Ultrafiltration with pressurized membranes enables all suspended solids to be fully removed from the water. Thanks to the pore size of approximately 0.02 µm, even bacteria and microbes can be captured. Ultrafiltration with pressurized membranes relies on the principle of filtrating water through hollow fiber membranes in a closed system, with the water (generally) traveling from the inside to the outside. Intermittent backwashing is performed to flush the separated pollutants out of the membrane capillary tubes and get rid of them. Every so often, backwashing with added cleaning chemicals is performed to ensure stable operation.

Ultrafiltration with submerged membranes enables all suspended solids to be fully removed from the water. Thanks to the pore size of approximately 0.02 µm, even bacteria and microbes can be captured. The modules of the submerged membrane are arranged in a frame called a “cassette”. This frame is submerged in a tank of water that is constantly fed with raw water during the filtration process. A pump installed on the filtrate side draws the water through the membrane fibers from the outside to the inside. As a result, the separated suspended solids are captured on the outside of the hollow fibers – which is the opposite approach to ultrafiltration with pressurized membranes. The separated pollutants are removed from the surface of the fibers by carrying out periodic backwashing with permeate and are discharged through tank drains.

With a pore size of around 0.1 µm, the ceramic membrane operates in the microfiltration range. This means that large quantities of water can be filtrated per m² of membrane surface. When combined with flocculation or oxidation, the degree of separation that can be achieved is similar to that of ultrafiltration. The ceramic membrane offers many advantages over standard ultrafiltration membranes made from synthetic material. Ceramic is completely insensitive to pH and does not oxidize. What's more, this material is extremely hard and stable (monolithic), which enables highly efficient backwashing using high-pressure water.

Filtration is one of the key processes involved in the treatment of water. The technology was developed in the 1960s – when the company was still called Sulzer – but has undergone continuous enhancement ever since. The origins of wastewater filtration can be traced back to the 1970s. Today, a whole host of systems featuring nozzle floor and drainage floor technology are available for every conceivable application.

WABAG filters are used for a variety of purposes in the treatment of drinking water. Specific treatment targets can be achieved by using a particular filter medium or a particular combination of media in the filters. To ensure a successful filtration process, it is just as important to know about the quality, origin, and possible combinations of filter media as it is to have a good grasp of hydraulic dimensioning and filter construction.

Any process that is used to treat surface water (lake and river water) as well as substandard spring or ground water, has to rely on a combination of physical, biological, and chemical treatment stages.

Various aspects of water quality can be improved by using a complete multi-barrier system. These quality parameters include not only turbidity in the form of inorganic particles and algae but also organic substances, and taste-, odor-, or color-inducing substances, for example.

Over the decades, we have repeatedly adapted the various process combinations to the latest tasks and have constantly enhanced each individual treatment stage. In the last 10 years, membrane technology has found its way into our multi-barrier system philosophy, as it removes particles even more effectively than the classic method of granular media filtration and ensures mechanical disinfection. The proven treatment stages of ozonation (oxidation) and active carbon filtration (adsorption and biodegradation of organics) are now being supplemented by ultrafiltration.

WABAG has been using this combination of processes in its multi-barrier systems for years. The ozone fully or partially oxidizes the micropollutants and makes other dissolved matter more easily biodegradable.

These substances, any reaction products created through ozonation, and other micropollutants are reduced to harmless concentration levels by a special filtration process that relies on biodegradation and/or adsorption. The latest research has revealed that this choice of filtration technology offers major advantages when removing by-products such as these because of the system's flexibility.

Not only that, but the quality of the resulting filtrate is just as high as with a “classic” filtration method.

Another way to remove micropollutants is adsorption by powdered activated carbon (PAC). The prerequisite for using PAC is that the target substance(s) must be absorbable. The process involves adding the finely ground carbon to the flow and removing it from the water again after a specific contact time. In the context of drinking water treatment, membrane filtration (ultrafiltration) is the ideal technology for separating the loaded PAC particles. The resulting backwash water containing the separated PAC has to undergo further treatment or final disposal, but depending on the location and size of the plant this is not always achievable. The handling of powder activated carbon calls for maximum safety measures and a carefully thought-out operational concept.