Photolysis, Sonolysis, and Photosonolysis of Trichloroethane (TCA), Trichloroethylene (TCE), and Tetrachloroethylene (PCE) Without Catalyst

Photolysis, sonolysis, and photosonolysis of common groundwater contaminants, namely 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, were investigated using a flow-through photosono reactor system. Simulated groundwater containing the chlorinated volatile organic compounds (VOCs) was exposed to ultraviolet light (UV), ultrasonication (US), and UV and US concurrently (UVUS), without a photo catalyst. VOC removal efficiencies of the UV, US, and UVUS treatment processes were computed from the VOC concentrations in influent and effluent of the reactor. The process using UVUS exhibited larger degradation efficiencies than that with UV and US separately in most cases; however, statistical analysis showed that the UVUS treatment efficiency is likely to be additive of the UV and US treatment efficiencies. The results also showed that the increase of the detention time from 26 to 60 min had no significant effect on the VOC removal efficiencies in these processes.     

A Comprehensive Study of Deep Catalytic Oxidation of Benzene, Toluene, Ethyl Acetate, and their Mixtures over Pd/ZSM-5 Catalyst: Mutual Effects and Kinetics

Reaction behaviors and kinetics of catalytic oxidation of benzene, toluene, and ethyl acetate with feed concentrations in the range of 700–5,000 ppm over Pd/ZSM-5 catalyst were investigated. Results for single components show that ethyl acetate (T ₅₀?=?190–200°C) is more easily oxidized than benzene (T ₅₀?=?215–225°C) and toluene (T ₅₀?=?225–235°C). The conversion of ethyl acetate was increased with the increase of its feeding concentration, while the opposite behaviors were observed for benzene and toluene as their conversion rates were decreased with the increase of the inlet concentration. Different behaviors were observed in catalytic oxidation of volatile organic compound (VOC) multi-components, the presence of benzene or toluene inhibits the conversion of ethyl acetate, and the aromatic hydrocarbons inhibit each other in all cases. Ethyl acetate possesses obvious inhibitory effect on benzene oxidation, while it is interesting to note that ethyl acetate has a promotion effect on toluene conversion. The kinetic data were fitted by the Power-law and Mars–van Krevelen kinetic models. The fitting result shows that the Power-law model is more suitable for predicting the conversion of benzene than the other VOCs, and the Mars–van Krevelen model can accurately express the reaction rate of all investigated VOCs.     

The Relationship Between Indoor, Outdoor and Personal VOC Concentrations in Homes, Offices and Schools in the Metropolitan Region of Kocaeli, Turkey

Human exposure to volatile organic compounds (VOCs) and residential indoor and outdoor VOC levels had hitherto not been investigated in Turkey. This study details investigations of indoor, outdoor, and personal exposure to VOCs conducted simultaneously in 15 homes, 10 offices and 3 schools in Kocaeli during the summer of 2006 and the winter of 2006–2007. All VOC concentrations were collected by passive sampling over a 24-h period and analyzed using thermal desorption (TD) and a gas chromatography/flame ionization detector (GC/FID). Fifteen target VOCs were investigated and included benzene, toluene, m/p-xylene, o-xylene, ethylbenzene, styrene, cyclohexane, 1,2,4-trimethylbenzene, n-heptane, n-hexane, n-decane, n-nonane, n-octane and n-undecane. Toluene levels were the highest in terms of indoor, outdoor, and personal exposure, followed by m/p-xylene, o-xylene, ethylbenzene, styrene, benzene and n-hexane. In general, personal exposure concentrations appeared to be slightly higher than indoor air concentrations. Both personal exposure and indoor concentrations were generally markedly higher than those observed outdoors. Indoor target compound concentrations were generally more strongly correlated with outdoor concentrations in the summer than in winter. Indoor/outdoor ratios of target compounds were generally greater than unity, and ranged from 0.42 to 3.03 and 0.93 to 6.12 in the summer and winter, respectively. Factor analysis, correlation analyses, indoor/outdoor ratios, microenvironment characteristics, responses to questionnaires and time activity information suggested that industry, and smoking represent the main emission sources of the VOCs investigated. Compared with the findings of earlier studies, the level of target analytes in indoor air were higher for several target VOCs, indicating a possible trend toward increased inhalation exposure to these chemicals in residential environments.     

