Portal de Periódicos da CAPES

Revue des reactions des algues aux micropolluants mineraux et organiques; consequences ecologiques et possibilites d'applications industriellesAlgae reactions to mineral and organic micropollutants, ecological consequences and possibilities for industrial-scale application: a review

1986; Elsevier BV; Volume: 20; Issue: 4 Linguagem: Francês

10.1016/0043-1354(86)90186-7

1879-2448

P Mouchet,

Chromium effects and bioremediation

Quand les métaux lourds ne sont pas directement accumulés dans les algues, ils sont souvent complexés par leurs métabolites extracellulaires pour former des composés organo-métalliques. Quant aux micropolluants organiques (phénols, hydrocarbures, pesticides, etc.), il sont soit également absorbés par les algues, soit métabolisés en produits qui sont en général inoffensifs, mais dont certains peuvent être parfois plux toxiques que le composé initial. Les conséquences écologiques de ces phénomènes présentent des aspects positifs ou négatifs suivant le cas. D'autre part, l'ensemble de ces observations effectuées en laboratoire ou dans le milieu naturel pourrait déboucher sur des applications dans de nouveaux traitements biologiques d'effluents industriels, basés sur des souches d'algues sélectionnées et mis en oeuvre soit dans des lagunes classiques, soit dans des procédés plus intensifs. Si ces derniers n'en sont encore qu'au stade du pilote, le lagunage naturel est une technique qui est maintenant éprouvée; par contre, ses applications antérieures souffraient déjà souvent d'une absence de traitement complémentaire des effluents, pour éliminer les algues et éventuellement les récupérer dans le but d'une valorisation énergétique ou alimentaire; dans les cas envisagés ici, ce complément de traitement serait indispensable pour protéger le milieu récepteur non seulement contre les algues elles-mêmes, mais aussi contre les micropolluants qu'elles auraient accumulés. Les principaux procédés disponibles pour la récolte des algues sont passés en revue: aucun d'entre eux n'est universel, ce qui explique la diversité des opinions. Suivant les cas, le microtamisage, la filtration directe, la séparation par membranes, la décantation accélérée à contact de boues et surtout la flottation à air dissous pourraient trouver des applications intéressantes dans ce domaine. An aquatic ecosystem may react to pollution in different ways, some of which combat the pollution actively; in particular, algae participate therein by developing various substances capable of complexing or degrading numerous organic or mineral pollutants. When heavy metals are not directly accumulated in algae, they can often be complexed by their extracellular metabolites (Hart, 1981), e.g. hydroxamates (McKnight and Morel, 1980; Jardim and Pearson, 1984), to form organo-metallic compounds; the ecological consequences of these phenomena, most often due to the presence of Cyanophyceae (Walsby, 1974), are varied: Useful effects: greater assimilability of certain indispensable trace elements (Provasoli et al., 1957; Johnston, 1964; Allen, 1976; Murphy et al., 1976; Gaechter et al., 1978), reduced toxicity of heavy metals brought in by pollution (Barber, 1973), etc.; Harmful effects: among others, antagonistic action against copper-based algaecidal treatments (Gaechter et al., 1978; Gnassia-Barelli et al., 1978; Van den Berg et al., 1979; McKnight and Morel, 1980). Organic micropollutants are often metabolized or even assimilated by algae, for instance: Hydrocarbons: assimilation by marine algae such as the diatom Chaetoceros calcitrans (Boutry et al., 1977a, b), or by fresh water algae (Krauss et al., 1973; Schroeder and Rehm, 1981a, b); Phenols: metabolization which can go as far as to completely remove them (Werner and Pawlitz, 1978; Stom et al., 1978), through the action of phenoloxidases which induce the formation of transient degradation products, in particular quinones (Stom et al., 1978); Pesticides: these more stable compounds are most often accumulated in algae (Soedergren, 1968; Vance and Drummond, 1969); however, certain algae are capable of causing their partial degradation (Miyazaki and Thorsteinson, 1972; Neudorf and Khan, 1975; Werner and Moerschel, 