Alireza Habibi

Degradation of formaldehyde at high concentrations by phenol-adapted Ralstonia eutropha closely related to pink-pigmented facultative methylotrophs

The ability of the phenol-adapted Ralstonia eutropha to utilize formaldehyde (FD) as the sole source of carbon and energy was studied. Adaptation to FD was accomplished by substituting FD for glucose in a stepwise manner. The bacterium in the liquid test culture could tolerate concentrations of FD up to 900 mg L−1. Degradation of FD was complete in 528 h at 30°C with shaking at 150 rpm (r = 1.67 mg L−1 h−1), q = 0.035 gFD gcell −1 h−1. Substrate inhibition kinetics (Haldane and Luong equations) are used to describe the experimental data. At non-inhibitory concentrations of FD, the Monod equation was used. According to the Luong model, the values of the maximum specific growth rate (μmax), half-saturation coefficient (kS), the maximum allowable formaldehyde concentration (Sm), and the shape factor (n) were 0.117 h−1, 47.6 mg L−1, 900 mg L−1, and 2.2, respectively. The growth response of the test bacterium to consecutive FD feedings was examined, and the FD-adapted R. eutropha cells were able to degrade 1000 mg L−1 FD in 150 h through 4 cycles of FD feeds. During FD degradation, formic acid metabolite was formed. Assimilation of FD, methanol, formic acid, and oxalate by the test bacterium was accompanied by the formation of a pink pigment. The carotenoid nature of the cellular pigment has been confirmed and the test bacterium appeared to be closely related to pink-pigmented facultative methylotrophs (PPFM). The extent of harm to soil exposed to biotreated wastewaters containing FD may be moderated due to the association between methylotrophic/oxalotrophic bacteria and plants.

Degradation of formaldehyde in packed-bed bioreactor by kissiris-immobilized Ralstonia eutropha

The ability of the Ralstonia eutropha cells to utilize formaldehyde (FA) as the only source of carbon and energy was studied in the kissiris-immobilized cell bioreactor (KICB) in batch-recirculation and continuous modes of operation. In batch-recirculation experiments, the test bacterium could tolerate concentrations of FA up to 1,400 mg/L at 30°C and aeration rate equal to 0.75 vvm (rS = 7.25 mg/L/h, qS = 0.019 gFA/gcell/h). However, further increase of initial FA concentration resulted in degradation reaction of FA to stop at 1,600 mg/L. Results of continuous mode experiments showed that the biodegradation performance of the KICB was dependent on both feed flow rate and inlet FA concentration parameters. The optimum feed flow rate which corresponded to the highest biodegradation rate (rS = 240.3 mg/L/h) was observed at Q = 18 mL/min when KICB did not operate under the external mass transfer limiting regime. Substrate inhibition kinetics (Edwards and Luong equations) were used to describe the experimental specific degradation rates data. According to the Luong model, the values of the maximum specific degradation rate (qmax), half-saturation coefficient (KS), the maximum allowable FA concentration (Sm), and the shape factor (n) were 0.178 gFA/gcell/h, 250.9 mg/L, 1,600 mg/L, and 1.86, respectively.

Formaldehyde degradation by Ralstonia eutropha in an immobilized cell bioreactor.

The formaldehyde (FA) degradation ability of the loofa-immobilized Ralstonia eutropha cells in a packed bed reactor was modeled using a statistically based design of the experiment (DOE) considering application of response surface methodology (RSM). The simultaneous effects of four operative test factors on the cells performance in terms of FA degradation rate and extent of the chemical oxygen demand (COD) removal were monitored. The combination of factors at initial FA concentration of 629.7 mg L−1h−1, recycling substrate flow rate of 4.4 mL min−1, aeration rate of 1.05 vvm, and the systems temperature of 28.8°C resulted the optimal conditions for the FA biodegradation rate and COD removal efficiency. Loofa porous structure was found to be a protective environment for the cells in exposing to the toxic substances and the scanning electron microscopy (SEM) images revealed extensive cells penetration within this support. Oxygen transfer analysis in the form of evaluating K la value was also carried out and at the optimum conditions of the DOE was equaled to 9.96 h−1and oxygen uptake rate was 35.6 mg L−1h−1.

Optimization of Lithotrophic Activities of Acidithiobacillus ferrooxidans toward Significant Reduction of Sulfur and Ash from Low Rank Bitumen

ABSTRACT In the present study, the potential application of Acidithiobacillus ferrooxidans for elimination of ash and sulfur from bitumen was investigated in batch experiments. A comparison between the bioleaching and abiotic treatments indicated that A. ferrooxidans cells enhanced ash and pyritic sulfur removal by 20 and 59%, respectively. The X-ray diffraction profiles of the samples indicated the precipitation of some mineral elements inside of bitumen decreased the bioleaching performance after 9 days from beginning of the experiments. The effects of bitumen particle size (X1), agitation speed (X2) and initial pH (X3) as interfacial factors each at three levels on the ash removal (Y1) and pyritic sulfur removal (Y2) were investigated by response surface methodology as a statistical design of the experiment. On the basis of quadratic models applied to the performance of the bioleaching process, 66.42% of the pyritic sulfur and 50.88% of the ash could be removed after 9 days under optimal conditions, namely a bitumen particle size of 100 µm, an agitation speed of 80 rpm, and initial pH of 2.