Imagine you are on a conveyor belt. The conveyor belt is circling around a box of pizza. Every time you get close enough, you take a slice of pizza. If the conveyor belt moves too fast, you can’t grab the pizza. But if it’s too slow, you’ll starve and the pizza won’t be nice and hot anymore and it might even start to grow mold. This is how the activated sludge process was explained to me in my first Environmental Engineering lecture many moons ago.
I went to see Moana with my family shortly after it came out. My sister will tell you that I keeled over laughing at the part where the crab says, “Oh I see, you used a barnacle covered in bioluminescent algae as a deception!” I can’t tell you why I cracked up. The truth is I’m not really sure why. Maybe I was surprised that a crab recognized the bioluminescent algae and barnacle as part of his environment, or that he pronounced algae the same way my biology professor did all semester.
When I visited the famed underground cistern of Istanbul, which once provided a constant water supply for a massive palace, I noted that fish swam around in the water to “reduce bacteria”. Of course we’ve all owned algae eating fish at one point or another that kept our goldfish tanks clean, but these were massive fish that took the form of catfish or maybe even koi. After much wonderment I had the chance to look further into this method of decontamination myself. It turns out that even scientists debate the effectiveness of using fish to clean water. With a little reading I discovered that fish might consume algae in reservoirs in developing countries, but they certainly don’t purify water enough to drink it. Fish catalyze a reaction that reduces ammonia from rain water, making the water more suitable for life but not quite drinkable. Frankly, it sounds like an experiment I’d really love to try. You can read more about fish and their capabilities to clean water online. Here is the link to a discussion forum for this topic.