RO Waste Water Conservation

[+Daniel]

In an effort to not waste my RO water, I was thinking about plumbing my RO waste water line into my hot water line. My RO input is obviously connected to my cold water line. I'm assuming that if the pressure of the waste water is higher than the pressure in the hot water line (via a booster pump), this should work out-- am I missing something else here? Seems like this COULD result in no waste water...let me hear your thoughts/concerns with this type of setup.

[+Daniel]

Found this article:

Zero Waste: A Look Into the Future

[Gonzobob]

Hm, I'll admit I didn't read the article referenced by Daniel but I had these thoughts.

Running waste water into the hot water supply would presumably impact sediment and scaling in your fixtures.

This being Texas I almost always run my ro waste out side and through a soaker hose for the lawn and garden. (I don't if it's raining or has just rained in which case I collect for later use)

That being said I do use my RO on an as needed as opposed to constant use which probably makes this easier.

[+Mitch]

I ended up picking up one of these:

http://www.bulkreefsupply.com/RO/DI-Filters-&-Systems-RO/DI-Systems/c9_10/p664/Water-Saving-150-GPD-RO-Upgrade-Kit/product_info.html

It supposedly will cut waste water in half. I have yet to test my RODI setup.

[caferacermike]

I don't see how that will cut the output in half.

I have a nice big green sago palm that appreciates the waste water it receives.

[+Mitch]

basically it's a 2-pass setup... wastewater of the 1st stage passes thru the 2nd "1st stage"... i've seen other retailers selling similar setups, so i'll assume it works... but as i said, i haven't tried it yet, so we'll see... and the rest of my wastewater will end up in a rain-collection barrel or the pool...

[reefman]

Just FYI, what you are doing is illegal. I'm sure the "grey water" police won't show up at your door, but if you ever have to get your home inspected or something like that it won't pass. Unfortunately there are many restrictions to re-using grey water (which is what this is) in Texas. Just wanted you to have all the facts.

Stephen

[mhart032]

Stephen is right, thats why (by law) anything that comes from the house being gray water must have whats called a back flow re stricter so nothing can flow the opposite way and contaminate the source.

[AlexKilpatrick]

I don't know the law on this stuff, but how can RO waste be grey water? Isn't it cleaner that what comes out of the tap, since it goes through the first stage?

[+Mitch]

more about the 2-pass approach...

from Russ @ BFS:

"With two membranes plumbed in series (waste water from the first to the "in" port of the second), treat the membranes as a single, long membrane."

thread where comment was found so you have full context:

http://www.plantedtank.net/forums/equipment/44443-rodi-system-recommendations-needed.html

[mhart032]

So you could do this if you added a second membrane to any ro/di? i was thinking about this before. just adding any membrane doesnt even have to be a certin gpd it could be a 25gpd and work? but i have always been told crap is crap you can polish it but its still crap, meaning the waste water is all the crap water, the bad stuff. I could see this ruining a new membrane fairly quick. seeing how it will be condenced with all the bad stuff from the initial filtration. anyone have any clue if this would be correct?

[+Mitch]

i am not sure about any other membrane... but i'm still learning about the whole rodi process so...

i think there are some other crucial things which influence efficiency of traditional rodi systems, namely water pressure and water temperature... and i remember reading something about backwashing every once in a while...

if you are able to confirm more about the 2-pass approach, please share =)

[caferacermike]

I'm going with the same theory that MHart had, that it will ruin the second filter faster. Heck why not just run the waste water through a giant DI series and make it usable? Oh wait, that's because the DI cost would kill.

Yeah they just went nuts about the grey water a couple of months ago. Not sure where online to check it out but there was a loooong story in the Austin American Statesman in regards to this practice as many people were talking about some great under ground storage and reclamation processes, but then the Govt. had their piece of the story. Basically they outlawed all grey water storage systems. Boooo!! The Statesman said something about being under 50g was probably "under the radar".

[offroadodge]

OOOPPPPSSS........ I keep my RO waste water and put it on the yard. I also have 55gallon barrells under my downspouts for rain water(2x55gal), and i have a 305 gallon storage tank in back yard full of rain water collected all year, crap i better get rid of some water(NOT) almost 500 gallons of perfectly good water that i didnt have to pay for i dont think so(rainwater collection) and 60-70 gallons of ro when i make water "who cares i say". Im diong my part to conserve. Its amazing on the rain water collection- In 10-15 mins or rain i can fill one 55gal barrell overfull depending on how hard it is raining. But yes the RO water does use excessive amounts of waste, Well not waste to me I USE IT!!!!!!!

[subsea]

I don't see how that will cut the output in half.

I have a nice big green sago palm that appreciates the waste water it receives.

