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Join Date: Aug 2014
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Rejected Water Might Causing a Problem

08/20/2014 8:42 PM

Hello everyone,

I have started my small water company and everything is working real fine, we are using RO to purify water.

I use well water and I use another well as for reject water.

when I started this, water TDS was around 4000 so we made the machine to handle 10,000 just to be safe.

After a month the TDS of the well (which is located around 50m more or less) started to get higher and higher, the current reading is 9900 TDS !!!

our product water is also getting higher, used to be around 70 to 90, now it is 120+.

The wells next to us are ranging from 4000 to 5000 TDS, only mine is getting 9000, and they are not too far, less than 100 meter.

could the reject water mixing underground with my well water ? I'm planning to move to different well which located around 80 meter away, but worried if this thing can happen again.

please advice

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#1

Re: Rejected water might causing a problem

08/20/2014 8:54 PM

After using my X-ray vision to look underground at your problem, I see that the reject water is mixing with the good water.

You will have to move to another well.

How much reject water are you pumping back into the ground?

How often do you clean the RO filters? Do you pre-filter the "good" water.

Perhaps a call to your filtration supplier might help. You have called them, right?

How does the water taste?

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Participant

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#2
In reply to #1

Re: Rejected water might causing a problem

08/20/2014 9:04 PM

lol Thanks for the reply,

Yes I'm working closely with the people made the machine, it produce around 50k g per day, I'll have to check regarding of the quantity rejected into the ground.

we do clean filters daily and sometime more than once, yes we do pre-cleaning.

the water is not for drinking, its for constructions and some manufacturing uses.

I'm kinda new to this, and someone told me that keep using the same well can result into this, which I don't think its logical specially we started at 5k TDS then 6, 8 and now 9k and in very short period.

Thats why I'm asking here to listen to different opinions and probable cause of this

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#3
In reply to #2

Re: Rejected water might causing a problem

08/20/2014 9:13 PM

Get local, competent help.

You won't find it here.

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#14
In reply to #2

Re: Rejected water might causing a problem

08/22/2014 9:57 AM

If the water is not for human consumption, why are you using RO to purify it ?

What is the draw-down rate of the well ? The well driller should be able to tell you that. Have you studied "Groundwater and Wells" ?

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#4

Re: Rejected Water Might Causing a Problem

08/20/2014 9:16 PM

Sounds like you have created a loop....your well isn't very deep to begin with, how far is the reject well from the supply well? Maybe you could filter the reject water with a low tech gravity sand and gravel filter or settling pool of some type.....Is the water brackish? ...or just high in minerals? Have you had the solids analysed? Is your RO combined with any chemical pre-treatments?

http://en.wikipedia.org/wiki/Reverse_osmosis

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#5

Re: Rejected Water Might Causing a Problem

08/20/2014 9:18 PM

you might have an underground plume...

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#6

Re: Rejected Water Might Causing a Problem

08/20/2014 10:44 PM

Yes it definitely is. Try using the brine reject to irrigate hardy, fast-growing plants before discharging it. Grow them in planters isolated from the ground with a final tank with a TDS sensor before discharging the water. The plants will remove much of the dissolved minerals thus greatly reducing the TDS.

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#7

Re: Rejected Water Might Causing a Problem

08/21/2014 4:31 AM

Of course it is. Send the reject water somewhere else and the well water TDS will fall slowly over time. Make sure the reject stream when blended with other waste streams falls within the local discharge consent limits. The local equivalent of the UK's Environment Agency can advise, only, don't tell them that the reject water has been pumped back underground otherwise prosecution may ensue for contaminating other nearby wells that might be used for other purposes.

Presumably there is a licencing arrangement in place for the abstraction of the water and reinjection of the reject? If not, then if another abstractor nearby can link its deteriorating water quality to the reinjection taking place then civil action might ensue in addition to any prosecution.

Consider blending the reject with the product water after it has been put to waste instead, thereby recombining the original streams.

