Most people call it pond scum; but to David Sinton and his research team at the University of Toronto’s Faculty of Applied Science & Engineering, it’s the future.
Pond scum—the greenish slime that forms on the surface of ponds and lakes—is made of green algae and cyanobacteria (once called blue-green algae). These photosynthetic microorganisms use sunlight and water to convert carbon dioxide into chemical products like sugar, giving off oxygen as a byproduct.
Most microscopic algae are usually barely visible in the water they inhabit; but during warm weather the algae can rapidly grow to form a large mass called an algal bloom that tends to concentrate on the water’s surface. Blooms usually occur during the summer and early fall, when temperature and light conspire to generate optimal conditions for massive growth. Dense blue-green algae blooms can make the water look like a bluish-green pea soup, or a shiny paint slick.
Green algae blooms are often bright green to yellow-green, forming a bubbling soup of growing and dying algae. In enriched streams and lakes, Cladophora or Spirogyra (known sat string algae) may form long skeins of green “hair” draped over rocks and waving with the current, like in the opposite image.
Fresh blue-green algae blooms often smell like fresh cut grass; older blooms often smell like rotten garbage. Most algae blooms are short-lived and will break down in a few days or weeks. Blue-green algae (cyanobacteria) are generally harmless; however, under certain circumstances some may produce toxins that can be harmful to humans and animals.
It’s generally thought that cyanobacteria oxidized the early reducing atmosphere, precipitating the “rusting of the Earth” (the Great Oxygenation Event) some 2.3 billion years ago. This would have dramatically changed the composition of life forms on Earth as increased oxygen stimulated biodiversity and complexity while negatively impacting anaerobic life that had previously flourished. Chloroplasts evolved from cyanobacterial ancestors via endosymbiosis in more complex eukaryotic cells and multicellular organisms.
Fast forward to the present day and why David Sinton is interested in pond scum.
Sinton’s research is focusing on optimizing the growth of these photosynthetic organisms, whose high levels of fat and oil could be refined into biofuels, and sugars fermented into ethanol (see two previous articles on this topic: growing fuel from algae and flying algal ships).
Researchers are still figuring out what the optimal conditions for growth and production are. Variables include light intensity and duration, light spectrum, nutrient and CO2 levels, temperature and many more. To best address the range of variables, Sinton’s team used microfluidics and optofluidics (two fields that look at how fluids and light can be conducted through very small channels or optical conductors) to design what they call a “lab on a chip”: an array of hundreds of individual chambers in which the microorganisms can grow.
“Each chamber sits on top of a single pixel from an LCD screen, allowing the researchers to control the light conditions with precision,” writes Tyler Irving of UofT Engineering News, February 16, 2016 issue. “The chamber acts as a self-contained greenhouse where the organisms can be grown on blue light, red light, bright light, pulsing light and a host of other possible conditions.” The next stage, says Tyler, is to expand the device and allow researchers to vary CO2, O2, and nutrient levels across all chambers. The platform could be expanded to thousands of chambers, allowing for simultaneous testing of many combinations of factors to find the best conditions for fast growth, oil accumulation or any targeted outcome for a given species of algae or cyanobacteria. The results will help researchers design large-scale facilities for microbial energy production.
Graham, Percival J., Jason Riordan and David Sinton. 2015. “Microalgae on display: a microfluidic pixel-based irradiance assay for photosynthetic growth.” Lab on a Chip 15: 3116-3124.