Johor River Water Works

 

Owner: Public Utilities Board, Singapore
Consultant: UGL (Singapore) Pte Ltd
Project Description: Design, supervise and construct for the existing treatment Plants A and B:

  • Installation of UV disinfection systems to achieve at least 4 log inactivation of Cryptosporidium at an UVT of 95%.
  • Upgrade existing sand filtration backwash and related processes such as filter control and chemical dosing to achieve filtered water turbidity of less than 0.15 NTU in at least 95 % of the measurements each month and at no time exceed 0.3 NTU.

 

Location : Johor River Water Works, Kota Tinggi

Scope of work :

  • SCADA network enhancement
  • Supply control panel and MCC panel for filtration system and chemical system
  • Process testing and commissioning for filtration system and chemical system.

 

Johor River WaterWorks

The Johor River Waterworks(JRWW)  extracts water from the Johor River upstream of Kota Tinggi and is currently the largest source of supply of potable water to Singapore.  The Waterworks has three water treatment plants A, B and C, providing a total output of 250mgd (UK gallons). 
Plants A(60mgd) and B (100mgd) were developed from late 1960s to early 1990s and use the conventional coagulation, clarification, sand filtration and chlorine disinfection as its main treatment processes.  Plant C (90mgd) was commissioned in 2001 and uses advanced ozonation and biological filtration on top of conventional water treatment.
The latest WHO and USEPA standards stipulated new requirements on the emerging waterborne disease – Cryptosporidium (Crypto).  Under PUB’s routine water quality monitoring programme, Crypto is monitored in both treated water and raw water.  The treatment records and routine quality monitoring confirmed that the supply of PUB’s potable water is free from crypto and other harmful pathogens. 
Based on the latest USEPA LT2 rule, the average concentration of Crypto in Johor River (source water) is in Bin 2 classification, which will require a total treatment performance target of 3 log for conventional water treatment. 
Treatment performance for removal of Crypto at Plants A & B has been validated through the use of aerobic spore tests to be around 4 log (99.99%).  The newer Plant C which has additional ozone and GAC treatment has treatment capability of more than 5.5 log.

Objectives

As a small country Singapore has much less tolerance for failure in our essential services such as water supply.  PUB therefore adopts a zero-tolerance approach and stays ahead of international standards in water quality control and water treatment technology.
In view that the source water quality may further deteriorate due to future development around the water catchments area, the bin classification may go up to Bin 3 or 4 and that will require higher than the existing 4 log treatment attained at Plants A & B.
PUB intends to upgrade the existing JRWW Plants A & B to achieve at least 5.5 log of removal of Cryptosporidium.  The two plants will be upgraded with additional treatment using UV disinfection systems and an enhanced filter backwash system to achieve at least 99.9997% removal (5.5-log removal) of Cryptosporidium and filtered water turbidity of less than 0.15 NTU in at least 95% of the measurements each month and at no time exceed 0.3 NTU.

 Chemical System

Chemical coagulation is one of the key processes that remove Cryptosporidium in conventional filtration treatment and determines the quality of settled water which is critical for good performance of filters and UV system.

The existing chemical preparation and dosing controls for Plants A & B are mostly local control with lime dosing system having automatic flow pace and quality pace controls, while alum dosing system having flow pace control. All adjustments for chemical treatment can only be done locally at site and time consuming as the various chemical control panels are all distributed quite far from each other. 
In order to meet more stringent water quality requirements with tighter control band for the chemical treatment and a faster response time to  react to any fluctuations in the source water quality or treatment performance, existing chemical systems have been enhanced to provide local automatic flow pace and quality pace controls, remote controls for quality pace setpoints adjustment, remote control for starting and stopping of duty/ standby pump, opening and closing of valves and remote selection of cyclic duty of the pumps at SCADA HMI.

Flow Pacing
Alum, Pre-Lime and Pre Chlorine Dosing are implemented with flow paced control. When flow-paced in selected indicates that the system will varies based on the flow variation, and operator entry is needed for treatment dosage (ppm).The required chemical solution feed rate is therefore defined from rate of flow signals, ppm setpoint  and the chemical solution density level, which is determined by laboratory tests.

Quality Pacing
Post-Lime, Intermediate Chlorine Dosing are implemented with quality paced control. When quality-paced in selected means the control shall be compound loop, first by flow then follow by total residual chlorine reading. The PID controller will now determine the ppm setpoint automatically by comparing difference with the quality sensor reading with the desire set point.
The required chemical solution feed rate is therefore defined from rate of flow signals, ppm set point  and the chemical solution density level, which is determined by laboratory tests.

 

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