Seventy-five percent of our Blue Planet is covered by water, yet only a tiny fraction (0.008%) of this vitally important resource is readily available to us in the form of freshwater on the Earth's surface. Considering that the human body is composed of between 60-70% water and the percentage of water making up our vital organs is even higher, with blood consisting of 94% water for example, our body needs water to remain healthy and hydrated, to conduct cellular activity, and to eliminate toxins and waste. Water is the lifeblood of the planet and it is essential for our survival. Yet it is a finite resource.
The global population is continually growing, and with an estimated 1.5 million people being added to the urban population every week, it is expected to reach 8 billion by 2025. With many regions of the world already experiencing extreme water stress, how do we expect to meet the water demands of a growing population in a world that is also becoming hotter and drier, and where water scarcity is rapidly becoming the norm?
One sustainable solution for improving water security is to recycle water, including sewage wastewater, and to treat it so that it can be reused for both non-potable and potable applications. Recycling wastewater for reuse offers several benefits. Firstly, it provides a source of water that is not dependent on climate/rainfall. This is vitally important, as it means that wherever this is implemented, we will be able to have access to a sustainable source of water whenever water is used, regardless of the climate and rainfall patterns. Many urban centers already have collection systems in place, and in some cases also have treatment facilities that can be easily upgraded. This makes it a cost-effective and relatively accessible option compared to desalination, which is expensive and is typically only viable for coastal cities. Recycling wastewater also offers environmental health benefits as it reduces or eliminates environmental impacts associated with wastewater discharges. For example, exposure to harmful pathogens or nutrient loading of aquatic systems — which can result in algal blooms and ocean dead zones — are reduced when wastewater is diverted for further treatment rather than being discharged into a river, water body or the ocean.
While recycling wastewater for non-potable use is widely accepted, using recycled wastewater as a source of drinking water is somewhat more controversial. Public perception regarding the safety of recycling wastewater into drinking water varies according to the level of knowledge and understanding. But it is important to note that current wastewater treatment technologies are able to render recycled wastewater clean and safe for drinking. The level of treatment (secondary, tertiary, advanced) depends on the water reuse application, with drinking water undergoing advanced treatment involving multiple stages of treatment using various water treatment technologies at each stage.
Wastewater that has been recycled for non-potable use (irrigation and Class A reuse) can be used for applications such as lawn and landscaping irrigation, food crop irrigation, fire-fighting, as well as for dual-pipe systems supplying water for toilet flushing, car washing and garden use. While Class A water has undergone primary, secondary and tertiary treatment to remove contaminants and pathogens to make it safe for the above applications, it has not undergone advanced treatment and therefore is not safe to use as drinking water.
Wastewater that has been recycled for indirect potable use is effectively tertiary-treated wastewater that has been treated further with advanced water treatment technology. After undergoing advanced treatment it is discharged into a natural freshwater source such as a groundwater basin or surface reservoir, where it is blended with naturally occurring freshwater. Wastewater recycled for indirect portable use is typically used to recharge underground aquifers and/or to boost surface water storage, where it is available as a source of drinking water after undergoing further treatment to meet drinking water standards.
Recycled wastewater intended for direct portable use is also tertiary-treated wastewater that has undergone advanced treatment to improve the quality further. However, instead of being discharged into a groundwater basin or surface reservoir, it is either treated more rigorously on site using advanced biological, chemical and physical wastewater treatment technologies before being sent directly to a water distribution network, or it is sent directly to a water treatment facility for further treatment to render it safe for drinking.
Raw source water that enters a water treatment plant can potentially contain animal feces and urine, dead organisms and other organic matter, together with a wide range of harmful contaminants such as pathogens, chemicals and heavy metals that could pose a risk to our health. Drinking water undergoes a rigorous water treatment process to ensure hazardous contaminants are removed rendering it safe for consumers to drink. To ensure that the water supplied to households meets the stringent standards outlined in the Australian Drinking Water Guidelines, drinking water treatment facilities employ state-of-the-art water filtration technologies that are usually specifically designed to remove the contaminants in the source water that the facility treats. Therefore water treatment facilities that obtain recycled wastewater as their source water will be specifically designed so that are capable of removing contaminants typically associated with this source.
