TreatmentCosts

Treating Hong Kong's Sewage

Wastewater is the main cause of water pollution in Hong Kong. Sewage is wastewater produced by people, and comes from homes, offices, restaurants and factories. Wastewater is also discharged from livestock farms. Runoff from urban areas and from fertilised fields in rural areas also contributes to water pollution.

Among the pollutants in sewage are :
	solids, such as paper and rags, which float and are unsightly ;
	organic material, which consumes oxygen from the water as it decomposes ;
	bacteria, which are a primary public health concern ;
	ammonia, which is highly toxic to fish ;
	nitrogen, which can cause excessive growth of algae, sometimes forming red tides ;
	toxic metals, which can accumulate in sediments and poison marine life and our seafood.
The degree of treatment and the final discharge method and location determine whether wastewater causes adverse impacts. Most of our wastewater is collected in sewers and is then screened and degritted to remove large solids prior to discharge via purpose-designed outfalls. Some also receive :
	primary treatment (sedimentation), which removes about 30% of organic material ;
	chemical treatment, which removes over 60% of organic material ;
	biological treatment, which removes up to 90% of the organic material as well as ammonia and some of the nitrogen ;
	disinfection, which provides much better removal of bacteria than is possible with the above processes.
Technology exists to provide further levels of treatment for greater removals of pollutants. However, for every level of treatment that is added, the costs escalate rapidly. Public money spent on removal of pollutants from sewage might not be justified if such removal could not demonstrate measurable effect on the environment. The objective of any treatment strategy is to ensure that sufficient treatment is applied and that favourable discharge locations are identified so that there is no adverse impact on aquatic resources or human uses of our inland and marine waters.
Measures that have been taken to address these problems so far include:
Source control
	Effluent discharge is subject to control under the Water Pollution Control Ordinance (WPCO), which ensures that discharges from industrial establishments into the sewage system contain minimal toxic substance.
	Chemical waste must be collected by licensed collectors and disposed of at licensed facilities under the Chemical Waste Control Scheme of the Waste Disposal Ordinance (WDO).
	Livestock farming is only permitted in certain areas, from which livestock waste must be either collected or treated to prescribed standards under the Livestock Waste Control Scheme of the WDO.
Wastewater Collection
	Old sewers are being replaced and new sewers provided to ensure that waste water is not discharged into rivers, at beaches or along sea-walls. The Sewerage Master Plans (SMPs) for each area also ensure that the waste water collected can be conveyed to treatment plants.
	Chart 1: An illustration of the effect of introducing the WPCO and implementing the SMP for Repulse Bay
Wastewater Treatment
	Due to works around the harbour, together with works on SMP's elsewhere in the territory, the volume of sewage which receives high levels of treatment (secondary or chemically enhanced primary treatment) has increased from about 80 million cubic metres in 1989 to about 650 million cubic metres in 2002.

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