TDS went down but clogging faster

[Mr. Met]

I live in NYC and the TDS has always been very low, around 30, but my pressure was never great. I wasn't using a booster pump so I would get maybe 40psi at the membrane and my 90gpd unit would make maybe only 50gpd, but I would go years without changing a single filter. About two months ago the TDS went down to around 12 and now I cant get more then two or three weeks out of a sediment filter without the pressure getting to near 0. I cant imagine the filter would clog faster with lower TDS water, so I was thinking maybe the psi got worse.

I got a second gauge to put before the sediment filter and it reads about 45 psi. I dont know, but I have to imagine that is lower then it use to be, so I changed all the filters and got a booster pump. I set the pump at around 75psi and production went up to around 120gpd, with a new filter. After about three weeks the pump starts making a strange noise. I check it and it seem the sediment filter must be clogged because the pump its not getting any water. I change the filter, and three weeks later the same thing.

So I guess my questions is, is the pressure going into the unit the problem? I know 45pis is not good, but I cant imagine its so bad as to starve the booster pump. But could lower TDS water somehow be clogging the prefilter so much faster? One thing I will also note is those TDS numbers come from two different inline meters that agree. The one I had was many years old, so I bought a new one. It has three probes and its saying the TDS after the prefilters is already 0. So, I guess I could buy a sediment filter with a larger micron rating, but that still doesn't explain why its clogging so much faster. One thing I have tried for now is putting the booster pump before the prefilters. Its at around 80psi, but I am only getting about 50psi at the membrane. Is 30psi a large delta? If so that would seem to confirm its clogging for some reason.

 

[Daniel@R2R]

Bumping this up for someone who might have some ideas on this. @Buckeye Hydro is an expert on RODI systems and could probably give some really solid advice.

 

[Shirak]

Isn't the booster pump supposed to be before the RODI unit?

Sounds like you have sediment in the water now that wasn't there before. Sediment filters are unaffected by TDS which is a measure of dissolved stuff, not particulates in the water which the sediment and carbon block will trap prior to the RO membrane.

 

[KStatefan]

@Buckeye Hydro recommends the booster pump be right before the membrane. It sound like something changed in your source water and now has a lot of sediment in it. Have you contact your water supply company?

 

[Shirak]

@Buckeye Hydro recommends the booster pump be right before the membrane. It sound like something changed in your source water and now has a lot of sediment in it. Have you contact your water supply company?

ok TY

 

[Mr. Met]

Isn't the booster pump supposed to be before the RODI unit?

Sounds like you have sediment in the water now that wasn't there before. Sediment filters are unaffected by TDS which is a measure of dissolved stuff, not particulates in the water which the sediment and carbon block will trap prior to the RO membrane.

I had always been told to put it right before the membrane because the pressure isn't good for the acrylic canisters.

I didn't think about larger sediment possibly being the issue. I know NYC water is unfiltered, but I never had any issue like this before. Do you think a larger micron washable filter before the sediment filter would help then?

 

[Mr. Met]

@Buckeye Hydro recommends the booster pump be right before the membrane. It sound like something changed in your source water and now has a lot of sediment in it. Have you contact your water supply company?

The water for the entire city comes from the same place, but I could see what NYC DEP has to say. I wonder if that is the case, if it could be something my apartment complex did.

 

[Shirak]

The water for the entire city comes from the same place, but I could see what NYC DEP has to say. I wonder if that is the case, if it could be something my apartment complex did.

My guess is maybe some work was done on one of the lines that feeds your building or within the building proper? Would think it would clear up fairly quickly though either way so your guess is as good as mine. Does the sediment filter look noticeably discolored? What micron rating is your sediment filter and carbon block? I would be concerned the carbon block is going to get clogged too as they are more expensive to change. Adding another sediment filter with a different micron rating might help but it really depends on what size the majority of the particles are. For example if they are large in the 10-20 micron size with a small percentage 5 micron and below and you are filtering everything with a 1 micron filter it will clog really fast. Adding a 10 micron filter will catch the large stuff and allow the smaller stuff through to the second filter. You will inevitably have to change two filters but it will be less often than changing just the one.

IMO since you have never had this problem before it could very well be a temporary thing and just having a box of extra sediment filters on hand for the next few months might be the easier way to go and see if it clears up.

 

[Buckeye Hydro]

Let's go through your post and tease apart the issues you describe.

I live in NYC and the TDS has always been very low, around 30, but my pressure was never great. I wasn't using a booster pump so I would get maybe 40psi at the membrane and my 90gpd unit would make maybe only 50gpd...
Realize that what you thought is a 90 gpd membrane is simply a relabeled 75 gpd membrane where the vendor tells you to run it at 10 psi over factory spec. Any Filmtec 75 gpd membrane will produce about 93 gpd (@77F) if you run it at 60 psi rather than the factory spec of 50 psi. 40 psi is about as low as most people are willing to put up with if we're referring to a Filmtec membrane. If you're using an off-brand membrane that is spec'ed at 60 psi or 65 psi, then 45 psi is certainly too low.

but I would go years without changing a single filter.
That tells us your water was low in sediment, and also low in hardness - so your sediment filter and membrane will last a long time. BUT... not your carbon block - it has a finite life in terms of ability to remove chlorine/chloramine.