Mike, hit the nail on the head with water the tree. The water in my well is full of calcium, magnisium, and sulfate (200 ppm). The discharge from your RO unit will increase whatever minerals are in your potable water. Much to do about nothing in my opinion. In agricultue we spread both lime, gypson and epsioum salt to suppliment depleted minerals. Why do you want to be an engineer about something that has already been engineered. Some people want to spend more resources just so that they can say "Look at how green I am". I leave green to the Jolly Green Giant. Ethanol is a classic example of much to do about nothing. It takes more energy to produce an equal volum of ethanol over gasoline. Ethanol producers less BTU's in its conversion to work energy. The effiecency of ethanol to gasoline is less than 80%. However, Washington burecrats want to buy votes and be green. To much voodo ******** for me.

Pat

[subsea]

I don't see how that will cut the output in half.

I have a nice big green sago palm that appreciates the waste water it receives.

Mike, hit the nail on the head with water the tree. The water in my well is full of calcium, magnisium, and sulfate (200 ppm). The discharge from your RO unit will increase whatever minerals are in your potable water. Much to do about nothing in my opinion. In agricultue we spread both lime, gypson and epsioum salt to suppliment depleted minerals. Why do you want to be an engineer about something that has already been engineered. Some people want to spend more resources just so that they can say "Look at how green I am". I leave green to the Jolly Green Giant. Ethanol is a classic example of much to do about nothing. It takes more energy to produce an equal volum of ethanol over gasoline. Ethanol producers less BTU's in its conversion to work energy. The effiecency of ethanol to gasoline is less than 80%. However, Washington burecrats want to buy votes and be green. To much voodo ******** for me.

Pat

[+Daniel]

Okay, so my understanding is that municipal water has a mixture of different things. Chlorine, heavy metals (maybe?), and sediment are all removed by the pre-filters, so most of what the RO membrane has to remove are dissolved solids such as calcium carbonates and sodium. My RO membrane produces one filtered gallon for every 5+ gallons of "concentrate." In terms of chemistry, it doesn't seem like the concentration is increasing by THAT much, considering the 7+ gallons of concentrate water. Furthermore, I would be diluting my "concentrate" with the 125+ (I have two tanks) gallons of hot water in my house.

As far as the code goes, some stuff from that link I posted suggested that two check valves to prevent back flow would address the legality of this-- "International Association of Plumbing and Mechanical Officials (IAPMO) requires the water from the outlet of the flow restrictor be routed through two check valves before flowing to the hot water supply line. These check valves ensure the hot water will never reach the membrane on the reverse osmosis system due to a surge or back pressure in the hot water system."

I think my only real concern is whether this stuff, primarily the calcium carbonate, will lead to build-up in my pipes. However, I think the quantities are sufficiently small that the impact will be minimal. Plus, if I run my RO system when the hot water is being used (shower, washing clothes, dish washing, etc) the concentrated water would spend less time settling in my pipes.

I have no problem watering the lawn, but 35+ gallons from 5 gallons of usable water is a lot more than I need/want to put into the ground.

Worst case, since I'll have to buy a booster pump to do this, I can just install the add-on kit that Mitch mentioned.

[caferacermike]

I'm not sure how you will get the water into your hot water heater.

Ok so it's already full, and say with 75PSI of pressure holding. Are you hoping to boost the pressure above this amount to force more water into your hot water heater? Have you considered how much water that will be? Ok so if you need to make up 20g of water, then you would need a place for 100g of waste water to go. With that said, remember your tanks are already "full". So how are you going to put another 100g into them? You need a place for the water to go. Now if someone was taking a shower at the time you were making clean water, then yes I could see how you could add your water to the tank along with city water. Keep in mind that your hot water tank never goes "low". It is constantly replenished with new cool water as you use up the existing hot water. It is a 1:1 ratio. Maybe if you ran every tap in your home on hot water all at once, but then again you have 2 tanks so you wouldn't be able to drain them faster then they would replenish.

Now if you plumbed them into your toilets in such a fashion that every time you flushed your toilet you filled them with waste water, however you would need to have your reservoir set up that it could receive water with every flush. Essentially if you had a 3g flusher you'd get about a half gallon of output into your reservoir. I considered that myself but you can't have your shutoff be on the waste side, it needs to be on your collection side, so it doesn't work. I'm sure you could reconfigure the shut off valve and adjust a float into the reservoir of the toilet if you really wanted to. So each flush would make about a half gallon of clean water.

I don't know much, I'm a dumb pipe fitter, but it doesn't make sense to think that you could force your waste water into your hot water tank that is already full at city pressure. It would only back up into your regular lines up to the pressure of your booster pump, say 80lbs. This being about a 10lb split would not take long to reach in a closed system. But then what? You'd stop sending waste water out of your RO membrane and instead it would tear the fabric membranes destroying them and then sending all of the water directly to your DI resin.

[+Daniel]

Thanks for the input Mike. This is seeming less practical, but I have been basing my desire to do this on the fact that there is a commercial product that does exactly what I've described. I wouldn't plumb the waste water directly into my hot water tank, but instead into the hot water line under my sink (but maybe that is essentially the same as plumbing directly to the hot water tank since this is a closed system?)

