Backyard Aquaponics
A place to discuss aquaponics

As you have been told a digestor can be as simple as a tank holding the solids with lots of aeration. This style of waste treatment processing is what sewerage farms use and there is excellent information out there on how to design them.

One of the reasons I don't favour them though is that they are relatively energy intensive. All that areation that is required to deliever the oxygen to the tank to meet the Biological Oxygen Demand (BOD) takes power and that power has to be paid for in terms of its environmental foot print and $.

But they do work and work well. If they didn't they wouldn't be so widely used commercially.

There are other options though that were previously discarded as uneconomical when electricity prices were low. Now that they are high these options are being reconsidered for a range of applications.

Thanks Stu.

Although for a backyard digester if I had a 70L barrel with one of my 6 air stones (40LPM pump) redirected to it from the FT wouldn't that be enough aeration and that wouldnt be much energy usage? would it.. or is that not enough air for say a 1000L FT with 50 jades in it?

I don't know. Once I understood the limits/disadvantages of the technology I stopped investigating.

Having said that this needs to be said again and again and again. These components (filtration components) need to be sized NOT based on FT size or the number of fish. They need to be sized on the amount of fish food you will feed your fish and the protein content of the fish food.

The hilarious thing is since ive been going off about how much i don't like them over the last few weeks with the renewed debate of to remove or not remove solids I may have a job where they will be needed despite their disadvantages coming up. Kind of ironic.

I hope it hurts (just a little) Stu.

Not if they pay me.

Any way my strong views are based on the objective facts (at lease I hope so). For example even in a system where solids are retained in the growout facility the quaruntine system to hold the fingerlings is pure RAS.

If a technology is the most appropriate choice then it is the most appropriate choice. Ideology is for politicians.

Hey Stuart, do you know a good general rule of thumb for how many litres of air are required? Or any relevant links?

Thanks

For backyard systems I wouldn't recommend them.

For commercial you need to get serious:

http://www.amazon.com/Water-Wastewater- ... +treatment

A digester? If so Id like to hear why Stu.

Sorry, Ill re-phrase/re-direct my conversation on that one..

My opinion lately has been that the re-intoduction of digested solids is required before a raft, this is based on personal experience with my own. Id like to hear all experiences on this topic, I watched my DWC suffer compared to my media beds this past year and I believe it was because I was removing too much and not re-introducing anything. From a nutrient defficiency point of view I cannot comment on what exactly it was but heavier bearing plants and also herbs suffered.

Didn't you bank any nutrients... into your "nutrient bank" Charlie....

They really don't take much power Stuart... I run 12,000L of mineralization tanks for $3 a month in electricity... It's actually extremely energy efficient IMO. Just don't make them 20' deep.

Also, it's definately not needed in all DWC Charlie as I ran that outdoor demo system for years with no offline mineralization tank. Mineralizing nutrients and adding them back to the main system water requires a different approach from the nutrient management side. It sounds like the easy thing to do to get everything out of the food but becomes MUCH more difficult to keep the nutrient profile I am striving to achieve.

Actually when specifically sizing mineralization tanks, you should size the equipment based on total volume of waste removed daily and multiply that volume by the expected rate of breakdown in the tank (temperature, O2 and design specific). Feed type and volume does matter but more so the volume removed via the specific mechanical filtration devices being used.