LAP - Purifying Water With New Technologies and Algea




Introduction: LAP - Purifying Water With New Technologies and Algea

About: I'm a French student that builds stuff, electronics, mechanics... I'll post about the stuff I build or programm. I also repair phones and have a YouTube channel where I explain how to repair pretty uch ever...

This Instructable is kind of a story where we will show you how our project has evolved through the year. Our project counts a few big blocks that we'll present in each Step, so tag along ! You don't have to read the whole intro, we'll present the technical features in the next steps (step 3 it comes to technical points).

So I'm in this Lycée in Toulouse, France, in the ingeneering section, and in order to have our degree, we have to make a project throught the year. This project has to include ingeneering, be a useful project, that can maybe someday realized. We made a group of 4 and looked for an idea, that was September 2015, we had 70 weeks to finish the project. We started looking at "what does the world need to resolve its problems". First results on Google were the need of food and water in poor countries. We found out that solutions to purify water exist, but they cost, sometimes use polluting products, cost a lot of energy, or a lot of time, and these solutions are sometimes hard to implement in foreign countries where they are needed.

We compared all the solutions that existed, as chlorine treatement, nitrogen treatement... But we had an idea: we all know plants feed on nutriments, and wastewater is full of nutriments ! What if we used a plant in order too purify wastewater ? Well the principle exists, its called "biofilter" (in french we say "phytoépuration"). Some water stations actually use these ! Well maybe we could use this too, but we needed something innovative. We thought about algea. They are basically 30um seaweeds. They live in water and reproduce astonishingly fast ! (their biomass doubles every 8-12h) That also means they feed on nutriments, but like, a LOT of them.

We soon found out Spirulina was a good candidate for our project. We all know about Spirulina don't we ? Maybe not. It's a green algea that people eat for its extreme concentration in protein (65%) and other good nutriments for you. You can buy these in pharmacies or Whole Foods kind of shops. Purifying water with a edible algea ? That souds good.

Now let's build something to contain these algeas ! Then we'll need a solution to extract the clean water...

Step 1: Building a Algea Harvester

As we searched ideas to make an algea incubator, we found out about Alg&You (, wich produces Spirulina incubator, but only to eat them afterwards. We went to their labs, talked about the projects, they showed us how their incubator worked and gave us a Spirulina sample (a liquid, living one) to start our own batch !

Now we had to build an incubator that would satisfy all of the Spirulina's needs.

On the first picture you can see our first incubator. It was basically an aquarium with an Aquarium Air Pump and a LED strip giving it light 18h a day (regulated with an Arduino). That wasn't technically hard to make, and the Algs died a week later.

Second try, a few months later, as we got a new batch of living Spirulina, we buit a better regulated system, this time with heating integrated, relays to command the air pump, the heating system (37°C=98°F) and the LED strip.

We used 5L of living Spirulina for 5L of nutriment mix (made within the school's lab) and 20L of tap-water (rain water is best) at about 30°C (=86°F). Little tip: make a powder mix, then only when you are about to start a batch mix it with water, if your water is not pure, all the "other" algea will develop and you don't want that.

I won't put the plans for this, because we made something better right after that.

Step 2: Purifying the Water

Now here we come. First I have to show you the global plan. I tried to translate it as best as I could.

We use 2 Solenoid valves to control the water flow. The activate coal filtrates all the chemicals, heavy metal, and give a clear color to the water. The UV lamp (357nm) is C category, it means it can 'desintegrate' micro-organisms (bacterias...). Theorically we should have almost pure water after our treatement. We made a few experiences and soon realized our algea worked: the concentration in Nitrate went down as the Nitrites went up (nitrites are made by nitrates when algs eat them). Then we showed that our activated coal would take away all the color (took a glass of red wine, became barely pink). For the UVC, we used Anis Ben Messaoud's thesis (

Now we need to make all of this automatic.

Step 3: Arduino - Preparation

Here is the intresting part. I mean theory is cool but not very fun for someone that likes to build, even though it is always necessary, how can people do projects otherwise ?

First pic, that's how small I managed to make this. Mashed it in a cardboard box, I'm sure I could've made something classier.

Second pic, thats the whole "keeping-these-algeas-alive" project, the rest is the WHOLE thing. The Fritzing is very full and the Arduino code is fairy big.


