Biorefractory Compounds Research Articles

Oxidation of sorbed hexachlorobenzene in soils using catalyzed hydrogen peroxide

The Fenton-like oxidation of a highly hydrophobic and biorefractory compound, hexachlorobenzene, was investigated in silica sand and a natural soil using a number of process conditions including catalysis by soluble iron and naturally-occurring iron minerals coupled with a range of hydrogen peroxide concentrations from 3 mM to 300 mM (100 mgl−1 to 10 000 mgl−1). In addition, hexachlorobenzene desorption rates were quantified and compared to the rates of oxidation. Using soluble iron and peroxide concentrations ⩾ 100 m1M, sorbed hexachlorobenzene was oxidized more rapidly than the measured desorption rate, indicating that it may have been, in part, oxidized on the surface of the silica sand. The results suggest that hydroxyl radicals may cross the liquid-solid interface under aggressive reaction conditions. Alternatively, the aggressive Fenton-like reaction conditions may alter the hexachlorobenzene sorption characteristics and increase its rate of desorption resulting in an enhanced coupled desorption-oxidation mechanism.In the second phase of study using natural iron minerals as the catalyst, hexachlorobenzene was oxidized more slowly than it was desorbed. The probable mechanism for mineral-catalyzed oxidation is desorption followed by oxidation through a Fenton-like process at the mineral surface. In the treatment of a natural sandy loam soil, hexachlorobenzene was oxidized at rates slower than it was desorbed. The most efficient process condition (mineral-catalyzed oxidation) was optimized using a central composite rotatable factorial design analysis. These experiments showed that maximum hexachlorobenzene removal occurred with H2O2 concentrations of 3 to 5 mM and slurry volumes of 25 to 30 times the field capacity of the soil.

Ozone Assisted Biological Treatment Of Industrial Wastewaters Containing Biorefractory Compound

Ozone pretreatment studies of organic compounds that are difficult to biodegrade were conducted to evaluate the effects of ozonation on biodegradability of these compounds. Initial testing was conducted in batch activated sludge experiments with and without preozonation to evaluate the impacts of ozonation on the ultimate BOD/COD and ultimate BOD/TOC ratios of these compounds. Experimental results indicated wastewater preozonation to be an effective pretreatment step for some compounds, ineffective for other compounds and detrimental to biological treatment of still other compounds. These same compounds were then investigated in continuous flow, complete–mix activated sludge systems. Complete material balances, including influent, effluent, waste sludge and off–gas specific compound analyses, were conducted so that the actual fate of the compound could be determined. Removal mechanisms of the ozonated or unozonated compound were then determined to be biodegradation, stripping, or sorption to the biomass. ...