November 27, 2019, by Susan Lim

Trip to regional sewage treatment plant

On 23 October 2019, the Chemical and Environmental Engineering department organised an industrial field trip for year 1 undergraduate students to the regional sewage treatment plant (RSTP) in Precinct 14 at Putrajaya (WPJ 001), where wastewater treatment takes place. This plant was built on 11 July 1997, and around RM54 million was invested on the construction. The plant was then handed over to Indah Water Konsortium by Putrajaya Holdings on 1 March 2002. This sewage treatment plant is the second-largest among all the functional plants in Putrajaya. It is designed to treat an average of 22,500 m3 of sewage sludge per day. The overall design of the plant is modern and within it is an odour control system.

The process flow starts from influent and enters into an inlet wet sump that contains wet walls, which holds the influent and provides gravity-flow to the system. The inlet pump is installed at the treatment station as a screen chamber for primary treatment, to distribute visible solid waste and liquid waste before sending it to the grit removal section. Subsequently, the grit chamber removes large settable particles and the overflow sent to the aeration tank. In the aeration tanks, organic materials are oxidised by microorganisms and air is supplied to cultivate microorganisms for respiration and digestion with Fine Bubbles Diffuse Aeration (FBDA). The microorganisms are suspended with uplift bubbles and the organic substances are oxidised to reduce biochemical oxygen demand (BOD). The blower in the aeration system uses a turbo capacity of 64 m3 per minute in 132 kilowatts.

After the aeration process, the partially treated water flows to the clarifiers for clarification where microorganism cells settle and are separated from the treated water. They overflow through weir plates and are discharged at the nearby weir Sungai Air Hitam. The sludge which contains microorganism cells settles at the bottom of the clarifier and is collected by the mechanical scraper. The excess activated sludge in the aeration tanks gets washed by the surplus activated sludge pumps and gets directly sent to the dewatering section. The remaining sludge gets flocculated by polymer to form larger particles for the ease of thickening and dewatering process. The dewatered sludge final product contains 92% solid content.

The main sources that result in odour formation are from a pump, screenings collection chamber, and sludge treatment section. The equipment are attached with air collector and further channelled to bio-scrubber by forced ventilation air ducting system. The end products of all of the sludge are bio-solids which are good enhancers for soil fertility, productivity and microbial activity in the soil. Bio-solids are produced as a dried end product in sewage treatment contains a high proportion of organic matter and nutrients for plant growth. The bio-solids have been applied in rubber plants to enhance the growth and productivity of rubber. The water quality upon discharge is 2 mg/l of BOD, 4 mg/l COD, 6.2 pH, 1 mg/l suspended solids, 3 mg/l for oil and grease and < 1 mg/l of ammoniacal nitrogen.

The trip was fruitful and insightful for the students regarding sewage treatment.

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