Characterisation of volatile organic compounds (VOCs) released by the composting of different waste matrices

A critical review on characterization, human health risk assessment and mitigation of malodorous gaseous emission during the composting process

Composting has emerged as a suitable method to convert or transform organic waste including manure, green waste, and food waste into valuable products with several advantages, such as high efficiency, cost feasibility, and being environmentally friendly. However, volatile organic compounds (VOCs), mainly malodorous gases, are the major concern and challenges to overcome in facilitating composting. Ammonia (NH3) and volatile sulfur compounds (VSCs), including hydrogen sulfide (H2S), and methyl mercaptan (CH4S), primarily contributed to the malodorous gases emission during the entire composting process due to their low olfactory threshold. These compounds are mainly emitted at the thermophilic phase, accounting for over 70% of total gas emissions during the whole process, whereas methane (CH4) and nitrous oxide (N2O) are commonly detected during the mesophilic and cooling phases. Therefore, the human health risk assessment of malodorous gases using various indexes such as ECi (maximum exposure concentration for an individual volatile compound EC), HR (non-carcinogenic risk), and CR (carcinogenic risk) has been evaluated and discussed. Also, several strategies such as maintaining optimal operating conditions, and adding bulking agents and additives (e.g., biochar and zeolite) to reduce malodorous emissions have been pointed out and highlighted. Biochar has specific adsorption properties such as high surface area and high porosity and contains various functional groups that can adsorb up to 60%-70% of malodorous gases emitted from composting. Notably, biofiltration emerged as a resilient and cost-effective technique, achieving up to 90% reduction in malodorous gases at the end-of-pipe. This study offers a comprehensive insight into the characterization of malodorous emissions during composting. Additionally, it emphasizes the need to address these issues on a larger scale and provides a promising outlook for future research.

Addressing the gaseous and odour emissions gap in decentralised biowaste community composting

Composting has demonstrated to be an effective and sustainable technology to valorise organic waste in the framework of circular economy, especially for biowaste. Composting can be performed in various technological options, from full-scale plants to community or even individual composters. However, there is scarce scientific information about the potential impact of community composting referred to gaseous emissions. This work examines the emissions of methane and nitrous oxide as main GHG, ammonia, VOC and odours from different active community composting sites placed in Spain, treating kitchen, leftovers and household biowaste. Expectedly, the gaseous emissions have an evident relation with the composting progress, represented mainly by its decrease as temperature or biological activity decreases. GHG and odour emission rates ranged from 5.3 to 815.2 mg CO2eq d-1 kg-1VS and from 69.8 to 1088.5 ou d-1 kg-1VS, respectively, generally being lower than those find in open-air full-scale composting. VOC characterization from the community composting gaseous emissions showed a higher VOC families' distribution in the emissions from initial composting phases, even though terpenes such as limonene, α-pinene and β-pinene were the most abundant VOC along the composting process occurring in the different sites studied. The results presented in this study can be the basis to evaluate systematically and scientifically the numerous current projects for a worldwide community composting implementation in decentralised biowaste management schemes.

Characterizing emissions of VOCs from the initial degradation of kitchen waste in household waste bins of residential areas in Beijing

In order to clarify the emission characteristics of VOCs during the initial degradation of kitchen waste, a year-long sampling campaign of kitchen waste in residential household municipal solid waste (HMSW) bins was conducted. A total of 93 VOCs with an average annual concentration of 2271 μg/m3 were detected. Alkanes and oxygenated compounds were the dominant released from the initial degradation of kitchen waste. Seasonal and daily variations were observed, with VOC concentrations generally higher in spring (1413 μg/m3) and summer (5882 μg/m3) and lower in autumn (505 μg/m3) and winter (1258 μg/m3). In addition, peak releases occurred earlier in the spring and summer (at 6 h) than in autumn and winter (at 24 h). Correlation analysis showed that ambient temperature correlated significantly with alkanes and oxygenated compounds (P < 0.01). 67 substances have been found to cause odor pollution. Based on the odor index, oxygenated compounds were the most significant odor pollutants. Acetaldehyde and 2-ketone required particular concern because of its high concentration and high odor index. This study not only enriched the understanding of emissions of VOCs from MSW front-end facilities but will also provide a scientific and theoretical basis for holistic management and odor control of MSW.

