Greywater treatment

human health threats (Water Resources Act, 1978). Namibian Water Act 24, 2004 states that the Government intends to ensure management, development, protection, conservation, and use of water resources; establish the Water Advisory Council, the Water Regulatory Board and the Water Tribunal; and provide for incidental matters. This is to ensure equitable water provisions, public and environmental health protection, sustainability and integrated management. In South Africa though legislation documents have been developed to protect water resources, little has been done to enforce them. In spite of the unending human ingenuity, the focus of water conservation in South Africa still excludes greywater as a viable water resource.

filters; sequencing batch reactor; membrane bioreactors; and biological aerated filters (BAF) (Ngqwala et al. 2013; Ghunmi et al. 2011).

2.6.3. Chemical treatment

Only three schemes using a chemical technology for greywater recycling were reported in the literature (see Table 2.2). The treatment technology of two of the schemes was based on coagulation with aluminium. The first one was a combination coagulation, sand filter and granular activated carbon (GAC) for the treatment of laundry greywater. This can also be a combination of electro-coagulation and disinfection for the treatment of low strength greywater. The most advanced domestic greywater treatment systems use a combination of biological and physical treatment. Such systems are best installed during construction and are not suitable for retrofitting into existing buildings due to cost and other practical difficulties.

There is another method that is called extensive treatment which refers to the technology combining physical and biological treatment, generally produces the highest quality water.

However, it needs careful operations and maintenance. This usually comprises constructed wetlands, such as reed beds and ponds (Tandlich et al. 2009; Zuma et al. 2009).

There are several greywater technology systems that have been developed (see Table 2.2), ranging from simple low-cost devices that divert greywater to direct reuse, such as in toilets or outdoor landscaping, to complex treatment processes incorporating sedimentation tanks, bioreactors, filters, pumps, and disinfection (NovaTec Consultants Inc. 2004). A number of greywater systems are home-built, meaning that the user is responsible for their maintenance.

Table 2.2: G reyw ater treatm ent m ethods, function and applications

Treatment method Function Advantages Disadvantage References

Disinfection This involves the use of chlorine, ozone, or ultraviolet light to disinfect greywater.

Highly effective in killing bacteria if properly designed and operated, low operator skill requirement.

Create toxic by-products, such as Ozone and ultraviolet, can be adversely affected by variations in organic content of greywater.

Solley et al. (2010), Stalter et al. (2010).

Activated carbon filter Activated carbon has been treated with oxygen to open up millions of tiny pores between the carbon atoms. These filters thus, are widely used to adsorb odorous or colored substances from gases or liquids.

Simple operation, activated carbon is particularly good at trapping organic chemicals, as well as inorganic compounds like chlorine.

High capital cost, only remove certain impurities

Rabban (2012); Sim et al. (2011); Reungoat et al. (2010).

Sand filter

Uses beds of sand or in some cases coarse bark or mulch which trap and adsorb contaminants as greywater flows through.

Simple operation, low operation cost and maintenance.

High capital cost, reduces pathogens, but does not eliminate them. Can clog and flood if overloaded.

Ghunmu, (2011);

Sandhu et al. (2010).

Biological treatment Involves the use of bacteria to digest the organic contaminants

High degree of operations accommodates greywater of varying qualities and quantities.

Expensive, complex operational requirements. Sometimes it does not remove all pathogens.

Joss et al. (2005);

Biyela et al. (2012)

Membrane bioreactor Uses aerobic biological treatment and filtration to consume organic

contaminants and filtration of all pathogens.

Flexible, accommodating greywater o f varying quality and quantity. Allows treated water to be stored indefinitely.

High capital cost and operating cost, complex operational requirements.

Cecen et al. (2011);

Leal et al. (2010).

2.7. G reyw ater econom y

Greywater reuse should be used to increase the economy while maintaining its cost for social and environmental benefits by contributing towards sustainable development and resource use. While greywater reuse is often considered primarily as a benefit in terms of water conservation, it also conserves energy, reduces waste water, and the water savings. Greywater reuse, such as toilet flushing saves municipal potable water. For example, in 2010, Johannesburg (Wits University) water tariff for potable water was R10.58/kl and, historically, this tariff has increased between 7 and 14% per annum (Olawale, 2012).

Financing efforts would benefit from a variety of approaches, at different scales and across various sectors.

Reduction in sewage tariff promotes environmental benefit, for example, greywater collected resulted in the reduction of sewage being conveyed to the sewage treatment works downstream. Van Zyl et al. (2006) reported that 83% of potable water demanded in a middle- income area typically becomes sewage. The quantity of sewage not discharged into the sewer due to greywater was therefore estimated to be 83% of the potable water saved. In this case financing efforts should consider the co-benefits that could be provided to (and could also be paid by the municipality) water suppliers, energy suppliers, wastewater utilities, and additional water users. The beneficiation of greywater could provide alternative water supplies for non-potable purposes and eliminate health threats posed by inappropriate handling of greywater. In this project the greywater system is to be used in the decentralised settings where the sewage collection infrastructure is not available or cannot be built. The environmental impact study was conducted by soil and plant analysis.