Coagulation as a Means of Water Treatment

TABLE OF CONTENT

Cover Page----------            1

Table of contents ---------              2

Abstract----------             3

Introduction----------   5

Water Treatment ----------             7

What are Coagulants -------            -             8

Inorganic Coagulants --------              8

Organic Coagulants -------            -           -           10

Coagulant Selection --------             11

Mechanism of coagulation ------            -            11       

Determination of coagulants dose------   12

Limitations of coagulants --------   13

Conclusion ----------            -             13

References----------              14

Abstract 

Coagulation is a process that occurs when a coagulant is added to water to "destabilize" colloidal suspensions. Coagulation is one of the most important steps in drinking water treatment. Its purpose is to destabilize the suspended colloidal and dissolved contaminants in water, so they may be removed by subsequent processes. World Health Organisation  has reported that billion of people in the developing nations lack access to potable water. Access by households to sufficient and safe water combined with adequate sanitation and hygiene could result in a substantial reduction of the 5 million deaths due to diarrhoea diseases that occur each year. Many people have introduced conventional water treatment which typically involves the following sequence of physicochemical processes: rapid mixing; slow mixing, or flocculation; sedimentation; filtration; and disinfection. This conventional water treatment means is made possible by adding coagulant to the water. Coagulants are chemicals that are used to assist with the removal of colour and turbidity present in untreated, raw water. This coagulants may be organic or inorganic. Inorganic coagulants include those commonly used chemicals that rely on aluminium or iron while Organic coagulants include the so-called polyDADMAC (polydiallyldimethyl ammonium chloride), polyaluminium hydroxychloride (PACl) range of cationic polymers. The choice of coagulant chemical depends upon the type of suspended solid to be removed, raw water conditions, facility design, and cost of chemical. The dose of the coagulant to be used can be determined via the Jar Test and  an automated device for determining the coagulant dose called Streaming Current Detector (SCD). Coagulation is the process by which particles become destabilized and begin to clump together. The entire process includes addition of chemicals i.e. (iron or aluminium salts), or polymers to the water. These chemicals are called coagulants, and have a positive charge. Coagulation is one of the most important steps in drinking water treatment.