Fungal biosorption in wastewater treatment: decolourisation and detoxification of textile and tannery effluents

Textile and tannery effluents contribute enormously to water deterioration. Actually they are among the most pollutant wastewaters on account of the considerable amount of suspended solids, salts, heavy metals and of their high COD, due to the massive presence of weakly biodegradable and very toxic substances such as dyes and surfactants. Moreover, since these wastewaters exhibit large fluctuations in terms of quantities and pollution load, pH and temperature, they are not adequately treated in conventional wastewater treatment plants and, therefore, pollutants accumulate in the environment. All known physico-chemical techniques tested so far present some drawbacks, since they are not always applicable and/or effective. Biosorption, is the most promising option for the removal of pollutants from aqueous streams because of its cost effectiveness and the possibility to treat large water volumes. Among the different biosorbents tested so far, fungal biomass has proved to be particularly suitable. In this Thesis, the biomasses of three fungal strains, Rhizopus stolonifer, Rhizomucor pusillus and Cunningamella elegans, were tested in the biosorption treatment of textile and tannery wastewaters, proving to be effective towards a wide variety of effluents characterized by different classes of dyes, different dye concentrations, additives, salts and pH values. C. elegans was investigated in greater detail, optimizing the culture conditions with two aims: to enhance the biomass production and the biosorption of pollutants. The biomass cultured on starch performed the best, in terms of production costs, detoxification, COD and salt removal and decolourisation yields, thanks to the presence of many different functional groups that can bind molecules. Such versatility, jointed to a very timely fashion effectiveness, has never been reported for any biosorbent and it is an essential feature for any in field application. Moreover, in order to confer robustness and stability to the biomass, C. elegans was subjected to chemical and physical pre-treatments, among which the lyophilization process provided very stable and porous biomass, which fasten the biosorption process irrespective of the biomass particle size. The optimized biomass resulted more competitive and versatile than other promising alternative biosorbents, such as industrial waste fungal biomasses and chitosan, which could be attractive from an economical point of view. Thus, C. elegans biomass was exploited in the treatment of spent dye baths and in different stages of the wastewater treatment plant, giving excellent results in both cases. In conclusion, C. elegans biomass is a promising candidate for the decolourisation and detoxification of textile and tanning wastewaters and the high applicative potential of C. elegans brought to an European patent deposition.