Odours and volatile organic compounds emitted from municipal solid waste at different stage of decomposition and relationship with biological stability

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.

Species profile and reactivity of volatile organic compounds emission in solvent uses, industry activities and from vehicular tunnels

A survey was conducted of the volatile organic compounds (VOCs) released from sources of solvent use, industry activities and vehicle emissions in Guiyang, a capital city of China. Samples were collected by canisters and analyzed by GC-MS-FID. The species profiles of VOCs emitted from sources were obtained. Results showed that xylenes, ethylbenzene, acetone and dichloromethane were the characteristics species for painting, 2-propanol and ethyl acetate for printing, α-pinene for solid wood furniture manufacturing, and 2-butanone for biscuit baking. These characteristics species could be as tracers for the sources respectively. In most of samples from the solvent use, the benzene/toluene (B/T) ratio was less than 0.3, indicating that the ratio could be as the indicator for tracing the solvent use related sources. The results also suggested that the toluene/xylene (T/X) ratio be as the indicator to distinguish the VOCs sources of painting (<2) from the printing (>2). Aromatics contributed the most to ozone formation potential (OFP) of most painting and non-paper printing sources, and oxygen-containing VOCs (OVOCs) were major species contributing to OFP of the sources from food production and paper printing. The OFP of the VOCs emissions from vehicle in tunnels and from other manufactures were dominated by both aromatics and alkenes. The α-pinene could explain 56.94% and 32.54% of total OFP of the VOCs sources from filing cabinet and solid wood furniture manufacturing, which was rarely been involved in previous studies of VOCs source profiles, indicating that the species of concern for VOCs sources are still insufficient at present.

Application of Composts' Biochar as Potential Sorbent to Reduce VOCs Emission during Kitchen Waste Storage

It is expected that due to the new European Union regulation focus on waste management, managing kitchen waste will become more important in the future, especially in households. Therefore, it is crucial to develop user-friendly and odour-free containers to store kitchen waste. The study aimed to test the effectiveness of composts' biochar in reducing noxious odours and volatile organic compounds (VOCs) released during kitchen waste storage. Various amounts of compost biochar (0%, 1%, 5%, and 10%) were added to food waste samples and incubated for seven days at 20 °C. The released VOCs were analysed on days 1, 3, and 7 of the storage simulation process. The results indicated that adding 5-10% of composts' biochar to kitchen waste significantly reduced the emissions in 70% of the detected VOCs compounds. Furthermore, composts' biochar can be used to eliminate potential odour components and specific dangerous VOCs such as ethylbenzene, o-xylene, acetic acid, and naphthalene. A new composts' biochar with a unique composition was particularly effective in reducing VOCs and could be an excellent solution for eliminating odours in kitchen waste containers.

Anthropogenic emission inventory and spatial analysis of greenhouse gases and primary pollutants for the Galapagos Islands

Climate change and air pollution are critical challenges that humanity is currently facing. Understanding the sources of emissions released into the atmosphere is of great importance to evaluate the local footprint, the impacts of human activities, and the opportunities to develop and implement solutions to mitigate emissions and adapt to climate change particularly in vulnerable places like the Galapagos Islands. In this study, we present an anthropogenic emissions inventory for Santa Cruz, San Cristobal, and Isabela Islands in which emissions were spatially mapped for greenhouse gasses (GHGs) and primary pollutants (PP). Emissions were estimated for the energy stationary sources, energy mobile sources, waste, and other sectors, and emissions for 2019 were spatially distributed along with an uncertainty assessment. Results demonstrated that energy mobile sources which are aerial, terrestrial, and maritime transportation generated the most significant emissions in the Galapagos Islands in terms of PP and GHGs. In fact, maritime transportation was the highest one in 2019, at 41% of total CO₂ emissions for Galapagos, with the most predominant PP being NOx and CO. The aerial transportation made up 36% of emissions, and the electricity generation contributed 15%. Emissions from waste and other sectors comprise a smaller percentage relative to the rest of the emission sectors. These results highlight the strong dependency of the islands on fossil fuels for transportation and electricity generation. Alternatives to mitigate and reduce emissions from the islands are discussed. This spatially mapped emissions inventory for the Galapagos Islands represents a powerful tool to make informed decisions to contribute to the long-term sustainability of the archipelago.

