Municipal wastewater tapped to grow oil-rich algae, prevent ‘dead zones’

Source: Katherine Ling, E&E reporter • Posted: Monday, April 6, 2015

Wastewater could be key to growing cheaper oil-rich algae for biofuels instead of feeding “dead zones” of algae blooms that choke aquatic life in lakes and bays, according to a new report from Rice University.

In a five-month study of a dozen open-topped tanks of filtered wastewater from Houston Public Works, the group was able to grow monocultures of oil-rich algal strains while removing 90 percent of nitrates and more than 50 percent of phosphorus from the wastewater, the scientists said. The report was published in the journal Algae.

Algae is currently being cultivated for producing higher-value, lower-volume products for pharmaceuticals, nutritional supplements, cosmetics and other products, with the eventual goal of creating biofuels that could replace petroleum. But the industry must bring down production costs first.

The algaculture industry also relies on chemical fertilizers to grow the algae, which bites into their profits and does not support an industry that aims to be a “greener” alternative to traditional chemicals and fuels.

Meanwhile, algae blooms have become a growing issue for states near large bodies of water, as an abundance of nutrients like nitrates and phosphorus pollute the water as a result of industrial, municipal and agriculture fertilizer runoff.

A toxic bloom in Lake Erie shut off the taps to Toledo, Ohio, for more than 48 hours last summer. The Gulf of Mexico currently has a dead zone of about 6,000 square miles that U.S. EPA and Mississippi River Basin states recently said would take at least two decades to shrink to 2,000 square miles. To reach that goal will require reducing the amount of nitrogen and phosphorus entering the Gulf of Mexico by 45 percent, according to EPA (E&ENews PM, Feb. 12).

While the idea of using wastewater as feedstock for productive algae had been considered before, there were concerns about using open tanks and whether the desired algae could be grown cost-effectively, according to study co-author Evan Siemann, a biology professor at Rice University.

“We were surprised at how little had been done to test these questions. There are a number of laboratory studies, but we found only one previous large-scale study, which was conducted at a wastewater facility in Kansas,” Siemann said.

Siemann added that wastewater treatment facilities currently have no cost-effective means of removing large volumes of nitrates or phosphorus from treated water, so algae production with wastewater has the potential of solving two problems at once.

The group will follow up this study with further work on whether the temperatures of the tank or the starting levels of the nitrogen and phosphorus had a significant enough effect on the algae production and nutrient absorption to make the process more enticing to investors, the scientists said.

The Rice study was four times more effective at removing the phosphorous than the Kansas study Siemann cited, for example, according to the research team.