Despite the potential advantages, more work is needed to optimize the resin approach. The use of resin beads is convenient for comparing prop­erties such as binding capacity and fouling for both commercial and our own laboratory-synthesized resins. Here we used a commercially avail­able strong cation exchange resin where sulfuric acid/methanol is used to elute the resin. It is entirely feasible to use a weakly basic anion exchange resin where raising the pH releases the algae from the resin [25]. At lower pH (7-8) these resins are positively charged and effectively bind algae. Raising the pH to ~pH 10 or above deprotonates the resin rendering it uncharged such that algae are released. Sodium methoxide in methanol, a strongly basic commercial transesterification reagent, would raise the pH, thereby releasing the algae and catalyzing the transesterification reaction. Here also, it would be critical to use a nonporous resin that did not entrain water.

Future directions are aimed at determining which approach, using strong or weak anion exchange resins is more effective in terms of binding capacity, fouling, and FAME yields. It will also be important to develop new modes for use of the resins such as thin film coatings or resin coated particles that do not entrain water. Finally, more studies of the transesteri­fication reaction are in order since, as shown with Neochloris, the one step conversion to FAME was not quite complete and was further affected by the nitrogen starvation.