Application of biochars and solid fraction of digestate to decrease soil solution Cd, Pb and Zn concentrations in contaminated sandy soils.

Biochar prepared from waste biomass was evaluated as a soil amendment to immobilize metals in two contaminated soils. A 60-day incubation experiment was set up on a French technosol which was heavily contaminated with Pb due to former mining activities. Grass biochar, cow manure biochar (CMB) and two lightwood biochars differing in particle size distribution (LWB1 and LWB2) were amended to the soil at a rate of 2% (by mass). Rhizon soil moisture samplers were employed to assess the Pb concentrations in the soil solution at regular times. After 30 days of incubation, soil solution concentrations in the CMB-amended soil decreased by more than 99% compared to the control. CMB was also applied to a moderately contaminated Flemish soil and resulted in lowered soil solution Cd and Zn concentrations. While the application of 4% CMB resulted in 90% and 80% reductions in soil solution concentrations of Cd and Zn, respectively, the solid fraction of digestate (as a reference) reduced the soil pore water concentrations by only 63% for Cd and 73% for Zn, compared to the concentrations in the control. These results emphasize the potential of biochar to immobilize metals in soil and water systems, thus reducing their phytotoxicity.

Dynamic performance of combined biochar from co-pyrolysis of pig manure with invasive weed: Effect of natural aging on Pb and As mobilization in polluted mining soil.

Due to the natural biochar aging, the improvement of soil quality and immobilization of soil pollutants achieved by biochar may change; understanding the dynamic evolution of the in situ performance of biochar in these roles is essential to discuss the long-term sustainability of biochar remediation. Therefore, in this study, combined biochar from co-pyrolysis of pig manure and invasive Japanese knotweed - P1J1, as well as pure pig manure - PM - and pure Japanese knotweed - JK - derived biochar were applied to investigate their remediation performance in a high As- and Pb-polluted soil with prolonged incubation periods (up to 360 days). Biochar application, especially P1J1 and PM, initially promoted soil pH, dissolved organic carbon, and EC, but the improvements were not constant through time. The JK-treated soil exhibited the highest increase of soil organic matter (OM), followed by P1J1 and then PM, and OM did not change with aging. Biochar, especially P1J1, was a comprehensive nutrient source of Ca, K, Mg, and P to improve soil fertility. However, while soluble cationic Ca, K, and Mg increased with time, anionic P decreased over time, indicating that continuous P availability might not be guaranteed with the aging process. The total microorganism content declined with time; adding biochars slowed down this tendency, which was more remarkable at the later incubation stage. Biochar significantly impeded soil Pb mobility but mobilized soil As, especially in PM- and P1J1-treated soils. However, mobilized As gradually re-fixed in the long run; meanwhile, the excellent Pb immobilization achieved by biochars was slightly reduced with time. The findings of this study offer fresh insights into the alterations in metal(loid)s mobility over an extended duration, suggesting that the potential mobilization risk of As is reduced while Pb mobility slightly increases over time.

Evaluation of South Korean marine waste resources for hydrochar production: Effect of process variables.

This study assessed the hydrochar production potential of fish and crustacean waste from 8 marine species (Scomber japonicus, Trichiurus lepturus, Larimichthys polyactis, Trachurus trachurus, Paralichthys olivaceus Litopenaeus vannamei, Portunus trituberculatus, and Penaeus monodon) through hydrothermal carbonization (HTC) of their waste fractions. The impact of reaction temperature (200 - 240°C), fixed residence time (5 h), and water-to-biomass ratio (7) on HTC was analyzed. The results showed that hydrochar yields varied between fish (15.1 - 21.5 %) and crustaceans (36.9 - 69.3 %). The elemental composition and surface properties of the hydrochar were influenced by reaction temperature, as indicated by the pH point of zero charge. The adsorption capacity of hydrochar was tested for methylene blue (MB, 2.7 - 10.8 mg/g) and methyl orange (MO, 5.9 - 9.2 mg/g), with MO showing higher adsorption, except for Scomber japonicus, Larimichthys polyactis, and Trachurus trachurus. These findings highlight the significant potential for converting marine waste into valuable hydrochar, contributing to waste management and sustainable resource utilization.

