At present, there is about 2.8 million cubic meters of sewage generated in Hong Kong every day, which is conveyed to the sewage treatment works (STWs) operated by Drainage Services Department for treatment. “Sludge” is the semi-solid by-product of sewage treatment. Every day, about 1,200 tonnes of sludge is delivered to STF from 11 major STWs by vessels or trucks. It is estimated that the amount of sludge will increase to 2,000 tonnes per day by 2030 due to growing population, sewage treatment upgrading or improvement works such as Harbour Area Treatment Scheme (HATS).
Sludge delivered to STF by Vessel
Sludge delivered to STF by Truck
Over 70% of sludge received by STF is from chemical enhanced primary treatment works and delivered by vessels. This could help to minimize the possible nuisance caused by road-based sludge transportation. The rest mainly from secondary treatment works is delivered by trucks.
The two types of the sludge are stored in separate enclosed bunkers with negative pressure maintained by ventilation system so as to prevent odour from escaping. The foul air is treated by deodourization plant prior to discharge.The sludge stored in the two bunkers is grabbed to the hopper, mixed by the double screw mixer and injected to the fluidized bed incinerators by the high pressure pumps.