Activated carbon filters - an overview!

Not all activated carbon filters are the same, here you will find out the most important differences

The type of activated carbon itself determines the filter's performance. From simple bitumen mixtures to high-quality activated carbon made from bamboo or coconut shells, everything is available on the market. A simple activated carbon is sufficient as a pre-filter, but only high-quality activated carbon should be used as a single filter. These cartridges are available.

Activated carbon granulate filter GAC : Activated carbon granulate fill, only suitable as a pre-filter

Activated carbon block filters (CTO): Larger surface area than GAC filters. A distinction is made between extruded and sintered filters.

• Extruded activated carbon filters: a mixture of plastics and activated carbon is bonded together to form a solid block
• Sintered activated carbon filters are the best activated carbon filters available on the market. The activated carbon is firmly bonded with a small amount of plastic. The result is a small pore size (mechanical filtration) combined with the absorption properties of the activated carbon. German suppliers here include Carbonit, Alvito, and Wasserstelle. All three rely on high-quality activated carbon made from coconut with optimal absorption properties. This is compressed into a solid block in a complex sintering process and sintered in a special baking process. The resulting carbon block now has an enormous number of fine pores and channels in a very small space. One cubic centimeter of activated carbon has a surface area comparable to that of a football field. This achieves an enormous filtration effect in a small area. As the flowing water passes through these high-tech activated carbon blocks, the pollutants are removed from the water. Alvito writes:

What is an activated carbon block filter and how does it work? Activated carbon for water filters can be made from coked coconut shells or certain hardwoods, as well as from hard coal. (Coking is a process in which a fuel with a high carbon content is treated with heat in the absence of oxygen.) The carbon is activated in special ovens with steam heated to over 800°C to open the pores. The finished activated carbon is then available in granular or powder form. To improve the properties of a filter with activated carbon, filter elements have been developed in which the water not only flows around the outside of the activated carbon granules, but is guided through a solid filter element made of activated carbon. The water flows through the fine channels inside the activated carbon and comes into close contact with the enormous surface structure. To produce activated carbon block filters, fine activated carbon powder is formed into a solid "block" with a special binder and sometimes other additives. This is where the term "block filter" comes from. A widely used method for producing block filters is "extrusion," in which the components are heated together and then the liquid "slurry" is formed into the desired shape – roughly comparable to the production of pasta. An alternative to this is "sintering," in which the components are filled into molds and baked in the oven – roughly comparable to the production of bread. Sintering is more complex to manufacture, but offers the advantage that less binder is needed, allowing a higher proportion of filter media (activated carbon) to be used, resulting in better filter properties. In an activated carbon block filter, three different principles complement each other in their effect: 1. The mechanical effect. Activated carbon block filters act like a sieve, retaining all particles larger than their pores. This mechanical action filters out, for example: bacteria, cryptosporidia (single-celled parasites), giardia (small intestinal parasites), suspended particles and sand, rust particles, asbestos fibers, etc. To achieve even finer and more reliable particle filtration than would be possible with pure activated carbon filters, some filter inserts also use a second filter stage in the form of a hollow fiber membrane. 2. The catalytic effect Activated carbon can convert certain substances that are smaller than the pores of the filter using its catalytic effect. These substances are then no longer in their original form. The catalytic effect, for example, eliminates the unpleasant taste of chlorinated water. Activated carbon is very effective in terms of its catalytic effect because it uses very little energy. The catalytic effect removes, for example, chlorine, CHCs, and CFCs from the water. 3. The adsorptive effect Activated carbon can absorb certain substances that are smaller than the pores of the filter using its adsorptive effect. During adsorption, the substances attach themselves to the activated carbon and remain stuck. The forces that cause this adhesion are not chemical bonds, but rather "van der Waals forces," which act similarly to magnetic forces on different substances. Activated carbon has the greatest adsorptive power of all known substances and is therefore particularly well suited as a filter medium. "Van der Waals forces," although very strong, are only effective at very close distances. The proximity to the contact surface and the speed at which the water flows past it are therefore crucial for the adsorptive effect. The finer an activated carbon filter is and the slower the water flows through it, the better the adsorptive filtration. This is where an advantage of block filters comes into play, as they have comparatively fine pores and slow down the water flow. Through its adsorptive action, an activated carbon filter can bind organic substances (carbon compounds) and a number of other substances that are undesirable in water for human consumption. The adsorptive action removes, for example, lead, copper, pesticides, herbicides, fungicides, hormone residues, drug residues, and odor- and taste-impairing substances.

