Algae to Help Solve the World’s Energy Problems
Donald B. Aulenbach, PhD, P.E.
Rensselaer Polytechnic Institute
Troy, NY 12180
Home: 28 Valencia Lane
Clifton Park, NY 12065-5800
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Abstract: Growth of algae is considered the most efficient method of converting solar energy into organic matter. The biomass produced can be used directly as a solid fuel, or the oil extracted and refined into liquid oil or gasoline. The growth of the algae depends upon the removal of carbon from its environment. Essentially no heat is produced in its growth. Treated wastes from a wastewater treatment plant can provide the needed nutrients for growth, and waste heat from a nearby thermal power plant can be used to maintain the optimum temperature for growth. The waste products are minimal, and the system would have only a minor consequence from a terrorist attack. Some research is needed to optimize a complete system.
Energy is essential to the operation of modern technology. Future growth of population and technology may be limited by sources of energy. We cannot continue to rely on our present sources of energy. We must plan now for future sources of energy, particularly sources that are not detrimental to the environment.
Nearly every source of energy in use today is either limited or has some harmful effect upon the environment. Presently we have adequate supplies of coal for several hundred years. However, any combustion of fuels adds carbon dioxide to the atmosphere, a substance related to global warming. In addition, coal combustion releases nitrogen and sulfur oxides that contribute to acid rain, and metals such as mercury that are undesirable in even low concentrations. Petroleum is presently available in adequate supplies. However, it is not evenly distributed around the earth, and some nations take advantage of this for political purposes. Petroleum products, particularly gasoline, are essential in transportation. They, too produce combustion byproducts.
Hydropower is more benign with reference to its impact on the environment. However, dams may impede travel of fish for spawning, and release of low oxygen content of water from the lower levels of a reservoir may also harm fish. Fish is an important food supply.
Nuclear power does not contribute carbon to the atmosphere. It does release heat to the environment, and there is concern for the radioactive wastes in the environment. There are also individuals who associate nuclear power with atomic bombs, and therefore, will not tolerate it regardless of the safety record of nuclear power plants. Photovoltaic solar energy is used primarily for the direct generation of electricity; however, at the present time it is very inefficient. It is generally uneconomical except in locations with constant sunlight and sufficient available land. Also photovoltaic solar collectors are constructed using materials that are scarce and/or hazardous. Storage of the energy generated is also a concern, with much research being done on battery storage. Wind power is also relatively pollution free, but it does have an impact on birds. It is also not constantly reliable. Research is also presently being conducted using hydrogen as a fuel, using fuel cells whose only discharge is water, but at the present time they have not been developed for common use. Production of hydrogen as a fuel requires another energy source.
It is evident that a better solution to energy production would be desirable.
The Role of Algae:
Algae are a class of organisms of generally small to microscopic size (although they produce large colonies in the ocean) that are capable of producing cell material (biomass) from water and carbon dioxide with the aid of chlorophyll as a catalyst and sunlight as a source of energy. Most are a shade of green, although other colors may also be observed. Since they are of small size, and they produce only simple biomass, they grow very rapidly. Because their biomass is predominantly protein, in addition to water and carbon dioxide, they need traces of nitrogen and phosphorus for growth. One group of algae can secure its source of nitrogen from the atmosphere. Some need traces of sulfur and other elements, and one group, the diatoms (diatomaceous earth), need silicon to form their shells. Many of the algae store food in the form of oils. Algae are considered the bottom of the food chain, since any larger organism that consumes them gains their energy less the amount of energy to consume them. This is why they are so important.
The first consideration with algae is recovery of the oils. Studies have already shown that these oils can be recovered and refined into the equivalent of gasoline. Additional research is needed to identify which algae produce the greatest amount of oil and under what conditions. Also, studies should be made to determine the most useful oil. Further research must be made to determine the ability to recover the oil from the algae.
After removal of the oil, the remaining biomass may be land applied as a fertilizer, or it may be dried and used as a fuel. Since the original source of carbon for the biomass was from the environment, burning either the oil or the biomass only returns the original amount of carbon used to the environment, thereby resulting in no net change.