Microwave assisted and conventional hydrothermal treatment of waste seaweed: Comparison of hydrochar properties and energy efficiency.

Waste seaweed is a valuable source for converting into value-added carbon materials. In this study, the production of hydrochar from waste seaweed was optimized for hydrothermal carbonization in a microwave process. The produced hydrochar was compared with hydrochar synthesized by the regular process using a conventional heating oven. The results show that hydrochar produced with a holding time of 1 h by microwave heating has similar properties to the hydrochar produced in a conventionally heated oven for 4 h (200 °C and water/biomass ratio 5): carbon mass fraction (52.4 ± 3.9 %), methylene blue adsorption capacity (40.2 ± 0.2 mg g-1) and similar observations on surface functional groups and thermal stability were made between hydrochars produced by both methods. The analysis of energy consumption showed microwave assisted carbonization consume higher energy in compare to conventional oven. The present results suggest that hydrochar made from waste seaweed and using the microwave technique could be an energy-saving technology for producing hydrochar with similar specifications to hydrochar produced by conventional heating methods.

Assessment of the properties of aging biochar used as a substrate in constructed wetlands.

Biochar has gained global recognition as an effective tool for environmental remediation, and is increasingly being used as an alternative substrate in constructed wetlands (CWs). While, most studies have focused on the positive effects of biochar for the pollutant removal in CWs, less is known about aging and longevity of the embedded biochar. This study investigated the aging and stability of biochar embedded in CWs post-treating the effluent of a municipal and an industrial wastewater treatment plant. Litter bags containing biochar were inserted into two aerated horizontal subsurface flow CWs (350 m2 each), and retrieved on several dates (8-775 days after burial) for assessment of weight loss/gain and changes in biochar characteristics. Additionally, a 525-day laboratory incubation test was conducted to analyze biochar mineralization. The results showed that there was no significant biochar weight loss over time, but a slight increase in weight (2.3-3.0%) was observed at the end, likely due to mineral sorption. Biochar pH remained stable except for a sudden drop at the beginning (8.6-8.1), while the electrical conductivity continued to increase (96-256 µS cm-1) throughout the experiment. The sorption capacity of the aged biochar for methylene blue significantly increased (1.0-1.7 mg g-1), and a change in the biochar's elemental composition was also noted, with O-content increasing by 13-61% and C content decreasing by 4-7%. Despite these changes, the biochar remained stable according to the criteria of the European Biochar Foundation and International Biochar Initiative. The incubation test also showed negligible biochar mass loss (<0.02%), further validating the stability of the biochar. This study provides important insights into the evolution of biochar characteristics in CWs.

Metal behavior and soil quality changes induced by the application of tailor-made combined biochar: An investigation at pore water scale.

The remediation performance of biochar varies based on the biomass used for its production. Further innovation involves developing tailor-made biochar by combining different raw materials to compensate for the limitations of pure biochar. Therefore, tailor-made combined biochar produced from the co-pyrolysis of pig manure and invasive Japanese knotweed (P1J1), as well as biochars produced from these feedstocks separately, i.e., pure pig manure (PM) and pure Japanese knotweed (JK), were applied to Pb and As contaminated soil to evaluate the biochar-induced changes on soil properties, microbial activity, DOM, and metal and metalloids solubility at the soil pore water scale. Biochar application reduced soluble Pb, whereas enhanced the As mobility; the increased soil pH after biochar addition played a fundamental role in reducing the Pb solubility, as revealed by their significant negative correlation (r = -0.990, p < 0.01). In contrast, the release of dissolved P strongly influenced As mobilization (r = 0.949, p < 0.01), especially in P-rich PM and P1J1 treatments, while JK showed a marginal effect in mobilizing As. Soils treated with PM, P1J1, and JK mainly increased Gram-negative bacteria by 56 %, 52 %, and 50 %, respectively, compared to the control. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis identified three components in pore water DOM, C1 (long wavelength humic-like), C2 (short wavelength humic-like), and C3 (protein-like), which were dominant respectively in the P1J1, JK, and PM-added soil. A principal component analysis (PCA) confirmed that the PM and P1J1 had similar performance and were more associated with releasing P and Mg and specific DOM components (C1 and C3). Meanwhile, P1J1 supplemented soil OM/OC and K, similar to JK. The results of this study suggest that combined biochar P1J1 can comprehensively enhance soil quality, embodying the advantages of pure PM and JK biochar while overcoming their shortcomings.