I'll contact Watts (the company with the system that has "Zero Waste") and see what they have to say. Their systems only produce enough RO for a 4 gallon pressurized tank, not a large storage vat.

Daniel

[caferacermike]

There is another company called Poly Bio tha produces a unit called Kold-Steril. They are a zero waste water purification unit. http://www.poly-bio-marine.com/products.html

[mhart032]

well you could plumb it into the line before the hot water heater and it would work. you woud need a backflow in the line coming from the ro and then a pressure pump to force the water into the line. that would work. i would worry about sedement in the tank though. but i have been thinking about this and this is the only way i see it working on the hot water side. but a check valve or a backflow re stricter would be a must.

[mhart032]

would be even better with a tankless water heater.. lol. i installed one in my house a few months before i sold it, it was the best upgrade i did to the house..

[caferacermike]

It won't work.

It just won't.

Only way to make it work is to drain the hot water tank and then refill it with the RO waste but what would be the point in that? I promise you cannot do it like you are thinking. If your hot water tank holds 60g of water and it is always full, how would you put another 100g into it? If you think you will be refilling it as you use the hot water your theory is ok but weak. How are you going to control the on and off mechanisms of the RO unit so it only works as you use your shower? It can only work while water is flowing through the hot water line. You cannot compress a liquid like you can air. It has to have a place to go and if the tank is already full, then it is FULL. I don't care how many back flows you add to the system. This is the same theory as to why you don't just keep adding more and more water volume and pressure to your pipes when you turn the water off. They can only hold so much and then they are full. Most homes have a pressure cut off valve in their meter boxes that limit your pressure to 80PSI. Most of the booster pumps only run to about 80-90 PSI. Even if your water pressure is only 65PSI with your water in the off position it would only take about 10-15 gallons of water forced into your system to raise your pressure to 80PSI. At that point your booster pump cannot add anymore water.

If you don't believe me I can certainly bring my hydrostatic testing pump to your house and we can destroy as many things as you'd like. We test huge sprinkler systems using 4"-10" pipes every day and once you have city pressure you only need to pump about 30-40g in them to raise the pressure to 240PSI. Your home is only about 1/1,000th the volume of some of these systems.

So again I ask you, where on earth are you going to store the 100g or so of waste water within your closed system?

You'd need some electronic diverter valves, a high pressure rated pump, a large storage tank and some sensing equipment. Basically you'd have to store the water in a large vat with a pump in it. When the vat is full it would need to trip an electronic sensor that would shut off the city side of the hot water line. As water is removed from the hot water tank, the pump in the vat would run to replace that water in the tank. The pump would need to be capable of producing at least 80lbs and have a check valve just after the discharge side to hold the built up pressure when the pump is shut off. When the faucet is turned off the pump would need to sense this using a jockey pump metering station, basically when 80PSI is met the pump would shunt itself and the check would hold the pressure. Every time a faucet is turned on and the pressure drop is over 10 lbs the pump would turn on. You'd then need another sensor in the holding vat so when the water gets low in that vat the diverter is activated and city water comes back online until you make more RO.

This is what I do every day to make those millions to afford the hobby and my motorcycles.

[mhart032]

Ahh yea didnt think about the city side and the pressure. what if you turned down the city pressure with a valve? then fed the line into the city line. just run the 1/2 or 1/4 inch tube whatever it may be into it and let it drip in like it comes out of the waste side of the ro their is very little pressure on the ro side. i would wonder if it not having very much pressure if it would even work.. Mike i hope im not frustrating you, not meaning to, im just wondering.

[caferacermike]

Other things to consider is that water, like electricity, flows through the path of least resistance.

Your waste line does not have much pressure coming out of it. If you try to restrict with something like placing your thumb over it, it will stop flowing. Why? Because you have created the path WITH the most resistance. That line won't keep building pressure. Instead it just forces all of the water through the delicate membranes and destroys them. Since you have an unrestricted end flowing water into your catch barrel, this then becomes the path of least resistance.

So if you need to overcome 65-80 PSI of residual pressure within the home plumbing system, where are you going to come up with 90 PSI? As the water tries to force it's way into the home system, it will instead hit a dead end and flow through the membranes instead. Keep in mind that if you raise the pressure in the RO system with a booster pump to 90 PSI it is split through 2 outlets. Neither outlet will have 90PSI as long as they are both open outlets. Close one and you could see 90PSI but you risk destroying your unit. So your booster pump won't cut it. This is part of the reason why you'd need to have an effluent run off holding tank to separate the systems and protect the RO unit itself. So what if you added a booster pump to the waste water side to boost up the pressure once it has left the RO unit? Hey good idea right? However keep in mind that the booster pump will suck water from the RO unit at a rate possibly higher than would be good for it. You wouldn't want to throw off the procedure because your waste water line is flowing faster than the rest of the RO unit.

I don't find it frustrating. I'm just trying to point out the flaws in theory, the practicality of of it all, and other things you may not have thought about.