Monitoring of odors emitted from stabilized dewatered sludge subjected to aging using proton transfer reaction-mass spectrometry

Effect of incubation temperature on identification of key odorants of sewage sludge using headspace GC analysis

Currently, headspace gas chromatography-mass spectrometry is a widely used method to identify the key odorants of sludge. However, the effect of incubation temperature on the generation and emission of key odorants from sludge was still uncertain. Thus, in this paper, headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS) were carried out to analyze the volatiles emitted from the sludge incubated at different temperatures (30 °C, 50 °C, 60 °C, and 80 °C). The results indicated that the total volatile concentration of the sludge increased with temperatures, which affected the identified proportion of sludge key odorants to a certain extent. Differently from the aqueous solutions, the variation of volatile emission from the sludge was inconsistent with temperature changes, suggesting a multifactorial influence of incubation temperature on the identification of sludge odorants. The microbial community structure and adenosine triphosphate (ATP) metabolic activity of the sludge samples were analyzed at the initial state, 30 °C, and 80 °C. Although no significant effect of incubation temperature on the microbial community structure of the sludge, the incubation at 80 °C led to a noticeable decrease in microbial ATP metabolic activity, accompanied by a significant change in the proportion of odor-related microorganisms with low relative abundances. Changes in the composition and activity of these communities jointly contributed to the differences in odor emission from sludge at different temperatures. In summary, the incubation temperature affects the production and emission of volatiles from sludge through physicochemical and biochemical mechanisms, by which the microbial metabolism playing a crucial role. Therefore, when analyzing the key odorants of sludge, these factors should be considered.

Release characteristics and risk assessment of volatile sulfur compounds in a municipal wastewater treatment plant with odor collection device

Due to the malodorous effects and health risks of volatile sulfur compounds (VSCs) emitted from wastewater treatment plants (WWTPs), odor collection devices have been extensively utilized; however, their effectiveness has rarely been tested. In the present investigation, the characteristics of VSCs released in a WWTP equipped with gas collection hoods are methodically examined by gas chromatography. The obtained results indicate that the concentration of VSCs in the ambient air can be substantially reduced, and the primary treatment unit still achieves the highest concentration of VSCs. Compared to WWTPs without odor collection devices, the concentration of H2S in this WWTP is not dominant, but its sensory effects and health risks are still not negligible. Additionally, research on the emission of VSCs from sludge reveals that the total VSCs emitted from dewatering sludge reaches the highest level. Volatile organic sulfur compounds play a dominant role in the component and sensory effects of VSCs released by sludge. This study provides both data and theoretical support for analyzing the effectiveness of odor collection devices in WWTPs, as well as reducing the source of VSCs. The findings can be effectively employed to optimize these devices and improve their performance.

Assessment of dimethyl sulphide odorous emissions during coal extraction process in Coal Mine Velenje

Underground coal extraction at Coal Mine Velenje occasionally gives rise to odour complaints from local residents. This manuscript describes a robust quantification of odorous emissions of mine sources and a model-based analysis aimed to establish a better understanding of the sources, concentrations, dispersion, and possible control of odorous compounds during coal extraction process. Major odour sources during underground mining are released volatile sulphur compounds from coal seam that have characteristic malodours at extremely low concentrations at micrograms per cubic metre (μg/m3) levels. Analysis of 1028 gas samples taken over a 6-year period (2008-2013) reveals that dimethyl sulphide ((CH3)2S) is the major odour active compound present in the mine, being detected on 679 occasions throughout the mine, while hydrogen sulphide (H2S) and sulphur dioxide (SO2) were detected 5 and 26 times. Analysis of gas samples has shown that main DMS sources in the mine are coal extraction locations at longwall faces and development headings and that DMS is releasing during transport from main coal transport system. The dispersion simulations of odour sources in the mine have shown that the concentrations of DMS at median levels can represent relatively modest odour nuisance. While at peak levels, the concentration of DMS remained sufficiently high to create an odour problem both in the mine and on the surface. Overall, dispersion simulations have shown that ventilation regulation on its own is not sufficient as an odour abatement measure.

