RODI slow?? What GPH should be expected?

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denierlexiese

Premium Member
I have a 5 stage RODI system that appears to be going too slow. It has a 75 gpd membrane on it.  Here's the stats:1)from the wall: 90 gph2)After sediment and 2 carbon filters at 1 micron it's running at 60 gph into the RO membrane with 46 psi.3) After the membrane it's coming out at 12 gph with the flush on - all down the water water line4) After the DI Resin the system is at 6gph, 1.4 gallons of low 9 TDS water, and 5.6 gallons of waste water.Base on the 75 gpd, i would expect around 3 gallons of good water an hour, and 12 gallons of waste water.  Is that the correct expectation?Please help!!!Thank you!!!
 
Your ratio is correct.  You should expect a 1 to 4 ratio of good water to waste water.   I have a 75gpd system and it takes me around 80 minutes to fill up a 5 gal jug.  Mine may be a little on the slow side since it is probably 5 years old.
 
Are you mixing up PSI and GPH in the first post?What is your incoming temperature (not normally an issue this time of year, but worth asking)?
 
Posted by: jccaclimber Are you mixing up PSI and GPH in the first post?What is your incoming temperature (not normally an issue this time of year said:
Good question.  It was GPH based on filling up a 1 gallon bucket. That said I think I figured out a big piece of the problem.  I vinegar bathed my 550 flow restrictor, and that brought the flow up from 230 ml / per minute to 480 ml / per minute.  Its still a little slow compared to 550, and perhaps I should get a new one.  Should I?The gallons per water of good water produced is now 2.5 gallons per hour, up from 1.25 gallons per hour!!!Based on this calculator, with 76 F water, and 45 psi gong into the 75 GPD membrane, I should expect 65 GPD.  24 hours / 64 GPD= 2.56 gallons per day, so it seems besides the flow restrictor I'm operating near expected flow rates.http://www.buckeyehydro.com/calculator/What do you all think?? Thanks!!!   
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That makes more sense.  I'm used to taking pressure readings at different points, but we can get decent information from flow.Assuming the 550 is mL/min at some common pressure that is probably fine.  By my math 75 gpd good water at a 4:1 waste ratio is 789 mL/minute waste.  If you are targeting 3:1 it would be 591 mL/min.You mention a 1 µm carbon filter in your OP.  Did you mean 1 µm sediment filter?  The carbon filter should never be smaller than the sediment filter (I like them larger), or it will clog up very quickly.  The carbon filters don't have nearly as many pores as the sediment filters.Your wastewater flow being too low should not (short term) change your good water production rate.  Too low and it will result in the membrane clogging over time, but this isn't seen short term, something is odd about that.  I wonder if the increased flow rate flushed the membrane a bit?  Have you tried flushing the membrane? (Note, lots of people call this back flushing, but there's nothing back about it.  Just take the restrictor off and let it flow wide open out the waste line for a few minutes).Do you have very high calcium in your water?  I thought I had really high calcium at my last house, but I never clogged a wastewater restrictor.I think the 65 gpd at 45 PSI sounds reasonable given that most membranes are rated a bit higher than that.In the OP you add 5.6 and 1.4, this should be 7, not 6.  Is this just incorrect addition?  No problem if so, I just want to make sure your output isn't say 0.4 and not 1.4 gph.Your TDS post-resin seems high (likely won't cause your reef any issues, but implies a DI resin issue).  What is it going in to the DI canister?All in all, 2.5 gph good water sounds reasonable for your system, so anything else is academic at this point.Out of curiosity what do you do with your waste water?  I put mine out in to the flower bed most of the year. 
 
