RESUMO
Microalgae biomass is a versatile feedstock with a variable composition that can be submitted to several conversion routes. Considering the increasing energy demand and the context of third-generation biofuels, algae can fulfill the increasing global demand for energy with the additional benefit of environmental impact mitigation. While biodiesel and biogas are widely consolidated and reviewed, emerging algal-based biofuels such as biohydrogen, biokerosene, and biomethane are cutting-edge technologies in earlier stages of development. In this context, the present study covers their theoretical and practical conversion technologies, environmental hotspots, and cost-effectiveness. Scaling-up considerations are also addressed, mainly through Life Cycle Assessment results and interpretation. Discussions on the current literature for each biofuel directs researchers towards challenges such as optimized pretreatment methods for biohydrogen and optimized catalyst for biokerosene, besides encouraging pilot and industrial scale studies for all biofuels. While presenting studies for larger scales, biomethane still needs continuous operation results to consolidate the technology further. Additionally, environmental improvements on all three routes are discussed in light of life-cycle models, highlighting the ample research opportunities on wastewater-grown microalgae biomass.
Assuntos
Biocombustíveis , Microalgas , Águas Residuárias , Biomassa , Tecnologia , PlantasRESUMO
The results of a 20-month period study in Brazil were analyzed to compare horizontal-flow constructed wetlands (CW) and waste stabilization pond (WSP) systems in terms of land area requirements and performance to produce effluent qualities for surface water discharge, and for wastewater use in agriculture and/or aquaculture. Nitrogen, E. coli and helminth eggs were more effectively removed in WSP than in CW. It is indicated that CW and WSP require similar land areas to achieve a bacteriological effluent quality suitable for unrestricted irrigation (10(3) E. coli per 100 mL), but CW would require 2.6 times more land area than ponds to achieve quite relaxed ammonia effluent discharge standards (20 mg NH(3) L(-1)), and, by far, more land than WSP to produce an effluent complying with the WHO helminth guideline for agricultural use (< or =1 egg per litre).
Assuntos
Reatores Biológicos , Eliminação de Resíduos Líquidos/métodos , Purificação da Água/métodos , Animais , Biodegradação Ambiental , Brasil , Conservação dos Recursos Naturais/métodos , Escherichia coli/metabolismo , Helmintos , Nitrogênio/isolamento & purificação , Contagem de Ovos de Parasitas , Poluentes Químicos da Água/isolamento & purificação , Áreas AlagadasRESUMO
This study evaluated the effect of high-rate ponds (HRPs) of different depths (20, 30 and 40â cm) on the carbon assimilation by microalgae cultivated in domestic sewage. The efficiency of the dissolution provided by the carbonation column and the carbon release to the atmosphere through the movement of the paddle wheels were also investigated. Dissolution efficiencies of 50%, 48% and 46% were obtained in the HRPs of 20, 30 and 40â cm depth, respectively. These differences can be attributed to the time necessary to recirculate the volume of each HRP in the carbonation column. The volumetric mass transfer coefficients regarding the release to the atmosphere were 0.0007, 0.0005 and 0.0004â min-1 for the 20, 30 and 40â cm HRPs, respectively. The carbon assimilation by the biomass was inversely proportional to depth, with values of 90%, 72% and 68% for the 20, 30 and 40â cm HRPs, respectively. Chlorophyll-a concentration was also higher in the 20â cm HRP. The radiation attenuation at the beginning of the operation was similar among the treatments, resulting in a greater fraction of the pond depth with available radiation in the 20â cm HRP.