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

Gaseous Formaldehyde Degrading by Methylobacterium sp. XJLW

Formaldehyde is harmful to human beings. It is widely used in chemical industry, medicine, and agriculture and is frequently discharged into the sewage. Microbial metabolism of formaldehyde has attracted increasing attention for its potential application in formaldehyde removal, especially for indoor gaseous formaldehyde degradation. Methylobacterium sp. XJLW capable of degrading formaldehyde was isolated and exhibited a strong activity for liquid formaldehyde degradation. In the present study, the survival rate of XJLW was evaluated under drought, 30 °C, 4 °C, 15 °C, 35 °C, and 40 °C. After 4 days, the average survival rate under 30°C is the greatest (83.97%) among the five temperatures. Whether the temperature was above or below 30°C, the average survival rate decreased significantly. However, the resistance of XJLW to reduced temperatures seemed better than that to increased temperatures. The average survival rate under 15°C and 4°C was 71.1% and 58.67%, while that under 35 °C and 40 °C was 49.47% and 0.1%. Two batches of gaseous formaldehyde treatments were carried out in an analog device with super absorbent polymer (SAP) as the carrier materials of XJLW. The results showed that XJLW could effectively degrade gaseous formaldehyde in the analog device for a long period.

Experimentation and CFD modeling of continuous degradation of formaldehyde by immobilized Ralstonia eutropha in a semi-pilot-scale plug flow bioreactor

This study focuses on continuous formaldehyde (FA) biodegradation by Ralstonia eutropha immobilized on polyurethane foam in a semi-pilot-scale plug flow packed-bed bioreactor. The stepwise increasing of the influent FA concentration from 43.9 to 1325.1 mg L^-1 was studied in the bioreactor during 70 days of operation. A complete removal of FA was achieved for inlet concentration up to 425.5 mg L^-1 and the initial specific biodegradation rate reached to its maximum value about 44.3 mg g_cell^-1 h^-1 at 425.5 mg L^-1. However, further increase of inlet concentration resulted in decrease of the biodegradation performance of the immobilized cells due to the inhibitory effect of FA on the enzymatic system involved in the biodegradation process. Based on kinetic modeling results, the Luong equation with the following constants could best describe the behavior of the bio-system: maximum specific FA biodegradation rate (q_max) of 124 mg g_cell^-1 h^-1, half-saturation constant (K_S) of 337.2 mg L^-1, maximum degradable FA concentration (S_max) of 1582 mg L^-1, and shape factor (n) of 1.49. Also, three-dimensional simulation of the bioreactor was performed using an integrated computational fluid dynamics (CFD) approach that takes into account both the biokinetic constants of the immobilized system as well as the fluid properties under steady-state condition. Eulerian computations successfully anticipated the concentration gradients through the reactor for different inlet FA concentrations, and uniform vertical velocity pathlines and non-dispersed plug flow inside the reactor were verified by the presented velocity distribution and flow streamlines.

Biodegradation of airborne acetone/styrene mixtures in a bubble column reactor

The ability of a bubble column reactor (BCR) to biodegrade a mixture of styrene and acetone vapors was evaluated to determine the factors limiting the process efficiency, with a particular emphasis on the presence of degradation intermediates and oxygen levels. The results obtained under varied loadings and ratios were matched with the dissolved oxygen levels and kinetics of oxygen mass transfer, which was assessed by determination of k_La coefficients. A 1.5-L laboratory-scale BCR was operated under a constant air flow of 1.0 L.min^-1, using a defined mixed microbial population as a biocatalyst. Maximum values of elimination capacities/maximum overall specific degradation rates of 75.5 gC.m^-3.h^-1/0.197 gC.gdw^-1.h^-1, 66.0 gC.m^-3.h^-1/0.059 gC.gdw^-1.h^-1, and 45.8 gC.m^-3.h^-1/0.027 gC.gdw^-1.h^-1 were observed for styrene/acetone 2:1, styrene-rich and acetone-rich mixtures, respectively, indicating significant substrate interactions and rate limitation by biological factors. The BCR removed both acetone and styrene near-quantitatively up to a relatively high organic load of 50 g.m^-3.h^-1. From this point, the removal efficiencies declined under increasing loading rates, accompanied by a significant drop in the dissolved oxygen concentration, showing a process transition to oxygen-limited conditions. However, the relatively efficient pollutant removal from air continued, due to significant oxygen mass transfer, up to a threshold loading rate when the accumulation of acetone and degradation intermediates in the aqueous medium became significant. These observations demonstrate that oxygen availability is the limiting factor for efficient pollutant degradation and that accumulation of intermediates may serve as an indicator of oxygen limitation. Microbial (activated sludge) analyses revealed the presence of amoebae and active nematodes that were not affected by variations in operational conditions.

Cometabolic degradation of ethyl mercaptan by phenol-utilizing Ralstonia eutropha in suspended growth and gas-recycling trickle-bed reactor

The degradability of ethyl mercaptan (EM), by phenol-utilizing cells of Ralstonia eutropha, in both suspended and immobilized culture systems, was investigated in the present study. Free-cells experiments conducted at EM concentrations ranging from 1.25 to 14.42 mg/l, showed almost complete removal of EM at concentrations below 10.08 mg/l, which is much higher than the maximum biodegradable EM concentration obtained in experiments that did not utilize phenol as the primary substrate, i.e. 2.5 mg/l. The first-order kinetic rate constant (kSKS) for EM biodegradation by the phenol-utilizing cells (1.7 l/g biomass/h) was about 10 times higher than by cells without phenol utilization. Immobilized-cells experiments performed in a gas recycling trickle-bed reactor packed with kissiris particles at EM concentrations ranging from 1.6 to 36.9 mg/l, showed complete removal at all tested concentrations in a much shorter time, compared with free cells. The first-order kinetic rate constant (rmaxKs) for EM utilization was 0.04 l/h for the immobilized system compared to 0.06 for the suspended-growth culture, due to external mass transfer diffusion. Diffusion limitation was decreased by increasing the recycling-liquid flow rate from 25 to 65 ml/min. The removed EM was almost completely mineralized according to TOC and sulfate measurements. Shut down and starvation experiments revealed that the reactor could effectively handle the starving conditions and was reliable for full-scale application.

