Sunday, April 24, 2016

Water security, energy use a difficult trade-off

Siau Ming En

April 23, 2016

SINGAPORE — While ramping up the nation’s water security by increasing its capacity to treat used water and seawater over the next few decades, the Republic could also expose itself to another form of vulnerability — an over-reliance on energy for water.

Within the next 14 years, the combined capacity from NEWater and desalinated water will be able to meet up to 80 per cent of the population’s water demands, up from the current 55 per cent. By 2060, these two sources of water can provide up to 85 per cent of the nation’s water needs. However, this will also mean Singapore is becoming increasingly reliant on energy consumption to meet its water security goals.

Speaking to TODAY, distinguished visiting professor at the Lee Kuan Yew School of Public Policy (LKYSPP) Asit Biswas pointed out that while half of Singapore’s water supply is generated from its own sources — local catchments, NEWater and desalinated water — 100 per cent of the energy used to treat the water comes from outside.

“Singapore has no energy … As Singapore becomes more and more self-sufficient (in water), it is becoming, energy-wise, more and more not self-sufficient. More and more energy (has to be) input in order to sustain the water sector,” added the world-renowned water expert.

Back in September 2013, Dr Vivian Balakrishnan, then-Minister for the Environment and Water Resources, spoke about how there has been a substitution of one critical vulnerability — water — with another critical vulnerability — energy — globally “simply because the process of reverse osmosis is energy intensive”.

Reverse osmosis is the process used to treat seawater at desalination plants — making desalinated water the most energy-intensive of Singapore’s four sources of water. Apart from water from local catchments and NEWater, the fourth source is imported water.

According to some international reports, the desalination process burns up more fossil fuel than sourcing for the same amount of fresh water from fresh water bodies. This makes desalination both a reaction — and one of the many contributors — to global warming, noted an article from Scientific American magazine.

Desalinated water can currently meet 25 per cent of Singapore’s water needs. From 2030, it will be able to meet 30 per cent of future water demands.

The next-most energy-intensive “tap” comes from NEWater, which requires about a quarter of the amount of energy needed by a desalination plant.

Currently, NEWater can meet up to 30 per cent of Singapore’s water demands, and the figure is set to increase to 50 per cent and 55 per cent by 2030 and 2060, respectively.

Dr Rajasekhar Balasubramanian, from the National University of Singapore’s Department of Civil and Environmental Engineering, noted that energy security, fresh water security and climate stabilisation are “competing goals”. For instance, Singapore tries to overcome extreme weather effects on its water resources through desalination.

“Desalination of seawater is an energy-intensive process. However, we are (also) trying to reduce our carbon footprint,” he added.

Professor Ng Wun Jern, executive director of Nanyang Environment and Water Research Institute at Nanyang Technological University, felt that the difficulty lies in the fact that “the link between water and energy and Singapore is constrained in both aspects”.

“We have few sources of fresh water and no fossil-fuel reserves, having to import fuel and rely on renewable energy to meet our energy needs,” he added.

The reliance on energy can get more costly even though current energy prices are very low, said Dr Joost Buurman, senior research fellow at LKYSPP’s Institute of Water Policy.

And with Singapore using more NEWater and desalinated water in future, he added: “If energy prices are going up significantly, it might also have an impact if your water supply system is more dependent on energy.”

However, national water agency PUB noted that the energy used to treat water here takes up a small percentage of Singapore’s overall energy consumption.

[If the last chart at this webpage means what I think it means, energy for water treatment takes up less than 3.9%]

PUB is currently producing energy through biogas at its water reclamation plants and will be expanding its energy production from solar. It is also investing in water research and development to bring down the energy consumption levels of the desalination plants here, among other things.

For example, there is the electrodeionisation technology in desalination, where ions carrying either a positive or negative charge are separated from the water when they are attracted to electrodes of the opposite charge.

This process uses about 1.65kWh to 1.8kWh of electricity for every cubic metre of desalinated water, about half the amount of electrical energy needed with the conventional reverse osmosis method.

Another method includes biomimetic or biomimicry techniques, which are currently being studied. One example is the development of a biomimetic membrane that uses water channel proteins (aquaporin) found in cell membranes to filter organic molecules and salts.

Biomimetic and biomimicry-based research aims to use about 1kWh per cubic metre of electricity.

[I think the last word is an error as electricity is not measured in cubic metres. Probably should be "water" or "desalinated water".

Anyway, facts from the last few para - Reverse Osmosis takes about 3 to 4 kWh to desalinate 1 cubic metre of sea water. Research is hoping to halve or even quarter that energy need. No clue as to when or how close we are to a breakthrough in these research that we can leverage on.

We use about 380 million gallons of water per day (mgd). Or about 1.7m cubic metres. Desalination is projected to provide 30% of our water needs. or about 0.6m cubic metres of water. At about 4 kWh to treat 1 cubic metre of water, that would be 2.4m kWh, or about 100,000 kWh per day. Or about 100 mWh.

NEWater can provide 50% of our needs by 2030, which is about 850,000 cubic metres. But it's energy cost is 1/4 of desalination, or about 1 kWh to treat 1 cubic metre. So 850,000 kWh, or 136 mWh.

Our energy demand is currently about 6500 mWh. 136 mWh is quite a small percentage of that - about 2%.

So while there is a trade-off as this article suggests. The situation is not that dire. According to the chart provided by the National Climate Change Secretariat, Industry and Transport are the largest users of energy, contributing to the greatest emission of greenhouse gases.]

No comments: