Chemical coagulation


A coagulation method for the removal of turbidity and some other contaminants. In the process, a coagulant (often aluminum-sulphate) is added to water. Positive coagulant particles attract to negatively charged turbidity particles, resulting in precipitating flocks. Settling or filtration step is required afterwards. Local availability of the coagulants might be problematic.


Initial purchase costs are minimal, any bucket or pot can be used. But on-going costs are high, every time new chemical coagulants need to be bought. In comparison with majority of HWTS methods, this is a medium-cost technology.


Normally applied for large systems, but can also be applied at household level. Method might be advocated from central level. Supply of chemicals might also be centrally organized. Training required about proper application, including dosing, mixing, settling and filtration.


Both chemical coagulants and contaminations from the water will end up in the sludge (in case of settling) or in the filter (in case of filtration). These residues present high risk for human health and therefore safe disposal is advised.


Coagulants are stored and added to water in solution form. Optimal dosing depends on composition/contamination of water. Coagulants need to be in water for >2 hours. Slowly mixing improves process. Settling or possibly sand filtration required afterwards. Container needs to be cleaned regularly.


Users need to be aware of applying the method correctly: proper dosing and mixing, enough settling time and careful pouring without mixing contaminated flocks with clean water. Improper use of method (e.g. overdosing of coagulant) poses increased health risk to users.

Relevant remarks:

No relevant remarks for Chemical coagulation.