Question 1

What is aluminium sulfate used for in water treatment in Oman?

Accepted Answer

Aluminium sulfate (alum, Al₂(SO₄)₃, CAS 10043-01-3) is the most widely used primary coagulant in municipal and industrial water treatment plants in Oman. When added to raw water, alum hydrolyses and forms positively charged aluminium hydroxide floc particles, which neutralise the negative charge on colloidal particles (clay, silt, organic matter, bacteria) that cause turbidity. The neutralised particles then aggregate (flocculate) into larger, rapidly settling floc that can be removed by sedimentation and filtration. Typical alum dosage for Oman's surface water treatment is 10–50 mg/L, determined by jar testing. Oman's drinking water treatment plants at Al Ghubrah, Wadi Dayqah Dam, and Falaj Al Qabail use alum or poly-aluminium chloride (PAC) as primary coagulants. Alum is also used in wastewater treatment for phosphorus removal, in paper manufacturing, and as a mordant in textiles. Liquid alum (8% Al₂O₃) is preferred for continuous dosing by chemical pump; granular alum is used where liquid storage is impractical. Global Chemicals LLC supplies both liquid and granular alum for Oman water treatment.

Question 2

What is the optimal pH range for alum coagulation in water treatment?

Accepted Answer

The optimal pH range for aluminium sulfate (alum) coagulation is 6.5–7.5, where aluminium hydroxide Al(OH)₃ floc formation is most efficient and the resulting floc is dense and settles rapidly. At pH below 6.0, aluminium remains in solution as Al³⁺ ions — no floc forms and coagulation fails. At pH above 8.0, aluminium hydroxide redissolves as the aluminate anion Al(OH)₄⁻, again preventing floc formation. Oman's raw water sources vary widely in natural pH: desalinated water from SWRO plants is slightly acidic (pH 5.5–6.5) and may require pH correction before coagulation; dam water from Wadi Dayqah is typically pH 7.5–8.5 due to carbonate geology, which is within the acceptable range; groundwater can be highly alkaline (pH 7.5–9.5). When treating alkaline Oman water with alum, the coagulant dose must be sufficient to overcome alkalinity buffering and achieve the target pH, or pre-acidification may be needed. Jar testing with each raw water source is essential to determine the optimal dose. Global Chemicals LLC provides jar test protocol support and alum optimisation services for Oman water utilities.

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