Dirtier harbour defies logic with treatment in place, expert says

PUBLISHED : Saturday, 12 February, 2011, 12:00am
UPDATED : Saturday, 12 February, 2011, 12:00am

Few people in Hong Kong know more about waste water treatment than Professor Joseph Lee Hun-wei. Yet the respected expert confessed yesterday that he was as baffled by the sudden surge in bacteria levels at the centre of Victoria Harbour as the public - particularly given the city opened a new disinfection centre just last year that reduced the amount of sewage released into the harbour.

Lee, an award-winning environmental hydraulic expert and now vice-president for research and graduate studies at the University of Science and Technology, admitted being frustrated at being unable to solve the mystery behind the growth of Escherichia coli bacteria in the harbour - just as the water quality seemed to be improving steadily.

'Obviously, something has happened. But I am not sure if this is a one-off thing or a chronic process,' said Lee, who advised the government on the HK$19 billion Harbour Area Treatment Scheme.

He suspected the cause could be damage to an undersea sewage pipe or malfunction of the city's newest and largest sewage treatment works on Stonecutters Island, although neither case could be proven as yet.

Lee, who received a top innovation prize from the State Council last year for developing a computer model for waste water disposal or flood prevention, said the harbour findings were very alarming.

He said the E coli level at a bathing beach should not exceed 180 units per 100 millilitres of water. The annual average reading at the harbour opposite Wan Chai was found to surpass 8,000 units. The high reading upsets the trend in declining E coli levels over the past decade and throws into doubt the revival of the historic cross-harbour swim. 'The reading is astronomical and unacceptably high even before the disinfection facility at the Stonecutters treatment works came into service last year,' Lee said.

That facility, as part of the centralised treatment works, started operation early last year to suppress bacteria levels in the treated effluent being discharged into the harbour. It handles daily about 1.4 million tonnes of sewage collected from Kowloon and eastern Hong Kong Island, or about 75 per cent of the total waste water generated in urban areas.

The remaining 25 per cent of sewage, amounting to 450,000 tonnes and mostly generated in the northern and western shores of Hong Kong Island, is pumped into the harbour after simple screening.

The polluting practice is expected to continue for four more years until a deep tunnel network channelling waste water from the two areas to Stonecutters is built. The bacteria-laden effluent has been drifting westwards, causing the closure of seven Tsuen Wan beaches since 2003.

Lee said the disinfection, through a process of chlorination and dechlorination, was so powerful that it could remove bacteria by up to 99 per cent, making the rise even more puzzling. 'The disinfection should have made the water quality better. There is no reason why the level has even gone up higher than before the facility was in place,' he said.

A spokesman for the Drainage Services Department, which is responsible for running the treatment works, said the disinfection facility had been operating smoothly and the E coli level in the discharged effluent was within normal standards.

He said the department was trying to see whether sewage outfalls in the harbour area had been damaged.

A spokesman for the Environmental Protection Department, which is in charge of sewage disposal policy, said E coli levels in the western harbour area were reduced by up to 57 per cent last year.