This is “Part 1 – Introduction to the RAS build” of Chapter 8 of the Urban Aquaponics Manual.
Chapter 8 is where we build the system…and its a big one…so I’ve broken it down into a series of sub-chapters:
- Part 1 – Introduction to the RAS Build
- Part 2 – The IBC Fish Tank
- Part 3 – The Radial Flow Separator
- Part 4 – The Packed Media Filter
- Part 5 – The Moving Bed Biofilter
- Part 6 – The Tricking Biofilter
- Part 7 – Putting It All Together
In Part 1, I’ll walk you through the water flowpath for our proposed build…and then we’ll look at the tools that I’m going to use. In Parts 2 to 6, I’ll show you how to build each of the major system components. In Parts 5 and 6, I present you with a choice…between a moving bed bio-reactor (very effective but at a cost) or a trickling biofilter (still quite good but much cheaper). In Part 7 – we hook our various components together.
It’s useful to have a clear picture of how our RAS will function so let’s begin by getting a grasp of the water flowpath. Since the water pump is located in the sump, we’ll start there:
- The pump starts and moves water from the sump to the IBC fish tank. The water enters the tank tangentially and imparts a circular motion in the water in the tank. Solid wastes are pushed outwards to the tank walls and fall to the bottom. When they reach the bottom, they begin to move toward the centre point at the bottom.
- The weight of the incoming water displaces water already in the fish tank and forces it up the suction end of the solids lifting outlet…drawing any solids that are within reach of the suction. The water passes through the fish tank wall and into the radial flow separator (RFS).
- The incoming water in the RFS is directed upwards into the water deflector which causes it to change direction – downwards. The downward movement of the water encourages the heavier particles (sedimentary solids) to gravitate to the bottom of the RFS. The lighter water (without the sedimentary solids) rises up to the weir where it overflows and drains into the packed media filter (PMF).
- As it enters the PMF, the water is directed to the bottom of the filter. As it reaches the bottom, the velocity of the water is reduced and it moves upwards. It rises slowly up through the static media in the PMF exposing suspended solids in the water to the sticky biofilms on the media. The ‘clean’ water overflows the weir and enters the moving bed bio-reactor (MBBR).
- The water is directed to the bottom of the MMBR slowly rising up and exposing the dissolved solids to the nitrifying bacteria that live on the gently tumbling bio-media. Once it reaches the surface, the water overflows the weir and drains into the sump tank…and so on – ad finitum.
I should point out, at this stage, that there’s another layout option…one where the pump is located in the fish tank. The water passes through the filters and then drains back into the fish tank. This layout requires that the filters be positioned above the fish tank. That means that we dig a hole in the ground large enough to accommodate the fish tank…or we put the filters on a platform high enough for them to be able to drain directly back into the fish tank.
The upside to this arrangement is that we no longer need a solids lifting outlet – or a sump tank – so the build is easier. One downside is that integrating growing systems will be a bit more challenging. And then there’s the digging part. My view is that life is too short to spend any of it digging holes that aren’t absolutely necessary.
The RAS Builder’s Toolkit
Building recirculating aquaculture systems, like our proposed unit, are like every other technical endeavour…may seem daunting to the unitiated but really it comes down to some very fundamental skills:
- Cut plastic – specifically the plastic bladders of IBC’s.
- Cut steel – specificically the galvanised steel frame of IBC’s.
- Hand grinder and ultra thin cutting disks
- Cut PVC pipe – in the range of 20mm to 90mm (3/4″ – 4″).
- Mitre saw
- PVC Hand Cutter
- Drill holes – specifically those required for the installation of bulkhead fittings and Uniseals.
- Drill and Drill bits
To this list, you can add the following:
- Tape measure and marker
- Eye and hearing protection.
- Wrenches – or (more specfically) any device that will enable you to grip bulkhead fittings during installation.
- Deburring tool
Before we start work, here are some other things I’d like you to note:
- With the odd exception, I’ll be leaving all of the pipe and fittings unglued. This is a basic recirculating aquaculture system and there will be things that we can do to enhance it…and, should you decide to embrace those enhancements at some later stage, doing so will all be much easier if we haven’t glued every fitting or piece of pipe. Having said that, unglued pipework is a risky proposition, so we need to demonstrate some commonsense around how we set things up.
- I’ll be using ball valves to enable us to isolate each major component. This allows us to work on a single component without having to drain the entire system.
- Each of the filters will be fitted with a dump valve…to enable us to clean and drain it.
That said, let’s build a fish tank.
I’ve had to call a halt on this rollout of the Urban Aquaponics Manual. You’ll find an explanation…in this article on my blog. I’d like to say that I’ll continue with the work but that depends on how I go with some other priorities. In the meantime, I’m reasonable satisfied with what I’ve published here so, if Aquaponics is for you, then I invite you to make ongoing use of the work.