Characterization of methanotrophic community and activity in landfill cover soils under dimethyl sulfide stress

Landfill cover soil is the environmental interface between landfills and the atmosphere and plays an important role in mitigating CH₄ emission from landfills. Here, stable isotope probing microcosms with CH₄ or CH₄ and dimethyl sulfide (DMS) were carried out to characterize activity and community structure of methanotrophs in landfill cover soils under DMS stress. The CH₄ oxidation activity in the landfill cover soils was not obviously influenced at the DMS concentration of 0.05%, while it was inhibited at the DMS concentrations of 0.1% and 0.2%. DMS-S was mainly oxidized to sulfate (SO₄^2-) in the landfill cover soils. In the landfill cover soils, DMS could inhibit the expression of bacteria and decrease the abundances of pmoA and mmoX genes, while it could prompt the expression of pmoA and mmoX genes. γ-Proteobacteria methanotrophs including Methylocaldum, Methylobacter, Crenothrix and unclassified Methylococcaceae and α-Proteobacteria methanotrophs Methylocystis dominated in assimilating CH₄ in the landfill cover soils. Of them, Methylobacter and Crenothrix had strong tolerance to DMS or DMS could promote the growth and activity of Methylobacter and Crenothrix, while Methylocaldum had weak tolerance to DMS and showed an inhibitory effect. Metagenomic analyses showed that methanotrophs had the genes of methanethiol oxidation and could metabolize CH₄ and methanethiol simultaneously in the landfill cover soils. These findings suggested that methanotrophs might metabolize sulfur compounds in the landfill cover soils, which may provide the potential application in engineering for co-removal of CH₄ and sulfur compounds.

Occupational health risks of VOCs emitted from the working face of municipal solid waste landfill: Temporal variation and influencing factors

Volatile organic compounds (VOCs) emission on the working face of a large sanitary landfill in northern China was characterized in a one-year long sampling campaign. A total of 67 VOCs with average annual concentration of 2903.01 μg/m³ were detected. Ethanol was the dominant species of detected VOCs, accounting for 76.4-82.3% of the total volatile organic compounds (TVOCs) concentration. VOCs emission showed seasonal variation as the highest concentration was detected in summer and lowest appeared in winter. Furthermore, 50 VOCs identified were non-carcinogenic chemicals and 21 of them were carcinogenic chemicals. Risk assessment showed that the average total non-carcinogenic risk value (HI_T) was 4.95, which far exceeded the threshold value of 1; and the average total carcinogenic risk value (Risk_T) was 8.45 × 10^-5, close to the limit of 1 × 10^-4. That means both the non-carcinogenic and carcinogenic risks of long-term exposure to these VOCs could not be ignored. Some of the oxygenated compounds (Acrolein, Ethyl acetate, etc.), halocarbons (1,1,2-Trichloroethane, 1,2-Dichloropropane, etc.) and aromatic compounds (Naphthalene, m + p-Xylene, etc.) consisted the main contributors to non-carcinogenic risks. Meanwhile, carcinogenic risks were mainly caused by halocarbons (cis-1,2-Dichloroethylene, FREON11, etc.) and aromatic compounds (Benzene, Ethylbenzene, etc.). In addition, statistical analysis revealed that the HI_T values were related to the concentrations of risk aromatic compounds, halocarbons and hydrocarbons; Risk_T values were only related to the concentrations of risk aromatic compounds and halocarbons. The research results provide an important theoretical basis for occupational risk management and VOCs emission prevention in landfills.

