Abstract:
The purpose of this thesis is to study the microbial behavior of anaerobic baffled reactor (ABR) and the removal efficiency of nitrate and sulfate from the synthetic wastewater. The experiments had been divided into two phases. In the first phase, three experimental runs had been performed at the same time using 3 separate reactors. There are no covers for all reactors and each reactor has 16 liters of working volume which divided into 4 equal-volume compartments and operated with 2 day-HRT. The reactors were initially seeded with anaerobic digested sludge and fed with the synthetic wastewater prepared from tap water using sugar as a carbon source. Three reactors were operated separately at varied COD/NOx-N (Nitrate + Nitrite) ratio of 1.43±0.23, 5.49±0.62 and 10.37±0.74 mgCOD/mgN respectively, and also at COD/Sulfate ratios of 0.65±0.11, 2.52±0.23 and 4.77±0.23 mgCOD/mgSO42-, respectively. It was found that the highest efficiency of nitrate and sulfate removal was obtained under the condition of COD/NOx-N ratio of 5.49±0.62. Nitrate was almost removed in the second compartment of reactor, while roughly 48% of sulfate could be removed in the forth compartment. On the contrast, under COD/NOx-N ratio about 1.43±0.23, significant concentration of nitrite was detected. This suggests the uncompleted denitrification due to insufficient COD. However, under COD/NOx-N ratio of 10.37±0.74, the sulfate removal efficiency could be less than 10%, it seemed to have inhibitory effect on sulfate reduction. In the second phase of work, effect of ferric iron addition was examined by varying two Fe3+: COD ratios of 0.02 and 0.10 mgFe/gCOD. The experimental results revealed that higher amount of ferric iron addition (Fe3+: COD = 0.10 mgFe/gCOD) could remarkably improve the efficiency of sulfate removal. In addition, under lower amount of ferric iron addition, the results suggested that significant amount of nitrate was reduced via the process of Dissimilatory Nitrate Reduction to Ammonia (DNRA) in the first compartment. Therefore, the amount of iron addition might affect on the shift between denitrification and DNRA.