Double-Stage Anaerobic Digestion for Biohydrogen Production: A Strategy for Organic Waste Diversion and Emission Reduction in a South African Municipality

Abstract

Landfilling of organic waste poses a significant environmental threat, heavily contributing to climate change. The diversion of waste is imperative, but pathways to implementing alternative waste management strategies are needed. Double-stage anaerobic digestion has been identified as a potential technique that can reduce greenhouse gas emissions and diminish the amount of waste landfilled. Still, further research is needed before its implementation at the municipal level. This paper explored the potential insertion of double-stage anaerobic digestion into the portfolio of alternative treatment methods using the case study of the eThekwini Municipality in Durban, South Africa, by proposing a source-separation waste management scheme and forecasting the organic waste generation for a 24-year timeframe until 2050. The WROSE model has been identified as the ideal tool for the analysis. A new scenario, including double-stage anaerobic digestion, has been introduced in WROSE after developing a country-specific emission factor. The technology has been assessed against similar techniques, namely anaerobic digestion and composting, according to the environmental indicators included in WROSE. Compared with the business-as-usual scenario and three other alternatives, the new scenario proved to be the second-most effective (−282% versus business-as-usual) after anaerobic digestion (−291%) in reducing climate-altering emissions, achieving analogous waste diversion rate (10.09%), landfill airspace (1,653,705 m3), and monetary savings (3.8 billion Rand) compared to composting and anaerobic digestion.