Depending on flowrates and the nature of the local terrain and its underground strata, 80m might be too close by a factor of 20.

If in doubt, hire a local Consultant.

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#8

Re: Rejected Water Might Causing a Problem

08/21/2014 10:04 AM

You may want to look into capacitive deionization of the source water before your RO purification.

http://www.environmental-expert.com/Files%5C5306%5Carticles%5C14119%5C560.pdf

http://en.wikipedia.org/wiki/Capacitive_deionization

You may have yet to contaminated your neighbor's wells time will tell. Ground water can be like a big lake or a bunch little cups. Where the little cups as they fill spill over into other cups. In your cup you are taking the water out and leaving the TDS behind. Cause your dumping the waste water back into the cup. Good rain and your cup fills up and spills over into your neighbor's cup and you could have a problem on your hands. It could be your on a lake and could take a little longer to contaminate your neighbor's wells. Soil acts as a filter which slow the movement of the water. At a high rate of removal. The pool surface will drop around the well. What you are dumping in is creating a higher pool level. It most likely running back toward the source well to level the pool surface. You need to remove the TDS not just move the well. Our your business will be suppling water to drink for your neighbors. Maybe paying them something for the damage and inconvenience you caused.

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#18
In reply to #8

Re: Rejected Water Might Causing a Problem

10/06/2014 6:10 PM

Good link. I learned something new.

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#9

Re: Rejected Water Might Causing a Problem

08/22/2014 12:54 AM

This seems an unlikely cause of your situation, but I have seen good water wells become contaminated because they were not properly cased/lined. If the drill passed thru strata of bad water before your well was eventually made at 50m and then the finished well was not properly cased the bad water can work its way done into the good strata. This effect would be accelerated if your well is pumped hard and the water level in the good strata drops. Did the driller pass thru some bad water strata when drilling your well? Also, if a neighbor is in the same strata of water and they failed to properly case their well, your well could become contaminated.

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#10

Re: Rejected Water Might Causing a Problem

08/22/2014 1:27 AM

It sounds like you have recycling of reject back into your feed. But I don't believe this is the case.

If the feed TDS has increased from 4000 mg/L up to 9000 mg/L, this is more than double - meaning the volume of the water has more than halved (unlikely).

You haven't said how big your RO is, but unless the permeate draw from the system is massive OR the volume of the aquifer between the two wells is unusually small- then a concentrate loop explanation doesn't make sense to me.

Have you calibrated your analysis equipment?

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#11

Re: Rejected Water Might Causing a Problem

08/22/2014 3:47 AM

Hi what you need to do is install air lines equiped with pressure gauges on each well/bore within the proximity that could possibly be affected by the draw down inital well that you use for major extraction.do not extract from any wells for a period of 24 hrs and then measure the depth of water in each well including your main measuring extraction well.Create a table of data measuring the depth of each well and recording at exact same time intervals over a 24 hr timefraim,eg 24 measurements for each well.This is the manual and cheapest method but you can lnstall electronic meters wich automatically record data.This will cteate a picture of what is going on underground and indicate as to weather you are all extracting from the same aquiferwhen you are carring out this test you do not extract from any other well except the well you are using for your main extraction.You also need to discard all test water away from the test area otherwise you will achieve a false report.

The pressure Line consists of an adequate gague connected to a valve which you can connect an air pump similar to a tyre valve,connected to an air line with a weight which will convey the line to the bottom of each well ,these lines may not be the same depth ,this does not matter it is the inital starting depth and hourly readings that will indicate any problems and underground interconnection.This data is very important for underground drawdown capabilities and neighbour liabilities,When you pump air into the valve connection air will escape out from the bottom open end where the weight is attached ,the gague will record the residule pressure left in the line,the higher the pressure the deeper the well

I have had to test bores within !/2 mile of the bore in question

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#12

Re: Rejected Water Might Causing a Problem

08/22/2014 7:44 AM

You location would help, for a Geological cross section.

also more information about your well. How deep is it. Production, ect...

