Biofiltration of composting gases using different municipal solid waste-pruning residue composts: monitoring by using an electronic nose

The concentration of volatile organic compounds (VOCs) during the composting of kitchen waste and pruning residues, and the abatement of VOCs by different compost biofilters was studied. VOCs removal efficiencies greater than 90% were obtained using composts of municipal solid waste (MSW) or MSW-pruning residue as biofilter material. An electronic nose identified qualitative differences among the biofilter output gases at very low concentrations of VOCs. These differences were related to compost constituents, compost particle size (2-7 or 7-20 mm), and a combination of both factors. The total concentration of VOCs determined by a photoionization analyser and inferred from electronic nose data sets were correlated over an ample range of concentrations of VOCs, showing that these techniques could be specially adapted for the monitoring of these processes.     

Biological treatment of n-hexane and methanol in trickle bed air biofilters under acidic conditions

This study focuses on evaluating the degradation of n-hexane/methanol mixture in trickle-bed-air-biofilters (TBABs). Two different concentration ratios of methanol:n-hexane were evaluated (3:1) for TBAB “A” and (5:1) for TBAB “B”. Both TBABs were run and fed with nutrients buffered at pH 4 for encouraging the growth of fungi. The TBABs were loaded with pelletized diatomaceous earth support media and were run at an empty bed residence time of 120 s. n-Hexane loading rates (LRs) ranged from 0.9 to 13.2 g/m³ h for both TBABs. The corresponding methanol LRs varied from 2.3 to 37.7 g/m³ h and from 4.6 to 64.5 g/m³ h for TBABs “A” and “B”, respectively. Experimental results have shown that the degradation of n-hexane in presence of methanol is enhanced for n-hexane LRs less than 10.6 g/m³ h as compared to previous study for sole-fed n-hexane, but for n-hexane LRs of 13.2 g/m³ h, the performance of TBABs in eliminating n-hexane depended on the methanol to n-hexane ratios. The impact was less severe for TBAB “A” (RE 85%) as compared to TBAB “B” (RE 72%). This is attributed to the high LRs of methanol in TBAB “B”. n-Hexane performance stability was another advantage attained.     

Bioremediation of leachate from a green waste composting facility using waste-derived filter media

The evaluation of two waste-derived materials used to treat compost leachate by biofiltration is described in this paper. Nine biofilters were constructed using 240 l, high density polyethylene containers. Three containers were filled without compaction with 200l of each of three types of filter media. Waste-derived filter media (compost and oversize) were compared to a mineral control (granite chips). The filters were fed with compost leachate from a typical green waste composting facility at hydraulic loading rates ranging from 0.05 m3/m3/day to 0.5 m3/m3/day over a period of twelve months. The oversize medium emerged as the most effective demonstrating characteristics of consistency of effluent quality and resilience to stress. The oversize medium produced an effluent of <10mg/l ammoniacal nitrogen on >95% of sampling occasions. The organic component of compost leachate was dominated by compounds that proved to be recalcitrant to biodegradation. The solids content of the treated effluent remained too high to be acceptable for direct discharge to a watercourse without further treatment and if discharge to a watercourse is to be considered, a polishing stage (e.g., reed bed) able to remove solids and dampen occasional peaks of ammoniacal nitrogen should be employed.     

Mechanistic studies on the binding of Acid Yellow 99 on coir pith

The interaction of Acid Yellow 99 (AY 99) with coir pith has been investigated in aqueous medium to understand the mechanism of adsorption and explore the potentiality of this biomass towards controlling pollution resulting from textile dyes. The obtained results establish that one gram of coir pith can adsorb 442.13 mg of AY 99. The adsorption process is found to be a function of pH of the solution, the optimum pH value being 2.0. The process follows Langmuir-Freundlich dual isotherm model. Scanning electron microscopic analysis demonstrates that on dye adsorption the biomass develops uneven and irregular surface. X-ray diffraction study indicates incorporation of the dye into the micropores and macropores of the adsorbent and thereby enhancing its degree of crystallinity. The results of Fourier transform infrared (FTIR) spectroscopy and chemical modification of the functional groups establish that binding of AY 99 on coir pith occurs through electrostatic and complexation reaction.     

