Odor Units Research Articles

Diffusion behavior and environmental impact of odorants and TVOCs detected in a wastewater treatment plant for collaborative leachate treatment in Northwest China

Wastewater treatment plants (WWTPs) are major sources of volatile gaseous compounds, especially in mixed-source systems such as domestic wastewater and landfill leachate. This study aimed to investigate the emission behavior and environmental impact of gaseous substances, such as hydrogen sulfide (H2S), ammonia (NH3), carbon sulfide (CS2), and phosphine (PH3), at a WWTP in Northwest China. Odorants were detected in the air surrounding the grid room (XGS), biochemical treatment tank (SHC), secondary sedimentation tank (ECC), and sludge dewatering room (NTS). For comparison, the upwind boundary (O-SF) and downwind boundaries (O-XF) monitoring points were used, with odor concentrations ranging from 3.95 to 725.27 odor units. The concentration ranges of the odorant substances were 5.27–88.69, 5.61–71.96, 5.70–32.63, and 0.12–5.87 mg/m3 for H2S, NH3, CS2, and PH3, respectively. Meteorological factors such as temperature, relative humidity, and wind speed and direction substantially influence odorant emissions. The concentrations of various odorants and volatile organic compounds (VOCs) detected at the O-XF monitoring point were higher than those detected at the O-SF monitoring point, indicating that the wind intensified their diffusion toward the downwind plant boundary. The average odor intensities of odorant substances emitted from wastewater or sludge treatment equipment were 3.37, 5.09, 4.42, 2.00, and 3.82 for total VOCs, H2S, NH3, CS2, and PH3, respectively. Among them four, with downwind diffusion, only H2S presented olfactory and chronic toxicity risks based on Gaussian plume model calculations. The hazard index ranking across monitoring sites was XGS > NTS > SHC > ECC > O-XF > O-SF. These findings emphasize the urgent need for effective measures to control and mitigate gaseous pollutants emitted by collaborative WWTPS, thereby protecting environmental quality and public health.

Determination of emission factors from a landfill through an inverse methodology: Experimental determination of ambient air concentrations and use of numerical modelling

The application of numeric modelling for determining the impact of landfills needs for reliable emission source data. In this study, a methodology for the characterization of the emission profiles of the different sources present in landfills for emission factors determination, applying an indirect methodology, is presented. Ambient air concentrations of volatile organic compounds (VOCs), hydrogen sulphide (H2S) and ammonia (NH3) were determined in three potentially emission sources in Can Mata landfill (Hostalets de Pierola, Catalonia, Spain): dumping areas, pre-closed zone and leachate reservoir as well as in biogas, for the determination of emission factors. Multi-sorbent bed and Tenax TA tubes were used for a wide range of VOCs sampling, and analysis was conducted through TD-GC/MS. H2S and NH3 were sampled and analysed using Radiello passive samplers. The highest total VOC (TVOC) concentrations were found in dumping areas (0.7–3.5 mg m−3), followed by leachate reservoir (0.3–0.6 mg m−3) and pre-closed area (77–165 μg m−3). On the other hand, the highest H2S and NH3 concentrations were found in leachate reservoir, presenting values of 0.8–1.1 mg m−3 and 1.7–1.8 mg m−3, respectively. With the application of odour thresholds to the concentrations obtained, the most critical compounds regarding odour annoyances were determined. The highest odour units (O.U.) were found in leachate reservoir due to H2S concentrations, whereas VOCs contributed mainly to O.U. in the dumping areas. The obtained ambient air concentrations were used for the indirect determination of the emission factors through numerical modelling using a Eulerian dispersion model. The emission factors obtained for the landfill for TVOC, H2S and NH3 were in the range of 0.44–10.9 g s-1, 0.16–1.02 g s−1 and 0.23–1.82 g s−1, respectively, depending on the emission source. Reliable emission factors are crucial to obtain landfill impact maps, which are essential for the correct management of these facilities.

