There are a number of technical bottlenecks that need to be addressed. Some of the

basic questions yet unanswered include the following:

1. In a full-scale field operation, what are the ideal strains of algae that will yield both a high-quality effluent and a high-quality biofuel?

2. What are the most efficient methods for separating and concentrating the algae? The transition from 300 mg/L in the pond to a slurry that is 20 % solids may take two or three steps.

3. What are the most efficient and cost-effective methods for breaking open algae cells for the production of a green crude or the separation of the lipid, aqueous, and solid fractions of the lysed cells?

4. What are the most efficient and cost-effective methods for converting the green crude or purified lipid into a commercially reliable biofuel? In the past few years, several new methods have been developed on a bench and demonstration scale, but no one process has been made the leap to be an industry standard for full-scale systems.

5. The companies that favor large photobioreactor systems have yet to show how their systems could be implemented on a grand scale. There is roughly an order of magnitude difference in capital and labor costs between photobioreactors and open pond systems. For algae-based biofuel system to be commercially viable, the output would need to be on the order of thousands to millions of liters of biofuel per day. While practitioners from the fields of biotechnology and bio­chemical engineering have very reliable data from their bench and demonstra­tion-scale bioreactors, the only two fields of engineering that have a long­standing history of working on systems that reliably process liquids on a grand scale are in the chemical/petroleum industry and wastewater treatment.

6. The photobioreactors can provide the initial step of a high-quality starter culture into an open pond system, but when one takes into account the energy needs and capital cost of mega-scale bioreactors, the economic feasibility of hundreds of hectares of photobioreactors fades rapidly.

7. A number of companies are trying to outdo their competition based on the hopes of genetically altered strains of algae. Considering the fact that it takes the approval of several different local and national regulatory agencies just to restore a disturbed habitat with native plant species, the likelihood of a company being allowed to generate 50 tons/day of genetically altered algae in open ponds could face some very tough opposition that would include regulatory agencies and well-organized citizen groups. In addition, the fate of genetically introduced microbes into the environment can be precarious; for example, consider the failure of engineered Rhizobium strains introduced into soybean fields to inoc­ulate seedlings but were outcompeted by native strains (Kent and Triplett 2002)

8. What will make or break this industry is the ability to produce biofuels on a mega-scale basis with a high degree of reliability. A serious economic analysis is needed for each step (i. e, culturing, harvesting, dewatering, lysing, and bio­fuel processing) in the development of algae-based fuels.

9. Most large wastewater treatment plants that process 200-1000 ML/day are located adjacent to dense urban landscapes with little available room for large — scale algae ponds. The ideal candidates for the system proposed in this chapter would be rural wastewater treatment plants that process 2-40 ML/day. Most often, these plants are located at a good distance from populated areas, and there is ample land that could be developed into algae-culturing ponds. In parts of the world where there is a cold or monsoon season, the plant can revert back to its original treatment process and use the ponds for short-term storage of wastewater.

6.2Conclusion

The ability to culture and harvest algae has improved dramatically over the past five decades. There are numerous treatment options that can be used to make the transition from concept to demonstration to full-scale implementation of algae biofuel programs. This will require the ability to adapt preexisting technologies from several disciplines. Many of the answers are already out there but have yet to put in the proper sequence or combination. There is no one technical solution to make this process commercially viable. As demonstrated in this chapter, it will require contributions from several disciplines to go beyond their technical comfort zones. While this is an emerging field with great promise, it will be built on the fundamental principles of engineering and science.

Acknowledgment H. Ahmadzadeh thanks ATF Committee for the financial support.