Wastewater Treatment Plants as a Source of Malodorous Substances Hazardous to Health, Including a Case Study from Poland

Using Poland as an example, it was shown that 41.6% of the requests for intervention in 2016-2021 by Environmental Protection Inspections were related to odour nuisance. Further analysis of the statistical data confirmed that approximately 5.4% of wastewater treatment plants in the group of municipal facilities were subject to complaints. Detailed identification of the subject of odour nuisance at wastewater treatment plants identified hydrogen sulphide (H₂S), ammonia (NH₃) and volatile organic compounds (VOCs) as the most common malodorous substances within these facilities. Moreover, the concentrations of hydrogen sulphide and ammonia exceed the reference values for some substances in the air (0.02 mg/m³ for H₂S and 0.4 mg/m³ for NH₃). A thorough assessment of the properties of these substances made it clear that even in small concentrations they have a negative impact on the human body and the environment, and their degree of nuisance is described as high. In the two WWTPs analysed in Poland (WWTP 1 and WWTP 2), hydrogen sulphide concentrations were in the range of 0-41.86 mg/m³ (Long-Term Exposure Limit for H₂S is 7.0 mg/m³), ammonia 0-1.43 mg/m³ and VOCs 0.60-134.79 ppm. The values recognised for H₂S cause lacrimation, coughing, olfactory impairment, psychomotor agitation, and swelling of the cornea with photophobia. Recognition of the methods used in practice at WWTPs to reduce and control malodorous emissions indicates the possibility of protecting the environment and human health, but these solutions are ignored in most facilities due to the lack of requirements specified in legislation.

Malodorous volatile organic compounds (MVOCs) formation after dewatering of wastewater sludge: Correlation with the extracellular polymeric substances (EPS) and microbial communities

Malodorous volatile organic compounds (MVOCs) are often the key odorants in determining sludge odor character and odor impact. However, the emission characterization and generation mechanisms of MVOCs from various dewatered sludge have not been sufficiently understood partly due to the diverse and complex composition and low concentration of odorants. In this study, waste activated sludge (WAS) was collected to examine the variation of MVOC emission from sludge after different dewatering treatment in lab-scale trials. The MVOCs were measured using the electronic nose (eNose), headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that centrifugation treatment promoted the generation of various odorous volatiles. The identified key odorants included dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), geosmin, and p-cresol according to their odor activity values (OAVs). The effects of the enhanced dewatering on volatile production were greater than thickening, however, the key odorants of dewatered sludge using gravity thickening varied more greatly than sludges from centrifuge thickening. The distribution of extracellular polymeric substances (EPS) and variation of microbial community showed correlations with the production of key odorants. Tryptophan-like substances in the inner layer of EPS (LB-EPS and TB-EPS) were better correlated with the key odorants. The bound EPS released by centrifugation may play the role of precursor for odorous microbial volatiles. According to the predicted functions of differential microbial genera, Desulfobulbus (Desulfobacterota), Gordonia (Actinobacteriota), and Hyphomicrobium (Proteobacteria) were associated with the production of DMS, DMDS, and DMTS, while Gordonia and Hyphomicrobium were related to p-cresol production.

Odour impact assessment using kinetics and optimization: case studies on removal of multiple volatile organo-sulphur compounds from sewage wastewater using porous functional materials

Expanding industries and booming population have led to the increase in the installation of wastewater and sewer systems, even in close proximity to residential areas. Emissions from these installations particularly volatile organo-sulphur compounds (VOSCs) such as methyl mercaptan (CH₃SH), ethyl mercaptan (C₂H₅SH), dimethyl sulphide (CH₃SCH₃) and carbon disulphide (CS₂) are a nuisance to people even when present in small concentration. Strategies for removal involve addition of chemicals or other chemical processes which are generally expensive. Biofilters, on the other hand, consume large amount of energy and wash waters. Hence keeping commercialization in mind, it is important to develop a strategy which would be cost-effective and at the same time be effective to remove most of the odorous compounds present in these systems. In the present research work, granular activated carbons (GAC) are functionalized with alkali solution to improve the adsorption capacity. Liquid phase batch adsorption is performed with GAC and various functionalized activated carbons (FACs) with the help of raw sewage water from a local sewage water treatment plant. Concentration of odour was evaluated by two methods-olfactometry-based analysis for sensory measurement and GCMS-based analysis for analytical estimation of a specific odorous compound. The adsorption capacities of the functionalized GACs are higher primarily because of complex formation at the surface of modified GACs. Pseudo-second-order kinetic model agreed well with experimental results with the rate constant being 0.0191 mg/l min and 0.0153 mg/l min for methyl and ethyl mercaptan adsorption onto FAC-NH₃. Boyd's film diffusion along with rate kinetic model supported that chemical adsorption forms the rate-limiting step. Response surface methodology (RSM) was used to optimize the removal of VOSCs with respect to different process parameters like adsorbent amount and time. The olfactometry removal of overall odour was also optimized taking 6 factors in the Box Behnken design. Variance of analysis results indicated that all the models displayed considerable goodness of fit with R² values close to 1. Methyl mercaptan turned out to be the highest contributor to the overall odour as confirmed both from experimental and optimization study. The optimized olfactometry odour removal (77.4%) along with CH₃SH removal (80.34%), C₂H₅SH removal (59.16%), CH₃SCH₃ removal (63.21%) and CS₂ removal (71.95%) was found at optimum process conditions, with amount of adsorbent of 10.29 g, adsorption time of 2.92 h. This result indicates that methyl mercaptan (CH₃SH) is the highest odour contributing component out of the studied VOSCs. The results show promising potential for the use of activated carbon as an adsorbent for removal of odorous compounds from STPs.

