Aggressive carbon dioxide causes corrosion on concrete, pipe systems, and hot water storages in black steel. The corrosion products make the water indistinct and colours it red with corrosion and ochre.

The carbon dioxide is often present in raw water in areas with decalcified stratums of earth. The lack of calcium means that there is no neutralization of the carbon dioxide.

Solution

Aggressive carbon dioxide can be neutralized in a pressure filter plant by means of a calcium-based filter material called Magno-Dol. In special cases, aggressive carbon dioxide can be degassed by heavy aeration.

Ammonium can be a sign of microbacteriological activity in the water and can be a result of fertilization, contamination, or it can be geologically conditioned.

Solution

Ammonium can be reduced by a biological process, in which ammonium is transformed into nitrate via nitrite.

The process calls for a great oxygen demand and sufficient filter material consisting of quartz sand or a porous calcium-based filter material.

Arsenic is a natural element and related to certain geochemical environments. Arsenic is found in two forms, As(III) and As(V), of which As(III) is more poisonous, harder to remove from the water, and more widespread.

WHO has assessed that arsenic forms a health risk when consumed and it is thought to be the reason for skin cancer, among other things.  

The increased authority demands (lowering of the threshold limiting value from 50 to 5 µg/l when leaving the waterworks) affect many water supplies for which it will be necessary to carry out a special water treatment in order to keep the quality requirements.  

Possible solutions

If the limit value for arsenic in the drinking water is exceeded, a sensible and inexpensive solution is to optimize the water treatment. Arsenic is adhesive to iron and is filtered off with iron. In places without sufficient iron in the raw water for this process, the iron content of the water can be increased by adding iron chloride or iron sulphate and using iron oxide granulates as filter material. 

This is an inexpensive solution to the arsenic problem and the method is used when there are small exceeding of the permitted arsenic content. However, this calls for sufficient filter capacity for this extra iron content.   

Alternatively, arsenic can be reduced by adsorption filtration in a pressure filter with a special filter material based on iron hydroxide. Dosing with either iron chloride or iron sulphate and the use of iron oxide granulate as filter material are both water treatment solutions that is gaining a footing. Grundfos offers both solutions and the choice depends on the actual conditions.

In order to measure the amount of bacteria in drinking water, the bacterial count is analyzed. This means the total number of bacteria found by culturing at 22°C and 37°C respectively.

At 22°C, there are bacteria which normally do not cause a disease. The bacterial count at 37°C indicates alien bacteria which often cause diseases. Thus, this count needs to be low. Micro-biological growth which is found in drinking water can consist of among other things bacteria, virus, algae, and fungus.

Solution

The bacteria can be effectively limited by ultraviolet light because micro-organisms are very sensitive to UV light. With a wavelength of 254 nm (nanometer), the UV light kills the bacteria, virus, algae, and fungus by breaking down the DNA of the micro-organisms. UV disinfection can be used for almost all water types.

Groundwater often contain a high amount of calcium and magnesium salts which cause hardness in the water. Water softening remove the hardness and prevent scale from forming in pipe systems and plumbing. 

Solution

If you require a certain amount of hardness in the water, nanofiltration can provide partial softening and without use of regeneration chemical. Removal of total hardness can be done by a softening unit. 

Hydrogen sulphide and methane are present many places in the groundwater and are formed by the decomposition of organic substances under oxygen-free conditions.

Both gasses give cause for different problems for a waterworks. Filters are clogged up by bacterial slime which reduces the content of oxygen and often, bad smell is also an indication of bacteria. In some cases, the bacteria can form hydrogen sulphide and methane.

It is important that all hydrogen sulphide and methane are removed because a residual amount of these gasses in the water will complicate the removal of iron and ammonium afterwards.

Solution

Both hydrogen sulphide and methane can be removed by heavy oxydation of the water. The oxydation takes place by aeration in order to add oxygen to the raw water.

Iron and manganese often cause the main problem of the waterworks' due to the substances' discolouring of the washing and sanitation at the consumer. Typical signs of increased iron and manganese content in the water are ochreous or dark water with a metallic taste. 

Raw water can contain different types of iron dependent on where in the country you are. Sand filtration is thus not always sufficient. It may therefore be necessary to use other methods in order to ensure continuous iron-free water. These differences cannot be seen in the ordinary analyses but calls for know-how and experience to determine iron type and treatment method.

Solution

After the oxydation, iron and manganese can be filtered through sand filtration. The filter materials used for removing iron are Gravel lll and Nevtraco l.

For removing manganese, Hydrolit-Mn is used. Also, the filter media Demantex has proven to be a very efficient material for manganese removal, even under difficult conditions with low pH values where many other types of filter media are insufficient.

Contamination of drinking water by pesticides is primarily linked to the historical use of products such as Caseron G and Prefix G for weed control. These products contain dichlorbenil, which degrades into the substance 2,6‑dichlorobenzamide (BAM). Today, waterworks routinely analyse raw water for a wide range of pesticides, and residues are found in many bore wells.

PFAS contamination originates from various industrial and environmental sources and is increasingly monitored due to its persistence and potential health impact.

Solution

Pesticides such as BAM are effectively reduced using pressure filters with activated carbon. Activated carbon is a natural material produced from stone, wood, or coconut shells and is widely used to remove pesticides and other organic substances from drinking water.

PFAS can be removed using activated carbon or by ion exchange with PFAS‑selective resins. The choice of solution depends on the concentration levels and specific PFAS compounds present in the water.

Solution

The content of sulphate, chloride, and fluoride in drinking water can be reduced by nanofiltration. 

Nanofiltration is applied to purposively reduce unwanted components in full or in part. Nanofiltration applies a pressure typically under seven bar, resulting in lower energy consumption.

Nanofiltration is a membrane technology, which in its mode of operation and construction is very similar to reverse osmosis. A nanofiltration membrane primarily restrains divalent ions and larger molecules.