What influences filter performance? Numerous parameters influence the filter performance of an activated carbon filter: » Carbon source material. » Pretreatment or activation of the carbon. » Amount of activated carbon in the filter element. » Processing of the activated carbon (chopped granular filter, extruded block filter, sintered block filter). For block filters, additional factors include: » Proportion and quality of the binding agent. » Pore size and even distribution within the filter element. » Wall thickness of the filter block and thus the distance the water travels within the filter. Block filters, in which water flows through the fine channels of a solid filter element, are generally superior to granular filters, in which water simply flows around activated carbon "crumbs." Besides their unreliable filter performance, granular filters have two further disadvantages: » To protect against microbial contamination, granular filters are treated with silver, although some of this is released into the water. Block filters, on the other hand, do not require silver plating if the pore size is sufficiently fine. » With granulate filters, there is also the risk that the absorbed substances will detach uncontrollably (bleed out), which does not occur with high-quality block filters. Once deposited, the substances remain permanently bound in the block filter and lead to a reduction in the flow rate. There are also different types of block filters: Extruded block filters consist of up to 50% binder, which holds the activated carbon dust together, but can cover part of the surface of the activated carbon. Sintered block filters require less binder, of which they contain only around 30% or, ideally, even less than 10%, depending on the manufacturing process. In addition, the binder cokes during production, exposing a larger surface area of the activated carbon for the filtering effect. The most efficient activated carbon block filters have an internal surface equivalent to the size of approximately 100 football fields. The uniformity of the pore size within a block filter is particularly important, because water prefers the path of least resistance. Therefore, it is more likely to flow through the larger pores, which have a poorer filtering effect. The finer and more uniform the pores and channels in the block filter, the better the filtering effect. However, the filtering effect depends not only on the filter element and its technical parameters, but also on the composition of the water and its use. The adsorptive performance of activated carbon varies for each substance and depends on many factors, including: » In what form/compound is the substance? » What is the concentration of the substance in the water? » Does the water contain other substances that compete with the substance to be filtered for adsorption sites on the surface of the activated carbon? » What is the pH value of the water (this has an influence for some substances)? » What is the flow rate and thus the possible contact time of the substance with the activated carbon? » How saturated is the activated carbon filter already with removed substances? (In principle, the filtering capacity decreases with the amount of substances already adsorbed.)

