An algae photobioreactor on the roof of MIT university.
The clear polycarbonate tubes are approx 3 meters high, and 10-20 centimeters in diameter.
It removes upto 86% of the NOx and 40% of the CO2 of the smokestack emissions that are bubbled through it. The algae are feeding on exhaust with 13% CO2 content. This size algae photobioreactor can't handle the entire exhaust emissions, it would need to be much larger for that.
This photobioreactor you see here on the roof of MIT, has since been dismantled and reassembled in Naboomspruit (now called Mookgopong) South Africa at a biodiesel plant.