Sequential kinetic parameter estimation of anaerobic fluidized bed bioreactor using an optimization technique

Mathematical model parameters for the methanogenic degradation of propylene glycol were estimated in a sequential manner by means of an optimization technique. Model parameters determined from an initial experimental data set using one bioreactor were then verified with the results from a second bioreactor. The proposed methodology is a useful tool to obtain model parameters for continuous flow reactors with completely mixed regime. Abbrevations: S – substrate concentration (mg COD l^–1); S _in – influent substrate concentration (mg COD l^–1); D _L – dilution rate (day^–1); – stoichiometric coefficients (ND); nx – number of microbial species (ND); X _S – fixed biomass concentration (mg biomass l^–1); X _L – suspended biomass concentration of (mg biomass l^–1); k _d – decay rate of biomass (day^–1); b _S – specific detachment rate of biofilm (day^–1); – specific growth rate of biomass (day^–1); _m – maximum specific growth rate of biomass (day^–1); K _S – half saturation constant (mg COD l^–1); K _I – inhibition constant (mg COD l^–1).     

Impact of liquid-to-gas hydrogen mass transfer on substrate conversion efficiency of an upflow anaerobic sludge bed and filter reactor

Efficient anaerobic degradation may be completed only under low levels of dissolved hydrogen in the liquid surrounding the microorganisms. This restraint can be intensified by the limitations of liquid-to-gas H₂ mass transfer, which results in H₂ accumulation in the bulk liquid of the reactor. Dissolved hydrogen proved to be an interesting parameter for reactor monitoring by showing a good correlation with short-chain volatile fatty acid concentration, namely propionate, which was not the case for the H₂ partial pressure. Biogas recycle was performed in a upflow anaerobic sludge bed and filter reactor. The effects of varying the ratio of recycled-to-produced gas from 2:1 (9 l/l reactor per day) to 8:1 (85 l/l reactor per day) were studied. By increasing the liquid—gas interface with biogas recycling, the dissolved hydrogen concentration could be lowered from 1.1 to 0.4 μ . Accordingly, the H₂ sursaturation factor was also reduced, leading to an important improvement of the H₂ mass transfer rate, which reached 20.86 h⁻¹ (±9.79) at a 8:1 gas recycling ratio, compared to 0.72 h⁻¹ (±0.24) for the control experiment. Gas recycling also lowered the propionate concentration from 655 to 288 mg l⁻¹ and improved the soluble chemical oxygen demand removal by 10–15%. The main problem encountered was the shorter solid retention time, which could lead to undesirable biomass washout at high gas recycling ratio. This could be circumvented by improving the reactor design to reduce the turbulence within the biomass bed.     

A Model for the Biofiltration of Butyl Acetate and Xylene Mixtures by a Trickle‐Bed Air Biofilter

A mathematical model that incorporates the rates of the mass transfer process and the biofilm reaction is presented to predict the performance of a trickle‐bed air biofilter (TBAB) for treating butyl acetate and xylene mixtures. A thorough understanding of the factors that influence these rates is necessary before the practical application of a TBAB for treating many kinds of pure and mixed volatile organic compounds (VOC) in the air stream. The model presented consists of a set of mass balance equations for butyl acetate, xylene and oxygen in the bulk gas phase and within the biofilm. The butyl acetate and xylene concentration profiles of the gas phase predicted by the model were in good agreement with the measured data documented in a previous study. The most relevant parameters were evaluated in a sensitivity analysis to determine their respective effects on the model performance. Four parameters were identified to strongly influence the model performance, the surface area of the biofilm per volume unit of the packing material (A_S), the empty‐bed residence time (EBRT), the maximum specific growth rate of the microorganism (μ_m), and the microbial yield coefficient (Y). The practical application of the model to derive the performance equation is also presented and discussed. This equation makes it possible to simultaneously obtain a relatively high VOC removal efficiency and to minimize the capital cost.     