Non-thermal Plasma as an Innovative Option for the Abatement of Volatile Organic Compounds: a Review

Volatile organic compounds (VOCs) cause global and local impacts, resulting in environmental, health, and economic adverse effects. Industrial and waste management activities are the main anthropogenic stationary sources of VOCs in the atmosphere. The traditional technologies for the treatment of VOC-contaminated air present several limitations when treating effluents with low VOC concentrations, high airflow rate, and with compounds with low solubility in water. However, a novel technology, based on non-thermal plasmas (NTPs) and catalysis, has shown promising results in air purification. In this framework, after an initial overview on NTP-catalysis principles, this review presents and discusses 20 recent papers, with a threefold purpose: evaluating the most recent applications of NTP and NTP-catalysis reactors to the treatment of air-VOC mixtures, analyzing all the parameters that may influence the abatement efficiency and the by-product formation, and providing the reader with insights into the choice of the preferable configurations to use, based on the effluent type and the destination of the treated air. As a result of this review, NTPs may represent a promising option for indoor air treatment, especially because of the lower expected byproduct formation when treating low-concentrated VOC mixtures with relatively low air flow rates. If the target is the abatement of higher VOC concentrations, the higher energy efficiency obtainable in such conditions makes NTP-catalysis a cost-effective option for industrial applications. In addition, the formation of simpler and more soluble by-products makes NTPs a suitable technology for air pretreatment upstream of water-based removal technologies, such as absorption columns and biofilters.     

Organics Wastewater Degradation by a Mesoporous Chromium-Functionalized γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with H<Subscript>2</Subscript>O<Subscript>2</Subscript> Assistance

In this study, a mesoporous chromium-functionalized γ-Al₂O₃ (Cr/γ-Al₂O₃) catalyst was prepared by an impregnation method, and the catalytic activity was evaluated by the degradation of organics wastewater. The prepared catalyst was characterized by X-ray photoelectron spectroscopy, X-ray diffraction, nitrogen adsorption-desorption experiments, and scanning electron microscopy. The characterization results confirmed that the pores in the Cr/γ-Al₂O₃ catalyst distributed broadly in the mesoporous region, and the active chromium species were highly dispersed on the catalyst surface. The catalytic activity tests showed that the Cr/γ-Al₂O₃ catalyst exhibited a superior performance for the degradation of organics wastewater with H₂O₂ assistance. And the methylene blue (MB) disappeared within 20 min and the COD removal reached 76.5% within 40 min for the MB-simulated wastewater; for the phenol-simulated wastewater, the phenol removal was above 95% and the corresponding COD removal reached 71% within 40 min. Such an excellent catalytic performance demonstrates that the Cr/γ-Al₂O₃ catalyst has a potential application in the degradation of complex organics wastewater simultaneously.     

气相抽提法（SVE）去除土壤中挥发性有机污染物的试验研究

通过模拟土壤气相抽提技术（Soil Vapor Extraction,SVE）通风处理甲苯、乙苯、正丙苯混合污染的黄棕壤,研究了不同通风流量、不同土壤含水率、间歇通风等因素对目标污染物去除率的影响。结果表明,通风流量和含水率是影响去除率的重要因素。当柱径14 cm、土壤粒径为10目连续通风时,最佳通风流量为0.15 L.min-1,最佳含水率约17.98%条件下,甲苯、乙苯、正丙苯的去除率分别为99.84%、99.45%、98.25%,总挥发性有机物（Total VOCs,TVOCs）去除率达到了99.30%,且优于间歇通风;含水率为6.01%、24.73%时,TVOCs的去除率仅为63.03%、89.03%,表明含水率过高或过低都不利于VOCs的去除;苯环上支链越长,分子量越大,沸点越高,越难以被脱附去除,反之亦然,表明有机物的分子结构和大小也是影响通风效果的重要因素。     

Hydroxyl Radical Generation and Contaminant Removal from Water by the Collapse of Microbubbles Under Different Hydrochemical Conditions

