WillsC

Had a go at building a RDF filter

41 posts in this topic

Great news I've already started building a RDF and have put my waterwheel and gasifers on the back burner for now😀 I see great potential in this mainly because of the use of drums and pvc in backyard AP already. Hopefully I don't run into too much problems but looks simply enough.koi water beware 😀

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Phri,

 

Good morning.

 

As to reliability as you say time will tell but it is a very simple design.......I do not see where a failure could occur.  The drum spins slowly and yes I have seen some of the commercial units that spin much faster but I see that as no advantage and as you know with speed comes more chance of a failure.  With water as the bearings there is no wear parts and even if something did fail how bad could it possibly be?    The sprayers work on pressure from the well, same as my home and it cleans the screen completely so see no need for an additional pressure pump.  Granted the spray heads use more water that those that would be higher pressure.  I am not concerned with conserving the water as it is all captured and used anyway.  If I wanted to minimize the waste water the addition of a booster pump for a lower flow higher PSI heads would be a good decision. 

 

 

I am curious where you think a failure could occur?  I just do not see many weak spots.  The only point of failure I could determine was IF the water level in the IBC tote fell due to a failure in the solenoid to trigger or a motor failures the drum would get VERY heavy as the water in the tote dropped but I solved that by making 3 of the screen panels breakaway and the screen would come out of the wiggle wire at that point and release the load of water. 

 

Yes in aquaculture you really do not want to filter out all of the fertilizer, I understand that but my set up is for aquaculture.  I have a fig nursery with 500 or so varieties but they are not in this loop other than the in ground plants benefiting from the fish water.  

 

Rotation speed should be low, as an example the newer large hydrotech units have a build in VSD so that you can reduce rotation speed even more.

 

obiviously, you expect failure first on moving parts: rotation mechanism etc, but you might have build a real winner.

 

If I am right you build yours from HDPE, this will deform under stress especially at higher temperatures. Screens will rip under shear stress.

 

One flaw I see is access to the inside of the drum and collection tray, if some larger fish get trough by accedent they can block the tray, while you don't see this or have access to this.

 

The disadvantage of using none system water for backwash is that you loose most of the fresh water directly. While with a pressure pump you can backwash with system water and top-up with clean water, thus flush out some of the accumulating salts.

 

At the end of the day you have to put it in context, in commercial aquaculture systems failure of the rdf will result in serious problems within 1/2 a day. Lower fish densities as in hobby systems give you much more time to fix things. Typical failure of a rdf will increase biofilter load, but if this isn't run flat out it will most likely digest the bulk of the extra solids.  As I descibed I have a commercial unit in my little home system, the way I use it currently is a waste of money. It works great, but I could achieve nearly the same results with a parabolic screen filter or a static bead filter.

 

btw I don't try to criticize you, kudos for your work 

Edited by phri (see edit history)
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Rotation speed should be low, as an example the newer large hydrotech units have a build in VSD so that you can reduce rotation speed even more.

 

obiviously, you expect failure first on moving parts: rotation mechanism etc, but you might have build a real winner.

 

If I am right you build yours from HDPE, this will deform under stress especially at higher temperatures. Screens will rip under shear stress.

 

One flaw I see is access to the inside of the drum and collection tray, if some larger fish get trough by accedent they can block the tray, while you don't see this or have access to this.

 

The disadvantage of using none system water for backwash is that you loose most of the fresh water directly. While with a pressure pump you can backwash with system water and top-up with clean water, thus flush out some of the accumulating salts.

 

At the end of the day you have to put it in context, in commercial aquaculture systems failure of the rdf will result in serious problems within 1/2 a day. Lower fish densities as in hobby systems give you much more time to fix things. Typical failure of a rdf will increase biofilter load, but if this isn't run flat out it will most likely digest the bulk of the extra solids.  As I descibed I have a commercial unit in my little home system, the way I use it currently is a waste of money. It works great, but I could achieve nearly the same results with a parabolic screen filter or a static bead filter.

 

btw I don't try to criticize you, kudos for your work 

Phri,

 

Hmmm........you are right that if a fish larger than 2.5" gets in that pipe I will have an issue.  I will cut out the section between two of the 2.5" holes on the next one to correct that, perhaps I should just install a downward facing 4" T in place of the 3 2.5" holes.  The piping of the shaft itself is glued but the 90 degree at the intake end connected to the shaft is not so if it happens I can pop the pipe off to get the blockage out.  