Improving biochar properties by co-pyrolysis of pig manure with bio-invasive weed for use as the soil amendment.

Over recent years, pyrolysis has grown into a mature technology with added value for producing soil improvers. Further innovations of this technology lie in developing tailor-made products from specific feedstocks (or mixtures thereof) in combination with adjusted mixing ratio-temperature regimes. In this context, co-pyrolysis of pig manure (PM) and the invasive plant Japanese knotweed (JK) at different mixture ratios (w/w) of 3:1 (P3J1), 1:1 (P1J1), and 1:3 (P1J3) and varying temperatures (400-700 °C) was studied to address the low carbon properties and heavy metals (HMs) risks of manure-derive biochars and beneficially ameliorate the bio-invasion situation by creating value from the plant biomass. Co-pyrolysis of PM with JK increased by nearly 1.5 folds the fixed carbon contents in the combined feedstock biochars obtained at 600 °C compared with PM-derived biochar alone, and all combined feedstock biochars met the requirements for soil improvement and carbon sequestration. The total HMs in PM biochars were significantly reduced by adding JK. The combined feedstock biochar P1J1 generated at 600 °C was the most effective in transforming Cu and Zn into more stable forms, accordingly reducing the associated environmental risk of heavy metal leaching from the biochar. In addition, the accumulation of macronutrients can be an added benefit of the co-pyrolysis process, and P1J1-600 was also the biochar that retained the most nutrients (P, Ca, Mg, and K).

Cell Behavior Changes and Enzymatic Biodegradation of Hybrid Electrospun Poly(3-hydroxybutyrate)-Based Scaffolds with an Enhanced Piezoresponse after the Addition of Reduced Graphene Oxide.

This is the first comprehensive study of the impact of biodegradation on the structure, surface potential, mechanical and piezoelectric properties of poly(3-hydroxybutyrate) (PHB) scaffolds supplemented with reduced graphene oxide (rGO) as well as cell behavior under static and dynamic mechanical conditions. There is no effect of the rGO addition up to 1.0 wt% on the rate of enzymatic biodegradation of PHB scaffolds for 30 d. The biodegradation of scaffolds leads to the depolymerization of the amorphous phase, resulting in an increase in the degree of crystallinity. Because of more regular dipole order in the crystalline phase, surface potential of all fibers increases after the biodegradation, with a maximum (361 ± 5 mV) after the addition of 1 wt% rGO into PHB as compared to pristine PHB fibers. By contrast, PHB-0.7rGO fibers manifest the strongest effective vertical (0.59 ± 0.03 pm V-1 ) and lateral (1.06 ± 0.02 pm V-1 ) piezoresponse owing to a greater presence of electroactive ß-phase. In vitro assays involving primary human fibroblasts reveal equal biocompatibility and faster cell proliferation on PHB-0.7rGO scaffolds compared to pure PHB and nonpiezoelectric polycaprolactone scaffolds. Thus, the developed biodegradable PHB-rGO scaffolds with enhanced piezoresponse are promising for tissue-engineering applications.

