Cultivo da microalga spirulina platensis em meio Zarrouk diluído e adicionado de resíduo da indústria láctea

Abstract

The most of energy consumed in the world isderived from non-renewable sources, such as coal, oil and natural gas, wich tend tobe depleted over time. The necessity of a renewable source of energy, to reduce the emissions of greenhouse gases, make the microalgae are detached by being photosynnthetic microorganisms, with high capability to synthesize carbohydrates and lipids, also because they don`t compet for space and water with food and there is a possibility that they can be produced from waste. To use microalgae as a feedstock to bioethanol, high yields of biomass and accumulation of the compounds of interest are required, as well asthe use of inexpensive culture media. The mixotrophic culture enables the use of waste such as carbon sources for algal cultivation. The aim of this study was the increase of cabohydrates in Spirulinawith the addition of residue from ultra and nanofiltration process of whey protein. The cultures ofSpirulina platensisLEB 52 were performed in photobioreactors of 1 L, at 30 ºC and photoperiod of 12 h, with initial cell concentration of 0.15 g.L-1. In all experiments, 0%, 1.25% and 2.50% (according with the Experimental Design) of residue was added in fed batch mode. To evaluate the influence of the concentration of the Zarrouk medium and of the residue a Mixed Experimental Design 21.31was used. It was used the Mixed Experimental Design 21.31 for each residue added (permeate ultrafiltration and nanofiltration retentate). The cultivation modes were also studied in crops in laboratory scale tested: the simple batch mode and fed batch mode. The detriment of nutrient in the Zarrouk medium to 20% and the addition of 2.50% of nanofiltration residue led to a high carbohydrates productivity (about 60 mg.L-1.d-1) and the amount of residue added to the end of the process was 10% v/v in this assay. This same condition, but added ultrafiltration residue has reached the same productivity in carbohydrates, however, in the end of the process the amount of waste was added 2% v/v. The two assays (20% Zarrouk and Zarrouk 20% with the addition of ultrafiltration permeate) who achieved high productivity in carbohydrates in laboratory scale had their condition tested in bioreactors type raceways 10 L. The testthat used only Zarrouk 30% showed high productivity protein, and therefore, this condition was tested in 10 L raceways. However, in all conditions tested inraceways reached high productivity in carbohydrates (72,42 mg.L-1.d-1, and 76,21 mg.L-1.d-1, in the condition using Zarrouk 20% and Zarrouk 20% added with 2,5% of ultrafiltration permeate, respectively). Even the condition that used Zarrouk 30% reached high carbohydrate productivity, about 66,40 mg.L-1.d-1. The culture conditions studied are good alternatives for increasing carbohydrates productivity in Spirulinaand are considered appropriate conditions when there is an interest of using microalgae as a feedstock in the production of bioethanol.