JG Afrika, a leading consulting firm of engineers and environmental scientists, has designed and is implementing one of the largest greywater reuse systems in Africa at Stellenbosch University’s (SUN) main campus in the Western Cape to improve campus water supply resilience and reduce dependency on municipal supply.
The system installation comprises two phases which, once complete, will flush more than 1 300 toilets used by about 25 000 university students to meet between 20% and 30% of campus water supply, as well as supplement campus irrigation.
Notably, the system was the Water Category winner at this year’s South African Institution of Civil Engineering (SAICE) Western Cape Regional Awards. Regional winners are entered into the SAICE National Awards, which recognises projects truly showcasing the art and science of civil-engineering to the general public.
Benjamin Biggs, a civil engineer in JG Afrika’s Municipal Infrastructure and Sustainability divisions, says that the firm was appointed by SUN to develop a sustainable water-management masterplan prior to the severe 2017 Western Cape drought.
“The plan focused on reducing potable demand and increasing campus supply resilience by using all identified water sources optimally and avoiding potable water for irrigation. Water-Sensitive (Urban) Design (WSD) principles were used as a framework to achieve sustainable water-management on campus. WSD is an internationally accepted concept that addresses limitations of conventional urban-water management,” Biggs says.
JG Afrika developed a comprehensive SUN water balance by first assessing and modelling eight representative buildings. Water characteristics from each type were extrapolated across campus to other similar buildings and calibrated against utility data.
Interventions focused on the top 40 users, comprising 80% of total water demand. WSD principles were then applied according to JG Afrika’s Water-Management Hierarchy, which focuses on first reducing demand before reusing and finally supplementing existing water supplies.
Notably, campus interventions introduced as part of the first “reduce” stage of the Water-Management Hierarchy decreased potable water demand by more than 50%. They included the installation of efficient fittings, addressing leaks and managing system pressures, in addition to educating staff and students in the efficient use of water.
The next implementation stage proposed in the Water Masterplan involved water “reuse”. Greywater reuse on campus was identified as a viable alternative supply and JG Afrika was appointed by SUN to design and implement a campus greywater system.
Biggs says that greywater is collected via sumps, manholes and grit traps in selected residences where shower drainage is isolated from blackwater and redirected into the collection system.
The centralised campus treatment plant has been designed to treat, store and distribute 105 m³/day of greywater in the first phase, and its hydraulic capacity will be doubled in the second phase of the project.
Treatment steps include primary sedimentation, aeration, solids removal/physical filtration and disinfection/sterilisation by means of hydrogen peroxide dosing.
The treated greywater will be stored in 20 k tanks at the treatment plant for daily toilet flushing and excess greywater is to be boosted into the existing irrigation network.
Treated greywater will then be pumped to a header tank with a booster system, which includes a municipal potable supply backup, situated on the roof of a ten-storey residence to pressurise the non-potable network.
After being plumbed directly into toilets in selected buildings, this network will be expanded to supply and collect from additional campus buildings during the second phase of the project.
Various health risks are associated with greywater reuse systems and, therefore, risk mitigation was an important part of the system.
An environmental regulation screening report was compiled assessing relevant legislation, such as the Water Act, Health and Safety, local municipal by-laws, as well as National Building Regulations, and possible triggers were identified.
Furthermore, the risk of cross-contaminating the potable municipal network was mitigated by using separate service networks (potable and non-potable); separate plumbing networks (direct non-potable feed to toilets and urinals); and an air gap to prevent the municipal backup supply pushing back into the potable network. Additionally, high-density polyethylene pressure pipes in the ground and internal plumbing pipes are colour coded and, as a final precaution, blue dye will be introduced into the treated water to identify future cross-connections should they occur.
The system installation will include a two-year operation and maintenance (O&M) plan for SUN, as well as the provision of training and technical instruction on the system for SUN staff.
Biggs says that one of the challenges has been coordinating such a diverse project team, comprising plumbers, wastewater treatment specialists, civil, electrical, electronic and mechanical contractors, sub-contractors and consultants.
Working in an operational environment, ongoing communication between all affected parties, including SUN’s facilities management team, staff and students, has also been critical. Therefore, project management, facilitated by Mathew Steven of Turner Townsend, has played an important role in the project.
To further build water resilience in the future, JG Afrika is investigating the possibility of rainwater and stormwater harvesting used in conjunction with sustainable drainage systems (SuDS) to manage aquifer recharge and thereby enable additional borehole abstraction.
Biggs concludes by lauding SUN for its continued focus on reducing its water footprint, just one of a number of their “greening” sustainability initiatives.