Combined Heat and Mass Transfer Associated with Kinetics Models for Analyzing Convective Stepwise Drying of Carrot Cubes.

Stepwise drying is an effective technique that promotes energy saving without additional capital cost. The stepwise drying mode was investigated for energy consumption and dried product qualities using a coupled heat and mass transfer model associated with kinetics equations of volume shrinkage and degradation of ß-carotene in carrot cubes. Simulations were performed using a finite element method with extension of a chemical species transport. Validation experiments were carried out under constant drying modes at 60 °C, 70 °C and 80 °C using a lab-scale convective hot air dryer. The verified models were subsequently employed to investigate the effects of two step-up drying modes (60 to 70 °C and 60 to -80 °C). The optimal drying condition was determined using the synthetic evaluation index (SI) with criteria of high specific moisture evaporation rate (SMER), low shrinkage ratio and ß-carotene degradation. Simulated results showed comparable agreement with experimental data of moisture content, shrinkage ratio and ß-carotene ratio. Step-up drying of 60 to 70 °C gave the highest SMER of 0.50 × 10-3 kg of water evaporated per kWh, while the operation at constant temperature of 80 °C gave the lowest value of 0.19 × 10-3 kg of water evaporated per kWh. Model-predicted results showed less shrinkage of carrot cubes, but higher degradation of ß-carotene under step-up drying compared to single-stage drying under temperature of 60 °C. Based on the highest SI value (0.36), carrot cubes were optimally dried under step-up mode of 60 to 70 °C.

Biochar and activated carbon enhance ethanol conversion and selectivity to caproic acid by Clostridium kluyveri.

Syngas from biomass or steel mills can be fermented into a dilute stream of ethanol and acetic acid, which requires energy intensive distillation for product recovery. This can be circumvented by selective secondary fermentation of the syngas fermentation effluent to caproic acid as easier recoverable platform chemical with Clostridium kluyveri. Here, we explore the impact of biochar and activated carbon on this process. Changes during the fermentation with biochar or activated carbon were monitored, different doses were tested and the recyclability of biochar and activated carbon was assessed. Biochar decreased the lag phase and increased the caproic acid production rate (up to 0.50 g·L-1·h-1). Upon recycling for subsequent fermentation, biochar retained this property largely. Activated carbon addition, especially at high dose, could potentially increase the conversion and selectivity towards caproic acid to 14.15 g·L-1 (control: 11.01 g·L-1) and 92% (control: 84%), respectively.

Superheated steam as carrier gas and the sole heat source to enhance biomass torrefaction.

Superheated steam (SHS) has been used as a carrier gas for pressurized steam torrefaction, steam explosion or pyrolysis, but is barely used as a heat source. However, SHS is superior in thermal capacity and heat transfer coefficient resulting in even heating and fast heating rates. Therefore, this work applied SHS as the sole heat source for torrefaction at ambient pressure. A setup was specially designed and capable of heating wood shavings at a rate >120 °C•min-1. Solid products were analyzed in many aspects and demonstrated the enhanced organics conversion owing to SHS torrefaction. Torrefied biomass was comparable to slow pyrolysis char in fuel quality and superior to that of conventional torrefactions. Moreover, SHS torrefaction was super-timesaving. A coal-like product (HHV of 27.84 MJ•kg-1) was achieved in only 15 min at 350 °C. Overall, SHS torrefaction boosted biomass densification and gaveriseto greater production efficiency.

Chemical stabilization of Cd-contaminated soil using fresh and aged wheat straw biochar.

