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Provision of wastewater recycling system to Architectural Services Department of HKSAR

The public toilet at Sai Wan Village    

Dunwell Engineering Co. Ltd. was commissioned by the Architectural Services Department in November 2007 to supply and install wastewater recycling systems for public toilets at Chek King, Ham Tin and Sai Wan of Saikung District. Due to the remote locations of the toilets, no public sewer has been connected in the past. In other words, they are still aqua privies, the appearance and smell of which can hardly meet the needs of modern lifestyle. From the environmental perspective, aqua privies are far from making the best use of wastewater which can be reused for flushing after being treated and disinfected.

The wastewater recycling system to be installed will initially remove the coarse solids from wastewater, followed by the removal of suspended solids upon sedimentation. Since a considerable amount of organic matters remain in the wastewater, micro organisms in the aeration tank will convert the organic matters into non-polluting carbon dioxide and water.

Despite the process in the aeration tank, small amount of organic matters still exist in the semi-treated water which will enter another system called bio-filter. The semi-treated water will spread from the top of bio-filter and pass through the bio media where micro organism on its surface will consume the remaining organic matters and achieve the water re-use standard.

Prior to discharge or re-use in flushing, the biological treated water will pass through the UV system to remove the bacteria inside the treated water.

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