Tratamento de efluente da produção de biodiesel utilizando processos físico-químicos e reações de Fenton

Abstract

In this work, the treatment of biodiesel wastewater by physical-chemical and Fenton reactions was evaluated. Firstly, the physical-chemical processes were evaluated, being compared the use of two inorganic coagulant FeCl3 and Al2(SO4)3, and determined the optimal conditions of the operational parameters (dosages of the coagulant ions, initial pH of solution, treatment time, aeration and stirring) by response surface methodology, monitoring the removal of turbidity as response factor. The optimized condition to Al3+ was 243 mg L-1 of the coagulant ion Al3+, initial pH of solution 9.6, and 70 minutes of treatment time while for Fe3+ the best condition was 56 mg L-1 of the coagulant ion Fe3+, initial pH of solution 5.0 and 53 minutes of treatment time, both in the presence of stirring and aeration. The treatment with Al3+ was applied in all the matrix due to the removal of observed toxicity, besides not being necessary the initial pH adjustment of the effluent. Under optimized conditions, the efficiency of both coagulants was evaluated in turbidity removal, color removal, suspended solids and oil & grease removal, being obtained high efficiency, between 82 and 99%. On the other hand, an inefficient removal of organic matter was observed, since there was 20 and 35% removal of dissolved organic carbon (DOC) and chemical oxygen demand (COD) removal were obtained, respectively. These results show the necessity of coupling with other treatment for degradation of the organic matter. In this context, advanced oxidation processes were combined with the physical-chemical process for the mineralization of organic matter. The contribution to the reduction of organic matter by evaporation of methanol and ethanol was also evaluated. The efficiency of the degradation process was monitored by removal of the organic matter given by decay of DOC, COD, consumption of H2O2 and total dissolved iron. Different H2O2 concentrations (500 - 4000 mg L-1) and Fe2+ (15, 25, 50 and 100 mg L-1) were evaluated, and, among the concentrations evaluated, the best removal of organic matter was obtained using 3500 mg L-1H2O2 and 25 mg L-1 Fe2+. The development of acute toxicity for Vibrio fischeri and biodegradability was also monitored in order to compare the viability of the process. There was an increase in toxicity during application processes, however, after 24 hours of photo-Fenton experiment the toxicity became similar to the initial sample. Based on these results, it can be observed that the coupling between the physical and chemical processes and photo-Fenton is a good alternative for the treatment of the effluent, since the physical-chemical process is effective for reduction of turbidity, color, sound suspended and oils & greases, while the photo-Fenton process is effective for the degradation of organic matter, occurring simultaneously degradation and volatilization.