Odor emission assessment of different WWTPs with Extended Aeration Activated Sludge and Rotating Biological Contactor technologies in the province of Cordoba (Spain).

In this study, five urban WWTPs (Wastewater Treatment Plant) with different biological treatment (Extended Aeration Activated Sludge - EAAS; Rotating Biological Contactor - RBC), wastewater type (Urban; Industrial) and size, were jointly evaluated. The aim was twofold: (1) to analyze and compare their odor emissions, and (2) to identify the main causes of its generation from the relationships between physico-chemical, respirometric and olfactometric variables. The results showed that facilities with EAAS technology were more efficient than RBC, with elimination yields of organic matter higher than 90%. In olfactometric terms, sludge managements facilities (SMFs) were found to be the critical odor source in all WWTPs compared to the Inlet point (I) or Post primary treatment (PP), and for seasonal periods with ambient temperature higher than 25 °C. Moreover, the global odor emissions quantified in all SMFs revealed that facilities with EAAS (C-WWTP, V-WWTP and Z-WWTP) had a lower odor contribution (19,345, 14,800 and 11,029 ouE/s·m2, respectively) than for those with RBC technology (P-WWTP and NC-WWTP) which accounted for 19,747 ouE/s·m2 and 80,061 ouE/s·m2, respectively. In addition, chemometric analysis helped to find groupings and differences between the WWTPs considering the wastewater (71.27% of total variance explained) and sludge management (64.52% of total variance explained) lines independently. Finally, odor emissions were adequately predicted from the physico-chemical and respirometric variables in the wastewater (r2 = 0.8738) and sludge (r2 = 0.9373) lines, being pH, volatile acidity and temperature (wastewater line), and pH, moisture, temperature, SOUR (Specific Oxygen Uptake Rate) and OD20 (Cumulative Oxygen Demand at 20 h) (sludge line) the most influential variables.

Environmental performance of an industrial biofilter: Relationship between photochemical oxidation and odorous impacts.

Biological techniques are widely used to treat gaseous streams derived from waste treatment plants. The generation of volatile organic compounds (VOCs) is one of the principal pollution sources in composting facilities from which nuisance odours are released. In addition, the generation of photochemical smog with other gases such as NOX can produce ozone at ground level due to their photochemical ozone creation potential (POCP). In this work, the performance of an industrial biofilter was evaluated from an environmental point of view. Specifically, this study evaluated the potential impact in terms of photochemical oxidation and odour emission derived from composting in a vessel under four different aeration conditions. Gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) was used to perform the chemical characterisation of the gaseous streams, while dynamic olfactometry was used to carry out the sensorial analysis. A total of 95 compounds belonging to 12 different families of VOCs were selected. Principal component analysis revealed the influence of each VOC family on each impact category and explained 88% of the total variance. Multivariate regression was used to study the correlation between photochemical oxidation and odour impact, which has never been reported before. The correlations obtained (r ≥ 0.97) evidenced the direct relationship between these two impacts. Photochemical oxidation and odour emission were proven to be important environmental impacts derived from composting facilities, whose abatement might be carried out by biofiltration systems.

Co-composting of sewage sludge and eggplant waste at full scale: Feasibility study to valorize eggplant waste and minimize the odoriferous impact of sewage sludge.

Sewage sludge and bulking agent with small proportions of eggplant waste (EP) (4.7 and 8.6%) were co-composted at full scale to evaluate the feasibility of their joint valorization and to reduce the odorous impact during composting. In this sense, physico-chemical, respirometric and olfactometric variables were monitored throughout the co-composting process. The physico-chemical variables studied were related to each other to evaluate their effect on the quality of the final product and the odoriferous impact. It was observed that the reduction in nitrogen concentration was not parallel to the removal of organic matter, which influenced the odor concentration emitted. Furthermore, during the hydrolytic stage of the co-composting process, the odor concentration was lower when the agricultural waste content was highest (8.6% EP: 6317 and 8192 ouE/m3) in comparison with the lowest concentration of EP (4.7% EP: 9214 and 14720 ouE/m3) or without the addition of EP (reference composting pile: 10200 and 22500 ouE/m3). Although sewage sludge is more biodegradable than eggplant waste, the co-composting process was carried out under suitable conditions. Approximately 90 days were required to obtain a stabilized compost. Consequently, co-composting might be a suitable alternative to valorize EP and reduce the odoriferous impact of sewage sludge, with the consequent economic, social and environmental benefits.

