The investigation of effects of heavy metals and salinity in upflow anaerobic sludge blanket (UASB) reactor

The effects of heavy metals and salinity on the performance of upflow anaerobic sludge blanket (UASB) reactors were investigated in this study. The study was carried out in the experimental set-up consisted of four upflow anaerobic sludge blanket reactors. Three reactors were used to investigate the effects of heavy metals and salinity, while fourth reactor was intended for control.Copper, chromium and zinc were chosen as tested heavy metal. The study fundamentally consisted of eight stages. In the first stage, to investigate the effects of copper concentrations, the reactors were fed with the synthetic influent containing 25, 100 and 250 mg/L of copper. At this instance, COD, TKN and TP removals were usually higher than those of the control reactor. At the tested three concentrations, copper removals were obtained to be higher than 90%. In the second stage, 300, 375 and 450 mg/L of copper were dosed. COD removals started to decrease at the higher concentrations than 300 mg/L. TKN removals were low, while TP removals were very high compared to control. In the third stage, the higher copper doses (500, 750 and 1000 mg/L of copper) were applied to investigate the effect over-dosing on the process performance. At these concentrations, although COD removals were dramatically decreased, TKN and TP removals were higher than those of the control reactor. Despite the copper removals decreased compared to first stage, it was also obtained the reasonable copper removal efficiencies (>70%).In the fourth stage, the tests related to chromium were begun and 100, 250 and 500 mg/L concentrations of chromium were applied to reactors. COD removals started to decrease as from 100 mg/L of chromium; while TKN and TP removals were higher than those of the control at tested three concentrations. Chromium removals were high at 100, 250 mg/L concentrations of chromium; while they were low at 500 mg/L.In the final stage (fifth stage) interested in heavy metals, the effects of zinc concentrations were investigated. At the reactors dosed 100, 250 and 500 mg/L of zinc, COD removals were high at first two concentrations, while they were low at the latter one. TKN removals were low at 100-250 mg/L concentrations of zinc; they were higher than those of the control at 500 mg/L concentration of zinc. TP removals were higher than those of the control at all of the concentrations. Zinc removals were high at 100, 250 mg/L of zinc; while they were significantly low at 500 mg/L of zinc.After the tests interested in heavy metals were completed, to investigate the effects of salinity, the reactors were fed with the synthetic wastewater containing 10 g/L, 25 g/L and 50 g/L of NaCl in the sixth stage. While COD removals were close to those of the control at 10 g/L of NaCl, they started to decrease at 25 g/L of NaCl and eventually decreased to 30% at 50 g/L of NaCl. TKN and TP removals were lower than those of the control at all of the tested concentrations.In the seventh stage of study, it was investigated the simultaneous effects of heavy metals and salinity. For this aim, two reactors were used in this stage. The first reactor was fed with synthetic wastewater containing 250 mg/L copper, 100 mg/L chromium, 250 mg/L zinc and 10 g/L NaCl and other reactor was used as control. COD and TKN removals were significantly low compared to previous stages; while TP removals were dramatically higher than those of the control. Copper, chromium and zinc removals were up to 90%.At the final stage of the study, to investigate the effects of salinity together with each heavy metal, the reactors were fed with synthetic wastewater containing 250 mg/L copper + 10 g/L NaCl, 100 mg/L chromium + 10 g/L NaCl, 250 mg/L zinc + 10 g/L NaCl, respectively. COD removals at the reactor fed with synthetic wastewater containing chromium and salt were close to those of the stage which chromium was dosed solely, while COD removals for copper and zinc were lower than the previous stages. TKN removals were close to those of stage in which every heavy metal was dosed solely; TP removals for chromium, copper and zinc were respectively close to those of the previous chromium stage, higher than the previous copper stage and lower than the previous zinc stage. Copper and chromium removals were >95%, while zinc removals was high in the beginning (>90%), it gradually decreased with time.