«The entire team at WABAG Water Technology Ltd is mindful of this important fact during day-to-day activities and when working on any new treatment plant. That is why the top priority is to minimize the use of chemicals during drinking water treatment whenever possible. Whether we are renovating/expanding an existing plant or building a brand new one, there is one key demand that we have to meet and which is our promise to customers: to select and use the optimum technology or process chain for the specific type of raw water concerned.».
CFO / Head of Execution
In Switzerland, where spring water is a common source of drinking water, some of the most widely used water treatment processes are particle separation and disinfection. Membrane filtration can take care of both tasks in one fell swoop.
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.
A whole host of different membranes and pressure modules are available on the market. As an independent system provider, WABAG uses only the best available membrane systems, all of which are tested in house and offer maximum performance and – above all – operational safety.
WABAG has been constructing and operating ultrafiltration plants with pressurized membranes for more than 10 years. The experience it has gained over this time is applied to each new UF project it undertakes. The main focus here is on minimizing the use of chemicals and implementing efficient backwashing strategies, as well as on ensuring the quality of the external auxiliaries required.
We have been piloting all sorts of different ultrafiltration types and configurations nonstop since 1996. In this way, we are managing to explore the limits of this technology – which is still very young – and perfect its operation. We have already succeeded in constructing large-scale plants for every kind of water, whether in the form of spring, lake, or ground water.
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.
The choice of using pressure or submerged membranes depend on the water quality and the project conditions on site. Which system is better suited has to be evaluated for each new project. One decision criteria used are online registered measurement data about the water quality. If there are no data existing, we will propose a measuring campaign which can last several months to register all relevant water quality data for the hydraulic dimensioning of the water treatment plant. The planned location for the ultrafiltration must be carefully selected as it is a important factor to be considered. WABAG constantly designs and builds both types of ultrafiltration systems in Switzerland.
We have executed several plants with submerged membranes without any addition of cleaning chemicals for the backwashing. This can have a significant advantage for water treatment plants which are not accessible during the winter or which have no connection to canalization.
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.
The unrivaled life span and material properties of this membrane make it a highly attractive solution. However, due to its current price, the ceramic membrane only becomes truly attractive when the long-term costs are analyzed. In Japan, more than 100 such plants are already successfully up and running.
What makes the ceramic membrane unique is the nature of the material. In contrast to “normal” membrane fibers, which are quickly destroyed by ozone, ceramic membranes respond positively to any residual ozone in the water: the ozone contained within the water minimizes the fouling potential on the membrane surface. In a best-case scenario, there is no longer any need for chemically enhanced backwashing. This process has already been tested by WABAG on a pilot-project scale using different grades of water. The technology is now ready for use on a large scale.
If you want an effective solution for removing sources of turbidity, dissolved organic substances, and inorganic matter such as iron or manganese , you need look no further than WABAG filtration technology. The filter floor system, the backwash water valve, and the combined entrance are key components of the WABAG filter. These were all developed in house and are what make it so special.
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.
WABAG not only offers an optimized solution for conventional nozzle floors but also the WABAG drainage floor system – a space-saving concept that is ideal for filter renovation projects.
Together with the wide range of available filter media, this means that WABAG can come up with the perfect configuration for any project.
The filters need various connections running through the filter front wall (for the filtrate and backwash water, scouring air, etc.). However, ducts such as these can lead to filter wall leaks.
It is for this very reason that WABAG has developed the combined entrance. This solution brings together all the connection elements in such a way that only one opening is required in the filter wall.
WABAG's nozzle floor filters feature an inspection window on the front of the combined entrance. This window has a light and a wiper so that the culvert of the filter can also be visually inspected.
Efficient backwashing is crucial for correct filtration. Optimized backwashing programs and equal distribution of the backwashing media across the entire filter area are fundamental to achieving this. To keep OPEX low, backwash water consumption needs to be as low as possible and – in particular – there should be no loss of the filter medium.
WABAG filters rely on the excess head backwashing principle and so are able to meet both of these primary objectives with results that are currently unparalleled. The backwash water flap valve, which was developed in house, is capable of drawing off all of the built-up backwash water. In Switzerland most concrete-type filters operate according to this principle. Thanks to the excess head backwashing principle, WABAG filters need around 30% less backwash water.
