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In the Netherlands, approximately 119 litres of water are used per person per day. Compared to 1995 this is 18 litres per person per day less. Most of the water is used for showers, followed by flushing the toilet and washing clothes. The decrease results from the fact that we flush the toilet with less and less water and use water-efficient washing machines, even though water consumption for showers (especially among those aged 25-34 years) has increased.
Although there is (still) no immediate need to save drinking water in the Netherlands, from the perspective of sustainability it is not desirable for us to use the valuable drinking water for low-grade applications. Moreover, we should set the example for other countries that suffer from frequent water shortages. Because the availability of freshwater will come under pressure in the coming years, especially abroad, it is important to work on new techniques for saving water. In the Netherlands, too, the situation may change in the future due to dehydration (less groundwater available) or climate change.
In addition to saving drinking water by using less water for showers, toilets and washing machines, reuse of wastewater is an important way to use less fresh water. Reusing water closes the water cycle.
Water often retains energy. Saving hot water for showers and washing machines means not only saving water, but also and above all, saving energy. A large part of the added energy goes down the drain with the wastewater. Some of this energy can be recovered by means of heat exchangers at the user’s premises or in the sewerage system.
In addition, wastewater is an important source of energy because the organic fraction can be fermented to produce biogas. Various concepts and systems have been developed to recover energy from wastewater. Fermentation is applied to black water (from the toilet), but also to sewage sludge. The energy content of water represents an important economic value.
Energy can also be obtained from mixing salt water and fresh water, from waves and from height differences between bodies of water, for example, in the case of tidal differences.
In addition to the global energy and water crises, there will also be a shortage of nutrients in the coming years, particularly phosphate. Phosphate can be recovered from wastewater and re-used in agriculture as a (synthetic) fertiliser.
Increased cooperation with agriculture on closing nutrient cycles is essential. At the moment there are already many initiatives by the agricultural sector, supported by the collaborating Frisian municipalities, in which input of knowledge is necessary.
In addition to nutrients, watercourses also play an important role in agriculture. An example of this is the greenhouse horticulture sector, where the aim is to close the cycle within the greenhouse. Various topics from the domestic water chain return here: removal of crop protection agents, reuse of water, production of irrigation water, and reuse of nutrients.
In many water-scarce countries, purified wastewater is used as irrigation water; this irrigation water must then be clean enough to prevent pathogenic microorganisms from contaminating the crops.
The water system consists of surface water, groundwater and the associated water sheds, banks and engineering structures, as well as the organisms living in them. All these components of the water system and the natural path of water are closely linked and consequently influence each other. The water system is the source of drinking water, industrial and irrigation water and the destination of treated wastewater and rainwater. Water companies, agriculture and industry therefore rely on the same, often scarce, sources.
The Water Framework Directive (WFD) has been introduced to monitor the quality of the water system. The goal is to improve the quality of the water in such a way that it is possible to produce drinking water using simple techniques, despite the fact that the ambition of water companies is often that contaminants should be undetectable or only present in very low concentrations. Increasingly stringent regulations with regard to phosphates, nitrates and, above all, organic micro-pollutants mean that either additional purification or measures at source are required.
In some cases, parts of the water system can be used as a buffer zone with a purifying effect. An example of this is the water harmonica.
Besides households, a lot of water is also used by agriculture and industry. Because the water issues within these sectors differ from those in the water chain, they are discussed separately.
In industry, specific requirements are set for process water. Sometimes this is of a lower quality than drinking water (the water must therefore be much cheaper), and sometimes it must be better than drinking water (and may therefore be more expensive). In industry, water as a utility is primarily an economic factor. This is often the motivation to save and/or reuse water.
The complexity and diversity of waste streams across sectors (agriculture, food, paper, metals, oleaginous) often require advanced and specific treatment processes. The purification of wastewater so that it can finally be discharged is an important cost item for many companies.
By focusing on industrial water, cooperation with the CEW is also interesting for companies where water technology is not a core business.
Sensors are becoming increasingly important in all kinds of processes, including water technology. Sensors can be used in different ways. They provide more information (variations over the course of the day) compared to laboratory analyses. Sensors can be implemented to control treatment processes depending on the quality of the feed water.
It is expected that sensor-assisted monitoring processes will become increasingly important in decentralised applications of water technology, whether in the production of clean drinking or process water, or the purification of wastewater. Sensors can guarantee the quality of the water, especially when it is reused.
Sensors can be used to better control the quality and presence of water, but also if it presents a threat. Sensor technology is a multidisciplinary subject. Students, teachers and companies with different skills can complement each other in order to produce an efficient, accurate sensor.