Environmental engineering applications of electronic nose systems based on MOX gas sensors

Nowadays, the electronic nose (e-nose) has gained a huge amount of attention due to its ability to detect and differentiate mixtures of various gases and odors using a limited number of sensors. Its applications in the environmental fields include analysis of the parameters for environmental control, process control, and confirming the efficiency of the odor-control systems. The e-nose has been developed by mimicking the olfactory system of mammals. This paper investigates e-noses and their sensors for the detection of environmental contaminants. Among different types of gas chemical sensors, metal oxide semiconductor sensors (MOXs) can be used for the detection of volatile compounds in air at ppm and sub-ppm levels. In this regard, the advantages and disadvantages of MOX sensors and the solutions to solve the problems arising upon these sensors’ applications are addressed, and the research works in the field of environmental contamination monitoring are overviewed. These studies have revealed the suitability of e-noses for most of the reported applications, especially when the tools were specifically developed for that application, e.g., in the facilities of water and wastewater management systems. As a general rule, the literature review discusses the aspects related to various applications as well as the development of effective solutions. However, the main limitation in the expansion of the use of e-noses as an environmental monitoring tool is their complexity and lack of specific standards, which can be corrected through appropriate data processing methods applications

Odour Detection Methods: Olfactometry and Chemical Sensors

The complexity of the odours issue arises from the sensory nature of smell. From the evolutionary point of view olfaction is one of the oldest senses, allowing for seeking food, recognizing danger or communication: human olfaction is a protective sense as it allows the detection of potential illnesses or infections by taking into account the odour pleasantness/unpleasantness. Odours are mixtures of light and small molecules that, coming in contact with various human sensory systems, also at very low concentrations in the inhaled air, are able to stimulate an anatomical response: the experienced perception is the odour. Odour assessment is a key point in some industrial production processes (i.e., food, beverages, etc.) and it is acquiring steady importance in unusual technological fields (i.e., indoor air quality); this issue mainly concerns the environmental impact of various industrial activities (i.e., tanneries, refineries, slaughterhouses, distilleries, civil and industrial wastewater treatment plants, landfills and composting plants) as sources of olfactory nuisances, the top air pollution complaint. Although the human olfactory system is still regarded as the most important and effective “analytical instrument” for odour evaluation, the demand for more objective analytical methods, along with the discovery of materials with chemo-electronic properties, has boosted the development of sensor-based machine olfaction potentially imitating the biological system. This review examines the state of the art of both human and instrumental sensing currently used for the detection of odours. The olfactometric techniques employing a panel of trained experts are discussed and the strong and weak points of odour assessment through human detection are highlighted. The main features and the working principles of modern electronic noses (E-Noses) are then described, focusing on their better performances for environmental analysis. Odour emission monitoring carried out through both the techniques is finally reviewed in order to show the complementary responses of human and instrumental sensing