 

I have complete access to the inside of the drum.  The fabric is held on by wiggle wire in wiggle wire track.  I can open the drum up and close it back up no tools required in under 30 seconds. 

 

The screen I am using is temporary while I wait on the screen I really wanted, it is still 80 microns but it is as thick as denim and it is beyond tough, you could toe a truck with it easily.   

 

I don't think the 4" pipe will deform under the loads this unit will see.   If it happens though I will upgrade it to schedule 80 pipe.  The entire load is carried on the toilet flanges which are located right next to the 4" Uniseals so in essence the load is actually carried mostly by the tote.   The 4" pipe is submerged, the water level in the barrel comes up just barely over the 4" pipe so the highest temperature it will ever see is about 90 degrees.  

 

Redundancy is a good thing and that is why there will be two of these units, one per side of the greenhouse.  Did it more for convenience then redundancy though.   

 

Far as the rinse water those few gallons a day are not of any concern as far as water exchange in the system.  I have a solenoid, part of the greenhouse watering system that puts water back in to the system, partial water change every day.  The water that leaves through a port at the high side of the lowest tote runs to a bed where I will grow duckweed.  Trying to make it all as automated as possible to save myself time.  

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You can easily slide a screen on your inlet pipeline to keep fish in. I have several sizes I use depending on the size of the fish. I make them out of plastic fish cage material and zip ties. 

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Obviously you always use suitable screens on your tank outlets. It's typical human error which result fish in rdf; ops I forgot to put the screen back after cleaning.... or something like that

 

Rdf screens need as much open area as possible as thats where the water passes. Thus wire need to be thin which doesn't give you much strenght. Also you don't want material which stretches much under load as this changes mesh openings. Most used cloth materials are polyester and stainless steel. Both work fine if properly supported. My preference is stainless steel 316 as it last longer (but cost more).

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My "screens" aren't like that and I have no issues with water passing. I just increase the mesh size as the fish get larger. They look like this:

 

IMG_0132_zps05fed2ce.jpg

 

This large one fits over an overflow pipe in a pond. The only issue is algae needing to be cleaned off of it but inside algae is not an issue. 

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My "screens" aren't like that and I have no issues with water passing. I just increase the mesh size as the fish get larger. They look like this:

 

IMG_0132_zps05fed2ce.jpg

 

This large one fits over an overflow pipe in a pond. The only issue is algae needing to be cleaned off of it but inside algae is not an issue. 

 

I only refer to drum screens here, not tank outlets. Cecil what you are using is stuff we call oyster mesh here, works on outlets but not my favorite, as it fouls up easy, not only algae but all sort of poop, while it doesn't stay in shape if you have bigger pipes. I used it in the past by covering large holes (2-3 inch square) in pvc pipes. Or even as media retaining screens for mbbr filters. As for outlets I prefer vertical cut slots cut in pipe as this seems to have the best self cleaning properties, You can make those easy with a dropsaw, size of cuts is related to fish size.

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I spoke with some local aquaponic guys who purchased a 10 grand RDF. They claim cleans water so good you could drink it. 0 percent fecal matter after cleaning they said. I'm gonna to pay them a visit this weekend or next.😀 Maybe take some pictures.

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I only refer to drum screens here, not tank outlets. Cecil what you are using is stuff we call oyster mesh here, works on outlets but not my favorite, as it fouls up easy, not only algae but all sort of poop, while it doesn't stay in shape if you have bigger pipes. I used it in the past by covering large holes (2-3 inch square) in pvc pipes. Or even as media retaining screens for mbbr filters. As for outlets I prefer vertical cut slots cut in pipe as this seems to have the best self cleaning properties, You can make those easy with a dropsaw, size of cuts is related to fish size.

 

Like I said indoors there is no algae and if the mesh is large enough I've never had issues with clogging from fecal waste. I have about four different sizes for the indoor tanks and change them out as the fish get bigger. 

 

Outdoors I have two of them. When one comes off to clean another goes on. I hose down the one that came off and it's ready for next time. Usually feed and check the ponds once a day, so it's not like I'm going out of my way to switch them out. And the outlet for the trout pond is under the shade of a Weeping Willow. Not much algae grows there. 

Edited by Cecil (see edit history)

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I spoke with some local aquaponic guys who purchased a 10 grand RDF. They claim cleans water so good you could drink it. 0 percent fecal matter after cleaning they said. I'm gonna to pay them a visit this weekend or next. Maybe take some pictures.