Full-scale composting of sewage sludge and market waste: Stability monitoring and odor dispersion modeling.

The aim of this study was to assess the odor immission derived from full-scale composting of different abundant and highly pollutant organic waste: sewage sludge with bulking agent (SL), sewage sludge pretreated through anaerobic digestion and supplemented with bulking agent (SL-AD), and market waste with olive leaves (MW-OL). The combination of dynamic olfactometry and Gaussian dispersion modeling allowed both the quantification of odor emissions from each waste and the evaluation of their global odorous impact in nearby urban areas. Wind speed, summer and winter seasons, and atmospheric conditions were considered in the dispersion model. The results revealed that high wind speed (2.6 m/s) increases the global odor immission in summer season, independently of atmospheric stability. However, the maximum odor immission concentration recommended for composting process was not exceeded in any case, which depends on each country/region. The experimental results also enable to evaluate the influence of several physico-chemical variables on odor emissions derived from composting. The removal of nitrogen and volatile solids was the main cause for odor generation. Moreover, the microbiological activity of each substrate was monitored throughout the process and different percentages of biodegradability were quantified depending on the type of substrate and pretreatment applied.

Effects of Dilution Systems in Olfactometry on the Recovery of Typical Livestock Odorants Determined by PTR-MS.

The present study provides an elaborate assessment of the performance of olfactometers in terms of odorant recovery for a selection of odorants emitted from livestock houses. The study includes three different olfactometer dilution systems, which have been in use at accredited odor laboratories. They consist of: (i) a custom-built olfactometer made of glass tubes, (ii) a TO8 olfactometer, and (iii) an Olfacton dilution system based on a mass flow controller. The odorants include hydrogen sulfide, methanethiol, dimethyl sulfide, acetic acid, butanoic acid, propanoic acid, 3-methylbutanoic acid, 4-methylphenol, and trimethylamine. Furthermore, n-butanol, as the reference gas in the European standard for olfactometry, EN13725, was included. All measurements were performed in real time with proton-transfer-reaction mass spectrometry (PTR-MS). The results show that only dimethyl sulfide was almost completely recovered in all cases, while for the remaining compounds, the performance was found to vary significantly (from 0 to 100%) depending on the chemical properties of the compounds, the concentration levels, the pulse duration, and the olfactometer material. To elucidate the latter, the recovery in different locations of the TO8 olfactometer and in tubes of different materials, that is, poly-tetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), stainless steel and SilcoTek-coated steel, were tested. Significant saturation effects were observed when odorants were in contact with stainless steel.

Centralized management of sewage sludge and agro-industrial waste through co-composting.

In this research study, the co-composting process of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent (SEFW, 190:1:22:90 ratio) was carried out in a dynamic-solid respirometer at pilot scale. The aerobic biodegradability of the mixture was previously ensured in a static-liquid respirometer. The advantages and drawbacks of the SEFW co-composting process were subsequently identified through the determination of respirometric activity and the physical-chemical characterization of the waste, as well as the monitoring of odor emissions. The evolution of the physical-chemical variables showed that pH increased slightly and that the organic matter concentration, expressed as volatile solids (VS, %) or oxidable organic carbon (COXC, %), decreased by around 15% in both cases and by approximately 56% in its biodegradable form (total organic carbon, TOC, %). The low odor emission rate (OER) in the least favorable scenario (the maximum odor generation) during SEFW composting was 1.59 ouE/s, whereas this figure reached 3.52 ouE/s when only the organic fraction of municipal solid waste (OFMSW) was composted. Consequently, the co-composting of SEFW is more favorable in terms of odor emission and permits the simultaneous treatment of different types of waste.

