RODI System Design

[wpeterson]

I'm setting up a new RODI system but don't know what I'm doing and would love help from the community in planning out what I need. I have two nano reefs that will consume between 5-10gal/week in water changes and top off water. I live in an apartment, but do have a basement with a laundry system.

My plan was to get a Buckeye hydro 4-stage RODI premium system and run it off the laundry water outlets and drains. I'm planning to put a water tank with the RODI and have an automatic float valve shutoff. I'm especially looking for help around accessories and connection plans for the small details.

Here's my current plan:

• 150 gpd 4-stage RODI
• Manual Flush Valve
• DM1 Dual Inline TDS Meter
• Brass 1/4" hose bib adapter
• Auto Shut Off Valve Kit - 1/4" Fixed Arm

I was planning to mount the RODI system on a board/stand without hard-mounting to my wall, so I can take it with me (I rent). I was going to get a Brute or similar water tank to put next to it and install the auto shut off on that.

What else am I missing? Anything I should be thinking about or need to know?

 

[ro_nicu]

You could get a squarish brute and install it on the brute. Also, a system that runs it for longer times would be preferable from what I understand.

 

[jdeb101]

You could get a squarish brute and install it on the brute. Also, a system that runs it for longer times would be preferable from what I understand.

This is correct, a lower gpd will give you a lower rejection rate. Seems like you got most of it covered though! One thing I would check is if your time has chloramines in the water and if it does get filters capable of removing them. Not a huge deal (I've been running w/o them all this time), but better off if you do. Also what's your plan for mixing fresh sw?

 

[andy01748]

Put the Brute on a stand (taller than your transfer container) and install a bulkhead fitting and valve on the bottom of the Brute. Then you can gravity drain into your container when you need RODI.

 

[wpeterson]

Put the Brute on a stand (taller than your transfer container) and install a bulkhead fitting and valve on the bottom of the Brute. Then you can gravity drain into your container when you need RODI.

This is genius, combined with ro_nicu's suggestion about a squared-off container to mount the RODI on the reservoir.

I currently mix saltwater in a 5gal bucket with a heater/powerhead in it. If I can elevate the RODI reservoir on a stand above the level of the bucket it should make filling it easy.

My plan would be to keep the reservoir filled by running a constant batch of RODI once a month or so with the security of knowing the auto-shutoff can prevent a flood.

 

[JohnK]

This is correct, a lower gpd will give you a lower rejection rate. Seems like you got most of it covered though! One thing I would check is if your time has chloramines in the water and if it does get filters capable of removing them. Not a huge deal (I've been running w/o them all this time), but better off if you do. Also what's your plan for mixing fresh sw?

I might be reading this wrong, but just in case -

rejection rate is determined by the membrane, some have a 90% rejection rate, some have 98% for example. This refers to the percentage of the TDS that makes it through the membrane and to the DI. Ie, with source water at 200ppm, and a 90% rejection rate membrane, under ideal circumstances the water coming out of the RO will be 20ppm. the same water running through a 98% rejection rate membrane will come out at 4ppm.

Rejection rate is determined by the membrane rating, but not the GPH rating. You can get a 75 gpd membrane with a higher rejection rate than both a 25 gpd and 100gpd for example.

Higher rejection rate membranes will also likely have a higher rejection ratio, and higher GPD membranes will produce a greater volume of waste water, but volume is different from "rejection rate"


If I just made this confusing, sorry, nevermind



On the big batches of water vs small thing - when the unit is turned on and off frequently you will see "membrane creep" which basically just means that the TDS coming out rises because the membrane isn't working under ideal conditions. This is why RO units should not be connected directly to ATO systems. (in addition to avoiding the consequences of diluting the entire system if you lose some saltwater)

 

[Buckeye Hydro]

Just to clear up any confusion:

Higher rejection rate membranes will also likely have a higher rejection ratio, and higher GPD membranes will produce a greater volume of waste water, but volume is different from "rejection rate"

We're mixing up two different issues here:
Rejection Rate = the % of TDS in the feedwater that DOES NOT pass through to the purified RO water. The higher the rejection rate the better.
Recovery = the % of the feedwater that becomes purified RO water. In this hobby most people characterize this by describing the ratio of concentrate ("waste water") to purified water. For reasonable membrane life on residential-scale systems, this ratio should be kept around a 4 to 1, regardless of the GPD rating on the membrane.

Russ

 

[JohnK]

Thanks for the clarification.

Do you know if there is any pattern of higher GPD membrances having higher or lower recovery rates? (I was just guessing about that)

 

[Buckeye Hydro]

No - like I mentioned above - For reasonable membrane life on residential-scale systems, this ratio should be kept around a 4 to 1, regardless of the GPD rating on the membrane.

Russ

 

[andy01748]

My understanding is that the higher the TDS in the incoming water, the higher the ratio you need to use. If you are adjusting a flow restrictor to set the ratio, this will vary as the incoming water temperature changes with the season due to changes in viscosity, so should be checked as the supply temperature changes with the seasons. In addition, a higher ratio is needed with colder supply temperatures, and the 'advertised' low ratios for production are usually based on a supply temperature of 70 degrees.

I know the Spectrapure systems double the capacity of a system (e.g. going from 90 gpd to 180 gpd) by having two membranes installed (I assume in parallel).

 

[Buckeye Hydro]

My understanding is that the higher the TDS in the incoming water, the higher the ratio you need to use.

In concept this is true, but there isn't data available do describe other influencing factors (like LSI for instance) for every customer's water to adjust the ratio that finely - so the 4:1 is a rule of thumb.

If you are adjusting a flow restrictor to set the ratio, this will vary as the incoming water temperature changes with the season due to changes in viscosity, so should be checked as the supply temperature changes with the seasons.

True. Another approach is (for $4) to have a summer (static) flow restrictor and a winter (static) flow restrictor.

In addition, a higher ratio is needed with colder supply temperatures, and the 'advertised' low ratios for production are usually based on a supply temperature of 70 degrees.

Colder feedwater temperatures cause a higher ratio - in a perfect world you'd adjust (close, or "tighten") the restrictor to compensate. This is a feature common on more expensive commercial units. All residential membranes I'm aware of, from numerous manufacturers, are spec'ed at 77F (25C).

I know the Spectrapure systems double the capacity of a system (e.g. going from 90 gpd to 180 gpd) by having two membranes installed (I assume in parallel).

Yes - you can plumb in additional membranes, in parallel or series, and increase the output.

Russ