Techno-economic assessment of decentralised waste beneficiation in South Africa.

Abstract

The introduction of the waste hierarchy promotes the diversion of waste away from landfills towards value-adding opportunities. However, there is no clear methodology for the comparison of waste beneficiation pathways for decentralised waste treatment options in South Africa. As a result, most waste is landfilled in the country even though it contains large amounts of recyclable and recoverable materials. This study investigates the use of techno-economic assessments to determine the viability of decentralised waste treatment options and compare them to larger scales in three selected South African locations (Calvinia, Garden Route District, and eThekwini). These preliminary results may estimate economics before intense, expensive, and time-consuming design and scoping are performed. A critical investigation of currently available literature from various data sources is performed to determine the national and local municipal waste landscape. This scoping exercise is essential for determining the variations of waste volumes and composition dependent on municipality size, which affect the capacity of the various treatment options. Hence, feedstock quantities are established for use in the techno-economic assessment. The three technologies assessed are engineered composting, anaerobic digestion, and pyrolysis of plastics, as examples of technologies that can be applied in various municipalities. Based on a simple cost-benefit analysis, techno-economic parameters are used to investigate the project feasibility based on historical Capital Expenditure data and certain assumptions for Operational Expenditure. Furthermore, a Discounted Cash Flow analysis assesses the variables of Net Present Value (NPV), Pay Back Period, and Internal Rate of Return. These assessments are considered preliminary, with an accuracy ranging between 30% and 50%. Sensitivity analysis determines the different breakeven points of the different economic parameters, indicating feasibility in the event of market fluctuations. Six different scenarios are investigated: the separation and recycling of waste streams (scenario 1), engineered composting (scenario 2a), anaerobic digestion (scenario 2b), pyrolysis of plastics (scenario 2c), and combination scenarios (composting and pyrolysis (scenario 4a), as well as anaerobic digestion and pyrolysis (scenario 4b)). The separation and recycling of waste from each location found a credit of R2.4 to R17.8 / t waste based on specific assumptions. The increase in municipality size positively influences the feasibility of this scenario. The economic parameter of the Net Present Value is used to analyse the feasibility of the remaining scenarios. None of the scenarios is economically feasible in Calvinia, with Net Present Values less than zero. Composting is feasible in the Garden Route District and eThekwini with a Net Present Value of R44 million and 89 million, respectively. Based on electricity sales, anaerobic digestion is feasible in Garden Route District (R14.5 million) and eThekwini (R208.6 million). Plastic waste pyrolysis is feasible in the Garden Route District and eThekwini. The combined pyrolysis scenario with either composting or anaerobic digestion also produces feasibility in the Garden Route District and eThekwini, with higher Net Present Values for the latter scenario. The inclusion of Extended Producer Responsibility targets decreases the Net Present Value of pyrolysis by reducing the amount of product and thus the revenue from fuel. Suppose Extended Producer Responsibility targets were fulfilled, and the recyclate stream was diverted to the Buy Back Centres for sales, the overall income could not overcome the capital and operational costs in any location. The different parameters investigated through sensitivity analysis determine the leverage points for each process and inform the influence of market fluctuations due to legislative instruments such as the Extended Producer Responsibility. The landfill credit can be considered a key parameter since the true cost of landfilling is not widely recognised and may be underestimated. This is exhibited by the minimum landfill cost of R577, R711 and R365/ t waste for the feasibility of the separation and recycling scenario. Separation and recycling is the only economically viable scenario in Calvinia, indicating that decentralised separation and recycling of waste is possible and should be considered in these locations. However, scenarios with higher capital and operational costs (scenarios 2(a)-(c) and 3) are not feasible. In such cases, incentives and government funding schemes must be investigated to support waste treatment opportunities in decentralised locations. As scale increases, all investigated scenarios became feasible in Garden Route District Municipality and eThekwini, indicating that the possible combinations of waste from different decentralised locations (i.e. multiple smaller municipalities like in the Garden Route District Municipality) could result in feasible treatment options in these parts of the country. Furthermore, between 35 and 72% of landfilled waste can be diverted through the different scenarios (depending on Extended Producer Responsibility targets and local compositions), indicating that such process implementation can aid South Africa in reaching diversion targets set in the National Waste Management Strategy and Polokwane Declaration.