Multistage A-O Activated Sludge Process for Paraformaldehyde Wastewater Treatment and Microbial Community Structure Analysis

In recent years, the effect of formaldehyde on microorganisms and body had become a global public health issue. The multistage combination of anaerobic and aerobic process was adopted to treat paraformaldehyde wastewater. Microbial community structure in different reaction stages was analyzed through high-throughput sequencing. Results showed that multistage A-O activated sludge process positively influenced polyformaldehyde wastewater. The removal rates of formaldehyde were basically stable at more than 99% and those of COD were about 89%. Analysis of the microbial diversity index indicated that the microbial diversity of the reactor was high, and the treatment effect was good. Moreover, microbial community had certain similarity in the same system. Microbial communities in different units also showed typical representative characteristics affected by working conditions and influent concentrations. Proteobacteria, Firmicutes, and Bacteroidetes were the dominant fungal genera in the phylum level of community composition. As to family and genus levels, Peptostreptococcaceae was distributed at various stages and the dominant in this system. This bacterium also played an important role in organic matter removal, particularly decomposition of the acidified middle metabolites. In addition, Rhodobacteraceae and Rhodocyclaceae were the formaldehyde-degrading bacteria found in the reactor.

Use of a packed-bed airlift reactor with net draft tube to study kinetics of naphthalene degradation by Ralstonia eutropha

Biodegradation of naphthalene by Ralstonia eutropha (also known as Cupriavidus necator) in a packed-bed airlift reactor with net draft tube (PBALR-nd) was studied; the Kissiris pieces were the packing material. The reactor hydrodynamics has been characterized under abiotic conditions and the dependencies of the superficial gas velocity (U G) on the gas holdup (εG), liquid mixing time, and mass transfer coefficient were determined. The improving role of the net draft tube in this small column reactor (height 42 cm, ID 5 cm) was confirmed. The flow regime was described using the εG α U G (n) expression, and bubbly flow was observed in PBALR-nd at U G < 2.83 cm/s. In the second step of the present work, the kinetics of biodegradation was modeled using the Haldane and Aiba equations. The fitting of the experimental results to the models were done according to the nonlinear least square regression technique. The biokinetic constants (q m, K s, and K i) were estimated and q m as the specific biodegradation rate was equaled to 0.415 and 0.24 mgnaph./mgcell h for the Haldane and Aiba equations, respectively. The goodness of fit reported as R (2) and root-mean-square error (RMSE) showed the adequate fitness of the Haldane and Aiba models in predicting naphthalene biodegradation kinetics. On the basis of the HPLC results, a hypothetical pathway for the biodegradation was presented.

Formaldehyde biodegradation by immobilized Methylobacterium sp. XJLW cells in a three-phase fluidized bed reactor

In the present study, the ability of a newly isolated strain, Methylobacterium sp. XJLW to degrade formaldehyde was investigated in shake flasks and in a bioreactor. The resting cells of Methylobacterium sp. XJLW showed high formaldehyde tolerance (60 g L(-1)) and high degradation rate (1,687.5 mg L(-1) h(-1)) in shake flasks. This biodegradation was initiated by a dismutation reaction since formic acid was formed and caused significant dropping of pH in the media. The addition of CaCO(3) to the media was found as an effective strategy to control the pH and keep the cells in high degradation bioactivity. A three-phase fluidized bed reactor (TPFBR) was designed to test the formaldehyde-biodegrading ability of immobilized Methylobacterium sp. XJLW. Using a repeated-batch degradation mode, the immobilized cells were able to degrade 5 g L(-1) formaldehyde (with a maximal degradation rate of 464.5 mg L(-1) h(-1) under the optimum conditions) and showed stable bioactivity after 20 batches of reuse in the TPFBR.

Dynamic mathematical models for biodegradation of formaldehyde by Ralstonia eutropha in a batch bioreactor

Degradation of formaldehyde by Ralstonia eutropha was studied in a batch bioreactor operated in recycling mode (30 °C, initial pH of 6.5, aeration rate 0.5 vvm, and a recycling flow rate of 6 mL min(-1)). Growth kinetics equations were described using four substrate inhibition models, and the initial formaldehyde concentration ranged from 54.5 to 993.0 mg L(-1). In each case, model parameters were estimated interactively using nonlinear regression analysis and on the basis of the goodness of fit, the fitness of the model to the experimental data was obtained (i.e., the coefficient of determination and the percent of standard deviation). The estimated parameters according to the Luong equation were μmax = 0.101 h(-1), KS = 54.1 mg L(-1), Sm = 1329 mg L(-1), and n = 2.07. According to the maintenance energies explained by Pirt, cell maintenance was quantified with q = Aμ + B; where A and B are the associated and non-associated growth parts of substrate consumption, respectively. The importance of these terms was verified using the developed models, which would efficiently describe the dynamic nature of growth and formaldehyde biodegradation.