I’m dubious about the idea of getting biodiesel from sewage sludge, as is recently being touted.
One reason I’m dubious is that we’ve yet to see a proper demonstration of the feasibility of getting oil from algae. Given that sewage sludge is a much more complicated beast, I don’t see its promise as a source of energy.
cell membrane of these microorganisms is a major component of sewage sludge and is composed primarily of phospholipids. It is estimated at 24% to 25% of dry mass of the cell and yields about 7% oil from the dried secondary sludge. Other studies have demonstrated that up to 36.8 wt % of the dry sludge is comprised of fatty acids and steroids
As has been also noted, algae can have as much as 30 percent (some claim more) of its solid mass as oil.
But, again, oil from algae, despite big government bucks, has yet to be demonstrated as being feasible. Oil from algae has added complications, such as feeding enough carbon dioxide on a large enough scale to make algae grow quickly, as well as waste disposal issues (which may not be receiving enough attention). Oil from sludge will have waste products to deal with, as well.
Now, don’t get me wrong. We need to keep up the research on these things. But we ought not lose sight of the fact that research is often talked up a lot in order to help garner funding. And, more importantly, we need to be focusing on what we know can work in reducing our dependence on foreign oil: namely, building effective public transportation networks tied to appropriate land-use planning.