Upflow GB (roughening filter)

[Pseudoreality]

I've been reading many previous posts since joining and noticed Gary's strong push for solid removal. There's a good argument for not letting solids get into your GB. I was wondering if anyone has thought of or ran their system in a upflow manner? I recently designed and built a pilot water treatment plant for a remote arctic village using roughening filters as a pre-treatment for slow-sand filtration. Reading the techniques on solid removal got me thinking about using a roughen filter type technology for solid removal in a aquaponics system.

A roughening filter is basically just a deep gravel bed where water flows at a slow rate (~0.3 to 1.5 m/hr). You can run them upflow, downflow, or horizontal. Upflow has the advantage of easy cleaning as you simple shut off the pump and divert the drain to waste. The water and pressure in the system is typically enough to remove solids that have attached to the media as most if it will be at the bottom.

In an aquaponics system I would run it continuously upflow from my fish tank using a pump. On top of it you can grow whatever you want. The outlet you can divert to a raft system or other media GBs if you want. Cleaning would be simple. Close a valve from the feed line into the system, shut off your pump, and then open a drain valve. The drain could go to a dirt garden or compost pile.

The main disadvantage of the system would just be the cost of the apparatus and media. In my case it looks like I may be forced to get a much larger load of media than I need. Roughening filters also work best if they are over 1.5 m deep (2.0 m ideally). Depending on your filter container you may need to support it.

Thoughts?

[GaryD]

Hi PR,

Your proposed filter will certainly remove solids but I do have some concerns about its use in aquaponics system:


It's going to mean a heap of work and some expense to put it together.
Its weight will mean that you will be limited in where you can put it.
When it's operating, it will place a significant biological oxygen demand on your system.
Depending on the size of your proposed aquaponics system, something that is 2m hight may be overkill (and will add to your operating expense (pumping head).
While it can be cleaned to some extent, it will always retain some volatile solids.

In short, there may be easier and more effective ways to achieve what you're looking to do (in an aquaponics context).

First of all, how big do you think your aquaponics system would be?

Gary

[Pseudoreality]

It's going to mean a heap of work and some expense to put it together.
Its weight will mean that you will be limited in where you can put it.
Depending on the size of your proposed aquaponics system, something that is 2m hight may be overkill (and will add to your operating expense (pumping head).
Agreed, but I have built 4 in the last 6 months and I understand the physical requirements. The sizing I gave you is for a potable water treatment plant to remove 80% of your turbidity bringing it below 10 NTU. I don't imagine we need to get our water that clean in an aquaponics system. So I would push the limits with respect to minimizing depth and maximizing loading rates. As I'm a home hobbiest and not in it commercially I can afford to experiment a little bit.



When it's operating, it will place a significant biological oxygen demand on your system.
It will increase the BOD, but there are ways to manage that.



While it can be cleaned to some extent, it will always retain some volatile solids.

Here I disagree. If something is volatile, by definition is does stick around for a long time.


First of all, how big do you think your aquaponics system would be?

My outdoor pond which I will set-up in May is about 680L. I haven't decided how dense I want to stock it or how big of a grow area I want yet. Just for initial sizing purposes let's say I use your favorite (joking) rate of one 1 change per hour. So to get a loading rate of 0.5m/hr I would need a 300mm diameter roughening filter. That's not too bad. Also, I could probably get away with 1.2m height.

I'm sure I'll have learned lots by the time I get around to putting it together from my indoor 110 L system that I should have set-up this week and by what I read here. My final product may be nothing like I think now.

Thanks for your comments.

[GaryD]

Hi PR,

The concern that I have with the device you've described is that in a water treatment context, there's no real issue if the dissolved oxygen levels go awry for a while, whereas with a fish system, it could prove fatal for the fish.

I'd be more inclined to use something like Kaldnes K1 manufactured plastic media in a static tank. It traps solids very effectively and can be cleaned quickly and easily by blowing air through it......as often as the situation requires.

A Moving Bed bio-filter (alongside the static filter).......utilising the same media but constantly being churned with air.......will provide excellent nitrification and aeration.

When I used the term volatile in my previous post, biologically-active would have probably been a better choice.

Gary