Comprehensive hygienic assessment of ambient air pollution in the area of food and processing industry enterprises’ location

The purpose of the study is to assess atmospheric air pollution in a city where food and processing enterprises operate using a complex of instrumental, olfacto-odourimetric, calculated, and survey methods.
 Materials and methods. Analytical studies of ambient air pollution were performed using the FOCUS GC-DSQ-II chromatography-mass spectrometer. Olfacto-odourimetric studies of the presence and intensity of odour in the area of the enterprises were carried out in accordance with the method of organoleptic control downwind at various distances from sources. The measurement of the odour level at the discharge of the coffee extract spray dryer was carried out by dynamic olfactometry on the ECOMA TO-8 olfactometer. The calculation of odour dispersion was implemented according to a program using a methodology for calculating concentrations of harmful substances in ambient air.
 Results. It was established that at the time of the research, the source of a persistent specific odour reaching the residential area was a coffee production enterprise. Up to seventy eight volatile organic compounds in concentrations not exceeding hygienic standards have been identified in the ambient air in the area of the enterprise’s location. Field olfacto-odorimetric studies and the conducted dispersion calculation indicate an offensive odour to be capable of causing “annoyance” to the population (3 points or higher with a probability of ≥ 5% according to the results of field studies or ≥ 3.5 OU (odour units) according to the calculation results) spreads up to 4 km from the main source of emissions.
 Limitations. The main limitation of the study is the peculiarities of the operating mode of different enterprises, which makes it difficult to fully assess the environmental situation in the area of their location at the time of the research.
 Conclusion. The results of these studies indicate the use of various methodological approaches (field olfacto-odorimetric measurements, calculation of odour dispersion), along with conducting population surveys, to significantly expand the possibilities of instrumental analysis for an objective assessment of ambient air pollution by complex multicomponent mixtures of odorous substances.

Ammonia emissions from livestock facilities around an international airport, Tehran, Iran: An experimental and mathematical study

AbstractAmmonia emissions from livestock farms are a major problem for staff and residents near these centers. Anaerobic decomposition of livestock waste and the collection and stacking of waste are the main sources of ammonia gas on livestock farms. This article examined ammonia emissions from livestock facilities near Tehran Imam Khomeini International Airport. First, field measurements were made in the summer (30°C), and collected samples were examined using the indophenol technique. AERMOD, based on Gaussian fluctuating plume theory, was constructed to model ammonia emissions. According to AERMOD, the maximum periodic‐seasonal 2‐hourly and 8‐hourly ammonia concentrations were 15.9, 229, and 63.7 OU (odor unit per unit volume)/m3, respectively. The hourly ammonia emission rate from livestock sources is also 0.0168 gm−2 h−1. AERMOD results mathematical model indicated reasonable agreement with the field measurement, which the coefficient of determination (R2), index of agreement (d), and efficiency coefficient (E) were 0.95, 0.97, and 0.91, respectively. Moreover, Statistical indices, including geometric mean bias (MG), geometric variance (VG), fraction of predictions within a factor of two of observations (FAC2), and normalized mean square error (NMSE), the root mean square error (RMSE) and mean absolute error (MAE) are also indicated by 1.36 and 0.67, respectively, were used to assess the reliability of the model results showed that AERMOD had a good agreement with the field measurement.

Determination of odour emission rates emitted by active area sources and dispersion of odour concentration in the surrounding air

In this study, the area of a biofilter representing an active area source was sampled by taking 12 odour samples from the gaseous effluent and measuring the physical parameters of the source, so that we can obtain the odour emission rate (OER) specific to the source. The odour sampling process is a crucial step in the assessment and monitoring of odour pollution. Direct measurement of odour concentration in the ambient air is often not sufficient to determine whether an activity is responsible for producing olfactory discomfort to the receptors. To observe the contribution of the source to olfactory pollution and air quality by estimating the odour concentration in the ambient air, the odour emission rate (OER) was taken into account, which is expressed in odour units per second (ouE/s) and is obtained as the product of the odour concentration and the airflow rate associated with the source. The odour emission rate was entered into the dispersion program AERMOD for mathematical modeling. In order to estimate the odour concentration in the surrounding air in the adjacent areas to the sampled biofilter, 2 mathematical models were made to illustrate the odour concentration on the site and in its vicinity in the most unfavorable weather conditions „Highest values” and „98th Percentile” to illustrate the concentration in the surrounding air excluding the 2% unfavorable weather condition.

