Sunday, March 29, 2009

Discover why the sky is blue

Discovery Posting Ninety:

Have you ever wondered why the sky is blue?

To answer this question, we need to explore about a little about earth's atmosphere and light.

Earth's Atmosphere
According to Wikipedia, Earth's atmosphere (or air) is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.
Other particles such as dust, soot and ashes, pollen and salt from the oceans can also be found in the atmosphere.

Light is made up of many colours. These colours include red, orange, yellow, green, blue, indigo and violet. At the same time, light is a kind of energy that travels in waves, just like sound. The colours that make up light possess different energy levels.

Violet, for example, possesses the highest energy and also, take note, the shortest wavelength. For the colour of red, it possesses the lowest energy and the longest wavelenght.

Why is the sky blue?
As light moves through the earth's atmosphere, most of the colours which have longer wavelengths pass straight through. Thus, little of the red, orange and yellow light is affected by the air.

However, colours with shorter wavelength is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. They then get scattered all around the sky. So whichever direction you look, some of this scattered blue light reaches you. And since you see the blue light from everywhere overhead, the sky looks blue.

For a more detailed reading on this topic, please refer to


Sunday, March 8, 2009

Discover Semakau Landfill Island @ 8 March 2009

Eighty Ninth Discovery Posting:

Do you have any idea how much waste is being thrown away each year?

A quick check on NEA's website yielded this result. In the year of 2006, a total of 2.56 million tonnes of waste was disposed of at the refuse disposal facilities and approximately 2.33 million tonnes or 90.8% was incinerated while the remainder went to the Semakau Landfill. The incinerated waste also goes to Semakau Landfill. So where is this place call Semakau Landfill? But before I answer this question, let us look more in detail regarding about the incineration plants in Singapore.

To date, NEA (National Environmental Agency) operates four incineration plants. These plants are not only just buildings that burns waste. More accurately, NEA names them as waste-to-energy plants (WTEP). In simple terms, they are plants which are able to generate energy from the incineration activities. And as I am typing this, the construction of the fifth WTEP is ongoing.

For your information, these four WETP has a combined incineration capacity of about 8,200 tonnes per day and has contribute to two to three per cent of Singapore's energy needs, around 954, 237 Mwh, in 2006.

So why bother to incinerate our waste?
Well, it's simply because through incineration, we can reduce the volume of the waste by almost 90 per cent!

So if we do not have our four WTEPs, a landfill the size of 300 soccer fields would need to be set aside every year for our waste! But with incineration, supported by other waste minimisation and recycling measures, we can extend the life of our only landfill, Semakau landfill, beyond 2040.

*The above information was extracted and edited from

So back to the topic of Semakau Landfill. Where is it? To have a better idea of the location of Semakau landfill, refer to the picture below. Look out for the red circle.
From the map above, you can see that Semakau Landfill is an island and located at the south of mainland Singapore.It is currently Singapore's only offshore landfill for waste, or more accurately incinerated and non-incinerable waste disposal. The landfill covers a total area of 350 hectares, which translates roughly to the size of about 175 football fields. From what I gather, Semakau landfill is also the only offshore landfill island in the world!

To create the required landfill capacity, reclaimation work had to be carried out and the Semakau landfill today is actually reclaimed from two islands, Pulau Semakau and Pulau Sakeng. To get an idea, look at the photo below I grabbed and edited from Google Maps (picture below).From the map above, you might notice a grey road-like thing which is surrounding most of the island. That is actually a 7km perimeter rock bund which was built to enclose a part of the sea off Pulau Semakau and Pulau Sakeng. The bund is lined with impermeable membrane and a layer of marine clay to ensure that leachate from the incinerated waste is contained within the landfill area and treated at the leachate treatment plant. And as the island is quite a distance away from mainland Singapore, other ancillary facilities were also built on the island to ensure self-sustainability of the landfill operation.

An thing to note is that during the construction of the landfill, a rigorous marine monitoring programme was established to ascertain if the still extant reefs around the reclamation had been impacted and/or recovered. Silt screens were also erected to protect the coral reef on the western side of Pulau Semakau from excessive siltation. And as a result of these efforts, the remaining natural part of Pulau Semakau that was not affected by the landfill construction has retained its enormous intertidal area which is rich in biodiversity and comprises of several ecosystems. And it is this intertidal area which I often visit for guiding groups or Project Semakau.

Guided walks?
As a volunteer guide for Raffles Museum of Biodiversity Research, I visit the intertidal area of Semakau about once a month to help in guided trips there. For more information about these walks, visit:

Project Semakau?

Project Semakau is a community involvement and conservation project, driven by volunteer-based research led by the Raffles Museum of Biodiversity Research, National University of Singapore, to collect data on the biodiversity of Pulau Semakau so as to realise and enhance the island's value as a nature education and conservation site. Project Semakau seeks to raise public awareness and appreciation of the rich biodiversity of the island in the following ways:
  1. Creating a detailed intertidal map of Pulau Semakau, to serve as the baseline for monitoring the biodiversity through a scientific survey with the help of volunteers from HSBC and other community volunteers.
  2. Creating a free, online database of Pulau Semakau’s rich biodiversity for public use.
  3. Identifying core habitats for regular monitoring using various transect methods.
  4. Conducting guided walks for schools and the public with the help of the project’s volunteers.
  5. Mapping out and targeting specific species of flora and fauna for detailed and widespread surveys with the help of scientific experts.
So how is incinerated and non-incinerable waste moved to Semakau Landfill Island?
First, they are brought from the individual WTEP to Tuas Marine Transfer Station situation. They are then loaded onto a barge and pushed by tagboats on a 25km journey to Semakau landfill island. This moving operation from Tuas to Semakau is done at night to maximise the usage of marine vessels and to avoid the heavier traffic in the day.

On arriving at Semakau, the barges move into a Marine transfer station and large excavators will unload the load onto large 35-tonne dump trucks or onto the tipping floor. And eventually, the load will find its way to the landfill cells, a place where the incinerated and non-incinerable waste is dumped into.

*Above information is extracted and edited from

So an intertidal walk at Semakau consists of...
Before going for the actual walk itself, participants and guides will have to walk through a kampung trail (picture below). Some people call it the kampung trail because there used to be people who lived on Pulau Semakau (and Pulau Sakeng) and this was a trail which was used by them before. The people who used to live there and on Sakeng were relocated to mainland Singapore before the project of constructing the landfill began.
Participants of the guided walks includes members of the public, school groups, etc. For the walk which was just over, WJ and me guided a group of teenagers from Boon Lay Secondary. Here are two group photos of the group (pictures below)., As this is already a long enough posting, I have decided not to blog about any of the marine creatures we saw during this trip. But if any discoverers are interested, you may visit to look at all the different creatures I've seen on the various trips to Semakau.

Finally, a BIG thanks to the group of spider conches who remain attentive despite the hot weather. =D

Extra (Other Entries for this walk):
a) Tidechaser's:
b) Manta's:
c) E's:
d) MY's: