Myers, founder of Environmental Health Sciences, calculates that pesticide costs the US more than $45 billion annually from health care costs and lost wages. Pesticide exposure causes an estimated 2 million lost IQ points and another 7,500 intellectual disability cases annually. The calculations are made from metrics developed by the Endocrine Society, WHO and the UN Environment Program. Additional illnesses will add to the pesticide drag due to the lag effect in heavy metals exposure. Many illnesses such as cancers, neurological, brain and respiratory diseases from toxic chemical exposure appear years after exposure.
Heavy metals are natural constituents of the environment, but indiscriminate use for human purposes has altered their geochemical cycles and biochemical balance. This results in excess release of heavy metals such as cadmium, copper, lead, nickel, zinc etc. into natural resources like the soil and aquatic environments. Prolonged exposure and higher accumulation of such heavy metals can have deleterious health effects on human life and aquatic biota.
The Geological Survey (USGS) and Fish and Wildlife Service (FWS) found that pesticide endocrine disruption causes sex changes among small and largemouth bass. Males had female eggs inside their testicles.
Algae are voracious pollutant scavengers for a broad category of chemicals released into the environment from the domestic, industrial and agricultural sectors. Besides the usual organic and inorganic fertilizer residue compounds present in the wastewater, algae cells can also assimilate and/or break down more persisting molecules such as hydrocarbons, antibiotics, PPCPs, EDCs and heavy metals.
Australia’s James Cook University demonstrated algae are effective at bioremediation of CO2 and heavy metals, (Al, As, Cd, Cr, Cu, Ni, and Zn), in situ at a coal-fired power station (right). Macroalgae inoculates were grown in vertical tubes, (right) and moved to shallow wastewater ponds containing CO2 and fly ash. The algae removed nearly all the metals.
Bioremediation of excess nutrients in wastewater by microalgae has been prevalent in the US for the past 70 years. When algae bioaccumulates toxic wastes, the biomass may not be useful for normal bioproducts. The toxic biomass can be converted to biochar through pyrolysis or gasification. The biochar can be used as soil amendment with reduced risk of leaching of toxic material such as heavy metals, since the pyrolysis process integrates and binds up the metals in the solid matrix.
Bioremediation uses naturally occurring organisms as a treatment to break down hazardous substances such as waste or pollutants into less toxic or non-toxic substances. Bioremediation with nutrient recovery serves as the first step in nutrient cycling. Considerable bioremediation research focuses on the capture of nutrients harmful to the environment, animals or people, such as toxic heavy metals from pesticides.
The role of microorganisms in biotransformation of heavy metals into nontoxic forms is well-documented. Understanding the molecular mechanism of metal accumulation has numerous biotechnological implications for bioremediation of metal-contaminated sites. Cell wall components of various algae groups related to the metal binding capacity of algae are described in Adsorption and Absorption of Heavy Metals by Microalgae, by Li Li.
After bioremediation, algae had accumulated the toxic heavy metals, so the biomass was not fit for anaerobic digestion or biofertilizer. Pyrolysis of the cultivated algae immobilized the accumulated metals in a recalcitrant C-rich biochar. While the algae biochar has 10 to 50 times higher metal concentrations than the algae feedstock, the biochar had very low leachable metals. The metals were bound up (chelated) into the biochar matrix, providing nutrients for crops but sequestering the toxic metals for decades.
Bioremediation lays the foundation for nutrient cycling. Nutrient capture in algae biosystems provides the feedstock for a wide variety of bioproducts. Since modern environments offer so many pollutive point sources for carbon and other nutrients, algapreneurs have many choices for nutrient collection. Carbon capture using current mechanical technologies cost $40 to $50 a ton, but those methods are not sustainable. Algae-based CO2 capture and sequestration currently costs more than conventional methods, but is more sustainable. In addition, algae produce bioproducts that can be monetized. Algae-based CO2 and nutrient capture will present a profitable business in the near future with rising oil prices, carbon trading and social policies directed at polluters.
Algae’s three immediate bioremediation contributions to agriculture will be recovering phosphorus, reducing nitrogen and carbon wastes, and capturing and sequestering toxic heavy metals from pesticide residues.
The strongest leverage to agriculture from algae bioremediation may be algae biofertilizers. Most importantly, algae-based CO2 abatement enables monetizing carbon credit + nutrient value + biomass value for bioproducts. A coal power plant produces about 1 ton of CO2 for every MWh of energy produced. Yield of algae biomass per hectare is about 0.3 to 1 ton per day. Algae biotechnology will offer a safe and sustainable solution to the problems associated with CO2 emissions from coal power plants and other carbon sources.
Once algae perform the magic of carbon and nutrient capture, the next important step is to repurpose those precious nutrients into useful bioproducts.