Utilization of water from rainwater basins at industrial laundry applications
Authors: Agnieszka Behrend, Mads Leth-Wahl, Kenneth Lambæk Sørensen, Stinne Plesner Skårup
With changing climate, sustainable development goals have to be incorporated in many fields. Stormwater management is one of them. At the same time, groundwater, the predominant source of drinking water in most of Europe, is an increasingly scarce resource. The concept of rainwater harvesting and merging it into certain drinking water applications can be considered as an attractive option, solving stormwater management problems and the issue of decreasing groundwater levels. Considering several drinking water applications, industrial use of drinking water account for around 20% of total consumption. To decrease that pattern, the possibility of using rainwater harvested from rainwater basins in the industrial laundry process was investigated.
The use of rainwater for industrial applications is determined by its amount and composition. Raw rainwater is soft and can be considered as free of pollutants. However, the rainwater collected contains pollutants from the atmosphere and surfaces that it has been in contact with. Therefore, utilizing rainwater requires documentation on the quality of water, necessitating a set of water quality limits to be defined in conjunction with water application and final product.
The project idea was investigated for industrial laundry - Midtvask in Skejby, Denmark. Through hydraulic modelling, two basins west of Skejby were investigated to see whether changes to outlets would be required, and what consequences these changes may have for quantity and quality of the harvested rainwater. One of the basins was found to be able to provide 100% of the water consumption requirements at Midtvask, which is equal to 100 m3/d, without changes to the outlet because of incoming drainage water. The second basin was found to provide at least 80%, depending on changes to the outlet location.
MidtVask’s demands for the water quality and existing legislations dictate the design of a suitable treatment process. A prototype rapid sand filter was tested and found to be an effective method for reducing the levels of several relevant pollutants, but might be required to be used along with a reverse osmosis membrane filter and UV disinfection to fully comply with the established limits.
Among others, price estimation for installation of rainwater treatment system was compared with annual drinking water cost and additional wastewater fee. The main conclusion from comparing results was that the new system is able to lower the annual costs due to overall savings.
The project brings rainwater harvesting which was initially applied for flushing toilets and household laundry into higher level, industrial applications, which can be a potential sustainability measure. The overall idea can be re-designed for different industries having the same or lower water quality demands, but can be also seen as a start-up point for industries with higher quality requirements.
The project comes with collaborative value for supply companies having to deal with increasing rainwater volumes and industries, which as one of the goals have a reduction in excessive consumption of drinking water.
