Secrets of StanleyBy Anne Holyoak and Daniel Tollefsen

The Process

Like most sewage treatment, Stanley has three major stages that the waste goes to. They are called primary, secondary and tertiary treatment. These stages help to decontaminate any waste in order for it to be safe enough to be released into the environment.

Primary Treatment

Secondary Treatment

Tertiary Treatment

Total

Percentage of process completed83%

17% <0.01% 100%

Primary TreatmentAfter the waste material leaves your house, it travels through a serious of pipes that eventually lead to the main sewage treatment facility located in Stanley. The first stage of treatment is called Primary treatment. At first the waste goes into tanks where the different types of material can be sorted. Gravity is the main force in sorting the solids between the heavy objects and the objects that float towards the top. The hard solids sink to the bottom where they are moved to be further decontaminated. This process mainly screens for coarse and fine material, which would be any wood or papers or other items that may be found in the sewage but not meant to be there. These items are removed during a coarse screening process as to ensure that the pipes do not get blocked.  Bars that filter the sewage, coarse material from fine

material

Primary Treatment

Bars filter the sewage, coarse material from fine material

Apart from the screening, there are large bars that remove solids with a diameter that is bigger than 6mm. Other bars also run through the screen as to pick up any sticky matter that may be in there. Any of the smaller solids are only screened by bars with a diameter of 6m. To finish the Primary treatment, various chemicals are added to remove TSS and BOD at an efficiency rate of 50-60%

Secondary Treatment

The secondary treatment is comprised of adding micro-organisms to the suspended solids as well as the liquid sludge.

The micro-organisms added, consume and consume the nitrogenous parts of the waste.

All of this occurs in an aeration tank where oxygen is continuously added in order to keep the micro-organisms suspended and alive.

Secondary Treatment

Next, the waste that now is left (nitrogen decreased) has chemicals added to it in order to cleanse and to kill off bacteria

Also, these chemicals are added in order to reduce the amount of TSS (total suspended solids) and the BOD (biochemical oxygen demand) to levels that are approved by the United States as well as Hong Kong government rules and regulations

The waste is treated to meet the 20mg/L BOD and 30mg/L TSS standard

Tertiary Treatment

The last stage that the waste must go through is the Tertiary Treatment. This stage must be completed before the materials flow into the environment, like in Stanley where it goes into the Sea. Part of the tertiary treatment is the filtration part. During this phase the waste gets rid of any remaining residual toxins. Along with removing toxins, waste must also be decontaminated of high levels of nutrients. Having too many nutrients released into an environment can cause a build up, eutrophication. As a side effect, the surrounding areas experience an overgrowth of unwanted plant life. When the plants decompose they use up a majority of the oxygen. This leaves little to none for the nearby animals. This is a vicious cycle that can be majorly avoided if the waste treatment is completed properly. Nitrogen and Phosphorus need to be removed before entering into an environment. Through denitrification, high levels of nitrogen are removed. Similarly, phosphorus is removed through a process called Enhanced biological phosphorus removal. Through these processes the contaminating parts of the waste materials are depleted making the waste safe for disposal.

Turtle Cove

Nitrogen Cycle

Nitrogen Cycle in Waste

The micro-organisms that decompose the nitrogenous parts of the waste are disposed of in landfills and other areas in Hong Kong

This helps in not making the area in which the waste itself is disposed in not so concentrated

The area that it is disposed in might feel the effects of eutrophication if the nitrogen is disposed constantly in the same area

If that happens, there might be a boom in the wildlife that is irregular and could lead to a change in the entire ecosystem

Is it Safe?

Yes, it is safe to swim in Turtle Cove. The Hong Kong government has spent billions of dollars into making a sewage system that is effective. The multiple step process ensures that the environment and the people will not be harmed. Chemicals and micro-organisms are added as an extra precaution to ensure the waste material will eventually be safe to swim in. According to standards met by the United States and Hong Kong, the water is safe to swim in.

Bibliography

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"FAQs." HATS. Hong Kong. Web. 21 Mar. 2010. <http://www.cleanharbour.gov.hk/english/g5.html#8>.

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