Biomass as a Cornerstone of a Circular Economy: Resources, Energy, and Environment

Abstract

The circular bioeconomy is one development strategy that has at their centre the use and management of the biomass. Biomass could transform the bases of a global economy highly dependent on non-renewable raw materials and fossil origin, to a mostly bio-based economy that can simultaneously address the three main global challenges: provision of safe water, accessible energy for all and climate change mitigation. For the circular bioeconomy to be more than a popular global objective, it is necessary to identify concrete measures that can make the concept operational, in order to politicians, decision makers and stakeholders can observe its practical implications. In this chapter, is reported an experience of an Integrated Waste Management Technology (IWMT) with microalgae in Argentina. The proposed IWMT includes microalgae as a complementary treatment of sewage effluents in waste stabilization pond systems, with the triple objective of wastewater purification, recovery of nutrients in biomass and mitigation of greenhouse gases by using bioenergy from the biomass generated. Experiments were carried out with the Scenedesmus quadricauda microalgae, growing it in four concentrations of effluents (T25%, T50%, T75% and T100%). Microalgae productivity parameters and energy and environmental qualities were studied. The species was able to grow successfully in T25% and T50% treatments, but not in T75% and T100%. This implies that it is still necessary to dilute the effluents to reduce their organic load, which at some times of the year (mainly the dry autumn-winter season) may exceed the limits allowed for their discharge. The crop has been able to grow without temperature control. The maximum CD in the treatments was around 70% higher than the control (only culture medium). The organic load reduction capacity was on average 83.4% ± 5% and 74.55% ± 4.2% (for T25% and T50%, respectively). The removal of phosphates and nitrates was 57.6% and 58.7% in T25%, and 54.6% and 76.9% in T50%. Total coliforms and fecal coliforms were reduced by 89.6% and 77.4% for T25%, and 86.6% and 68.7% by T50%. In all cases, it was possible to confirm the ability of the microalgae to remove nutrients and reduce the organic load and pathogens. The water treated with microalgae has reached permitted values for be discharged. The biomass generated has a high energy potential in comparison with other fuels, close to 4.41 ± 0.43 kWh / kg. The integration of algae in tertiary systems could improve the treatment of wastewater and water cleaning, with the possibility of achieving the reuse of water. The proposed system was simple, and can be easily replicated on larger scales, including some optimization factors if necessary. Under the pressure of climate change, the IWMT will be essential technologies particularly in regions with low water and energy availability, mitigating GHG emissions and strengthening local communities.