Page 37 - Energize February 2021

TECHNICAL

Case study: New Horizons Energy, Athlone Small onsite food waste biodigestion projects
Clean Energy Africa (CEA) and Wastemart developed a large- Case study: Bayside Mall, Table View
scale biogas plant in Athlone, Cape Town, which was Bayside Mall is a large shopping mall in Table View, Cape Town with
commissioned in November 2016. Wastemart, as waste over 100 commercial tenants and 8-million visitors annually. The mall
collectors and separators, run a zero-waste-to-landfill has significant water and energy requirements, which motivated the
operation, collecting, separating, and utilising the waste implementation of several sustainability measures, one of which was
collected. The waste management facility accepts 500 to 600 a biogas installation.
t/day of mixed, high organic waste, including source separated Mixed organic waste, mainly food waste, amounting to an average
MSW, instead of being limited to the use of pure organic waste. of 570 kg/day, as shown in Table 2, is collected daily from retailers and
This has increased the flexibility of the plant to accept waste the mall common areas. The waste is sorted by hand, (Figure 5)
otherwise destined for landfill. macerated and blended with water before being fed into the digestor.
The biogas generated from the facility is separated into The digestor was buried in the ground to save space and to help
compressed bio-methane and liquefied carbon dioxide. The regulate temperatures to support mesophilic digestion and optimum
digestate from the plant is suitable for use as a compost. As biogas production. Technical specifications are given in Table 4. The
part of the operations, any recyclables are recovered, baled, biogas was intended to be used for electricity generation, with a
and provided to recycling companies. potential reduction of grid energy of 300 kWh/day.
The glass, plastic and paper are separated for various The electrical generation portion of the project was later
recycling streams, while most of the waste, (organic matter) is cancelled. The plant was originally envisaged to generate electricity,
routed to two large biodigestors. The waste is drawn from but the scale was not large enough.
normal municipal solid waste (the regular black bags), as well
as waste from food manufacturers, shops, and bakeries, most Case study: N1 City Mall, Cape Town
of it with a high organic content. Food scraps from restaurants Growthpoint Properties, in partnership with the Dutch green
are also included in the mix. Table 1 reflects the plant’s technology provider Waste Transformers, installed an on-site
technical details. anaerobic digestor, which uses organic waste to produce electricity,

Project developers Clean Energy Africa and Waste-Mart energy
Technical specifications MRF: Manual sorting, magnetic and physical separation, air blowing, organic extruder press
Feedstock 500 to 600 t/day high organic mixed waste (200 to 300 t/day organics)
3
3
Gas production 1200 Nm /h biogas, separated into approx 760 Nm /h biomethane and 740 Nm /h CO2 (18 t/day CO2)
3
Table 1: Technical details of New Horizon plant (Wastemart Energy).
Waste description Daily mass (kg) Total solids (% of mass) Volatile solids (kg)
Starches 150 50 67,8
Meat and protein 107 20 19,3
Fruit and vegetables 302 12 32,7
Liquid waste 10 10 0,9
Totals 569 - 120,6
Table 2: Composition of organic waste collected daily at Bayside Mall (Jeffares & Green).

Location Bayside Mall
Project developer JG Africa, WEC projects (EPC), Biogas SA
Proposed energy output Total 215 MWh/y, Electrical 92 MWhe ≈ 13 kWe

Heat 123 MWhth ≈ 18 kWth
Technical specifications 30500 m /y gas production, 35 to 39°C mesophilic operation
3
21 days hydraulic retention time
Table 3: Proposed performance of digestor. 4

Waste volume 600 kg
Gas production 60 m 3
Energy production 240 kWh
Liquid fertiliser 492 kg
Dry compost 12 kg
Table 4: Daily capacity of Waste Transformer unit (Waste Transformers).

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