Effects of fungal agents and biochar on odor emissions and microbial community dynamics during in-situ treatment of food waste

The effects of the co-addition of fungal agents and biochar on physicochemical properties, odor emissions, microbial community structure, and metabolic functions were investigated during the in-situ treatment of food waste. The combined addition of fungal agents and biochar decreased cumulative NH₃, H₂S, and VOCs emissions by 69.37%, 67.50%, and 52.02%, respectively. The predominant phyla throughout the process were Firmicutes, Actinobacteria, Cyanobacteria, and Proteobacteria. Combined treatment significantly impacted the conversion and release of nitrogen from the perspective of the variation of nitrogen content between different forms. FAPROTAX analysis revealed that the combined application of fungal agents and biochar could effectively inhibit nitrite ammonification and reduce the emission of odorous gases. This work aims to clarify the combined effect of fungal agents and biochar on odor emission and provide a theoretical basis for developing an environmentally friendly in-situ efficient biological deodorization (IEBD) technology.

A critical review on odor measurement and prediction

Odor pollution has become a global environmental issue of increasing concern in recent years. Odor measurements are the basis of assessing and solving odor problems. Olfactory and chemical analysis can be used for odor and odorant measurements. Olfactory analysis reflects the subjective perception of human, and chemical analysis reveals the chemical composition of odors. As an alternative to olfactory analysis, odor prediction methods have been developed based on chemical and olfactory analysis results. The combination of olfactory and chemical analysis is the best way to control odor pollution, evaluate the performances of the technologies, and predict odor. However, there are still some limitations and obstacles for each method, their combination, and the prediction. Here, we present an overview of odor measurement and prediction. Different olfactory analysis methods (namely, the dynamic olfactometry method and the triangle odor bag method) are compared in detail, the latest revisions of the standard olfactometry methods are summarized, and the uncertainties of olfactory measurement results (i.e., the odor thresholds) are analyzed. The researches, applications, and limitations of chemical analysis and odor prediction are introduced and discussed. Finally, the development and application of odor databases and algorithms for optimizing odor measurement and prediction methods are prospected, and a preliminary framework for an odor database is proposed. This review is expected to provide insights into odor measurement and prediction.

Measures for Controlling Gaseous Emissions during Composting: A Review

Composting is a promising technology for treating organic solid waste. However, greenhouse gases (methane and nitrous oxide) and odor emissions (ammonia, hydrogen sulfide, etc.) during composting are practically unavoidable, leading to severe environmental problems and poor final compost products. The optimization of composting conditions and the application of additives have been considered to mitigate these problems, but a comprehensive analysis of the influence of these methods on gaseous emissions during composting is lacking. Thus, this review summarizes the influence of composting conditions and different additives on gaseous emissions, and the cost of each measure is approximately evaluated. Aerobic conditions can be achieved by appropriate process conditions, so the contents of CH4 and N2O can subsequently be effectively reduced. Physical additives are effective regulators to control anaerobic gaseous emissions, having a large specific surface area and great adsorption performance. Chemical additives significantly reduce gaseous emissions, but their side effects on compost application must be eliminated. The auxiliary effect of microbial agents is not absolute, but is closely related to the dosage and environmental conditions of compost. Compound additives can reduce gaseous emissions more efficiently than single additives. However, further study is required to assess the economic viability of additives to promote their large-scale utilization during composting.

Effect of biochar addition on the improvement of the quality parameters of compost used for land reclamation

The 5% addition of biochar in composting in rows contributes significantly to reducing volatile organic compound(VOC) emissions. When composting with the addition of biochar, the average temperature increased by 13 ± 6.7 °C during the whole period, and the thermophilic phase was extended by 11 days. The higher temperature supported a reduction in the time necessary for achieving the biological stability observed by the oxygen uptake rate by more than 10 days. For organic compounds formed by the degradation of easily degradable primary components (proteins), the addition of biochar significantly reduces the release of organic compounds with heterocyclically bound nitrogen (N_org-VOCs) and volatile sulfur compounds (VSCs). The end of the biodegradation process is indicated by a decrease in VOC concentrations below initial values in the input material. This state was achieved in the compost with added biochar after 47 days, while in compost without added biochar, it lasted 60 days.

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.