Characteristics of odors emitted from municipal wastewater treatment plant and methods for their identification and deodorization techniques.

Odors emitted from municipal wastewater treatment plants belong to a group of pollutants, which is the main cause of people complaining about atmospheric air quality. The limitation of emissions of unpleasant odors generated by wastewater treatment plants by using appropriate deodorization methods is omitted on numerous occasions. This can have a negative influence on public trust and the quality of atmospheric air. The article presents basic information on the characteristics of odors from wastewater treatment lines and wastewater processing and management lines in a model biological wastewater treatment plant conducting the biogas recovery process and also information is provided on deodorization methods, such as odor masking, biofiltration, thermal disposal and diffusion through activated sludge dedicated to neutralization of odors in biological treatment plants. The main focus is on the field olfactometry technique, which is one of the tools used in environmental protection. Its application facilitates performance of tests concerning the assessment of olfactory properties of odorants in polluted air.

Monitoring of pile composting process of OFMSW at full scale and evaluation of odour emission impact.

In this study, the evolution of odour concentration (ouE/m(3)STP) emitted during the pile composting of the organic fraction of municipal solid waste (OFMSW) was monitored by dynamic olfactometry. Physical-chemical variables as well as the respirometric variables were also analysed. The aim of this work was twofold. The first was to determine the relationship between odour and traditional variables to determine if dynamic olfactometry is a feasible and adequate technique for monitoring an aerobic stabilisation process (composting). Second, the composting process odour impact on surrounding areas was simulated by a dispersion model. The results showed that the decrease of odour concentration, total organic carbon and respirometric variables was similar (around 96, 96 y 98% respectively). The highest odour emission (5224 ouE/m(3)) was reached in parallel with the highest microbiological activity (SOUR and OD20 values of 25 mgO2/gVS · h and 70 mgO2/gVS, respectively). The validity of monitoring odour emissions during composting in combination with traditional and respirometric variables was demonstrated by the adequate correlation obtained between the variables. Moreover, the quantification of odour emissions by dynamic olfactometry and the subsequent application of the dispersion model permitted making an initial prediction of the impact of odorous emissions on the population. Finally, the determination of CO2 and CH4 emissions allowed the influence of composting process on carbon reservoirs and global warming to be evaluated.

Chemical and olfactometric inventory of gaseous spot vents in Mt. Amiata volcanic-geothermal area (Italy).

Geothermal areas are typically characterised by the presence of gases and odours in the background atmosphere, stemming from natural emissions and possible mining exploitation of the area. This study presents the first olfactometric investigation of endogenous gas emissions from natural and archaeo-industrial vents in a geothermal area. Mt. Amiata is known for its complex geology and historical cinnabar mining. This study offers an inventory of spot gas emissions, not only in terms of odour and chemical concentration but also including flux data, a ground-breaking achievement in this field. The primary challenge of this investigation was estimating the emitted flow from ground holes or mine entrances, posing the risk of hazardous anoxic conditions. To address this challenge, an innovative and adaptive approach was adopted. The main breakthrough method involved the adaptation of a balometer, typically employed for indoor ventilation systems, to measure the flow of endogenous gases. Field surveys revealed odour concentrations that can exceed 106 of ouE/m3, surpassing industrial emission level considerably. Chemical concentrations, primarily consisted of CO2 (80/90 %v/v) and CH4 (∼10%v/v), providing critical insights into the global warming potential (GWP) associated with natural emissions. Moreover, these spots, often located at ground level and lacking a substantial atmospheric dilution, pose potential risks to nearby individuals, with concentrations of gases such as H2S surpassing safety thresholds. Total emissive flux of the investigated spot vents in the Mt. Amiata area, showed that the emission rate of H2S is notably substantial (55 kg/h), roughly equivalent to emissions from approximately four 20 MW geothermal plants, as along with odour emission rates in the order of 107 ouE/s. Considering the GWP derived from emitted gases, the total inventory assessment of the spot vents resulted in 36 t/h or 23 t/h CO2eq, depending on the time horizon considered (GWP20 or GWP100 respectively).

