The eThekwini municipality’s cleansing and solid waste unit, Durban Solid Waste (DSW), is building a R140-million 1 200 t/d waste transfer station to serve the Durban area.
This new waste management facility will provide a modern and mechanised means of transferring municipal general solid wastes to landfill sites efficiently and cost-effectively.
Engineering and environmental consultant Jeffares & Green, the company responsible for designing the Electron Road waste management facility, in Durban, was appointed to design a modern and mechanised waste transfer station (WTS) at Electron Road, in Springfield Park – an industrial and commercial area north of Durban, near the banks of the Umgeni river.
The main structure, a refuse transfer station and compaction hall, where waste will be offloaded, compacted and containerised for bulk transportation, will be built on a 4 ha site.
The facility will reduce the unavoidable expense of having to transport solid waste to landfills, which are sited further and further from the point of generation, says Jeffares & Green.
At present, most of the waste from City of Durban is disposed of at the Bisasar Road landfill site, in Springfield Park, which is reaching full capacity. When this happens, waste collection vehicles will have to travel to the Buffelsdraai landfill site about 33 km away from the city – more than double the 15 km distance that is considered an economic travelling cost for collection vehicles.
These prohibitive transport costs have made the provision of a WTS financially prudent, particularly since the Electron Road site is less than 1 km from the Bisasar Road site.
The shorter transportation distance will also reduce fuel consumption and wear and tear on road systems, while creating an overall carbon emission reduction by implementing this efficient transport system.
The Electron Road WTS will comprise a four-storey building and some 4 290 m2 in floor space, in which waste will be offloaded into compaction units, compacted into purpose-made containers for bulk transportation and transported to the new Buffelsdraai landfill site.
Associated infrastructure will include a three-storey office block adjacent to the main compaction house, which will provide facilities for DSW employees, as well as an auditorium for education and training purposes.
Further, upgrading of Electron road to provide dedicated access to the site will be undertaken, while access roads to the various handling areas within the site, a security building, weighbridge kiosks for the monitoring and recording of waste mass, wash bays for the waste fleet, a carpark and a covered waiting area at the entrance to the facility, will also be built.
The contract involves the construction of infrastructure, the structures and civil works, including the mechanical plant for the operation of the facility, as well as building-related mechanical, electrical and electronic works.
The civil works include the refuse transfer station, a compaction hall, container-handling operations, offices, weighbridge infrastructure, mechanical equipment and plant. It also entails the construction of a workshop, wash bay, diesel storage facility, security facilities, entrance building and weighbridges, says Jeffares & Green.
Additionally, the design includes the use of natural lighting and ventilation, stormwater treatment, pollution control by means of litter traps, silt traps and oil traps.
Specific stormwater treatment processes were designed to control pollution and allow discharge of an acceptable effluent from the site.
A unique feature of this project is the compaction process that will be used for the first time in South Africa.
This system was accepted as an alternative design proposed by the successful bidder, construction company Aveng Construction. The Husmann Compaction System, which is imported from Germany, does not use conveyors but provides a quick and clean answer to waste compaction.
Construction started in March and will continue for 78 weeks, although Jeffares & Green says the contractor is targeting an earlier completion date.
Aveng Construction has started with piling and layer works.
Aveng Construction senior contract manager Brad Wyatt says the company will be using a unique approach to the required 156 concrete columns.
“Instead of doing 7.5 m columns in the conventional way, we will be precasting them on the ground and then lifting them into place. This will result in outstanding quality, as well as a safer and quicker method compared with the conventional way,” he says.
Another innovative construction approach will be the tilt-up wall system, which will be erected on site. Instead of conventional brickwork that needs to be laid layer by layer, these walls are cast in moulds that have the same face-brick finish as a conventional wall and are then erected as complete units.
Piling is currently under way in less-than-ideal foundation conditions, as the site is underlain by deep alluvial deposits, which are typical of the low-lying areas in and around Durban, reports Jeffares & Green.
These harbour beds comprise unconsolidated sediments of sand, silts and clays in variable layer thicknesses, which extend to considerable depths. The soft clay horizons have a high organic content and are highly compressible, which results in long-term settlement of the clays once an imposed load is applied.
The main transfer-station structure imposes heavy loads of up to 2 000 kN for each column onto the subsoils. Owing to this, the use of shallow raft foundations was discounted as a result of the unacceptably high predicted settlements of up to 150 mm. The solution was to install deep pile foundations, says the company.
Specialist piezocone testing was undertaken across the footprint of the structure. The piezocone equipment is a modification from the original cone penetration test, otherwise known as the Dutch Cone.
The results of the piezocone testing indicated that a competent founding medium of dense coarse sand was encountered only at a depth of about 25 m below ground level.
Several piling options were investigated and the precast driven pile was the one most suited to the site, as it is capable of extending to significant depths and is relatively quick to install, says Jeffares & Green.
The final design included more than 400 350 mm x 350 mm precast driven piles to depths of between 25 m and 29 m. Some recently driven piles have even reached a depth of 39 m, the company adds.
DSW will apply to the Electron Road facility the same award-winning environmental approach it used at the Mariannhill Landfill Conservancy site, just outside Durban, which is today considered a best-practice ecosystem restoration project.
The successful process is driven by Plant Rescue and Relocation Unit (Prunit), which is headed up by horticulturalist and rehabilitation specialist Richard Winn. Prunit applied the philosophy of moving plant species once only and uses a rehabilitation nursery as a backup, if direct relocation is not possible.
The basic principles of the unit are to try and relocate species to their original aspect;
to import no foreign soils; to relocate grasslands with original top soil; to
relocate original watercourse species to wetland nurseries for future use; to create a similar habitat to that which originally occurred; and to only relocate species within 50 km, as per international biodiversity protocol.
This ecosystem restoration project has created a large holding nursery for the storage of indigenous vegetation, which has been hardened-off to withstand rigorous conditions with little or no maintenance.
For example, a nursery of wetland plants has been grown for the future establishment of “leachate through wetland” processes of returning water to the environment, adding that these plants have been specifically hardened-off for contaminants found in the waste industry.
Little plant material could be salvaged from the Electron Road site and DSW, Prunit and Jeffares & Green worked closely together to develop an automatic computer-aided design of what could potentially be provided by the holding nursery.
This, says Jeffares & Green, is an attempt to create a sustainable ecosystem where every plant is selected and planted to fulfil a specific purpose.
The engineered stormwater swales, rainwater harvesting and stormwater ponds have been designed to interlink and are to be planted with indigenous vegetation that are selected to help provide functional solutions to issues identified on site.
Street furniture, lighting, signage, benches, tables and water points have been incorporated into the landscape design, together with habitat-creation opportunities including bird totem poles, structures for fly traps and bat and owl houses.
This is linked to the rodents, insects and reptiles that the company says are likely to appear with the operational activities of the site.
A deck area has also been included on the western stormwater attenuation pond, which is linked to the office building on site. These measures are an attempt to ameliorate environmental impacts with natural, green solutions.
Green Engineering Initiatives
Various elements, over and above those already mentioned, have been considered during construction, says Jeffares & Green. One item that has been carefully designed is the Bio-Swale, a carefully landscaped and shaped, open stormwater system that is built to enhance the removal of solids, metals and other waste from the stormwater.
Another element is the stormwater inlets, which are designed to effectively remove litter and sediment before they reach other systems.
Rainwater will be captured for the washing of containers, floors and vehicles on site.
Visual aids to monitor energy consumption on site are being considered to create awareness around this issue, says Jeffares & Green, adding that the team is constantly looking into opportunities to hand over a facility that supports sustainability and economics.