Metal mining and smelting activities can introduce a substantial amount of potentially toxic elements (PTE) into the environment that can persist for an extended period. That can limit the productivity of the land and creates dangerous effects on ecosystem services. The effectiveness of wheat straw biochar to immobilize Cd in contaminated soil due to metal smelting activities was investigated in this study. The biochar carbon stability and long-term provisioning of services depend on the biochar production conditions, nature of the feedstock, and the biotic and abiotic environmental conditions in which the biochar is being used. Within this context, three types of wheat straw biochar were produced using a screw reactor at 400 °C, 500 °C, and 600 °C and tested in a laboratory incubation study. Soil was amended with 2 wt% of biochar. Both fresh and aged forms of biochar were used. Biochars produced at lower temperatures were characterized by lower pH, a lower amount of stable C, and higher amounts of acidic surface functional groups than the freshly produced biochars at higher production temperatures. At the end of the 6 months of incubation time, compared to the soil only treatment, fresh and aged forms of wheat straw biochar produced at 600 °C reduced the Cd concentration in soil pore water by 22% and 15%, respectively. Our results showed that the aged forms of biochar produced at higher production temperatures (500 °C and 600 °C) immobilized Cd more efficiently than the aged forms of lower temperature biochar (400 °C). The findings of this study provide insights to choose the production parameters in wheat straw biochar production while considering their aging effect to achieve successful stabilization of Cd in contaminated soils.

Effluent recirculation enables near-complete oxidation of organics during supercritical water oxidation at mild conditions: A proof of principle.

This work presents a continuous set-up for SCWO, which was operated at mild conditions (380 °C, 25 MPa, oxidant equivalence ratio of 2.0 and residence time of 26 s) to oxidize cellulose, lignin, and acetic acid as model compounds. The aim was to oxidize different organics consecutively to near completion in the same mild reaction conditions and set-up. These conditions can overcome some drawbacks associated to SCWO. To combine near complete oxidation with the applied mild process conditions, aqueous effluent from SCWO, containing intermediates from incomplete oxidation, was recycled for consecutive oxidation. Meanwhile, fresh feedstock was continuously fed to retain the process capacity. Upon recycling the aqueous effluent three to four times, depending on the feedstock, the oxidation efficiency increased from 63.9%, 45.3% and 28.3% in a single pass for cellulose, lignin, and acetic acid, respectively, to near 100%. The principle of effluent recirculation should allow a compact set-up to perform almost complete oxidation of different organics at mild conditions. The principles and effects of effluent recirculation are outlined, as well as practical consequences and perspectives of this novel principle to SCWO.

Complete oxidation of organic waste under mild supercritical water oxidation by combining effluent recirculation and membrane filtration.

Supercritical water oxidation (SCWO) is a technology that can oxidize various organic (wet) wastes into CO2. Complete oxidation of specific organics with SCWO goes in tandem with tailored conditions, typically involving elevated operating temperatures, long residence times, high oxidizer-to-waste ratios, or a combination of those, which promote difficulties, e.g., corrosion. These challenges hamper the practical implementation of SCWO, albeit SCWO offers excellent oxidation efficiencies. This work proposes a novel process combining mild supercritical water oxidation (SCWO) with membrane filtration to enhance the oxidation of organics. The modified SCWO works at mild reaction conditions (i.e., 380 °C, 25 MPa and oxidizer equivalence ratios as low as 1.5) to potentially decrease the risks. The membrane filtration discards clean effluent and recycles the retentate (containing incomplete oxidized organics) back to the mild SCWO process for further oxidation, thereafter resulting in near-complete removal of organics. Fresh feed is continuously added, as in the conventional process, along with recycled retentate to guarantee the throughput of the modified SCWO process. A mixture of SCWO-resistant volatile fatty acids (TOC = 4000 mg·L-1) was studied to validate the proposed process. The proposed process in this study enhances the organic decomposition from 43.2% to 100% at mild conditions with only 10% capacity loss. CO2 was the dominant gas product with traces of CO and H2. Carbon output in the gas products increased with recirculation and got close to the carbon input of the freshly added feed ultimately. The results indicated that the proposed process maximized the benefits of both technologies, which allows the development of a technological process for supercritical water oxidation, as well as a new stratagem for waste treatment.