The present study addresses the mechanism of hydroxyl radical (·OH) generation by the collapse of microbubbles in water solution. The influence of gas supply and flow rate, solution pH, and ionic strength on the aeration efficiency, free radical generation, and contaminant removal (take methylene blue as an example) are elucidated. The results showed that the degradation rate of methylene blue by ·OH increased with flow rate as well as in acidic or alkaline solutions compared to that in neutral conditions. ·OH was shown to be produced by the reaction between protons and oxygen radicals generated by the decomposition of O₂ rather than water molecules. A greater concentration of O₂ or H⁺ thus promoted the reaction, resulting in effective removal at a high flow rate or low pH. Nevertheless, there was considerable methylene blue removal at high pH, driven by the production of the dye cation through the dissociation of methylene blue and the high electronegativity of bubbles at high pH, thus enhancing interface adsorption and degradation, as well as by the high ionic strength of the solution helping to generate ultrafine bubbles and maintaining them through ionic shielding. The current work provides useful insights into the application of microbubble as a promising technique.     

Bioremoval of Surfactant from Laundry Wastewater in Optimized Condition by Anoxic Reactors

Effects of ethanol and nitrate on linear alkyl benzene sulfonate (LAS) degradation were investigated using central composite design. At experimental design, removal of 99.9% was observed in batch reactors (1 L) with 9.8 to 41.2 mg L^?1 of LAS. The batch reactors were kept under agitation at 120 rpm and 30 °C. Ethanol (co-substrate) and nitrate (electron acceptor) were statistically significant factors (p?<?0.05) in surfactant removal. Optimal values were 97.5 and 88 mg L^?1 for ethanol and nitrate, respectively. LAS removal was kinetically investigated by varying surfactant concentration while using optimal values. Batch I (27 mg L^?1 LAS) exhibited greater degradation rate (K^LAS) (0.054 h^?1) in the presence of ethanol and nitrate. Nonetheless, in Batch II (60 mg L^?1 LAS), the K^LAS values decreased in those reactors probably due to inhibition by excess substrate for same concentrations of nitrate and ethanol added in reactors. As LAS concentration increased, the dominance of bacterial populations also increased, whereas diversity index decreased from 2.8 (inoculum) to 2.4 and 2.5 for reactors with both added nitrate and ethanol and those with only added ethanol, respectively. Probably, a selection of microbial populations occurred in relation to LAS concentration. The nitrate and ethanol, at able concentration, made it possible the induction of denitrifying microrganisms foward to LAS removal.     

Heavy metal and volatile organic chemical removal and treatment in on-site wastewater infiltration systems

Solvents, greases, and rinse waters from routine vehicle maintenance contain heavy metals and volatile organic chemicals (VOCs). In Wisconsin, these fluids enter catch basins along with rinsing waters and are discharged to soil infiltration systems drainfields after mixing with domestic wastewaters in a septic tank. The purpose of this study was to monitor heavy metal and VOC removal and treatment in catch basins and septic tanks at four publicly-owned motor vehicle service stations (MVSS). Cadmium, chromium, and lead were found in catch basin wastewater, septic tank effluent, and septic tank sludge at concentrations ranging from 0.002–7.7 mg L^?1. Lead was found in the highest concentration. The highest concentrations of metals were in septic tank sludge. Of the >50 VOCs scanned for in catch basin wastewater, septic tank effluent, and septic tank sludge samples, 29 were found in concentrations that exceeded analytical detection limits. Concentrations of detected VOCs ranged from 1.0–15,800 µg L^?1 and the highest concentrations of VOCs were found in catch basin wastewater and septic tank sludge. Acetone, ethylbenzene, toluene, and xylenes were the most commonly found VOCs at all sampling locations. Thus, heavy metals and VOCs were not completely removed in catch basins and were discharged to septic tanks where removal occured possibly as these contaminants settled with solids in the sludge. The level of treatment was, however, inadequate and heavy metals and VOCs were discharged to drainfields.     

Removal of Natural Organic Matter from River Water Using Potassium Ferrate(VI)

In this research, we have investigated the removal efficiency of natural organic matter (NOM) from river and stream water using potassium ferrate(VI). For the study, ferrate was added in 100-ml water sample mixed either with humic acid or with fulvic acid. The removal efficiency at the ferrate dose of 2–46 mg/l (as Fe) was 21–74% for 10 mg/l humic acid and 48–78% for 10 mg/l fulvic acid. NOM was more effectively removed either at lower pH or at higher temperature. The removal performance by ferrate was comparable to that by traditional coagulants (i.e., alum, FeSO₄·7H₂O, and FeO(OH)). In addition, the removal rate of humic acid using traditional coagulants was improved by pretreatment with a very small dose of ferrate. The reaction between ferrate and humic acid was completed within 60 s, while showing first-order kinetic, and then reached a steady state.     

