Backyard Aquaponics
A place to discuss aquaponics

I am attempting to build a photobioreactor, in other words a water-filled system for growing algae. I'm using a series of 1.5" clear tubes to hold the water, the bottoms of which will connect to a PVC manifold I've assembled by gluing a bunch of tees together. The nominal pipe/fitting size I'm using is 1-1/4" schedule 40 PVC.

There are ten tubes (currently) and I need to be able to bubble air through each tube to deliver carbon dioxide to the algae. I don't know how to run the air tubing into the manifold underneath each tee to deliver the air bubbles. The tubing and fittings I'm using for air are actually 1/4" drip irrigation parts.

I'm attaching some photos of what I have tried so far...

First attempt: drilled 1/4" holes, pushed tubing in, silicone around each hole. Result: leaks
http://i.stack.imgur.com/3oS4m.jpg

Second attempt: Enlarged holes slightly (5/16"), siliconed the "misting" drip irrigation fitting right to the hole. Result: came apart during handling.
http://i.stack.imgur.com/fjIVl.jpg
http://i.stack.imgur.com/oo30P.jpg

My next attempt was going to involve enlarging the hole and tapping 1/4" NPT threads into the wall of the fitting, and screwing a barbed adapter directly in. The reason I didn't do this from the beginning is because of the cumulative cost of all the extra fittings. I'm looking for other suggestions or perhaps some part or fitting I've not heard of that will make this easier.

WHY

What about one (or more) of those long thin air stones in the manifold with the gas supplied from above. No need to drill holes

Why what?

why not?

I still have the problem of how to pass the tubing into the internal part of the manifold. Also, i've already drilled the holes in the PVC ...

what sort of algae? stringy algae?

why not make an algae scrubber instead?

this is to grow feed i gather.

The tapped and threaded version will work, might need to use some teflon tape. Another way to do this would be to use grommets and push the airline through the grommet, works like a uniseal - something like these - http://www.amazon.com/Botanicare-6mm-THG-Rubber-Grommet/dp/B003B5RKIQ. You should be able to find them at some local hydroponic stores up there

Tapping 1/4" NPT threads in would be the way to go, I'm about to build something similar I've got 2 - ACO-003 35W 220V Electromagnetic air pumps that are starting to get a bit noisy so I'm building a 25mm PVC manifold to reduce the total number of airlines & air stones and have less pressure on the pumps. The reason I run 2 pumps is in case one breaks down, with a manifold I can have less air stones because all pumps will use the same air lines & air stones.

By running both the air pumps and the backup 12v air compressor all into a manifold I can reduce the number of air lines and air stones by 2 thirds. There are 6 air lines running from each pump plus the compressor, the 6 air stones from the compressor only run when there's a power outage by using a manifold I can lose those 6 backup air lines and half of the others.

I will tap 1/8 BSP Male Thread Pipe Fitting to 6mm Barb Hose Tail Connectors into 25mm PVC Pressure pipe, if I use the plastic fittings they can be glued in place, and as Scotty said the metal fittings will need Teflon Tape.

The plastic fittings are quite strong and would take a lot too break them off plus they have a rubber seal so I will probably use the plastic fittings.

Thanks for all the replies. I did a quick test where I took a 1-1/4 Spigot x 1/2 Slip reducing bushing, and drilled out the end-stop in the bushing, which allowed me to push a 1/2" PVC pipe all the way through the bushing. I then drilled and tapped a #10-32 hole into the wall of the 1/2" PVC and threaded one of my drip irrigation misters into it, which fit perfectly. with this configuration, I should have no issues getting the air inside the manifold because the reducing bushing can be glued into the end of the manifold and the 1/2" pipe can have a threaded fitting glued on the end for connecting my air line to.

The next "problem" is that the aquarium air pumps I have don't develop enough pressure to bubble air when there is 4+ feet of water sitting on top of the air outlet. I'm considering purchasing a oilless compressor designed for airbrushing, because they can be used for things like cake decorating so i'm sure it won't introduce any contaminants. A regulator should allow me to tune the pressure for exactly what I need.

How much do you think adding the air at the bottom of the column will help? I'm thinking that it will make about a 12% difference (based on 1 ATM = approx 33 ft depth of water.).

4/33 = X/1 so X = 4/33 or roughly 0.12 (12% of one atmosphere)

Assuming I did this right, it would be tempting to add the air near the top so that it rises against the current before the water enters if there is a way to do this. Just food for thought.

Cheers

Hi
It is late on a Friday night so I maybe be a bit off base.
You mentioned CO2 so I thought you were using compressed gas!
Consider this:
A small pump on continuos flow with a Venturi.
This will supply air to the individual tubes
The manifold is at an angle: say 45*. To enable bubbles up each tube.
Vary the angle to get air to each tube.
An external open ended tube as a sump. This will set the water height in the glass tubes. The water height will be constant but the tube length will vary.
Just a closed loop pump return system..The air from the Venturi is the thing you want