Showing papers by "Qiang He published in 2002"

Induction characteristics of reductive dehalogenation in the ortho -halophenol-respiring bacterium, Anaeromyxobacter dehalogenans

Abstract: Anaeromyxobacter dehalogenans strain 2CP-C dehalogenatesortho-substituted di- and mono-halogenated phenols and couples this activity to growth. Reductive dehalogenation activity has been reported to be inducible, however,this process has not been studied extensively. In this study, theinduction of reductive dehalogenation activity by strain 2CP-C is characterized. Constitutive 2-chlorophenoldechlorination activity occurs in non-induced fumarate-grown cells, with rates averaging 0.138 μmol of Cl- h-1 mg of protein-1. Once induced, these cultures dechlorinate 2-chlorophenol (2-CP) at rates as high as 116 μmol of Cl-1 h-1 mg of protein-1. Dechlorination of 2-CP is induced by phenol,2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol,and 2-bromophenol. Of the substrates tested, 2-bromophenol shows the highestinduction potential, yielding double the 2-chlorophenol dechlorination rate when compared to other inducing substrates. No induced dechlorination is observed at concentrations less than5 μM 2-CP. When fumarate cultures were diluted 100-fold, fumarate reduction rates were reduced roughly according to the dilution factor, while dechlorination rates were similar in fumarate grown cells amended with 2-CP and cells diluted 100-fold prior to the addition of chlorophenol. This indicates that the majority of the fumarate-grown cells in late log phase were not induced when exposed to inducing substrates such as 2-CP. This observation may have ramifications on the success of bioaugmentation using halorespiring bacteria, which traditionally relies on growing culturesusing more readily utilized substrates. The rapid dechlorination rate and unique induction pattern also make strain 2CP-C a promising model organism for understanding the regulationof reductive dehalogenation at the enzymatic level.

Performance Variations of COD and Nitrogen Removal by Vegetated Submerged Bed Wetlands

Abstract: Vegetated submerged bed wetlands can supplement treatment of onsite wastewater systems. This study evaluated vegetation, media, and seasonal impacts on system performance in six meso scale rock plant filters with and without narrow leaf cattails (Typha augustifolia). Daily chemical oxygen demand (COD) reductions in planted cells averaged 85 percent and weekly total nitrogen (TN) reductions averaged 50 percent. Planted cells had 17 percent greater COD reduction and 76 percent greater TN reduction than unplanted cells, both significant differences. Media type affected COD reduction, particularly in unplanted cells. COD treatment in planted cells was highest for fine crushed limestone (87±13 percent) and least variable for coarse river gravel (85±11 percent). No significant difference in TN reduction was observed for different media types (48 to 51 percent range). Seasonal influences on treatment included a significant decrease during late fall and early spring and a significant increase with temperature. After a step increase in organic loading, treatment efficiency decreased sharply but returned to prior levels after an adaptation period of about one month. Planted cells not only exhibited higher treatment efficiency but also had a retarded organic matter breakthrough, appearing after three to seven times the period for a bromide tracer. This supports a hypothesis that retardation of contaminant movement through the treatment cells results in enhanced removal. These results support the use of rock plant filters, but demonstrate the need to account for performance variations in system design. (KEY TERMS: constructed wetlands; seasonal effects; subsurface flow; Typha augustifolia; onsite wastewater treatment; water quality.)

Assessing removal kinetics of organic matter in rock–plant filters

Abstract: Rock–plant filter wetlands are a potential alternative to supplement onsite wastewater treatment systems. A plug–flow with dispersion (PF/D) model and an ideal plug–flow (IPF) model combined with first–order kinetics were tested for the prediction of treatment performance in rock–plant filters. Six meso–scale rock–plant filters growing narrow–leaf cattails (Typha augustifolia) were studied to verify the models with actual internal performance data. Tracer studies were conducted during summer, fall, and spring to estimate effective values of model parameters. First–order kinetics was applicable for organic matter removal, but the effective rate constant (KT,eff) values were consistently less than empirical design rate constant (KT,emp) values when plants were not dormant. The KT,eff in planted cells showed less temperature dependence than expected, in one case varying as little as from 0.0310 to 0.0324 h–1 throughout the year. This might have resulted from the offsetting effect of prolonged hydraulic retention time caused by evapotranspiration when temperature increased. Both IPF and PF/D models were reasonably accurate for performance prediction, but the increased complexity in the PF/D model resulted in little improvement in performance prediction. The accuracy of the IPF model was enhanced by using effective data derived from tracer studies, which reduced least square errors up to 90% compared to using the same model with empirical design values. Seasonal effects were not significant when using media of smaller particle size. Plants also contributed to the reduction in temperature dependence in treatment performance. The results of this study verified that the first–order IPF model could reasonably predict treatment performance.