Coagulant:

Commonly used inorganic coagulants include aluminium sulphate ("alum"), polyaluminium chloride, ferric sulphate and ferric chloride. Selection of the appropriate compound is a function of cost, raw water quality and the selected treatment process. For soft, coloured, waters, either aluminium or iron coagulants may be used at their respective optimal pH ranges: 6.5 to 7.5 for lowland surface waters or 5.5 to 6.5 for highly coloured upland waters (aluminium based coagulant) and 4.0 to 5.0 (iron based). Iron coagulants have an advantage relative to aluminium in this application, as they operate at a much lower coagulation pH to maximise the removal of dissolved organic matter and consequently reduce the potential for THM formation. For harder waters, iron coagulants are often used if coagulation pH values of 8.0 or more occur; such pH values would not be appropriate for aluminium coagulants unless accompanied by a separate acid dosing process.

Increasing the dose of metallic salts will further depress the pH, but will result in an undesirable increase in the soluble metal content of the water, which will carry through the filters to supply. Dosing with a strong mineral acid, such as sulphuric acid, will depress the pH without the unwelcome increase in the soluble metallic content of the water.

Lautan Luas has an extensive range of coagulant products including:

A. Poly-Aluminium Chloride (PAC) are aluminum-based coagulants. They are effective coagulant to remove microscopic suspended matter quickly over a wide range of turbidity, temperature and pH as encountered in natural surface waters. It is also effective for removing algae. They similar to alum, with several important differences:

• Partially pre-neutralised (higher basicity than alum)
• Contain Cl instead of SO4
• Contain up to 3 times the aluminum content.

B. Aluminium Chlorohydrate (ACH) is a high basicity, highly polymerized coagulant that has little effect on alkalinity and pH and is ideal for treating low alkalinity or high turbidity source waters. Due to its higher Al2O3 content (min 23{bae455710082ffc188be46a81919e0436c70756a3753dc21b8bd47cd33e92f3b}), ACH can generally be dosed at lower feed rates reducing sludge generation and reducing tank size and delivery frequencies.

C. Aluminium Sulfate (Tawas) is an effective primary coagulant based on trivalent aluminium. It works by neutralising the negative charge on suspended and colloidal matter to produce compact flocs suitable for easy removal by either settlement or flotation processes and promotes more efficient sludge digestion and dewatering.

D. Organic Primary coagulants are highly cationic charge products use to destabilise negatively-changed colloidal praticles and promote rapid floc formation.

Coagulation with ferric salts is most effective in a pH range between 5 and 8. For aluminum salts, the optimal range is 5 to 7; at pH values above 7, the efficiency of aluminum-based coagulants falls significantly. To increase coagulant effectiveness, the pH level of feed water should be brought into the target pH range before the coagulant is added. To adjust pH levels Ca(OH)2 or Soda Ash is applied.