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Engineering Assessment of Algae Biofuel Production

Quiz Questions

1. Figure 1.1 shows:
Micrographs of commercially cultivated algae species
Micrographs of natural algae species
Micrographs of corn algae
2. In Fig 2.5, In a microalgae wastewater treatment, several thousand small (< 10‐hectare) and a few large‐scale (>100‐hectare) algae pond systems are currently operated for municipal wastewater treatment in the US. The essential function of the algae is:
To provide dissolved oxygen for the bacterial breakdown of the wastes.
To reduce the greenhouse effect
To block the sun to stop the evaporation of the water in the pool.
3. The first Algae Mass culture experiment was tested on a rooftop at MIT university on 1953
4. Algae oil production is the focus of almost all current interests in algae biofuels. However, algae do not produce oil in copious quantities, and when they do, it is generally only under duress (i.e., nutrient limitation) and at low rates. The process of domesticating algae is just beginning.
5. Algae biofuel production requires an initial step of learning how to grow algae of a chosen species at large‐scale, at low cost, consistently, and at high productivity. The objective is to grow algae:
With light as the only limiting nutrient, thus assuring that all light will be used as efficiently as possible.
With carbon as the most important nutrient.
6. The major environmental factor limiting algae biofuels production, at least in the US, is likely temperature. Algae productivity is maximal in a rather narrow range compared to what is found in temperate climates. The optimal temperature regimes for algae strains currently used in mass cultures show steep productivity declines below about 20°C and, on the high end, above about 35oC.
7. Unlike field crops where plant biomass accumulates until harvest, algae must be harvested
8. Regions with average temperatures of 15°C have been considered unsuitable for algae mass cultivation (Harmelen and Oonk, 2006), but that cut‐off is simplistic. Diel temperature regimes are more significant, and hour‐by‐hour pond temperatures can be accurately predicted for any location with models that use local historical weather data (e.g., Benemann and Tillett, 1987). From these models, it can be determined that in most desert regions of the US, the limiting factor in algae growth rate would likely be low night‐time temperatures. These impact photosynthesis rates by then requiring a long time to warm up during the day. Some literature data suggests that this will reduce photosynthesis
9. Ways to ameliorate this problem have been considered previously, such as covering ponds with foam or cheap plastics or increasing pond depth or the size of the settling ponds to allow for greater night‐time storage, etc. However, none of these methods appeared to be sufficiently low cost for biofuels production. Although, perhaps a combination of approaches could be practical in some cases.
10. Control of culture biology is:
the most complex and difficult issue in mass algae production.
A natural and ordinary process.
11. Perhaps no subject, outside nuclear energy, has raised so much hope and engendered as much fear, as the development of molecular genetics, giving rise to genetically modified organisms (GMOs). To achieve the goal of high microalgae productivity with a high content of oil, molecular genetics will be a necessary tool.
12. Open ponds for algae production are relatively (compared to PBRs) simple in construction and operation. As already discussed, they fall into three configuration categories: unmixed, circular, and raceway. Unmixed ponds are not controllable, cannot be supplied with CO2 efficiently, and are of low productivity. (However, none of these constraints have detracted from the success of the beta‐carotene plants in Australia (Figure 2.3), or similar ponds in Mexico for Spirulina production, where land availability made productivity not a major issue.)
13. To approach maximal economies of scale, individual growth ponds should be about 4 hectares in area. Currently the largest known ponds of 1.25 ha are just starting operations for biofuels production in New Zealand (Figure 3.5). The largest known ponds in New Zealand are:
1.25 hectare pond
Four 1.25 hectares ponds
One 4 hectares pond
14. Ponds should be within certain depth. Lower depth results in large temperature variations, hydraulic mixing problems and, perhaps most critical, in too high a rate of out‐gassing of CO2. The depth of the ponds should be:
Between 10 cm and 15 cm in depth
Between 25 cm and 35 cm in depth
Between 1 meter and 3 meter in depth
15. Figure 4.1 shows:
Pond characteristic and optimum size
Schematic of an algae biofuel production process
A biofuel plan
16. Solar radiance and temperature determine the length of the growing of the season and also directly affect algae productivity. Although algae survive over a wide range of temperatures, each strain has a particular temperature range for maximum productivity. According to Fig 4.2 the temperature zone projected to be suitable for algae biofuel feedstuck production is above
10 degrees centigrade
15 degrees centigrade
35 degrees centigrade
17. The evaporation from outdoor algae ponds is a function of, mainly, air temperature, wind and relative humidity. Evaporation from reservoirs can be estimated from standard evaporation (“Pan A”) data after applying correction factors (e.g. for humidity, wind speed, etc.). However, algae ponds are not reservoirs, being much shallower and mechanically mixed, and thus are expected to have higher evaporation rates. The maximum evaporation rate in the US is typically found in Yuma, Arizona – with annual losses of up to 12 ft (~3.6 m) recorded, though more typically net annual evaporation rates are 6 to 8 feet (~1.8 – 2.4 m) in most of the areas considered suitable for algae biofuel production.
18. A reliable, ample and low‐cost water supply is a critical for algae biofuel production. A water supply is necessary to make up for water lost through evaporation and blow down. One of the important factors that set algae biomass production technology apart from technologies reliant on terrestrial crop production is the ability of algae to utilize water of poor quality, unsuitable for crop production, which generally means brackish and higher salinity inland waters and ocean seawater.
19. Land requirements are thus for large tracts of nearly flat land, with clay or similar low permeability soils. The footprint of algae production facilities would typically be several hundred hectares (except for wastewater treatment facilities, which could be significantly smaller, see Chapter 5). Candidate sites should be level or nearly level since terracing would require significant expenditure for earth moving to construct the ponds. A large slope would also require additional pumping costs for water supply and recycling. Soil characteristics are also important, with sandy soil, resulting in high percolation rates, being unsuitable. Ponds will tend to be self‐sealing, and sandy soils could be sealed with a thin clay liner, at additional costs.
Better suited
20. Carbon dioxide is a critical nutrient for all photosynthetic plants species, but all conventional higher plant production systems can obtain it from air, algae production is the exception in that it requires an enriched source, as atmospheric CO2 is not sufficient. The reasons for this is the limited gas exchange at the pond surface interface, limiting productivity to well below the productivity achieved by higher plants, and the excessive energy that would be required to provide CO2 by sparging air through a culture system. Many sources of enriched CO2 can be considered, from merchant (100%, compressed, liquefied) CO2, to flue gas from power plants, the latter being the focus of most of the activities in this field. Other sources include wastewater treatment plants, ethanol plants and similar biorefineries, petroleum refineries, agricultural, urban and industrial solid waste facilities, and other such sources.
21. Every potential site where algae biofuels could be produced will have unique characteristics and thus the environmental impacts to air, soil and water resources will be vary. These will also depend on the production technologies, in addition to land, CO2, nutrient and water inputs.
22. According to table 5.15 the total cost of production per barrel of oil is:
23. According to table 5.18 total cost of production per KWh is :
24. From this report, It is clear from this report that algae oil production will be neither quick nor plentiful – ten years is a reasonable projection for the R&D to allow a conclusion about the ability to achieve relatively low-cost algae biomass and oil production, at least for specific locations.