Xylem’s Oxelia Technology Offers Advanced Treatment

Oxelia technology from Xylem combines ozone for oxidation with biological media filtration to rid water of difficult-to-treat organic compounds.
Xylem’s Oxelia Technology Offers Advanced Treatment
Schematic diagram of the Oxelia treatment process.

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Wastewater reuse today looks beyond irrigation to include direct and indirect potable reuse. That calls for treatment approaches more advanced than biological treatment followed by media or membrane filtration.

Xylem now offers the Oxelia ozone-enhanced biologically active filtration system designed for reuse applications. The company also offers variations on the same basic process for drinking water and industrial wastewater treatment.

In each case, the process first uses an oxidant to break down recalcitrant organic compounds into biodegradable components. Then, naturally occurring microbes attached to media in a fixed-bed filter provide aerobic biological treatment of the partially oxidized organics, leading to essentially complete destruction of total organic carbon (TOC), trace contaminants and oxidation byproducts.

The process integrates offerings from three or more Xylem brands under a central control system that optimizes filter operation based on oxidant dosage and effluent water quality. Tony Callery, lead product manager for Xylem’s Leopold and Sanitaire product lines, described the technologies in an interview with Treatment Plant Operator.

TPO: What was the driving force behind bringing these offerings to market?

Callery: There are different value propositions for the three versions of the technology. On the water reuse side, value is driven by scenarios involved with drought, population growth, urbanization and requirements for smarter reuse water source management. The aim is to take wastewater effluent and treat it to where it is suitable for direct or indirect potable reuse.

That raises issues with trace organic contaminants that may pose health concerns. These include pharmaceutical and personal care product residuals that pass through the treatment process. They can be grouped under total organic carbon contaminants — a long list of substances that are regulated or are intended for regulation sometime in the future.

TPO: So this technology is not aimed at water reuse for irrigation but specifically for return to the potable water supply?

Callery: That’s right. In treating water for irrigation use, you’re concerned mainly with vector attraction and BOD and COD loadings. Those are generally handled well within regulatory requirements by a good secondary treatment process, commonly followed by tertiary filtration and a UV disinfection system. Oxelia technology is for potable reuse where you’re typically discharging to a reservoir and ultimately a water treatment plant. In the case of Europe, it’s applicable to discharge into sensitive waters used for fishing and other recreation.

TPO: What is the function of ozone in this process?

Callery: Ozone breaks down naturally occurring and synthetic organic compounds to a biodegradable state so they can be destroyed in a biologically active filter. The filter also serves to significantly reduce ozonation byproducts. The total process avoids issues related to the creation of a waste stream that then needs to be managed.

TPO: Please describe how the process works from start to finish.

Callery: Effluent from secondary wastewater treatment enters a contact chamber where ozone is added to start the breakdown of the organic contaminants. The water then travels to a downflow filter, generally with anthracite, sand, or sand and anthracite media, depending on the application and the type of contaminants to be removed. Backwash times are extended. We bump the filter from time to time to clear any buildup of gases or contaminants. We calculate the runtime based on the contamination level and the filter’s biological health. The final effluent is near or at potable water quality, based on the regulatory parameters.

TPO: How is the process controlled?

Callery: The system uses online sensors in a multi-loop configuration to automatically adjust the process to achieve treatment goals at an economical cost. UV sensors are placed in three locations: at the inlet to the ozone contact chamber, where the water passes to the filter, and at the filter outlet. An algorithm uses those three inputs to control the ozone dosage, which is critical from a water-quality perspective and for economics, as well.

TPO: How do the treatment issues differ in using Oxelia for drinking water as opposed to reuse applications?

Callery: In drinking water, the common concern tends to be taste- and odor-causing pollutants, and a second target is recalcitrant organic micropollutants. These are often man-made, from pharmaceuticals or personal care products, but natural micropollutants also can form, such as from algae beds on a lake in early summer. Pesticides can find their way into water supplies, along with NDMA, MTBE, 1-4 dioxane and other organics that aren’t easily handled by conventional filtration. Biostability in the water sent to the distribution system is also a concern.

TPO: In view of that, how is the Oxelia process for drinking water different?

Callery: It still uses a downflow filter and a very similar control algorithm. However, the oxidant used may differ with the application. For example, if not looking for removal of any specific micropollutant, just a general taste and odor application, we would use ozone and a biological filter. For a seasonal condition like algae in a lake or a chemical leakage in the area that poses concern about water contamination, we would look at ozone plus hydrogen peroxide as the oxidizing agent — that is much faster and stronger than ozone by itself.

TPO: How were these technologies developed?

Callery: As separate companies, we’ve been doing this for years. Wedeco would put in the ozone systems, Leopold would install the biofiltration, and YSI or WTW would sell sensors into a specification on projects. Over the past few years we have pooled our expertise to tie these offerings into an operative whole that allows us to offer process performance guarantees.

TPO: What has been done to prove these technologies?

Callery: We’ve done a tremendous amount of pilot work with very good results. We’ve also participated in Water Research Foundation studies, so we have verifications from third-party sources in how well the systems operate.

TPO: In a nutshell, how does the industrial version of Oxelia differ from the others?

Callery: On the surface it looks like the same process, but it’s really quite different. We use ozone as the oxidant, but we use an upflow aerated biological filter with a Leopold underdrain system that provides the aeration — there is no need for a separate aeration grid. The primary application is the reduction of COD in the paper mills, oil and gas and other heavy industry sectors, especially in developing countries.

TPO: What size facilities are best suited for these technologies?

Callery: Generally speaking, our experience indicates that the technology is best suited to plants with flows of 1 mgd and up. Practically speaking, many applications will be in much larger regional plants.



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