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RE: aerated rock filters

bugwisperer — Sat, 20 Oct 2007 17:53:37 GMT

I think what we are talking about here is fixed film. Add fixed film to the process since we dont have a formal MLSS in a pond process and we grow bugs on the film. The nitrfiers are especially appreciative of this if you provide the fixed film at a point in the process where CBOD reduction is all but achieved.

Rock filters have been know to plug if stone supplied is not washed at the quarry; I believe Illinois requires it (post 1989 I think). The orignal idea of rock filters was to provide a psuedo tube settler to reduce algae in discharge as I understand. Dont think they worked.

There are some folks who have developed a concept of aerating rock filters by sinking plastic pipe wells into the rock and dropping aeration in at these points. But, the problem is how does one move the aerated water throughout the filter? I am presently trying several aspirating aerator mixers at the face of a rock filter to see if I can carry DO through it; we'll see.

My issue with them is how do i keep them from ultimately plugging? I aerate, grow bugs, they die and slough of and I cant clean them out. With a floating curtain type of fixed film system the bugs slough off but I can move my curtains.

Mark

RE: aerated rock filters

TerryF — Thu, 13 Sep 2007 03:03:57 GMT

Casey,

Most of my info came from E J Middlebrooks article in the Journal of Water Polluttion Control Federation Vol 60 No9 p1657-1662 from 1988 and a paper he delivered at a conference in 1993. This has been picked up by many authors of textbooks (Crites and Tchobanoglous for example)as an authorative example of design guidelines.

The State of Illinois publishes or used to publish a guidance note on such things , although i don't have any easy reference to it.

Regards

TerryF

RE: aerated rock filters

Casey Wichert — Wed, 12 Sep 2007 17:51:56 GMT

Thanks Terry,

Sounds like we read some of the same googled information. It sounds like the idea for rock filters started in the late 70's then lost interest until recently in England when someone thought to aerate them. On the surface this seems like a really cost effective waty to bring small municipal pond facilities into compliance without building complicated traditional facilities. I'm thinking about trying this.....I just don't want to reinvent the wheel if someone has already experiemented with this idea.

RE: aerated rock filters

TerryF — Wed, 12 Sep 2007 17:29:00 GMT

Casey,

Some design information from lagoon rock filter systems around the country is shown below,

Typical depth of media- 5to 7 ft

Rock size- 1 to 6 inches typically 2 to 5 Rock should be free of fines and soft weathering rock , and no flat rocks.

Hydraulic loading rate 1-1.5 ft/day , but some go up to 4 ft/day in summer.

The State of Illinois appears to have special requirements in that they recommend post aeration ability and chlorination of the post aeration cell.As your in California this may not be an issue for you but i have included it anyway. They specify a depth of media 1 foot above water surface , a rock size between 3.2 and 6 and a hydraulic loading rate of 2.6 ft/day.

Hope this is useful.

Regards

TerryF

aerated rock filters

Casey Wichert — Wed, 12 Sep 2007 16:55:44 GMT

Does anyone have any experience working with aerated rock filters as a means to polish pond system effluent? I'm considering using it for a small pond system in CA as a means to lower BOD, TSS, and NH4. In particular I'm interested in any design parameters such as depth of media, volume of media, etc.