“What is the most effective method of disinfection for treated sewage water, Ozonation or Ultra Filtration? How much can we expect from Ozonation?” asks Tajuddin Shaik, Assistant Manager-Sales and Proposals, Zion Enviro Systems Pvt Ltd. Excerpts of a Linkedin Discussion.
Misha Shifrin, Ozone Application Engineer-Absolute Ozone®: Ozone is the most effective and economical way to disinfect water; however it is unreasonably expensive to be used instead of filtration or bulk BOD/COD removal. That is the place where mechanical filtration, bio-filtration, aeration etc. are most efficient and cost effective.
Ultra filtration is way too expensive to be used for waste water, because of large power consumption and maintenance costs. Most of the ultra-filtration systems could easily become breeding grounds for bacteria and viruses.
Jim Wark, Application Specialist-Neotech Aqua Solutions: Depending on the clarity, (actually UVT%) UV could be a way. We have several companies we are working with in water reuse using UV as the primary disinfectant and if needed chlorine for residual. The three most important things needed are Peak flow rate, UVT % and what one is treating.
Alfonso Carpio, Water Treatment Professional: UV is usually 4 log reduction but can be sized for as many log reduction as needed. I would use mixed oxidant disinfectant generator as it leaves a good amount of residual that can be an assurance for a complete kill of the entire population in the spectrum.
Orlando D. Gutierrez Coronado, Project Engineer-GEOFUTURE: In general, the ozone could give the best cost-effective performance in the long run. If you will evaluate the project just for a few months, then you could disinfect with any other chemical substance as PAA, or even rent an ozone machine.
The UV lamps could have a good performance when you have a high UVT value (UV Transmittance). There is no clarity however, as both solids and dissolved material could absorb the UV light.
In this case we are considering the sewage treated water that could have some of the above described substances to interfere with the UVT.
Alfonso: I suppose UF has been mistakenly mentioned to be UV. UF is not a disinfecting equipment but a filtration medium. To further advance my advocacy on mixed oxidant, it’s more advantageous in providing the residual especially in long distribution pipelines where one would like to measure the amount of residual present to give you peace of mind. It also eliminate the biofilm which can house those organisms that we don’t usually see in any bacterial count in the field.
Colin Deakin, Process Engineer UF/MBR, GE Water & Process Technologies: I agree with Alfonso. UF is a filtration system, but has an extremely high degree of retention of particles including parasites, bacteria and viruses. Typically current system designs will clean and therefore sanitise themselves daily, and can also test themselves for integrity at the same frequency. These two factors go together in maintaining the desired quality. However, meeting something like title 22 for recycle water quality involving human contact requires demonstration of disinfection to 5 log virus. For something like this, UF and disinfection is likely to be required. UF does the bulk of the work removing the major part of the particulate load allowing the disinfection step to work optimally and reliably.
Øyvind Thorsen, Sales Engineer at Sterner AquaTech AS: I support those who have noticed the importance of not forgetting UV as an alternative. There is a huge development in UV for the time being. Look at Wedecos Duron system which we already have installed in Norway where you have longer life time on lamps and much higher UVC output per lamp than we had previously.
Jim: UV is very effective in wastewater treatment when the proper pretreatment and analysis is done. It in fact is one of the least expensive in overall operating and capital costs. The three things which are absolutely needed for UV to be considered:
1. UVT% which is the transmissivity of UV through water, unlike turbidity or colour, can be very tricky. Ocean water for example handles UV well, bottled water with a pinch of sugar does not.
2. Peak Flow rates: UV must be sized for the highest flow, although in most cases, it can be run at lower flow rate.
3. What you are trying to reduce? Is it crypto? Giardia? E-Coli? or something else, it then must be dosed properly.
UV has changed dramatically over the last few years; we can now treat higher flows with less energy and a much smaller footprint if the water clarity is good. If not, calculations need to be made for proper sizing and equipment choices.
Simon Tarlovsky, Regional Sales manager-Aquatech: Just as an additional comment, Ozone and UV are in the same family of treatment, they will kill but not remove, UF is different, will remove but not kill. You need to also consider the failure option in your analysis, what if your execution fails and your kill or removal are not complete.
The problem with UF is that it can be a breeding ground and it can just stop working when slimed.
The problem with UV and Ozone is that it kills but does not remove some spores which are resistant to this treatment. If you don’t keep track of the system, you can have local or general under kill.
In the beverage industry, reuse of any water that has been in contact with waste water, is not yet acceptable, but with enough care and supervision, waste water is not worst than any other water for drinking, when properly treated.
Misha Shifrin: Most of the people here not only know how UV works, but have actual experience with using UV. Without cost comparison UV is only good for people who sell it as they make money on service and light bulb replacement for years to come.
Unlike UV, zone will kill, remove bacteria, viruses, etc., and there are no ozone resistant organisms as ozone is the strongest commercially available oxidizer and it simply burns all organic materials and oxidizes minerals if applied correctly.
Jim: Why then are there more UV systems in use for wastewater treatment than O3 in the US? Ozone is a fine treatment method, no question…But others have abilities too.
Louis Coulthard, Cricket Manager-USRC-Millennium: I have used UV, O3 & straight up simple chlorine to good effect depending on the circumstance. In industrial waste water treatment, turbidity is often a problem negating UV and associated lamp replacement costs and clyptosporidium are unheard of negating the need for & dangers of O3 in unskilled hands. Most cases, straight up chlorination & de-chlorination is simplest & best.
Misha: UV today in the long run will considerably be more expensive than ozone and other alternatives and does not really present an economical solution for large spectrum of applications. Especially wastewater treatment. However it is a great business for people who sell UV tubes every year and I perfectly understand why UV is so vigorously promoted. Water treatment in general has taken a hard beating by
those who used to go around and make claims that couldn’t be justified and took people’s money. Education and 3rd party certifications are taking us at least to a better medium.