Kerry N. McPhedran

Effect of Media on Biofilter Performance Following Ozonation of Secondary Treated Municipal Wastewater Effluent: Sand vs. GAC

Ozone has been shown to be effective in the transformation of several chemicals of emerging concern that escape the wastewater treatment process, but there is concern whether toxic transformation products are formed. Two parallel biofilter columns with granular activated carbon (GAC) and filter sand following a pilot-scale ozone unit to treat secondary treated municipal wastewater were studied. Results show reduced wastewater genotoxicity following ozonation and further reduction following biofiltration. The BAC biofilter outperformed the sand biofilter in terms of reduction in both organics and genotoxicity. Biofilter performance correlated with biological indicators (dissolved oxygen reduction and effluent E. coli counts) but not with ATP bioactivity measurements. Limited bacterial (E. coli) regrowth was observed in treated effluent from both biofilters.

Evaluation of the gas stripping technique for calculation of Henry's law constants using the initial slope method for 1,2,4,5-tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene.

Henrys law constant (HLC) is an important factor used in environmental risk assessment and fate and transport models to describe mass transfer of chemical between water and air. HLCs and structure-property relationships were assessed for 1,2,4,5-tetrachlorobenzene (TeCB), pentachlorobenzene (PeCB), and hexachlorobenzene (HCB). HLCs were determined using the volatilization rate (kv) of sparged chemical at 25 °C. Despite the assumption that kv should be constant throughout the stripping duration, results indicated that kv decreased over time according to three separate slope regions. Results of ANCOVA indicate that kv is statistically different in the third slope region, which leads to the conclusion that use of the entire stripping data set would lead to biased HLCs. This decrease in kv may be attributed to desorption from sparger surfaces, which has not been considered widely in the literature. Statistical analysis was possible because of the robustness of the current experimental procedure which included numerous replications (15 total spargers) and extensive data points available to discern key slope changes. HLCs determined using the gas stripping technique were 57, 33, and 30 Pa m(3) mol(-1) for 1,2,4,5-TeCB, PeCB, and HCB, respectively. In comparison to literature values, current TeCB and HCB HLCs were within wide reference ranges spanning approximately an order of magnitude for each chemical. PeCB HLC of the current study was two times lower than the lowest reference data.