Department of Hydraulics and Sanitation, São Carlos School of Engineering, University of São Paulo, Av. Trabalhador São-Carlense, 400, 13566-59, São Carlos, São Paulo, Brazil.
Department of Hydraulics and Sanitation, São Carlos School of Engineering, University of São Paulo, Av. Trabalhador São-Carlense, 400, 13566-59, São Carlos, São Paulo, Brazil.
J Environ Manage. 2020 Jan 15;254:109825. doi: 10.1016/j.jenvman.2019.109825. Epub 2019 Nov 13.
Microalgae harvesting is one of the major bottlenecks for the production of high-value microalgal products on a large scale, which encourages investigations of harvesting methods with better cost-benefits. Among these harvesting techniques, flotation stands out as a promising method, however it is still minimally explored when compared to the sedimentation method. In this study, the pH modulation followed by dissolved air flotation (DAF) was tested as a harvesting method for Chlorella sorokiniana cultivated in wastewater. The main aims of this study were to optimize the operational parameters of coagulation (pH, velocity gradient, and mixing time) and flotation (recirculation rate), check their reproducibility and resilience with the variability of wastewater characteristics, and evaluate the final wastewater quality after treatment using an optimized harvesting method. Parameter optimization was carried out using the one-factor-at-a-time method. The optimal parameters were a velocity gradient of 500 s, mixing time of 30 s, pH 12, and 20% of recirculation rate. High efficiencies were obtained for C. sorokiniana removal (96.5-97.9%), making it a successful process. Moreover, the photobioreactor effluent quality was also improved significantly after microalgae harvesting, with high nutrient removal (88.6-95.1% of total Kjeldahl nitrogen and 91.8-98.3% of total phosphorus) and organic matter removal (80.5-86.8% of chemical oxygen demand). The results showed the pH modulation and DAF as an effective process for wastewater treatment and biomass harvesting. This study also indicated the importance of operational optimization, not studied until now, in which the achieved results could be potentially applied as practical guidelines for microalgae harvesting on a large scale.
微藻收获是大规模生产高价值微藻产品的主要瓶颈之一，这促使人们研究具有更好成本效益的收获方法。在这些收获技术中，浮选作为一种很有前途的方法脱颖而出，然而与沉降法相比，它的研究还很少。在这项研究中，pH 调节后再进行溶气浮选（DAF）被测试为一种从废水中培养的小球藻（Chlorella sorokiniana）的收获方法。本研究的主要目的是优化混凝（pH、速度梯度和混合时间）和浮选（再循环率）的操作参数，检查其在废水特性变化时的重现性和弹性，并使用优化的收获方法评估处理后的最终废水质量。参数优化使用单因素法进行。最佳参数为速度梯度 500 s、混合时间 30 s、pH 值 12 和再循环率 20%。小球藻的去除效率很高（96.5-97.9%），这是一个成功的过程。此外，微藻收获后光生物反应器的出水质量也得到了显著改善，具有高养分去除率（总凯氏氮的 88.6-95.1%和总磷的 91.8-98.3%）和有机物去除率（化学需氧量的 80.5-86.8%）。结果表明，pH 调节和 DAF 是一种有效的废水处理和生物质收获工艺。本研究还表明了操作优化的重要性，直到现在，这一尚未研究的方面，可以为大规模微藻收获提供潜在的实际指导。
