Aquarium Filtration: Moving Bed Biofilm Reactor (MBBR)

A Moving Bed Biofilm Reactor (MBBR) is a very efficient filtration method for biologic digestion in aquaria, ponds, and full-scale water treatment facilities. The MBBR consists of a reactor vessel with a fluidized carrier media. Biota will colonize on the surface and inside the media, while the vigorous mixing makes the reactor self-cleaning by constantly eliminating old and ineffective microbes.

This project details the small-scale unit I built for my home aquarium, which is a 55 gallon freshwater tank with a 29 gallon sump.

MBBRs can be used as aerobic or anaerobic applications. Aerobic MBBRs are most common in general, and most beneficial for aquarium or pond use. By using this little unit, I'm able to decrease the ammonia concentration and slow the buildup of algae in the system. From the water chemistry perspective, a few things are happening :

- Increasing nitrification to convert ammonia and nitrogen in organic compounds to nitrates

- Reducing biochemical oxygen demand (BOD) & chemical oxygen demand (COD)

Project estimate: $15

Step 1: Gather Materials

Grab a few things:

(1) Bioreactor container, about 1/2 gallon or 1 gallon capacity. A round container is best, so there are few corners that trap media.

(1) Air stone - capable of producing medium-coarse bubbles. Avoid fine bubbles, they do not mix the carrier media vigorously enough.

(1) Weight - I used a 1" x 1/2" galvanized reducer

(1) Mini suction cup

Air hose, length TBD based on your setup to reach air pump or air distribution manifold

Air pump, air flow should equal the volume of carrier media, in cubic feet per minute

Carrier media, approximately 50% of the volume of your reactor container

"K1 Kaldnes" is the branded name, and there are numerous generic version available through vendors (like this) on Amazon. Typically this is sold by the gallon or cubic foot (which is 7.5 gallons).

Step 2: Build Reactor

Using a 3/16" bit, drill holes for

- Influent screen - use enough holes that the suction pressure is decreased so fish won't get stuck

- Effluent screen - use plenty of holes so the bubbles flow easily, without building up to larger sized "burping" bubbles

- Suction cup - double check the size of the suction cup's nub

- Air hose - standard size line is 6mm, or slightly less than 1/4"

Step 3: Add Carrier Media

My reactor capacity is 1/2 gallon, so I used approximately 1/4 gallon of a generic Kaldnes carrier media. As with anything you add to an aquarium, give it a good rinse to get rid of any dust of leftover debris.

Initially, it's recommended to use media equivalent to 30-50% of the reactor capacity. After the biologic colony is established, you could go up to 70% to increase the treatment capacity.

Step 4: Add Air Stone & Finish Assembly

Feed the air line through the designated hole, add the air stone, then pull it back into the mouth of the reactor.

Lay the reactor on its side, add the weight, and screw on the cap of the reactor.

Step 5: Install and Startup

Place the reactor on the floor of your tank, securing the suction cup to a wall. I like to route air hoses inside my tank with small suction clips, it's totally optional though.

Turn on the air flow to the reactor. There should be enough air that the entire media layer is mixing, see the short video for a demonstration of complete and effective mixing action.

My reactor is 1/2 gallon, so I used 1/4 gal of carrier media - which means I need 1/4 gal of air per minute at the air stone which is 18" deep in the water. In more common units for air pump evaluation: I'm using about 1 Liter per minute (LPM) of air @ .65 psi.