| Title |
Removal of Nitroaromatic Compounds from Artificial Groundwater by Granular Activated Carbon ( GAC ) : 1 . The Effects of Dissolved Oxygen and Pretreatment of GAC |
| Abstract |
The impacts of dissolved oxygen on the removal of phenolics (phenol, o-nitrophenol (ONP) , and 2, 4-dinitrophenol (DNP)) by granular activated carbon (GAC) from an artificial groundwater were investigated with isotherm, rate, and extraction experiments. The isotherm experiments were conducted at pH 4 and pH 7.5 under oxic and anoxic conditions. Pretreatment of GAC with a reductant (Fe(Ⅱ)) were conducted to determine whether sorption of target compounds by GAC could be improved. The removal of target compounds by virgin GAC was somewhat affected by the presence of dissolved oxygen, particularly phenol and DNP. Removal of phenol and DNP was enhanced by at least 200%. Pretreatment of GAC deteriorated the sorption of phenol but improved sorption of ONP and DNP, except for DNP at pH 7.5 under oxic condition. Sorption of these compounds with pretreated GAC was also affected by the presence of dissolved oxygen and solution pH. Sorption rate experiments were conducted at pH 4 under oxic and anoxic conditions followed by GAC extractions using a microscale Soxhlet extraction apparatus. Sorption rates of phenol and DNP were very similar: That is, the approach to equilibrium in the presence of dissolved oxygen was longer than in the absence of dissolved oxygen. However, the sorption of ONP was not changed greatly by the presence of dissolved oxygen. GAC extraction efficiencies for phenol sorbed under oxic conditions were decreased with increasing contact time whereas extraction efficiencies for anoxic conditions did not show such a considerable trend. Extraction efficiencies of ONP and DNP from GAC showed a trend that decreased with increasing contact times from the GACs sorbed under both oxic and anoxic conditions. A plausible explanation for the observed results in the experiments for sorption rate and extraction is that there were some chemical reactions other than oxidative coupling occurred on GAC surfaces in the presence/absence of dissolved oxygen. |