Biomass accumulation and clogging in biotrickling filters for waste gas treatment. Evaluation of a dynamic model using dichloromethane as a model pollutant

A dynamic model is developed that describes the degradation of volatile acidifying pollutants in biotrickling filters (BTFs) for waste gas purification. Dynamic modelling enables the engineer to predict the clogging rate of a filter bed and the time it takes the BTF to adapt to changes in its inlet concentration. The most important mechanisms that govern the behaviour of the BTF are incorporated in the model. The time scale of the accumulation of biomass in a filter is investigated, and an approach is presented that can be used to estimate how long a BTF can be operated before its packing has to be cleaned. A three-month experiment was carried out to validate the model, using dichloromethane (DCM) as a model acidifying pollutant. Valuable experimental data about biomass accumulation and liquid hold-up in the reactor were obtained with an experimental set-up that allows the continuous registration of the weight of the BTF. The results show that in BTFs eliminating DCM from a waste gas, clogging is not to be expected up to concentrations of several g/m3. Model calculations based on the measurements also suggest that the maximum carbon load that can safely be applied per unit void packing volume should not exceed 0.5-1.6 C mol/(m3. h), depending on the density of the biofilm formed. The model is a good predictor of the elimination of the pollutant in the system, the axial gas and liquid concentration profiles, the axial biomass distribution, and the response of the system upon a stepwise increase in the DCM inlet concentration. The influence of the buffer concentrations in the liquid phase upon the performance of the BTF is investigated.     

Quantifying the climate change effects of bioenergy systems: Comparison of 15 impact assessment methods

Ongoing concern over climate change has led to interest in replacing fossil energy with bioenergy. There are different approaches to quantitatively estimate the climate change effects of bioenergy systems. In the present work, we have focused on a range of published impact assessment methods that vary due to conceptual differences in the treatment of biogenic carbon fluxes, the type of climate change impacts they address and differences in time horizon and time preference. Specifically, this paper reviews fifteen different methods and applies these to three hypothetical bioenergy case studies: (a) woody biomass grown on previously forested land; (b) woody biomass grown on previous pasture land; and (b) annual energy crop grown on previously cropped land. Our analysis shows that the choice of method can have an important influence on the quantification of climate change effects of bioenergy, particularly when a mature forest is converted to bioenergy use as it involves a substantial reduction in biomass carbon stocks. Results are more uniform in other case studies. In general, results are more sensitive to specific impact assessment methods when they involve both emissions and removals at different points in time, such as for forest bioenergy, but have a much smaller influence on agricultural bioenergy systems grown on land previously used for pasture or annual cropping. The development of effective policies for climate change mitigation through renewable energy use requires consistent and accurate approaches to identification of bioenergy systems that can result in climate change mitigation. The use of different methods for the same purpose: estimating the climate change effects of bioenergy systems, can lead to confusing and contradictory conclusions. A full interpretation of the results generated with different methods must be based on an understanding that the different methods focus on different aspects of climate change and represent different time preferences.     

Dictyostelium Myosin Bipolar Thick Filament Formation: Importance of Charge and Specific Domains of the Myosin Rod

Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) “head” is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines.     

Effects of pH, CO2, and flow pattern on the autotrophic degradation of hydrogen sulfide in a biotrickling filter

In this study, the effects of pH, CO(2), and flow pattern on the performance of a biotrickling filter (BTF) packed with plastic Pall rings and treating a H(2)S-polluted waste gas were investigated to establish the optimum operating conditions and design criteria. The CO(2) concentration had no effect on the biodegradation at H(2)S concentrations below 50 ppm. In the range of 50-127 ppm H(2)S, CO(2) concentrations between 865 and 1,087 ppm enhanced H(2)S removal, while higher concentrations of 1,309-4,009 ppm CO(2) slightly inhibited H(2)S removal. The co-current flow BTF presented the advantage of a more uniform H(2)S removal and biomass growth in each section than the counter-current flow BTF. Examination of the pH-effect in the range of pH 2.00-7.00 revealed optimal activity for autotrophs at pH 6.00. Under optimal conditions, the elimination capacity reached 31.12 g H(2)S/m(3)/h with a removal efficiency exceeding 97%. In the present research, autotrophic biomass was developed in the BTF, performing both a partial oxidization of H(2)S to elemental sulfur and a complete oxidization to sulfate, which is favorable from an environmental point of view. Results showed that around 60% of the sulfide concentration fed to the reactor was transformed into sulfate. Such autotrophic trickling filters may present other advantages, including the fact that they do not release any CO(2) to the atmosphere. Besides, the limited growth of autotrophs avoids potential clogging problems. Experimental performance data were compared with data from a mathematical model. Comparisons showed that the theoretical model was successful in predicting the performance of the biotrickling filter.     

