Gray Water Reuse in Urban Areas

Abstract

The reduced quality and yield of surface and groundwater due to droughts and changing climatic conditions lead to an increase to reusing wastewater (WW) in the Czech Republic. Reusing WW can be implemented at the wastewater treatment plant or in the building. The concept of reused WW in buildings is based on the treatment of low polluted gray water (GW) by gray water treatment system (GWTS) which produces whitewater. GW represents WW from showers, basins, washing machines, kitchen sinks, and dishwashers. Whitewater does not meet such strict parameters as drinking water and can be used for toilet flushing, irrigation or for other use. The WW reuse with GW in urban areas is designed and implemented in the guidelines of a number of countries: UK, Germany, Australia, Canada, USA, and internationally by WHO. Use of treated GW and RW in the buildings in the Czech Republic has not yet been legislatively approved. The characteristic domestic WW as rainwater, gray water, and black water were described. The dark GW (from kitchen and laundry), light GW (from the bathroom), and non-separated GW were reported on their chemical, physical, and microbiological properties. The production of GW represents 70% of total domestic WW, and the toilet flushing represents 30% of the demand for water in the household building. The selected chemical–physical and microbiological indicators of whitewater were described. The groups of GW treatment processes were reported: simple, extensive, chemical, physical, biological and MBRs treatment. The MBRs represent a modern treatment of WW and also are associated with biological treatment and separation of solid and liquid substances. The MBR is directly installed in the biological activated process and replaces settlement tank. The buildings with a high level of GW production and with the high level of demand for whitewater represent the suitable solution for ecological and economical management of WW. GWTS has been provided data on MBRs technologies (microfiltration or ultrafiltration) that seem to be the acceptable solution in the building. In the CR, the system reuses GW only sporadically, but present droughts and changing climatic conditions represent a challenge in the disposal of WW reuse management.