Comprehensive in situ and ex situ β-glucosidase-assisted assessment reveals Indian mangoes as reservoirs of glycosidic aroma precursors

Mango, a valued commercial fruit in India is popular mostly because of its attractive flavour. Glycosidically bound volatiles (GBV), an underrepresented warehouse of aroma, remain completely unexplored in Indian mangoes. In this study, GBV were profiled in pulps and peels of 10 Indian mango cultivars, leading to detection of 66 GBV which were dominated by monoterpenoids and phenolics. Peels were quantitatively and qualitatively richer in GBV than pulps. Hierarchical clustering and principal component analysis indicated higher contribution of peel GBV to the distinctness of cultivars. Linalool, geraniol, and eugenol were the significant contributors based on the odour units. Direct β-glucosidase treatment to the juice resulted in the release of lesser number of volatiles than those released from the purified GBV extracts. Apart from providing a comprehensive catalogue of GBV in mangoes, our data suggests the need of critical assessment of the usefulness of β-glucosidases in aroma improvement of fruit juices.

Low-Temperature Extraction of Lipid Fractions from Vegetable Raw Materials Using Liquefied Freons

This paper presents the method of cryogenic extraction by means of liquefied freons. Using the equipment to extract lipid fractions from biological raw materials, a freon extract from bay leaves (Laurus nobilis) was experimentally obtained. A low-temperature extraction of lipid fractions from bay leaves was first realized using liquefied freons within the temperature range of –2...–8°С. The difference in composition of these fractions from that of the oils, obtained within the standard temperature ranges of 30...50°С was shown. Dependence of the finished product weight on extraction time as a result of three consecutive cycles of 23 hrs each was demonstrated. Using gas chromatography, 68 components of freon extract were identified, and their quantitative composition and dominant compounds were detected. The content of essential oils and aroma-forming substances, stipulating the number of odour units was specified. These findings may be the basis for novel technological approaches to separation of lipid fractions, isolated from biological raw materials of plant and animal origin. Here, we described the device version with a three-stage cryogenic system of freon solvent recovery for effective implementation of the designed technology. Key words: bay leaf, low-temperature technologies, liquefied freon R406A, extract, gas chromatography, number of odour units.

Hydrothermal pretreatment and compound microbial agents promoting high-quality kitchen waste compost: Superior humification degree and reduction of odour

Present study investigated the effects of hydrothermal pretreatment (HTP) and addition of compound microbial agent (CMA) on humification, odour generation and metabolism functions of bacterial communities during composting of kitchen waste (KW). Surprisingly, HTP and CMA addition treatment could promote the humification of compost and the control of odour units in contrast to the control (without HTP and CMA addition). The humic acid to fulvic acid ratio of end compost increase by 187.30 %, while humification index (HIX) increased by 18.87 %. 3D-EEM fluorescence spectroscopy of dissolved organic matter (DOM) demonstrated that it facilitated the synthesis of humified compounds and the decomposition of biodegradable compounds. Moreover, the SUVA254, SUVA280 and E253/E203 increased by 118.6 %, 115.25 % and 42.11 % after HTP and CMA addition indicating an increase in aromatic carbon abundance. VFAs had the higher degradation rate (84.91 %) than other treatments (57.46–77.72 %). Meanwhile, the main contributor to the malodorous odour was isovaleric acid, followed by butyric acid and acetic acid during composting. Mantel test indicated that the humification degree was significantly influenced by environmental parameters (temperature, pH, etc.) and metabolic products (HA, DOC and VFAs). Metagenomic analysis indicated that the biodegradation processes at the thermophilic stage were controlled mainly through genes involved in microbial metabolism. HTP and CMA addition was an eco-friendly and efficient strategy to reduce odour emission and improve the compost quality.