Assessment of carbon recovery from solid organic wastes by supercritical water oxidation for a regenerative life support system.

The carbon recovery from organic space waste by supercritical water oxidation (SCWO) was studied to support resource recovery in a regenerative life support system. Resource recovery is of utmost importance in such systems which only have a limited total amount of mass. However, the practical waste treatment strategies for solid space wastes employed today are only storing and disposal without further recovery. This work assesses the performance of SCWO at recovering organic wastes as CO2 and water, to discuss the superiority of SCWO over most present strategies, and to evaluate the different SCWO reactor systems for space application. Experiments were carried out with a batch and a continuous reactor at different reaction conditions. The liquid and gas products distribution were analyzed to understand the conversion of organics in SCWO. Up to 97% and 93% of the feed carbon were recovered as CO2 in the continuous and the batch reactor, respectively. Residual carbon was mostly found as soluble organics in the effluent. Compared with the batch reactor, the continuous reactor system demonstrated a ten times higher capacity within the same reactor volume, while the batch reactor system was capable of handling feeds that contained particulate matter though suffering from poor heat integration (hence low-energy efficiency) and inter-batch variability. It was concluded that SCWO could be a promising technology to treat solid wastes for space applications. A continuous reactor would be more suitable for a regenerative life support system.

Assessment of biomass demineralization on gasification: From experimental investigation, mechanism to potential application.

Considering the advantages (e.g. agglomeration mitigation) and disadvantages (e.g. inorganic species catalysis removal) of biomass demineralization, it is valuable to investigate its effects on gasification performance, thus assessing its necessity prior to performing gasification. To accomplish this, corn straw (CS) was demineralized to different degrees with H2O and HCl, respectively. H2O and HCl demineralization behaved different abilities to inorganic species removal. Cellulose and hemicelluloses content decreased, while lignin content increased, especially with HCl demineralization. The experiments were investigated by using a bench-scale downdraft fixed-bed gasifier at 600-800 °C and were further analyzed via thermogravimetric coupled with Fourier transform infrared spectrometry. Demineralization demonstrated a positive effect on gasification at lower temperatures (600-700 °C) for a dominant effect of lignin content and an insignificant effect of inorganic species removal. However, the catalysis of inorganic species increased as the temperature increased, resulting in the highest H2 (11.30 vol%) and CO (16.02 vol%) production of raw CS compared to demineralized CS at 800 °C. Inorganic species had a dual positive effect on CO generation, promoting both CO2 and char generation leading to a higher CO yield following Boundouard reaction, and increasing the formation of active intermediates thus producing more CO. These effects enhanced when the gasification temperature increased. Additionally, inorganic species catalyzed the aromatic rings rearrangement to generate more H2O, thus driving the endothermic Primary water-gas to produce H2. This was also positively correlated with gasification temperature. Therefore, raw CS demonstrated higher H2 and CO production than demineralized CS at a higher gasification temperature. Moreover, the promotion effect of inorganic species on thermal devolatilization of methoxyl groups and Methanation reaction led to the higher CH4 production of raw CS. This research clarifies the effects of biomass demineralization on its gasification and suggests the potential application.

Analytical Py-GC/MS of Genetically Modified Poplar for the Increased Production of Bio-aromatics.

