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Typhoon Mangkhut

Race against time to repair major Hong Kong sewage treatment facility damaged in Typhoon Mangkhut

Officials to roll out temporary chemical treatment as a stopgap measure, with full repairs not likely until the end of the year

PUBLISHED : Friday, 28 September, 2018, 7:01am
UPDATED : Friday, 28 September, 2018, 7:00am

A major Hong Kong sewage plant damaged by Typhoon Mangkhut will not be fully repaired until the end of the year, but drainage officials are racing to upgrade effluent treatment to safer levels.

Storm damage to pipes and treatment facilities at the Sai Kung Sewage Treatment Works was so serious last week that sewage treatment has been reduced to a “primary” level – basic filtering of grit, solid waste and suspended solids, which only eliminates half of the pollutants in raw sewage.

Potassium alum – a chemical compound – is also being added to the effluent to increase purification.

In normal times, waste water is purified through “secondary treatment”, a more advanced biological process, where nutrients are decomposed by microorganisms, before being discharged into Inner Port Shelter via a 450m long submarine pipeline.

To buy time, the Drainage Services Department said it would try to employ a higher level of “chemical treatment” by mid-October, which is somewhere between primary and secondary and able to rid the waste of 80 per cent of pollutants, as a temporary fix.

Hong Kong sewage treatment facility leaking waste into waters off Sai Kung after being damaged in Typhoon Mangkhut

“We will not be able to restore secondary treatment for at least another two to three months or before the end of the year,” a spokesman said.

According to the department’s most recent figures, the E coli count near pump station No 3 clocked in at 200 colony-forming units (cfu) per 100ml of water on September 22, higher than the Environmental Protection Department’s 180cfu/100ml allowance for beach water quality. Repair work on the coastal plant’s smashed sea wall also began on Wednesday and will be completed within a week, the department said. Plans are also being mulled as to whether to raise it and build a flood barrier in anticipation of more extreme weather.

Commissioned in 1988, the 2.2 hectare Sai Kung Sewage Treatment Works services 20,000 people in the district and has a daily capacity of more than 8,000 cubic metres per day.

Plans were floated in 2014 to move the plant into a nearby cavern in Tsui Hang, possibly tripling its capacity and freeing up the existing site for other uses. A feasibility report on the move will be completed at the end of the year.

Meanwhile, repairs to at least one of three damaged sections of pipe in the Southern District – one near the Deep Water Bay barbecue site – has been completed. That leaves sections near Mills and Chung Path and in Shek O requiring repairs.

Army of 300 volunteer law enforcement officers to help clear debris across Hong Kong after Typhoon Mangkhut

Water quality at surrounding beaches including Trio, Hap Mun and Kiu Tsui was rated “good” or “fair” on Thursday. Only one beach in the territory’s eastern waters – Big Wave Bay Beach in Southern District – is currently graded as “poor”.

The government has warned the public not to swim at the beaches.