Smart instrumental Odour Monitoring Station for the efficient odour emission management and control in wastewater treatment plants.

Odour emission assessment in wastewater treatment plants (WWTP) is a key aspect that needs to be improved in the plant management to avoid complaints and guarantee a sustainable environment. The research presents a smart instrumental odour monitoring station (SiOMS) composed of an advanced instrumental odour monitoring system (IOMS) integrated with other measurement units, for the continuous characterization and measurement of the odour emissions, with the aim of managing the potential odour annoyance causes in real time, in order to avoid negative effects. The application and on-site validation procedure of the trained IOMS is discussed. Experimental studies have been conducted at a large-scale WWTP. Fingerprint analysis has been applied to analyze and identify the principal gaseous compounds responsible for the odour annoyance. The artificial neural network has been adopted to elaborate and dynamically update the odour monitoring classification and quantification models (OMMs) of the IOMS. The results highlight the usefulness of a real-time measurement and control system to provide continuous and different information to the plant operators, thus allowing the identification of the odour sources and the most appropriate mitigation actions to be implemented. The paper provides important information for WWTP operators, as well as for the regulating bodies, authorities, manufacturers and end-users of odour monitoring systems involved in environmental odour impact management.

Characterization of odour emissions in a wastewater treatment plant using a drone-based chemical sensor system.

Conventionally, odours emitted by different sources present in wastewater treatment plants (WWTPs) are measured by dynamic olfactometry, where a human panel sniffs and analyzes air bags collected from the plant. Although the method is considered the gold standard, the process is costly, slow, and infrequent, which does not allow operators to quickly identify and respond to problems. To better monitor and map WWTP odour emissions, here we propose a small rotary-wing drone equipped with a lightweight (1.3-kg) electronic nose. The "sniffing drone" sucks in air via a ten-meter (33-foot) tube and delivers it to a sensor chamber where it is analyzed in real-time by an array of 21 gas sensors. From the sensor signals, machine learning (ML) algorithms predict the odour concentration that a human panel using the EN13725 methodology would report. To calibrate and validate the predictive models, the drone also carries a remotely controlled sampling device (compliant with EN13725:2022) to collect sample air in bags for post-flight dynamic olfactometry. The feasibility of the proposed system is assessed in a WWTP in Spain through several measurement campaigns covering diverse operating regimes of the plant and meteorological conditions. We demonstrate that training the ML algorithms with dynamic (transient) sensor signals measured in flight conditions leads to better performance than the traditional approach of using steady-state signals measured in the lab via controlled exposures to odour bags. The comparison of the electronic nose predictions with dynamic olfactometry measurements indicates a negligible bias between the two measurement techniques and 95 % limits of agreement within a factor of four. This apparently large disagreement, partly caused by the high uncertainty of olfactometric measurements (typically a factor of two), is more than offset by the immediacy of the predictions and the practical advantages of using a drone-based system.

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.

Evaluation of the odor impact of some environmental gaseous pollutants: calibration of the methodology and preliminary results.

During the last decades, it has been observed a growing interest on odor impact because of the frequenter social acceptability problems about energy plants handling and processing stored organic materials (e.g., biogas plants, landfills, farms, distilleries, etc.). In this context, the UNI EN 13725:2004 indicates the "dynamic olfactometry method" as validated, recognized, and adequate measurement procedure for estimating the odor concentration. This protocol is carried out by a panel of specifically trained and selected human receptors, but alternative analytical methodologies are currently under discussion. This work aims to describe the initial steps of a wider research toward the definition of a new analytical protocol for monitoring odor concentration. The alternative methodology is here presented through the implementation of a case study: stored organic materials exploited on an energy plant in Central Italy. The paper describes the preliminary activities related to the survey of the case study (i), the definition of alternative methods and devices for conducting emissions sampling (ii), and the adopted experimental approach (iii). Finally, preliminary results are also presented (iv). The resulting protocol, once validated, could be employed by local authorities to measure both the odor impacts and the effectiveness of specifically designed mitigation strategies.

Monitoring of the composting process of different agroindustrial waste: Influence of the operational variables on the odorous impact.

