Brackish water treatment

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Rmk9785e

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A friend from the South-Asian subcontinent wants to provide free drinking water in his small ancestral village (~800 people) where the underground water has turned brackish and the municipal water supply system only works when there is river water available through a canal which runs for 6-8 months annually. He is considering installing a RO system generating about 6,000 gallons per day. They will have the water tested after a well is bored.
Looking for advice on what all should be considered for this type of a project. Thank you for sharing your knowledge and expertise.
 

Plant.One

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one thing to consider is where the discharge of wastewater is going to go.

even a high quality recirculating RO system is going to at best be around 3:1 product:waste water ratio. Lesser quality units can be as much as 1:3 or 1:4 product:discharge (waste) water. make sure that the system has a suitable boost pump as part of it to help with efficiency. low pressure = lower efficiency. most membranes that i'm familiar with are GPD rated for 50 psi at 50*F. this also helps so that your well pump isnt taking the load of the strain of keeping the membrane under pressure. if you can increase the pressure via a boost pump to lets say 80 PSI, you can significantly increase the production capability of the system.

if they're going to utilize the full capacity of the RO system, they're going to need to be able to dump minimum 2000 gpd (and possibly as much as 20,000 gpd) somewhere where its not going to cause harm to the local ecosystem. the brine (salt) concentration on the waste is going to be higher than the well conditions so keep that in mind.

second - the well of course is going to have to be capable of producing consistently 8000-12000 gpd minimum



i used to be a spectrapure dealer some years back, and we owned/used one of their 1000 gpd "pumped up" commercial units. i would strongly suggest getting in contact with them (or a similar quality company) and get their recommendations for the situation. even if you dont go with one of their units, they should be able to provide him the kind of technical information needed to achieve the goals necessary for that village.



a further consideration, since RO water is nearly chemically pure H20 and has zero buffer capacity, theres likely going to need to be some sort of PH treatment added if the piping system has any lead components to it. if the water goes acidic, you could easily end up in a situation like what happened here in Flint, MI where extremely high levels of lead were leeching into the drinking water when they switch to the flint river and ph treatment protocols were ignored.

HTH
 

TJanak

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Not much to add here except your mention of Spectrapure caught my attention. I've used their RO systems in greenhouses with high TDS water. So when I built a house and needed treatment for high TDS well water, I investigated whole house RO and talked to Spectrapure. The "expert" there (not a salesperson) recommended dumping the waste water back down the well. He said it's done all of the time. It may be, but that sure seemed counter-productive to me...
 

Plant.One

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im guessing they're going on the assumption that your RO water wasnt going to be your sole supply for the entire home and that there would be other usage from said well - regardless if thats agricultural, washing, toilets, etc. therefore it would end up being an eventual flushing due to non RO usage taking advantage of that recirculated water. sounds pretty slick solution if you ask me for what to do with the wastewater and not having to flush it thru your septic/drain field constantly, or have a separate dump spot for it.
 

Sqwm6t4l

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Brackish water is a type of saltwater that is derived from the mixing of seawater with underground aquifers. It has been used for irrigation, drinking, and industrial purposes for centuries, but inappropriate handling and wastewater disposal practices have resulted in contamination of the aquifers. With the realization that many brackish resources might be contaminated and need to be monitored properly, there is a great need for effective brackish water treatment technologies.

For example, reverse osmosis (RO) was one of the most widely applied methods for brackish water purification in the past; however, it not only needs high energy requirements but also large-scale pretreatments such as coagulation, flocculation, sedimentation, and RO processes. In addition, it generates a stream of concentrated saltwater discharge that may cause environmental problems.
 
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Sqwm6t4l

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Water has the property of dissolving many substances. It is more appropriately known as a solvent. Dissolved substances include inorganic compounds like salts and organic compounds such as sugars and amino acids. In freshwater, however, the dissolved substance is in many cases beneficial to the organisms that live in water, especially to those that can metabolize dissolved oxygen (O2), as well as dissolved CO2.
The high concentrations of salts often found in water that comes from the sea, for example, is essentially poison for most living things. While it has been established for years now that “salt” treatment of water is capable of removing harmful pathogens, just how effective this process is at removing other types of foulants is often left unconsidered by purveyors of the technology used to treat brackish water.
watertechguide
 
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Sqwm6t4l

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Brackish water is a type of saltwater that is derived from the mixing of seawater with underground aquifers. It has been used for irrigation, drinking, and industrial purposes for centuries, but inappropriate handling and wastewater disposal practices have resulted in contamination of the aquifers. With the realization that many brackish resources might be contaminated and need to be monitored properly, there is a great need for effective brackish water treatment technologies. For example, reverse osmosis (RO) was one of the most widely applied methods for brackish water purification in the past; however, it not only needs high energy requirements but also large-scale pretreatments such as coagulation, flocculation, sedimentation, and RO processes. In addition, it generates a stream of concentrated saltwater discharge that may cause environmental problems.
 

Sqwm6t4l

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Brackish water is salty and loosely defined as groundwater with a total dissolved solids content above 10,000 ppm (mg/L). Brackish water treatment methods are used for different purification processes such as desalination and pre-treatment of water for the aquaculture industry. The desalination process in brackish water involves the removal or reduction of the salts (including sodium chloride) making the water potable https://bit.ly/3oWTpZF. Brackish water can be found in underground aquifers and shallow saline lakes, and this finding has led to large-scale desalination plants which are used in many parts of the world including the US, Middle East, and China.
 
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