Water Treatment

Raw Surface Water Destabilization, Coagulation and Sweep Flocculation

Raw surface water drawn from Kenyan rivers, dams, and reservoirs—such as Tana River, Sasumua, Ndakaini, and Lake Victoria—carries variable seasonal turbidity ranging from fine colloidal clays and silts to natural organic matter (humic and fulvic acids). Because colloidal clay particles carry negative surface charges that prevent natural settling, raw water remains turbid indefinitely without chemical coagulation.

In water treatment plants, Polyaluminium Chloride (PAC 30% Al2O3) or Aluminium Sulfate (Alum 17%) is rapidly flash-mixed into raw water channels. The trivalent aluminium ions compress electrical double layers, neutralizing negative surface charges within seconds. At neutral to slightly alkaline pH, aluminium species hydrolyze into insoluble amorphous aluminium hydroxide precipitates, forming 'sweep flocs' that entrap colloidal silt, organic color, and microorganisms into heavy pin-flocs.

Flocculation Bridging, Rapid Sand Filtration and Terminal Chlorination

Gentle mechanical or hydraulic baffle flocculation bridges micro-flocs into large, rapid-settling agglomerates with the assistance of trace Polyacrylamide (PAM) coagulant aids. Supernatant clarified water decants from sedimentation basins into rapid gravity sand filters, which trap residual micro-particulates to achieve turbidity below 1.0 NTU. Finally, disinfection is performed using Calcium Hypochlorite 70% or Sodium Hypochlorite, dosing enough available chlorine to achieve breakpoint disinfection and maintain a protective free chlorine residual of 0.5 to 1.5 ppm throughout the distribution network in compliance with KEBS KS-459.