Browsing by Author "Zhang, Weiyan"

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Degradation of xenobiotic compounds in situ: capabilities and limits
(1994-10) Bouwer, Edward J.; Durant, N.; Wilson, L.; Zhang, Weiyan; Cunningham, Alfred B.
Exploiting microorganisms for remediation of waste sites is a promising alternative to groundwater pumping and above ground treatment. The objective of in situ bioremediation is to stimulate the growth of indigenous or introduced microorganisms in regions of subsurface contamination, and thus to provide direct contact between microorganisms and the dissolved and sorbed contaminants for biotransformation. Subsurface microorganisms detected at a former manufactured gas plant site contaminated with coal tars mineralized significant amounts of naphthalene (8–43%) and phenanthrene (3–31%) in sediment-water microcosms incubated for 4 weeks under aerobic conditions. Evidence was obtained for naphthalene mineralization (8–13%) in the absence of oxygen in field samples. These data suggest that biodegradation of these compounds is occurring at the site, and the prospects are good for enhancing this biodegradation. Additional batch studies demonstrated that sorption of naphthalene onto aquifer materials reduced the extent and rate of biodegradation, indicating that desorption rate was controlling the biodegradation performance.
Mineral formation during bacterial sulfate reduction in the presence of different electron donors and carbon sources
(2016-04) Han, Xiqiu; Schultz, Logan N.; Zhang, Weiyan; Zhu, Jihao; Meng, Fanxu; Geesey, Gill G.
Sulfate-reducing bacteria have long been known to promote mineral precipitation. However, the influence of electron donors (energy sources) and carbon sources on the minerals formed during sulfate reduction is less well understood. An investigation was therefore undertaken to determine how these nutrients affect sulfate reduction by the bacterium Desulfovibrio alaskensis G20 in a marine sediment pore water medium. Monohydrocalcite and a small amount of calcite formed during sulfate reduction with formate as the electron donor; Mg-phosphates and calcite precipitated when hydrogen served as the electron donor and when acetate and dissolved inorganic carbon served as carbon sources; and greigite and elemental sulfur were deposited when lactate was used as the electron donor and carbon source. The experimental results were generally consistent with geochemical modeling, suggesting that it may be possible to predict the processes and conditions during formation of these minerals in natural environments.