Odor Emissions Factors for Bitumen-Related Production Sites

Bitumen-related production sites are facing increasing difficulties with nearby residents due to odor emissions. This parameter is still not regulated for these plants and little is known about the emissions that these plants have put into the atmosphere with the technologies available today. In this study, emission data from 47 Italian production plants were collected and analyzed to assess which values could describe the current situation in Italy. The results of the analysis showed that emissions are very variable, with odor concentration values between 200 to 37,000 ouE/m3, but data have a normal distribution. The mean value of the stack odor concentration was found to be 2424 ouE/m3. It was also possible to calculate emission factors of the plants, such as odor emission rate (OER), which represents the quantity of odor emitted per unit of time, and is expressed in odor units per second (ouE∙s−1) and odor emission factor (OEF) per ton of product, expressed in ouE/t. The values obtained were 7.1 × 104 ouE/s and 1.4 × 106 ouE/t. respectively. These data could provide a starting point for the definition of shared values among various stakeholders for the definition of regional guidelines for the emissions of these plants, in order to adjust available technologies towards emission parameters that are protective of the surrounding environment.

Characterisation of aroma profile and evaluation of aroma quality in sweet cream butter

The objective of this study was to determine which volatile compounds are responsible for the aroma of fresh sweet cream butter, using a liquid–liquid extraction method coupled with a Porapak Q column and limited odour units (Lod) as technical methods. Sixty-four compounds were quantitatively identified. Assessors determined 100 ppm as the critical concentration for good aroma. Individual Lod100 were calculated at 100 ppm of the extracted oil using each compound's thresholds and then twenty-three chemicals such as δ-dodecalactone, δ-decalactone, γ-decalactone, acetaldehyde, and decanoic acid were selected as the potent aroma compounds in terms of Lod100 values greater than one.

Prediction of human odour assessments based on hedonic tone method using instrument measurements and multi-sensor data fusion integrated neural networks

A Cyranose 320 (eNose) and a Fast Gas Chromatograph (CG) analyser (zNose™) were used to measure the headspace odour of solid samples from dairy operations. The measurements of both sensors were trained by Levenberg–Marquardt Back-propagation Neural Network (LMBNN) to match human assessments. A trained human panel was used to assess the odours based on hedonic tone method and provide the model targets. A multi-sensor data fusion approach was developed and applied to integrate the eNose and zNose readings for higher predictive accuracy compared to each sensor alone. Principle Component Analysis, Forward Selection, and Gamma Test were applied to reduce the model input dimensions. Measurement fusion models and information fusion model approaches were applied. The information fusion prediction models were shown to be more accurate than all other models, including single instrument models. The information fusion model based on eNose with Gamma Test data reduction + zNose showed the best results of all cases in validation mean square error (0.34 odour units), R value (0.92), probability of the prediction falling within 10% of the target (96%), and probability of the prediction falling within 5% of the target (63%).

Evaluation of the Efficacy of SIFT-MS for Speciation of Wastewater Treatment Plant Odors in Parallel with Human Sensory Analysis

Odors from wastewater treatment plants (WWTPs) have frequently been attributed primarily to hydrogen sulfide (H2S). Low-to-medium cost hydrogen sulfide sensors have been utilized as odor indicators. However, other odorous species are usually present that may have lower odor thresholds than hydrogen sulfide. Hydrogen sulfide is not always present in odorous environments and the correlation of hydrogen sulfide to odor at a treatment facility is inconsistent. Such factors determine hydrogen sulfide an inconsistent indicator and more sophisticated measurement techniques are required to accurately predict odor intensity from complex gaseous mixes. In this paper, the performance of a direct mass spectrometric technique, selected ion flow tube mass spectrometry (SIFT-MS), is evaluated for analysis of odors from diverse sources at a modern WWTP. The soft chemical ionization employed in SIFT-MS provides detection and quantification of a wide range of potential odorants to below, or close to, the human odor detection threshold (ODT). The results presented demonstrate that methyl mercaptan is almost always a more significant odorant at this WWTP than hydrogen sulfide and confirm that the relative abundances of these odorants vary significantly. Parallel SIFT-MS chemical analysis and human sensory analysis (olfactometry) was conducted in this study. Good agreement was observed for samples of moderate to strong “sewage” or “chemical” character. However, in samples that were otherwise low in odor intensity, sensory analysis did not attribute “sewage” odor notes as the predominant odor character. Chemicals attributed with this odor character were present significantly above the ODTs in the mixed samples and were detected by SIFT-MS. A weak correlation was obtained between total odor activity values measured using SIFT-MS and the odor concentration (in odor units per cubic meter) determined using dilution olfactometry. The complexity of the wastewater matrix and complexity of human odor recognition from mixed samples is thought to be the underlying cause of less-than-ideal correlation, perturbing both olfactometry and SIFT-MS analyses.

