turtle cove beach - safe to swim?

Turtle CoveSafe to swim?

Angela Lau and Daryl Ko

IntroductionAre you wondering whether the Turtle Cove Beach east of Stanley is safe to swim?If you are, then probably you’ve arrived to the right place.

This presentation will include an detailed explanation of the sewage treatment in Stanley, the conditions of Turtle Cove, how the nitrogen cycle plays in the role of waste treatment and comparing and contrasting the sewage treatments in other major cities.

By the end of this powerpoint, you will be able to determine for yourself whether it is actually safe to swim in Turtle Cove Beach.

ENJOY !

What is Sewage Treatment?Sewage treatment is the process of purification of mixtures of

humanwaste and domestic waste• Process of removing microorganisms and contaminants

from wastewater

In another words how our urine/feces gets treated

Sewage Treatment

Sewage Treatment Process• Typical sewage

treatment includes:o Preliminary

treatmento Primary treatmento Secondary

treatmento Tertiary treatment

Stanley Sewage Treatment Works

• First underground “municipal” Sewage Treatment in Asiao Includes 3 large caverns (large cave)

120m long, 15m wide, 17m high

• Treatment serves 27,000 people living in Stanley, Redhill, Tai Tam, Chung Hom Kok areas

• Undergoes secondary treatment/stage (biological treatment)

Inside a cavern

Process Treatment Flow

Preliminary TreatmentPreliminary treatment – removes materials collected from raw wastewater

• Includes process of coarse screen, fine screen, grit removalo Screening main function - remove solid matter

Comes in range of size and shape

Course Screen• Rotating bar type – 50mm spacing between bar

Function:• Screen out large solids

o Small, sticky substance stick on bar so that it can get through screen

Course screen

Continuing…• Fine Screen – for screening

smaller solidso 6mm opening

• Grit Removal o Sand, grit chamber

Function:o Control sand, grit, stones to settleFine

Screen

Grit removal facility

Grit

Continuing…

• Detritor – where grits are removedo 6m diameter

Outside of detritor

Detritor

* Grit settle in holding tank swept to device sent to landfill

Primary Treatment Not specifically mentioned yet part of the sewage treatment

• Sewage flows through large tanks (“primary sedimentation tank”)

Function: allow particles to settle into sludge

• Tanks large enough to settle – grease and oil rise to the top of sewage and skimmed off

Sedimentation tank

Biological Treatment (Secondary)• “Activated sludge process and extended aeration” occurs during

biological treatmento Activated sludge – traps material, under certain condition convert ammonia

nitrite nitrate nitrogen gaso Aeration – process of exposing to air

Aeration tank:Function: oxygen pump diffused air system• Install to sustain growth of

micro-organisms

3 zones in aeration tank:1. Contact Zone2. Anoxic Zone3. Aerobic Zone

Aeration tank

Steps in Biological Treatment

1. Sewage from preliminary treatment enters aeration tank

2. Flows to contact zone (complete mixing)

3. Reaches anoxic denitrification zone• Denitrification – process of releasing nitrogen back to

atmosphere

4. Sewage flows to aerobic zone for nitrogen removal

Lastly:• “Treated sewage flows to final sedimentation tank on

aerated interconnecting channel”

Contact Zone

Anoxic Zone

Final Sedimentation• Sedimentation – settling of suspended solid particles in

liquid

• Treated sewage flows here for sludge removalo Inside tank: inclined lamella plates installed

Useful for sledge settling

• Effluent (water mixed with waste matter) launders installed longitudinal along lamella plateso Provides effective weir (small dam in rivers) length

Images of Final Sedimentation

Lamella Plates

Final Sedimentation Tank

Sludge Treatment• Sludge collected from final sedimentation tank

o Part of sludge return to aeration tank – regenerate microorganisms

o Other part of sledge sent to sludge press feed chamber dewatered by belt press

• After process complete, sludge transport to landfillo Site for disposing waste

Images of Sludge Treatment

Sludge TankSludge Dewatering Unit

Belt Press

Disinfection of Effluent (Tertiary Treatment)