About two months ago the TDS went down to around 12 and now I cant get more then two or three weeks out of a sediment filter without the pressure getting to near 0. I cant imagine the filter would clog faster with lower TDS water, so I was thinking maybe the psi got worse.
Realize that the amount of sediment in your water IS NOT reflected in your TDS reading. TDS is an abbreviation for Total Dissolved Solids - Sediment on the other hand is UNdissolved solids. So you absolutely can have low TDS and lots of sediment.

...so I changed all the filters and got a booster pump. I set the pump at around 75psi and production went up to around 120gpd, with a new filter. After about three weeks the pump starts making a strange noise. I check it and it seem the sediment filter must be clogged because the pump it's not getting any water. I change the filter, and three weeks later the same thing.
It looks like your sediment filter is doing the job you want it to do - capturing sediment. The amount of sediment in your water can vary over time. Nonetheless... it is what it is and you have to deal with it. The first thing that comes to my mind is I'm wondering what the spec are on the sediment filter you're using. Is it a 0.5 micron by chance? Also - what is the micron rating for your carbon block? Are the micron ratings compatible?

So I guess my questions is, is the pressure going into the unit the problem? I know 45pis is not good, but I cant imagine its so bad as to starve the booster pump. But could lower TDS water somehow be clogging the prefilter so much faster?
The problems you're seeing are not mutually exclusive - so yes, your feedwater pressure is low and the system performance would improve with a pump; AND for some reason your feedwater sediment load is higher than it used to be and it is clogging your sediment filter. Remember that your TDS reading is not correlated with your sediment load.

One thing I will also note is those TDS numbers come from two different inline meters that agree. The one I had was many years old, so I bought a new one. It has three probes and its saying the TDS after the prefilters is already 0.
Sounds like those TDS meters could benefit from being calibrated. The DM1 (two probes with blue face) and TRM1 (three probes with green face) are both factory calibrated with 342 ppm calibration fluid. You'd benefit from use of a lower TDS calibration fluid. You'll find that both those meters only have a single calibration pot (short for potentiometer), so when you adjust the reading for one probe you're actually adjusting the readings from all probes - so calibrate all probes at the same time with all probes submerged in the same fluid.

If you jump up to better inline meters - like the DM2 or the DM3, the calibration process is digital, and each probe can be calibrated independently.

So, I guess I could buy a sediment filter with a larger micron rating, but that still doesn't explain why its clogging so much faster.
You have a couple options to deal with sediment filters that clog faster than you'd like.
1. Use a sediment filter with a higher micron rating. If you do this don't go any larger than 5 micron (this is the limit recommended by membrane manufacturers). Remember that you may also need to adjust the carbon block you're using (let me know if you need more discussion on this).
2. Add another housing and sediment filter in front of (up stream of) your existing sediment filter. Use a sediment filter with a higher micron rating in the new housing.

One thing I have tried for now is putting the booster pump before the prefilters. Its at around 80psi, but I am only getting about 50psi at the membrane. Is 30psi a large delta? If so that would seem to confirm its clogging for some reason.
I do not recommend putting the pump prior to the prefilters. The clear housings are the weakest components in your system in terms of ability to withstand high pressure. Put the pump after the prefilters and get your sediment filter situation squared away. Yes - a 30 psi delta is too much - it indicates a clogged filter. Good catch on your part to notice that the sound of the pump changed when it was starved for water. Because the pump is a membrane pump rather than a rotary vane pump it's unlikely you did any damage to the pump by running it for a short time with inadequate feedwater.

We stock sediment filters rated at: 0.2 mic absolute, 0.35 mic, 0.5 mic, 1 mic, 5 mic, 10 mic, 20 mic, 50 mic, and 150 mic - and can order in just about any other micron size you'd like.

Russ

 

[Mr. Met]

@Buckeye Hydro wow, I really appreciate your response.

Realize that what you thought is a 90 gpd membrane is simply a relabeled 75 gpd membrane where the vendor tells you to run it at 10 psi over factory spec.

I was mistaken, it is a 100gpd unit. The current membrane is from AquaFX. It says its rated at 50psig, which I guess would mean 65psi.

That tells us your water was low in sediment, and also low in hardness - so your sediment filter and membrane will last a long time. BUT... not your carbon block - it has a finite life in terms of ability to remove chlorine/chloramine.

I know the carbon block has a finite life, but I do ICP tests that include RODI water and have never had anything show up. From my understanding chlorine also damages the membrane? And I have never had an issue with that.

The first thing that comes to my mind is I'm wondering what the spec are on the sediment filter you're using. Is it a 0.5 micron by chance? Also - what is the micron rating for your carbon block? Are the micron ratings compatible?

I have always used a 1 micron sediment filter and a 0.5 micron carbon. I have read you should use a smaller sediment filter than carbon but I have never had the carbon filter clog, just the sediment filter.

Sounds like those TDS meters could benefit from being calibrated.

That could be. I had a DM1, but it was old and I wanted one with three probes, so I replaced it when the problem started and it was reading 12ppm. I was just pointing out that the new meter gave the same reading out of the box. Where would I find a low TDS calibration solution? Everything I can find is 342 or higher.

If you jump up to better inline meters - like the DM2 or the DM3, the calibration process is digital, and each probe can be calibrated independently.

I bought the AutoAqua Titanium S3. I cant seem to find what its calibrated with from the factory, but each probe is calibrated separately.

2. Add another housing and sediment filter in front of (up stream of) your existing sediment filter. Use a sediment filter with a higher micron rating in the new housing.

That's what I was thinking of doing. I was thinking of trying something washable, like your pleated filters. Do you think 5 or 10 microns would be a good choice?