Browsing by Author "Chen, Ching-I"

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Analysis of biofilm disinfection by monochloramine and free chlorine
(1993) Griebe, Thomas; Chen, Ching-I; Srinivasan, Rohini; Stewart, Philip S.
Biocide action of monochloramine on biofilm systems of pseudomonas aeruginosa
(1993-01) Chen, Ching-I; Griebe, Thomas; Characklis, William G.
Monochloramine was used to inactivate biofilm cells of Pseudomonas aeruginosa. Experimental results indicated that the clean RotoTorque system had no monochloramine demand. The dose of 4 mg·l−1 killed in situ biofilm cells more than 99·99% within 60 min, while the dose of 3 mg·l−1 killed 80% and the dose of 2 mg·l−1 showed no significant killing. Computations of pseudo steady state surface gradient of monochloramine and the observable modulus indicated that there was no marked mass transfer resistance in the biofilm for the 4 mg·l−1 treatment, moderate mass transfer resistance for the 3 mg·l−1 treatment, and high mass transfer resistance for the 2 mg·1−1 treatment. Mass transfer resistance within the biofilm impacts the biocide performance.
Biofilm parameters influencing biocide efficacy
(1995-06) Srinivasan, Rohini; Stewart, Philip S.; Griebe, Thomas; Chen, Ching-I; Xu, Xiaoming
The influence of biofilm areal cell density, species composition, and the presence of abiotic particles on the disinfection and removal of bacterial biofilms by monochloramine was investigated. Mono- and binary population biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown on stainless-steel slides in a continuous flow annular reactor. Biofilms were treated in the reactor with a pulse/step dose of 4 mg/L monochloramine for 2 h. Biofilm samples were disaggregated and assayed for colony formation on R2A agar and for total cell numbers by acridine orange direct counts. These data were used to determine apparent first order rate coefficients for the processes of disinfection and detachment. Disinfection rate coefficients exceeded detachment rate coefficients by as much as an order of magnitude and the two coefficients were poorly correlated (r = 0.272). The overall decay rate coefficient (disinfection plus detachment) depended strongly on the initial biofilm areal cell density. It displayed a parabolic dependence on cell density with a maximum near 108 cfu/cm2. This result points to multiple factors influencing biofilm susceptibility to antimicrobial challenge. Decay rates of K. pneumoniae measured in binary population biofilms were comparable with those measured in monopopulation biofilms (p = 0.61). P. aeruginosa decayed more slowly in biofilsm dominated by K. pneumoniae (p = 0.028), indicating some interaction between species. The presence of kaolin and calcium carbonate particles in the biofilm reduced disinfection efficacy. © 1995 John Wiley & Sons, Inc.
Characterization of microbial souring in berea-sand porous medium with a north sea oil field inoculum
(1996-04) Chen, Ching-I; Reinsel, Mark A.
Microbial souring (H2S production) in porous medium was investigated in an anaerobic upflow porous medium reactor at 60°C using produced waters obtained from the North Sea Ninian oilfield as the inoculum. Multiple carbon sources commonly found in oil field waters (formate, acetate, propionate, iso‐ and n‐butyrates) with inorganic sulfate as the electron acceptor were used as the substrates. Stoichiometry and the rate of souring in the reactor column were calculated. A large proportion of H2S was trapped in the column as FeS and possibly as a gas phase. Concentration gradients for the substrates (organic acids and sulfate) and H2S were generated along the column. At steady state, the highest volumetric substrate consumption and H2S production were found at the front part (inlet) of the reactor column. The average volumetric sulfate reduction rate after H2S production had stabilized was calculated to be 203 ± 51 mg sulfate‐S.l‐1.d‐1. Comparison of the results with the authors’ previous work on the Alaska Kuparuk oilfield waters indicates that the two different microbial inocula (produced waters) exhibited the same experimental trends (rates and location) for souring in the experimental reactor system. This indicates that abiotic factors, as well as microbial parameters, may play an important role for microbial souring in the system.
Effects of various metal substrata on accumulation of pseudomonas aeruginosa biofilms and the efficacy of monochloramine as a biocide
(1993-11) Chen, Ching-I; Griebe, Thomas; Srinivasan, Rohini; Stewart, Philip S.
Kinetic analysis of microbial sulfate reduction by desulfovibrio desulfuricans in an anaerobic upflow porous media biofilm reactor
(1994-02) Chen, Ching-I; Mueller, Robert Franz; Griebe, Thomas
An anaerobic upflow porous media biofilm reactor was designed to study the kinetics and stoichiometry of hydrogen sulfide production by the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans (ATCC 5575) as the first step for the modeling and control of formation souring (H2S) in oil field porous media. The reactor was a packed bed (50 × 5.5 cm) tubular reactor. Sea sand (140 to 375 μm) was used as the porous media. The initial indication of souring was the appearance of well-separated black spots (precipitates of iron sulfide) in the sand bed. The blackened zones expanded radially and upward through the column. New spots also appeared and expanded into the cone shapes. Lactate (substrate) was depleted and hydrogen sulfide appeared in the effluent. Analysis of the pseudo–steady state column shows that there were concentration gradients for lactate and hydrogen sulfide along the column. The results indicate that most of the lactate was consumed at the front part of the column. Measurements of SRB biomass on the solid phase (sand) and in the liquid phase indicate that the maximum concentration of SRB biomass resided at the front part of the column while the maximum in the liquid phase occurred further downstream. The stoichiometry regarding lactate consumption and hydrogen sulfide production observed in the porous media reactor was different from that in a chemostat. After analyzing the radial dispersion coefficient for the SRB in porous media and kinetics of microbial growth, it was deduced that transport phenomena dominate the souring process in our porous media reactor system.
Kinetic investigation of microbial souring in porous media using microbial consortia from oil reservoirs
(1994-07) Chen, Ching-I; Reinsel, Mark A.; Mueller, Robert Franz
Microbial souring (H2S production) in porous media was investigated in an anaerobic upflow porous media reactor at 60°C using microbial consortia obtained from oil reservoirs. Multiple carbon sources (formate, acetate, propionate, iso- and n-butyrates) found in reservoir waters as well as sulfate as the electron acceptor was used. Kinetics and rates of souring in the reactor system were analyzed. Higher volumetric substrate consumption rates (organic acids and sulfate) and a higher volumetric H2S production rate were found at the from part of the reactor column after H2S production had stabilized. Concentration gradients for the substrates (organic acids and sulfate) and H2S were generated along the column. Biomass accumulation throughout the entire column was observed. The average specific sulfate reduction rate (H2S production rate) in the present reactor after H2S production had stabilized was calculated to be 11062 ±2.22 mg sulfate-S/day g biomass. © 1994 John Wiley & Sons, Inc.