Difference between blackwater and greywater - Global Water

Water is a crucial asset – without it we simply would not survive. Every day we use it, and most of it is collected as wastewater.

Above: Wastewater treatment facility in Glenelg, South Australia

Wastewater can be classified into two categories: blackwater and greywater. Although they are both wastewaters, they have different levels of contamination, which is why they must be treated differently. Both varieties can be recycled through treatment systems and are often reused for irrigation and cleaning.

Discover the differences between blackwater and greywater…

Blackwater: is the wastewater from bathrooms and toilets that contains faecal matter and urine. Water from kitchens and dishwashers are also considered blackwater due to the contamination by pathogens and grease (Department of Industry, Science, Energy and Resources 2013, Your Home, Australian Government, Canberra). It is also referred to as sewage or brown water and can carry disease and bacteria, both of which could be harmful.

How to treat blackwater:  biological or chemical treatment and disinfection are required for treating blackwater. There are several accredited treatment systems available for outdoor use.  

The most common wastewater treatment and reuse system in Australia is the aerated system – which involves the following steps:

• wastewater solids settle;
• effluent is aerated to assist bacterial breakdown of organic matter, and;
• disinfection by chlorine pellets.

There are also microfiltration systems available for domestic use.

Greywater: is the wastewater that comes from sinks, washing machines, bathtubs and showers. It contains lower levels of contamination, making it easier to treat and process.

Recycled greywater is commonly used in irrigation and constructed wetlands – as long as no harmful chemicals are present. Greywater that contains food particles can nourish plants, it can also be used for washing and flushing toilets. Where water is scarce - greywater is valuable.

How to treat greywater: it can be reused in gardens with little or no treatment through a subsurface irrigation system to evenly spread water around in the garden. This method is safer for untreated greywater; however all treatment recommendations depend on the condition of the greywater.

Greywater offers an economical water source for those who do not have access to mains or are unable to collect enough rainwater for indoor use. By reusing treated greywater for toilet flushing you can save approximately 50L of potable water in an average household every day (Department of Industry, Science, Energy and Resources 2013, Your Home, Australian Government, Canberra). 

How to ensure water quality for greywater and blackwater:

The quality of reused water will depend on the treatment system, the water’s previous use and chemicals used at the source. Consider the following to simplify the treatment requirements:

• minimise use of harsh chemical cleanings, consider natural cleaning products instead;
• use low or no sodium laundry detergents, soaps and shampoos;
• clean and replace you lint filter to ensure water can flow through;
• do not dispose of household chemicals down sink – your local council will have chemical collection services available;
• use a sink strainer in the kitchen to prevent food scraps and other solid material entering the wastewater facilities.

Global Water offers cost-effective trade waste and wastewater treatment solutions for gaseous emissions, odour, fat, grease, sludge and sewage control and management.

For more information on how Global Water can help you with your wastewater treatment,  contact our team.