Experiences with the use of TiO2 for water treatment?

[susannagrub]

Hi, my name is Susanna. I am working on an innovation project with Grundfos.
In a prior stage of the project we found out that Developing Advanced Treatment possibilities is an important task that we want to address.

I have read a lot about TiO2 and am now searching for people who have already made experiences with the use of TiO2 for water treatment.

Do you have experience within that field, or could tell me possible advantages / disadvantages for the usage of TiO2 for treating water?

Your help and information is of great value for this project. I appreciate any hints and ideas that come to your mind regarding the topic!

If you have any other questions regarding the project or the company, don’t hesitate to contact me.
Thank you!
Susanna

 

[moltenmetal]

Do a little literature research: this process has been studied for over thirty years, and at least 300 research groups have published papers on the subject. It's lovely in theory: shine UV light on water in the presence of anatase, and you get photolysis of water resulting in oxidation of organic compounds in the water. No need to add chemicals- you add only light energy. What's not to like?

There are a few firms already building commercial water treatment systems using this technology. Its limitations are well known: the photocatalyst, anatase TiO2, works best in slurry phase, which means that any water treatment system using this technology needs to be/incorporate a fine particulate filter. No problem if you're treating ultrapure water, but a significant problem to solve for real wastewaters which contain species like iron(II). All attempts to immobilize the anatase on a substrate result in significant reductions in catalyst activity. The catalyst is not inexpensive (ie. unlike ordinary pigment grade TiO2) and does tend to deactivate over time, which represents a variable operating cost. But the worst thing about this technology is that the efficiency with which it uses light decreases vastly with increasing light intensity: this means you need a vast number of low-power UV lamps (ie. rather than a few high power units emitting the same total power) to avoid wasting a lot of the UV you produce. Lots of lamps means lots of labour to replace them, lots of quartz sleeves to separate them from the water/catalyst slurry, lots of power supplies, and lots of space etc. This also means lots of capital cost.

The more conventional UV/peroxide treatment process suffers from none of these disadvantages. Considering that most TiO2 treatment systems also add peroxide (to reduce the size/cost of unit needed for a given flowrate of water), it begs the question: why bother with the anatase?

Solar applications of this technology have been studied to death by NREL and others. The result is that solar water treatmentt applications are hampered by the low light intensity limitation, such that solar collectors/intensifiers are basically useless. Some people are now selling so-called "self cleaning" surfaces containing a layer of anatase, which sounds like it has some promise.

 

[susannagrub]

Dear moltenmetal!

Thank you for your reply and your inputs. As you said, there are a lot of other treatment methods like UV / peroxide treatment processes. As far as I know, all existing methods however are not able to fully remove all contaminants alone. One of the challenges for the future will probably be, as we are facing an increasing lack of water and more and more wastewater reuse, that there are some contaminants in the water that are unknown and therefore not treated (e.g. from pharmaceuticals). Have you had any experience on that or do you think that there might be some applications within other areas that use more efficient ways of removing contaminants than RO and e.g. Ozone?

Susanna

 

[orenda1168]

Susanna:

You might want to speak with Dave Orlebeke about his patented electrolytic/catalytic oxidation technology and it's applicability to low level contaminant removal from water. He can be reached via

http://www.EOH2O.com.

Orenda

 

[moltenmetal]

susannagrub: no single technology for water treatment can address all contaminants, and each treatment technology addresses some contaminants efficiently and others poorly at best. Activated carbon doesn't work for soluble compounds, bioeractors don't work for non-degradable ones, oxidation doesn't work on compounds that are difficult to oxidize etc., and none of these deal with most inorganics at all. Appropriate combinations of technologies, arranged in the correct order, CAN address even complex mixtures of contaminants. To save capital and operating cost, you can eliminate some or all of the treatment steps if a particular class of target micropollutants aren't there. That's wastewater engineering 101.

There is no shortage of water: there is merely a shortage of clean, fresh water produced and stored by nature. The difference between contaminated water and water suitable for a particular re-use is energy, reagents and labour (ie. money). And engineering of course.

As to contaminants being "unknown" (ie. pharmaceuticals), what you really mean is that we're now concerned about compounds which act detrimentally at very, very low concentrations, some of which are recalcitrant to some of the easier to implement, less expensive conventional water treatment technologies. We're also concerned about a larger number of target micropollutants every year. Analyzing for these compounds is a very significant challenge. Once you can analyze for them accurately, treating them is far less of a challenge. It is very difficult to treat an analytical artifact (ie. a compound which isn't really there in the water but which shows up on the analysis).