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2.1.04 Water recycling in hotels – business as usual during conversion work

Water consumption per person is much higher in hotels and guest houses than it is in private households: a guest in a German hotel uses around 300 litres of water a day on average – more than twice the amount they would use at home. If the venues also have golf courses and swimming pools, consumption can be as much as 1,000 litres per overnight guest per day. The amount of fresh water used could be reduced significantly if the greywater produced on site were to be treated. One project shows that it is possible to make the necessary conversions without suspending business operations.

“Production integrated measures for environment protection in hotel and catering industry in special consideration of existing built volumes” was a research project run by the Institute for Environmental Engineering (ISA) at RWTH Aachen University from June 2006 to May 2009 that investigated how the concept described in its title could be implemented. The focus was on demonstrating that even standard systems for treating process water can considerably reduce the consumption of drinking water in hotels, and that the conversion work can take place with hotel business running as usual.

The ISA was able to secure the four-star “Hotel Am Kurpark” in Bad Windsheim (Middle Franconia) as a project partner. Founded in 1981, the hotel has 50 guest rooms with 90 beds, a restaurant seating around 100, plus conference rooms and a sauna. The bulk of the accommodation is located in the main building, with 20 guest rooms and the seminar rooms in a separate building (built 1992, extended 1998). The hotel’s water consumption increased considerably between 2001 and 2007 (see diagram).

Greywater treatment system

The greywater treatment system was installed by Hans Huber AG (Berching) in November 2008. The structure of the building made installation of the new water pipes unexpectedly difficult as they had to be integrated into the existing pipeline shafts. As hotel business was not to be interrupted, chasing and tiling was restricted to a bare minimum. While the seminar building was connected within the ten-day construction phase, work in the main building’s cellar and the connecting shaft between the two buildings was conducted outside of this period. Overall, 460 metres of piping were laid for greywater and process water.

Progression of water consumption in the “Am Kurpark” hotel from 2001 to 2007

Progression of water consumption in the “Am Kurpark” hotel from 2001 to 2007
Progression of water consumption in the “Am Kurpark” hotel from 2001 to 2007
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Other sources integrated

The low amount of greywater specifically from the guest rooms (shower, bath, hand basin) made it necessary to connect other sources of greywater to the treatment system in order to make it financially viable. The ISA therefore split operation of the system into three phases for evaluation purposes.

During the first phase of operation, a greywater yield of 35 to 130 litres per guest per day was recorded, with the average being 52 litres. When the washing machines were added as an extra source in the second phase, the average guest-specific greywater yield rose to 72 litres per guest per day. The bar and the glass/dishwashers were connected in the third phase of operation, bringing the specific yield to a final average of 82 litres. Including other sources of greywater in the treatment concept (connecting the bar and glass/dishwashers) meant that automated extraction of excess sludge was required.

Diagram of the greywater treatment system at the “Am Kurpark” hotel

Diagram of the greywater treatment system at the “Am Kurpark” hotel
Diagram of the greywater treatment system at the “Am Kurpark” hotel
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Comparison of the chemical-physical and microbiological properties of greywater and process water for the three phases of operation (averages)

Comparison of the chemical-physical and microbiological properties of greywater and process water for the three phases of operation (averages)
Comparison of the chemical-physical and microbiological properties of greywater and process water for the three phases of operation (averages)
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Connecting extra greywater streams resulted in increased outflow concentrations: operating phase I recorded only three breaches of microbiological limits in the white water, but the microbiological quality of the white water deteriorated when other sources of greywater were connected. For some microbiological parameters, for which the ultrafiltration membrane (ultrafiltration) serves as a secure barrier (particularly for E. coli), the increased concentrations could only be traced back to recontamination effects within the permeate pipe. Adapting the recirculation rate enabled the required hygienic quality of the white water to be maintained even after tests in operating phase III (the diagram opposite provides a properties summary for the greywater and process water at all three phases).

Greywater becomes process water

The wastewater from the showers and baths is treated to turn it into high-quality process water, which is hygienically harmless and meets the requirements of the German Drinking Water Ordinance. This process water is used to flush toilets, in the prewash cycle of dishwashers and for irrigation and cleaning.

The project has demonstrated that concepts for water recycling can be implemented without affecting the running of the hotel. However, the extra construction effort involved may sometimes be considerable, thus increasing costs. Implementation is more economic in new builds or as part of general sanitation measures.

RWTH Aachen University
Institute for Environmental Engineering
Prof. Johannes Pinnekamp
Mies-van-der-Rohe Straße 1
D-52074 Aachen, Germany
Tel.: +49(0)2 41/8 02 52 07
Fax: +49(0)2 41/8 02 22 85
E-mail: sekretariat@isa.rwth-aachen.de
Internet: www.isa.rwth-aachen.de
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