RO vs softener vs vacuum distillation 1

[MedicineEng]

Hi Guys:

I am now studying some water treatment solutions for luxury restaurant kitchens in our property and the traditional solution has been to install RO systems in the most expensive equipments in order to protect them from scaling.
The income water is potable, meeting the WHO standards and the maximum hardness during dry season is 250mg/lt.
There is a "cultural" bias in our top brass regarding RO systems, but I believe we are "overdoing" the solution since I don´t really think we need RO systems to treat this water.
In that sense, I was looking for water treatment alternatives and 2 popped up:
a) Install softeners:
There are a couple of disadvantages that I seeing with this solution:
1. I am afraid that the treated water will have some taste, when calcium and magnesium ions are replaced by sodium, so I am not sure if we have to install a polishing filter to get rid of this taste,
2. The regeneration cycle. Some of our restaurants work 24hrs/ day which means that during the regeneration cycle we would have to be working with " untreated water",
3. Salt charges: I am afraid that for the chefs working in the kitchens seeing a guy putting a 25kgs salt bag in their water treatment would raise some eyebrows

The biggest advantage is a question of cost and water savings,

b) Vacuum distillation
The biggest issue that I have with this solution is that in my search for equipment providers on this, I could only find small office style equipment, with a production of around 30lts/day ,when I would need something in the range of 3000lts/day. Also, since I couldn´t find any information on this kind of systems, I am not sure about the noise level or footprint of these equipment. I managed to find some equipment that use vacuum distillation for thinner recovery, but I could not find any bigger application on water treatment.

The traditional RO solution, has the advantage that everybody in the kitchens is confortable with it, but from an engineering point of view is an expensive solution, with expensive running costs and maintenance.

Any suggestions on the direction to take?

Thanks a lot.

 

[bimr]

The water is very hard and water treatment is recommended.

You are best off staying with the RO system for many uses especially where water will end up in the food. It may be possible to use water softeners for some equipment such as the dishwasher, but I would expect the dried dishware may have some salt residue after drying.

The taste of your water will highly depend on the incoming water supply. Sediment, chemicals and organics that can affect the appearance, taste and odor of your water are not affected by softening your water. If these parameters are present, you would need the RO system. It is only possible to find out what your water would taste like after softening by conducting a taste test of softened water.

Here are some tips:

1. It may be possible to outsource the water treatment to an outside firm so that the restaurant does not have to take care of the problem.

2. Carbon filters are typically used to remove taste and odor. You should think about installing carbon filters as well.

3. Distillation equipment is not as commercially available as other water treatment methods.

4. Most water treatment equipment is available with a bypass (treated water and/or not treated water).

5. There may be some taste and odor with the RO system unless carbon filtration is used.

6. The taste of the water softened water should not be affected by the salt. Most of the sodium chloride is passed through the water softener during regeneration leaving only the sodium ion, not the chloride ion.

Taste is a matter of preference. Often people tend to favor the type of water they grew up with for drinking or are used to. Some would say that softened water is bland.

Some people say they prefer the taste of softened water in tea and coffee. The difference in taste compared to hard water can be quite significant.

Generally softened water is recommended for:

Espresso
Iced Tea
Dishware Washing

Espresso machines boil water at a very high temperature and pressure, much more so than coffee brewers. Because of this, hard water will create scale at a very fast rate in espresso machines. Normally softened water causes over extraction of the coffee grounds, which is why it is not used with coffee brewers. However, because extraction time is so short with espresso, it does not cause the same problem. Hard water can cause iced tea to become cloudy. With dishwater washing applications, hard water causes spotting on glassware and excessive detergent usage.

Water softening is not recommended for:

Ice making
Coffee and tea brewing
Fountain beverages

Soft water can slow the freezing process in ice making. With coffee and tea brewers soft water can over extract the oils and flavors in the coffee grounds or tea leaves. The major bottling companies have also asked water treatment professionals to avoid the use of water softeners with fountain beverage equipment because softened water can affect the taste profile and cause excessive foaming.

 

[MedicineEng]

bimr:

Thanks a lot for your very detailed answer.
Just to be clear: when I mention about RO system, in reality the system is a 4 or 5 stage RO system, so it includes the carbon filter that you referred.

 

[PEDARRIN2]

Softening the water is a must, especially if you have dishwashing or any kind of steam using equipment (ovens, etc.). Some equipment manufacturers will not warrantee their equipment unless hardness is less than ~51 mg/L.

There are many opinions, but I think water used for beverages and ice should not be softened (for the reasons already expressed), but should have carbon filtration to remove any chlorination disinfection products which are what produces the objectionable taste, but does not remove chlorides (Cl-). These are usually wall mounted canister units near the beverage area.

If the use is constant, I would recommend a duplex softening (or even triplex) system. When one unit is spent, the other comes on line so there is no hard water bypass. If you are concerned about the amount of salt used, there are some units that use a part of the softened water to produce the brine for the regeneration. The units are a bit larger in size, but use less salt since the brine water does not have any Ca or Mg ions to lessen the backwash effect.

In my opinion, RO might be overkill. Most softeners, when operated correctly, will generate <17 ppm (mg/L) of hardness in the effluent. Only if the TDS is excessive, >500 ppm would I consider using RO. An issue I would have is RO tends to be low in output for the size (and expense) of the equipment. You would have to balance that with whatever perceived benefits would come from using an RO.