Dictyostelium myosin bipolar thick filament formation: importance of charge and specific domains of the myosin rod

Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) “head” is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines.     

Biodegradation of gas-phase styrene in a high-performance biotrickling filter using porous polyurethane foam as a packing medium

A biotrickling filter (BTF) packed with porous polyurethane (PU) foam sheets was developed and operated for removal of gas-phase styrene. The specific surface area and void fraction of the PU foam sheet were determined to be 497 m²/m³ and 0.92, respectively, by using mathematical modeling and experimental measurement. The effects of gas flow direction (co-current and counter-current), styrene loading rate and empty bed residence time on the efficiency of the BTF were analyzed. The BTF achieved a high elimination capacity of 4.0 ∼ 5.0 kg styrene/m³ day due to the high specific surface area of the PU foam. The BTF could be operated repeatedly when excessively-grown biomass was periodically removed, using circulating NaOH solution for 2 h every four days.     

Biofumigation potential of brassicas

The relationship of global climate change to plant growth and the role of forests as sites of carbon sequestration have encouraged the refinement of the estimates of root biomass and production. However, tremendous controversy exists in the literature as to which is the best method to determine fine root biomass and production. This lack of consensus makes it difficult for researchers to determine which methods are most appropriate for their system. The sequential root coring method was the most commonly used method to collect root biomass data in the past and is still commonly used. But within the last decade the use of minirhizotrons has become a favorite method of many researchers. In addition, due to the high labor-intensive requirements of many of the direct approaches to determine root biomass, there has been a shift to develop indirect methods that would allow fine root biomass and production to be predicted using data on easily monitored variables that are highly correlated to root dynamics. Discussions occur as to which method should be used but without gathering data from the same site using different methods, these discussions can be futile. This paper discusses and compares the results of the most commonly used direct and indirect methods of determining root biomass and production: sequential root coring, ingrowth cores, minirhizotrons, carbon fluxes approach, nitrogen budget approach and correlations with abiotic resources. No consistent relationships were apparent when comparing several sites where at least one of the indirect and direct methods were used on the same site. Until the different root methods can be compared to some independently derived root biomass value obtained from total carbon budgets for systems, one root method cannot be stated to be the best and the method of choice will be determined from researcher's personal preference, experiences, equipment, and/or finances.     

Population dynamics of free-floating and attached bacteria in a styrene-degrading biotrickling filter analyzed by denaturing gradient gel electrophoresis

Population dynamics was studied in a 52-l biotrickling filter (BTF) operated for 182 days and used to clean air contaminated with styrene vapors. In the BTF, biomass grew either as free-floating (planktonic) or attached (sessile) microorganisms. PCR-amplified 16S rDNA fragments from planktonic and sessile cells within the bioreactor were analyzed using denaturing gradient gel electrophoresis (DGGE). The results indicated that the complexity of biofilm community was always more pronounced than the complexity of the planktonic cell community. Notably, Rhodococcus erythropolis was identified, based on DNA sequence analysis, as one of the biofilm-specific strains. It was also shown that the inoculum, even when enriched with styrene-degrading bacteria, was not adapted to the growth conditions imposed by the BTF. After a 35-day microbial acclimation period, the DGGE analysis also showed less variation in the banding pattern representing the microbial complexity of the biofilm. In addition, the phylogenic fingerprinting method used demonstrated similar banding profiles in the biofilm along the filter bed. Electronic Publication     

OST1‐mediated BTF3L phosphorylation positively regulates CBFs during plant cold responses

Cold stress is a major environmental factor that negatively affects plant growth and survival. OST1 has been identified as a key protein kinase in plant response to cold stress; however, little is known about the underlying molecular mechanism. In this study, we identified BTF3 and BTF3L (BTF3‐like), β‐subunits of a nascent polypeptide‐associated complex (NAC), as OST1 substrates that positively regulate freezing tolerance. OST1 phosphorylates BTF3 and BTF3L in vitro and in vivo, and facilitates their interaction with C‐repeat‐binding factors (CBFs) to promote CBF stability under cold stress. The phosphorylation of BTF3L at the Ser50 residue by OST1 is required for its function in regulating freezing tolerance. In addition, BTF3 and BTF3L proteins positively regulate the expression of CBF genes. These findings unravel a molecular mechanism by which OST1‐BTF3‐CBF module regulates plant response to cold stress.     

