A. Not in the way the term “ATU” is currently understood. ATU is an acronym for “Aerobic Treatment Unit,” but it has evolved into industry shorthand for technologies that use a “suspended growth” treatment process. (This process involves pumping air into a liquid medium, where wasteeating microbes are grown, “suspended” in the liquid). By contrast, AdvanTex Treatment Systems are packed bed filters that use an “attached growth” treatment process. (Attached growth uses physical filtration devices on which waste-eating microbes are grown.) Since both these treatment processes use oxygen, technically they are both Aerobic Treatment Processes; the differences in performance, however, are significant. Suspended growth processes in residential applications are typically on-demand, gravity-discharge and rely solely on complete mixing and the biochemistry of aeration to treat waste. Any disruption of this delicate biochemical process (peak loads, power outages) can cause untreated waste to gravity right through the unit and into the drainfield. In contrast, attached growth packed bed filters like AdvanTex are typically time-dosed, pump discharge and use both biochemical AND physical removal treatment processes. So they can handle peak loads reliably and no untreated waste is bypassed under any circumstances. Attached growth packed bed filters have other benefits as well: quick start-ups, low O&M costs, and low power consumption.

Q. Are your AdvanTex textile filters a new technology?

A. Yes, but the textile filter treatment process is based on a proven technology: packed bed filters. At the end of this section, Orenco includes a chapter on “Intermittent and Recirculating Packed Bed Filters” from the definitive textbook on decentralized waster water treatment: Small and Decentralized Wastewater Management Systems (Crites and Tchobanoglous, 1998). In that chapter, on page 714, there is a brief summary of the history of packed bed filters: “Early Development and History of Use.” We’ve also included an article that discusses the use of textile media in wastewater treatment: “Performance of Packed Bed Filters,” (T. Bounds, E. Ball, H. Ball, 2000). Additional documentation can be provided at your request.

Q. How can you take a 360-square-foot packed bed filter, like a sand or gravel filter, and compress it into just 10 to 30-square-feet?

A. Because of the increased surface area of the textile media, combined with its large void spaces and its water holding capacity. This is a treatment process based on sound science, incorporating fundamental principles of physics (mass loading), chemistry, and biology.

Q. Why does textile have such a bigger surface area and void space than sand or gravel?

A. Because the textile media is fibrous, not solid. With a solid grain of sand or gravel, only the outside surface area is available for the attachment of bacteria. With textile, the surface area around each and every fiber is also available. As a result, the surface area is more than 5 times greater than that of sand media.

Q. According to Orenco System Inc. research, you’re loading your textile filters as high as 60 gpd / ft2. That’s much, much higher than the typical loading rates for intermittent sand filters (1.25 gpd / ft2) and recirculating sand filters (5 gpd / ft2). How can you do that?

A. There are a number of reasons why. The first reason is the larger surface area of the textile media, as noted in the previous question. The larger surface area gives greater colonies of bacteria an inter-face for oxygen exchange. The second reason is the greater void space in textile media, which is about 5 times greater than that of sand. Void space does two things; it allows for a free flow of oxygen and provides a larger void for solids accumulation. Free flow of oxygen combined with a large interface for oxygen trans-fer optimizes bacterial digestion. The SAR (Solids Accumulation Rate) is a measurement of how long a filter will last before it clogs with organic and inorganic particles, as well as grease and oil. The greater the SAR, the longer life a filter will have. The third is the greater water holding capacity of the textile media. An increased water holding capacity equates to a more sustainable environment for bacteria to live in. A poor water holding capacity creates an environment where bacteria dry out and sloughing can occur. Finally, water-holding capacity is important, because high water-holding capacity gives bacteria the time to digest organic waste. Textile media has about five times the water-holding capacity of sand. It’s important to note that these factors combine to allow substantial increases in loading rates. For example, one cubic foot of ISF sand media has about twice as much surface area as one cubic foot of RSF sand media. ISF sand media also has a better water holding capacity. However the loading rate of the RSF sand media is actually five times higher due to the greater void space. If we compare the sand medias, the ISF has more surface area and greater water holding capacity while the RSF has greater void spaces. To conclude, textile media optimizes treatment with a large surface area, greater void space, and increased water holding capacity, which allows the combination of the best attributes of the ISF and the RSF into one compact, packed bed filter.

Q. How long will the media last?

A. The media should last indefinitely under normal domestic discharge conditions. The synthetic fibers are made of durable and biodegradation-resistant polymers.

Q. Will the media need to be discarded or replaced, and, if so, how frequently?

A. No. The media hang in aligned sheets. This style is built to accommodate solids accumulation, and, under normal conditions, should last indefinitely. It can be easily maintained by cleaning with a hose or pressure washer. We expect the nominal interval between cleanings to be several years, although, as with all biochemical processes, that will depend on the mass loading of the system. Also, the biomat that develops on the media is where treatment occurs, so excessive cleaning does not assure improved performance; maintenance should be done by a knowledgeable and qualified operator.

Q. Occasionally I see references to an “RX Series” textile filter. But most of your material discusses the “AX Series.” What's the difference between the AX and the RX?

A. The AX Series uses aligned sheets of hanging textile material, while the RX Series – an earlier version of the product – uses random chips (aka “coupons”) of textile material. The AX Series is a refinement of the technology and is the one Orenco Systems Inc. are now promoting except in regions that have approved the RX Series but have not yet approved the AX Series.