 So let's talk today a little bit about the basic processes behind the treatment of drinking water. Obviously, this is an important issue for civil engineers and for municipalities as they have the responsibility of making sure that people have water that is clean and safe to drink. So why do we want to treat the water? Well, a couple of reasons. Number one, water that has stuff in it, well, all water has stuff in it, but there's certain stuff in the water that might not taste very good and might make it unpleasant to drink. In addition, it might not smell very good and would also make it unpleasant to drink. But even more importantly, we don't want the water to be bringing with it some sort of contaminant, something that would actually make us sick if we were to expose ourselves to it as we ingest the contaminant along with the water. So first kind, there's a bunch of contaminants we would call pathogens, things that will make us ill. Among those pathogens include bacteria, viruses, protozoa, all of which are living beings which our body may not be happy to have within us and may interact poorly with our gut or with other parts of our body. And then in addition, we also have chemicals that might be within it that will have an adverse effect on our body. So water treatment is designed to remove all of these things or to minimize the opportunity for any of these pathogens to enter our system along with the water we drink. So one of the things that we consider first when we're actually cleaning up water is solids, the things that are in the water that are solid clumps. And you can sort of see here some sort of dirty water, a picture of dirty water here. And solids can be classified in a couple different ways. One of our first classification, if we're talking about total solids, we can split them into two portions, one or what are called dissolved solids and what are the one category that's called suspended solids. And generally, the difference here is whether or not the solids are greater than two microns in diameter. In other words, there's a certain size that determines whether something suspended or dissolved. But ultimately, suspended means that it's floating in the water and could potentially settle to the bottom of the water, whereas dissolved means that it's sort of permanently mixed into the water and it is unlikely to settle out or at least not in a reasonable time frame that it will stay mixed in the water and other processes need to be made to remove it. In addition, we can also separate these into categories of volatile and fixed. Volatile basically means that if we take the solids and we evaporate all the water, we get rid of all the water, we dry out all the water and leave it behind, you'll be left with your total solids. But if you take and heat those up, some of them will also evaporate if they're heated up extensively. And usually, that corresponds to things that are organic in nature, things that were created by some form of life. Maybe it is living things. Maybe it's the bodies of bacteria. Maybe it's decomposing material, et cetera. Generally, the volatile substances are ones that are more organic in nature, whereas fixed solids are things like minerals, et cetera, that are left behind, perhaps from the erosion of rocks or other things. So one of the things we'd like to do is to clean out the solids. One of the ways that we can sort of measure the amount of solids is by simply looking at the water. How clear is the water? As light passes through the water, it's intercepted by things that it runs into that it's either absorbed by or reflected from and prevents some of the water from going through. And so a measure of this is something we call turbidity, which is basically the cloudiness of the water. Now, it's sort of a mix. You can have turbidity that has color associated with it, as you can see on the right-hand side here. There's one that's relatively brown, but it does not have to have color. It really has to deal with the opacity, how easy it is to see through. And usually, if we have a large amount of suspended solids or dissolved material, those will both increase the turbidity of the water. So turbidity is one of our standard measurements of how, well, definitely how clear water is, but then it also corresponds to how clean the water is. So solids in the water, one of the reasons to remove them is because they often carry pathogens. They'll either have chemicals mixed in them, but more frequently, you'll have bacteria or viruses or other things that are either attached or sort of hide in the different particles that can't exist very safely or easily in the water itself, but are more protected by being attached to or hidden in the nooks and the crannies and the crevices of the particles that are within there. So that's one of the reasons why we actually want to remove solids as well is because they are typically carriers from any of the pathogens we're concerned about. So here's the general process for treating drinking water, okay? The steps are all listed here. You'll see in the upper center here, we have a water source, a lake or a reservoir that we draw the water from, okay? And then we go through a series of processes. The first process is something called flocculation, which we'll talk about in a little bit, okay? Followed by sedimentation, which is a timely process where we let the water sort of where the sediments come out of the water, then filtration, aeration, which is not shown here, disinfection, and finally, we store the water for a period of time until it's distributed as clean and usable water to homes and or businesses for your use. And so any water that you normally get out of your tap, if you're in an urban setting, will generally have gone through these different drinking water treatment processes. If you get water from a well or other source, there'll be variations of these things, but it may not be receiving the same level of treatment, although many of these treatments are based on natural processes that occur as the water flows through the ground, for example. So let's look at each of these steps with a little more detail. First of all, flocculation. The idea here is that in the water, there are lots of small particles and these small particles will have bacteria and other organisms in them. And also generally, these small particles will increase the turbidity in making the water cloudy and unappealing and as well dangerous. However, if the particles are small enough, they will generally not settle out. Even if you let the water sitting there, they're too light to float down. Gravity will affect them, but very slowly and it will take a long, long, long time before they settle out to the bottom and can maybe be separated from the water. However, most particles in water will have a charge associated with them and so what we can do is we can add flocculants, which are certain chemicals that have positive charges. And as we know, opposites attract from chemistry, so what'll happen is these positive charge chemicals will attract a lot of the negatively charged particles and they'll combine together and clump. And that's the idea of flocculation. A flock is basically a clump or a lump of materials that are sticking together. And so a number of these small particles sticking together is called a flock and then they become heavy enough to settle out of the water in a short period of time. So after we've created flocs using the addition of flocculants, then we use a process called sedimentation. Basically, sedimentation uses gravity to do a lot of the work. You simply allow the water to sit in a very still environment, slow it down until it's almost still or very close to still and at that point, there is not enough motion to sort of keep the floating flocs, the clumps in place and they will eventually sink to the bottom. And if you allow them to sink to the bottom, then what you can do is you can let the water, filter the water off the top, let it flow away. It