Spatiotemporal footprints of odor compounds in megacity's food waste streams and policy implication

Odor pollution is one of the most critical issues in food waste (FW) recycling and has significant implications for human health. However, knowledge of their occurrence and spatiotemporally dynamic in urban FW streams is limited, making it not conducive to implement targeted odor management. This work followed the occurrence of 81 odor compounds (OCs) in nine FW-air environments along the Shanghai's FW streams for one year. Results showed that NH₃, acetic acid, acetaldehyde, acetone, 2-butanone, and methylene chloride were consistently the predominant OCs, despite the distinct differences in OCs profiles across seasons and treatment sites. Ridge regression and principal coordinate analysis demonstrated that seasons might play a non-negligible role in shaping odor profiles, and ambient temperature and humidity could account for the seasonal variation in OCs levels. Based on the modified fuzzy synthetic evaluation system, the screened priority pollutants in different FW-air environments were found broadly similar and the regulated air pollutants released via FW should be expanded to aldehyde and ketone compounds, especially for acetaldehyde. To our knowledge, this study is the first to track the spatiotemporal footprints of OCs within urban FW streams, and provides new insights into the control policy on FW-derived odor issues for megacities.

Odors Emitted from Biological Waste and Wastewater Treatment Plants: A Mini-Review

In recent decades, a new generation of waste treatment plants based on biological treatments (mainly anaerobic digestion and/or composting) has arisen all over the world. These plants have been progressively substituted for incineration facilities and landfills. Although these plants have evident benefits in terms of their environmental impact and higher recovery of material and energy, the release into atmosphere of malodorous compounds and its mitigation is one of the main challenges that these plants face. In this review, the methodology to determine odors, the main causes of having undesirable gaseous emissions, and the characterization of odors are reviewed. Finally, another important topic of odor abatement technologies is treated, especially those related to biological low-impact processes. In conclusion, odor control is the main challenge for a sustainable implementation of modern waste treatment plants.

Health risks of inhalation exposure to BTEX in a municipal wastewater treatment plant in Middle East city: Shiraz, Iran

Benzene, toluene, ethylbenzene, and xylene, known as BTEX, adversely affect human health. This study aimed to measure BTEX concentration and assess the health risk through inhalation exposure to these compounds in a municipal wastewater treatment plant. The ambient air samples were collected using the active sampling method in summer and winter. Sampling sites were close to wastewater treatment units, including bar screen & grit chamber (Site-1), aeration tank & secondary clarifiers (Site-2), anaerobic sludge digester (Site-3), and office & control building (Site-4). Results indicate that the mean levels of benzene and toluene in winter were higher than in summer. The levels of benzene and toluene were below the occupational exposure levels of the American Conference of Governmental Industrial Hygienists (ACGIH) and Occupational Safety and Health Administration (OSHA). The carcinogenic risk (CR) and hazard quotient (HQ) were assessed using the United States Environmental Protection Agency (U.S.EPA) method, and Monte Carlo simulation (MCS) was applied to quantify the uncertainty and sensitivity analysis. The CRs for all sampling sites were below the U.S.EPA threshold limit (1.0 × 10^-4). The HQ values for benzene nearby Site-2 were above 1.0, indicating inhalation exposure could pose a health hazard. Besides, the HQ results for exposure to toluene in all sampling sites were less than 1.0. The sensitivity analysis had shown that the risk determinant for carcinogenic and non-carcinogenic risk was exposure time, followed by concentration.

Diffusion simulation, health risks, ozone and secondary organic aerosol formation potential of gaseous pollutants from rural comprehensive waste treatment plant

Comprehensive waste treatment plants (CWTPs) are significant sources of gaseous pollutants such as odors, volatile organic compounds (VOCs) and nitrogen oxides (NOx), polluting the environment and endangering human health. This study conducted on-site investigations on gaseous pollutants emissions from different areas of a CWTP. A total of 10 pollutants were identified of which ammonia (11.32 mg/m³ in average) was the main odorous substance, and benzene (19.51 mg/m³ in average) and toluene (42.07 mg/m³ in average) were the main VOCs. The feeding workshop (FW) was considered the main source of gaseous pollutants. The Gaussian plume model demonstrated that the pollution became more serious after spreading in the southeast downwind direction. Occupational exposure risks of on-site workers were mainly attributed to hydrogen sulfide, ammonia, benzene, and toluene, as their hazard index (HI) and lifetime cancer risk (CR) exceeded the recommended occupational safety limits. The gaseous pollutants diffused from CWTP may still pose a potential health risk to residents within a range of up to 7.5 km. The emulation and quantification of ozone formation potential by methods of Propyl-Equiv and MIR demonstrated that the contribution rate of toluene presented in each stage of CWTP exceed 80 %. Toluene was also the largest contributor to secondary organic aerosol with the contribution rate reached 56.34-85.14 %, followed by benzene (14.72-38.52 %). This research provides a basis for the reduction and control of gaseous pollutants in the treatment and disposal of rural domestic waste.

