We take turning on our taps to get clean drinking water for granted in many developed countries but the truth is, clean drinking water is a luxury in many countries of the world. However, the process of cleaning the water into drinkable form is easy enough to understand for any person. Trevor English, a Civil Engineer, demonstrated this when he built his own miniature water purification plant with the help of two of his engineer buddies.
They started off with 55 gallons of murky river water and made it clean by following simple processes of coagulation/ flocculation, sedimentation, disinfection, and filtration. These are the basic steps that all water treatment plants follow, no matter how big in size they are. Their goal was to get clean water and kill off all bacteria and pathogens in which they succeeded. Take a look at how they achieved this in the following video. The whole process is also explained at different stages in this article.
Coagulation or Flocculation is the process of removing all of the clays, silts, and dirt particles suspended in the water. To remove these, English and his fellows added Aluminum Sulfate (Alum) which causes all the tiny dirt particles to stick together. They built a rapid mix tank or coagulation chamber where the water and the chemical were stirred together and outflowed into a basin where the particles were allowed to stick and settle to the bottom so that they could be separated later.
Actually the process of settling down of particles is called sedimentation and is performed in a sedimentation basin. This process took the team about 2.5 hours and later the water was allowed to flow over a weir. The cleanest water is on the top of the sedimentation basin and the weir makes sure that only clean water is moved to the next step. The water leaving this basin looked very clear, and virtually all sediment had been removed from out alum addition.
After the weir, water travels through a short tube into a plug flow reactor. It is built like a maze to increase the amount of time water spends in the system. Chlorine was added to the water to kill off all the preliminary bacteria. The chlorine must be added in specific concentration as adding large amounts of it can be harmful as well. The tap water in the USA also contains traces of chlorine. This whole process is called disinfection and takes about 1 hour.
Sand Filter (Filtration)
The sand filter is exactly what it sounds like, a basin with different grain sizes of sand that caught any other particles or contaminants that weren’t picked up in previous treatment. Sand filters are used in virtually every water treatment plant as they are the most effective way to clean water. This is by far the longest part of the process and takes about 5 hours for the water to flow through.
Final Clean Product
The outflow of this miniature water treatment plant was improvised but it got the job done. Small pieces of torn off t-shirts directed the water into holding basin from where it was pumped into a 55 gallon drum via small pumps. The team started off with 55 gallons of dirty water with visibility of little over an inch and got 42 gallons of clean drinking water which could have been increased if the water losses in the system were prevented.
The best part…
The best part about this system is that it is totally portable and you can take this anywhere you want to. It requires a little bit of knowledge of chemistry and engineering and it is inadvisable to do water purification without proper knowledge but if you wanted to, you could purify water for a small village with this small purification plant.
Exact numbers: In total, they added 10.4 mL of 6% bleach, which worked out to a final concentration of around 3.15 mg NaOCl in the final treated water. For alum, they added 62 mL of 10g/L Alum solution every hour. This worked out to a total of about 1.3 L of Alum solution needed. The final testing flow rate was about 14 L/hr or 4 mL/min.