It is easy to overlook the differences between the kinds of waste water we produce; they are generally considered to fall within two broad categories:
Grey water and Black or Brown water
Grey water or Sullage
Q: Why not dishwasher waste and kitchen sink waste?
A: These both contain extremely high levels of organic solids which lead to unhealthy populations of pathogens and excessive nutrients both of which pose a risk to health.
Grey water treatment and uses containing little worse than skin particles, dirt and soap Grey water waste is relatively easy to treat and recycle.Firstly most Grey water is warm when we finish with it so some form of storage tank to allow cooling is required. This can also incorporate a heat exchanger to allow some of the waste heat to pass to the incoming cold supply heading for the hot water tank.
This cooling area doubles as the primary settling tank which allows solids to sediment out. Remaining contaminants have to be removed by some kind of filtration; this can be mechanical eg. Carbon and sand filters or biological eg. Reed bed or more often a combination of the two.
Once filtered the recycled grey water should not be stored for too long or remaining bacteria and algae will cause putrification and render it more hazardous than before.
The filtered Grey water can then be used for flushing toilets and irrigation.This not only reduces the volume of water required initially but also reduces the load on sewage treatment especially where a septic tank is in use.
Black or Brown water
Black or Brown Water Disposal or Treatment
Q: Can black water be recycled?
A: Yes but rarely on a scale that is commercially viable or practical for anyone who isn’t able to process it on an industrial scale
Waste from sinks that are used for food preparation or dish washing and the waste water from dishwashers must be treated in the same way as foul sewage from toilets.
If water from these sources is allowed to enter soak-aways, reed beds, sand filters or most domestic sediment filter systems the suspended solids, oil and grease will rapidly clog and in most cases totally block these devices.
The high levels of nutrients will allow rapid multiplication of pathogenic organisms and undesirable algae resulting in a foul smelling and highly hazardous ‘soup’ which is very hard to neutralize or remove.
In most cases the treatment of foul waste is outside of the scope of domestic householders.
Those with a connection to a public sewer are fortunate but can still do a lot to help these sewer systems function properly;
Some of these things sound silly but the most common blockages of sewer systems are caused by the items listed above though far worse have been found.
For those with a septic tank or localized treatment plant see our section on Septic tanks and Tertiary treatment systems.