The Use of Chemical Sensors to Monitor Odour Emissions at Municipal Waste Biogas Plants

Municipal waste treatment plants are an important element of the urban area infrastructure, but also, they are a potential source of odour nuisance. Odour impact from municipal waste processing plants raises social concerns regarding the well-being of employees operating the plants and residents of nearby areas. Chemical methods involve the determination of the quantitative composition of compounds comprising odour. These methods are less costly than olfactometry, and their efficiency is not dependent on human response. The relationship between the concentration of a single odorant and its odour threshold (OT) is determined by the odour activity value (OAV) parameter. The research involved the application of a multi-gas detector, MultiRae Pro. Measurements by means of the device were conducted at three municipal waste biogas plants located in Poland. In this paper we describe the results obtained when using a detector during the technological processes, the unitary procedures conducted at the plants, and the technological regime. The determination of these relationships could be useful in the development of odour nuisance minimization procedures at treatment plants and the adjustment to them. This is of paramount importance from the viewpoint of the safety and hygiene of the employees operating the installations and the comfort of residents in the areas surrounding biogas plants. Monitoring of expressed odorant emissions allows the course of technological processes and conducted unit operations to be controlled.

Targeted genome editing of plants and plant cells for biomanufacturing

Plants have provided humans with useful products since antiquity, but in the last 30 years they have also been developed as production platforms for small molecules and recombinant proteins. This initially niche area has blossomed with the growth of the global bioeconomy, and now includes chemical building blocks, polymers and renewable energy. All these applications can be described as “plant molecular farming” (PMF). Despite its potential to increase the sustainability of biologics manufacturing, PMF has yet to be embraced broadly by industry. This reflects a combination of regulatory uncertainty, limited information on process cost structures, and the absence of trained staff and suitable manufacturing capacity. However, the limited adaptation of plants and plant cells to the requirements of industry-scale manufacturing is an equally important hurdle. For example, the targeted genetic manipulation of yeast has been common practice since the 1980s, whereas reliable site-directed mutagenesis in most plants has only become available with the advent of CRISPR/Cas9 and similar genome editing technologies since around 2010. Here we summarize the applications of new genetic engineering technologies to improve plants as biomanufacturing platforms. We start by identifying current bottlenecks in manufacturing, then illustrate the progress that has already been made and discuss the potential for improvement at the molecular, cellular and organism levels. We discuss the effects of metabolic optimization, adaptation of the endomembrane system, modified glycosylation profiles, programmable growth and senescence, protease inactivation, and the expression of enzymes that promote biodegradation. We outline strategies to achieve these modifications by targeted gene modification, considering case-by-case examples of individual improvements and the combined modifications needed to generate a new general-purpose “chassis” for PMF.

Integral evaluation of granular activated carbon at four stages of a full-scale WWTP deodorization system

Odor emissions from wastewater treatment plants (WWTPs) have always been a public concern. In this work, the physico-chemical, olfactometric and textural characterization of granular active carbon (GAC) used by an urban WWTP as a deodorization system, as well as the chromatographic quantification of the retained odoriferous compounds, have been carried out. These techniques have allowed an integral evaluation of the contaminated GAC and the characterization of the retained gaseous emission from four different stages of the wastewater treatment (pretreatment header: GAC-1; sand and fat removal: GAC-2; sludge thickening: GAC-3; sludge dehydration: GAC-4). A larger amount and variety of retained odoriferous compounds were found in GAC samples from the wastewater line deodorization (GAC-1 and GAC-2) after the same operation time (one year), GAC-1 being the adsorbent bed that retained the highest mass of volatile compounds (approximately 150μg/g GAC). Furthermore, some variables such as the removed specific odor concentration and free micropore volume were inversely correlated (R²=0.9945). The analysis of odor contribution showed that sulfur-containing compounds were the major odor contributors (61-97%). However, hydrogen sulfide cannot be considered a key odorant in this particular WWTP, since the elimination of this compound does not reduce the significant contribution of other (organic) sulfur compounds to the global odor (especially dimethyl disulfide). Consequently, multi-technical analysis might be a suitable alternative to better understand odor removal by GAC adsorption.

Advancements in Microfabricated Gas Sensors and Microanalytical Tools for the Sensitive and Selective Detection of Odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans' olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoring.