Use of Alternative Cover Materials to Control Surface Emissions (H2S and VOCs) at an Engineered Landfill

Between 2010 and 2015, the Bellechasse Regional County Municipality (Bellechasse RCM) was affected by particularly noxious odors issuing from its Municipal Solid Waste Landfill (Bellechasse RCM MSWL) in Armagh, Canada. A study carried out in 2015-2016 by Centre de recherche industrielle du Québec (CRIQ) confirmed that it was still possible for hydrogen sulfide (H2S) emissions to cause odor issues in and around the site. The experimental project carried out by CRIQ in cooperation with Bellechasse RCM, Englobe, Quebec City and the Regroupement des récupérateurs et des recycleurs de matériaux de construction et de démolition du Québec (represented by AIM Éco-centre) made it possible to test three (3) different industrial residue as an alternative cover materials on site and study how they controlled H2S emissions, volatile organic compounds (VOCs) and odors at the Bellechasse RCM’s landfill. The site was monitored from November 2016 to September 2017 to confirm the effectiveness of alternative biofiltration cover materials (soil + compost), domestic waste incineration bottom ash and 0 to 2.5-inch concrete residues and to compare the results with the sand cover currently used as the cover material. Effectiveness was determined by measuring the Area Source Emission Rate (ASER) with a 3 m x 3 m static flux chamber developed for the project. Methane measurements were concomitantly taken to confirm that the biogas could escape through the cover materials. The monitoring results made it possible to demonstrate that domestic waste incineration bottom ash as well as 0-2.5 in. concrete received the highest load of H2S and showed an H2S capture performance of greater than 83ϿFor volatile organic compounds, materials such as 0-2.5 in. concrete and the alternative biofiltration cover materials were most effective for capture (greater than 73Ͽfor the highest loads. The lowest content of CH4 after covering was measured for the alternative cover materials. The site where the incineration bottom ash was used managed to decrease odors by ±200 odor units. Overall, we have demonstrated in this project, the capacity of different alternative cover materials under real condition for the control of gas emissions from landfill.

ON ODOUR EMISSION RATE FROM THE WORKING AREA OF A MUNICIPAL SOLID WASTE LANDFILL IN CHINA

To investigate the odour emission rate from the surface of a municipal solid waste landfill working area in China, a wind tunnel sampler was used to measure the emission rates of volatile organic compounds (VOCs), H 2 S and odour units. The results showed that the odour emission rate from the non-point source landfill is closely connected with the environmental temperature and the velocity of surface sweeping. In summer, the emission rates of VOCs (measured by PID as isobutylene), H 2 S and odour units are 385-680 μg•(m 2 •s) –1 , 4-7 μg•(m 2 •s)- –1 , and 46.5-136 OU•(m 2 •s) –1 , respectively; in winter, the emission rates are 140-280 μg•(m 2 •s) –1 , 0.5-1.8 μg•(m 2 •s) –1 , and 8.5-16.2 OU•(m 2 •s) –1 , respectively. The emission rate measured in the high temperature season is nearly 6 times higher than that in the low temperature season. In the experimental wind sweeping velocity range of 0.6 to 4 m•s –1 , there is a linear relationship between the emission rate and the wind sweeping velocity. The continuous sweeping experiment shows that the emission rate measured with clean air sweeping is the greatest possible emission rate, which needs to be adjusted when used to estimate the odour concentration in some cases, such as if the sampling time exceeds 10 min or when estimating an area emission.

