CONSERVATION DEIONIZATION ECONOMICS EDI MEMBRANES MERCURY PHARMACEUTICALS REVERSE OSMOSIS SEMICONDUCTORS TECHNOLOGY DEVELOPMENT UV WASTEWATER WATER REUSE  

Abstract

(Editor’s note: This column is based on recent discussions in the LinkedIn Ultrapure Water Group. This column seeks to accurately reflect comments from each contributor. On occasion, there may be the need to edit contributor comments for clarity or length. Readers are invited to join the Ultrapure Water Group and to participate in discussions. An important purpose of the group is to provide a forum for practical examination of issues facing endusers of high-purity water.)

Wastewater

Alternatives for Reusing Waste High-Purity Water

(Editor’s note: This column is based on recent discussions in the LinkedIn Ultrapure Water Group. This column seeks to accurately reflect comments from each contributor. On occasion, there may be the need to edit contributor comments for clarity or length. Readers are invited to join the Ultrapure Water Group and to participate in discussions. An important purpose of the group is to provide a forum for practical examination of issues facing endusers of high-purity water.)

Ultrapure Wastewater?

Is there such a thing as ultrapure wastewater? Is it reusable?

Anthony: “Yes, absolutely. Generally this is (still) of very good quality and can be reused. One example is reverse osmosis (RO) reject from the second-pass RO that can often be used as feedwater to the first-pass RO. However, generally one needs to be careful when reusing wastewater as feedwater because of the potential for forming closed-concentration loops. Another example is using wastewater for other purposes onsite, such as cooling tower top-up. I hope this helps.”

Mike: “Anthony, thanks for your useful thoughts. Have you or other group members seen these recommendations in use?”

Martin: “Are you referring to reuse of permeate/deionate, or reuse of the reject from the process?”

Mike: “Martin, thanks for your question. I'm thinking about the following: 1. the high-purity water at the end of the line after it is used— as in a microelectronics fab or say a pharma plant rinse stream from a cleaning process; and 2. a water stream as you suggest that at that point in time would not meet the normal quality specifications for high-purity water at the start of the process where the water is used. What are your observations or that of other group members? Please feel free to bring into discussion high-purity process waters that may be outside of numbers 1 and 2.”

Martin: “The MF/UF technology in form of silicon carbide membranes has excellent properties as pre-RO treatment and when retaining particle-bound pollutants and oil from industrial wastewater such as the metal and semiconductor industry.”

Mark: “Yes it is possible to produce high-purity water from wastewater, including from industrial wastewater.”

Andres: “We have wastewater from the electrodeionization (EDI) stage (that is, the reject stream from that step) which could be as much as four times cleaner than municipal water, although very far away from any classification as "ultrapure" as of the ASTM D5127 standard. That water could be perfectly used for cooling processes and sanitary applications.

Even if purer than municipal water, authorities won't allow that water to be used in cafeterias or other human consumption applications.”

Fritz: “Concerning EDI, two concentrate streams were always used in the past. One to be recirculated, one to the drain to remove hydrogen (e.g., old USF H30/60/... modules). That resulted in about a 90 to 95% yield. With newer EDI modules, it is possible to keep all of the concentrate and recirculate it before RO. The result is that your EDI yield is 100%. For that, two things are needed:

1. Let the concentrate stream have contact with fresh air for degassing.

2. Calculate the maximum possible concentration of hydrogen in the air and make sure that you can never reach explosion limit. 

Another possibility to reuse water could be the RO concentrate for use on the garden/lawn. That would also save wastewater costs. But, I guess the concentrate must be combined with potable/well water to reach 1,000 to 2,000 microsiemens per centimeter (µS/cm). Has anybody experiences with that idea?”

Marc: “I believe that waste management will become more and more a focus point. It will require a different mindset in how we construct and operate water treatment system lay outs in order to manage waste quality...or in other words manage upstream processes to create valuable reusable product streams that we today call "waste". This is all about the dynamics of water composition in upstream (pretreatment) processes and how they affect waste quality. That goes beyond the current thinking in unit operations with the purpose to achieve a specific product water quality and requires a bit of out-of-the-box thinking.”

Fab: “All the waste streams from the RO/EDI, or even the pretreatment can be recovered > %90+ with the help of technologies such as electrodialysis reversal (EDR) or high-efficiency RO. The concern becomes the money spent and the final < 10% reject stream of the recovery system. The salts and organics will be so concentrated that one may have issues with the local discharge criteria. So, before any recovery is discussed, it is important to look at what you can discharge. If money is no issue, the recovery-system's concentrate can be sent to zero liquid discharge. Hope this helps.”

UV- Conventional versus LED

Mike: “Any thoughts on the use of conventional 185- and 254-nanometer (nm) UV lamps versus using LED UV lamps?

Nikhilesh: “Both UV-LEDs— at 269 and 282 nm— that are currently available on the market have better disinfecting action than a conventional 254-nm UV lamp. Both show an increase of the inactivation with an increasing fluence. Between UV-LEDs, at 269 and 282 nm, 269 nm shows better disinfection than at 282 nm for a similar fluence. However, the emission output is better with 282 nm - UV-LEDs. Therefore, an optimum configuration with respect to power input versus disinfection is necessary.”

Mike: “Do the new UV-LEDs offer advantages over conventional UV? Why make the switch?”

Matt: “LED advantages would be life and energy consumption. In previous applications, I would assume the same applies.”

Jean-Francois: “Unlike conventional UV lamps, the UV LED lamps do not require mercury in the lamp to operate. It is therefore easier to dispose of UV LED lamps according to environmental laws. This advantage may become critical at a time when antipollution laws become more and more stringent. Transporting mercury or products that contain mercury (even if the amounts are small) may also become increasingly difficult as new legislations emerge in different countries. In addition, the UV LED lamps last longer than conventional UV lamps, and this means reducing the maintenance time, at least by a factor of 2. The UV-LED lamps take less space, a benefit that can be useful in specific cases. Finally, the UV-LED lamps require less energy to operate.” 

What are your thoughts? You may join this or other discussions at the Ultrapure Water group. Simply go to www.LinkedIn.com. After logging in, or setting up an account, go to the “Interests” section and search for Ultrapure Water under groups. You may also click on the “LinkedIn” button on our website. We welcome new members.

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