Biosensor-rivi erinevate reovete biokeemilise hapnikutarbe uurimiseks

A Thesis for applying for the degree of Doctor of Philosophy in Engineering Sciences.Väitekiri filosoofiadoktori kraadi taotlemiseks tehnikateaduse erialal.The basis of all life on Earth is the existence of clean water. The state of water must be constantly monitored to ensure that the water is clean. One critical parameter in accessing water purity is the content of organic pollutants. A universal parameter - biochemical oxygen demand (BOD) – is widely used to assess this. The BOD test determines the amount of biodegradable organic compounds in wastewater. The dissolved oxygen concentration in the test sample is measured at the beginning and end of the incubation period, and the BOD value is calculated from the difference. The incubation period during which the decomposed organic matter content is measured is 5 days according to the American standard (BOD5) and 7 days according to the Swedish standard (BOD7). Such a long incubation time is a severe disadvantage of this method, as, during this time, elevated BOD can have irreversible consequences for the water body. An alternative method for measuring BOD is to use biosensors that can estimate the BOD value of the sample in minutes. A biosensor is an analytical device consisting of a biological recognition element and physicochemical transducer. BOD biosensors use microorganisms as the biological recognition element and the dissolved oxygen sensor as the transducer. The accuracy of the biosensor depends mainly on the microorganisms used. Microorganisms with a broad substrate spectrum that use different types of organic compounds for their activities provide a better match to the BOD7 value. There are several other solutions for the selection of microorganisms. Mixed bacterial cultures have a broader substrate spectrum however, their composition changes over time and causes signal instability. One possibility, when it comes to approaching these issues, is to use different bacterial cultures in a sensor array in which different cultures are spatially separated from each other. The use of spatially separated pure microbial cultures makes it possible to prevent contamination between different sensors in the array while also ensuring a longer lifetime for the sensor. Different possibilities for constructing a BOD sensor array were investigated in this work. Microchips based on various technologies were first studied, and their suitability for electrochemical measurements was tested. The experiments showed that the screen-printed electrode array was suitable for the biosensor. The biosensor array was then constructed using the bacterial culture Pseudomonas putida Pc15, and its behaviour in different solutions was investigated. It was shown that the BOD of water samples could be estimated with the obtained biosensor array. In the future, it may be feasible to measure BOD values with the sensor array consisting of several membranes that have been modified with different pure bacterial cultures.Kogu elu alus maakeral on puhta veel olemasolu. Selleks, et tagada vee puhtus tuleb selle reostustaset pidevalt jälgida. Üks oluline parameeter vee puhtuse hindamisel on orgaanilise reostuse sisaldus. Selle hindamiseks kasutatakse laialdaselt universaalset parameetrit - biokeemiline hapnikutarve ehk BHT. BHT väljendab lahustunud hapniku hulka, mis kulub vees leiduva orgaanilise aine lagundamiseks ning anorgaaniliste ühendite oksüdeerimiseks teatud aja jooksul ja kontrollitud tingimustel. Selle leidmiseks mõõdetakse lahustunud hapniku kontsentratsioon uuritavas proovis inkubatsiooniperioodi alguses ja lõpus ning nende vahe alusel arvutatakse BHT väärtus. Inkubatsiooniperiood, mille vältel lagunenud orgaanilise aine sisaldust mõõdetakse on vastavalt Ameerika standardile 5 päeva (BHT5) ning Rootsi standardile 7 päeva (BHT7). Nii pikk inkubatsiooniaeg on antud meetodi puhul tõsiseks puuduseks, sest sellise aja jooksul võivad kõrgenenud BHT-l olla veekogule pöördumatud tagajärjed. Alternatiivse võimalusena kiiremaks BHT määramiseks on mikroorganismidel baseeruvad biosensorid, mis võimaldavad anda hinnangu proovi BHT kohta minutitega. Biosensor on analüütiline seade, mis koosneb bioloogilisest äratundmiselemendist ja signaali muundurist. BHT biosensorites kasutatakse bioloogilise äratundmissüsteemina mikroorganisme ja muundurina lahustunud hapniku andurit. Biosensori mõõtetäpsus sõltub suuresti kasutatud mikroorganismidest. Parema kokkulangevuse BHT7 väärtusega tagavad laia substraadispektriga mikroorganismid, mis kasutavad oma elutegevuseks erinevaid tüüpe orgaanilisi ühendeid. Mikroorganismide valikuks on mitmeid erinevaid lahendusi. Kuigi mikroobide segude kasutamisega saavutatakse lai substraadispekter ja tundlik sensor, on antud sensorid lühikese kasutuseaga ja ebastabiilsed kuna mikroorganismide kooslus membraanis muutub pidevalt. Selle vältimiseks on võimalik kasutada puhaskultuuridel põhinevaid sensor-rivisid, mis koosnevad paljudest erinevatest biosensoritest ning kus erinevad mikroorganismide kultuurid on omavahel ruumiliselt eraldatud. Antud töös uuriti erinevaid võimalusi BHT sensor-rivi koostamiseks. Selleks uuriti esmalt erinevatel tehnoloogiatel põhinevaid mikrokiipe ning iseloomustati nende sobivust teostades erinevaid elektrokeemilisi mõõtmisi. Katsete tulemusena osutus sobivaks siiditrüki meetodil valmistatud sensor-rivi kiip. Järgnevalt koostati biosensor rivi kasutades bakterikultuuri Pseudomonas putida Pc15 ja uuriti selle käitumist erinevates lahustes. Doktoritöö tulemusena leiti, et antud põhimõtet on võimalik kasutada sensor-rivide valmistamisel ning saadud biosensor-rividega on võimalik hinnata veeproovide BHT-d. Edasistes uuringutes tuleks uurida erinevate, ruumiliselt eraldatud bakterkultuuride samaaegset kasutamist sensor-rivis.Publication of this thesis is supported by the Estonian University of Life Sciences. This study has been supported by Doctoral School of Energy and Geotechnology III (Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”), European Regional Development Fund and Archimedes Foundation

