UV disinfection for sea water entering RO system

[randyandy]

HI all. We are currently bidding for a big (at least for our company) size RO sea water desalination plant, 60.000 m3/day with 45% recovery i.e. the inlet sea water to the plant is 5555 m3/hr, and this water has to be disinfected before the filtration + RO membranes. We are used to dose NaOCl as disinfection method, but we are worried about the operating costs for such plant (running is also within our scope of work)and huge amounts of chemicals required. So i was fancying about UV sterilization. Apart from installation costs and power consumption, which is low compared to the other plant systems, do you have any feedback about existing plants, drawbacks, problems, etc. with using such technology instead of typical chemical dosing? Thank you in advance for support and wishes of happy new year to all!
Andrea

 

[25362]

As far as I'm aware the beneficial effects of UV irradiation may be lost because of the presence of organics and iron salts, etc., that absorb a great part of the rays.

Probably the following site may be of help:

http://www.waterknowledge.com/pdfs/disinfectbyuv.pdf

 

[quark]

25362 is right. Opacity of water reduces the efficiency of UV Rays. Further, it may not be a cheaper option for, you have to maintain certain exposure time for water to be in contact with UV Light.

Have you thought of generating NaOCl from NaCl? Once you buy the equipment then you have to evaporate sea water

I wish us all A Happy and Prosperous New Year

 

[moltenmetal]

Contact people in the business directly, such as Trojan Technologies and Calgon Carbon Oxidation Technologies. A simple web search will put you in touch with them.

I would suspect you would be better off with a low pressure mercury arc system, even though this will mean large numbers of lamps, because the medium-pressure mercury UV units generate a greater fraction of their light below 254 nm where seawater may be unproductively absorptive.

The absorptivity of seawater to 254 nm light may not be the biggest problem. The potential for fouling of the lamp sheaths has to be considered and dealt with by design.

 

[randyandy]

thanks to all of you guys. i see the production of NaOCl from NaCl a bit difficult as there would be requirement of steam, etc. as this is a RO and ot a MSF system. Which could be the reference paramter on whose basis ask the supplier to refer to in its guarantees? could be water TDS , SS and turbidity values enough or there should be other reference?
he referred to a light transmittance of 90%, but i guess this should be more a parameter HE fixes on the basis of my water characteristics, rather an input value I should give him. What is your opinion?

 

[tickle]

I thought that you could generate NaOCl from seawater by electrochlorination (ie using electricity).

I recommend using the vessel with internal electrodes as opposed to using the pipe as one of the electrodes. I have experience of the pipe rupturing in the later case.

In the past I have seen the effectiveness of uv sterilisation improved by using a "water bell" over the uv lamp. This was at the research phase when I saw it but believe that it has been implemented in industry. The bell is formed by impacting the water onto a plate and a thin skin of water forms a bell that is stabilised by an internal pressure (air). The advantages are no contact with uv lamp and a thinner film of water reducing the absorption by solids etc.

 

[oxilume]

Dear RandyAndy,

For a UV light system that does not use a traditional lamp, and you must wear a welder's helment with #14 filter installed to look at the arc see the Plasma Whirl Arc Light at:

http://www.oxilume.com

The system also produces copious amounts of ozone and hydroxyl radicals. A 100 KW system is currently in operation with a flowrate capacity of up to 1660 m3/hr. The ArcLight can be built with power supplies upwards of 5 MW with only one ArcLight in a vessel. This should easily disinfect and reduce organic loading for the influent to your RO system at a flowrate of 5555 m3/hr.

respectfully,

Todd



Todd

http://www.oxilume.com

 

[orenda1168]

Randyandy:

Tickle is correct about chlorine generation by application of current salt water chlorine generator technology.....this is a preferred method in recreational water systems. Though these are far smaller volume systems than yours, the technology should be a direct scale-up, and might be best addressed via slipstream treatment where the optimum sodium chloride concentration can be maintained by RO water dilution. No additional chemical input is required.

Orenda

 

[EdStainless]

UV works very well on clear water. I have seen an ArcLight instalation, though I don't know any of the technical details about that instalation.
Since you are dealing with seawater you need to read up on using Br.
Many systems use one treatment method regularly, and then periodicly treat with a different process/chemical just to make sure that things stay clean. If you choose to just use one treatment you need to have a way of burst treating at a higher level once in a while.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[cub3bead]

So how do you deal with all of the bromate you just made with the UV and/or chlorination?

 

[oxilume]

To EdStainless,

As the inventor of the "ArcLight," I sure would like to know where you saw that installation. The "ArcLight" is not a standard UV light system.

Todd

Todd

http://www.oxilume.com