低温等离子体耦合Fe2O3催化剂去除粮食仓储环境中磷化氢

为了探究低温等离子体（Non-Thermal Plasma,NTP）耦合催化剂对粮仓中磷化氢（PH3）的去除效果,该文采用介质阻挡放电低温等离子体与催化剂耦合的反应装置,研究了NTP与Fe2O3催化剂耦合对PH3去除率的影响,并对耦合反应后的催化剂进行表征,分析产物及反应机理。结果表明,载体和催化剂与NTP耦合改变了NTP的放电状态,提高了PH3去除率;不同载体负载Fe2O3后,在输入功率超过53 W时,NTP与Fe2O3催化剂耦合对PH3去除率均高于无填充,Fe2O3/Al2O3与NTP耦合效果最好,去除效率达到了100%。耦合前后催化剂的表征结果表明,耦合反应之后,Fe2O3/Al2O3催化剂的比表面积降低了11.23%,Fe3+/(Fe2++Fe3+)含量提高了21.06%,Osur/(Olatt+Osur+Oads)含量减少了2.24%,Fe含量降低了4.69%,P含量增加了4.34倍。产物分析表明耦合后生成的主要产物为磷酸。研究结果表明NTP耦合Fe2O3/Al2O3催化剂具有很好的PH3去除效果,为粮食仓储行业去除磷化氢提供理论依据。     

Substrate-induced volatile organic compound emissions from compost-amended soils

The agronomic effects of composts, mineral fertiliser and combinations thereof on chemical, biological and physiological soil properties have been studied in an 18-year field experiment. The present study aimed at tracing treatment effects by evaluating the volatile organic compound (VOC) emission of the differently treated soils: non-amended control, nitrogen fertilisation and composts (produced from organic waste and sewage sludge, respectively) in combination with nitrogen fertiliser. Microbial community structure was determined by denaturing gradient gel electrophoresis (DGGE). Aerobic and anaerobic soil VOC emission was determined after glucose amendment using proton transfer reaction–mass spectrometry (PTR-MS). After inducing VOC production by substrate (glucose) addition and at the same time reducing oxygen availability to impair degradation of the produced VOCs, we were able to differentiate among the treatments. Organic waste compost did not alter the VOC emissions compared to the untreated control, whilst sewage sludge composts and mineral fertilisation showed distinct effects. This differentiation was supported by DGGE analysis of fungal 18S rDNA fragments and confirms earlier findings on bacterial communities. Three major conclusions can be drawn: (1) VOC patterns are able to discriminate among soil treatments. (2) Sewage sludge compost and mineral fertilisation have not only the strongest impact on microbial community composition but also on VOC emission patterns, but specific tracer VOCs could not be identified. (3) Future efforts should aim at a PTR-MS-linked identification of the detected masses.     

Suitability of Test Chambers for Analyzing Air Pollutant Removal by Plants and Assessing Potential Indoor Air Purification

A unique test chamber system, which enables experiments with plants under highly controlled environmental conditions, was used to examine the pollutant removal efficiency of plants. For this purpose, the removal of two different volatile organic compounds (VOC) (toluene, 2-ethylhexanol) from the air by aerial plant parts of two common indoor plant species (Dieffenbachia maculata and Spathiphyllum wallisii) was monitored. While the control over environmental conditions (temperature, relative humidity, CO₂ content, and light condition) worked very well in all experiments, control experiments with the empty chamber revealed high losses of VOC, especially 2-ethylhexanol, over the test duration of 48 h. Nonetheless, compared to the empty chamber, a significantly stronger and more rapid decline in the toluene as well as in the 2-ethylhexanol concentrations was observed when plants were present in the chamber. Interestingly, almost the same VOC removal as by aerial plant parts could be achieved by potting soil without plants. A comparative literature survey revealed substantial heterogeneity in previous results concerning the VOC removal efficiency of plants. This can be mainly attributed to a high diversity in experimental setup. The experimental setup used in the current study offers an excellent opportunity to examine also plant physiological responses to pollutant exposure (or other stressors) under highly controlled conditions. For the analysis of VOC removal under typical indoor conditions, to obtain data for the assessment of realistic VOC removal efficiencies by plants in rooms and offices, a guideline would be helpful to achieve more coherent findings in this field of research.     