1978; Goulding and Ellis, 1981), but this may result in the temporary appearance of metabolites more toxic than the initial product (e.g. DDE from DDT); PCBs: these still more stable micropollutants are fixed, without being metabolized, by living algae (Keil et al., 1971; Veber, 1980), and even dead ones (Urey et al., 1976). The various reactions we have just seen above explain that in nature, certain algae prove specifically tolerant to various industrial wastes that contain mineral pollutants (Madgwick and Ralph, 1977; Say et al., 1977; Palmer, 1980; Strong et al., 1982), or organic pollutants (Palmer, 1980; Walsh et al., 1982). These observations, made both in the laboratory and in the field, could well lead to new applications in the biological treatment of industrial waste water; such possibilities have already been proved for vascular plants, for instance for the removal of heavy metals (Wolverton, 1975a, b and c; Tridech et al., 1981; Muramoto and Oki, 1983) or phenols (Seidel, 1965; Seidel and Kickut, 1967; Karaseva and Papchenkov, 1974; Kaminskii and Gvozdeva, 1976; Stom et al., 1978). The new generation of biological treatments of industrial effluents will be based on selected algae species acting in symbiosis with bacteria (Yurovskaya et al., 1968; Bagnyuk et al., 1975) in traditional lagooning or through more intensive processes, e.g. "activated algae" (McGriff and McKinney, 1971; McKinney et al., 1971) or cultures of algae immobilized in agar beads (Pore and Sorenson, 1981) or on rotating discs (Przytocka-Jusiak et al., 1984b), etc. Where the latter are still in the pilot plant stage, natural lagooning is now a tried-and-tested technique which has already been applied to certain industrial effluents (Lee et al., 1978; Palmer, 1980; Rebattu, 1981; Altona et al., 1983), but without previous selection of the species of algae to be used: they will be selected as a function of their ability to remove pollutants: either by bioaccumulation as for heavy metals (Filip et al., 1979; Shumate et al., 1980; Nakajima et al., 1981; Becker, 1983) or pesticides or else by metabolization and/or assimilation as for phenols (Stom et al., 1978), nitrogen-laden effluents (Matusiak et al., 1976, 1977; Przytocka-Jusiak et al., 1984a, b), hydrocarbons, etc. In addition, it should be pointed out that in its conventional applications, natural lagooning often suffered from the lack of additional clarification of the effluent; the latter may contain over 100 mg 1−1 of residual algae (Shelef et al., 1972; Bratby and Marais, 1974; Harris et al., 1977; Russell et al., 1983; Przytocka-Jusiak et al., 1984a), which then bring in a high additional BOD5, especially after their death (Varma and Digiano, 1968; King et al., 1970; Rance Bare et al., 1975; Friedman et al., 1977; McGimpsey, 1978). Therefore, it is always more advisable to remove the algae and possibly use them as a source of energy or food. In the cases studies here, this additional treatment would be absolutely essential to protect the receiving water not only from the algae themselves, but also from the micropollutants that they would have accumulated. The different processes available for harvesting algae are listed: filtration through sand (Harris et al., 1977; Filip et al., 1979; Russell et al., 1983), microstraining (Kormanik and Cravens, 1978 and 1979; Cravens and Lauritch, 1982; Harrelson and Cravens, 1982), dissolved air flotation (Van Vuuren et al., 1965; Funk et al., 1968; Bratby and Marais, 1974; Rance Bare et al., 1975; Stone et al., 1975; Shelef, 1982; Viviers and Briers, 1982), sedimentation (Friedman et al., 1977), separation through microfiltration or ultrafiltration membranes (Shelef et al., 1972; Castelas et al., 1984), etc. In fact, there is not one system which is universally applicable: this explains the wide-ranging opinions on the subject. Depending on the case, microstraining, direct filtration, accelerated settling with sludge contact, membrane technology and above all dissolved air flotation may well be usefully applied in this field. The performances of the various processes are examined, and several principles for the choice of a method of separation of algae as a function of local conditions are proposed.