More of us are drinking recycled sewage water than most people realise



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The Hawkesbury’s waters look beautifully natural but treated sewage makes up to 20% of the river flow where the North Richmond Filtration Plant draws its water.
Karl Baron/flickr, CC BY

Ian Wright, Western Sydney University

The world is watching as Cape Town’s water crisis approaches “Day Zero”. Questions are being asked about which other cities could be at risk and what can they do to avoid running dry. In Perth, Australia’s most water-stressed capital, it has been announced that the city is considering reusing all of its sewage as part of its future water supply.




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Cape Town is almost out of water. Could Australian cities suffer the same fate?


Drinking recycled sewage is a very confronting topic. But what many people don’t realise is that we already rely on recycled sewage in many Australian water supplies. Even in Australia’s biggest city, Sydney, it is an important part of the water supply. This is because many large towns discharge their treated sewage into the catchment rivers that supply the city.

But Perth is now looking to recycle all of its treated sewage. At the time of writing, the city’s water storages were at a low 35.3%. Cape Town’s reserves, by comparison, are at a critical low of 23.5% – but Perth was close to that point just a year ago when it was down to 24.8%.

Perth has been progressively “drought-proofing” itself by diversifying the city water supply. River flow and storage in dams accounts for only 10% of this supply. Desalination and groundwater extraction provide about 90% of the city’s supply. Only about 10% of Perth’s sewage is recycled, through advanced treatment and replenishment into its groundwater supplies.




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Justifiably, many people have concerns about drinking recycled sewage. This reflects long-standing concern about hazards of contaminated water. An example is the devastating waterborne disease of cholera, which claims the lives of more than 100,000 people a year. Cholera is rare in many countries, but is endemic in waters across Africa and much of Southeast Asia.

As wastewater treatment technologies improve and urban populations grow, however, interest in using treated sewage in drinking water supplies has been increasing. No Australian urban water supply currently uses “direct potable reuse” of treated sewage, but the concept is being seriously considered.




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So how is treated sewage being indirectly reused?

There is, however, indirect reuse when water is drawn from rivers into which recycled sewage is discharged upstream. For instance, the catchment of Sydney’s giant Warragamba Dam has a population of about 116,000 people. This includes the large settlements of Goulburn, Lithgow, Moss Vale, Mittagong and Bowral. These communities discharge their treated sewage into the catchment rivers.

Several large towns discharge treated sewage into rivers supplying Warragamba Dam, which holds 80% of Sydney’s water reserves.
popejon2/flickr, CC BY-NC-ND

The New South Wales Environment Protection Authority regulates these discharges, which form a small part of the total annual catchment inflow to the dam. Such recycling of sewage is termed “indirect potable reuse”.

Residents in some parts of northwestern Sydney also drink water that is partly supplied by another form of indirect reuse of treated sewage. The North Richmond Water Filtration Plant extracts and treats water drawn directly from the Hawkesbury-Nepean River. A major contributor to the river flow is treated sewage discharged from upstream treatment plants.

These include plants in the Blue Mountains (Winmalee), St Marys, Penrith, Wallacia, and West Camden. The largest individual discharge of treated sewage to the river in recent weeks is from St Marys Advanced Water Recycling Plant, one of the biggest in Australia. This plant uses advanced membrane technology to produce highly treated effluent before it is discharged into the river.

St
Marys Advanced Water Recycling Plant, one of the biggest in Australia, treats sewage and discharges the water into the Hawkesbury-Nepean River.

Ian Wright, Author provided

Available data are limited, but in the very low river flows in the recent dry summer I estimate that treated sewage comprised almost 32% of the Hawkesbury-Nepean flow in the North Richmond area for the first week of January. The water is highly treated at the Sydney Water-owned North Richmond plant to ensure it meets Australian drinking water guidelines.

Every year the river receives more and more treated sewage as a result of population growth. This is certain to continue, as Greater Sydney is forecast to gain another 1.74 million residents in the next 18 years. Much of this growth will be in Western Sydney, one of the most rapidly growing urban centres in Australia. This will result in more treated sewage, and urban runoff, contributing to the Hawkesbury-Nepean River flow.




Read more:
As drought looms again, Australians are ready to embrace recycled water


Paying for desalination while water goes to waste

However, most of Sydney’s sewage is not recycled at all. Three massive coastal treatment plants (at North Head, Bondi and Malabar) serve the majority of Sydney’s population. These three plants discharge nearly 1,000 million litres (1,000ML) of primary treated sewage into the ocean every day. That is roughly an Olympic pool of sewage dumped in the ocean every four minutes!

