Algae and Wastewater: A Love that Will Not Die

As long as humans continue to pursue large scale industry, agriculture, and continue to live in cities, there will be wastewater. But because humans like clean water, they are always looking for better ways to turn wastewater back into clean water. As it happens, algae will thrive on all types of wastewater -- municipal wastewater, agricultural runoff, industrial wastewater, and so on. This love affair between algae and wastewater might lead more clever humans to find ways to kill three or four birds with one stone.

Every day, the oil and gas industries produce millions of barrels of process water during the refining process. This stream, which usually ends up being injected back underneath the ground, is considered waste. The Center of Excellence for Hazardous Materials Management (CEHMM) in Carlsbad, N.M., however, has found that the characteristics of this “produce” water are excellent for the cultivation of oil-making algae. “This is a nearly inexhaustible resource that nobody wants,” said Douglas Lynn, executive director for CEHMM.

...using waste water from either the oil and gas industries or the unutilized sources from underground reservoirs put no pressure on domestic water supplies. This allows the process to avoid the criticisms which claim that biofuels add pressure to natural resources instead of alleviating it. _Bioenergy

Even NASA is getting into the wastewater algae game, with a proposal to grow algae in large plastic bags offshore:

We're going to deploy a large plastic bag in the ocean, and fill it with sewage. The algae use sewage to grow, and in the process of growing they clean up the sewage," said Trent.

It is a simple, but elegant concept. The bag will be made of semi-permeable membranes that allow fresh water to flow out into the ocean, while retaining the algae and nutrients. The membranes are called “forward-osmosis membranes.” NASA is testing these membranes for recycling dirty water on future long-duration space missions. They are normal membranes that allow the water to run one way. With salt water on the outside and fresh water on the inside, the membrane prevents the salt from diluting the fresh water. It’s a natural process, where large amounts of fresh water flow into the sea.

Floating on the ocean's surface, the inexpensive plastic bags will be collecting solar energy as the algae inside produce oxygen by photosynthesis. The algae will feed on the nutrients in the sewage, growing rich, fatty cells. Through osmosis, the bag will absorb carbon dioxide from the air, and release oxygen and fresh water. The temperature will be controlled by the heat capacity of the ocean, and the ocean's waves will keep the system mixed and active. _Wastewater

Of the four main pillars of algal fuels,

1. robust growth of desired species
2. harvesting of crop
3. separation of oil
4. refining of oil to fuel

considerable research is going into each one in the effort to cut costs and increase yields. Eventually, microbial fuels will be one of the factors to drive demand for petroleum down to almost nothing. Algal fuels will be a big part of overall microbial fuels production.