Tertiary Treatment• Referred to effluent polishing• Carried to improve water quality• Most wastewater plant include at least one process

Processes include:• Filtration (process – fluids pass through a filter)• Nutrient Removal• Disinfection

Disinfection• Secondary wastewater goes to infection• Disinfectant : sodium hydroxide

o Dissolves in water HCl

Reacts with ammonia

• Hydrochloric acid reacts with alkalinity

• After disinfection, wastewater discharged to Sheung Sz Mun

Process Flowchart

Discharged to Sheung Sz Mun

2.3 km

Water/ Ocean Currents

As shown on the map, we can see exactly where the sewage comes out of the pipes from the sewage plant. As soon as the water leaves the pipe and enter the sea water, a current drifting north will carry all the water in that direction. Thus people swimming in Turtle cove would be swimming in sewage water coming from the pumping stations. It is safe to say that when excluding dispersing factors, the sewage water would go to that spot somehow.

Beach Conditions

Grading:• Environment Protection Department grades the

beaches in Hong Kong on a scale of 1 to 4. 1 being the highest beach water quality and 4 being the lowest beach water quality

Turtle cove – Grade 1

Continuing…

Annual Beach Grading (according to Hong Kong EPD)• Gives people overview of quality of beach

In four categories:• Good• Fair• Poor• Very poor

The first two (good, fair) meets Hong Kong’s Water Quality Objectives• Should not swim if the beach belongs to the category of poor or very

poor

Annual Grading

Difference between Sewage Treatments in Hong Kong and Sewage Treatments internationally

The Sewage treatments vary from country to country. Hong Kong is one of the countries which are fortunate enough to have a sewage water treating system. Thought what is important is that Hong Kong does not have the most sophisticated sewage water treatment in the world. Take simply the Stanley sewage treatment works, it is an organized system to purify sewage water. But in comparison to other countries, one significant difference already is the fact that Hong Kong already lacks a primary treatment. Although they all go through the same process, one that does not do a certain step will definitely have disadvantage to it. The treatments may share the secondary and tertiary treatment, but in-between the sub-levels, some things may differ. The sewage process maps show that they have different steps and branches but in the end achieve the same thing.

Continued

• This would be something that is not seen in Hong Kong as it is used in the treatment that sewage treatments in this place do not require.

Nitrogen Cycle – Key Words• Mineralization – “process in which organic compound (dead plant, animal material) is converted to inorganic compound (nitrate, carbon dioxide)”

• Denitrification – process of nitrates forming to gaseous nitrogen

• Nitrification – oxidation of ammonia to nitrate nitrogen

• Bacteria Fixation – From N2 to bacteria

• Leaching – washed through or out of the soil

• Eutophication – increase in nutrients, system which increases primary productivity

• Anerobic – capable of living without oxygen

How the nitrogen cycle worksStep 1: Nitrogen-fixation.

Atmospheric: Happens when Nitrogen (N2) is oxidized at high temperatures (by lightning) to make nitrite (NO2). This can combine with water to form nitric acid (H2NO3), which is deposited on earth through rainfall.Biological: Done by bacteria which can convert N2 into ammonia (NH3) if an energy source is present. Some get this energy by directly absorbing sunlight (blue-green algae) or by living in the roots of plants (legumes, alder trees), who provide them with food (Rhizobium, Azospirillium).

Step 2: Conversion to Ammonia. As amino acids and nucleic acids require N in the form of Ammonia, if nitrate (NO3) present, it must be converted to NH3.

Step 3: Biological Use. Ammonia is incorporated into proteins, nucleic acids

Step 4: When organism dies, ammonia is released back into the biosphere through the process of Ammonification, in which water is added to proteins to make carbon dioxide and ammonia. This process happens during digestion, and is also done by bacterial and fungal decomposers.