The variation of odor characteristics of wastewater sludge treated by advanced anaerobic digestion (AAD) and the contribution pattern of key odorants

Identification of the odor characteristics of wastewater sludge is important in the evaluation of sludge quality and disposal options considering that sludge odor nuisance may cause major environmental issues. In this study, raw sludge and sludge cake were collected from five WWTPs applied advanced anaerobic digestion (AAD) sludge treatment process to clarify the variation of odor characteristics using sensory analysis and instrumental analysis. The electronic nose, gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) were used to profile and identify the chemical composition of key odorants. A total of 20 odorants were identified and quantified, including 6 groups of chemicals, among which volatile sulfur compounds (VSCs), indole, 3-methylindole and geosmin were identified as key odorants. The odor of the dewatered digested sludge was improved by means of changing the odor character from fecal/sulfide to earthy odor due to the reduction in VSCs concentration. The AAD and subsequent dewatering process resulted in effective removal of VSCs, which are important constituents that impact the sludge odor characteristics through synergistic effect on fecal odorants and masking effect on earthy odorants. Moreover, due to the variation of sludge quality after AAD treatment, the emission capacity of indole, 3-methylindole, and other volatiles increased, which could not be neglected for the formation of unique sludge odor.

Chemical identification and quantification of volatile organic compounds emitted by sewage sludge

The recycling of organic waste products (e.g. sewage sludge, SS) is currently being promoted as a substitute for mineral fertilizers for agricultural lands. The spreading of SS allows the recycling of the nutrients and organic matter it contains. SS contains various pollutants such as volatile organic compounds (VOCs) that adversely affect the ecosystem and human health through ozone production and serve as critical precursors of atmospheric secondary organic aerosols. There are very few studies quantifying the gaseous compounds emitted from SS, and those studies primarily address their odorant properties for identifying suitable odour abatement techniques. There is an urgent need for more comprehensive quantitative information on VOCs emitted from SS as aerosol precursors. In this context, an experimental study was performed on SS samples taken from a wastewater treatment plant located in France. Undigested SS (UDSS), digested SS (DSS) and SS with 30% and 60% dryness were collected from different stages of treatment sequence and analyzed using atmospheric simulation chambers coupled to proton-transfer-reaction quadrupole ion-guide time-of-flight mass spectrometer. Our study revealed that SS samples emitted a large spectrum of VOCs. 380 compounds were detected, quantified and classified into different chemical groups. The VOC emissions increased with the increase in the dryness of the sample; the highest being in SS 60%, followed by SS 30%, UDSS and DSS. OVOCs were dominant in SS 60%. The statistical analysis showed that the anaerobic digestion and the dewatering to 60% of dryness decreased the emissions of sulphuric compounds. Aromatic compounds and indoles (e.g. skatole) were emitted significantly from the UDSS. Some of these VOCs can serve as precursor gases for atmospheric aerosol formation. The experimental dataset obtained in this study provides an accurate inventory reference for the VOC emissions from SS samples and shows the impacts of the treatment on emission characteristics of VOCs.