Benzene Biodegradation under Anaerobic Conditions Coupled with Metal Oxides Reduction

Anaerobic benzene biodegradation was performed in batch experiments using Rhine River sediment as inoculum and amorphous Mn(IV) or Fe(III) as independent final electron acceptors. Benzene (4.5 μmol) was degraded in 80 and 710 days in batch experiments under Mn(IV) and Fe(III) reducing conditions, respectively. Highest benzene degradation rate, 0.07 μmol/day, was obtained under Mn (IV) reducing conditions, with soluble Mn(II) and CO₂ recoveries of 71.5% and 93% regarding to the stoichiometric values, respectively. Likewise, benzene biodegradation was performed in a continuous column coupled to the reduction of Mn(IV). Efficiency of benzene biodegradation was up to 97% under steady state operation in a sediment column operated continuously for more than 160 days. The carbon dioxide and Mn(II) recoveries were 88% and 77%, respectively, of the theoretical ratio according to the stoichiometry for benzene biodegradation.     

Volatile organic compounds (VOCs) in soils

Soils may act as sources or sinks of volatile organic compounds (VOCs). Many of the formed VOCs are produced by microorganisms, and it would be a challenge to investigate soil microbial communities by studying their VOC profile. Such “volatilomics” would have the advantage of avoiding extraction steps that are often a limit in genomic or proteomic approaches. Abundant literature on microbially produced VOCs is available, and in particular novel detection methods allow additional insight. The aim of this paper was to give an overview on the current knowledge of microbial VOC emissions from soils.     

猪场VOCs特征及减排技术研究进展

挥发性有机化合物（volatile organic compounds, VOCs）是大气污染物的重要组成成分，对环境和人体健康有潜在危害。生猪养殖业是畜牧业的支柱产业，但其发展受到猪场排放的VOCs等引起的空气污染严重制约。该研究从特征和减排技术两个方面对猪场的VOCs进行综述，重点介绍了猪场VOCs的来源、种类及其特征、致臭性VOCs的特征和检测方法等，从源头减排、过程控制与末端处理 3 个环节对猪场VOCs减排技术进行分析和探讨，并对该研究领域的发展趋势与研究重点进行展望，以期为开展畜牧业VOCs污染减排技术研究和推动畜牧业可持续发展提供参考。     

Ricinus communis as an Element Biomonitor of Atmospheric Pollution in Urban Areas

Iopromide has been frequently detected in different environmental compartments. However, the biodegradation of iopromide was limited, and significantly different removal efficiencies by various methods were reported. In this study, a Pseudomonas sp. I-24 isolated from activated sludge in a sewage treatment plant was used to degrade iopromide. Four different cosubstrates were selected as the cometabolic carbon and energy sources. The results showed that cosubstrate starch was able to increase catabolic enzymatic activity and enhance iopromide degradation. The degradation efficiency of iopromide was as high as 88.24 %, which was much higher as compared with other cosubstrates (38.58–51.44 %) and blank sample (2.81 %). Additionally, the highest enzymatic activity of 0.182 mU for iopromide degradation was also obtained when adding starch as a cosubstrate, somehow supporting that higher enzymatic activity resulted in higher degradation efficiency for iopromide. Although little was illuminated about the molecular mechanism during the degradation process of iopromide with starch addition, the two-dimensional gel electrophoresis results indicated that the iopromide-degrading cells growing with cosubstrate starch underwent significant physiological changes.     

