Waste water treatment: How can we convert dirty water into a resource?

Why not turn a problem into a solution?

Every year the Earth's growing population requires more water while simultaneously producing more waste water. Providing people sustainably with clean water for consumption, industry and agriculture will be one of the major challenges of the century. Part of the solution is seeing waste water as a resource rather than a discharge problem. With the right technology it can become a valuable and sustainable alternative to groundwater and surface water. It can also generate energy and serve as fertiliser. What is required are reliable and efficient pumps.

Infographic of available renewable water resources per capita, shown by continent

We have to re-think the use of water

With the world’s population rising and the standard of living in emerging economies increasing, global water consumption by humans has gone up by one percent per annum for the last 40 years – and will continue to do so in future. This will become a problem if we use water faster than natural water reservoirs, such as aquifers, are replenished. According to data from the Food and Agriculture Organization (FAO), the internal renewable water resources per capita worldwide decreased by 20 % between 2000 and 2018. A distinct increase in lack of water will be experienced by dry regions such as Northern Asia, North Africa or the Middle East as well as specific parts of Europe and the USA. And the more water the human population consumes, the more waste water is generated. Waste water production is expected to rise by 24 % by 2030 and 51 % by 2050. Why not turn the waste water problem into a solution by using it as a resource?

Waste water can provide more than just water

Waste water can be an alternative to extracting groundwater or surface water. It is available wherever people are living. Recycling waste water uses relatively little energy. Treating waste water to drinking water quality is estimated by the International Water Association to cost between 0.45 and 0.75 US dollars per cubic metre. By way of comparison, the price for seawater desalination for large systems is between 0.50 and 1.80 US dollars per cubic metre, depending on the energy costs and location.

Waste water is much more than just a source of usable water. Phosphorus can be gained from it, for example, which is a key base material for producing fertilisers. It has been forecast for mineral phosphorus resources to become scarce or even run out in the next 50 to 100 years. An estimated 22 % of the global phosphorus demand could be covered by recycling domestic waste water. For phosphorus to be utilised it does not even need to be isolated from the water as fields and green spaces can be directly irrigated by treated waste water.

Energy, too, can be gained from waste water. The aerobic digestion of sludge in waste water treatment plants generates biogas, for example, which usually contains more then 60 % of methane. This, in turn, is used for producing power and heat in combined heat and power plants. The energy stored in waste water in chemical form is clearly exceeded by energy in thermal form. This can be reclaimed with proven and environmentally friendly technologies such as heat exchangers or heat pumps in order to be used for district heating, agricultural greenhouses and for drying sewage sludge.

In dry regions, recycled waste water can be an important alternative to extracting groundwater or surface water. It can prevent aquifers from running dry and add to the diversification of water supply. However, it should never be employed as a sole measure for fighting dry conditions.

Key measures should always focus on enhancing the efficiency of water use and limiting water consumption. Suppliers and municipalities further have to be aware and consider for their planning that water recycling may affect the ecosystem and the water cycle in its own way. If waste water is used for irrigation, for instance, rather than being discharged into rivers and lakes, the water level of these rivers and lakes may fall.

Fit for purpose: The right water for every application

Recycling waste water is not a new technology. New is only how it is being used: Rather than only providing water of drinking water quality, suppliers now offer different types of water of various degrees of cleanliness. Consumers can select the type that best fits their application. This principle is referred to as fit for purpose. The water for fire-fighting or for irrigating a golf course, for example, does not need to be of drinking water quality. Treated waste water is more cost-efficient and sustainable, plus its properties often make it particularly suited for specific purposes. For example, stormwater that has been collected in stormwater drains and treated is ideal for cleaning tasks, car washes and industrial applications as it is low in lime and nutrients. By contrast, domestic waste water is rich in phosphates and nitrates, which makes it a good choice for the irrigation and fertilising of plants.

The treatment processes of waste water prior to being reused hardly differ from those in municipal waste water treatment plants or drinking water treatment systems. The water passes up to four consecutive treatment stages. Depending on the degree of cleanliness it can be used for different purposes. First are the mechanical and biological treatment stages. Water that has been through the first two stages can be used for irrigating parks, for example. The third treatment stage can be chemical treatment, filtering or additional biological treatment. After these stages, the water is suitable for toilet flushing, industrial applications or irrigating edible plants. Water that has passed a fourth stage, such as reverse osmosis, ultrafiltration or activated charcoal filtering, can be used directly as drinking water or for filling artificial lakes or aquifers used for drinking water supply. Disinfection by chlorine or UV radiation is required before the water is used, regardless of the application.

Making waste water potable? That can be done too.

Advanced treatment processes such as ultrafiltration, reverse osmosis and UV radiation safely turn waste water into drinking water. Treated waste water is usually not fed directly into the drinking water supply system but is used for filling water reservoirs such as artificial lakes or aquifers. Australia, the USA or Singapore, for example, have enhanced their drinking water supply this way. Singapore even covers up to 40 % of its water requirements with treated waste water, called NEWater. By 2060, NEWater is planned to cover up to 55 % of Singapore's water demand. Direct use of treated waste water as drinking water is also possible. Windhoek, the capital of Namibia, has been treating waste water for use as drinking water since 1968, for example. At present, between 25 and 30 % of the drinking water its 400,000 inhabitants are supplied with is reclaimed water.

Image: Wikimedia Commons / Z22 / CC BY-SA 4.0 DEED

Solutions in practice: Vendée in France

What recycling of waste water looks like in practice can be seen in Europe's unique project in the Département Vendée in the west of France, at the Atlantic coast. KSB is involved in this project, which will be completed in 2024. About 90 % of the drinking water for the Département is supplied by 14 reservoirs with a storage capacity of 56 million m³ of water. Consequently, the water supply strongly depends on rainfall. In dry summer months the Département fell short by up to 8 million m³ of drinking water. This is why Vendée Eau, the public water supplier, started the Jourdain project, a programme for reclaiming waste water.

Some of the water leaving the waste water treatment plant Les Sables-d’Olonne is to be treated by ultrafiltration, reverse osmosis and UV radiation in order to be reused. The water reclaimed in this way is then to be transported via a 27 km pipeline to the Jaunay dam, where it will be discharged into a vegetation zone. This is where it will mix with river water and flow into the artificial Jaunay lake. The lake is where the drinking water station of Le Jaunay extracts its water. The water treatment plant will secure the supply of 150,000 people with drinking water during the summer. KSB has supplied the project with Amarex pumps for extracting waste water as well as Etanorm and Multitec pumps for feeding water into the ultrafiltration and reverse osmosis stages or serving as backwash pumps. One of the reasons the KSB products were chosen is their corrosion resistance as close proximity to the ocean means a high chloride content in the water. This is a challenge the project had to tackle.

Efficient and reliable solutions for reclaiming waste water

Systems for waste water treatment often secure the water supply of tens of thousands of households. Failure is not an option, yet systems are expected to work as cost-effectively and energy-efficiently as possible – for decades at a time. This is the reason consultants, engineering contractors and plant operators need an experienced partner who knows every detail of the application. As one of the market leaders, KSB offers pumps and valves that cover all stations of the water cycle: from water extraction and drinking water treatment right through to the disposal and treatment of waste water. KSB products commonly employed for drinking water supply are pumps from the Multitec or Etanorm type series, for example. They are fast and easy to install, made of corrosion and abrasion resistant materials, run smoothly with low vibration levels, keep operating costs down and provide reliable operation. To ensure optimum operation, these products are expertly selected for the fluid handled and the specific application. The pump manufacturer’s decades of experience helps water suppliers operate their systems reliably, smoothly and with low life cycle costs.

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