Abstract
South Africa is a semi-arid country, where the prevalence and intensity of heatwaves and drought is increasing, which is exasperated within the City of Johannesburg Metropolitan Municipality, where inadequate infrastructure maintenance and electricity loadshedding is severely impeding on freshwater reticulation. This stresses the need to further explore water conservation and reuse initiatives.
The Constitution of South Africa accords the right to access sufficient water and sanitation to all people, whilst various legislations and policies guarantees free basic sanitation for the impoverished, including a minimum of 25 ℓ/c.d of freshwater within a 200 m cartage distance.
Informal settlements predominantly comprise of informal dwellings (shacks), which do not comply with standards and regulations and are typically built with scrap materials without approved architectural plans, often illegally on private or public land. Formalised/sewered areas of informal settlements are often built in paved areas, with more permanent services, such as flushing toilets and yard taps. Non-formalised/non-sewered/unserviced areas are typically built on open soil with public standpipes and shared sanitation. Within such settlements, freshwater provision is often prioritised over greywater management. Informal settlements are marred with extreme poverty, unemployment, and rampant crime, to which Zandspruit is no exception.
Greywater is domestic wastewater which excludes toilet water, and is not presently controlled by national legislation, but rather relegated to municipalities to manage by means of by-laws. Within the context of this study, disposal refers to systems which discards of greywater, such as reticulation to sewers, septic tanks, artificial wetlands, or collects greywater for treatment and reuse. Removal refers to a universal mechanism which accepts greywater from residents at surface level, in order to interface with existing and future greywater disposal systems, as dictated by guidelines, by-laws and any future explicit greywater legislation.
In the absence of explicit legislation on greywater disposal and reuse, various guidelines exist for greywater disposal within informal settlements. These guidelines are typically linked to the dwelling density and greywater generation rate, which was found in this study to be 129 du/ha and 5,839 ℓ/ha.d, respectively, for Zandspruit, for which guidelines recommend off-site disposal. These figures are particularly high, indicating a very dense settlement likely resulting in poor spatial planning with approximately 520,000 ℓ of freshwater used and 362,000 ℓ of greywater generated per day.
The survey on water use and disposal was conducted within the non-formalised area of the Zandspruit informal settlement by means of systematic cluster sampling. The freshwater use was found to be 456.47 ℓ/du.w, with the greywater generated 317.63 ℓ/du.w and theoretical greywater generated 342.35 ℓ/du.w [75% theoretical return factor (Carden, et al., 2007c)], with a return factor of 69.58% calculated. These figures align with literature for informal settlements and low-income communities.
Whilst 85% of households indicated as discarding their mixture of light and dark greywater straight away, 61% of households reported to discard of their greywater outdoors. This was either on open ground, within the street, in a ditch, or stormwater drainage channel, whilst 6% of households discarded inside a stormwater drain, 4% in a basin, and 28% in a toilet, foregoing any reuse possibility. This results in a significant amount of greywater discarded at surface level, and when coupled with the various health and environmental concerns which households reported, frames the context within which greywater management strategies should be contemplated within the settlement.
Zandspruit’s greywater is found to vary significantly in chemical quality throughout the settlement, as per chemical tests by Water Lab and the WHRC at UJ. The latter detected significant concentrations of coliforms and in particular, E. coli, within 87% and 43.33% of greywater samples, respectively. This poses significant health concerns for the community, given the present disposal practices. The selectively sampled laundry and household cleaning greywater from Zandspruit was used as mixing water for a concrete experiment conducted with Go Consult. The greywater concrete only attained 70.40% < 90% strength of a distilled water control, but still achieved 30.65 MPa at 28-days, attaining 78.50% strength of the control, which is encouraging.
The survey results with regards to greywater generated and present disposal habits within Zandspruit, in addition to the chemical and microbial parameter results, form the considerations for the conceptual design of a safe, practical, and universal greywater removal system.
The recommended conceptual design prioritises community safety by eliminating corners and sharp edges, in an effort to prevent injury. The system consists of three hefty interlocking single-casted concrete chamfered components. This comprises a round base, core, and cap (45⁰ chamfer: 10 mm cap; 25 mm core and base) with slits to help prevent items falling into the cavity. The concrete has a 40 MPa specified strength with a target of 60 MPa. The resulting infrastructure has an assembled mass of 231.87 kg with a low centre of gravity, proving
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economical, stable, and durable. Additionally, the concrete design should be inert to greywater interaction, as per personal communications conducted with Chryso South Africa
(Barker, 2022) and with Go Consult (Du Plessis, 2022).
The 620 mm OD × 300 mm high base is to be fixed into position, 200 mm below ground level, allowing for universal articulation to various disposal options by means of 50D, 300 mm ND concrete stormwater/sewer pipe as per national standards. The 410 mm OD, 300 mm ID × 325 mm high core and 520 mm OD, 420 mm ID cap is removable and forms a flush fit to prevent the build-up of scum, whilst the resulting 33.58 ℓ cavity will allow for a fat trap. These components are also reversible, such that improper installation or maintenance, ideally conducted by the community, should not impact on functionality. The assembled height at 350 mm above ground level will allow the most common greywater containers identified within the community to be easily tilted and lifted, using the edge of the cap as a fulcrum, whilst the cap lip should reduce spillage.
This design should prove cost-effective, durable, and inert to greywater interaction, undesirable for theft, portable for upgrading non-formalised to formalised settlements, and user-friendly.
Keywords: greywater generation; greywater reuse; greywater removal; greywater disposal; greywater concrete; informal settlements; Zandspruit informal settlement.