In recent years, the Water Supplies Department (WSD) has been introducing numerous advanced technologies that enhance its water treatment capability to ensure that water is clean and hygienic. The Tai Po Water Treatment Works (WTW), of which the expansion was completed earlier, is no exception. Apart from applying innovative technology for the construction works, the Tai Po WTW has adopted the latest technologies in water quality monitoring and water treatment, and with sustainable features embedded, making the entire water treatment process more environmentally friendly. This time, I have invited a WSD colleague to introduce the special features of the expansion of the WTW and how its operation has been improved.

Output capacity doubled after the expansion

At present, there are 17 WTWs in operation treating and supplying an average of 2.7 million cubic metres of fresh water per day for a population of 7.5 millions in Hong Kong. The expansion of the Tai Po WTW was commenced in 2013 and completed by end 2018. Before the expansion, the output capacity of the Tai Po WTW was 400 000 cubic metres per day, accounting for 15% of fresh water demand in Hong Kong. After the expansion, the output capacity of the Tai Po WTW has doubled to 800 000 cubic metres per daycapable to meet the increase in fresh water demand arising from population growth and development in Tai Po, part of West and Central Kowloon and Central and Western District of the Hong Kong Island. The expansion of Tai Po WTW also takes up part of the loading of Sha Tin WTW to facilitate the latter’s in-situ reprovisioning of its South Works.

Use of Building Information Modelling (BIM) technology

To avoid disruption of fresh water supply, the expansion of the Tai Po WTW had to be carried out without affecting its existing operation. Engineer of WSD, Ms CHAN Hoi-wing, says that as the works involved the construction of new facilities among the existing facilities and the site areas available were very limited, every construction process had to be carefully planned and arranged. By using the BIM technology, the project team carried out design and construction work in a virtual environment to simulate the alignment of the new water mains and arrange the construction sequences in advance so as to avoid affecting the adjacent facilities and enhance the project efficiency.

Use of innovative water treatment technologies

At the same time, the WSD has taken the opportunity of the expansion of the Tai Po WTW to introduce several advanced water treatment technologies, including the use of dissolved air floatation (DAF) clarifiers to pump compressed air into water until saturation for producing a large quantity of micro bubbles that adhere to suspended matters in water and bring them to the water surface, creating a layer of sludge blanket that will subsequently be removed by an automated sludge scraper. This innovative water treatment technology can remove impurities quickly and reduce the use of chemicals.

Installation of an on-site chlorine generation facility

Since there is no chlorine gas supplier in Hong Kong, the Tai Po WTW has been importing liquid chlorine from the Mainland for disinfection of drinking water. In the expansion of the Tai Po WTW, an on-site chlorine generation facility has been specially incorporated in the plant to generate the amount of chlorine on demand for immediate chlorination of the treated water to produce residual chlorine. This will eliminate the risk of chlorine leakage during transportation and storage of imported liquid chlorine.

Monitoring water quality with the help of zebrafish

To enhance the monitoring of raw water quality and ability to provide early warning of changes in water quality, the laboratory of the Tai Po WTW has adopted the Biosensing Alert System developed by the WSD. The System uses zebrafish, which have a genetic composition very similar to that of humans, as its partner in water quality monitoring. As zebrafish are highly sensitive to contaminants in water, the System can continuously monitor the quality of raw water entering the WTW by way of using a computer system to automatically analyse and detect the behaviour and activities of zebrafish.

Achieving zero effluent discharge

Furthermore, the expansion of the Tai Po WTW has incorporated sustainable features into its design and operation. For example, for better use of our precious water resources and to minimise the environmental impact, treated effluent produced during the treatment process will flow back to the WTW intake for use as raw water, so that 99.7 percent of raw water can be turned into quality drinking water. The remaining 0.3 percent of raw water is contained in the sludge produced during the treatment process, which will also be used for greening and planting in the WTW premises to achieve “zero effluent discharge” in the entire water treatment process.

There is also a recycling system in the WTW to treat rainwater collected and water samples that have been tested for water quality and use them for irrigation and flushing purposes. Besides, about 700 photovoltaic panels, each with an area of approximately 1.6 square metres, have been installed in the WTW to generate about 200 000 kWh of electricity annually for on-site facilities.

Water treatment is a science under constant development. I encourage the department to enhance its water treatment capability by continuous improvement and introducing advanced technologies. The WSD will continue to review its existing water supply facilities and upgrade them when necessary. For example, by reprovisioning Sha Tin WTW – South Works, and expanding Ngau Tam Mei WTW and Siu Ho Wan WTW, the department works to continuously enhance its water treatment capacity in order to provide the public with a reliable water supply and quality drinking water.