Macrokinetic and quantitative microbial investigation on a bench-scale biofilter treating styrene-polluted gaseous streams

Variations in microbial community structure and functional gene expression in bio-treatment processes with odorous pollutants

Engineered microbial ecosystems in biofilters have been widely applied to treat odorous gases from industrial emissions. Variations in microbial community structure and function associated with the removal of odorous gases by biofilters are largely unknown. This study performed a metagenomic analysis to discover shifts in microbial community structures in a commercial scale biofilter after treating odorous gas. Our study identified 175,675 functional genes assigned into 43 functional KEGG pathways. Based on the unigene sequences, there were significant changes in microbial community structures in the biofilter after treating odorous gas. The dominant genera were Thiobacillus and Oceanicaulis before the treatment, and were Acidithiobacillus and Ferroplasma after the treatment. A clustering analysis showed that the number of down-regulated microbes exceeded the number of up-regulated microbes, suggesting that odorous gas treatment reduced in microbial community structures. A differential expression analysis identified 29,975 up- and 452,599 down-regulated genes. An enrichment analysis showed 17 classic types of xenobiotic biodegradation pathways. The results identified 16 and 15 genes involved in ammonia and sulfite metabolism, respectively; an analysis of their relative abundance identified several up-regulated genes, which may be efficient genes involved in removing odorous gases. The data provided in this study demonstrate the changes in microbial communities and help identify the dominant microflora and genes that play key roles in treating odorous gases.

Waste gas biofiltration: advances and limitations of current approaches in microbiology

As confidence in gas biofiltration efficacy grows, ever more complex malodorant and toxic molecules are ameliorated. In parallel, for many countries, emission control legislation becomes increasingly stringent to accommodate both public health and climate change imperatives. Effective gas biofiltration in biofilters and biotrickling filters depends on three key bioreactor variables: the support medium; gas molecule solubilization; and the catabolic population. Organic and inorganic support media, singly or in combination, have been employed and their key criteria are considered by critical appraisal of one, char. Catabolic species have included fungal and bacterial monocultures and, to a lesser extent, microbial communities. In the absence of organic support medium (soil, compost, sewage sludge, etc.) inoculum provision, a targeted enrichment and isolation program must be undertaken followed, possibly, by culture efficacy improvement. Microbial community process enhancement can then be gained by comprehensive characterization of the culturable and total populations. For all species, support medium attachment is critical and this is considered prior to filtration optimization by water content, pH, temperature, loadings, and nutrients manipulation. Finally, to negate discharge of fungal spores, and/or archaeal and/or bacterial cells, capture/destruction technologies are required to enable exploitation of the mineralization product CO(2).

Confirmation of monod model for biofiltration of styrene vapors from waste flue gas

BACKGROUND

The objective of this research was to investigate the kinetic behavior of the biofil¬tration process for the removal of styrene.

METHODS

A three stage compost based biofilter was inoculated with thickened activated sludge. The reaction order rate constants were obtained from continuous experiments and used as the specific growth rate for the Monod equation.

RESULTS

The measured concentration profiles show a linear dependence on the bed height in the biofilter at higher loadings, such as 75 and 45 g m-3 h-1. This is the condition of reaction limitation for a reaction with zero-order kinetics. From the experimental data, maximum elimination capac¬ity (ECmax) was estimated to be 44, 40 and 26 g m-3 h-1 at empty bed retention times (EBRTs) of 120, 60 and 30 s, respectively. However, at lower loadings, the measured concentration profile of the biofilter is one of exponential increase, which is the condition of both reaction and diffusion limitations for a reaction with zero-order kinetics. Maximum elimination capacities found from the experimental results were the same as Monod model predictions. Both the experimental re¬sults and the model predictions showed the influence of EBRT on the removal rate of styrene, particularly for the highest loading rate.

CONCLUSION

In terms of the practical applications of the proposed models have the advantage of being simpler than Monod kinetics and Monod kinetics requires a numerical solution.

