Grey water recycling and MBR

Greywater recycling with membrane bioreactor (MBR) technology

Greywater (also spelled graywater, grey water, gray water) or sullage is all wastewater generated in households or office buildings from streams without fecal contamination. By definition greywater is generally waste water from showers, baths, basins, and washing machines. Greywater treatment is easier than municipal wastewater treatment, generating a large interest in its reuse and recycling. Typical applications for greywater recycling and re-use are toilet flushing, irrigation and other non-potable uses.

Reusing wastewater is a crucial part of the sustainable management of water resources.  Greywater can be an important alternative water source, especially in arid and touristic areas, where the biggest water demand is usual in the dry period. The potential ecological benefits of greywater recycling include:

• Reduced freshwater extraction from rivers and aquifers,
• Less environmental impact from septic tanks and water treatment plants,
• Reduced energy use and chemical pollution from water treatment,
• Groundwater recharge and reclamation of nutrients.

However, greywater can be contaminated with different kinds of soluble and insoluble substances and must be treated properly. Contaminants in greywater include traces of dirt, food, grease, hair, and certain household cleaning products. Typically, aerobic and biological treatments are used as primary greywater treatment to remove dissolved and suspended biological matter, followed by ultra-filtration to prevent particles, bacteria and viruses of passing through. Ultimately, greywater can be disinfected with ultraviolet and/or chlorination, to ensure residual disinfection at point-of-use.

In densely urbanized touristic areas, where space is short and has a high value, compact and reliable solutions are required, turning the membrane bioreactor technology into a very attractive option. The MBR process is a combination of the activated sludge process with membrane filtration (ultrafiltration or microfiltration). MBR has some distinctive advantages compared with conventional treatment systems (Figure 1 and 2):

• Very stable process and compact design,
• High effluent quality and low sludge production.

Membrane bioreactors replace clarifiers, media filters and reduce reactor size by combining physical membrane barriers with biological treatment. These characteristics make MBR the perfect solution for a greywater treatment system and for greywater recycling. Greywater systems usually comprise of plumbing, pumps and a bioreactor tank where the biological treatment occurs and the water passes through a membrane filter.