Measuring volatile emissions from biosolids: A critical review on sampling methods

As a by-product of wastewater treatment, biosolids are a source of volatile emissions which can lead to community complaints due to odours and other pollution risks. Sampling methods play a significant role in collecting gas emissions from biosolids-related sources (i.e., pure biosolids, landfilling, land application and composting of biosolids). Though a range of different sampling techniques (flux hood, wind tunnel, static chamber, headspace devices) have been explored in many published papers, the management and best practice for sampling emissions from biosolids is unclear. This paper presents a comprehensive review of sampling methods for collecting gaseous emissions from biosolids. To account for the inconsistent terminologies used to describe sampling devices, a standard nomenclature by grouping sampling devices into five categories was proposed. Literature investigating emission sampling from biosolids-related sources was reviewed. Subsequently a critical analysis of sampling methods in terms of design, advantages, and disadvantages were compiled based on literature findings and assumed mechanistic understanding of operation. Key operational factors such as the presence of fans, purge gas flow rates, insertion depth, and incubation conditions were identified and their level of influence on the measurement of emissions were evaluated. From the review, there are still knowledge gaps regarding sampling methods used to collect gases from biosolids-related sources. Therefore, a framework for the management of emission sampling methodologies based on common sampling purposes was proposed. This critical review is expected to improve the understanding of sampling methodologies used in biosolids-related sources, by demonstrating the potential implications and impacts due to different choices in sampling methods.

Effect of low-temperature thermal drying on malodorous volatile organic compounds (MVOCs) emission of wastewater sludge: The relationship with microbial communities

Sludge treatment processes are the main source of nuisance odors in wastewater treatment plants. Apart from well-known odorants such as NH₃ and H₂S, malodorous volatile organic compounds (MVOCs) contribute largely to nuisance odors but are less concerned. In this work, the emission of MVOCs from wastewater sludges at different processing stages was measured, and the effects of dewatering and low-temperature thermal drying on the generation of sludge odor were investigated. The MVOCs were analyzed by olfactory measurements, headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Low-temperature thermal drying treatment changed the odor categories and increased the odor intensity (OI) from moderate level (8-9) for raw sludges to strong (>10) for dried sludge. The odor emission capacity of MVOCs, namely the concentration of MVOCs, increased for dried sludge. The major odorants of sludge after different processes included 2-MIB, geosmin, dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), hexanal, and decanal according to their odor activity values (OAVs). The bacterial community structures showed a correlation with the key MVOC odorants. Specifically, there was a significant positive correlation between the concentration of key odorants and the relative abundance of the phyla of Actinobacteria and Chloroflexi. Thus, low-temperature thermal drying had a significant effect on odor formation by acting on the microbial community of sludge.

Odour Nuisance at Municipal Waste Biogas Plants and the Effect of Feedstock Modification on the Circular Economy—A Review

The increase in the amount of municipal solid waste (MSW) generated, among other places, in households is a result of the growing population, economic development, as well as the urbanisation of areas with accompanying insufficiently effective measures to minimise waste generation. There are many methods for treating municipal waste, with the common goal of minimising environmental degradation and maximising resource recovery. Biodegradable waste, including selectively collected biowaste (BW), also plays an essential role in the concept of the circular economy (CE), which maximises the proportion of waste that can be returned to the system through organic recycling and energy recovery. Methane fermentation is a waste treatment process that is an excellent fit for the CE, both technically, economically, and environmentally. This study aims to analyse and evaluate the problem of odour nuisance in municipal waste biogas plants (MWBPs) and the impact of the feedstock (organic fraction of MSW-OFMSW and BW) on this nuisance in the context of CE assumptions. A literature review on the subject was carried out, including the results of our own studies, showing the odour nuisance and emissions from MWBPs processing both mixed MSW and selectively collected BW. The odour nuisance of MWBPs varies greatly. Odour problems should be considered regarding particular stages of the technological line. They are especially seen at the stages of waste storage, fermentation preparation, and digestate dewatering. At examined Polish MWBPs cod ranged from 4 to 78 ou/m3 for fermentation preparation and from 8 to 448 ou/m3 for digestate dewatering. The conclusions drawn from the literature review indicate both the difficulties and benefits that can be expected with the change in the operation of MWBPs because of the implementation of CE principles.

Gaseous emissions from wastewater facilities

A review of the literature published in 2019 on topics relating to gaseous emissions from wastewater facilities is presented. This review is divided into the following sections: odorant emissions from Water Resource Recovery Facilities (WRRFs); greenhouse gas (GHG) emissions; gaseous emissions from wastewater collection systems; physiochemical odor/emissions control methods; biological odor/emissions control methods; odor/GHG characterization and monitoring; and odor impacts/risk assessments. © 2020 Water Environment Federation PRACTITIONER POINTS: Provide a quick reference list for readers who do not have time to go through the 2019 published articles. This prescreening of relevant literatures will save them time and effort. Utilities, engineers, and researchers can identify knowledge gaps, which help them to plan for future testing and R&D needs. Designers can make use of the lit review findings to support their design.

