Demineralization Plant "Rejects"

What are the effective and economical solutions for evacuation or treatment of rejects comes from a reverse osmosis plant?

N.B: RO-Plant  is located in an area away from the sea and wastewater treatment plant

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Taxonomy

• Solid Waste Management
• Solid Waste Treatment
• RO Systems
• Reverse Osmosis
• Waste to Value
• Waste Disposal
• Waste disposal

11 Answers

1. Hello Ghazali,

   There are many factors that determine what the most appropriate and cost effective solution to your particular RO concentrate handling problem. 

   First off is how much brine waste are you talking about?

   What is the regulatory environment?

   And what are your realistic disposal avenues?

   What are your available sources of energy and their respective costs? If you have low-grade waste heat you could look to a Humidification-Dehumidification process.

   What are the reliability and availability requirements of the process? A tightly integrated process with no buffer storage can quickly run into problems if shutdown of the downstream processes causes/requires shutdown of the upstream process ('the tail is wagging the dog').

   Do you have to get to a "Zero Liquid Discharge"? (If doing anything other than simple solar evap, this can become a complex and very expensive process).

   Is land cheaply available for evaporation ponds and is the climate conducive to evaporation. This is a low tech solution, though it is not without limitations and drawbacks.

   What is the subsurface geology like - deep well injection can also be effective, though you need to be confident that the target strata can both accept the flow (and is chemically compatible) and is also isolated from other geological sequences to prevent migration/cross contamination. This can also be quite expensive if the target strata is very deep and if there is significant probability of drilling dud wells.

   Otherwise - there are numerous methods for further concentrating RO brine, most of which are some variant of (energy intensive) thermal desalinatio processes - these are often quite complex and expensive systems to build and to operate, typically requiring pre-treatment steps to reduce or remove alkali earth metals (Ca, Mg, Ba, Sr) and Silica to prevent scaling of great transfer surfaces. They also require operators with the right skills and experience to run them, which can be a considerable expense in order to get them to come/stay at remote locations.

   I'm afraid there's no single simple solution - there's an entire industry around trying to tackle the very problem you describe!

   Happy to answer more questions. Good luck!

2. Hello Ghazali, Considering the water source coming from a river, the discharged concentrate could be placed in a lined pit and allowed to evaporate. You of course would need to calculate the total daily discharge from the RO, approximate evaporation, and the size of the pit required. Also it would be advisable to have a second lined pit below the first as an overflow retention pond. This is done here in the US. for Mining Clean-Up Sites where the waste water is toxic with Heavy Metals and Arsenic. Good Luck!

3. Please mention the Analysis of Reject Water to be treated and quantity so that economical solution can be provided. Simple and economical solution is to put 2nd pass RO system and then evaporator to evaporate the rest of water. 

   1 Comment

   1. attached raw water analysis, production 100 m3/h with salinity less than 0.8 g/l 

4. Hello

   You have great question.  The solution depends on the parameters of RO concentrate and quantum to be handled. There are country specific regulations to dispose of the concentrate. Variety of technologies for Zero Liquid discharge are available like thermal evaporation, forward osmosis etc.  The optimal solution depends on CAPEX and OPEX conditions associated with local regulations.  Startup groups have come with innovative energy efficient technologies as well

   1 Comment

   1. Source is river,  attached raw water analysis,  production 100 m3/h with salinity less than 0.8 g/l 

5. Around 75% of the Water fed into a RO filter, is wasted. Only 25% gets extracted as drinking Water.

    I think that given the high conductivity of the RO reject, electro dialysis could also be considered.The answer depends on the cost you are waling to pay for concentrate disposal and the volume of concentrate that has to be disposed of per day.  For small volumes (less than 1,000 m3/day) the lowest cost disposal is the discharge to the closest sewer system.  With the increasing cost of water and waste discharge, more companies are looking to recover and reuse RO reject water. While it is possible to reuse the reject water from an RO system by feeding it directly into a 2nd RO unit, the likelihood of scaling or fouling the 2nd RO without pre-treatment is rather high.