Characterization of the Gaseous and Odour Emissions from the Composting of Conventional Sewage Sludge

Many different alternatives exist to manage and treat sewage sludge, all with the common drawback of causing environmental and odour impacts. The main objective of this work is to present a full inventory of the gaseous and odorous emissions generated during the bench-scale composting of conventional sewage sludge, aiming at assessing the process performance and providing global valuable information of the different gaseous emission patterns and emission factors found for greenhouse gases (GHG) and odorant pollutants during the conventional sewage sludge composting process. The main process parameters evaluated were the temperature of the material, specific airflow, average oxygen uptake rate (OUR), and final dynamic respiration index (DRI), resulting in a proper performance of the sewage sludge composting process and obtaining the expected final product. The obtained material was properly stabilized, presenting a final DRI of 1.2 ± 0.2 g O2·h−1·kg−1 Volatile Solids (VS). GHGs emission factor, in terms of kg CO2eq·Mg−1 dry matter of sewage sludge (DM–SS), was found to be 2.30 × 102. On the other hand, the sewage sludge composting odour emission factor (OEF) was 2.68 × 107ou·Mg−1 DM–SS. Finally, the most abundant volatile organic compounds (VOC) species found in the composting gaseous emissions were terpenes, sulphur compounds, ketones, and aromatic hydrocarbons, whereas the major odour contributors identified were dimethyldisulphide, eucalyptol, and α-pinene.

Characterization of the volatile compounds emitted from municipal solid waste and identification of the key volatile pollutants

Gaseous emissions from municipal solid waste (MSW) have raised many concerns and complaints. Identifying the key volatile pollutants in the complex gaseous emissions from MSW is significant for the efficient mitigation of their odor nuisances and health risks. For this purpose, we present an integrated investigation of the key volatile pollutants in the gaseous emissions of MSW from the perspectives of emission patterns, odor concentrations and health risks. Air samples were collected during four different emission stages of the waste matrix for both chemical and olfactometric analyses. The total chemical concentrations of the volatile compounds in the air samples were in the range of 21.49 mg m^-3 to 295.61 mg m^-3, and the odor concentrations varied from 1122 ou_E m^-3 to 17,782 ou_E m^-3. The odor concentrations in the air samples were well correlated with the odor activity values (OAVs) of sulfur compounds, oxygenated compounds and ammonia (r = 0.922, 0.879 and 0.780, respectively, for n = 17 and p < 0.01). Moreover, from an integrated perspective involving chemical emissions, the proportions of odor concentrations and health risks, ethanol, methyl mercaptan and hydrogen sulfide were identified as the key volatile pollutants in the gaseous emissions from the waste matrix during the airtight storage stage, and dimethyl disulfide, 1,2-dichloroethane and trichloroethylene were the key volatile pollutants during the ventilation stage.

Emission characteristics and health risk assessment of VOCs from a food waste anaerobic digestion plant: A case study of Suzhou, China

The process of anaerobic digestion in food waste treatment plants generates a large amount of volatile organic compounds (VOCs). Long-term exposure to this exhaust gas can pose a threat to the health of workers and people living nearby. In this study, VOCs emitted from different working units in a food waste anaerobic digestion plant were monitored for a year. Variations in VOCs emitted from each unit were analyzed and a health risk assessment was conducted for each working unit. The results show that the concentration of VOCs in different units varied greatly. The highest cumulative concentration of VOCs appeared in the hydrothermal hydrolysis unit (3.49 × 10⁴ μg/m³), followed by the sorting/crushing room (8.97 × 10³ μg/m³), anaerobic digestion unit (6.21 × 10² μg/m³), and biogas production unit (2.01 × 10² μg/m³). Oxygenated compounds and terpenes were the major components of the emitted VOCs, accounting for more than 98% of total VOC emissions. The carcinogenic risk in the plant exceeded the safety threshold (ILCR<1 × 10^-6), while the non-carcinogenic risk was within the acceptable range (HI < 1). The carcinogenic risk from the hydrothermal hydrolysis unit was the highest, reaching 4.4 × 10^-5, and was labeled as "probable risk." The carcinogenic risk at the plant boundary was 1.2 × 10^-5, indicating exhaust gases can cause a health threat to neighbors. Therefore, management VOCs in anaerobic digestion plants should receive more attention, and employees should minimize the time they spend in the hydrothermal hydrolysis unit.