#jccaclimber - perhaps I should take pressure points instead of flow.  I have a push connect pressure gauge before the RO membrane so it wouldn't be hard to move it around.Your math make sense.  The system is currently doing a 4:1 ratio. I calculated the 4:1 ratio by using a bathroom scale on the outputs of waste and good.  To improve the ratio I would probably need a booster pump right? if the system is not losing pressure already through the carbon/sediment chambers.  I should probably check that right?I believe the sediment and carbon filters are both 1 micron.  I used the universal kit from BRS linked here thinking that would be better than the 5 microns kits...IDK?http://www.bulkreefsupply.com/brs-5-stage-universal-replacement-filter-kit.htmlI'm not sure about the calcium.  I can check I presume with the calcium test that I do on my fish tank water.  Is that correct?Yes, you are correct it should have been 7 in the OP.  The system is now making 2.5 gph of good water and 10 gallons waste water, 12.5 gph total.Yes, sorry I was unclear about the DI resin, going into the DI resin, after the RO membrane is 9 TDS, 0 TDS after the DI resine,  the TDS going in has crept up a bit to around 12 TDS my last two 1 hour runs [Resin looks to be about 10% used up, only at the bottom of the cannister.  My water is 340 TDS out of the tap so that's about a 96% rejection rate, based on the BRS 99% rejection rate under ideal conditions of 60 PSI. Which I don't have 60 PSI, so hopefully 96% percent rejection rate is reasonable for 45 psi... I hope. :)  i do have 76 F water.http://www.bulkreefsupply.com/75-gpd-reverse-osmosis-membrane-dow-filmtec.html#jccaclimber I'm trying to figure out what I will do with the waste water too. Currently I'm trying to do water changes on my 200 gallon cichlid tank with it and use it for my indoor plants.  I'm adding declorinator [prime] to the freshwater tank after I dump in the wastewater, but I"m not sure I need to because wouldn't the carbon filters get rid of most the chlorine?  I guess I need some chorine test strips...Thank you for all your help and feedback!!S    
 
Depending on your ability to measure there is going to be pressure drop along every filter, every section of piping, every bend, etc.  The membrane and outlet restrictor will probably be the main pressure drops, but you will see it across others as well.  In industrial applications we put pressure gages across all sediment filters and use that to determine when they need to be replaced.  This won't work with a carbon filter, but will with a sediment filter.  On the other hand, as cheap as sediment filters are it is often easier to just replace them periodically.I suspect the guys at BRS know what they are doing regarding filter sizing, so no need to change there.  I mainly wanted to make sure you were not running (for example) a 5 µm sediment filter followed by a 1 µm carbon block.Bathroom scale is fine for determining ratio.  I usually time seconds to fill a 1 gallon container and calculate, but there are plenty of valid ways to do this.  If you're comfortable with 4:1 I see no reason to change anything.  The RO membrane will last longer with more waste water (per product), but you will go through more sediment and carbon blocks.  The local cost of water is low, so that doesn't really drive the decision from an economic perspective.  You could change this with a booster pump which would get you more product water, or with a different restrictor which would just cut back your wastewater production*.Pre and post DI resin numbers sound fine.  Note that the water when you first start up an RO system will have higher TDS than after it has run for a bit, although in your case the DI will catch it either way.Using wastewater on indoor plants (or even tap water which is close) will result in long term calcium buildup in the plants, so you may need to repot every couple years.  Not an issue for most, but worth being aware of.The cichlid tank is a good application for wastewater as they appreciate the harder water anyways.For calcium (and really I mean hardness) I usually just look up the water quality report that most water districts publish annually.  This won't apply if you are on a well.If you run your carbon blocks too long you will get ammonia passing through the membrane from the breakdown of chloramine (dissolved gasses pass through RO membranes).  Since the wastewater does not go through the DI, using Prime is a decent safety precaution.  You might look in to using Seachem Safe.  This is the concentrated powder version of Prime and costs less.  I have about a lifetime supply I could sell you some of if you don't feel like ordering online.  I will warn you that Safe has the same unpleasant smell that Prime does, although I haven't noticed it as much if it is placed in an open area or glass container.  The powder does need to be kept dry.*In theory (and my past experience) more restriction would cut the wastewater rate while leaving production constant, although your experience cleaning your restrictor seems to contradict this so there is at least one hole in this theory
 
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