Recovery of vinasse with combined microalgae cultivation in a conceptual energy-efficient industrial plant: Analysis of related process considerations

Abstract

Resource recovery from agro-industrial wastes in the sugar-ethanol industry is a strategy under wide development. Besides promoting sustainability of the biorefinery plant and mitigating its negative environmental impacts, this strategy may also economically benefit the agro-industry by commercializing recovered added-value resources. In this regard, the sector commonly exploits by-products such as biofuels and biomaterials. This study proposes to build a critical review of a hypothetical integrated biogas plant combined with vinasse treatment and microalgae cultivation annexed within a sugar-ethanol mill. It addresses an innovative approach by proposing a sustainability-oriented plant (in terms of energy and resources) that combines different processes individually discussed in the literature. This strategy contributes to maintaining a closed-loop in the sugar-ethanol industrial plant. The primary data on algal cultivation in a mixotrophic medium (pretreated vinasse) and biogas generation from the anaerobic co-digestion of vinasse and algal biomass are listed. It then focuses on implementing resource recovery techniques aiming at achieving biorefinery sustainability, viz., valorizing nutrients from the biosolids as biofertilizers and disposing of treated vinasse for fertigation of sugarcane crops. In addition, biogas purification may generate biomethane (as a source of heat and electrical energy) and promote supplementary carbon for microalgae cultivation. Lastly, the proposed plant's viability is demonstrated by calculating the system's energy balance and net energy ratio (NER), whose results are +14.49 MJ.m−3vinasse and 2.0, respectively.