Emissions of non-methane volatile organic compounds from a landfill site in a major city of India: impact on local air quality

Emissions from landfills are a significant source of non-methane volatile organic compounds (NMVOCs) in urban environments. NMVOCs play an important role in atmospheric chemistry, and elevated concentrations of some compounds are responsible for air quality deterioration. This study is based on the measurements of a suite of 20 C₂–C₈ NMVOCs at 21 upwind and downwind sites of the largest landfill in western India. Ethane, ethylene and aromatics were the dominant compounds; the concentrations of BTEX in the downwind regions were up to three times higher than their concentrations at upwind sites. The emission ratios of BTEX and other NMVOCs were different from those for residential, commercial, and industrial sources characterizing the emissions from burning and decomposition of organic material. The slope of ΔToluene/ΔBenzene of 0.64 is about three times higher than that determined at the main road junctions of the city. Ranking by Prop-Equiv, the top NMVOCs were isoprene, cis-2-Butene, m + p-xylenes, propylene, ethylene and trans-2-Butene account for 72–75% of the total Prop-Equiv concentrations. Alkenes played the dominant role in ozone formation, followed by aromatic and alkane groups. In addition to landfill emissions, contributions from traffic-related emissions to ambient concentrations of aromatic VOCs were also significant at some sites. Although the experiment was not designed to characterize the emissions from a specific source, the analysis suggests the substantial contributions from both decomposition and burning of landfill materials. The main difficulty in characterizing VOC emissions from landfills is the spatial and temporal variability of emissions from a large area.

A systematic study on the odorants characterization and evaluation in a plain reservoir with wetlands ecosystem

The odor problems in plain reservoirs are more complex compared to valley reservoirs and ground water reservoirs. Just as YL Reservoir with wetlands ecosystem in Lixiahe Plain, Jiangsu Province has been suffering from complex odors, however, the odorants were unclear. In this study, a systematic study on odorants characterization and evaluation of plain YL reservoir was accomplished. Totally musty, septic, fishy, chemical and grassy odors were first identified simultaneously, twenty-four odorants were identified correspondingly. According to odor activity value ranking, 2-methylisoborneol and geosmin, with odor activity values of 14-18 and 2.5-3.8, were major musty odorants, while bis(2-chloroisopropyl) ether, dimethyl disulfide, dimethyl trisulfide, pentanethiol and indole, with odor activity values of 15.3-18.8, 1-1.3, 1.5-2.3, 2-3 and 0.7-0.9, were major septic compounds. Fishy and grassy odors were associated with 2,4-decadienal, hexanal, nonanal, decanal, benzaldehyde and β-cyclocitral, while chemical odor was related to indane, eucalyptol, 2-nitrophenol, 2-methylphenol, tetramethylpyrazine, 1,4-dichlorobenzene, p-xylene and ethylbenzene. By reconstituting tests, 98, 95, 88, 85 and 81 % of musty, septic, fishy, chemical and grassy characteristics in source water could be explained. It was notable that wetlands ecosystem has almost no effect on odor removal. This study would offer more understandings and supports for odors's control in such source waters.

Integrated model for estimating odor emissions from civil wastewater treatment plants

The objective of this research project was the design and development of an integrated model for odor emission estimation in wastewater treatment plants. The SMAT's plant, the largest wastewater treatment facility in Italy, was used as a case study. This article reports the results of the characterization phase that led to the definition and design of the proposed conceptual model for odor emission estimation. In this phase, concentrations of odor chemical tracers (VOC, H₂S, NH₃) and odor concentrations were monitored repeatedly. VOC screening with GC-MS analysis was also performed. VOC concentrations showed significant variability in space and magnitude. NH₃ and H₂S were also detected at considerable concentrations. Results were elaborated to define a spatially variable linear relationship between the sum of odor activity values (SOAV) and odor concentrations. Based on the results, a conceptual operational model was presented and discussed. The proposed system is composed by a network of continuous measurement stations, a set of algorithms for data elaboration and synchronization, and emission dispersion modeling with the application of Lagrangian atmospheric models.