Dvader has good advice for handling your high strength waste (retentates) depending on production which EPA or DNR (or some government environmental agency) could get involved ..., a little more information would help.

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#13

Re: Rejected Water Might Causing a Problem

08/22/2014 8:35 AM

50K gallons/day is a lot of water. You may be overtaxing your well. You may have damaged your screen at the bottom of the well. Screen replacement is a common procedure on drilled water wells.

If you have yours inspected and replaced, have them put in something like smaller slots in for the screen. For example if you have a 15 slot currently installed have it replaced with a 10. The smaller slots may reduce the volume you can pump but it will be cleaner.

Your screen size information should be on record at the health department, licensed drillers usually are required to have the well information on file including the screen size used.

Try not pump the reject water into the same aquifer, in fact try to discharge it in a shallow well as possible so the ground can filter out the TDS as the water migrates to the pumping aquifer. It is the dirt, sand, gravel and rocks that filter out contaminates in water.

One last suggestion depending on your pumping level above the screen is to fill the bottom of your casing with fine crushed rock. If you could get 15-20' of that material on top of your screen inside the casing it would serve to filter your water after the screen and before the pump.

Caution: if you put crushed rock on top of your screen inside the casing...you will not be able to ever replace the screen again. I would say this is a last case scenario, but it could work.

Good Luck!

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#15

Re: Rejected Water Might Causing a Problem

08/22/2014 5:42 PM

Thanks everyone for the reply and suggestions,

As I mentioned earlier I'm not expert in this field, I have been given this business to handle for now.

our RO capability is 110000 GPD which is currently not enough for the business and we are planning to expand to at least 100,000 more, but that is not the total amount we are getting because the machine goes off for cleaning ,change shift...etc so we get around 80% of that, approx.

There is something I forgot to mentioned, the well depth is around 45m, and because we were trying to save some money, we did not have sand filter only disc filters, but we had so much dust and stuff coming out and had to clean the filters every couple of hours, the well driller company suggested to lift the well machine up 10 meters (35m) to reduce the amount of dust coming out.

I'm not sure when the TDS start to raise up, but I'm sure it was during that period. In my area we do not have many expert or experience people on this, so getting help around here is kinda difficult.

again I would like to thank everyone for the help and suggestion

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#16
In reply to #15

Re: Rejected Water Might Causing a Problem

08/23/2014 7:19 PM

It sounds like you, in effect, might be trying to pump waste-water ''uphill''... (I.e.: upwards against the downward slopes of the subterranean soil layers, which will typically be of different soil densities, and permeability's... )

You could go at least an equal distance, in the opposite direction, from the supply-well, and bore a replacement waste-well...

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#17

Re: Rejected Water Might Causing a Problem

08/24/2014 12:44 PM

Try using reject water for irrigation & not putting it back down a well because of coarse its mixing with your well water and contaminating it, By using the reject water to irrigate you let the water permeate through the ground thereby filtering it so when it reaches the water table it should be as pure as the water you are pumping up.

Bazzer.

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#19

Re: Rejected Water Might Causing a Problem

10/06/2014 6:16 PM

Maybe you should consider this: ZLD: zero liquid discharge. Depending on solar input in your area, the RO reject could be sent to second smaller RO (addtional recovery), but more treatment upstream of this might be required. Then the much smaller quantity of concentrate is routed through a compression evaporator, yielding more pure water (small yield compared to RO), and a very high salt content concentrate to be solar evaporated in a pond. If that is not an option, you might try aquaculture using the concentrate to grow algae.

The well you are on now might clean up, or not once production is halted on it for a time. It could be that by producing this well, you started drawing water in from the formation in a buffer that is quite salty, actually I doubt your problem is from your concentrate changing the well characteristics, but even that is possible on a limited capacity well.

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