After Exxon pulled the plug on algae biofuels development last month in an attempt to refocus on the "basic science" of algae growth, CEO Rex Tillerson explained that the company's $100 million investment might not pay off for 25 years.

Not exactly a ringing endorsement for the near-term potential of algae-based biofuels.

The lack of any significant commercial scale for algae biofuels points to the difficulties in scaling up production: factors such as problems engineering algae strains, failure to get dense algae yields, high water and energy input costs, and soaring capital costs for commercial plants are all dogging producers. But there are still a handful of companies chipping away at those problems, even if biofuels at scale are still a decade or more away.

In order to stay afloat, algae companies have relied on markets other than biofuels. Pharmaceuticals, cosmetics, fish feed and biochemicals are some of the products that offer near-term revenue potential. But there are some interesting applications emerging that are creating new opportunities for algae producers.

OriginOil is one of those companies that has moved into new markets. Since its inception in 2007, OriginOil has shifted its focus away from biofuels production and toward licensing its technology -- a two-step process that separates organic matter from water -- for wastewater cleanup in the fracking industry. The move is an example of what some are calling "next-wave investing" among cleantech companies looking for a unique path to market that doesn't involve building an entirely new infrastructure.

"It's all about figuring out a way to monetize the core technology," said OriginOil CEO Riggs Eckelberry in an interview about the company's changing business model.

One of OriginOil's more interesting projects is called "urban algae," which Eckelberry calls a potential "game-changer" for wastewater treatment and energy efficiency in the built environment.

At the end of last year, OriginOil partnered with the wastewater company Ennesys to install and test a hybrid wastewater/heating system at a building near Paris. OriginOil built a small, modular "entry-level" harvester that processes a gallon of wastewater per minute, and Ennesys integrated the system. Early test results show that the algae are able to clean up 99.9 percent of waste in the water. The microorganisms also generate heat while consuming that waste, which could be used to offset heating needs in a building.

Eckelberry said the application is very promising for OriginOil. But calling the technology a game-changer is like calling algae biofuels a game-changer -- it's still way too premature.

The project in France is extraordinarily small. And while Eckelberry wouldn't talk about specific costs, he bluntly said that if it weren't for a French law requiring all new commercial buildings to process their own wastewater and to be net-zero energy consumers by 2020, "no one would bother doing this."

Still, Eckelberry said the company is concentrating on building more modular systems to prove its concept and carve out a new niche where the market allows.

"The current stage for us is shipping more wastewater treatment systems," he said. "That system will be a prototype of how waste can be sanitized and separated. The algae industry is trying to move toward monetization, and it's all about building a new revenue stream."

There are other examples of urban algae starting to emerge. It's still uncertain, however, if they have the potential to scale.

In April, the world's first building with an "algae skin" was completed in Hamburg. The building features 129 bioreactors mounted on the southeast and southwest walls that circulate nutrients and carbon dioxide to feed algae. The algae blooms are harvested and fermented at a local power plant to generate methane for electricity production. The algae panels also capture waste heat in a manner akin to solar thermal panels for use in the building's water or geothermal system.

The problem is that this type of algae system is extremely costly. In a New York Times story on the Hamburg project, one expert estimated that the levelized cost of electricity from the $6.5 million system is seven times higher than solar PV.

Another California-based startup, Grow Energy, wants to build residential algae bioreactors that look like PV panels. The system would harvest algae grown on a rooftop and combust it in an on-site generator for electricity production. This type of distributed system would be even harder to integrate. (How the company will manage a system with all those moving parts while building a maintenance and installation infrastructure from scratch is a big unknown -- particularly as solar PV costs continue to drop and the solar market rapidly matures.)

The problem with algae technologies for buildings isn't that they're uncompetitive with conventional fossil-based technologies. It's that they're far more expensive than conventional alternatives like solar PV, solar thermal, energy-efficient boilers and onsite water recycling.

So until more governments start crafting strong net-zero building laws like France's, algae companies will likely be sticking closer to pharmaceuticals and cosmetics than the built environment.

Here's a video produced by OriginOil last year on its project with Ennesys in Paris.

OriginOil Ships First Production System to Paris-Based Ennesys from OriginOil, Inc. on Vimeo.