The general filtering properties of activated carbon are well known and have been extensively scientifically studied. While organic compounds (carbon compounds), for example, are generally well adsorbed, the absorption capacity for inorganic compounds (salts) is rather low. Since activated carbon does not remove hardness-forming substances (limescale), it is not suitable for water softening. Scientific studies show that activated carbon block filters remove the following substances well to very well: » Particles or suspended solids that are larger than the pores of the filter. » Bacteria and parasites that are larger than the pores of the filter. » Chlorine and chlorine compounds. » Organic compounds (carbon-based chemical compounds), for example pesticides and pesticide residues, herbicides, insecticides, drug residues, hormones and hormone-like substances. » Certain heavy metals such as lead and copper. The substances that activated carbon block filters cannot or can only barely remove include: » Organic and inorganic particles or suspended solids that are smaller than the pores of the filter. » Dissolved salts: natural minerals such as calcium and magnesium ions (which may also be usable by the body), nitrate, nitrite, ammonium, etc. The question of how well a specific substance is removed from the water cannot be answered simply and generally. Concrete statements about the filter's effectiveness always depend on the individual situation. Due to the many parameters that can have an influence, the removal capacity must be determined in each individual case through a test. While exemplary tests are possible, their transferability to the specific situation is limited. The fact that practically all chemical elements do not occur in pure form in water, but in a variety of compounds, makes determining a specific adsorption capacity even more difficult. Random tests for specific contaminants (for example, lead and copper) are simple and relatively inexpensive to carry out. Investigations for complex groups of substances (e.g. pesticides) or investigations over a longer period of time and with a defined volume of water, particularly germ tests, are very complex. When it comes to determining whether an activated carbon block filter filters a certain substance out of the water, it must first be clarified whether this substance is present in the water at all, in what concentration it is present in the water, and what health significance the substance has at this concentration. A suitable answer to this question is whether an activated carbon filter can remove aluminum from the water. Aluminum is rarely present in water as a pure element, but almost always as a chemical compound, i.e., as a salt with phosphate, silicate, fluoride, nitrate, etc. However, since the adsorption capacity of activated carbon varies for each chemical compound, it cannot be generally stated for aluminum as an element. This means that the question of whether aluminum is removed from the water by activated carbon cannot be answered with a simple yes or no. Due to many influencing factors, the adsorption of the various aluminum compounds would have to be considered in the specific situation. Viewed from a different perspective, the question of aluminum's adsorption capacity is put into perspective: the main absorption of aluminum does not occur from drinking water, but from solid foods, cosmetic products, and other sources such as packaging, medications, and vaccines. The concentration of aluminum in tap water is typically low and is restricted by a limit set by the Drinking Water Ordinance. The fact is: Most undesirable substances are often present in much higher concentrations in solid foods than in tap water. Therefore, the primary goal of filtering tap water for home use (in our view) is not to remove as many substances as possible. A filter makes sense for optimizing the content and taste of already good tap water using a reliable, easy-to-use, and affordable technology.

Tap water in Germany is of good quality and is ideal for optimization with activated carbon. The Drinking Water Ordinance defines limit values for many substances that regularly occur in water and that are of importance to health or consumption. Water from natural sources (e.g., wells), on the other hand, often cannot be adequately treated with activated carbon. This is because activated carbon cannot filter some substances (e.g., iron and manganese), or can only filter them in small quantities. The tap water provided by water suppliers for human consumption in Germany undergoes extensive treatment to ensure that it complies with the Drinking Water Ordinance (TrinkwV) and protects human health from the adverse effects that can result from water contamination by ensuring its suitability for consumption and purity. However, the variety of substances that can be dissolved in water is enormous – it is estimated that more than 50,000 different chemical compounds can occur in water. Only a few of these are detected during water supplier inspections. A high-quality activated carbon block filter is useful in the home for many reasons. It protects not only drinking water, but also coffee, tea, and cooking water from known and unknown contaminants, and optimizes the taste. Unlike bottled water, which is rarely used for cooking and preparing hot beverages, a water filter is widely used in the kitchen and provides the best water for the entire household. Because a filter system is installed directly at the point of use (usually in the kitchen), it also protects against potentially undetected contaminants from the plumbing. These include influences from the waterworks pipes or from the pipes in the house, which can release various substances, as well as hygiene problems that can arise from stagnation (water standing in the pipes). The health implications of individual substances in water, which are occasionally dramatized by the media, should be considered in their entirety. This makes it clear that the reporting in newspapers, magazines, and on television is sometimes more about attracting attention than a realistic examination of the issue. While water should generally contain as few undesirable substances as possible, we believe that the proportionality and reasonable effort of filtration are also important when striving for clean drinking water. Above all, the water should not be adversely affected by filtration and should remain in its natural balance. Furthermore, it should be clear that by far the most harmful substances do not come from our drinking water, but from food and industrially produced beverages. The filter systems offered by Alvito use high-quality, sintered activated carbon block filters that reliably remove a variety of undesirable substances from tap water, but not dissolved, valuable minerals. Experience has shown that these filter systems are ideal for optimizing tap water in the home. The extraction capacity is so large that it is only partially consumed for the use recommended by Alvito (maximum filter capacity with a 6-month service life). The filter inserts offer more than sufficient safety for standard tap water that complies with the Drinking Water Ordinance. Changing the filter every 6 months is recommended to prevent a decrease in water flow due to usage and to ensure hygienic use. With proper maintenance of the filter system, clean, tasty drinking water should be available at all times.