With the right combination of processes, any kind of water can be transformed into high-quality drinking water. For more than 60 years, this principle has been used in Switzerland to build multi-barrier systems for lake water treatment. Virtually all of these plants – with just a few exceptions – have been designed and implemented by WABAG Water Technology Ltd.
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.
After teaming up with the Zürich water supply authorities and the Aquatic Research Institute of ETH Zürich (Eawag), WABAG worked on a joint study from 2006 to 2009 (and beyond) that examined how innovative and comprehensive water analytics could be combined with highly promising treatment technology – setting new standards in both areas in the process.
The aim was to develop a modern treatment process that would meet – and continue to meet – the requirements of consumers, and of plant and network operators, from both a quality and an operational perspective.
This has provided us with some extremely valuable experience and findings, which we apply every time we work on a new lake water treatment plant.
As a result of improved water analysis methods, organic trace elements are becoming increasingly easy to detect in waterbodies and other drinking water resources. These micropollutants, with their concentrations ranging from ng/l to μg/l, are not only garnering the attention of researchers but also of politicians and enforcement agencies.
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.
Conventional diffuser systems only provide a relatively small gas-water contact surface. This effect is particularly apparent on plants that are operated at below full capacity or when maintenance has not been performed on the diffusers for a long time.
WABAG has developed a special side stream gas feed system to help improve this process significantly and ensure that all the water being treated actually comes into contact with the ozone.
As a result, less ozone is required, the adsorption factor of the ozone in the water is higher and – most importantly – the ozone is distributed more effectively throughout the entire flow. Most existing plants featuring diffusers can be easily retrofitted with an ozone side stream feed system.
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.
One gram of powdered activated carbon has a specific surface of approximately 1,000 square meters for adsorbing the undesired dissolved substances in the water. As the adsorption capacity of the PAC is not completely exhausted after coming into contact with the water only once, its full potential is not utilized if it is separated from the water.
That is why WABAG has registered a patent for a PAC recirculation process so that the PAC can be reused. This system is due to be used on a large scale for the first time at the Muttenz water treatment plant in Switzerland, which is currently under construction.
Extreme geogenic factors can have a major impact on certain quality parameters of a drinking water resource. This creates all kinds of different challenges for the water supply companies. We can provide a solution to most of these challenges.
A karst substrate can dramatically increase the hardness of spring water. This problem can be solved by means of a water softening process. In the vast majority of cases, the hard water is treated by end users with technical equipment rather than centrally by the water supplier. A central softening system has both advantages and disadvantages, which must be carefully weighed up.
Processes that can be used: electrodialysis, ion exchanger, nanofiltration, reverse osmosis
Water containing too much free carbon dioxide causes corrosion in the distribution network and long-term damage to the infrastructure.
A suitable filter medium can be used to capture the free carbon dioxide, thereby restoring the carbonate balance.
As well as using a chemical deacidification process, WABAG also employs a physical one. The basic principle is to create as large a phase boundary as possible between the water that is undergoing deacidification and the air that is receiving the excess carbon dioxide. The individual methods associated with this process (which is called “stripping”) are categorized according to how the flows are routed in relation to one another. WABAG relies on the crossflow aeration method, where the raw water is routed horizontally through a low tank by means of finely distributed air bubbles that rise up from aeration elements.
As well as ensuring that a balanced pH value is achieved very quickly, the other advantage of this is that it eliminates the need for chemicals or self-depleting filter media. Once stripped, the carbon dioxide can be released back into the ambient air without any problems.
In oxygen-poor aquifers, iron and manganese will dissolve more readily. These can then precipitate in reservoirs and distribution networks, leading to incrustation.
For this reason, iron and manganese removal systems are often used in such scenarios. Based on the concentration of one or other of these elements, the water is aerated to oxidize the iron and manganese.
At the end of this process, the iron and manganese are mainly present in trivalent form and can be removed by downstream filtration with a special filter medium.
Due to geogenic factors, water can sometimes contain concentrations of arsenic and uranium (or other heavy metals) that exceed the applicable limits.
For details of our complete range of technology, please visit the WABAG Group homepage: www.wabag.com