- Arduino nano (actually it's a chinese copy I got for 1$)

- LCD 2x14 I2C (about 5$ in Europe, 2$ in China) you know a component is I2C when it only has 4 wires: +5V, GND and 2 communication

- 1 led strip (I used 12V) (5$)

- a few leds to have extra indicators if you don't have enought room on the LCD screen

- 5 transistors: choose them accordingly to your components (check the schematic), use an Ampmeter to know how much current your comonents need then check your transistors datasheet. You can also use W/V=A (24W/12V=2A)(.10)$

- photoresistor ( it's okay to buy a few they are fragile (.06$)

- heat sensor (used LM35) get a few if you can they break easily (.10)$

- water sensors (x2) ( (1$)

- a little buzzer (1$)

- 5 relays (12V)(5$)

- 2 solenoid valves (8$)

- 12V DC power source (3$)

- resistors

- lot of wires and breadboards, or you can solder everything if you like !

Step 4: Wiring

Here are the schematics, I'm sure you guys know how to read these. I tried to use red for +5/12V and black for GND, colors are usually connected to Arduino. (Note: the step motors are red and black on Fritzing but they are communication wires.

Problems encountered:

- using breadboard and plug-n-play wires is not great when you have a ton of components, I keep having disconnections. I you can, please do solder everything in place.

- all these components use current. A simple USB port is barely enought (0.5A), you can try it yourself, the LCD screen will be barely lit, the values of the components wrong, leds flickering... I used a DC power source of 2.5A (phone charger) and everything worked fine.

You'll want to be very careful with polarities, use color cables to make it easier ! I used a lot of phone cables (I had a few meters in my garage).

Also, I made "connectors" for my exterior components (heat sensor, light sensor, water sensors, solenoids, motors). These female connectors are just peeking out of my box, and when I install my system, I can just plug in my components.

In order to make a waterproof heatsensor (because you'll want the water temperature) you can use thermal jacket or pistole glue.

Step 5: Coding

I won't detail the code here, I've posted it on GitHub ( and I will comment it in english. For now the comments are in French (I had to use french for my teachers and my group).

Don't forget to download the libraries and to add them ! (In Arduino IDE > Croquis > Include library > Add ZIP)

The code is fairly easy, long but easy. Basically:

- need a constant temperature of 34-37°C

- need 18h of good light per day

- need agitation (air pump) 18h a day (same time as light)

- let the algs feed on the wastewater for 3-4 days then open the solenoid

- activate motors for filter (I haven't detailed it here)

- activate UV lamp (10 min for each "pack" of water)

- activate last solenoid to let the purified water go out.

I use the water sensors to know where my water is and what level, is use them so I won't have any leaks and stuff.

The LCD show lots of infos as teperature, if its day or night, lot of light, water levels...

I added LEDs for 'uv lamp ON' or 'motors ON'....

Step 6: Almost There

Now that I have a working code and working electronics, I just tried to compact all of this, in my little box.

I also decided that'll be cool to have a "live" feature I could have on a website of something, so I use a little Python program. Look at the 5th pic to have an idea of the result. It's also uploaded on GitHub ( under the name "". It's a beta so it's not perfect. You'll need a few libraries as MatPlotLib, numpy and drawnow. You'll find tutorials on google to install them, it's fairly easy. I'll maybe do a "package" later, to simplify the installation.

I reccommend using this uy's website ( as I directly used his work in order to realize mine ! Thanks to him !

Now you guys can use this, a part of this, modify it, give me ideas, share it, improve it !

If you have any questions, I can send you work files, code, explanations...

Thanks for reading !

PS: You've wondered what 'LAP' stands for ? "L'Aqua-Potabilisateur"... Potabiliser in french means pretty much "making it drinkable"

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    2 Discussions


    4 years ago

    Purifying water with an edible algae does sound like a good idea. I just wonder about eating a plant which was grown in potentially contaminated water. Would not the plant also then be contaminated?


    Reply 4 years ago

    Oh I did forget to specify this, the downside is that you can't eat these, BUT you can use them as biomasse ! I think it need a treatement in order to use it as a fuel, I haven't studied this aspect very much. Also, I've forgotten to mention that this project uses very little energy: the peaks are when the heater, agitator and LEDs are on at the same time. Arduino is about 2W; LEDs 8W and Heater 20W.