Perhaps if Sydney was as chronically short of water as Perth there would be plans to recycle more of its sewage. Instead, Sydney has adopted desalination as a “new” source of drinking water, rather than treating larger volumes of sewage for any form of potable reuse.

Sydney’s desalination plant sits idle about 10 kilometres south of the Malabar treatment plant. It has a capacity for supplying 250ML a day. Even though it isn’t supplying water now, it is very expensive. In 2017, the privately owned plant, sitting on standby, charged Sydney Water A$194 million.

Only when Sydney’s storages fall below the trigger of 60% will the plant supply drinking water. With storages at 76.5%, the plant will not operate for a while.


The Conversation


Read more:
The role of water in Australia’s uncertain future


Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University

This article was originally published on The Conversation. Read the original article.

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How protons can power our future energy needs



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The proton battery, connected to a voltmeter.
RMIT, Author provided

John Andrews, RMIT University

As the world embraces inherently variable renewable energy sources to tackle climate change, we will need a truly gargantuan amount of electrical energy storage.

With large electricity grids, microgrids, industrial installations and electric vehicles all running on renewables, we are likely to need a storage capacity of over 10% of annual electricity consumption – that is, more than 2,000 terawatt-hours of storage capacity worldwide as of 2014.

To put that in context, Australia’s planned Snowy 2.0 pumped hydro storage scheme would have a capacity of just 350 gigawatt-hours, or roughly 0.2% of Australia’s current electricity consumption.




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Where will the batteries come from to meet this huge storage demand? Most likely from a range of different technologies, some of which are only at the research and development stage at present.

Our new research suggests that “proton batteries” – rechargeable batteries that store protons from water in a porous carbon material – could make a valuable contribution.

Not only is our new battery environmentally friendly, but it is also technically capable with further development of storing more energy for a given mass and size than currently available lithium-ion batteries – the technology used in South Australia’s giant new battery.

Potential applications for the proton battery include household storage of electricity from solar panels, as is currently done by the Tesla Powerwall.

With some modifications and scaling up, proton battery technology may also be used for medium-scale storage on electricity grids, and to power electric vehicles.

The team behind the new battery. L-R: Shahin Heidari, John Andrews, proton battery, Saeed Seif Mohammadi.
RMIT, Author provided

How it works

Our latest proton battery, details of which are published in the International Journal of Hydrogen Energy, is basically a hybrid between a conventional battery and a hydrogen fuel cell.

During charging, the water molecules in the battery are split, releasing protons (positively charged nuclei of hydrogen atoms). These protons then bond with the carbon in the electrode, with the help of electrons from the power supply.

In electricity supply mode, this process is reversed: the protons are released from the storage and travel back through the reversible fuel cell to generate power by reacting with oxygen from air and electrons from the external circuit, forming water once again.

Essentially, a proton battery is thus a reversible hydrogen fuel cell that stores hydrogen bonded to the carbon in its solid electrode, rather than as compressed hydrogen gas in a separate cylinder, as in a conventional hydrogen fuel cell system.

Unlike fossil fuels, the carbon used for storing hydrogen does not burn or cause emissions in the process. The carbon electrode, in effect, serves as a “rechargeable hydrocarbon” for storing energy.

What’s more, the battery can be charged and discharged at normal temperature and pressure, without any need for compressing and storing hydrogen gas. This makes it safer than other forms of hydrogen fuel.

Powering batteries with protons from water splitting also has the potential to be more economical than using lithium ions, which are made from globally scarce and geographically restricted resources. The carbon-based material in the storage electrode can be made from abundant and cheap primary resources – even forms of coal or biomass.




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Our latest advance is a crucial step towards cheap, sustainable proton batteries that can help meet our future energy needs without further damaging our already fragile environment.

The time scale to take this small-scale experimental device to commercialisation is likely to be in the order of five to ten years, depending on the level of research, development and demonstration effort expended.

Our research will now focus on further improving performance and energy density through use of atomically thin layered carbon-based materials such as graphene.

The ConversationThe target of a proton battery that is truly competitive with lithium-ion batteries is firmly in our sights.

John Andrews, Professor, School of Engineering, RMIT University

This article was originally published on The Conversation. Read the original article.