Alum

Clean and pure water is essential to human health. Therefore, removal of contaminants from wastewater is important to ensure that we consume only clean water. Flocculation is a process in water treatment operation which is useful in separating out sediment, removing harmful substances, and to treat colloids in water. The degree of flocculation can be increased by adding flocculating agents, also known as flocculants. [1]

Aluminum sulfate, commonly known as alum, is a type of flocculating agent which has been known for centuries and is widely used in water treatment applications. [2] However, there are possible health risks due to presence of aluminum in water despite of its effectiveness and other benefits. As alum may be health threatening, should it continue be used?

Alum is effective in treating wastewater as it settles out a wide variety of unwanted materials. This is due to the highly charged aluminum ion produced when alum dissolves in water. [3] Iron compound flocculants have similar floc characteristic to alum. However, residual iron in water gives an unpleasant taste and it may also cause staining and blockage of water lines. [2] On the other hand, organic flocculants is effective in forming flocs but do not produce large volume of flocs compared to alum which is useful in entrapping bacteria as they settle. Also, alum precipitates organic colour bodies whereas organic flocculants do not. [1]

Both solution and dry alum are available as flocculant. The former is easier to dispense but must kept warm to prevent crystallization. It is easier to handle compared to iron salts and organic flocculants. Iron salts are generally more corrosive and difficult to dissolve while synthetic organic flocculants are viscous solution due to their high molecular weight which presents problem on handling, shipping, and dissolving. [1]

According to a report, the value of flocculating agents used in United States in 1990 was $115.2 million for alum, $40.0 million for iron salts, $51.0 million for other inorganics and $221.0 million for polymers. As we can see, the value used in alum is high. Because alum is a high volume/low unit price commodity, its pricing is affected by increase in shipping and raw material costs, which pushed prices up recently. [1] However, the price of alum is relatively low compared to others such as organic polymers which are several times more expensive due to the synthesis of polymers. Iron salts are