A three-phase dynamic mathematical model based on mass balances describing the main processes in biotrickling filtration: convection, mass transfer, diffusion, and biodegradation was calibrated and ...validated for the simulation of an industrial styrene-degrading biotrickling filter. The model considered the key features of the industrial operation of biotrickling filters: variable conditions of loading and intermittent irrigation. These features were included in the model switching from the mathematical description of periods with and without irrigation. Model equations were based on the mass balances describing the main processes in biotrickling filtration: convection, mass transfer, diffusion, and biodegradation. The model was calibrated with steady-state data from a laboratory biotrickling filter treating inlet loads at 13–74 g C m−3 h−1 and at empty bed residence time of 30–15 s. The model predicted the dynamic emission in the outlet of the biotrickling filter, simulating the small peaks of concentration occurring during irrigation. The validation of the model was performed using data from a pilot on-site biotrickling filter treating styrene installed in a fiber-reinforced facility. The model predicted the performance of the biotrickling filter working under high-oscillating emissions at an inlet load in a range of 5–23 g C m−3 h−1 and at an empty bed residence time of 31 s for more than 50 days, with a goodness of fit of 0.84.
•A dynamic model was applied for simulating styrene-degrading biotrickling filters.•Discontinuous and fluctuating emissions and intermittent trickling were considered.•The model was calibrated at laboratory with several inlet loadings conditions.•The model also predicted the dynamic pattern of the outlet emission.•Model was validated by 52 days of an on-site biotrickling under oscillating loading.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Simultaneous Saccharification/Fermentation: greater efficiency on biofuel production.•One-step process increased substantially productivity reducing the production cost.•Significant factors in SSF ...were enzyme loading (with greatest effect) and yeast extract.•Citrate showed an inhibitory effect on Clostridium beijerinckii.•Microwave-processed rice straw has great potential to produce butanol.
Rice straw (RS) is one of the lignocellulosic wastes with the highest global production. The main objective of this study was to maximise the butanol production by Clostridium beijerinckii DSM 6422 from RS pretreated by microwave-assisted hydrothermolysis. Two different fermentation strategies were compared: separate hydrolysis and fermentation (SHF, two-step process) and simultaneous saccharification and fermentation (SSF, one-step process). In parallel, the variables that significantly affected the butanol production were screened by using fractional factorial designs. Butanol concentration and productivity at 48 h were, respectively, 8% and 173% higher in SSF than in SHF. A one-step process was more efficient than a two-step process, especially considering the time savings derived from much higher productivity. From these results, SSF was further optimised by response surface methodology with central composite design over the key factors on the butanol production at 48 h: initial pH, enzyme loading and yeast extract concentration. The optimum point yielded a butanol productivity of 0.114 g L-1h−1, with a butanol-biomass ratio of 51 g kg−1 of raw RS (ABE-biomass ratio of 77.0 g kg−1 of raw RS). The parameter with the greatest effect was enzyme loading, with an optimal value of 13.5 FPU g-dw-1. This study showed that microwave-processed RS has great potential as a substrate for the butanol production from ABE fermentation when combining process stages by SSF.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Characterisation of the fouling attached to PVDF membranes treating an anaerobic effluent for dissolved CH
4
recovery was carried out. A commercial flat-sheet PVDF membrane and a PVDF functionalised ...by grafting of organofluorosilanes (mPVDF) that increased its hydrophobicity were subjected to a continuous flux of an anaerobic reactor effluent in long-term operation tests (> 800 h). The fouling cakes were studied by the membrane autopsy after these tests, combining a staining technique, FTIR, and FESEM-EDX, and the fouling extraction with water and NaOH solutions. Both organic and inorganic fouling were observed, and the main foulants were proteins, polysaccharides, and different calcium and phosphate salts. Also, a significant amount of live cells was detected on the fouling cake (especially on the non-modified PVDF). Although the fouling cake composition was quite heterogeneous, a stratification was observed, with the inorganic fouling mainly in the bulk centre of the cake and the organic fouling mainly located in the lower and upper surfaces of the cake. The mPVDF suffered a more severe fouling, likely owing to a stronger hydrophobic-hydrophobic interaction with the foulants. Irreversible fouling remained on both membranes after the extraction, although a higher irreversible fouling was detected in the mPVDF; however, a complete polysaccharide removal was observed. Regarding the operation performance, PVDF showed a lower stability and suffered a severe degradation, resulting in a lower thickness and perforations. Finally, the decrease in the methane recovery performance of both membranes was associated with the fouling depositions.
Graphical Abstract
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The capacity of activated carbon as a buffer pretreatment combined with biotrickling filtration for volatile organic compound (VOC) removal has been studied. The adsorption capacity of commercial ...activated carbons for m-xylene, acetone and n-butyl acetate (typical paint solvents) was evaluated, including the response to the interchanging of adsorbed compounds and to mixtures over fluctuating inlet conditions. The adsorption of m-xylene and n-butyl acetate was mainly irreversible and more than three times higher than for acetone. The prior use of activated carbon influenced adsorption and buffer capacities in consecutive adsorption/desorption cycles. The Dubinin–Radushkevich equation was used to correlate the results. VOC removal in a full-scale biotrickling filter treating industrial emissions confirmed the benefit of using a passive activated carbon prefilter. A combination of these technologies increased the elimination capacity and promoted a more efficient performance of the biological process. The VOC removal improvement depended largely on the pattern and composition of emissions.