Odor emission rate of a municipal solid waste sanitary landfill during different operation stages before final closure

This study investigated the odor emission rate from different areas of a municipal solid waste landfill. The surface odor emission rate (SOER) of eight odorous compound groups were determined by flux chamber method. The SOER of working face, seams of daily cover, membrane surface of daily cover, seams of temporary cover, membrane surface of temporary cover, seams of intermediate cover, membrane surface of intermediate cover were 138.34, 49.83, 13.56, 90.35, 14.48, 4.05, and 8.14 μg/(m²·s), respectively. Therefore, odor emission hotspots were at seams of daily and temporary cover areas. Converting the odor emissions at emission hotspots to the entire membrane cover surface, the average SOER of working face, daily cover area, temporary cover area and intermediate cover area were 138.34, 17.95, 22.43, and 6.24 μg/(m²·s), respectively. Combined with the size of each landfill area, the total odor emissions of the four above areas of a landfill zone were 830, 108, 1346, and 5175 mg/s, respectively, suggesting the necessity to control the odor emission of membrane cover stages especially for large-scale landfills. In terms of odor components, alcohols (38.7 %), sulfur compounds (22.9 %) and aldehydes (15.7 %) were major odorous groups.

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.

Emission behavior and impact assessment of gaseous volatile compounds in two typical rural domestic waste landfills

Landfill sites are sources of gaseous volatile compounds. The dumping area (LDA) and leachate storage pool (LSP) of two typical rural domestic waste landfill sites in north China (NLF) and southwest China (SLF) were investigated. We found that 45, 46, 61 and 68 volatile organic compounds (VOC) were present in the air of NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. And there were 27, 29, 35 and 37 kinds of odorous compounds being detected. Oxygenated compounds (>48.88%), chlorinated compounds (>6.85%), and aromatics (>5.46%), such as organic acid, 1-chlorobutane, and benzene, were the most abundant compounds in both landfills. The SLF-LDA had the highest olfactory effect, with a corresponding total odor activity value of 29,635.39. The ozone-formation potential analysis showed that VOCs emitted from SLF landfills had significantly higher potential for ozone formation than those from NLF landfills, with ozone generation potentials of 166.02, 225.86, 2511.82, and 1615.99 mg/m³ for the NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. Higher chronic toxicity and cancer risk of VOCs were found in the SLF according to method of Risk Assessment Information System. Based on the sensitivity analysis by the Monte Carlo method, concentrations of benzene, propylene oxide, propylene, trichloroethylene, and N-nitrosodiethylamine, along with exposure duration, daily exposure time, and annual exposure frequency, significantly impacted the risk levels. We provide a scientific basis, which reflects the need for controlling and reducing gaseous pollutants from landfills, particularly rural residential landfills, which may improve rural sanitation.

Characteristics of leachate from refuse transfer stations in rural China

The properties of leachate from refuse transfer stations (RTSs) in rural China were indefinite. In this study, a total of 14 leachate samples from RTSs in nine provinces of China were characterized for their pH, electric conductivity, chromaticity, concentration of organic substances, nitrogen distribution, volatile organic compounds (VOCs), organic phosphorous pesticide, and heavy metals. The structural composition of fluorescent dissolved organic matter (FDOM) was also determined. To evaluate the leachate pollution potential in this study, a leachate pollution index was derived and used. Chromium (Cr) was the most polluting heavy metal present in rural leachate. Ethanol and ethyl acetate were the most frequently detected VOCs at high concentrations. Three-dimensional fluorescence excitation-emission matrix spectra were used to characterize the FDOM. Three components, tryptophan (C₁), tyrosine-like (C₂), and humic acid- and fulvic acid-like (C₃) substances, were identified from all 14 samples. Tryptophan was the major component of FDOM and present in 45.7% of the samples by calculating the fluorescence intensity percentage, on average. Pearson correlations revealed that the fluorescence intensity of C₁ and C₃ was strongly related to soluble chemical oxygen demand and dissolved oxygen carbon, while C₂ had significant positive correlations with ammonia nitrogen and total phosphorus of the solid waste. This study provided detailed data and findings that could serve as a preliminary basis for broadening options for the treatment and management of leachate from rural RTSs in China.

