Populations are growing and freshwater suppliers are under stress, not just in developing countries but in many parts of the United States. In response, wastewater utilities turn increasingly to reuse of effluent, even as drinking water.

Now, an ozone-enhanced biologically active filtration system is being offered with the promise to remove difficult pollutants like personal care products, active pharmaceutical ingredients and endocrine-disrupting compounds, and do it cost-effectively. The Leopold Oxelia technology from Xylem is designed to help expand options for water reuse for industrial processes, groundwater recharge, farm irrigation and direct potable reuse.

The company calls the technology a multi-barrier solution for municipal wastewater treatment that combines ozone oxidation, filtration and analytical instrumentation to deliver optimal treatment for reuse or for discharge into sensitive waters. The company says the process costs less than reverse osmosis and does not produce a waste stream that needs added treatment.

Achim Ried, Ph.D., chief engineer for treatment solutions with Xylem, talked about the technology in an interview with Treatment Plant Operator.

TPO: What creates the need for this technology in a marketplace where many water reuse solutions already exist?

Ried: The so-called gold standard in reuse is microfiltration and reverse osmosis followed by UV disinfection. That combination probably yields the highest quality of water. However, it is also a costly solution, and not all reuse applications require such high-quality effluent. The challenge for alternative treatment processes, like our ozone-enhanced biologically active filtration, is to produce the effluent quality required for the specific reuse application, and do it more cost-effectively than membrane filtration solutions.

TPO: What are the basic aims of this process?

Ried: On one hand, we want to achieve disinfection and create a barrier for trace organic contaminants in the water. And we want a further barrier for total organic compounds [TOC], and some filtration effect for suspended solids and turbidity. With our combination of treatments, we can achieve high-quality effluent for all those parameters.

TPO: What is the role of ozone treatment in the process?

Ried: Ozone comes first. It disinfects the water and is able to destroy most of the trace organic contaminants – the chemicals of emerging concern such as pharmaceuticals, industrial chemicals, pesticides and endocrine disrupters. Ozone partially oxidizes these substances and makes them more biologically degradable.

TPO: What is the function of the filtration step?

Ried: Biologically active filtration further reduces the partially oxidized contaminants. So the ozone oxidation with filtration provides a combined barrier to destroy those toxic compounds while eliminating disinfection byproducts and reducing turbidity in the system effluent.

TPO: How does biologically active filtration work?

Ried: It’s a type of media filtration that is well-known and widely used in the wastewater industry. Over time, a thin growth of biofilm develops on the surface of the media. The ozone pretreatment generates more food for the bacteria, which then degrade the partially oxidized organic compounds. It is possible to foster the growth of an optimal balance of microbes on the media surface by operating the ozone step effectively and controlling filter backwash sequencing.

TPO: What kind of media is used for the biologically active filtration?

Ried: We have a choice between two types of standard media. We normally use anthracite, which is also used widely in wastewater filtration, or activated carbon. Both media have advantages and disadvantages. Depending on the overall treatment goal, we choose the best type of media for the specific case.

TPO: Can the ozone treatment phase also be tailored to fit the final effluent goal?

Ried: Yes, and that is important to the overall process, because the generation of ozone consumes the largest share of the operating expense. It is essential to regulate the dose so that the ozone is limited to the amount needed to achieve the specific treatment goal. With this system’s optimized integral control, ozone dosage is influenced not only by incoming water quality but also by the system effluent quality.

TPO: How is the ozone dosage optimized in this process?

Ried: It is accomplished through online measurement. Real-time, online sensors are important to running the process efficiently. The sensors measure the TOC concentration and enable automated adjustment of the ozone dosage. Research has proven a relationship between the amount of TOC and the ozone dosing range. With this specific ratio, it is possible to achieve a specific reduction rate for the organic contaminants. By measuring with online sensors and dosing at a rate from 0.3 to 1.2 grams of ozone per gram of TOC, the process can be adjusted to meet a specific treatment goal.

TPO: Is this system fed with secondary effluent? And has the influent already been disinfected at some level?

Ried: The influent consists of secondary effluent. Normally, there is no disinfection step ahead of the Leopold Oxelia process. The disinfection is accomplished through the ozone oxidation and the filter.

TPO: How effective is this process against parasites like Giardia and Cryptosporidium?

Ried: It is highly effective. Ozone is known as an effective disinfection agent. Studies from the WateReuse Research Foundation have shown that depending on the dosage, ozone treatment achieves log 2 to log 3 removal, which in most cases is sufficient. In addition, if an ozone system is operated correctly, it can achieve the high reduction rates required by California Title 22. But not all reuse water needs to meet that high a standard.

TPO: What sizes of clean-water facilities can use this process most effectively?

Ried: The Leopold media filter is designed to perform optimally at flows of 1 mgd or higher, but there is no limitation on higher flows.

TPO: To what extent has this technology been proven in testing and commercial application?

Ried: The global response to the technology has been very good. For example, the government of Switzerland issued a regulation at the beginning of 2014 that the 100 largest municipal wastewater treatment plants in the country must build an additional treatment barrier for specific micropollutants, or trace organic contaminants. Ozone-enhanced biologically active filtration is one of the treatment processes approved to fulfill the treatment requirement while also being cost-effective.

Extensive testing also continues in the United States with the Oxelia system and alternative technologies for direct and indirect reuse applications. I would say we have passed through the years of research and full-scale demonstration, and now we can see the first commercial projects coming.