The active bacteria that make our biofilters work require oxygenated water to survive and thrive. Oxygen enrichment of water going to the biofilter will meet this need for the bacteria. Enrichment may be achieved through the use of airstones (along with air pumps), aeration towers (where you pump water up to a higher level, then allow it to fall through larger diameter pipe that allows air to enter and mix with the falling water) or use a venturi.

My favorite is the venturi. The venturi, which is a common application of Bernoulli's Principle (The pressure is lowest where the velocity is highest) is an effective aerating device, and is cheap to build and operate. You can either utilize a separate pump to operate the venturi or valve some water to it from your existing pond pump. Use of the existing pond pump is effective only where you have a high enough waterfall to create sufficient pressure at the venturi level. I am using a supreme magnetic drive 350 pump (AquaDirect) which has a 350GPH rating but I am also operating another water feature off the same pump (spitting fish).

First, I will show you a diagram of the venturi:

The venturi operates much like a carbureter, except instead of drawing fluid into a low pressure created by moving air, the watergarden venturi draws air into low pressure created by moving fluid.

My venturi is made from 3/4" PVC pipe and fittings and one brass fitting. The brass fitting forms the nozzel for the venturi.

Here are the venturi parts unassembled. Note: the only parts cemented are the short 1" piece of 3/4 PVC cemented into the elbow and the brass fitting which is then sealed in the other end with silicon caulk.

Here is the business end. It is a brass fitting sealed into a 3/4 inch PVC pipe with silicon caulk.

Here, the assembly is almost complete.

The assembled venturi.

This shows where the venturi will be installed. This is the first stage of my biofilter, which is also a settling and prefilter tank. The 3/4 PVC pipe that comes up from ground level and bends across the side of the vessel is the source of water to operate the venturi.

The large 2" PVC fitting near the bottom of the photo is an overflow bypass that feeds unfiltered water to the pump vessel in the event that the biofilter stages become clogged.

Here is the venturi in operation. Note the bubbles it produces.

Venturi, Another view.


Last modified on February 9, 1999

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