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2017 IWA Symposium of Lake and Reservoir Management
Shanghai, China, 22-26 May, 2017
Strategies and Approach to Monitoring and Management of Cyanotoxins in
Singapore’s Reservoirs
Mong Hoo Lim *, Hui Shi Melissa Tay, (PUB, Singapore) (* indicates Corresponding Author)
Presenting Author: Mong Hoo Lim
Keywords: Reservoir management; nutrients control; algae; cyanobacteria, cyanotoxins.
Abstract
Introduction
Singapore is a small island nation with a total land area of only 719 km2 but with a substantial
population size of 5.5 million. Although it receives abundant rainfall of about 2400 mm
annually, it is deemed to be a water scarce nation because of its limited land to collect and
store the rain. Singapore ranked 171th among 182 countries in terms of fresh water availability
(United Nation World Water Development Report 2003). Notwithstanding this disadvantaged
situation, PUB, the national water agency of Singapore, strived and succeeded in attaining
sustainable water supply through effective management and technologies. Singapore’s water
demand is met by its 4 National Taps which are the following 4 water sources: local water
catchments (waterways and reservoirs in Singapore), imported water from Malaysia,
NEWater (high grade reclaimed water) and desalinated seawater.
The local water catchments comprising two-third of the entire land area of Singapore and
there are 17 reservoirs to collect catchment runoff through an extensive network of waterways.
The protection of water quality in waterways and reservoirs is an important part of the PUB’s
integrated water quality management to ensure safe and wholesome drinking water supply
and safety of water recreational activities. Poor management of reservoirs can lead to algae
bloom and production of excessive cyanotoxins and taste and odour (T&O) compounds such
as 2-MIB and Geosmin. Presence of excessive cyanotoxins poses threats on water safety
whereas T&O compounds affect wholesomeness of drinking water which leads to complaints
from consumers who may also cast doubts on safety of the drinking water supply.
There has been substantial progress in the perception of cyanotoxins as risk to human health
and risk management approach has been widely adopted in management of cyanobacteria
and cyanotoxins in water bodies. In Singapore, safeguard on water safety in association with
cyanotoxins is incorporated in PUB’s Water Safety Plan for reservoirs management in
accordance with the framework proposed by WHO (2004).
This presentation focuses on the PUB’s strategies and approach to monitoring and
management of cyanotoxins in Singapore’s reservoirs. It briefly covers the aspects of risk
assessment and management which lead to formulation of measures for pollution source
control and water quality monitoring. It also shows the findings of in-house studies which
facilitate development of targeted operational measures and objectives, and utilization of
technologies to enhance water quality monitoring and control of algae growth.
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2017 IWA Symposium of Lake and Reservoir Management
Shanghai, China, 22-26 May, 2017
Source control
Source control of nutrient loadings is universally known to be a key strategy to control algae
growth. It forms an important part of PUB’s integrated catchment water quality management.
The measures for source control principally focus on minimizing nutrients loadings from
potential pollution sources, for examples, reducing sewer leaks through sewer rehabilitation,
putting in place measures to prevent pollution loadings into the waterways from food centers,
preventing soil erosion from construction sites where bare soil has been exposed, reducing
flotsam and litter by using float booms and gratings in waterways, reducing other pollutants
(eg oil & grease) through improving housekeeping at workshops and use of
environmentally-friendly watercraft, etc. Other mitigating measures to control algae growth
include aeration and improving water circulation through inter-reservoirs transfer, e.g., Marina
Reservoir Recirculation Scheme was implemented for this purpose. Another important
initiative in source control is public engagement through the Active, Beautiful, Clean Water
program in which waterways and reservoirs are beautified with pollution control measures put
in place to attract recreational activities and simultaneously educating the public to always
keep the water clean to value and enjoy the invaluable water bodies in Singapore.
Water Quality Monitoring
To ensure water safety, PUB has a comprehensive water quality monitoring program from
source to customer tap. With respect to management of cyanotoxins in the reservoirs, besides
the general parameters inclusive of nutrients monitored by online vertical water quality profiler
and laboratory analyses, mass of chlorophyll-a, cell counts and concentration of cyanotoxins
are also being closely monitored. Risk assessment approach is used to establish alert levels
to trigger step-up monitoring and initiation of mitigating measures to put the situation in check.
To illustrate, PUB, together with the water regulator and using the WHO’s recommended
approach, have established 50 µg/L of chlorophyll-a to be a level associated with significant
risk for presence of cyanotoxins at levels of concern. Also, in-house studies showed that to
control Microcystin-LR below WHO guideline of 1 ug/L (for drinking water), the population of
Microcystis cells should be kept below 10,000 cells/ml. It has also been observed in the
studies that total nitrogen (TN) and total phosphorous (TP) are important factors affecting the
growth of Microcystis. Our data showed that by keeping the ratio of TN:TP>18 and TP at
<0.035 mg/L, Microcystis cells are kept below 10,000 cells/ml and hence reduces the risk of
Microcystin-LR concentration exceeding the WHO guideline of 1 ug/L.
Table 1. Summary of cyanotoxins concentrations monitored in Singapore raw water
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2017 IWA Symposium of Lake and Reservoir Management
Shanghai, China, 22-26 May, 2017
Technologies
PUB is constantly exploring technologies to enhance control of algae growth and water quality
monitoring. Some of the new technologies for raw water quality monitoring which are being
studied and validated include New Smart Water Assessment Network (NUSwan),
Autonomous Underwater Vehicle (AUV), Hyper Spectral Imaging (HSI), Water Insight
Spectrometer (WISP-3) and SMART LEDIF (LED-Induced Fluorescence). Also, testbedding
of an ultrasonic system to control algae growth is being carried out in one of the reservoirs to
test the effectiveness.
Conclusion
There has been increasing concern on cyanotoxins in water as risk to human health and risk
management approach has been widely adopted in managing cyanobacteria and cyanotoxins
in water bodies. In Singapore, safeguard on water safety associated with cyanotoxins is
incorporated in PUB’s Water Safety Plan for reservoirs management in accordance with the
framework proposed by WHO (2004). Source control of nutrient loadings which is universally
known to be a key strategy to control algae growth forms an important part of PUB’s
integrated catchment water quality management. PUB also has a comprehensive water
quality monitoring program and risk management approach is used to establish alert levels for
triggering of step-up monitoring and initiation of mitigating measures to put the situation in
check. PUB is constantly exploring technologies to enhance control of algae growth and water
quality monitoring. More details on source control measures, water quality monitoring, data of
in-house studies which facilitate development of targeted operational measures and
objectives, and utilization of technologies to enhance water quality monitoring and control of
algae growth will be shown in the presentation.
References
United Nation World Water Development Report 2003.
PUB. (2016). PUB: Storm water management. Retrieved from:
https://www.pub.gov.sg/drainage/stormwatermanagement
Singapore Department of Statistics. Latest Data. Retrieved from:
http://www.singstat.gov.sg/statistics/latest-data#16
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