Avaliação de reatores fototróficos e aeróbio na oxidação biológica de sulfeto

Odour emissions in UASB reactors are mainly related to hydrogen sulphide, produced during the reduction of sulphate present in domestic wastewater. This study evaluated the performance of two phototrophic reactors as alternative to post-treat the effluent of UASB reactor applied to the treatment of domestic wastewater, focusing on sulphide oxidation to elemental sulphur. The phototrophic reactors were operated with or without packing material (polypropylene rings) and different hydraulic retention times (HRT), 6h, 4h and 2h. The performance of an aerobic reactor (THIOPAQ®) and the feasibility of phototrophic and aerobic reactors under different operational conditions were also evaluated. The results obtained for both reactors showed high median sulphide removal efficiencies at the HRT of 6 h, 92% and 75%, for the reactor without and with packing material, respectively. Biological oxidation of sulphide was observed in both reactors for all tested operational conditions, however higher elemental sulphur concentrations were observed in reactor with packing material than in control reactor for all HRT tested. The highest effluent quality was obtained for the packed reactor, with COD and TSS values below 105 mgCODtotal.L-1 and 30 mgTSS.L-1, respectively. Differences among nitrogen compounds determined in the effluent of bioreactors and the UASB reactor effluent were not observed. Purple bacteria were microscopically observed and sulphur bacteria similar to Chlorobaculum sp. and Thiocapsa sp. were identified by PCR-DGGE analysis. Expressive differences in microbial diversity between the bioreactors were not observed, yet slightly higher diversities were observed at the HRT of 6 h. In relation to the high sulphide loading reactor THIOPAQ®, it was observed that operational conditions (i.e. HRT and nutrients concentration) have influence on the stability and performance of the system. The results of this research showed the potentiality of using phototrophic bioreactors to post-treat the effluent of UASB reactors treating domestic wastewater, aiming at the partial oxidation of sulphide to elemental sulphur and the overall improvement of the effluent quality. Additionally, it is possible to state that the introduction of modifications on the natural conditions naturally present in the reactors would probably result in the improvement of the levels of sulphide oxidation to elemental sulphur.