Entrepreneurs have been trying for years to get something valuable out of algae.

It has not been easy, and not just because algae are an unsightly nuisance (and sometimes dangerous, as is the Lake Erie bloom that has endangered drinking water this month).

Although algae grow prodigiously and contain potentially useful molecules — especially lipids, which can be turned into high-energy fuel and other products — extracting those molecules has proved complicated and expensive. So far, virtually the only marketable products based on algae have been high-end skin creams.

But a Nevada company, Algae Systems, has a pilot plant in Alabama that, it says, can turn a profit making diesel fuel from algae by simultaneously performing three other tasks: making clean water from municipal sewage (which it uses to fertilize the algae), using the carbon-heavy residue as fertilizer and generating valuable credits for advanced biofuels.

If it works, the company says, the process will remove more carbon from the atmosphere than is added when the fuel is burned.