Composting is a conventional but economical and environmentally friendly way to transform organic waste into a valuable, organic soil amendment. However, the physico-chemical characterization required to monitor the process involves considerable investment in terms of cost and time. In this study, 52 samples of four compostable substrates were collected randomly during the composting process and analyzed physico-chemically. The physico-chemical characterization was evaluated and reduced by principal component analysis (PCA) (PC1 + PC2: 70% variance). Moreover, a study of the relationship between odor and the raw material and odor and the operational variables was carried out at pilot scale using PCA and multivariate regression. The substrates were grouped by PCA (PC1 + PC2: 87% variance). The odor emission rate (OER) and dynamic respirometric index (DRI) were found to be the most influential variables in the sample variance, being relevant to identify the different emission sources. Dynamic respirometry and multivariate regression could be suitable tools to predict these odor emissions for the majority of compostable substrates, identifying successfully the emission source.

Pragmatic evaluation of odour emissions from a rendering plant in southern Brazil.

In the food industry and linked activities, environmental impacts relate mainly to the generation of liquid and gaseous effluents. Rendering plants, which process animal by-products, are strongly associated with malodorous emissions. Thus, effective odour-control technologies are required to minimise odour annoyance in nearby communities and thereby public complaints. In this paper, the effectiveness of a biofilter for the treatment of odours from a meat-rendering plant located in southern Brazil was evaluated based on German guideline VDI 3477:2004-11. Samples were collected upstream and downstream of the gas treatment system using a pragmatic approach in order to minimise the cost of such a study. Odour concentration was determined according to European standard EN 13725:2003. The results showed an OER of 8.82 × 108 ouE h-1 and odour removal efficiency lower than the established benchmark set by SEMA Resolution 054/2006, taken as reference for being the only Brazilian regulation to establish quantitative odour emission criteria. Enhancement of the biofiltration system and/or association with other odour abatement technologies are required to increase odour removal, limit impacts and comply with regulatory requirements. The paper also includes a discussion on the current odour regulation in Brazil.

Automated Collection of Real-Time Alerts of Citizens as a Useful Tool to Continuously Monitor Malodorous Emissions.

The evaluation of odor emissions and dispersion is a very arduous topic to face; the real-time monitoring of odor emissions, the identification of chemical components and, with proper certainty, the source of annoyance represent a challenge for stakeholders such as local authorities. The complaints of people, often not systematic and variously distributed, in general do not allow us to quantify the perceived annoyance. Experimental research has been performed to detect and evaluate olfactory annoyance, based on field testing of an innovative monitoring methodology grounded in automatic recording of citizen alerts. It has been applied in Taranto, in the south of Italy where a relevant industrial area is located, by using Odortel(®) for automated collection of citizen alerts. To evaluate its reliability, the collection system has been integrated with automated samplers, able to sample odorous air in real time, according to the citizen alerts of annoyance and, moreover, with meteorological data (especially the wind direction) and trends in odor marker compounds, recorded by air quality monitoring stations. The results have allowed us, for the first time, to manage annoyance complaints, test their reliability, and obtain information about the distribution and entity of the odor phenomena, such that we were able to identify, with supporting evidence, the source as an oil refinery plant.

Effect of IGF-II genotype and pig rearing system on the final characteristics of dry-cured Iberian hams.

The effect of the IGF-II genotype (AG vs. GG) on the morphological and compositional parameters, the fatty acid composition of intramuscular fat, the odour concentration (analysed by dynamic olfactometry) and the volatile compound profile (analysed by proton transfer reaction time-of-flight mass spectrometry) of dry-cured Iberian ham was studied for the first time, and compared to the effect of pig rearing system (high-oleic concentrated feed vs. acorn and grass). The IGF-II genotype had no effect on most variables. However, it influenced the concentration of some odorants (methanethiol and octanal), although it did not affect odour concentration. Conversely, the rearing system had a significant effect on a large number of ham variables. Results indicate a negligible effect of the IGF-II genotype on the final ham quality and confirm that the rearing system has a marked effect.