CHARACTERIZATION OF VOLATILE ORGANIC COMPOUNDS AND ODOUR POLLUTION IN ATMOSPHERE AT OIL AND GASOLINE HANDLING AND PROCESSING IMPACT ZONE

Air quality pollution problem is still one of the crucial points for citizens in Europe for already receiving increasing attention, particularly because of the major European cities 10 and more years. Although the EU's long-term goal is to achieve levels of air quality that do not impact and risks to human health and the environment, many of member states still didn`t reach stated goals. Additionally, to gaseous pollutants, recently specific type of pollution, - odour, seems to become more important. Usually in order to determine pollution levels, national, municipal and private monitoring equipment is used. For this research municipal monitoring site in Riga (Latvia), at Milgravja Street 10, controlling gaseous pollutants (SO2, O3, BTX, PM10) and airborne particulate matter, and private monitoring results from Riga, Milgravja Street 16, where odour pollution was obtained, are analysed. Distance between both stations are just 500 m. Measurements at municipal monitoring site is obtained by DOAS and gravimetric sampling, while at Milgravja 16 by photoionization method or so-called “electronic nose”. Monitoring results in municipal station show that in 2017 the average benzene concentration was 4,87 ug/m3, toluene – 8,89 ug /m3 and xylene – 5,07 ug/m3, while the odour pollution level does not exceed 5 odour units. In general estimation of pollution averaged annually do not show and explain variability of pollution levels. It`s well known that high BTX and odour pollution episodes occur in shorter periods, thus short term limit values would be useful in order to characterize short term effects on human health and well-being.

Towards a Harmonized Odour Guideline for Some Austrian Provinces

Currently some provinces in Austria attempt to set up a harmonized regulation for assessing odour nuisance. The Austrian laws do not stipulate that any nuisance is to be prevented, but only “unacceptable” nuisance. “Unacceptable” is not a scientific or medical term but needs to be interpreted in a legal context. In the new guideline different odour impact criteria (OIC) are set up with regard to the hedonic tone of odours. For each category a maximally allowed frequency is defined. Frequencies are to be assessed on the total number of hours of a year, where the computed 90th percentile within one hour is above a certain threshold concentration (e.g. 1 odour unit [ou] per m³). Such is termed an odour hour. Dispersion modelling is the major methodology for odour assessments. Unlike in Germany, no specific model is prescribed, but model developers need to prove the capability of their model to accurately simulate the 90th percentile odour concentration of an hour. For instance, the Lagrangian particle model GRAL, which is frequently used in Austria, offers a new module to compute the 90th percentile based on the work of Oettl and Ferrero (2017a). The 90th percentile is thereby a function of the three dimensional odour-concentration field and the atmospheric turbulence, thus, the model is able to take into account the effects of overlapping odour plumes, too. It could be demonstrated that modelled odour-hour frequencies using this novel approach are in very good agreement with observed odour hours assessed by field inspections following the new European standard EN 16841-1. Field inspections, therefore, may also be used for odour assessment, whenever modelling is not possible (e.g. unknown source strengths). OICs are derived upon dose-response relationships, which were established by evaluating historical citizen’s complaints using the dispersion model GRAL. Relationships between the percentage of annoyed residents and modelled odour-hour frequencies were found to be quite different for odorants having a very high potential of offensiveness and such with a moderate potential. Discontinuous odour sources are assessed by using OICs based on the 0.5th percentile evaluated for concentrations larger than 1 ou m-3. The corresponding concentration thresholds for the four distinguished hedonic tones were derived by matching the affected non-attainment areas resulting from the regulations for continuous sources with those resulting from the 0.5th percentile regulation.

