What are inorganic coagulants?

Inorganic coagulants are soluble salts which are used to purify drinking water and waste water from municipalities and industry. The term ‘inorganic’ simply indicates that the coagulants are not derived from living matter. Typically aluminium and iron salts are used to make coagulants.

These materials are abundant in the Earth’s crust and can also be derived from the recycling processes of industries such as steelmaking.

Inorganic coagulants provide a cost-effect, environmentally friendly method of water purification.

How do inorganic coagulants work?

Coagulants have a positive electrical charge. By contrast, particles which are dissolved or suspended in water typically have a negative charge. The positive charge of the inorganic coagulant neutralises the negative charge of the particle and the two bind together (coagulate) in larger particles in a process known as flocculation.

These larger particles (known as floc) are heavy and quickly settle to the bottom of the water in a process called sedimentation. Lighter flocs can be removed from the water using filters. Different coagulants target different types of particles in the water.

Do inorganic coagulants affect human health?

Inorganic coagulants have been used for thousands of years without adverse impact on people or the environment. In fact, inorganic coagulants have saved millions of lives by delivering safe, healthy drinking water which is vital for life.

Do inorganic coagulants affect the environment?

Inorganic coagulants have been used by mankind for over 5,000 years in applications such as water purification, papermaking and the dyeing of fabric. To date, no harmful effect on the environment has been recorded. Inorganic coagulants also ensure that waste water does not pollute the environment.

What is the carbon footprint of inorganic coagulants?

Inorganic coagulants are soluble salts which are used to purify drinking water and waste water from municipalities and industry. The term ‘inorganic’ simply indicates that the coagulants are not derived from living matter. Typically aluminium and iron salts are used to make coagulants.

These materials are abundant in the Earth’s crust and can also be derived from the recycling processes of industries such as steelmaking.

Conducted by the Karlsruhe Institute of Technology (KIT) on behalf of INCOPA, the LCA study found that the cradle-to-gate emissions of all coagulants studied averaged 0.106 kg CO2-eq/mole Fe3+ or Al3+. The value is extremely low.

Inorganic coagulants provide a cost-effect, environmentally friendly method of water purification.

How long have inorganic coagulants been used in water treatment?

Alum has been used at least since Roman times for purification of drinking water (cf. Chemistry of Water Treatment – Samuel D. Faust, Osman M. Aly (1999)). It is also reported that Egyptians used alum coagulant as early as 1500 BC to reduce the visible cloudiness in the water.

In the modern times, London became the first city to mandate that drinking water should be purified using coagulants, after an outbreak of cholera in 1854. By the start of the 20th Century, scientists better understood the role of inorganic coagulants in water purification and their use spread worldwide. The treatment of waste water with inorganic coagulants started on a large scale in the 1950s.

Are inorganic coagulants sustainable?

Inorganic coagulants are made from commonly occurring elements. Aluminium is the third most abundant material in the Earth’s crust, closely followed by iron. However, iron-based coagulants are typically derived from producing titanium dioxide and the recycling processes in steelmaking.

Are there alternatives to inorganic coagulants?

Inorganic coagulants offer a sustainable, cost-effective and environmentally friendly method to purify water. Other methods exist, however, they are more expensive and have a significantly higher carbon footprint.

What happens to the sludge produced by inorganic coagulants?

When inorganic coagulants react with the impurities in the water, sludge is produced. The coagulant is removed from the water with the sludge. Good quality sludge, which has no trace of toxins, can be used in agricultural applications as fertiliser. Depending on its composition, sludge can also be used as biomass to produce biogas, incinerated, or placed in landfill.

How is the use of inorganic coagulants regulated?

The quality of drinking water treated with inorganic coagulants is regulated according to standards published by the European Union and organisations such as the European Committee for Standardisation (CEN). Under these regulations, local water authorities are required to monitor and certify that drinking water is fit for human consumption.

All substances are registered under REACH (the European regulation which deals with the Registration, Evaluation, Authorisation and Restriction of Chemical substances).

What quantity of coagulant is required to provide clean water for a typical European?

The average European uses approximately 150 litres of water per day which equates to almost 55,000 litres per year. To treat this amount of waste water requires approximately 1.1 kilograms of inorganic coagulant per annum.

 

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