The Potted-Plant Microcosm Substantially Reduces Indoor Air VOC Pollution: II. Laboratory Study

Indoor air-borne loads of volatile organic compounds (VOCs) are usually significantly higher than those outdoors, and chronic exposures can cause health problems. Our previous laboratory studies have shown that the potted-plant microcosm, induced by an initial dose, can eliminate high air-borne VOC concentrations, the primary removal agents being potting-mix microorganisms, selected and maintained in the plant/root-zone microcosm. Our office field-study, reported in the preceding paper, showed that, when total VOC (TVOC) loads in reference offices (0 plants) rose above about 100 ppb, levels were generally reduced by up to 75% (to < 100 ppb) in offices with any one of three planting regimes. The results indicate the induction of the VOC removal mechanism at TVOC levels above a threshold of about 100 ppb. The aims of this laboratory dose-response study were to explore and analyse this response. Over from 5 to 9 days, doses of 0.2, 1.0, 10 and 100 ppm toluene and m-xylene were applied and replenished, singly and as mixtures, to potted-plants of the same two species used in the office study. The results confirmed the induction of the VOC removal response at the lowest test dosage, i.e in the middle of the TVOC range found in the offices, and showed that, with subsequent dosage increments, further stepwise induction occurred, with rate increases of several orders of magnitude. At each dosage, with induction, VOC concentrations could be reduced to below GC detection limits (< 20 ppb) within 24 h. A synergistic interaction was found with the binary mixtures, toluene accelerating m-xylene removal, at least at lower dosages. The results of these two studies together demonstrate that the potted-plant microcosm can provide an effective, self-regulating, sustainable bioremediation or phytoremediation system for VOC pollution in indoor air.     

Volatile organic compound (VOC) emissions from soil and litter samples

The production of nonmethane volatile organic compounds (VOCs) by soil microbes is likely to have an important influence on soil ecology and terrestrial biogeochemistry. However, soil VOC production has received relatively little attention, and we do not know how the emissions of microbially-produced VOCs vary across soil and litter types. We collected 40 root-free soil and litter samples from a diverse array of ecosystem types and conducted laboratory incubations in order to compare the types and quantities of VOCs emitted. VOC production rates were higher in litter samples than in soil samples, and the rates were correlated with microbial biomass and CO₂ production levels. On average, the litter samples produced more types of VOCs than the soil samples with litters emitting a number of VOCs (including terpenoids) that were not generally emitted from the soil samples. Across all of the samples, we identified 100 VOCs, and more than 70% of these compounds could not be positively identified by GC/MS analyses. Of those VOCs that could be identified, furfural and similar furan compounds were noteworthy in that they were emitted in large amounts from nearly every sample examined. Other identifiable VOCs produced across a range of soil and litter samples included propanoic and butanoic acids, which are known products of microbial fermentation. Together these results suggest a need for additional research examining the specific factors influencing VOC emissions from soil and the identification of specific VOCs emitted from soil and litter as many of these compounds are likely to have important effects on belowground ecology.     

Biodegradation of Organic Chemicals in Soil/Water Microcosms System: Model Development

The chemical interactions of hydrophobic organic contaminants with soils and sediments may result in strong binding and slow subsequent release rates that significantly affect remediation rates and endpoints. In order to illustrate the recalcitrance of chemical to degradation on sites, a sorption mechanism of intraparticle sequestration was postulated to operate on chemical remediation sites. Pseudo-first order sequestration kinetics is used in the study with the hypothesis that sequestration is an irreversibly surface-mediated process. A mathematical model based on mass balance equations was developed to describe the fate of chemical degradation in soil/water microcosm systems. In the model, diffusion was represented by Fick’s second law, local sorption-desorption by a linear isotherm, irreversible sequestration by a pseudo-first order kinetics and biodegradation by Monod kinetics. Solutions were obtained to provide estimates of chemical concentrations. The mathematical model was applied to a benzene biodegradation batch test and simulated model responses correlated well compared to measurements of biodegradation of benzene in the batch soil/water microcosm system. A sensitivity analysis was performed to assess the effects of several parameters on model behavior. Overall chemical removal rate decreased and sequestration increased quickly with an increase in the sorption partition coefficient. When soil particle radius, a, was greater than 1 mm, an increase in radius produced a significant decrease in overall chemical removal rate as well as an increase in sequestration. However, when soil particle radius was less than 0.1 mm, an increase in radius resulted in small changes in the removal rate and sequestration. As pseudo-first order sequestration rate increased, both chemical removal rate and sequestration increased slightly. Model simulation results showed that desorption resistance played an important role in the bioavailability of organic chemicals in porous media. Complete biostabilization of chemicals on remediation sites can be achieved when the concentration of the reversibly sorbed chemical reduces to zero (i.e., undetectable), with a certain amount of irreversibly sequestrated chemical left inside the soil particle solid phase.