World Water Day is on March 22. This year, the focus is on used water and what we can get out of it. Because we preferably like our water cold, clear, and clean. Once we have used the water, it no longer meets these requirements. Then we usually want to get rid of it as quickly as possible. But in fact, it is this used water that is the valuable water. We do not want to drink it or wash in it, that's true. It is not very appealing to look at, that's true. But it contains a lot of nutrients that we just flush away. So many nutrients, in fact, that it creates problems where it ends up. The ocean is unique when it comes to receiving nutrients. Because there is enormous production in the sea, and it needs lots of nutrients. We are used to the ocean absorbing everything it gets. But even here, it can be too much. Some of us may remember the algal blooms at the end of the 1980s. It was the dinoflagellate Chrysochromulina polylepis, which first bloomed along the west coast of Sweden and then followed the currents along the coast of Norway. It killed or damaged almost everything in its path, including fish, shellfish, and algae (seaweed and kelp). The bloom was due to overly nutrient-rich water, favorable temperatures, and other conditions being conducive to a massive bloom. There have also been several such blooms of different types of algae, but none with such extensive damage. In Northern Norway, we are more sparsely distributed, and there are fewer of us, so we are not as exposed. But even here, it is important to limit the discharge of nutrients.
Freshwater does not have as high production as seawater. Neither are mechanisms like tides, changing currents, and wave dynamics present, at least not to the same extent as in seawater. Therefore, freshwater is much more sensitive to nutrients than seawater. Especially phosphates lead to eutrophication in freshwater. In the area around Mjøsa, almost only phosphate-free detergents are used, which, together with other measures, have had dramatic effects on the water quality in the lake.
It is important to take care of water quality, both in rivers, lakes, and especially in the sea. If there are too many nutrients, eutrophication occurs, leading to overgrowth in the water, which becomes brown and murky, and dead plants and animals sink to the bottom. In the bottom sediments, bacteria break down the dead material. These bacteria consume the oxygen in the water. In the bottom sediments themselves, anaerobic decomposition processes take place. The result of these processes includes hydrogen sulfide, a toxic gas that smells like rotten eggs. The water becomes toxic and oxygen-deprived.
The same can happen in the sea as well. In fact, it is normal in threshold fjords where there is no exchange of bottom water beyond the threshold. Organic material sinks down and forms bottom sludge. This decomposes without oxygen and makes the water toxic. Occasionally, such water can be stirred up and come up from the depths, causing fish deaths. The discharge of nutrients from sewage and runoff from agriculture can pollute large sea areas and disrupt the natural growth cycles in the ocean. This can lead to algal blooms and oxygen depletion.
There are several ways to treat wastewater. The simplest is to let it flow into a tank so that the solid substances settle and form a layer at the bottom. The water then continues and infiltrates into the ground. This is how a septic tank works. That system works in sparsely populated areas. In more densely populated areas, a communal treatment plant is made. This means collecting the wastewater from several houses and treating it in a shared facility. Then it is also possible to further increase the level of sedimentation by adding a substance that causes the smallest particles to clump together so that they settle more easily. This can be combined with mechanical filtration. Sand filters are effective, but they take up a lot of space and require much work to clean. One method that produces almost completely clean water is to let the water trickle over bio-bodies, plastic units with a large surface area, while air is blown through the system. This creates a bacterial layer, a biofilm, on the surface of these units. This bacterial layer consumes the nutrients. Any pathogens are also consumed and deactivated. The bacterial layer on the bio-balls grows and must be removed periodically. Then, the bio-balls become ineffective until they develop a new bacterial layer. Therefore, this is usually done as a continuous process where a certain number of bio-balls are cleaned at any given time while the remaining ones continue to perform their function. The material removed from the bio-balls is a good fertilizer and soil improvement product. The same applies to sludge from sand filters and septic sludge, though following a maturation process in which bacteria and yeast break down nutrients and harmful bacteria.
Water is important! It is our most important nutrient. We cannot live without water. No animal can. Even camels and dromedaries, which can convert the fat stored in their humps into water, have to drink. And they drink a lot when they do. Some animals get all the water they need from the food they eat, but if they don’t get the water, they die. The sea is important. A large part of our food comes from the sea. As the world’s population demands more food, it is probably only the sea that has the capacity to provide this food. Moreover, a large part of the oxygen that life on Earth needs is produced in the sea.
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