Greywater recycling is a key technology for achieving water neutrality. It separates the relatively clean wastewater from showers, bathtubs, and hand basins (greywater) from the heavily contaminated wastewater from toilets and kitchens (blackwater).
The Treatment Technology: Membrane Bioreactor (MBR)
The most advanced and safest method for greywater treatment is the Membrane Bioreactor. The process involves several steps:
- Mechanical Pre-filtration: Hair, fibers, and coarse particles are removed by a filter.
- Biological Treatment: The greywater flows into an aeration tank. Here, microorganisms (bacteria) biologically break down organic contaminants like soap residue, skin particles, and shampoos.
- Membrane Filtration: The biologically treated water is forced through extremely fine membranes (ultra- or microfiltration). These membranes act as a physical barrier, retaining all remaining solids, bacteria, and even viruses.
- Disinfection (Optional): For absolute safety, the filtered water can be additionally disinfected with UV light, which kills any remaining germs.
Safe Reuse in the Hotel:
The result is clear, odorless, and hygienically safe non-potable water. While not drinking water quality, it can be safely used for many purposes in the hotel, thus replacing valuable potable water:
- Toilet flushing (the biggest savings lever)
- Irrigation of green areas and gardens
- Cleaning purposes (e.g., for floors or facades)
- Laundry operations (in combination with suitable detergents)
Such a system can reduce a hotel’s potable water demand by 30–50%.
