While we are not equipped to do a formal life cycle analysis and feel it would be premature given the improvements needed in resin technology, nevertheless a comparison of the proposed resin-based processing to current approaches seems in order. Figure 5 presents a general schematic for current algal processing schemes derived on published evaluations [5,29]. For the most part, the cost of growing algae would be the same. The use of resins could impact growth in terms of the need for nitrogen starvation or growth of monocultures as discussed below. Primarily, our one-step harvest to biodiesel approach would impact the most expensive steps in processing algae to biofuel, namely the harvesting and extraction steps.

Currently harvesting typically requires both pumping the algal suspen­sion and some treatment such as centrifugation, flocculation or dissolved air flotation. Centrifugation and dissolved air flotation both have relatively large capital costs and substantial electricity. Where resins could make a difference is by eliminating the need for pumping water. While we have used resin beads for comparisons, we do not feel this is the best way to deploy them for harvesting. Resin beads are porous with a large internal volume that can trap water. The pores are typically 10-30 nm in diameter whereas the algae are on the order of 2-3 pm in diameter so they cannot enter the resin. Our measurements show that after the bulk water is re­moved, about 100 mg of water/gram resin is retained either inside the resin or entrained between the beads. A better alternative is to use thin films of resin where the internal volume is low compared to the surface area. We have proposed elsewhere a belt harvester type approach where a belt moves from the pond, where it picks up the algae to a vat which, in this case would contain sulfuric acid/methanol [25]. In that study we estimated that a bristled belt 1 m wide x 7.5 m long could collect 3 kg algae per one complete turn of the belt. Other modes are possible such as mesh bags con­taining nonporous resin-coated particles that float or are semisubmerged.

Once the algae is harvested and eluted, the conversion to biodiesel is direct. There is no need for lysing, further drying and solvent extraction, steps that are considered quite expensive [5]. Hexane extraction requires recovery of the hexane and a certain amount will be lost to the environ­ment. Furthermore, hexane only recovers the neutral lipids (mainly TAG). Our experience at measuring TAG in pond-grown algae is that TAG levels rarely surpass 5% DCW and we have never seen them greater than 12% DCW. One of the advantages of this approach is that FAME is generated from both polar and neutral lipids thereby increasing the yield from the

A Conventional

В Resin-based

algae. Our data suggest improvements of up to 4-fold were possible with an alga (KAS 603) that made 10% TAG.

The improved yield could affect several aspects of the algal growth process. Firstly, our data suggested that there was not so much to be gained by nitrogen starvation. Both starved and unstarved algae contained similar amounts of total lipid. Admittedly, the spectrum of fatty acids was differ­ent and this might be a factor. Secondly, resin-based conversion of total lipid to biodiesel might make it less important for growers to maintain a
monoculture of high TAG-producing algae. Of course, high TAG produc­tion is a benefit but it is difficult to maintain monocultures in open ponds or in potentially other attractive scenarios where algae are grown in con­junction with wastewater treatment plants. Finally production of biodiesel onsite eliminates the transportation cost of moving algal oil to a biodiesel plant. While the biodiesel must be recovered from the sulfuric acid metha­nol, we believe this can be done using a low solvent or even solventless hollow fiber extraction system. In commercial biodiesel plants, the glyc­erol separates from the biodiesel layer and the separation is facilitated by water. This may be possible as well but more study is needed to determine how best to fractionate the spent sulfuric acid/ methanol mixture. There will be many cellular components in the final sulfuric acid/methanol solu­tion, some of which may be valuable as side products.