It is like the Goldilocks fable. Too much algae chokes up an ecosystem. Too much nutrients can cause excessive biological growth. The just right amount of algae can balance the system just right. An article published in the June issue of BioScience describes the early scale-up stage of a new biotechnology with environmental benefits and possible commercial potential. Algal turf scrubbers are field-sized, water-treatment systems that can extract excess nutrients from streams, canals, and lakes polluted by agricultural, domestic, and some industrial runoff. They use sunlight as their principal source of energy and simultaneously restore oxygen levels. The devices work by pulsing contaminated water across algae that are allowed to grow on screens. algal turf scrubbers produce waste suitable for use as a nitrogen- and phosphorus-rich fertilizer and for conversion to biofuel or high-value nutraceuticals. Some algal turf scrubbers can even operate in open water, thus minimizing loss of agricultural land to the systems.
The BioScience article, by Walter H. Adey of the Smithsonian Institution, Patrick C. Kangas of the University of Maryland, and Walter Mulbry of the US Department of Agriculture, notes that the need to clean wastewater and various types of runoff contaminated with nitrogen and phosphorus is immediate in many places where natural waters are polluted.
Excessive runoff of nutrients can lead to an algal bloom which is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments.
Freshwater algal blooms are the result of an excess of nutrients, particularly phosphorus. The excess of nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes, these nutrients can then enter watersheds through water runoff. Excess carbon and nitrogen have also been suspected as causes.
When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decay. The decay process consumes dissolved oxygen in the water, resulting in hypoxic conditions. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers.
The article stresses that algal turf scrubbing is not likely to ever be profitable just as a way of making a fuel crop. Although more productive than terrestrial crops, algae, like other potential sources of biofuel, are expensive to cultivate, harvest, process, and convert into useful amounts of energy. However, algal turf scrubbing could become common if the economic value of nutrient removal can be applied to the cost of building and running the units. That might depend on public policy that imposes a predictable cost on pollution of natural waters.
After noon EDT on 1 June and for the remainder of the month, the full text of the article will be available for free download through at www.aibs.org/bioscience-press-releases/.