Potential of low-cost materials for biogas purification, a review of recent developments

Rampant use of fossil fuels resulting in environmental pollution has necessitated the exploration of renewable energy sources. Sustainable development goal 7 stipulates the need for affordable, clean energy to meet human and industrial needs. Abundance of organic waste, in developing economies, makes methane from biogas a major source of renewable energy. The main limitation being that the raw biogas contains carbon dioxide, hydrogen sulfide and other unwanted gases, therefore it requires purification to remove non-methane components. However, existing biogas purification and upgrading systems are relatively expensive and require sophisticated technology and skills to operate them, hence they are unaffordable especially in many developing economies. Besides, these technologies are mainly applicable to large scale systems and are unsuitable for the small-scale systems mostly found in developing economies. This review critically evaluates the potential of low-cost biogas purification materials such as iron rich soils, activated carbon from solid waste, waste iron fillings, and biomass ash for use in household and small-scale biogas plants. These materials have demonstrated considerable performance achieving the following removal efficiencies; clay (90 %); iron-rich New Zealand Brown soil (93.8 %); commercial steel wool (95 %); and compost (80 %). This study proposes new ways to improve the performance of these materials through proper pretreatment of biomass ash to reduce moisture content, surface modification of activated carbon for improved acid gas uptake, integration of adsorbents to create synergy, regeneration and reuse of these adsorbents to promote sustainability. Low-cost materials demonstrate great promise towards achieving SDG 7 especially in developing economies.