Thursday, July 5, 2018

PUB aims to double water supply by 2060 without using more energy, producing more waste

By Louisa Tang

04 July, 2018


SINGAPORE — National water agency PUB has set a target to double the amount of clean water it produces today by 2060 without using more energy.

That is one of several long-term goals that the PUB committed to on Wednesday (July 4), as it soldiers on with research and development (R&D) efforts to increase water resources for the future and improve water treatment efficiency.

Through new technologies, it aims to reduce the energy used in desalination by more than two-thirds, increase the amount of NEWater recovered from used water to 90 per cent at low energy levels, and produce as much energy as it uses in treating used water.

Since 2002 till last year, the agency, its research partners and the National Research Foundation have pumped in S$453 million in 613 water R&D projects, more than three-quarters of which have moved towards full-scale deployment.

The agency is also looking into reducing the amount of waste — produced in the form of sludge — that it has to dispose of. Sludge, a mixture of organic materials, minerals and other waste materials filtered out during water treatment, is costly to incinerate and dispose of in the landfill.

Of Singapore's four national taps, desalinated water and NEWater meet up to 70 per cent of today's water demand. That is projected to go up to 80 per cent in 2030 and 85 per cent in 2060.

Desalinated water, which currently meets up to 30 per cent of water demand and will meet 30 per cent of future demand in 2060, is the most energy-intensive water source. NEWater, on the other hand, currently makes up 40 per cent of water demand, and meet up to 55 per cent of future demand in 2060.

However, both desalinating seawater and getting NEWater from used water require between five and 17 times more energy than the conventional method of treating rainwater.

Mr Harry Seah, PUB's assistant head of future systems and technology, said that if PUB sticks to current technologies, it will have to use four times more energy and produce twice as much sludge as today to meet Singapore's water demand in 2060. This is unsustainable and can only be overcome using innovative technologies.

"The question is affordability. We are expecting the cost of energy to go up," he added. "If we don't do anything today, the cost of producing water is going to go up too."

While Mr Seah stopped short of saying this would lead to higher water prices for consumers, he noted that being efficient with energy usage is key to maintaining water prices.

"There are a lot of other factors besides energy — there's manpower, for example. We do our part through efficiency to drag (having to increase prices) as long as possible," he said.


Over the next five to 10 years, the agency plans to reduce its energy consumption for desalination by more than half. In the long term, it plans to whittle this down to more than two-thirds.

One method PUB is testing out at its R&D facility in Tuas is the electro-deionisation technology. This technology uses an electric field to pull dissolved salts from seawater, which requires less energy than the current method of reverse osmosis — pushing seawater through membranes that filter out salts and impurities.

The PUB plans to implement the technology, alongside reverse osmosis, next year at the newly opened Tuas Desalination Plant. It also plans for Singapore's sixth desalination plant, which has not been identified yet, to process seawater using purely electro-deionisation.

Another method being tested at the Tuas R&D facility is the biomimetic membrane. These membranes use natural proteins found in cell membranes that can desalinate seawater more efficiently.

As for NEWater, where the current amount of energy used turns only 75 per cent of the treated used water into NEWater through reverse osmosis, PUB's goal is to up the production to 90 per cent using less than half of the energy used.

[From "The Real Cost of Drinking Water" and my comment then:"The problem with such systems, such as reverse osmosis, is that up to 80 per cent of the water treated is wasted, and its quality leaves much to be desired."

I'm not sure what he means by "treated water is wasted". The link I got from Googling is actually for a home RO system, and it does jive with that claim the ratio of wasted water to treated water is 4:1. Or 80% of the water is "wasted". My instinctive understanding of this is that for 100 gallons of waste water, only about 20 gallons can be recycled by RO treatment. This makes sense. The waste water to be recycled is pressured against the RO membrane and about 20% of the water passes through the membrane and is purified. The rest of the water remains as waste water, except now, it is "concentrated" 125% - the contaminants from 100 gallons are now in 80 gallons). This concentrated waste water would be harder to recycle or rather pure water would be harder to extract from this concentrated waste water, so most likely, we would not.

I do not know what he means by "quality leaves much to be desired". 

More importantly, NEWater is supposed to provide 55% of our water by 2061, but if the 20% "recycling" ratio is correct, this is impossible! If we used 800 mgd (by 2060) but RO waste 80% of the water, then even if every drop of waste water is "treated" - 800 mgd - we would only "recover" 20% of 160 mgd. But the plan is for NEWater to provide 55% or 440 mgd. 
Now it makes sense. If we can recover 75% NEWater from waste water, then 55% is feasible. And if we can raise that to 90%, the capacity of the NEWater plants can increase, without building new plants.]

Lastly, in the short term, the agency wants to be able to produce as much energy as it uses in water reclamation plants. To do so, it is tapping on sludge, which is usually seen as a waste product.

However, when sludge breaks down, it produces biogas, which can be used as a source of energy. Since at least the 1990s, PUB has been using sludge to produce biogas, which it then uses to power the water reclamation plants.

Currently, this method of using sludge to produce biogas allows PUB's water reclamation plants to produce 25 per cent of the energy it requires. The plan is to move the energy self-sufficiency level to 75 per cent, with the ultimate goal set at 100 per cent.

Through this, PUB can also reduce the amount of sludge it has to dispose of by more than 50 per cent in the long term. The process will double the amount of used water that can be treated at today's sludge footprint too.

The various technologies being tested will be showcased at Singapore International Water Week 2018, to be held from Sunday (July 8) to July 12.

[In 2003, SG broke off talks with Malaysia after Mahathir went back on agreement after agreement and finally came back with the ridiculous price of RM6 per 1000 gallon. As this was equal to or more than the price of desalinating water, we told him to desalivate himself, the negotiation was over. Over the next few months, we announced NEWater, and officially open our NEWater Visitor Centre, and two NEWater plants.

In the face of such utter disdain and disrepect, Mahathir resigned as PM.

Well, that's how I'm telling the story.

Alternatively, we could say, "coincidentally, after the talks broke down, and SG announced the opening of NEWater plants, perhaps realising his dream of selling over-priced river water to SG was dead, Mahathir resigned as PM of Malaysia in deep despair. Maybe. It might have just been a coincidence."

The point is, we don't know. But it's plausible, right?

So this time around, we can only hope.] 

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