Dissolved air flotation applied to separation of microalgae cultivated in photobioreactor, fed with physico-chemically pretreated vinasse, aiming its potential use as biofuel

Author(s)

Gabriel Dibbern Sacchi

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2015-11-23

Examining board members

Marco Antonio Penalva Reali; Maria Lúcia Calijuri; Luiz Antonio Daniel; Luiz Olinto Monteggia; Edson Aparecido Abdul Nour

• Advisor: Marco Antonio Penalva Reali; Mirna Helena Regali Seleghim

Abstract

Considered a sustainable fuel, ethanol produced from sugar cane, leaves a major liability during its production process, which has been deposited in the own sugar cane fields. The vinasse is generated, on average, in the proportion of 12 liters per liter of produced ethanol, is rich in different nutrients, which can be used for many purposes, such as the microalgae cultivation. This study evaluated in the first step the vinasse clarification by coagulation with cationic polymer, followed by crossflow microfiltration on a hollow fibers filter, which enable a reduction over 77% for apparent color, 99%for turbidity and 20% for COD, facilitating the use of this effluent for microalgae cultivation. In a second step, was evaluated the microalgae Chlorella vulgaris cultivation in bench scale and batch operation, in a medium prepared from the vinasse dilution in water from a deep well, getting an increase in the biomass production, measure in terms of chlorophyll-a, for a vinasse concentration below 7.5%, and an inoculum of approximately 106 individuals. These data allowed the microalgae cultivation in a continuous flow pilot-scale photobioreactor, which produced biomass that was used in the next stages of the study, for the evaluation of the biomass separation by dissolved air flotation. The first DAF tests carried out in bench scale and batch operation allowed to identify the optimum operation conditions, which were then evaluated in a continuous flow pilot scale dissolved air flotation unit (DAF). The DAF unit produced a sludge with a solid content greater than 2%, which was submitted to a final dewatering by centrifuge. The dewatering tests allowed to check that the use of the same polymer used for the clarification step, permit to obtain a more stable sludge when compared with the sludge without chemical add, and in the best cationic polymer dosage of 6 g.kg-1. The conclusion of this work has shown the possibility of use vinasse as a grow medium for microalgae cultivation, reducing one of impacts caused by ethanol production. In addition, it was possible to observe the potential of FAD, for biomass thickening, produced in photobioreactors. (AU)

• FAPESP's process: 11/07264-8 - Dissolved Air Flotation applied to the separation of microalgae grown in photo-bioreactor fed with physico-chemically pre-treated vinasse, in order to produce biodiesel
• Grantee: Gabriel Dibbern Sacchi
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)