Analysis of aromatic constituents of apricot ‘Jinkaite’ at different developmental stages

The aromatic constituents of apricot 'Jinkaite' were analyzed at different developmental stages by static headspace and gas chromatography-mass spectrometry (GC-MS). The results showed that 46 aromatic constituents were detected in 'Jinkaite' apricot fruit. The main aromatic components were esters, alcohols, and aldehydes. The aromatic constituents and contents both showed significant differences during various fruit developmental periods. Specifically, 31, 32, and 24 aromatic constituents were detected at green-ripe, commercial-ripe, and full-ripe stages, respectively, and the contents of esters were highest at each stage, respectively representing 61.33, 70.03, and 61.48% of the total aromatic compounds. The characteristic aroma compounds of apricot fruit included acetic acid hexyl ester, ethyl hexanoate, propanoic acid 2-methylhexyl ester, and 1-hexanol, the odor units of which at the full-ripe stage were 448.5, 29.86, 7.85, and 3.54.

Complementary use of GCxGC\u2013TOF\u2013MS and statistics for differentiation of variety in biosolid samples

Formation of biosolid cakes, which are one of the main wastes generated in wastewater treatment plants, is connected with emission of many hazardous chemical compounds, including odoriferous ones. To optimize particular processes of biosolid cake processing, it is necessary to assess chemical composition of the gas mixtures containing the compounds released from the cakes. The paper proposes application of two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC–TOF–MS) to identification of the compounds released from four main types of biosolid cakes and to quantitative determination of the markers characteristic for particular types of cake. Based on the analysis of variance, the following compounds, which could be potential markers of the investigated biosolid cakes, were selected: 1-propanol, 2-hexanone, toluene, o-xylene, p-xylene, and organosulfur compounds (methanethiol, ethanethiol, dimethyl sulfide, dimethyl disulfide, and diethyl disulfide). Theoretical odour concentrations of four investigated types of biosolid cakes were determined, based on measured concentrations and olfactory thresholds of the aforementioned compounds. The highest concentration was revealed for a primary cake (634 ou/m3), whereas the lowest concentration was found for an excess cake (136 ou/m3) (ou/m3—odour unit per m3; one odour unit is equivalent to collective odour threshold of odorants mixture present in 1 m3). The proposed methodology allows preliminary evaluation of the odour nuisance markers connected with formation of the biosolid cakes, without a need for quantitative analysis of all determined compounds.Graphical abstract

Odour assessment in the vicinity of a pig-fatting farm using field inspections (EN 16841-1) and dispersion modelling

The assessment of odour annoyance varies vastly among countries even within the European Union. Using so-called odour-hour frequencies offers the distinct possibility for either applying dispersion models or field inspections, both generally assumed to be equivalent. In this study, odour-hours based on field inspections according to the European standard EN 16841-1 (2017) in the vicinity of a pig-fattening farm have been compared with modelled ones using the Lagrangian particle model GRAL, which uses odour-concentration variances for computing odour hours as recently proposed by Oettl and Ferrero (2017). Using a threshold of 1 ou m−3 (ou = odour units) for triggering odour hours in the model, as prescribed by the German guideline for odour assessment, led to reasonable agreements between the two different methodologies. It is pointed out that the individual odour sensitivity of qualified panel members, who carry out field inspections, is of crucial importance for selecting a proper odour-hour model. Statistical analysis of a large number of data stemming from dynamic olfactometry (EN 13725, 2003), that cover a wide range of odorants, suggests that the prescribed method in Germany for modelling odour hours may likely result in an overestimation, and hence, equivalence with field inspections is not given. The dataset is freely available on request.

Development of an electronic nose to characterize odours emitted from different stages in a wastewater treatment plant

Wastewater treatment plants have widely been described as a significant source of odour nuisance, which has led to an increase of neighbourhood complaints. Therefore, to mitigate the negative impact of odours, the detection and analysis of these emissions are required. This paper presents a measurement system based on an electronic nose for quantitative and qualitative odour analysis of samples collected from six different stages on a wastewater plant. Hence, two features vectors were performed in order to represent quantitative trends of the gaseous mixture sampled on the facility. In addition, odour fingerprints and a PCA were computed to discriminate odours from its sources and to detect relationships among the samples. This approach also comprises a dynamic dilution olfactometer. A PLS regression model was performed to predict the odour concentration by the electronic nose in term of odour units per cubic meter. The results show that the developed electronic nose is a promising and feasible instrument to characterize odours from wastewater plants.