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.

Odor emissions: A public health concern for health risk perception

The olfactory nuisance, due to the emissions of active molecules, is mainly associated with unproperly managed waste disposal and animal farming. Volatile compounds e.g., aromatics, organic and inorganic sulfide compounds, as well as nitrogen and halogenated compounds are the major contributor to odor pollution generated by waste management plants; the most important source of atmospheric ammonia is produced by livestock farming. Although an odorous compound may represent a nuisance rather than a health risk, long-term exposure to a mixture of volatile compounds may represent a risk for different diseases, including asthma, atopic dermatitis, and neurologic damage. Workers and communities living close to odor-producing facilities result directly exposed to irritant air pollutants through inhalation and for this reason the cumulative health risk assessment is recommended. Health effects are related to the concentration and exposure duration to the odorants, as well as to their irritant potency and/or biotransformation in hazardous metabolites. The health effects of a single chemical are well known, while the interactions between molecules with different functional groups have still to be extensively studied. Odor emissions are often due to airborne pollutants at levels below the established toxicity thresholds. The relationship between odor and toxicity does not always occurs but depends on the specific kind of pollutant involved. Indeed, some toxic agents does not induce odor nuisance while untoxic agents do. Accordingly, the relationship between toxicity and odor nuisance should be always analyzed in detail evaluating on the characteristics of the airborne mixture and the type of the source involved.

Health risks of odorous compounds during the whole process of municipal solid waste collection and treatment in China

The high moisture content and perishable organic waste of municipal solid waste (MSW) in China have caused the severe odor nuisance to be one of the crucial reasons for resident complaints. Understanding the environmental risks of odorous compounds lays the foundations for resolving the problems. This study collected concentration data of 86 odorous compounds in five types of MSW processing facilities/equipment which can well represent the whole process of MSW stream, including waste bins and transfer stations for collection, compost plants and anaerobic digestion plants for utilization, and landfills for final disposal. The results revealed that the occupational health risks of odorants were not fully consistent with the compound concentrations and olfactory annoyance. Higher odorous compound concentrations and more severe olfactory annoyance can be found in the MSW utilization and disposal facilities, but the occupational carcinogenic risk (2.79 × 10^-5-1.12 × 10^-3) was non-negligible along the whole MSW stream. Aromatic hydrocarbons and halogenated hydrocarbons were crucial contributors to the carcinogenic risk of odorous compounds emission from these facilities. Particularly for estimating the adverse impact range of MSW facilities, the carcinogenic risk was the most critical factor, implying impact distance of ∼1.5 km for MSW transfer station and ∼5 km for landfill, and even higher for the regions (such as southwest China) with lower wind speed and higher atmospheric stability. In addition to current regulations, another 5 compounds (acetaldehyde, 1,3,5-trimethylbenzene, 1,2-dichloroethane, acrolein, and benzyl chloride) that displayed high carcinogenic risks were suggested to be concerned. This study provided insights for the policymakers regarding MSW odors management, especially underscoring the importance of considering the health risks of odorous compounds.

Reduction in VOC emissions by intermittent aeration in bioreactor landfills with gas-water joint regulation

