Miguel de Jesus Pereira

Microalgae are present in the aquatic environment and produce bioproducts of great added value (e.g. carbohydrates, lipids, fatty acids, pigments, protein) through the conversion of solar energy into chemical energy by fixing atmospheric CO2. Therefore, microalgae biomass has many potential applications in several industries, for example, cosmetics, pharmaceuticals, agricultural biopesticides, biofuel production, and food supplements. However, microalgae harvesting involves energy consumption and high operating costs (about 30 % of the total production cost). Thus, this paper aims to review the main achievements of microalgae harvesting processes, their efficiencies, and the main advantages and disadvantages of each harvesting method. Coagulant dosage, mixing time, and velocity gradient are parameters that affect the efficiency of microalgae harvesting. Therefore, the optimal conditions of these variables will be presented in this review article. On the other hand, coagulation, followed by flotation, is influenced by attraction-repulsion forces between cells and the coagulant agent. Factors such as cell size, viability, density, possible cell damage, strain properties, sedimentation rate, the salt concentration of each algae species of microalgae, energy demand, final product, and the reuse of culture medium determine if will be necessary one or methods combined for harvesting the microalgae biomass. However, coagulation and flocculation are still relevant for the harvesting of algae cells.

The use of microalgae and natural coagulants in biological water treatment has been explored, as the use of chemical products can generate contaminants harmful to human health. Chlorella vulgaris primarily uses nitrogen and phosphorus as nutrients, managing to develop in various media where these and other compounds are present, removing them. In coagulation processes, Moringa oleifera is able to remediate effluents and raw water in a biodegradable manner, being an effective substitute for aluminum and iron-based coagulants and avoiding problems caused by them. Experiments with Chlorella vulgaris and Moringa oleifera were carried out in order to, firstly, analyze the growth of the microalga in the water of the Poxim River and verify its efficiency in removing chemical substances, followed by the evaluation of the capacity of Moringa oleifera in removing the microalga. The results showed that Chlorella vulgaris completely removed chlorite and glyphosate and reduced the concentration of other compounds, including nitrate, phosphorus, and iron. This study has proven that microalgae can be used to remove contaminants from raw water and that Moringa oleifera helps the microalgae to settle more quickly.

O soro de queijo é um subproduto correspondente à porção líquida resultante da produção de queijo e outros produtos lácteos, é rico em lactose, proteínas e micronutrientes. O descarte incorreto do soro de queijo é uma preocupação ambiental, por isso surge a necessidade de reaproveitamento desse resíduo. O soro de queijo vem sendo utilizado como substrato barato para a produção de enzimas industrialmente importantes, como a β-galactosidase, algumas linhagens de microalgas têm sido cultivadas em águas residuais para produção desta enzima, sendo a Chlorella vulgaris uma de grande destaque devido à sua alta capacidade de remoção de nutrientes (N e P) e demanda química de oxigênio (DQO). Desse modo, esse trabalho teve objetivo produzir β–galactosidase utilizando a microalga Chlorella vulgaris tendo o soro de queijo como substrato. O permeado de soro de queijo foi preparado e testado em várias concentrações completados com BG-11 (meio de cultivo para a microalga), depois disso foram realizados cultivos variando a concentração de uma das fontes de N do meio, durante 5 dias. A atividade enzimática máxima obtida foi de 8,88 U L-1 no cultivo contendo 60% (v/v) de permeado e meio BG-11 com 2300 mg L-1 de NaNO3, seguidos pelo cultivo de 20% (v/v) de permeado com 700 mg L-1 de NaNO3 e 20% (v/v) de permeado com 1500 mg L-1 de NaNO3, concentração de 6,29 U L-1 e 5,55 U L-1, respectivamente. Evidenciando que o permeado de soro de queijo foi um bom meio de cultivo para a produção da enzima β-galactosidase por Chlorella vulgaris.