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The organisms we highlight on this channel are all aquatic, they must be submerged in water in order to thrive.

Residing in ponds, swamps, rivers, and oceans, but also places that we don’t think of as bodies of water...places that are simply wet. When you’re a microbe, the thin film of water on a snail’s back, or clinging to moss on a tree, can be a deep well of that good stuff.

Of course, we humans are also dependent on water, in a sense...our cells are aquatic. We carry our rivers inside of us. And to fill our internal aquatic environment, we drink.

We also bathe in water, we cook with it, clean with it, flush with it, and we make things with it. And when we’re done with water, the result of our use of it is something we call wastewater: a mix of sewage, storm runoff, and other water that has, in some way, come in contact with us. And, you know, less idyllic than your local pond, wastewater is nonetheless a promising habitat for many a microbe.

That’s part of what makes wastewater dangerous, both for us and the environment. Diseases born out of bacteria, viruses, and parasites can thrive in wastewater, which may also be filled with pollutants like metals or the ingredients of our own pharmaceuticals and toiletries. And should the wastewater come in contact with different ecosystems, the combined decay of organic matter and excess of nutrients can create a chain of events that depletes oxygen from the water and affects the balance of life previously maintained there.

Dealing with wastewater has inspired engineering across civilizations, from Mesopotamian stormwater drains to Mohenjo-daro latrines to Roman sewer systems. Those have all built up towards our modern wastewater treatment systems that clean the water, a feat of engineering that is nonetheless built on microbial ecosystems whose history is much, much more ancient than our own existence. Bodies of water have to deal with pollutants, whether they be the product of local shifts in nature, death and decay, or just plain old fashioned feces.

To us, these bits of organic matter are contaminants, but to microbes, it’s a veritable buffet, leading to a process called self-purification. Bacteria, coming from the water or the waste itself, shape this self-purification, consuming organic and inorganic matter while producing compounds that benefit their neighbors. As they eat, the bacteria grow and divide.

But just because this water is full of waste doesn’t mean that the bacteria within it is immune from the drama of the food chain that dominates nature at all scales. The waste-consuming bacteria become plentiful, creating an attraction for various protozoa that have a range of dining habits. Peritrich ciliates, like Vorticella and Epistylis, use a ring of cilia around their mouths to create tiny vortexes in the water, allowing them to draw in and consume their bacterial prey rapidly.

You might also find amoebas dining on bacteria, crawling and increasing in size and number. These protozoa themselves then become the prey of multicellular organisms like rotifers, water bears, and nematodes, and the excretions of those organisms provide waste that further feeds the bacteria whose excretions provide waste that further feed the bacteria. The consuming done by unicellular and multicellular organisms helps clear the water, creating an ecosystem that doesn’t just feed, it cleans.

We are then living in a world that has its own built in wastewater treatment system, but not necessarily one constructed to handle the large volumes of wastewater created by dense gatherings of people, whether in the form of towns, cities, or industries. And so we’ve created sewage treatment plants that are, at their core, these same ecosystems recapitulated in an industrial setting, with reactors full of microbes consuming and being consumed as the particulates of waste are eaten and broken down. The primary difference between how this works in nature and how it works in reactors is that we can control the reactor, tuning the temperature and oxygen levels to keep the microbes happy and cleaning.

One of the common methods used in wastewater treatment is called activated sludge, which is sludge, but alive with bacteria, fungi, and protozoa. When mixed with wastewater, that sludge becomes a version of the self-purifying ecosystem from nature. The microbes consume the waste or each other, clumping together into particles called flocs that settle to the bottom as a new mass of activated sludge, with clearer water floating above.

The activated sludge can be removed and potentially even reused, while the cleaner water goes through more cleaning to be ready for release back into the environment. There are so many ways that we have learned from or taken inspiration from the world around us, whether it’s the colors, the sounds, or the creatures who spark our imaginations. But wastewater treatment is probably one of the most important.

Indeed, wastewater treatment is the largest industrial, reactor-based use of microbes, even beyond brewing or baking. One recent study analyzing about 1,200 samples of activated sludge from 23 countries found that there about 1 billion types of bacteria represented around the world, with only a fraction of a fraction of a fraction of a percent representing species that we have even begun to study. While not a particularly glamorous job, our modern towns and cities are built on sludge and microbes that, by just living their own lives and eating what looks good to them, make our clean water possible.

Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you as well to all of our patrons on Patreon. We are tremendously grateful that we can share our enthusiasm for microbes and also wastewater treatment with the world, and our patrons are the reasons why. if you want to see more from our Master of Microscopes James.

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