Degradation of organics from laundry water by photoelectrochemical and electrochemical processes on α-Fe2O3 nanostructure

In this study, organics from laundry water, and sodium dodecyl sulfate were degraded by electrochemical (EC) and photoelectrochemical (PEC) processes on aFe203 nanostructure. The applied voltage was between 1 and 3 V. The experimental data were also well simulated by the proposed kinetic models. The results present an economical and environmentally friendly method for developing countries where centralized wastewater facilities are not available

Pool-spetsiifiliste BHT biosensorite uurimine biosensor-riviks

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Reovee reostuse taset määratakse selle biokeemilise hapnikutarbe alusel (BHT). BHT iseloomustab hapniku hulka, mis on vajalik proovis leiduva orgaanilise aine biokeemiliseks lagundamiseks. Kuigi BHT analüüs ei ole spetsiifiline ühelegi saasteainele, on see siiski väga oluline üldine indikaator aine potentsiaalsest keskkonnaohtlikkusest pinnavetele. Paraku kulub analüüsi tulemuste saamiseks 5 või 7 päeva ning seetõttu on reoveepuhastusseadmete juhtimine selliseid teste kasutades väga keeruline. Antud probleemi lahendamiseks koostati lihtsad ja usaldusväärsed pool-spetsiifilised BHT biosensorid, mis võimaldasid tulemuse saada vähem, kui 30 minutiga. Antud biosensoritega oli võimalik hinnata BHT-d, mis oli põhjustatud raskesti lagundatavatest ühenditest, mille suhtes nad olid pool-spetsiifilised. Samas kui universaalne biosensor ja biosensorid, mis on pool-spetsiifilised mõnele teisele raskesti lagundatavale ühendile, ei määranud seda ja alahindasid proovi BHT7 umbkaudu selle raskesti lagundatava ühendi poolt tekitatud BHT väärtuses, 10-25%. Kuigi biosensorid alahindasid enamike reaalsete tööstuslike reoveeproovide BHT7, võimaldasid pool-spetsiifilised biosensorid siiski saada täpsemaid tulemusi kui universaalne biosensor, mis alahindas proovi BHT7 suuremas ulatuses. Seega on pool-spetsiifilised biosensorid sobivamad BHT mõõtmiseks tööstuslikes reovetes, kui universaalne biosensor, kuid ainult juhul, kui on olemas eelinfo proovi koostise ja päritolu kohta, mis võimaldab valida sobiva pool-spetsiifilise biosensori. Antud probleem lahendati erinevate pool-spetsiifiliste biosensorite ühendamisega sensor-riviks – „bioelektrooniliseks keeleks“. Selle sensor-rivi signaali analüüsiks rakendati mitmemõõtmelise andmete analüüsi meetodeid. Antud meetodite rakendamisel võimaldas PCA eristada proove nende koostise ja BHT7 väärtuse alusel ning PLS võimaldas märgatavalt paremini hinnata proovide BHT7 väärtusi kõigis proovides.Pollution load of wastewaters is determined on the basis of their biochemical oxygen demand (BOD) which measures the oxygen required for the biochemical degradation of organic material. Although the BOD test is not specific to any pollutant, it continues to be one of the important general indicators of the substance potential to be an environmental pollutant for surface waters. However, it takes 5 or 7 days to gain results and management of wastewater treatment facilities can be very difficult using this kind of tests. To address this limitation, simple and reliable semi-specific BOD biosensors were constructed which enabled us to gain results within less than 30 minutes. In addition, these biosensors can measure BOD derived from refractory compounds to which they are semi-specific. Therefore, better estimation of BOD is gained. On the other hand, universal biosensor and biosensors not semi-specific to that certain refractory compound cannot detect it and thus, underestimate the BOD7 of the sample to the extent made up by this compound, 10-25%. Although biosensors underestimated the BOD7 of most real industrial wastewater samples, the semi-specific biosensors still produced better correlation of sensor-BOD and BOD7 in real samples than universal biosensor which underestimated the BOD7 of samples to a greater extent. Therefore, semi–specific biosensors are more appropriate for measuring BOD in specific industrial wastewaters than universal biosensor. However, it is vital to have a prior knowledge about samples composition and origin to select the suitable sensor. This problem was overcome by using different biosensors as an array – bioelectronic tongue - and application of multivariate data analysis. Qualitative information was extracted by using PCA, which enabled us to distinguish different samples by their composition and BOD7 values. In addition, PLS was used for quantitative analysis which resulted in good correlation of sensor-BOD and BOD7 in all samples