Landfill mining and reclamation is a new strategy for addressing the lack of space available for new landfills and realizing the sustainable development of landfills. A gas-water joint bioreactor landfill is regulated by injecting water and/or recirculating leachate, and a blasting aeration system to optimize waste stabilization. In this study, four landfill reactors were constructed to investigate the effects of ventilation methods, including continuous (20 h d^-1) and intermittent aeration (4 h d^-1 in continuous or 2-h aeration per 12 h, twice a day), on the degradation of organic matter and volatile organic compound (VOC) emissions in comparison with traditional landfills. A total of 62 VOCs were detected in the landfill reactors. Among them, halogenated compounds had the highest abundance (39.8-65.4 %), followed by oxygenated compounds, alkanes and alkenes, and aromatic compounds. Both intermittent and continuous aeration could accelerate the degradation of landfilled waste and increase the volatilization rate of VOCs. Compared with intermittent aeration, the degradation of landfilled waste was more quickly in the landfill reactor with continuous aeration. However, intermittent aeration could create anaerobic-anoxic-aerobic conditions, which were conducive to the growth and metabolism of anaerobic and aerobic microorganisms in landfills and thereby reduced more than 63.4 % of total VOC emissions from the landfill reactor with continuous aeration. Moreover, intermittent aeration could reduce the ventilation rate and decrease the cost of aeration by 80 % relative to continuous aeration. Firmicutes, Bacteroidetes, Proteobacteria and Tenericutes predominated in the landfill reactors. The environmental variables including organic matter and VOCs concentrations had significant influences on microbial community structure in the landfilled waste. These findings indicated that intermittent aeration was an effective way to accelerate the stabilization of landfilled waste and reduce the cost and environmental risks in bioreactor landfills with gas-water joint regulation.

Research trend analysis of composting based on Web of Science database

Bibliometric analysis was used in this study for the quantitative evaluation of current research trends on composting. The research articles indexed from the Science Citation Index-Expanded in Web of Science database published from 2000 to 2019 were investigated. The USA, China and Spain were the top three countries considering the number of papers. Amongst the research institutes, CSIC of Spain, Chinese Academy of Sciences and Agriculture & Agri-Food Canada ranked the top three in total publication amount. Journals that published a significant number of literature regarding topics of composting included Environmental Sciences & Ecology, Agriculture and Engineering. In terms of research content, keywords such as heavy metal, heavy metal and biodegradation appeared frequently. In addition, the analysis of keywords revealed the following research hotspots in future studies: investigation of heavy metal passivator, optimisation of composting conditioner, development of all kinds of microorganisms, rational management of the composting process and improvement of solid waste life cycle assessment. To some extent, it helps to understand the current global status and trends of the related research.

Evaluation of Occupational Exposure Risk for Employees Working in Dynamic Olfactometry: Focus On Non-Carcinogenic Effects Correlated with Exposure to Landfill Emissions

This work aims to evaluate the non-carcinogenic health effects related to landfill odor emissions, therefore focusing on workers involved in dynamic olfactometry. Currently, the most common technique to quantify odor emissions is dynamic olfactometry, a sensorial analysis involving human assessors. During the analysis, assessors are directly exposed, at increasing concentrations, to odor samples, and thus to the hazardous pollutants contained therein. This entails the need to estimate the associated exposure risk to guarantee examiners’ safety. Therefore, this paper evaluates the exposure risk for olfactometric examiners to establish the minimum dilution level to be adopted during the analysis of landfills’ odorous samples to guarantee panelists’ safety. For this purpose, an extensive literature review regarding the pollutants emitted by landfill odor sources was conducted, comparing compounds’ chemical concentrations and threshold limit values (TLVs) to calculate the Hazard Index (HI) and thus establish a minimum dilution value. The data collected indicate that a non-negligible non-carcinogenic risk exists for all landfill emissions considered. However, from the data considered, the minimum dilution factor to be adopted is lower than the typical odor concentration observed for these sources. Therefore, the olfactometric analysis of landfill samples can be generally conducted in safe conditions.

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.

Composition and profiles of volatile organic compounds during waste decomposition by the anaerobic bacteria purified from landfill

Volatile organic compounds (VOCs) become concerned pollutants in landfill gases, and their composition and concentration varied significantly during waste decomposition. Many environmental factors are known to affect VOC emissions, while the effect of indigenous bacteria in wastes on VOC production remains elusive. In this study, a simplified anaerobic degradation experiment, with the single substrate and the purified bacteria from a landfill, was set up to measure the degradation process and the dynamic changes of VOCs. The experiment excluded the abiotic factors for VOC variation. The two isolated bacteria, identified as Sporanaerobacter acetigenes and Clostridium sporogenes, could anaerobically ferment amino acids by Stickland reaction. They produced 51 and 57 species of VOCs in the experiment, respectively. The concentration changes of VOCs over bacterial growth and fermentation were clustered into four types by principal component analysis: three profiles were regular, similar to the variation of nitrate, hydrogen sulfide, and the major fermentation products (carbon dioxide, ammonium, and volatile organic acids), respectively; while one profile was unique to any degradation indicator. The various concentration profiles indicated different origins for VOCs, possibly from the extracellular environment, fermentation, and secondary reactions. The findings provide insights into the understanding of VOC diversity and variability during waste decomposition.