The strongest potential for recycling wastewater for reuse lies in indirect portable reuse (IPR) applications. Using recycled wastewater to replenish groundwater or top up freshwater reservoirs offers a natural and sustainable solution to alleviate water scarcity, and it is not dependent on rainfall. As there is no shortage of wastewater, it is a particularly alluring water management strategy for water-stressed regions that are seeking to become more resilient to the impacts of climate change.
Advanced wastewater treatment technologies — which currently include reverse osmosis, ultrafiltration and ultraviolet disinfection — are capable of removing chemical contaminants and pathogenic microbes to ensure the recycled water is of high quality and meets the Australian guidelines for drinking water. However, since they tend to be relatively expensive, there is a growing need for the development of new cost-effective technologies for treating municipal wastewater.
There are many great examples of how various cities around the world have solved water security issues by recycling wastewater for both direct and indirect potable reuse.
Namibia, the global pioneer in terms of wastewater recycling, opened the Goreangab wastewater treatment plant in the country's capital city, Windhoek, over fifty years ago back in 1968. This wastewater treatment plant converts wastewater generated by Windhoek's 300,000 residents into safe drinking water, helping to address the water needs of residents living in a city surrounded by desert.
Locally, WaterCorp's Groundwater Replenishment Scheme in Perth is pioneering wastewater recycling in Australia. The first trials and public education began in earnest in 2010. The scheme started recharging Perth's deep underground aquifers with recycled wastewater in 2017 and aims to supply 20% of Perth's water needs with recharged groundwater by 2060. As a water-stressed city home to over 2 million people, Perth ultimately hopes to recycle all the sewage it generates and to use this recycled water to replenish its groundwater supply for future use in an effort to improve its water security and make it more resilient to climate change.
Another great example of an Australian city that is utilising recycled water to improve its water security is Salisbury in South Australia, where a mixture of recycled wastewater and stormwater is supplied to 10,000 residents in 4,000 homes in Mawson Lakes, as well as 6,000 employees working at local businesses and 7,500 students at educational institutions. Since its implementation, usage of drinking water in Mawson Lakes has reduced by 50% (compared to the Adelaide average), resulting in a saving of 800 megaliters (equivalent to 800 thousand cubic meters or 800 million liters) of drinking water per year.
Its also important to note that the potential for wastewater recycling is not limited to cities. Recycling wastewater and providing drinking water in remote locations can be tricky. A modular 'plug-and-play' wastewater treatment plant, such as the one installed at the Davis research station in Antarctica, offers a cost-effective mobile solution for treating wastewater onsite and also has the potential of providing a source of safe drinking water in remote locations.
Yet, while the above examples illustrate the benefits of recycling wastewater, some governments of water-stressed regions around the world, including in Australia and New Zealand, have not embraced this concept. Recycling wastewater to augment drinking water supplies is a somewhat contentious issue primarily because of public perceptions around drinking what is essentially recycled sewage effluent. Many consumers have raised concerns regarding exposure to contaminants such as cholera or other harmful pathogens responsible for waterborne diseases. But are these concerns well-founded?
While we may find the thought of drinking recycled wastewater rather gross, the stark reality is that all water on the planet is constantly being recycled in what is known as the water cycle or hydrological cycle. Many towns and cities discharge their treated wastewater effluent into rivers and streams, which flow downstream and eventually empty into lakes or dams that supply residents further downstream with drinking water. The volume of treated sewage discharged into rivers is likely to increase as the population living upstream grows. This means that anyone living downstream from a wastewater effluent discharge outlet will effectively be drinking recycled wastewater. Yet since the wastewater has undergone multiple stages of treatment at the wastewater treatment plant, before being diluted with river water from the river into which it is discharged, and then treated further at the drinking water treatment plant to meet drinking water standards, the risk of exposure to pathogenic contaminants is minimal.
So regardless of whether the source water comes from upstream or from groundwater, we are constantly drinking recycled water in some shape or form. Wastewater recycling programs just speed up this process using state-of-the-art water treatment technologies to make safe water readily available for human consumption. The wastewater recycling initiatives above are just a few examples of the many recycled water initiatives around the world that have proven to provide a safe, sustainable water supply to address local water scarcity issues and help meet the growing demand for water.
As the human population and its water demands steadily increase and water becomes an increasingly scarce commodity, exacerbated further by the impacts of climate change, recycling wastewater to provide a source of water to irrigate our crops as well as a source of safe drinking water may be the only solution for ensuring both water and food security in a world where demand for water is rapidly outstripping supply.
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