will have less of the sediment in it, less of the flocs in it and then every so often you can actually clean off the sediment of the bottom by scraping it away and clearing it away and disposing of it. So our third process, the flocculation gets rid of most of the chunks but not necessarily all of them. Some of them may not have settled to the bottom. So the third process is then to run the water through a filter. And basically a filter, any of you have used a sieve or a colander. If you have your spaghetti mixed in with water and you pour it into something that has small holes but the holes are small enough to let the water through, I mean, small enough to let the water through, well large enough to let the water through but small enough to prevent the spaghetti from going through and then you're able to separate the two. Well, that's basically the same process. What you do is you run the water through progressively smaller and smaller filters, things that have progressively smaller and smaller holes and then things get trapped in there, the larger flocs and other particles get stuck. If you provide appropriate barrier of appropriate sizes and you can capture even protozoans and bacterium and other things and there's different types of materials you can use. Usually you start with the materials that have larger holes in them and then you progress to materials with smaller holes so larger chunks are captured outside and then smaller chunks are left behind with the progression of filters. Filters can be made of a bunch of different things, sand, plastic. Again, sometimes filters will take advantage of charge in the same way that flocculants do and use the fact that they're charged to sort of help capture not just by the size but also by the electric charge. The difference in positive and negative charge will help to retain and trap some types of contaminants and then the water continues to sort of pass through. After filtration, you have relatively clean water but another process that sometimes can be used is the idea of aeration because within the water you might have things that are small enough to be filtered through because basically there are molecules of particular types of gases and these gases are dissolved in the water but and they could be harmful, they could cause taste or odor things along those lines. Sometimes you'll find that even in households you'll have this sort of smell that smells a little bit like rotten eggs. That smell comes from something called hydrogen sulfide and that's often a pretty common contaminant or dissolved gas in many systems and you'll often sort of smell that or you can sense that it'll often collect in your pipes and that can cause sort of unwanted odors which will make it, you know, the water not really, you won't really want to drink the water. But what aeration does is it runs bubbles of common air or you can actually run particular gases through the water and what happens is then when that water, those bubbles run up and bump up against something that's dissolved in the water, that will tend to actually get freed from the water itself and sort of released into the air bubble in which case it flows to the surface with the rest of the air bubble and sort of released. And so that aeration kind of creates the surface area, lots of surface area where there's a gas fluid surface where there can be lots of interchange of the gases that are in the water, okay? And yes, you do end up adding gas to the water but in this case you can add gases like oxygen, for example, that are harmless or even a little bit beneficial to the water and the gases that are not wanted in the water are allowed to escape. Basically, the rule is that the percentage of gases within each bubble is gonna tend to balance with the percentage of gases within the water. So, you can either bubble air through or another way you can do it is you can take the water and spray the water out basically spreading the water droplets in the air. Either way, you're basically aerating the water, okay? A similar thing happens in your aquarium where you actually bubble water through with the express purpose of adding oxygen to the water so that your fish and your fish tank can actually do better. Last but not least, disinfection. Now, in this particular case, you may not have been perfect in removing all of the pathogens, all of the bacteria or the viruses or the other pieces, okay? So, what you can do in this case is you add very small amounts of chemicals that are used that will actually kill the bacteria or the other pathogens or dismember the other pathogens that are there, break apart viruses and things like that. You can either add chemicals, you can also do other processes like ozone or UV light that can kill them. The benefits of something like ozone or UV light is that they actively can kill the pathogens but then will not remain in the water. That said, the pathogens that aren't killed could come back again or continue to survive, whereas more typically what we'll do is add small amounts of things like chlorine or variations of chlorine that will remain in the water. And then, yes, the drinker will be exposed to those but those are in such low levels that they will not affect the human drinker but they will ultimately continue to kill the bacteria that might attempt to establish themselves in the water supply. Last but not least, you need to move the water out and into locations where it's going to be used, okay? So, water is generally piped from the water treatment plant and it's very clean when it leaves the water treatment plant, okay? However, it's very possible that it could be recant contaminated after it leaves the treatment plant. Often, this is the case of what happens if the water's on its way to your home and something's wrong with the pipes on the way to your home. If there's a crack somewhere, you could potentially have things leaking into the pipes although most the time leaking into the pipes is not quite a big deal if the pipes are under appropriate pressure because the pressure in the water will sort of spray out. However, leaks and cracks can actually end up contaminating the water somewhere in the use to your home. There might be things that are in the pipes that the pipes degrade that end up adding things to the water that are undesirable, et cetera. So, keeping extra disinfectant in there helps to prevent those things but it doesn't necessarily remove whatever's added to the water and so sometimes if there are problems with water, you will end up getting dirty water coming from your tap and usually that's a problem with the distribution system. Most of the time your treatment is fine, it's the distribution system that's a problem if you're getting bad water to your home. So, one of the things we're gonna do in the class is we're gonna do a little water treatment activity of our own here. We're gonna start by creating some swamp water, basically mixing some water and dirt and other things that you probably wouldn't wanna drink straight up and then we're going to mimic the process that's done in water treatment plants. We'll do some aeration. We'll add alum, which is a common flocculent and something that's easy to sort of purchase. You can actually purchase it in the spice section of your common grocery store, okay. We'll do some mixing to let the alum flocculate. You'll allow sedimentation and then you'll spend some time doing some filtering of your own and filter the water. You'll design a filter that you can use and filter the water. We will not actually go through, I mean, you could disinfect the water, but we're not going to go through the process of actually drinking the water as the sort of details about disinfecting and appropriate amounts of disinfectant would be something that would be unwise to try to mimic in the high school classroom level. So, look for the water treatment activity and hopefully this talk gave you enough information about the water treatment process.