Profiling and characterization of odorous volatile compounds from the industrial fermentation of erythromycin

Complaints caused by odors from the fermentation production of pharmaceuticals are common in China. The elimination of odor remains a challenge for the pharmaceutical industry to meet the increasingly strict environment regulations. Erythromycin is a representative antibiotic produced by microbial fermentation. The fermentation exhaust gas of erythromycin fermentation has an unpleasant odor, but the composition of the key odorants has not been identified. The major odorants from the fermentation production of erythromycin API were analyzed by electronic nose, olfactory measurements, gas chromatography-coupled ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS) analysis. Two compounds, 2-methylisoborneol (2-MIB) and geosmin, were identified as the major odorants of erythromycin fermentation. These had not been detected before using only GC-MS analysis of exhaust gas. Aldehydes, including hexanal, octanal, decanal, and benzaldehyde, also contribute to the odor. The composition analysis of odorants using the fermentation broth headspace was more efficient and reliable, considering the significant dilution effect of exhaust gas. The concentration of 2-MIB and geosmin in the fermentation broth greatly exceeded their odor thresholds. The production of major odorants started in the early fermentation stage and became significant in the middle stage (30-70 h). Due to the extremely low odor thresholds of 2-MIB and geosmin, advanced purification may require deodorization of erythromycin fermentation exhaust gas.

Filling in sewage sludge biodrying gaps: Greenhouse gases, volatile organic compounds and odour emissions

In the present work, a complete study of the sewage sludge (SS) biodrying technology was conducted at bench-scale, aiming at assessing its performance and providing a valuable insight into the different gaseous emission patterns found for greenhouse gases (GHG) and odorant pollutants. As process key parameters, temperature, specific airflow, dynamic respiration index, final moisture content and Lower Calorific Value (LCV) were evaluated. At the end of the biodrying, a product with a 35.9% moisture content and a LCV of 7.1 MJ·kg^-1product was obtained. GHGs emission factor was 28.22 kgCO_2eq per Mg of initial mass of dry matter in the SS (DM₀-SS). During the biodrying process, maximum odour concentration measured was 3043 ou·m^-3 and the estimated odour emission factor of the biological treatment was 3.10E + 07 ou per Mg DM₀-SS. Finally, VOCs were completely identified and quantified. The most abundant VOCs found in the biodrying gaseous emissions were terpenes, sulphur-compounds and ketones.

Volatile sulfide compounds (VSCs) and ammonia emission characteristics and odor contribution in the process of municipal sludge composting

Malodor is becoming the main secondary pollution in the municipal sewage sludge-composting process. Ammonia and volatile sulfide compounds (VSCs) are the representative odorants that generated and emitted during the composting process. The emission characteristics of ammonia and VSCs were studied at different workshops in a full-scale municipal sludge-composting plant in North People's Republic of China. Results show that ammonia was the most dominant odorant of all the workshops and relative high concentrations of VSCs were detected at sludge stacking yard and composting workshop. The odor pattern of VSCs at the composting workshop and stacking yard were different. The odor pollution occurred mainly in the first 15 days of the composting process, in which the odor contribution of ammonia increased with time and the VSCs contributed largely in the first 5 days. The cumulative release concentration of VSCs from compost materials was in the order of DMDS (dimethyl disulfide) > DMS (dimethyl sulfide) > CS2 > MT (methyl mercaptan), and the total VSCs release concentration was in the range of 50-3200 μg·m^-3. The production of ammonia correlated to the temperature and nitrogen content and state changes, however, the production of VSCs was more complicated due to the reaction and transformation of VSCs. Optimization of aerobic composting conditions and process parameters should be further studied to reduce the emission of odor gas from compost. Implications: Along with the widespread use of sludge aerobic composting in People's Republic of China, the malodor pollution during the composting treatment is becoming a serious environmental issue. The odor pollution occurred mainly in the first 15 days, and ammonia was the main odorant of all the workshops and need to be controlled. Relative high concentrations of VSCs were detected at sludge stacking yard and composting workshop, however, the odor impact of VSCs were different. The generation of VSCs is more complicated than ammonia due to the reaction and transformation of VSCs.