Step 5: If ammonia released into oxygen rich soil, other bacteria can convert it into nitrite or nitrate through the process of Nitrification.

This is a problem, as it gives the molecule which contains Nitrogen a negative charge, which repels it from soil particles, causing it to be easily leached into streams and groundwater.

Step 6: If soils remain anaerobic, another group of poop will convert it back into inert, atmospheric N2 through the process of Denitrification. In this process, bacteria use nitrate as an Oxygen source for respiration.

Nitrogen Cycle

How does waste treatment play in nitrogen cycle?

Large amounts of nitrogen release to the environment is extremely bad for the environment because in certain areas, the nitrogen level is high which makes the some of the plant utilize the nitrogen in order to grow faster. This results in leaving fewer resources and thus making certain plants become extinct and because of this many species of animals, insects and birds are directly affected by this.

Onsite sewage facility are wastewater systems that are made to treat and dispose effluent on the same place that it produces wastewater. Examples like septic tanks and holding tanks release a vast amount of nitrogen in to the atmosphere. This is done by discharging through a drain field which are removing the contaminants and impurities from the septic tank into the ground. Because of this, the nitrogen cycle has been greatly altered by humans thus creating a bad environment to the atmosphere.

Conclusion

All in all, it is essential that we go back and look at the question, “Is it safe to swim in turtle cove?” Beach conditions do mark the overall status of the beach, as far as it shows, it had been able to maintain itself at a good level. The fact that the water quality could be tested and marked in the good to fair range, it is actually considered pretty good. What’s important to note is the fact that this water, is also the same water that is being washed North from the sewage discharge pipe near the treatment works. As the current is in such a perfect spot to carry the sewage water up, there’s really no way Turtle cove can prevent itself from receiving it. Thus, the questions is answered. The beach has its monthly checks on water quality to make sure that the level doesn’t fall too low, since that is the case, that means that it has been okay for quite a long time as till now, many people swim there. So we can say that there is definitely sewage water flowing into turtle cove, but it does not have any major impact on the people who swim or play around there. As long as the water quality is good and safe for us to swim in, then there is no reason to say that it is not safe to swim in Turtle Cove Beach.

Bibliography"9(s) The Nitrogen Cycle." PhysicalGeography.net Welcome Page. Web. 23 Mar. 2010. <http://www.physicalgeography.net/fundamentals/9s.html>.

"EPD - Beach Water Quality." Web. 23 Mar. 2010. <http://www.epd.gov.hk/epd/english/environmentinhk/water/beach_quality/bwq_current_hk_tc_grading.html>.

"GovHK: Beach Water Quality." GovHK - One-stop Portal of the Hong Kong SAR Government. Web. 23 Mar. 2010. <http://www.gov.hk/en/residents/environment/water/beachwater.htm>.

"Nitrogen - The Bad Guy of Global Warming - The Naked Scientists 2007.03.21." The Naked Scientists Online, Science Podcast and Science Radio Show. Web. 23 Mar. 2010. <http://www.thenakedscientists.com/HTML/articles/article/nitrogenthebadguyofglobalwarming1160583306/>.

Continue…"Nitrogen Cycle" Wikipedia, the Free Encyclopedia. Web. 23 Mar. 2010. <http://en.wikipedia.org/wiki/Nitrogen_cycle>.

"Stanley, Underground, Sea Outfall." Civil Engineering Computer Aided Learning (CIVCAL). Web. 23 Mar. 2010. <http://civcal.media.hku.hk/sewage/stanley/default.htm>.

"Wastewater Treatment -- Britannica Online Encyclopedia." Encyclopedia - Britannica Online Encyclopedia. Web. 23 Mar. 2010. <http://www.britannica.com/EBchecked/topic/666611/wastewater-treatment>.

"YouTube - The Nitrogen Cycle." YouTube - Broadcast Yourself. Web. 23 Mar. 2010. <http://www.youtube.com/watch?v=ZCogeBk92NA&feature=related>.

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