topographic features and a routing configuration that connects inflows from 232 sewage treatment plants. The maximisation of the topography reduces susceptibility
to
service interruptions, operations and maintenance activities associated with network pumping. In addition to efficiency, these connections have also been planned for future growth.
A range of trenchless technological options is also adopted for sewer laying to achieve minimal disruption or potential damage to existing infrastructure and properties. This process involves any identification of deviations from existing guidelines governing the per capita sewage contribution, as well as the optimal design and construction of sewers based on both technological and practical aspects. Buried utilities posed as the biggest challenge and involved repeated modifications necessary to design drawings and construction methods.
The Langat CSTP is to be located in the Kajang-3 area near the Upper Langat River Basin. The plot of land assigned for this project is not only irregularly shaped but it is also only a mere 7.3 hectares in area. Based on the Malaysian Sewerage Industry Guidelines (MSIG) as published by Suruhanjaya Perkhidmatan Air Negara (SPAN), 7.3 hectares is able to support just under 300,000 population equivalent (PE). To address this issue, the engineers propose using Deep Aeration Method, which can cater for 920,000 PE within the same site, more than a three- fold increase in capacity.
The selection of treatment process balances efficiency and footprint compactness, with full compliance to stipulated statutory and legal provisions. In addition to this, there is also provision of complementary benefits at the central plant such as community facilities and a centre of knowledge.
DEEP AERATION METHOD Langat CSTP uses a wastewater treatment system adopted from the Japanese technology: Modified Conventional Activated Sludge Process utilising the Step-Feed Multi-Stage De-Nitrification with Deep Aeration Method. Deep Aeration Method aims to make best use of available land by designing an aeration tank with smaller footprint with approximate depth of 10 metres, compared with a conventional aeration tank of 5-metre depth. The use of the deeper tank and the special air diffuser and baffle wall will allow more efficient oxygen transfer and mixing characteristic.
The Modified Conventional Activated Sludge Process is most suitable to be used on an extremely tight plant area with heavily contaminated water containing high levels of ammonia that is non-compliant with the environmental standard. The process helps to improve and achieve low levels of ammonia and nitrogen removal ratio up to 80 per cent, according to the effluent parameters limit in the Standard A category under the MSIG.
MECHANISM The influent sewage first arrives at the Screen/Grit Chamber. Bulky waste and grit down to 0.2 millimetres is removed at this stage. The sewage is then lifted by the main pumps in the Inlet Pump Station up to the Distribution Tanks and the Influent Chambers. Oil and grease are removed in this area before gravity brings the sewage into the Primary Clarifiers. Any excess sewage flow above average flows at this stage drains into the balancing tanks and are sent back during low flow periods to the grit chamber.
After primary clarification, the sewage enters the reactor tanks to undergo the Step-Feed Two-Stage De-Nitrification Process with Deep Aeration. Following treatment, the mixed liquor is settled in the Secondary Clarifiers. Effluent disinfection structure will be provided for future disinfection of the effluent when the need arises. Effluent flows into a measurement tank before being finally discharged into the river. Return activated sludge is recirculated to the reactor tanks to maintain suitable mixed liquor suspended solids in the reactor tanks.
SUSTAINABILITY The batching plant was built next to a CSTP site for the concreting works. For equipment selection, there has to be compliance with the list of approved equipment by SPAN. Mostly the equipment can be locally procured except for a few models and capacity for blowers pump and submersible mixers are imported. Beside the usage of energy savings starter using Variable Frequency Drive (VFD), the selection and sizing of equipment also takes into consideration on the operational cost whereby we manage to get SPAN approval on the design deviation to have two small pumps and five big pumps for the inlet pumps arrangement to cater for the low
Engineers working on the installation
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