Alternative uses for high TDS waste from RO or DI system?

A1. What is the TDS measurement before your treatment? If you are adding TDS by treatment then you should examine that process. Chances are, your reject water is worthless. The most effective way to dispose of high TDS water is a deep well. The next is probably evaporation. But the best is to prevent the TDS to begin with.

A2. Hi
The various methods of disposal of 7000 ppm TDS RO reject is as follows.
1. watering plants.
2. send to sewage disposal.
3. can reuse by passing through softener bed.
4. you can also evaporate , condensate can be reused, but costly, will lead to scaling/fouling.
5. you can also use this High TDS water for toilet flushing.

Hope this may help you.
bye,

A3. My company uses a phased approach to this problem - We build the RO system with multiple passes, using interstage pumps and membranes designed for the high TDS water.

Then, to get rid of the very high TDS waste stream this creates, use a precipitation stage and clarifier to settle the solids, and put the water back into the front of the process.

You should be able to achieve 95%+ usage of the water.

A. Hi Urvish. Please try to synthesize a proposed/tentative answer to your questions from the enlightenment already offered to us by Mssrs. Morkovsky, Mukesh, and Watson, and then ask if your idea sounds promising or not. Okay? We won't win points by blowing off the very helpful efforts they've already put in and starting over :-)

A. Hi Komal. Panjala has indicated that flushing toilets is likely a good application, as is watering plants. I doubt that it can practically be directly precipitated and clarified at this concentration, as Jeff was describing a substantially more complex operation. But in any case, such answers are probably more along the line of "food for thought and experiment" than simple yes/no responses. Good luck.

Regards,

A. Sorry for the difficulties, Vikram, but I don't know exactly what question you are asking...

A generalized ETP regimen to handle any volume of any ETP waste under unknown conditions is a subject which fills whole aisles in technical libraries :-)

Or are you saying that you've already treated the waste, and now you want to put this treated waste into an R.O. system to pull some pure water out of it, to be used for some purpose? Generally, treated waste water is so high in salts that it's a poor candidate for R.O. treatment.

Sorry, but if you can clarify and limit your question the readers may be able to help answer that specific question, whereas if you want to learn the whole subject of chemical and R.O. treatment you would need at least a book or a course on the subject. Please clarify. Thanks.

Regards,

A. Hi cousin Manish. As you see, this question has been addressed before in this forum, so we appended your inquiry to it. If the previous answers aren't sufficient for your needs, please expand upon the matter. Thanks.

Regards,

  Excellent question, Wilson. Unfortunately, it requires a good knowledge of the subject of leather pickling and tanning, about which I know nothing. Hopefully another reader has experience there. Sorry I don't know any industrial use for this type of salty water.

Regards,

A. Hi Adithya. If you are speaking of the 'reject' water, first it sounds very unlikely. Please see
waterquality.montana.edu/docs/homeowners/tds_fact_sheet.shtml
for a really quick intro to the subject. But further, the idea that reject water that is unfit for other purposes should be drunk is hard to swallow :-)

If you are asking whether the 'good' portion of the water coming out of an RO unit can be drunk, the general answer is yes -- desalination plants, for example are built with this in mind. But simply passing the water through an RO unit is of course no guarantee that it is drinkable ... the water must still be analyzed for, and possibly treated for, all sorts of contaminants; and there may have been contaminants in the influent that rule it out. Good luck.

Regards,

A. While RO reject water is usually not suitable for drinking, there are many possible ways to re-use it. If the hardness is low, it can be used in cooling towers or fume scrubbers. It can also be used to flush toilets, and if the TDS concentration is no more than 600-800 mg/L, then is could be used for irrigation (some plants are more tolerant than others to water with over 600 mg/L of TDS).

A. It is fairly easy to precipitate the hardness from RO concentrate by raising the pH and settling out the precipitate. After settling, the pH can be re-adjusted lower.

There are also electrochemical devices that will do this.

A. Uses for the RO reject depend mainly on its composition. If it is < 600 mg/L in TDS, then it could be used for irrigation.

A. Hi Dilip,
If you are going to use the water on the garden, the conductivity will be fine for that.
It may be worth a biological lab test to be certain it does not contain any bacterial or viral hazard.
Ground water can pose a health hazard if you are not certain as to the sources of water draining into it from the environment in the wider neighborhood.
After all, the lab you mentioned did advise that you filter the water before you drinking it anyway.
Check with them what they found in the water.
You can add a simple U.V. lamp system to the reject water stream to bring any bacteria count down.
Best regards
Mark.

A. Well it is not always cost effective to make an RO system double pass or multiple pass since with increase in TDS the electricity consumption will increase tremendously.

3.5 HP high pressure Pump verses 7 HP Pump.

Secondly the type of membranes will more than double once you step up from brackish (less than 7000 TDS) to Sea water, (over 12000 TDS)

Thirdly the life of membrane will reduce to 12 months rather than a normal 36 months.

Therefore recycle of RO reject can only be worked out once you know the following.

a) Cost and quantity of feed water.

b) Electricity cost.

c) Membrane replacement cost.

d) Whether the product is acceptable for industrial, domestic use (up to 380 TDS) or you need theoretically zero TDS (actually 12 to 40TDS) where minerals are added to create desired flavour or taste.

The best use of RO waste I have seen so far is its use in huge artificial sea water fish ponds (33000 to 40000 TDS).

A. Hi Srinidhi. The reason DM water is expensive is that you remove the contaminants chemically, by a substitution reaction, and you must consume a lot of chemical to do so. So the more contaminants, the more expensive.

Thus you might be able to reduce the cost of DM water by passing raw water through an RO unit and then demineralizing the RO water, but not by demineralizing the reject water. I only recently heard of electronic demineralizing, which uses no chemicals, but I assume that the electricity use and additional maintenance means it isn't cheap either.

Regards,

A. Hi Deepak. It certainly sounds plausible to me, but we also used to think it was okay to bury drums of waste.

I think it's a matter of analyzing what is actually in that RO water (hopefully nothing but the original water hardness ingredients) and then doing a lit search to find out what people have actually determined regarding that thesis, and then also checking with the authorities regarding what is legal and what is the structure of your aquifer because you don't want to dump into a spring. Some foolish stuff is legal and some wise stuff is illegal, so we want to both be smart and obey the law rather than making assumptions :-)

Luck and Regards,

Readers: With 7 questions posted in a row and no answers (except my musings as site curator), we need people to start offering their thoughts about possible answers. One of the best ways to learn is to attempt to teach, so if you have a question, please also include your thoughts on one of the already open questions. It's a public forum, not a consulting service.

Regards,

! Well said @Ted. The best way to Learn is by trying to educate. In that spirit, I would like to say what I have in mind. First, I got here as I was trying to find the best solution (which am still in search of) to RO waste water.
I hail from a region that's not well developed in road systems and there isn't much ground cover. It's a fairly arid/semi-arid area. So I was thinking this waste water from my RO system could be sprinkled along roads to reduce and avoid dust.
Better yet, it could be used to irrigate/grow grass for playing fields.
Well, I don't know how effective this is. I mean, in either way, I shall be engaging in some sort of evaporation related solution. Just my thoughts.
Looking forward to readers' input.

Regards.