Controls and rates of acid production in commercial-scale sulfur blocks.

Acidic drainage (pH 0.4-1.0) from oxidizing elemental sulfur (S(0)) blocks is an environmental concern in regions where S(0) is stockpiled. In this study, the locations, controls, and rates of H(2)SO(4) production in commercial-scale S(0) blocks ( approximately 1-2 x 10(6) m(3)) in northern Alberta, Canada, were estimated. In situ modeling of O(2) concentrations ([O(2)]) suggest that 70 to >97% of the annual H(2)SO(4) production occurs in the upper 1 m of the blocks where temperatures increase to >15 degrees C during the summer. Laboratory experiments show that S(0) oxidation rates are sensitive to temperature (Q(10) = 4.3) and dependent on the activity of autotrophic S(0)-oxidizing microbes. The annual efflux of SO(4) in drainage water from a S(0) block (5.5 x 10(5) kg) was within the estimated range of SO(4) production within the block (2.7 x 10(5) to 1.2 x 10(6) kg), suggesting that H(2)SO(4) production and removal rates were approximately equal during the study period. The low mean relative humidity within the block (68%; SD = 17%; n = 21) was attributed to osmotic suction from elevated H(2)SO(4) concentrations and suggests a mean in situ pH of approximately -2.1. The low pH of drainage waters was attributed to the mixing of fresh infiltrating water and low-pH in situ water. Heat generation during S(0) oxidation was an important factor in maintaining elevated temperatures (mean, 11.1 degrees C) within the block. The implications of this research are relevant globally because construction methods and the physical properties of S(0) blocks are similar worldwide.

Microbial response to environmental gradients in a ceramic-based diffusion system.

A solid, porous matrix was used to establish steady-state concentration profiles upon which microbial responses to concentration gradients of nutrients or antimicrobial agents could be quantified. This technique relies on the development of spatially defined concentration gradients across a ceramic plate resulting from the diffusion of solutes through the porous ceramic matrix. A two-dimensional, finite-element numerical transport model was used to predict the establishment of concentration profiles, after which concentration profiles of conservative tracers were quantified fluorometrically and chemically at the solid-liquid interface to verify the simulated profiles. Microbial growth responses to nutrient, hypochloride, and antimicrobial concentration gradients were then quantified using epifluorescent or scanning confocal laser microscopy. The observed microbial response verified the establishment and maintenance of stable concentration gradients along the solid-liquid interface. These results indicate the ceramic diffusion system has potential for the isolation of heterogeneous microbial communities as well as for testing the efficacy of antimicrobial agents. In addition, the durability of the solid matrix allowed long-term investigations, making this approach preferable to conventional gel-stabilized systems that are impeded by erosion as well as expansion or shrinkage of the gel.