Raw water for production of drinking water is seldom of a sufficiently high quality to be used without treatment.  Raw water sources which include groundwater, lakes, rivers and reservoirs are affected by both people and nature.  The more people are concentrated in towns and municipalities, the greater the impact they have on the water source, and the greater the pollution.

In order to protect human health, all water from lakes and rivers has to be purified against pathogens before being used for human consumption.  In order to be palatable and enjoyable, drinking water should be colourless.  Coagulation with aluminium and iron salts is the most commonly used technique for removing particles, clay, colour, algae, bacteria, virus, and other pathogens.

During the coagulation process, the impurities form aggregates, ie. formation of flocs.  The choice of precipitation chemical is important for creating optimal flocculation and separation conditions.

In order to protect the environment and health, it is of great importance to treat wastewater both from municipalities and industries.  Organic substances, particles, nutrients, heavy metals, bacteria and viruses should be reduced to acceptable levels before the water is released from the treatment plant.  Different chemical, physical and biological methods can be used when treating wastewater.  Normally a combination of physiochemical and biological methods gives the best treatment result.  Aluminium and iron coagulants are used in a broad range of applications.

Phosphorus reduction: Phosphorus is an essential nutrient for living organisms.  When an excess of phosphorus is released into our waters, the growth of algae increases dramatically (eutrophication).  By using aluminium or ferric coagulants, phosphorus is precipitated from the wastewater.  The precipitate is then separated in a physical process like sedimentation, flotation and filtration and a treated wastewater with very low phosphorus content leaves the wastewater plant.

Particle removal: The turbidity in water is caused by particles.  Smaller particles are hard to separate by sedimentation or filtration.  Coagulants are therefore used to agglomerate the smaller particles into larger ones.  This is done by neutralising the negative charge on the particle surface by adding a sufficient amount of the positively charged coagulant.  Particles will also be removed by being captured by the aluminium or ferric hydroxide flocs that are formed.  The flocs are normally separated by sendimentation but also flotation and filtration technologies are used.

Bulking sludge: The activated sludge process is dependent on good flocculation and settling for high effluent quality and good dewatering of the sludge. However, excessive growth of filamentous bacteria greatly affects the settling properties of the sludge and can result in poor treatment and foaming. In many cases, coagulants can be used to improve the conditions in the activated sludge process ensuring that treatment targets are fulfilled.

Sludge dewatering: The target of sludge dewatering is the separation of solid particles from the liquid phase. Coagulants enhance the sludge dewatering in combination with polymers and can significantly reduce the amount of the organic coagulant.  Utilising a coagulant in the water or sludge dewatering phase normally improves the dewatering properties.  A higher dry solids content is achieved and less sludge needs to be disposed of.

Energy optimisation: Coagulants can be used to improve the energy balance in many ways.  First of all, a coagulant can be used prior to the biological water treatment.  By doing that, the oxygen demand in the activated sludge tank is reduced and electricity savings are achieved.  With the pre-treatment, more energy rich primary sludge is produced.  Part of that sludge is transferred to biogas (methane) in anaerobic digesters.  The biogas can be used for electricity production, vehicle fuel and heating with a very low carbon footprint.  Iron coagulants can also directly affect the efficiency of an anaerobic digester by precipitating hydrogen sulphide.