Environmental and medical applications of molecularly imprinting polymer sensor for the detection of progesterone

Molecularly imprinted polymers are spatial technique with artificial recognition sites compatible to the template size, shape, and functional groups arrangement. The MIPs have shown high selectivity and affinity for the target molecules with a substantial potential for the hormones detection as an environmental sensor. The objective of this research is to fabricate a label-free molecular imprinted polymer (MIPs) sensor and investigate the sensing ability for progesterone detection in aqueous solutions and blood. The Progesterone (PGN) is a cholesterol-long biosynthetic endocrine disruptor steroid and is naturally occurring estrogenic compound with a majority effect to alter the vital functions of the human body. The MIPs detection was based on the reflectance mechanism of inverse opal film, after the PG attachment into the photonic MIP binding sites modified the Bragg diffraction spectra of the films due to swelling and refractive index changes, producing the optical signal. MIPs were investigated by equilibrium binding, kinetics experiments, and UV- visible spectra that occurs with the rebinding at different progesterone concentrations in deionized water and 150 mM NaCl solutions. The MIPs response were investigated with progesterone concentration in the 1-100 [mu]g L-1 range; with LOD of 0.5 [mu]g L-1, reaching the detected range of hormone in natural waters. Furthermore, hydrogel MIP films were successfully tested in various real water matrices, they revealed satisfactory recognition ability towards the analyte, and a promising performance in challenging, unknown natural water samples. Moreover, the MIPs film exhibited good selectivity towards the progesterone hormone when exposed to structurally similar molecules, evidenced by a larger response than non-imprinted films (NIPs) due to the specific adsorption provided by molecular imprinting. Computational studies suggested that size along with surface potential influenced the binding of analog compounds. The molecularly imprinted polymer (MIP) were applied to whole blood and plasma samples of three different animals, the levels of free and total PG were analyzed along with different days of the estrous cycle of the cows. The commercial PG kits test results followed the same trend with MIPs test results for the non-bound PG in the blood samples. The measurements revealed the minimum concentration at day 0, and highest level between day 10 and 14. Both MIPs and commercial PG kits test results were in agreement in evaluating the PG levels trend during the estrous cycle, however, there was some variance in evaluating the exact concentrations of PG hormone during the cycle, but no discrepancy in determining the cow's pregnancy profile.Includes bibliographical references

Novel Nanostructured Metal Oxide Materials for Water Treatment and Advanced Rechargeable Batteries