Biofiltration of isopropyl alcohol by a trickle-bed air biofilter

The performance of trickle-bed air biofilter (TBAB) for the removal of isopropyl alcohol (IPA) was evaluated in concentrations varying from 100 to 500 ppmv and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete IPA removal could be achieved for influent carbon loading between 6 and 88 g/m^3·h. The TBAB appears efficient for controlling IPA emission under low-to-high carbon loading conditions. Carbon recoveries of 95-99% were achieved demonstrating the accuracy of results. Applicable operating conditions of TBAB for controlling IPA emission were suggested.     

Textiles wastewater treatment using anoxic filter bed and biological wriggle bed-ozone biological aerated filter

In this study, the performance of the anoxic filter bed and biological wriggle bed-ozone biological aerated filter (AFB-BWB-O₃-BAF) process treating real textile dyeing wastewater was investigated. After more than 2 month process operation, the average effluent COD concentration of the AFB, BWB, O₃-BAF were 704.8 mg/L, 294.6 mg/L and 128.8 mg/L, with HRT being 8.1-7.7 h, 9.2 h and 5.45 h, respectively. Results showed that the effluent COD concentration of the AFB decreased with new carriers added and the average removal COD efficiency was 20.2%. During operation conditions, HRT of the BWB and O₃-BAF was increased, resulting in a decrease in the effluent COD concentration. However, on increasing the HRT, the COD reduction capability expressed by the unit carrier COD removal loading of the BWB reactor increased, while that of the O₃-BAF reactor decreased. This study is a beneficial attempt to utilize the AFB-BWB-O₃-BAF combine process for textile wastewater treatment.     

Benzene vapor treatment using a two-phase partitioning bioscrubber: an improved steady-state protocol to enhance long-term operation

The performance and stability of a two-phase partitioning bioscrubber (TPPB) containing 33% (vol.) n-hexadecane as an immiscible phase was investigated during 30 days of continuous gaseous benzene treatment. Elimination capacities of 141 ± 12 g/m³ h were achieved by Achromobacter xylosoxidans Y234 while maintaining >99% removal throughout. A new steady-state operating strategy that limits excessive biomass production by directing substrate consumption to maintenance energy has eliminated the requirement for frequent exchange of liquid contents. Simplifying the operating protocols in this manner has dramatically reduced material costs and rendered the TPPB operational requirements as more comparable (in terms of frequency of required operator inputs) with other vapor-phase bioreactors. The practicality of the proposed simplification to the operating protocol was confirmed by demonstrating that intermediate metabolites were not accumulating in the TPPB, inorganic nutrient requirements were readily predictable, and that high culture viability could be sustained for prolonged cell retention times (30 days).     

Biofiltration of toluene and acetone mixtures by a trickle-bed air biofilter

Toluene and acetone mixtures are commonly encountered from the manufacture of semi-conductor or opto-electronic apparatus. This study attempts to employ a trickle-bed air biofilter (TBAB) for treating toluene and acetone mixtures under different gas flow rates and influent concentrations. In the pseudo-steady-states, the elimination capacities of toluene and acetone increased but the removal efficiencies decreased with the increase of influent carbon loading. The removal efficiencies of toluene were higher than those of acetone, indicating that toluene is a preferred substrate in the mixtures. Greater than 90% removal efficiencies were achieved with influent carbon loadings of toluene and acetone below 125 and 15 g/m³ h, respectively. The TBAB appears efficient for controlling toluene and acetone mixture with medium toluene and low acetone loadings. Applicable operating conditions of TBAB for treating mixed toluene and acetone emission are suggested.     

Detection of aromatic catabolic gene expression in heterogeneous organic matter used for reduction of volatile organic compounds (VOC) by biofiltration

A qualitative procedure of purified DNA/RNA co-extraction from complex organic matter, used as biofilter support for removing volatile organic compounds, was set up and applied to detect xylene monooxygenase gene expression by RT-PCR. A DNA/RNA extraction protocol based on a combination of sample lyophilization pre-treatment and CTAB––phenol/chloroform extraction procedure was optimized for the recovery of purified nucleic acids [100–500 ng DNA (10 kb) and 0.5–2 μg of rRNA 16S from 100 mg matrix]. PCR and RT-PCR protocols were established to detect xylene monooxygenase gene expression starting from differentially induced organic matrices obtained by biofiltration technology. This work allowed the microbial degradation activities in heterogeneous organic solid media to be studied and suggests a rapid method to follow specific biological activities during solid and/or semisolid organic substrates biotransformation.     

