Submerged, rotating cylinder algae scrubber (with video)

Update.
Screen growing lots of green algae, but it seems to be turning white. The intensity was set to 60% and the duration was 12 hours. I updated the code a while ago, but never uploaded that code to the controller. Also, the algae hasn't been firmly attaching to the screen, it didn't come off by itself while in operation, but could be easily removed just by fairly gently rubbing it off.

Today I updated the controller with the new code and thoroughly cleaned the screen with a toothbrush. It's hard to know why it didn't attach firmly, I suspect it's either due to the 3d printed screen itself, the whiting from the dead diatoms/hair algae below the GHA or a combination of the two. The algae from a previous experimental scrubber had no problems attaching to the 3d printed screen, but the shape and print size of that screen were different.

The scrubber is now running with a clean bare screen at 50% at 6 hours per day, half the previous duration. Hopefully this will stop the whiting. I'll be getting the laser cut pieces for version four tomorrow. I had major issues with trying to get the LEDs to fit to the heatsink I wanted to use, so I'm getting a MCPCB made to make things easier there. I'll be printing a new screen for v4 as the dimensions are a lot different to this scrubber, and will make changes to (hopefully) ensure the algae can attach firmly. I'll run both scrubbers side by side and compare the growth results.

 

10th week update:
Nitrate: 5ppm
Phosphate: 1.21ppm

Not much to report. Screen is still pretty much bare after it was cleaned a few days ago.

 

11th week update:
Nitrate: 10ppm
Phosphate: 0.86ppm

Again not much to report.

 

12th week update:
Nitrate: 40ppm
Phosphate: 1.04ppm

Took the scrubber offline yesterday. Revision 4 will be up and running soon so will start testing with that and post some pics. I'm also putting doors on the front of the tank frame, which don't fit with the brackets on the previous version.

 

Tis, but version 4 will use nylon mesh around the cylinder, to rule out any issues with growth on the 3d printed material.

 

Update - version four up and running as of today.

Edge around the face of the screen to minimized light leakage. (More on this below)
Scrubber screen is now orientated vertically. Makes removal of the screen much easier.
Uses the traditional mesh screen to rule out issues with algae not attaching to the 3d prints.
Aluminium PCB has four deep red LEDs and one hyper violet.
PCB is housed inside the LED side. A single input to power both the controller and LEDs.

A few pics:









Short video, with the lid off:



A few notes of interest:
It turns out that opaque white acrylic...isn't all that opaque. As seen in the video, intense light can pass through the acrylic. I went with white because the company that cuts the acrylic didn't have any 2mm black acrylic in stock. Pretty annoying, so will switch back to black acrylic for any future revisions.

I'm sticking with four deep red LEDs (not 6). I did some inverse law calculations and six LEDs would have been too much at the distance the LEDs are from the screen.

The hole at the back (which the water exits from) is a 3/4 inch tap size. I don't have a 3/4 inch tap (the intake is 1/2 inch), but if the design works the I'll tap the hole so a 90 degree hose barb can be attached. It'll block out most of the light exiting the hole, and also allow for tubing to be attached, so the output can be directed away from the input.

I won't bother with including the nitrate and phosphate levels of the tank until (and if) I get some green growth on the screen.

Scrubber is running at 50% intensity for 9 hours per day.

 

It's a shame, I prefer the look of it in white. I thought it may also help reflect some light back onto the screen, as opposed to having a black interior.

Yeah hopefully. This tank has been without lights since it was set up (a few months ago). They should be up and running in a week or two. Considering the high nutrient levels in the tank, there's definitely going to be some algae growth happening...I just hope it's in the scrubber.

 

Been running for almost a week. Quick pic:

 

Thanks. If growth continues like that I'll start testing from next week. It's already much darker and thicker than the previous pic.

 

Going to give it a light rinse as it's pretty dark and slimy. LEDs are still running at 50%, I think I'll notch this up 10% each week, starting Monday.

 

Yeah way faster. I think I'll ditch the idea of using a 3d printed screen as the growth material, at least for now.

Hopefully I'll start to see some green growth in the next couple of weeks.

 

Second week update:
Looks similar to the last pic after a light cleaning a couple of days ago. I think I am starting to see a slight green tinge on parts of the screen, so I'll just leave it for now and see how it goes.
LED intensity now at 60%.

 

Had a look today and there are some detachment spots on the screen, where the brown algae has detached off the screen completely.
A bit odd...maybe the flow is too high.

 

Third week update:
Most of the brown algae has died/detached, which left bare spots on the screen. Now I'm getting some green algae growth over the surface of the cylinder.

 

Slightly early fourth week update:

The growth has been pretty weird. Green algae grows, then seems to die off.



There's plenty of nutrients in the tank and the lighting should be spot on, so the only thing I can think would cause this is the flow, maybe it's too high, and the algae can't establish itself. It'd really surprise me if that's the case...but the only way to find out for sure is to decrease the rotation speed of the scrubber and see what happens. I've dropped the flow of the Eheim pump, and now it's spinning at approximately one revolution per second (before it was spinning at >2rpm).

Will give it a good clean and hopefully will have better news to report in the next few weeks.

 

1st Week update (after the screen being cleaned).

Algae growth appearing on the screen again, this time though the algae is much darker shade of green than previously seen.