Clean water and energy shortage problems are pressing issues human facing today, as they not only cause many problems including public health and environmental deteriorations, but also threaten sustainable development of human society. It is urgent and critical to address and solve these problems. Among various technologies, photocatalysis and adsorption applications in water and wastewater catch a lot of attention in recent years, for their low costs and for no requirement for chemical additives or thermal inputs. Photodegradation of contaminants by nanomaterials as catalysts is an important method in water and wastewater treatment. The adsorption is mainly through complexation between dissolved metals and the oxygen in metal oxides. Nano-adsorbents offer significant improvement with extremely high specific surface area and associated sorption sites, short intraparticle diffusion distance, tunable pore size and surface chemistry. Metal oxides such as iron oxide, titanium oxide, aluminum oxide and zirconium oxide are effective, low cost adsorbents for heavy metals and radionuclides. Same as the situation of clean water supply, energy shortage is another urgent problem. As energy demand and consumption of conventional fossil fuel increase constantly, the resulting energy crisis and environmental problems caused by combustion of fossil fuel drive us to look for more sustainable energy sources. Renewable energy resources appear to be an effective and promising solution. To overcome the variability for better renewable energy utilization, suitable energy storage devices are required. Nanotechnology and nanomaterials are actively pursued to both improve existing technologies and develop new technology. TiO2 nanomaterials have been intensively investigated in various applications, as photoelectrode, catalyst, sensor, energy storage. TiO2 nanomaterials possess fascinating properties such as biological and chemical inertness, photostability, low cost, nontoxicity and superior oxidization ability. However, the wide electronic band gap and fast electron recombination rate limit the photocatalytic application and energy conversion efficiency of TiO2 nanomaterials. Though TiO2 can retain capacity at fast charge/discharge rates, and it is also electrochemical stable in common electrolytes and lack of harmful solid-electrolyte interfacial layer, the capacity of TiO2 is relatively low. Zirconium oxide has valuable chemical and physical properties, including high melting point, mechanical and thermal resistance, low electrical conductivity, biocompatibility, chemical inertness (resistant to oxidant agent and acids/bases, non-toxic, and not dissolvable in water) is a widely used inorganic material. ZrO2 is practical applied in fuel-cell technology, catalyst or catalyst support, oxygen sensor, thermal-barrier coatings and so on. In this study, different modification strategies are carried out to improve the performance of TiO2 and ZrO2 in water treatment and energy storage applications. There are three objectives in this proposal. The first objective is to demonstrate high-efficiency photocatalysts using innovative hybrid nanostructures that consist of Pt nanoparticles and rGO co-modified three-dimensionally ordered microporous (3DOM) TiO2. The excellent charge-separation property and high adsorption capacity of rGO increased the charge carrier lifetime and affinity to organic molecules. The introduction of Pt nanoparticles increased spectral response to visible light through surface plasmon resonance and suppressed charge recombination. This study entails the synthesis and characterization of Pt/rGO-TiO2 for application in methyl orange photodegradation. The second objective of this study is to demonstrate high-performance Lithium-ion battery electrode using hybrid nanomaterials consist of Fe2O3 nanospindles assembled on 3DOM TiO2 with carbon coating. The carbon coated TiO2@Fe2O3 material showed good electrochemical performance with exhibits a large reversible capacity about 570 mAh g-1, which is about four times of the reversible capacity of 3DOM TiO2. In addition to the high reversible capacity, the obtained material also exhibits good cycle performance and superior rate capacity. This rationally designed composite benefits from both good stability of TiO2, high capacity of Fe2O3, and good electron conductivity of carbon. The third objective is to study zirconium modified clays as absorbents of phosphate from aqueous solution. Comparing three clays, zirconium modified MT (2:1), VT (2:1) and KT (1:1) exhibit different structure and surface properties, and thus performance differently toward phosphate adsorption. The adsorption kinetics data of phosphate on zirconium modified clays could be well described by the pseudo-second-order model, indicating that the adsorption was through chemisorption. The experimental equilibrium data of phosphate adsorption on modified clays were fitted better by Langmuir isotherm model than the Freundlich, implying monolayer adsorption. The effect of water chemistry (pH, co-existing anions, ionic strength, DOC) was also studied. These low-cost, abundant and effective are easily synthesized and have potential for practical wastewater treatment

Real-Time Water Quality Monitoring with Chemical Sensors

Water quality is one of the most critical indicators of environmental pollution and it affects all of us. Water contamination can be accidental or intentional and the consequences are drastic unless the appropriate measures are adopted on the spot. This review provides a critical assessment of the applicability of various technologies for real-time water quality monitoring, focusing on those that have been reportedly tested in real-life scenarios. Specifically, the performance of sensors based on molecularly imprinted polymers is evaluated in detail, also giving insights into their principle of operation, stability in real on-site applications and mass production options. Such characteristics as sensing range and limit of detection are given for the most promising systems, that were verified outside of laboratory conditions. Then, novel trends of using microwave spectroscopy and chemical materials integration for achieving a higher sensitivity to and selectivity of pollutants in water are described