Application of artificial neural network model for the development of optimized complex medium for phenol degradation using Pseudomonas pictorum (NICM 2074)

Biodegradation of phenol using Pseudomonas pictorum (NICM 2074) a potential biodegradant of phenol was investigated for its degrading potential under different operating conditions. The neural network input parameter set consisted of the same set of four levels of maltose (0.025, 0.05, 0.075 g/l), phosphate (3, 12.5, 22 g/l), pH (7, 8, 9) and temperature (30 degrees C, 32 degrees C, 34 degrees C) on phenol degradation was investigated and a Artificial Neural Network (ANN) model was developed to predict the extent of degradation. The learning, recall and generalization characteristic of neural networks was studied using phenol degradation system data. The efficiency of the model generated by the ANN, was tested and compared with the results obtained from an established second order polynomial multiple regression analysis (MRA). Further, the two models (ANN and MRA) were used to predict the percentage of degradation of phenol for blind test data. Performance of both the models were validated in the cases of training and test data, ANN was recommended based on the following higher coefficient of determination R (2); lower standard error of residuals and lower mean absolute percentage deviation.

Microbial degradation of styrene: biochemistry, molecular genetics, and perspectives for biotechnological applications

Large quantities of the potentially toxic compound styrene are produced and used annually by the petrochemical and polymer-processing industries. It is as a direct consequence of this that significant volumes of styrene are released into the environment in both the liquid and the gaseous forms. Styrene and its metabolites are known to have serious negative effects on human health and therefore, strategies to prevent its release, remove it from the environment, and understand its route of degradation were the subject of much research. There are a large number of microbial genera capable of metabolizing styrene as a sole source of carbon and energy and therefore, the possibility of applying these organisms to bioremediation strategies was extensively investigated. From the multitude of biodegradation studies, the application of styrene-degrading organisms or single enzymes for the synthesis of value-added products such as epoxides has emerged.

Characteristics of styrene degradation by Rhodococcus pyridinovorans isolated from a biofilter

A novel strain (PYJ-1) of Rhodococcus pyridinovorans that was isolated from a biofilter was able to degrade styrene at a maximum rate of 0.16 mg (mg protein)(-1) h(-1) in batch culture at 97 mg l(-1) of initial styrene gas concentration. The optimum pH and temperature for styrene degradation were 7 and 32 degrees C, respectively. The degradation kinetic constants were obtained using substrate inhibition kinetics. In a perlite-packed biofilter the maximum styrene removal rate by the strain was 279 gm(-3)h(-1). Styrene removal in the biofilter was more sensitive to the temperature than in the batch culture.

Biodegradation of styrene laden waste gas stream using a compost-based biofilter

Biological treatment of waste gas styrene vapor was investigated in a three-stage bench-scale biofilter. Yard waste compost mixed with shredded hard plastics in a 25:75 v/v ratio of plastics:compost was inoculated with thickened municipal activated sludge. Microbial acclimation to styrene was achieved by exposing the system to an inlet concentration (C(In)) of 0.25 gm(-3) styrene and an empty bed retention time (EBRT) of 360 s for 30 days. Under steady-state conditions, maximum elimination capacity (EC) obtained was 45 gm(-3)h(-1) at a loading rate (L) of 60 gm(-3)h(-1) (C(In) of 2 gm(-3) and EBRT of 120 s). Reduction of retention time adversely impacted the performance resulting in the maximum EC of 39 and 27 gm(-3)h(-1) for EBRT of 60 and 30 s, respectively. Evaluation of the concentration profile along the bed height indicated dominance of first-order kinetics at C(In) < or = 0.45 gm(-3) and zero-order for higher concentrations.

Thermophilic biohydrogen production from glucose with trickling biofilter

Thermophilic H2 production from glucose was studied at 55-64 degrees C for 234 days using a continuous trickling biofilter reactor (TBR) packed with a fibrous support matrix. Important parameters investigated included pH, temperature, hydraulic retention time (HRT), and glucose concentration in the feed. The optimal pH and temperature were 5.5 and 60 degrees C, respectively. With decreasing HRT or increasing inlet glucose concentration, volumetric H2 production rate increased but the H2 production yield to glucose decreased gradually. The biogas composition was almost constant at 53 +/- 4% (v/v) of H2 and 47 +/- 4% (v/v) of CO2. No appreciable CH4 was detected when the reactor was under a normal operation. The carbon mass balance showed that, in addition to cell mass, lactate, n-butyrate, CO2, and acetate were major products that comprised more than 85% of the carbon consumed. The maximal volumetric H2 production rate and H2 yield to glucose were 1,050 +/- 63 mmol H2/l.d and 1.11 +/- 0.12 mol H2/mol glucose, respectively. These results indicate that the thermophilic TBR is superior to most suspended or immobilized reactor systems reported thus far. This is the first report on continuous H2 production by a thermophilic TBR system.