 

Now and then I sent culture water to the lab to determine bacteria count. This is virtually always from systems with rdf. Bacteria counts is general in the millions per liter. Also suspended solid smaller then the rdf mesh just pass. You can drink everything if your stomach is strong enough, but I wouldn't recommend it.

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Just as an update.....the RDF has been running for almost 2 months now I guess and has performed flawlessly.  Not a single issue has popped up so far.  

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Just as an update.....the RDF has been running for almost 2 months now I guess and has performed flawlessly.  Not a single issue has popped up so far.  

 

Awesome! 

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So going on two years since I installed the first homemade RDF and I LOVE it.   A couple of observations.....I took the advice and added a screen of sorts, PVC standpipes with small holes in them to all 28 IBC totes that have fish to prevent fish entering the drains because as was pointed out they will and did:) .  I never got a blockage though as if a fish did lodge in the holes that go inside the RDF the water level in the tanks would all rise and the pressure would pop them out, they would be dead of course but did not happen often.  Mostly I just got tired of having to net the fish out of the rdf, BUT it does make a GREAT fry trap.  Since the original post I have also added 6 more 600 gallon rectangular tanks to the front GH and plumbed them in as well.   Because of the added volume I added a second RDF of the exact same design to the first one and each one filters 14 IBC totes and 3 600 gallon tanks.   

I was using well pump switches to sense and trigger the on /off cycles but it proved to be clunky and hard to fine tune meaning the barrels spun more often than needed and much longer than needed.  I switched to micro switches also triggered by the rise and fall of a jar inside a 4" line connected to the two filter totes.  Going that route I also had to add a solid state relay to trigger the sprayer solenoid and a regular automotive relay to take the electrical load off the micro switches as they can't handle it.  All easy and very cheap.

Originally I was using very very fine silk screen material around the barrel but it proved to be a bit wimpy.  The second attempt was using a sewing machine (with the help of my wife) and attached the silk screen material to window screen for strength.  That worked perfectly as the silk screen material still did the filtering but the window screen gave strength.  The only issue was they proved to be throw away screens as after 3-4 months of use they would get mineralized blocking the fine pores in the silk screen material making the filters spin more often than needed.  I tried acid washing them as that is the only way to remove the build up but that made the silk screen material fragile.  While sewing the two materials together was not a hard thing to do I decided to bite the bullet and bought a 100' long by 40" wide roll of 320 mesh (44 microns)  316L stainless steel cloth which was a bit pricey, $500 but enough to do a dozen filters I suppose.  When it gets mineralized every 3-4 months I remove it from the drum which takes about 2 minutes, soak it in an acid water bath which dissolves the minerals and 5 minutes later it is good as new.  What I will do with the rest of the roll I have no clue but buying a roll was the same price as the material to cover just the two filters which makes NO sense at all.

At first I was using an old dewalt drill motor 12V that had been retired to power the spinning of the drum which worked but about 6 months in it died and replaced it with a MUCH larger motor that is designed to roll the tarp back and forth on dump trucks, $125.  

With the new microswitches you can fine tune it and all the drum does now is turn 1/8th of one revolution which is enough to bring a fresh screen segment around, so it has to come on 8 times to make 1 complete revolution.  It takes about 3 seconds for the drum to turn that far and the sprayers also spray just 3 seconds.  Because of that the amount of water used that goes to waste has been reduced by 95%.  

As I said before (I think) the waste effluent water that flows out of the now two RDF's comes out looking like chocolate milk, well actually much darker than that.  Flows in to a common sump, a half buried blue barrel.  When the water level rises in that barrel to 3/4 full a pump kicks on and pumps it 100 feet or so to an IBC tote in the back GH.  Because the effluent is MUCH more concentrated now with the 95% reduction in water going to waste what fills the tote is a thick sludge that looks like chocolate pudding.  That sludge has got to be the BEST fertilizer I have ever used.  It takes about a year to fill a 300 gallon IBC tote to the top with that fish poop sludge.

 

 

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Posted (edited)

Hi Wills C

Thanks for your update :thumbsu:

Would be nice to see a few pics of the new heating system you described in the heating green house  thread

cheers 

Edited by ande (see edit history)
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Ande.

 

I will post them for you, I had a thread on it on my fig forum so already have the pics.  

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