Utilization of pretreated coir pith for the optimized bioproduction of cellulase by Aspergillus nidulans

The present study is aimed at simultaneous cellulase synthesis and coir pith degradation by Aspergillus nidulans using coir pith as chief substrate. The lignocellulosic biomass, coir pith is known to be an excellent carbon source for microbial cellulase production under solid state fermentation. The alkali pretreatment with sodium hydroxide was seen to enhance enzymatic hydrolysis. The effect of coir pith weight, moisture content, initial pH and growth temperature on cellulase activity and yield were investigated by response surface methodology (RSM) employing a four-factor-five-level central composite design (CCD). The results of Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and Scanning electron microscopy (SEM) of coir pith showed structural changes through pretreatment, in favor of enzymatic hydrolysis. Maximum carboxy methyl cellulase activity (CMCase) of 28.64 U/g and cellulase yield of 66.32% were achieved with 8 g coir pith at 70% moisture content and 40 °C temperature with pH 5 as evident from run numbers 25 and 30. Filter paper (FPase) and cellobiase (CBase) activities of 10.23 U/g and 4.31 U/g respectively were observed on the 11th day after the inoculation.     

Biosoftening of coir fiber using selected microorganisms

Coir fiber belongs to the group of hard structural fibers obtained from coconut husk. As lignin is the main constituent of coir responsible for its stiffness, microbes that selectively remove lignin without loss of appreciable amounts of cellulose are extremely attractive in biosoftening. Five isolated strains were compared with known strains of bacteria and fungi. The raw fiber treated with Pseudomonas putida and Phanerocheate chrysosporium produced better softened fiber at 30±2 °C and neutral pH. FeSO₄ and humic acid were found to be the best inducers for P. chrysosporium and P. putida, respectively, while sucrose and dextrose were the best C-sources for both. Biosoftening of unretted coir fibers was more advantageous than the retted fibers. Unlike the weak chemically softened fiber, microbial treatment produced soft, whiter fibers having better tensile strength and elongation (44.6–44.8%) properties. Scanning electron microscopy photos showed the mycelia penetrating the pores of the fiber, removing the tylose plug and degrading lignin.     

Biochemical characterization of xylanase produced from Streptomyces sp. CS624 using an agro residue substrate

An extracellular and cellulase-free xylanase (EX624) was produced by Streptomyces sp. CS624 using an agricultural residue (wheat bran) as a growth substrate. EX624 was purified from culture supernatant using ammonium sulfate precipitation, ion exchange and gel filtration chromatography. The SDS-PAGE and the zymogram analysis of the purified xylanase indicated molecular mass of 40 kDa. Biochemical characterization of the purified EX624 revealed its highest activity at a temperature of 60 °C and pH 6.0. The xylanase was adequately stable in the pH range 4.5–10.0 and at temperatures ≤50 °C. EX624 displayed enhanced activity in the presence of several metal ions including Fe²⁺, Co²⁺ and Ca²⁺. HPLC results showed that EX624 was not only able to hydrolyze commercially available pure beechwood xylan to xylose, xylobiose and xylotriose, but also abundantly available lignocellulosic agricultural residues in nature such as wheat bran to xylooligosaccharides.     