Most frequently, the first thought in growing algae is an outdoor pond. This may pose problems in terms of variations in temperature, wind and lack of control of the species of algae. In addition, as the algae reproduce they fill the pond and obscure the sunlight to any algae not near the surface of the pond. A novel concept to ameliorate this problem is to place the growing algae in a mixed tube or shallow tray that allows greater exposure to the sunlight. Obviously any tubing would have to be constructed of a glass (silica) or plastic that allows the ultra-violet light to penetrate to the algae. Within reason the tubes or trays could be enclosed in a temperature controlled structure that would still allow penetration of the sunlight. Studies should be performed to determine optimum depths, mixing rate, and temperature.
Temperature control could be provided by any nearby facility that has waste heat needing disposal. This could even be a plant utilizing the dried algae as a source of fuel for any operation including electricity generation. This would help reduce heat that would otherwise be discharged to the environment.
As mentioned, some nutrients, particularly nitrogen and phosphorus are required for the algae growth. It may be possible to locate an algae growth facility within reasonable distance from a wastewater treatment facility. There are increasing restrictions on discharges of nitrogen and phosphorus from wastewater treatment plants. If treated effluent from a treatment plant can provide the nutrients needed for the algae growth, this may preclude the need for additional biological or chemical treatment for nitrogen and phosphorus removal at the treatment plant. Treatment plant effluent would also provide some additional carbon, and most likely some trace nutrients. The National Society of Professional Engineers (NSPE) has chosen an algal water purification system as its New Product Award winner in the small-sized company category (1). Few details are provided in its citation, but the system is effectively removing nitrogen and phosphorus in a treated waste effluent using less than 10% as much space and an equivalent wetland treatment system. The nutrient enhanced algae biomass is used for compost and as a fertilizer. Again, studies should be made to determine the specific requirements for the algae coupled with the amounts available in the treated effluent.
If the prime use of the growth of algae is for recovery of the oil and it is proven economical, it is suggested that continued night time growth can be achieved by the use of ultraviolet lights, with a concomitant consumption of energy. The electrical consumption cost could be overcome by the direct recovery of the oil as opposed to the fermentation of biomass to produce ethanol.
A possible benefit of the use of treated wastewater effluent for the growth of algae is the concern for constituents of emerging concern (CEC) and personal care products (PCP), which includes pharmaceuticals. These substances have been shown to be present in trace concentrations in treated wastewater and in some drinking water supplies. It is possible that these products may be broken down by the algae metabolism or incorporated in the algae biomass. In either event, they would be successfully removed from the water environment. Further research needs to be done in this field.
Studies will have to be made to determine if this total program would be practical, feasible, economical, and environmentally sound. The amount of land needed to produce the needed amount of algae to produce the oil or biomass desired under specific sunlight (daylight) conditions would have to be determined. The costs and facilities needed to grow the algae, to provide pumping for mixing, for separation of the biomass from the liquid and the oils from the biomass, for processing the oils to a desirable level, and for the use or disposal of the remaining biomass must be determined.
The concept of the growth of algae is nothing new. The optimization of the growth and the use of the algae are known. The design of growth and processing equipment does not involve any novel concept. This is a start, but to optimize a complete system and put it all together will take some study and time. It won’t be done in an instant, but if we don’t get started, it won’t get done in time to save the environment.
Algae should be part of any study for the resolution of our energy concern. They efficiently convert carbon and water with small amounts of nitrogen and phosphorus to biomass, including oils, using only the power of the sun. The oils can be separated and refined to provide transportation fuels (gasoline). Their combustion results in no net change of carbon in the environment since their production is dependent on sequestering carbon from the environment. Their uptake of nitrogen and phosphorus may assist in reducing the release of these nutrients from treatment plant effluents. Their use is environmentally benign compared to other methods of producing energy: no acid rain or mercury release as from combustion of fossil fuels, no high temperature or radioactive wastes as from nuclear power plants, no interference with fish life as from hydropower dams, no killing of birds as with windmills, and no use of scarce and hazardous materials as in photovoltaic solar collectors. Research is needed in order to optimize the growth of the most desirable algae and engineering is needed to design the system to work most effectively. Funding for this research is needed now before it is too late, or before we waste money on other systems that are not as efficient. The time to get started in earnest is now.
1. Algal Water Purifier Among New Product Award Winners, Professional Engineer, 16, August/September 2009.