This is the energy content of “used water”, also known as sewage. I learned this at Prof. Ng Wun Jern’s inaugural Tan Chin Tuan Lecture at NTU today. So if a family has 2 toilets, flushes them 7 times daily (the US average), and each toilet is 1.2 gallons, then in about 15 days a m^3 of used water is created. The average family in the USA consumes 30 kWh/day, so lets see… in a year produces enough energy through sewage to meet its energy demand for an entire day.
Archive for March, 2009
1.7 kWh/m^3
Thursday, March 26th, 2009Rosy Trumpet Tree
Monday, March 16th, 2009If you walk around NTU campus this week you can see their massive blooms. One whole street is lined with these trees, and the fallen flowers carpet the street and cover the parked cars.
Thanks to my colleagues I know the name of this tree: the Rosy Trumpet Tree, botanical name Tabebuia Rosea.
Flower carpet of the Rosy Trumpet Trees
2^-1024 = 0?
Thursday, March 12th, 2009At least Google thinks so. Click here to see Google’s error.
But 2^-1023 is not zero to Google.
Recycled water
Monday, March 9th, 2009
NewWater facility, Tanah Merah
Singapore obtains 15% of its water supply from recycling. Recycling means all the water that normally goes down the drain, or into the sewers, is processed and filtered into potable water again.
The filtering process is demonstrated at the Tanah Merah plant if you take the free 1hr 15 tour. First the icky part: water is separted from solids at the Tuas plant, not far from where I live. This is not part of the tour. Next, the purification process, which is done at Tanah Merah, proceeds in three stages: microfiltration, reverse osmosis, and UV sterilization. Actually, the last stage (UV) is not necessary, but is done to add an extra layer of (psychological) safety. At the end of the tour they give you a half-liter bottle of “NewWater” to drink. It doesn’t have any taste.
Aside from the 15% from recycling, Singapore has 3 other water sources. There is a desalination plant, which provides another 10% of the water supply, imported water from Malaysia, which provides 40%, and 35% from catchment of rain.
Recycling is cheaper than desalination, particularly if the energy in the solids is used (biogas).
Compare Singapore’s forward-looking water strategy with the USA: this article on Yahoo claims that water recycling in Southern California, an area that is always short of water, faces tough criticism. I don’t know if there really are critics. But there is no doubt that every water district in California should have a recycling plant, and that, so far, only one does: Orange County, which only started a year ago.