   ENCON Mechanical Vapour Compression (MVC) Evaporators and ENCON Thermal Evaporators have proven to be effective technologies for dewatering RO reject / RO concentrate waste streams. In brief, evaporation is a time-tested methodology for reducing the water portion of water-based waste. The evaporator converts the water portion of water-based waste to water vapour, while leaving the higher boiling contaminants behind. This greatly minimizes the amount of waste that needs to be hauled off-site

   Evaporation technology has always been more “hands off” than other wastewater treatment methodologies resulting in a dramatically lower labour cost. Evaporation technology can handle a much wider range of waste streams compared to membranes and traditional physical / chemical treatment methodologies. Finally, evaporation does a much better job of concentrating waste streams compared to other methods, thereby yielding a lower disposal volume and cost.

   The various methods of disposal reject is as follows.
   1. Watering plants.
   2. Send to sewage disposal.
   3. 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.

   6. Waste water reusing method for washing clothes.

    

    

   1 Comment

   1. Thank you for information, it's really interesting as a proposal for reuse of these rejects, do you know what types of plants can support salt water, since for this project the treated water is used for irrigation drips. so I can propose to keep an area for these kind of plantes which supports salt water

6. A pond :)

7. It is necessary to study the retentate analysis, but one of the variants of electrodialysis, it allows you to concentrate the salts to 100-130 g / l, followed by vacuum evaporation. Either to divide the salts into constituents and get the comercial products.

8. the first and best thing is to eliminate the waste or reduce the waste water. As you cannot eliminate RO waste you can alteast reduce the reject volume by adopting ultra high efficiency water treatment systems which are capable of recovery up to 98%. To recommend a suitable technology and process we will need complete details about raw water sources, capacity, raw water characteristics, down stream process and water quality details etc.

   Raman

   1 Comment

   1. Source is river,  attached raw water analysis,  production 100 m3/h with salinity less than 0.8 g/l 

9. Some people are using evaporation bonds. they are made of concrete. But they require a very large spaces. Other solutions is to dispose the reject to the groundwater via a borewell, but you have to get a permission from the government and keep the reject well away from the feed wells. These two solutions are economic.

   Finally other solutions like demineralization plants and zero liquid discharge systems are used, but they cost. However they have a better environmental impact.

10. Agreed terry. This is too vague for a specific answer. The only general answer from a scientists point of view is to clearly state the compounds and elements you are dealing with. In addition what are their parameters.  When you have a good grasp on these then you may proceed with an in situ bioremediation process. The Archaea species will reduce all compounds and chelate all metals into their elemental state. 100% recycle/reuse is then possible. If a certain element is considered in access then search your data base for plants that require more ppm of the item you consider to be too much.

     

    1 Comment

    1. Hi McGowen, thanks for advise, the raw water comes from a riverand the RO-Plant is located on the farm, is not possible to return the concentrated water to the river.  So our proposal it is realized a storage tank of the rejects, but it seem not economic as the discharge rate is high (about 25 m3 / h), so  we are looking for other solutions to evacuate these discharges. (raw water does not contain heavy metals just mineral salts

11.   You have asked a generalized question as so many do here. Without knowing the application the RO is used for; or more specifically what is in the concentrate and at what levels, how can anyone give an answer. If it is just average ground or surface water, then there are no special requirements (these would be concentrated mineral/metallic salts) as if the water had evaporated. But if you are targeting certain contaminants, such as Arsenic, Uranium, Saltwater, or certain Industrial By-products; then the waste stream must be considered Toxic or Hazardous and must be dealt with accordingly (lined pits,tanks,etc.) then taken to a Toxic dump for disposal.

    2 Comments

    1. Source is river,  attached raw water analysis,  production 100 m3/h with salinity less than 0.8 g/l 

    2. Hi Terry, thanks for advise, the raw water comes from a riverand the RO-Plant is located on the farm, is not possible to return the concentrated water to the river.  So our proposal it is realized a storage tank of the rejects, but it seem not economic as the discharge rate is high (about 25 m3 / h), so  we are looking for other solutions to evacuate these discharges. (raw water does not contain heavy metals just mineral salts)