28 February 2012

Water cleaning with sunlight

Algal turf scrubber - water purifer

Filamentous algae on rock

"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." (source: "Algal turf scrubbers clean water with sunlight," EurekaAlert)


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. Furthermore, some ecologists are worried about global supplies of phosphorus for use in fertilizer, so a byproduct of this process could become more valuable over time.

This is a both biomimetic and bioutilization. It is bioutilization because it uses an organism, algae, to perform the scrubbing. It is biomimetic because, like the products Biolytix® water filter and Eco-Machine wastewater management, it mimics a natural system. According to a BioScience article (see citation below), coral reefs often have primary productivity values 5 to 10 times higher than forests and agriculture. The primary source of the productivity-driving photosynthesis is the dense, biodiverse turf of filamentous algae that covered roughly 40% of the reefs’ carbonate surfaces. The oscillating motion caused by tradewind wave action plays an important role in this productivity. 

Algal turf scrubbers (ATS) have been used for water quality improvement since the 1980s. They integrated water flow and surge with high light intensity and frequent harvest to reach high levels of primary productivity and control water quality in a considerable variety of enclosed microcosms and mesocosms of coral reefs, estuaries, rocky shores, and freshwater systems. HydroMentia, Inc. has ATS that can handle 1 to 25 million gallons to day and when combined into a single facility can clean hundreds of millions of gallons per day.
Adey WH; Kangas PC; Mulbry W. 2011

_Berta Pérez Gumà

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