LAUSR

Abstract Polycyclic aromatic hydrocarbons (PAHs), especially those having four or more rings, are abundant and toxic environmental contaminants that are highly persistent and difficult to remove from contaminated ecosystems. Bioreactors with microalgae have been used to remove some low-molecular-weight PAHs. Immobilization is a good choice for the recovery of biomass from reactors once its function of removing contaminants is fulfilled. Alginate is a natural material that is transparent, is permeable and acts as a protective barrier against other microorganisms and harmful particulates suspended in water. Therefore, in this study, we designed and evaluated four mini-bioreactors packed with alginate beads that contain two microalgal species, Selenastrum capricornutum and Scenedesmus acutus which are capable of removing the high-molecular-weight PAHs benzo(a)anthracene and benzo(a)pyrene. One of the bioreactors was a batch reactor with a continuous magnetic stirring tank, and the other bioreactors were enclosed tubular bioreactors operating in semi-continuous mode with two cycles. The influence of parameters such as the reactor shape, stirring speed, flow, number of alginate beads, number of cells and cell species ratio, as well as the time of contact and the use of two operation cycles were studied. The amounts of the remaining PAHs after exposure tests with microalgae were determined. It was found that the shape and the mode of operation of the bioreactor markedly influenced the efficiency of removal. The removal capacity of these mini-bioreactors and the advantages and the disadvantages of using these mini-bioreactors were analyzed.