Control of methanol vapours in a biotrickling filter: performance analysis and experimental determination of partition coefficient

Methanol vapours were treated in a biotrickling filter (BTF) packed with inert polypropylene spheres. The effects of the nitrogen concentration in the nutrient solution, the empty bed residence time (EBRT) and the methanol inlet concentration, on the BTF performance, were all examined. The elimination capacity (EC), the biomass and the carbon dioxide production rates were all increased with the rising of the nitrogen concentration and the EBRT. The EC also rose with increasing methanol inlet load (IL) when the methanol inlet concentration and the EBRT were varied, from 0.3 to 37.0 g m(-3), and from 20 to 65 s, respectively. The BTF reached its maximum EC level of 2160 g m(-3) h(-1) when it was operated at an IL level of 3700 g m(-3) h(-1). The input methanol was removed through two mechanisms: biodegradation and absorption in the liquid phase. The partition coefficient for the methanol in the BTF was determined at five EBRTs and along the packed bed. It generally followed the Henry model, having an average value of 2.64 x 10(-4)[mol L(-1)](gas)/[mol L(-1)](liquid).     

Hydrogen sulfide removal performance of a bio-trickling filter employing Thiobacillus thiparus immobilized on polyurethane foam under various starvation regimes

In the present study a biotrickling filter (BTF) with countercurrent gas/liquid flow packed with open-pore polyurethane foam — as a carrier of Thiobacillus thioparus (DSMZ5368) — was subjected to various starvation regimes such as non-contaminant loading, idleness, and complete shutdown. During the starvation periods specific oxygen uptake rates of microorganisms (SOUR) on packing were monitored. The BTF was subjected to non-contaminant loading (up to 16 h), cyclic non-contaminant loading (for 4 days) and gas shut-off (up to 24 h), and it recovered to its pre-starvation removal efficiency within a 2 ～ 3 h period after resuming normal operating conditions. The recovery time values obtained during the runs in which these starvation regimes were imposed could be indirectly correlated with the corresponding SOUR values suggesting that the recovery time after such starvation regimes are dependent on the degree to which the aerobic biological activity has been reduced as a result of the imposed starvation regime. In the case of the complete shutdown of the BTF, the recovery time increased substantially after 1 and 2 days of complete shutdown, and after 5 days of complete shutdown the pre-starvation removal efficiency was not achieved even after 12 days of normal operation.     

The Biotechnology Facility for International Space Station

The primary mission of the Cellular Biotechnology Program is to advance microgravity as a tool in basic and applied cell biology. The microgravity environment can be used to study fundamental principles of cell biology and to achieve specific applications such as tissue engineering. The Biotechnology Facility (BTF) will provide a state-of-the-art facility to perform cellular biotechnology research onboard the International Space Station (ISS). The BTF will support continuous operation, which will allow performance of long-duration experiments and will significantly increase the on-orbit science throughput.     

Long term performance of biotrickling filters removing a mixture of volatile organic compounds from an artificial waste gas: dichloromethane and methylmethacrylate

Two problems still hamper the widespread industrial application of biotrickling filters (BTFs) for waste gas treatment in practice: clogging of the filters at higher carbon loads and a decrease in the elimination of a target compound when more than one compound is present in the waste gas. To investigate these phenomena three identical BTFs removing dichloromethane (DCM) from an artificial waste gas were operated counter-current wise for 12 months at a DCM load of 0.94 Cmole-DCM/(m_r³ · h). After five months of operation methylmethacrylate (MMA) was added to the waste gas. Three different MMA loads were applied: 0.5, 1.0 and 1.5 Cmole-MMA/(m_r³ · h). Although the elimination of DCM in all three BTFs decreased after the introduction of MMA to the air stream, it stabilised at a lower steady-state value than before the MMA addition. MMA was completely degraded during the applied standard conditions. In all three filters biomass accumulation eventually caused clogging of the packing. In the filter with the lowest MMA load the first signs of clogging were observed only after 7 months of stable operation, illustrating the need for long term studies to evaluate process stability. Short term experiments have provided information about the system's dynamics and showed that an accumulation of intermediates and a subsequent adaptation of the biomass in the BTF will occur upon a step increase in MMA load. To evaluate whether a stable BTF operation without clogging is possible, a novel process parameter (the rate of Carbon Conversion per unit void packing Volume) is introduced which possibilities and limitations are discussed.