Odor generation patterns during different operational composting stages of anaerobically digested sewage sludge

This study aimed to evaluate the global patterns of odor generation and odorant composition for different operational stages of anaerobically digested sewage sludge (ADS) composting at pilot scale. To this end, gas emissions were sampled and analyzed during storage, forced aeration treatment (active phase), turning process and curing. For each operational stage, odors were monitored by measuring the odor emission rates (OER in OU_E h^-1 kg^-1ADS) through dynamic olfactometry and computing the odor activity values (OAVs) of compounds quantified by analytical methods (i.e., GC/MS). Ammonia and volatile sulfur compounds (VSCs) were the most abundant air pollutants, representing 55.5% and 20.6% of the cumulative mass emitted, respectively. The first eight days of aerobic treatment and the first turning of the compostable mixture were the critical steps for odor generation with OER ranging from 30 to 317 OU_E h^-1 kg^-1ADS. Particularly, the first turning process was responsible for strong odor episodes that were emitted in a short process time (295 OU_E h^-1 kg^-1ADS). Based on the OAVs approach, dimethyl disulfide, dimethyl sulfide, and methanethiol were the predominant odorants along these early operational stages. Odor potential and composition shifted for the middle and later active phase, second turning, and curing stage where OER fluctuated from 0.18 to 12.6 OU_E h^-1 kg^-1ADS, and hydrogen sulfide showed the most substantial odor contribution. A principal component analysis explaining 77% of the variability in odor concentration and OAVs datasets eased the recognition of these odor patterns.

A systematic study on the VOCs characterization and odour emissions in a full-scale sewage sludge composting plant

Sewage sludge management is known to cause odour impact over the environment. However, an information gap exists about odour emissions quantification from different treatment strategies. In the present work, odorous emissions generated in a full-scale sewage sludge composting plant were characterized, aiming at providing specific odour emission factors (OEF) and to determine their variability depending on the composting time. Additionally, characterization of VOCs emitted during the process was conducted through TD-GC/MS analyses. Odour emission and VOCs characterization considered both (1) a first stage where a raw sludge and vegetal fraction mixture were actively composted in dynamic windrows and (2) a second curing stage in static piles. After increasing the composting time, a reduction of 40% of the maximum odour concentration referred to the dynamic windrow stage was estimated, whereas a reduction of 89% of the maximum odour concentration was achieved after turning of curing piles. However, global OEF increased from 4.42E + 06 to 5.97E + 06 ou·Mg^-1 RS - VF when the composting time increased. Finally, different VOCs such as isovaleraldehyde, indole, skatole, butyric acid, dimethyl sulphide and dimethyl disulphide were identified as main potential odour contributors. Results obtained are a valuable resource for plant management to choose an appropriate sewage sludge composting strategy to mitigate odour emissions.

Chemical and odor characterization of gas emissions released during composting of solid wastes and digestates

Hazardous and odorous gas emissions from composting and methanization plants are an issue of public concern. Odor and chemical monitoring are thus critical steps in providing suitable strategies for air pollution control at waste treatment units. In this study, 141 gas samples were extensively analyzed to characterize the odor and chemical emissions released upon the aerobic treatment of 10 raw substrates and five digestates. For this purpose, agricultural wastes, biowastes, green wastes, sewage sludge, and municipal solid waste (MSW) were composted in 300 L pilots under forced aeration. Gas exhausts were evaluated through dynamic olfactometry and analytical methods (i.e., GC/MS) to determine their odor concentration (OC in OU_E m^-3) and chemical composition. A total of 60 chemical compounds belonging to 9 chemical families were identified and quantified. Terpenes, oxygenated compounds, and ammonia exhibited the largest cumulative mass emission. Odor emission rates (OU_E h^-1) were computed based on OC measurements and related to the initial amount of organic matter composted and the process time to provide odor emission factors (OEFs in OU_E g^-1OM₀). The composting process of solid wastes accounted for OEFs ranging from 65 to 3089 OU_E g^-1OM₀, whereas digestates composting showed a lower odor emission potential with OEF fluctuating from 8.6 to 30.5 OU_E g^-1OM₀. Moreover, chemical concentrations of single compounds were weighted with their corresponding odor detection thresholds (ODTs) to yield odor activities values (OAVs) and odor contribution (PO_i, %). Volatile sulfur compounds were the main odorants (PO_i = 54-99%) regardless of the operational composting conditions or substrate treated. Notably, methanethiol was the leading odorant for 73% of the composting experiments.