Importance of 2,4,6-Trichloroanisole (TCA) as an odorant in the emissions from anaerobically stabilized dewatered biosolids

Odours from stabilized biosolids after anaerobic digestion of wastewater sludge can cause local community impact. Apart from the well-known odorants such as sulfur compounds, contributions from other volatile organic compounds (VOCs) to nuisance odours is limited. The presence of compounds with low odour detection thresholds (ODTs) at low concentrations, can present challenges for analytical identification. Thirty-six biosolids samples were taken after anaerobic stabilisation and dewatering at a wastewater treatment plant, Sydney, Australia. Biosolid cake samples were stored outside in loosely covered trays under aerobic conditions, however without interactions with soil microorganisms as it would be in reality. All biosolids cake samples were analysed over a period of 35 days. Emissions were collected onto Tenax TA sorbent tubes using a U.S. EPA flux hood method at storage days 1, 3, 7, 10, 14, 21 and 35. Gas chromatography (GC) coupled with mass spectrometer detector (MSD) and an olfactory detection port (ODP) was used to identify a musty/moldy/earthy type odorant in the biosolids emissions as 2,4,6-trichloroanisole (TCA). Measured odour intensities, classified on a scale from 1 to 4, and odour characters were specified by three ODP assessors. TCA was identified in all biosolid cake emissions. The measured odour intensities of the TCA did not significantly alter as the biosolids were aged, however varied between biosolids cakes. Due to its odour intensity, 85% frequency of detection and its low ODT, which is orders of magnitudes lower than sulfur compounds, TCA should be considered as a potential odorant of concern in biosolids emissions.

Differences between selected volatile aromatic compound concentrations in sludge samples in various steps of wastewater treatment plant operations

Sewage sludge, one of the main wastes generated during wastewater treatment, constitutes an important source of emissions of volatile chemical compounds such as volatile aromatic compounds These substances may undergo various changes as a result of operations and unit processes, which affects their concentrations in sewage sludge. An important factor determining the potential hazardousness of volatile organic compounds is the quality of wastewater delivered to wastewater treatment plants and the technical and equipment solutions applied to wastewater. In this study, a rapid and sensitive headspace gas chromatography method, coupled with tandem mass spectrometry using the standard addition method, was developed for the determination of selected volatile aromatic compounds in sewage sludge samples collected at different stages from three wastewater treatment plants located in Poland. This study attempted to assess the relationship between differences in the emissions of representative VACs and the given stage of the technological process within three analysed wastewater treatment plants. Toluene was detected with the highest frequency in analysed samples, at concentrations varying from 0.234 ± 0.035 ng/g of sludge to 28.3*10²±3.2*10² ng/g of sludge. The highest concentration levels were determined for p-cresol, with concentrations ranging from 44.0*10¹±5.6*10¹ ng/g of sludge (sludge from aerobic chamber, wastewater treatment plant no.2) to 47.7*10²±6.9*10² ng/g of sludge (sludge from aerobic chamber, wastewater treatment plant no.1), while the lowest concentration levels were observed for chlorobenzene, with concentrations ranging from 0.1300 ± 0.0030 ng/g of sludge (sludge from anaerobic chamber, wastewater treatment plant no.2), to 0.2606 ± 0.0046 ng/g of sludge (primary sludge, wastewater treatment plant no.1). The repeatability of the method was better than 10%, with accuracy levels in the ranges 89%-108%.Wastewater treatment technologies and residual sludge management in the selected wastewater treatment plantsinfluenced volatile aromatic compounds emission. Furthermore, the diversity of the wastewater quality, depending on the catchment area, is also an important factor determining the differentiation in volatile aromatic compounds emission. The microbial composition of raw wastewater highly influenced not only the treatment effectiveness of wastewater treatment plants but also the production of intermediate products, such as volatile aromatic compounds, which may contribute to odour emissions.

The Use of Artificial Neural Networks and Decision Trees to Predict the Degree of Odor Nuisance of Post-Digestion Sludge in the Sewage Treatment Plant Process

This paper presents the application of artificial neural networks and decision trees for the prediction of odor properties of post-fermentation sludge from a biological-mechanical wastewater treatment plant. The input parameters were concentrations of popular compounds present in the sludge, such as toluene, p-xylene, and p-cresol, and process parameters including the concentration of volatile fatty acids, pH, and alkalinity in the fermentation sludge. The analyses revealed that the implementation of artificial neural networks allowed the prediction of the values of odor intensity and the hedonic tone of the post-fermentation sludge at the level of 30% mean absolute percentage error. Application of the decision tree made it possible to determine what input parameters the fermentation feed should have in order to arrive at the post-fermentation sludge with an odor intensity <2 and hedonic tone >−1. It was shown that the aforementioned phenomenon was influenced by the following factors: concentration of p-xylene, pH, concentration of volatile fatty acids, and concentration of p-cresol.