RBC made of plastic media

[Cecil]

If I decide to build another RBC I'm thinking of building a cylinder of plastic cage mesh material, and filling it with plastic media around an axle -- with several circular pieces of closed cell foam for flotation -- just as I do on my RBC that consists of plates. I'm thinking of doing this because:

I won't have to go out and buy a couple hundred dollars worth of fiberglass roofing material and polystyrene plastic and go through the nightmare of cutting and drilling the fiberglass. I don't have a bandsaw and cutting 50 fiberglass plates with a sabre saw is quite challenging and one coes through several blades.

I have plastic media on hand from when I used it to aerate and blow gases off of my borehole water to the trout pond. Obviously it will have more surface area than the plates, which could even up my safety net for biological filtration.

One of the downsides I see is the weight of the RBC could get quite heavy over time, but the media does float and I can compensate by adding additional flotation in construction to compensate. Or simply mount the axle through the tank walls so that it cannot sink if it gets heavy.

Another possible downside is clogging of the media over time, but the water in the separate tank the RBC will be rotating in will be clarified before it gets there.

Thoughts?

[GaryD]

Hi Cecil,

Have you considered a moving bed biofilter as an alternative to the RBC? It would be far less hassle to set up and operate......and, from what I understand, no less effective.

Gary

[Cecil]

Hi Cecil,

Have you considered a moving bed biofilter as an alternative to the RBC? It would be far less hassle to set up and operate......and, from what I understand, no less effective.

Gary

What are the power requirements and what is the initial capital cost vs. a homemade RBC? Can you illustrate exactly what we are talking about here? I assume a vessel under pressure which contains the plastic media that is used for biofiltration?

[Cecil]

I sent the same question via email to my mentor Steve VanGorder. I thought you all might find his response interesting. He has not led me astray so far and what he says makes a lot of sense.

What you are considering has been tried often in the past. In fact, a drum filled with high-surface area material was designed back in the 60's for the sewage treatment industry. And Dr. Timmons from Cornell, and Losordo from NC State built an rbc from spools of plastic material banded together. Lots of surface area, but all of these designs had one problem. They greatly increased the drag through the water. It was completely impossible to rotate the units using a waterwheel ... just too much resistence. And in every case that I'm aware of, the mechanical problems quickly developed. The gears on the motors stripped, the pillow blocks wore out, and finally, whatever methods were used to bind or enclose the media always failed.

This is similar to what happened when we were first developing the small rbc's. We didn't like to have to waste the fiberglass by cutting the plates into circles, so we built units with square plates. Of course, we tried rotating them without a motor but had to go back to it, but we ended up with a pretty nice design. But within a single season, the units just deteriorated.

Sorry. Hope this helps.

[GaryD]

Hi Cecil,

What are the power requirements and what is the initial capital cost vs. a homemade RBC?

I imagine the running costs would be comparable. While your RBC operates as something of a waterwheel, you still have to pump the water up to the waterwheel. A moving bed filter is driven by an air pump.

Can you illustrate exactly what we are talking about here? I assume a vessel under pressure which contains the plastic media that is used for biofiltration?

A moving bed bio-filter consists of a tank or drum containing some manufactured plastic media (Kaldnes K1 in my case). A current of air sets up a simmering action in the neutrally-bouyant media which not only provides an oxygen-rich environment for the nitrifying bacteria but also allows the media to self-clean.

It would require far less effort to put together than an RBC.

Is it better? I don't know how effective RBC's are so I can't say one way or the other......but I do like the ease that attends moving bed technology.

Gary

[kellenw]

Some people use nylon pot scrubbies in place of kaldnes or bio balls with good success.

[Cecil]

Hi Cecil,
I imagine the running costs would be comparable. While your RBC operates as something of a waterwheel, you still have to pump the water up to the waterwheel. A moving bed filter is driven by an air pump. Gary

But wouldn't yours be more than the RBC set up as you need a pump AND a blower? Wouldn't that increase running costs and initial capital expenditure? Also with more equipment needed doesn't that mean there is more that can go wrong?

How much noise does the blower make? I've been in a large University RAS complexe where the blower(s) make a heck of a racket. Sounded like some factories I've worked in. At least my submergable pump is under water and doesn't make much noise. The only sound I hear with my RBC set up is water splashing off the baffles and the agitator.

A moving bed bio-filter consists of a tank or drum containing some manufactured plastic media (Kaldnes K1 in my case). A current of air sets up a simmering action in the neutrally-bouyant media which not only provides an oxygen-rich environment for the nitrifying bacteria but also allows the media to self-clean. Gary

So the particulate laden water goes right to the biofilter which in this case is the media? But instead of a clarifer the simmering action keeps the media free of particulates? If so do you have to periodically drain and refill? Is that how you add your make up water?

It would require far less effort to put together than an RBC. Gary

I have no doubt about that but this time if i build another one I will have a bandsaw and drill press!

Is it better? I don't know how effective RBC's are so I can't say one way or the other......but I do like the ease that attends moving bed technology.Gary

Conversely i can't say if the RBC is better as I haven't tried the moving bed technology. However other than the building aspect I find the RBC set up relatively easy to operate.

[Ravnis]

http://nsgd.gso.uri.edu/vsgcp/vsgcpc...8001_part6.pdf

Some comparison numbers of effeciency can be found on pg 47 of this pdf. WHen trying to decide which route I would go to add additional filtration, I wound up going with trickling filter for ease of use and low cost. The fluidized bed was better by quite a margin in this study.

[GaryD]

Hi,

There's a YouTube video of a miniature moving bed bio-filter....here. It will give you some idea of what happens.

The media goes black when it's in peak operating condition........something I've yet to experience. The best that I've been able to achieve so far is light grey.

When the media is new, it floats......but as it gets conditioned, it achieves something close to neutral bouyancy......which is what allows it to turn the way it does.

....I wound up going with trickling filter for ease of use and low cost

I like trickling bio-filters for the same reasons......coupled with the fact that they reach operating condition much quicker than most other options.

The fluidized bed was better by quite a margin in this study.

The biggest issue with fluidised bed sand (or bead) filters is that amount of pumping capacity that is needed to keep the water flowing. While they are supposed to be excellent when it comes to nitrification (and for trapping solids), they can clog quickly and will require regular adjustment to maintain an acceptable flow.

Gary

[Cecil]

Thanks Gary I'll have to check it out.

Cecil