Effects of ambient temperature and aeration frequency on emissions of ammonia and greenhouse gases from a sewage sludge aerobic composting plant

This study analyzed emissions characteristics of NH₃ and greenhouse gases (i.e. N₂O, CH₄, and CO₂) from a municipal sewage sludge aerobic composting plant. Samples were collected during different seasons in which ambient temperatures and aeration frequencies varied. Results revealed (1) the maximum gas emissions occurred during the mesophilic phase for N₂O (22%-56%) and CH₄ (65%-95%), and in the thermophilic phase for NH₃ (84%-86%) and CO₂ (65%-74%); (2) raising ambient temperatures promoted emissions of NH₃ and greenhouse gases, while improved aeration frequency increased NH₃ but decreased greenhouse gas emissions; (3) CO₂ and N₂O were found to be the key greenhouse gases emitted during aerobic composting according to assessment of the CO₂ equivalent. The results obtained from this study suggest that adjusting ambient temperature to -3 to 5 °C and aeration frequency in composting workshops can be useful approaches for the reduction of NH₃ and greenhouse gas emissions from municipal sewage sludge composting plants.

Relationships between emitted volatile organic compounds and their concentration in the pile during municipal solid waste composting

Composting operations taking place at municipal solid waste (MSW) treatment plants represent a source of volatile organic compounds (VOC) to the atmosphere. Understanding the variables governing the release of VOC at these facilities is crucial to assess potential health risks for site workers and local residents. In this work the changes in the VOC composition of a composting pile were monitored and compared to the VOC emmited from the same pile in order to understand the impact of composting operations on the release of VOC. More than one hundred VOC were indentified in the solid phase of the composting piles, which were dominated by terpenes (about 50% of the total amount of VOC) and in a lower quantity alcohols, volatile fatty acids and aromatic compounds. There was a reduction in the total concentration of VOC in the pile during composting, from 45 to 35 mg/kg, but the compostion and distribution of VOC families remained stable in the pile even in the mature compost. However, there was no correlation between the emitted VOC and their concentration in the composting pile. The VOC emission pattern was affected by the biological activity in the pile (measured by temperature, CO₂ evolution and the presence of CH₄ emissions). The highest VOC emissions were detected at early stages of the process, alongside with the generation of CH₄ in the pile, and then decreased sharply in the mature compost as a consequence of biodegradation and volatilisation. These results pointed to the importance of composting operation rather than the composition of the raw materials on the release of VOC in composting plants.

Emission characteristics of volatile sulfur compounds (VSCs) from a municipal sewage sludge aerobic composting plant

The emission of volatile sulfur compounds (VSCs) causing strong odors is a major problem in municipal sewage sludge composting plants (MSSACPs). Improving the knowledge on characteristics of VSCs emission in MSAACPs is of particular significance to elimate odors, but the studies conducted on-site to identify them are scarce. To this purpose, characteristics of VSCs emission were studied on-site from a MSSACP during different ambient temperatures corresponding with seasonal variations. Results reveal that (1) the total emission of VSCs which included methyl disulfide (DMDS), methyl sulfide (DMS), carbon disulfide, methyl mercaptan, and hydrogen sulfide (H₂S) was 561.89 mg/dry kg in summer, 358.45 mg/dry kg in spring, and 215.52 mg/dry kg in winter, and the greatest amounts of VSCs were emitted during the mesophilic and pre-thermophilic phases; (2) although DMDS and DMS contributed the most towards total VSCs emissions during winter (81.93%), spring (82.55%), and summer (83.90%), their odor contributions were less than that of H₂S; (3) in summer, the odor nuisance of total VSCs was higher than that in winter and spring; (4) sulfur loss in the form of VSCs emissions and total sulfur loss both increased with rising ambient temperatures during the sewage sludge aerobic composting. Results obtained in this study will be beneficial towards the elimation of odors released from MSSACPs.

Different Ways to Apply a Measurement Instrument of E-Nose Type to Evaluate Ambient Air Quality with Respect to Odour Nuisance in a Vicinity of Municipal Processing Plants

This review paper presents different ways to apply a measurement instrument of e-nose type to evaluate ambient air with respect to detection of the odorants characterized by unpleasant odour in a vicinity of municipal processing plants. An emphasis was put on the following applications of the electronic nose instruments: monitoring networks, remote controlled robots and drones as well as portable devices. Moreover, this paper presents commercially available sensors utilized in the electronic noses and characterized by the limit of quantification below 1 ppm v/v, which is close to the odour threshold of some odorants. Additionally, information about bioelectronic noses being a possible alternative to electronic noses and their principle of operation and application potential in the field of air evaluation with respect to detection of the odorants characterized by unpleasant odour was provided.