Genetic engineering is a powerful tool to steer bio-oil composition towards the production of speciality chemicals such as guaiacols, syringols, phenols, and vanillin through well-defined biomass feedstocks. Our previous work demonstrated the effects of lignin biosynthesis gene modification on the pyrolysis vapour compositions obtained from wood derived from greenhouse-grown poplars. In this study, field-grown poplars downregulated in the genes encoding CINNAMYL ALCOHOL DEHYDROGENASE (CAD), CAFFEIC ACID O-METHYLTRANSFERASE (COMT) and CAFFEOYL-CoA O-METHYLTRANSFERASE (CCoAOMT), and their corresponding wild type were pyrolysed in a Py-GC/MS. This work aims at capturing the effects of downregulation of the three enzymes on bio-oil composition using principal component analysis (PCA). 3,5-methoxytoluene, vanillin, coniferyl alcohol, 4-vinyl guaiacol, syringol, syringaldehyde, and guaiacol are the determining factors in the PCA analysis that are the substantially affected by COMT, CAD and CCoAOMT enzyme downregulation. COMT and CAD downregulated transgenic lines proved to be statistically different from the wild type because of a substantial difference in S and G lignin units. The sCAD line lead to a significant drop (nearly 51%) in S-lignin derived compounds, while CCoAOMT downregulation affected the least (7-11%). Further, removal of extractives via pretreatment enhanced the statistical differences among the CAD transgenic lines and its wild type. On the other hand, COMT downregulation caused 2-fold reduction in S-derived compounds compared to G-derived compounds. This study manifests the applicability of PCA analysis in tracking the biological changes in biomass (poplar in this case) and their effects on pyrolysis-oil compositions.

Sub- and supercritical water oxidation of anaerobic fermentation sludge for carbon and nitrogen recovery in a regenerative life support system.

Sub- and supercritical water oxidation was applied to recover carbon as CO2, while maintaining nitrogen as NH4+ or NO3-, from sludge obtained from an anaerobic fermenter running on a model waste composed of plant residues and human fecal matter. The objective was to fully convert carbon in the organic waste to CO2 while maintaining nutrients (specifically N) in the liquid effluent. In regenerative life support systems, CO2 and nutrients could then be further used in plant production; thus creating a closed carbon and nutrient cycle. The effect of the operational parameters in water oxidation on carbon recovery (C-to-CO2) and nitrogen conversion (to NH4+, NO3-) was investigated. A batch micro-autoclave reactor was used, at pressures ranging between 110 and 300 bar and at temperatures of 300-500 °C using hydrogen peroxide as oxidizer. Residence times of 1, 5 and 10 min were tested. Oxidation efficiency increased as temperature increased, with marginal improvements beyond the critical temperature of water. Prolonging the residence time improved only slightly the carbon oxidation efficiency. Adequate oxygen supply, i.e., exceeding the stoichiometrically required amount, resulted in high carbon conversion efficiencies (>85%) and an odorless, clear liquid effluent. However, the corresponding oxidizer use efficiency was low, up to 50.2% of the supplied oxygen was recovered as O2 in the effluent gas and did not take part in the oxidation. Volatile fatty acids (VFAs) were found as the major soluble organic compounds remaining in the effluent liquid. Nitrogen recovery was high at 1 min residence time (>94.5%) and decreased for longer residence times (down to 36.4% at 10 min). Nitrogen in the liquid effluent was mostly in the form of ammonium.

Accelerated solid-phase dynamic extraction of toluene from air.

Solid-phase dynamic extraction (SPDE) belongs to the most innovative sample preparation and enrichment techniques. However, there is still a lack of knowledge on the fundamentals of SPDE and its applicability in the field of environmental monitoring. A homemade sampling device is constructed to make a detailed study of SPDE kinetics for toluene extraction. It proved that at least 50 aspirating and dispensing cycles were necessary to obtain toluene equilibration between gas and coating phase. A mechanistic model is proposed to explain that in every dispensing step during SPDE, significant losses of retained analytes (up to 48%) occur due to desorption processes. A new accelerated solid-phase dynamic extraction procedure (ASPDE) has been developed that avoids dispensing stages during extraction. The resulting extraction time proves to be 1.7 min, being a reduction by a factor of 37 compared with the SPDE extraction time. ASPDE proved to have high potential in ambient/indoor air monitoring. The limit of detection for toluene was determined to be 56 ppb(v), i.e. a factor of respectively, 6 and 35 lower than obtained with SPME and conventional headspace sampling with gas syringe.