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Due to health concerns of natural organic matter (NOM) and algae presence in surface water and difficulties encountered in their removal in the water treatment, this paper reviews coagulation and chlorination processes which are largely used in water treatment technology. In the conventional water treatment, coagulation and slow filtration treatments have better efficiency to reduce the NOM in water especially for the hydrophobic portion than the hydrophilic one. However, the pre-chlorination treatment for raw water has been proved to increase the dissolved organic carbon concentration due to the lysis of algae cells and disinfection by-products formation. The impact of water treatment processes on disinfection byproducts formation remains complex and variable, as demonstrated by recent literature. It is concluded that no pre-, no inter-, only post-chlorination preceded by optimised coagulation for NOM and algae removal is the best available technology for the conventional water treatment which would be reinforced by at least adsorption on powdered activated carbon or nanofiltration in the short terms. Finally, the conventional water treatment will not remain a viable solution for drinking water from source waters containing NOM as their quality deteriorates and water quality standards become more difficult to achieve.

This review paper deals with the formation of disinfection by-products (DBPs). Water basin remains a wonderful chemical reactor that allows the occurrence of intricate secondary disinfection chemical reactions, forming several hundreds of DBPs at the same time with microorganisms killing. The kinetics of DBPs formation is tightly dependent on water physicochemical characteristics such as temperature, hydrophobic/hydrophilic fractions in natural organic matter (NOM), pH, and pretreatment. Reducing DBPs levels in drinking water is not a relevant measure as the newly-developed analytical techniques and the health-related research reveal that the tolerable DBPs' levels must be further decreased and would be detected at ng L-1 instead of μg L-1 scale. Furthermore, because of the fact that man is being exposed to DBPs concentrations in drinking water in his lifetime, there will be a cumulative effect of these toxic chemical products even at their more reduced concentrations. Hence, the removal of these chemical products is sought for and is considered a real challenge and the main objective of water treatment technology for mankind survival.

This review focuses on rapid mixing in the coagulation process for improved natural organic matter (NOM) removal in water treatment. Rapid mixing aims to instantly and efficiently disperse coagulant species into raw water, before flocculation, sedimentation, and filtration processes. Mechanical mixing with a longer retention time cannot guarantee an instantaneous and uniform coagulant dispersion. For this reason, the so-called pump diffusion mixer (PDM) has been proposed. Using various rapid mixing devices to test the sedimentation performance, it is showed that in-line hydraulic jet and static mixers are able to achieve performance equivalent to that of the mechanical mixing type at a lower coagulant dosage. On the other hand, the removal of NOM as disinfection by-products (DBPs) precursor by chemical coagulation (CC) has been extensively studied. It is well reported that enhanced coagulation (EC) by adjusting the pH downwards to 4-5 prior to coagulant addition will encourage the formation of soluble NOM-Al complex from low-turbidity waters. In case of most waters, therefore, acid must be added to maintain the desired coagulation pH for EC, and excess coagulant is required to improve the removal of NOM. However, CC using in-line hydraulic jet mixer such as PDM is a reasonable method for the improvement of coagulation process compared to EC, since it is possible to obtain good removals of NOM as well as turbidity using a lower dosages of coagulant without supplementary addition of chemicals for pH control and thus producing a smaller volume of waste solids.