Feasibility of atmospheric methane removal using methanotrophic biotrickling filters

Methane is a potent greenhouse gas with a global warming potential ~23 times that of carbon dioxide. Here, we describe the modeling of a biotrickling filtration system composed of methane-consuming bacteria, i.e., methanotrophs, to assess the utility of these systems in removing methane from the atmosphere. Model results indicate that assuming the global average atmospheric concentration of methane, 1.7 ppmv, methane removal is ineffective using these methanotrophic biofilters as the methane concentration is too low to enable cell survival. If the concentration is increased to 500–6,000 ppmv, however, similar to that found above landfills and in concentrated animal feeding operations (factory farms), 4.98–35.7 tons of methane can be removed per biofilter per year assuming biotrickling filters of typical size (3.66 m in diameter and 11.5 m in height). Using reported ranges of capital, operational, and maintenance costs, the cost of the equivalent ton of CO₂ removal using these systems is $90–$910 ($2,070–$20,900 per ton of methane), depending on the influent concentration of methane and if heating is required. The use of methanotrophic biofilters for controlling methane emissions is technically feasible and, provided that either the costs of biofilter construction and operation are reduced or the value of CO₂ credits is increased, can also be economically attractive.     

Modeling of growth kinetics for <Emphasis Type="Italic">Pseudomonas putida</Emphasis> during toluene degradation

Glucose has been often used as a secondary substrate to enhance the degradation of primary substrate as well as the increase of biomass, especially for the inhibitory range of substrate concentration. In this study, we investigated the effect of glucose concentration on growth kinetics of Pseudomonas putida during toluene degradation for a wide concentration range (60–250 mg/l). Batch microcosm studies were conducted in order to monitor bacterial growth for three different initial concentrations (2, 5, 10 mg/ml) of glucose for a given toluene concentration. Modeling of growth kinetics was also performed for each growth curve of glucose dose using both Monod and Haldane kinetics. Batch studies revealed that bacterial growth showed a distinct inhibitory phase above some limit (∼170 mg/l) for the lowest (2 mg/ml) glucose dose, but the degree of inhibition decreased as the glucose dose increased, leading to three different growth patterns. The bacterial growth followed each of the modified Wayman and Tseng, Wayman and Tseng, and Luong model as the glucose dose increased from 2 to 10 mg/ml. This indicates that glucose has a prominent influence on bacterial growth during toluene degradation and that different kinetics should be adopted for each broth condition.     

Production of toluene cis-glycol using recombinant Escherichia coli strains in glucose-limited fed batch culture

Production of toluene cis-glycol (TCG) was investigated using recombinant Escherichia coli strains that express toluene dioxygenase under the tac promoter. E. coli TG2 was selected as the host for the recombinant plasmid, pTAC365, because the TCG yield was 64% higher than with strain JM105 as the host. By using fed-batch culture, TCG production could be improved by 4.4-fold compared with batch cultures, with a toluene vapor feed. A further improvement of 1.2-fold was obtained by using a two-liquid phase culture system, but the improvement was 1.6-fold when the feed rate of toluene vapor was reduced by 75%. When the period of growth in fed-batch culture was extended and the reduced vapor feed was used, the maximum TCG concentration increased to 4 g/l, an overall improvement of 10-fold compared with the batch culture system used initially. However, product consumption was observed during the late stages of fed-batch growth and in stationary phase, resulting in the formation of o-cresol, 3-methylcatechol and benzyl alcohol. We conclude that the key to optimizing TCG production by recombinants is to prolong growth of the cells to ensure sustained growth-linked product formation, and to optimize the supply of the toxic substrate, toluene, but further work is needed to eliminate by-product formation.     

Biological treatment of indoor air for VOC removal: potential and challenges

There is nowadays no single fully satisfactory method for VOC removal from indoor air due to the difficulties linked to the very low concentration (microg m(-3) range), diversity, and variability at which VOCs are typically found in the indoor environment. Although biological methods have shown a certain potential for this purpose, the specific characteristic of indoor air and the indoor air environment brings numerous challenges. In particular, new methods must be developed to inoculate, express, and maintain a suitable and diverse catabolic ability under conditions of trace substrate concentration which might not sustain microbial growth. In addition, the biological treatment of indoor air must be able to purify large amounts of air in confined environments with minimal nuisances and release of microorganisms. This requires technical innovations, the development of specific testing protocols and a deep understanding of microbial activities and the mechanisms of substrate uptake at trace concentrations.