Sewage & effluent treatment · STPs and ETPs

Sewage treatment plants at hotels, camps, compounds and factories in Oman use chemicals to settle solids, dewater sludge, keep the biology healthy, control foam and odour, and disinfect treated water for reuse. Oman Chemical supplies coagulants such as PAC, alum and ferric chloride, polyelectrolytes, bacterial cultures, antifoams, hypochlorite and dechlorination chemicals from Barka.

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Reverse-osmosis membrane racks and pumps in a water treatment plant

STP problems and the chemicals that solve them

Treated sewage effluent in Oman is widely reused for landscape irrigation, so plants must meet the limits in their environmental permit. Most small and medium STPs are activated-sludge or MBR package plants, which are sensitive to shock loads, grease and disinfectant from cleaning.

  1. Healthy biology

    The bacteria that treat sewage die back after start-up, shock loads or toxic discharges, and effluent quality drops.

    Chemical typesBacterial seed cultures and activated sludge accelerators; nutrient balance; keeping bleach and strong disinfectants out of the drains.

  2. Coagulation and phosphorus removal

    Fine solids and colloids stay suspended, and phosphate must be removed to meet limits.

    Chemical typesCoagulants: poly aluminium chloride (PAC), aluminium sulphate (alum) and ferric chloride, which also precipitate phosphate.

  3. Flocculation and sludge dewatering

    Small flocs settle slowly, and sludge must be thickened before disposal.

    Chemical typesPolyelectrolytes (polyacrylamides): cationic grades for dewatering organic sludge, anionic grades for clarifying mineral solids, chosen by jar test.

  4. Foam and odour

    Foam spills from aeration tanks, and sumps and wet wells smell of hydrogen sulphide.

    Chemical typesAntifoams and defoamers as a short-term control while the cause is fixed; odour control products.

  5. Disinfection and dechlorination

    Treated effluent must be disinfected before reuse, and some discharges must be free of chlorine.

    Chemical typesSodium hypochlorite or calcium hypochlorite in a contact tank; sodium bisulphite, sodium metabisulphite or thiosulphate to remove residual chlorine where required.

  6. pH and alkalinity

    Nitrification consumes alkalinity, and low pH stalls the process.

    Chemical typesCaustic soda or lime to restore alkalinity; acid to correct high pH.

STP chemicals buyers order most

Ordered by our own sales records and the products our customers mark for repeat orders.

Also supplied for this work

Part numbers are RXSOL codes; quote them when you order. See this industry in the catalogue

Sewage and water product categories

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Sewage treatment chemicals: questions buyers ask

Which polyelectrolyte is used for sludge dewatering?

Usually a cationic polyacrylamide, because sewage sludge particles carry a negative charge. The best grade and dose depend on the sludge and the dewatering machine, so they are chosen by jar test.

Why does an STP foam?

Common causes are detergents, young sludge after start-up, and filamentous bacteria. An antifoam controls foam in the short term, but the cause needs fixing: check sludge age, dissolved oxygen and what is entering the plant.

How is an STP restarted after a shock load?

Stop the source of the shock, keep aeration running, and reseed with bacterial culture or sludge from a healthy plant. Check pH, dissolved oxygen and nutrients until effluent quality recovers.

PAC, alum or ferric chloride: which coagulant?

All three neutralise particle charge and remove phosphate. PAC works over a wider pH range and lowers alkalinity less; alum is economical; ferric chloride forms heavy flocs and also controls H2S, but it is corrosive and stains. A jar test on your water decides.

How is treated effluent disinfected for irrigation?

Usually with sodium hypochlorite or calcium hypochlorite dosed into a contact tank to reach the residual your permit requires. Where effluent is discharged to a sensitive environment, it may need dechlorinating afterwards.

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