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IJS, KILJ, NUK, PNG, UL, UM
Superhydrophobic poly(vinylidene fluoride) (PVDF) membranes were obtained by a surface treatment consisting of oxygen plasma activation followed by functionalisation with a mixture of silica ...precursor (SiP) (tetraethyl-orthosilicate TEOS or 3-(triethoxysilyl)-propylamine APTES) and a fluoroalkylsilane (1H,1H,2H,2H-perfluorooctyltriethoxysilane), and were benchmarked with coated membranes without plasma activation. The modifications acted mainly on the surface, and the bulk properties remained stable. From a statistical design of experiments on surface hydrophobicity, the type of SiP was the most relevant factor, achieving the highest water contact angles (WCA) with the use of APTES, with a maximum WCA higher than 155° for membranes activated at a plasma power discharge of 15 W during 15 min, without membrane degradation. Morphological changes were observed on the membrane surfaces treated under these plasma conditions, showing a pillar-like structure with higher surface porosity. In long-term stability tests under moderate water flux conditions, the WCA of coated membranes which were not activated by oxygen plasma decreased to approximately 120° after the first 24 h (similar to the pristine membrane), whilst the WCA of plasma-treated membranes was maintained around 130° after 160 h. Thus, plasma pre-treatment led to membranes with a superhydrophobic performance and kept a higher hydrophobicity after long-term operations.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The abatement of typical paint solvent compounds as individuals and in mixtures was carried out in an annular TiO2 supported reactor, for concentrations up to 900 mg C m–3. Two different fiberglass ...supports were compared, and the catalyst supported over a fiber mat showed better performance, with a lower pressure drop (>35% of reduction) and a slightly higher removal efficiency (about 2%) than that supported over glass wool. For every target compound in the whole range of relative humidity studied (4–75%), the photocatalytic activity increased with the air water content. The removal of the compounds in the binary and ternary mixtures was depressed, even >90% for toluene, compared with individual tests. Xylene was the main compound responsible for the inhibition effects in the mixtures, followed by toluene and butyl acetate. Photodegradation of individual compound data was well fitted by both simple and bimolecular Langmuir–Hinselwood (LH) kinetic models.
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IJS, KILJ, NUK, PNG, UL, UM
A three-step surface modification consisting of activation with NaOH, functionalisation with a silica precursor and organofluorosilane mixture (FSiT), and curing was applied to a poly(vinylidene ...fluoride) (PVDF) membrane for the recovery of dissolved methane (D-CH4) from aqueous streams. Based on the results of a statistical experimental design, the main variables affecting the water contact angle (WCA) were the NaOH concentration and the FSiT ratio and concentration used. The maximum WCA of the modified PVDF (mPVDFmax) was >140° at a NaOH concentration of 5%, an FSiT ratio of 0.55 and an FSiT concentration of 7.2%. The presence of clusters and a lower surface porosity of mPVDF was detected by FESEM analysis. In long-term stability tests with deionised water at 21 L h−1, the WCA of the mPVDF decreased rapidly to around 105°, similar to that of pristine nmPVDF. In contrast, the WCA of the mPVDF was always higher than that of nmPVDF in long-term operation with an anaerobic effluent at 3.5 L h−1 and showed greater mechanical stability, since water breakthrough was detected only with the nmPVDF membrane. D-CH4 degassing tests showed that the increase in hydrophobicity induced by the modification procedure increased the D-CH4 removal efficiency but seemed to promote fouling.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A full-scale biotrickling filter (BTF) treating acetone air emissions of wood-coating activities showed difficulties to achieve outlet concentrations lower than 125 mg C m
−3
, especially for high ...inlet concentrations and oscillating emissions. To solve this problem, a laboratory investigation on acetone removal was carried out simulating typical industrial conditions: discontinuous and variable inlet concentrations and intermittent spraying. The results were evaluated in terms of removal efficiency and outlet gas emission pattern. Industrial emissions and operational protocols were simulated: inlet load up to 70 g C m
−3
h
−1
during 2 cycles of 4 h per day and intermittent trickling of 15 min per hour. The outlet gas stream of the pollutant was affected by intermittent spraying, causing a fugitive emission of pollutant. Complete removal efficiency was obtained during non-spraying. Average removal efficiencies higher than 85% were obtained, showing the feasibility of BTF to treat acetone. The outlet gas stream showed a clear dependence on the pH of the trickling liquid, decreasing the removal at pH < 5.5. Thus, a proper control of alkalinity, with regular NaHCO
3
addition, was required for successful operation. The laboratory findings were fruitfully transferred to the industry, and the removal of acetone by full-scale BTF was improved.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The influence of the addition of granular activated carbon (GAC) on the anaerobic treatment of wastewater with a mixture of ethanol and 1-ethoxy-2-propanol (E2P), which are typical pollutants from ...the flexographic/printing industry, was evaluated. For this purpose, the reactor performance and microbial community in two continuous stirred tank reactors (CSTRs),
i.e.
control and GAC supplemented, were assessed. Both reactors, seeded with anaerobic granular biomass, showed similar global performance (RE > 93%), except after organic load shocks and after E2P addition. GAC supplementation substantially enhanced the response of the biological system to organic load shocks and reduced the acclimation period for E2P degradation. This improvement was found to be related to the effect of GAC on the microbial community which, in turn, is related to an increase in the degradation rate of intermediates (acetone and isopropanol). The microbial community was analysed through denaturing gradient gel electrophoresis and high-throughput sequencing. Both methods showed an evolution from the inoculum to the final time point and considerable enrichment in microorganisms involved in direct interspecies electron transfer, such as
Geobacter
species in the final biomass samples, especially in the biomass attached to the GAC.
Granular activated carbon addition could promote specific microorganisms which favour the anaerobic removal of non-readily biodegradable solvent compounds through their influence on the degradation (methanogenesis) of intermediates.
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