Reducing odor emissions from feces aerobic composting: additives

Aerobic composting is a reliable technology for treating human and animal feces, and converting them into resources. Odor emissions in compost (mainly NH₃ and VSCs) not only cause serious environmental problems, but also cause element loss and reduce compost quality. This review introduces recent progresses on odor mitigation in feces composting. The mechanism of odor generation, and the path of element transfer and transformation are clarified. Several strategies, mainly additives for reducing odors proven effective in the literature are proposed. The characteristics of these methods are compared, and their respective limitations are analyzed. The mechanism and characteristics of different additives are different, and the composting plant needs to be chosen according to the actual situation. The application of adsorbent and biological additives has a broad prospect in feces composting, but the existing research is not enough. In the end, some future research topics are highlighted, and further research is needed to improve odor mitigation and element retention in feces compost.

Aerobic composting is a reliable technology for treating human and animal feces, and converting them into resources. The addition of additives can reduce the production of odor during the composting process.

Evaluation of Inoculated Waste Biological Stabilization Degree by Olfactometric Methods

As a result of compounds’ transformation in the waste biostabilization phases, there is an increase in odor nuisance and health problems among people exposed to odorants. Linking the odor concentration to the degree of waste biostabilization may be an important tool for the assessment of individual technological variants of biostabilization. The study aimed to link the odor emissions to the biostabilization degree in individual process variants that differed in the inoculum. The tests were carried out on inoculated windrows on the waste mechanical-bological treatment open site. Odor concentrations were measured during the entire seven-week process of biostabilization (weeks 1–7) and compared with kinetics parameters of organic compounds’ decomposition. The olfactometric tests showed the necessity of using the preparation to reduce the value of odor concentration. Research proved that the decrease of odor concentration values could be useful to indicate the particular phases of biostabilization. Also, the proposed method provides an opportunity to optimize the process concerning the function related to the low degree of odor nuisance of the technologies, including selection of environmentally safe inoculum. This issue has application values that may result in the implementation of new control systems for waste stabilization bioreactors and the evaluation of applied technological solutions.

Impact of storage duration and micro-aerobic conditions on lactic acid production from food waste

Food waste (FW) is an abundant resource with great potential for lactic acid (LA) production. In the present study, the effect of storage time on FW characteristics and its potential for LA production was investigated. The largest part of sugars was consumed during 7 to 15 days of FW storage and the sugar consumption reached 68.0% after 15 days. To enhance the LA production, micro-aerobic conditions (13 mL air/g VS) and addition of β-glucosidase were applied to improve polysaccharides hydrolysis, resulting to increase of monosaccharides content to 76.6%. Regarding fermentative LA production, the highest LA titer and yield of hydrolyzed FW was 32.1 ± 0.5 g/L and 0.76 ± 0.01 g/g_-sugar, respectively. Furthermore, L-LA isomer was higher than 70% when FW was stored for up to 7 days. However, attention should be paid on controlling the FW storage to approximately one week.

VOCs released from municipal solid waste at the initial decomposition stage: Emission characteristics and an odor impact assessment

The nuisance from odor caused by municipal solid waste (MSW) is resulting in a growing number of public complaints and concerns. Odor pollution occurs in the initial decomposition stage of MSW, including waste collection, transportation and early pre-treatment. Furthermore, decomposition takes place in waste facilities that are often close to living areas, which can result in odor impacts on local inhabitants. However, this aspect of odor impact from MSW has not been well studied. In the current study, lab-scale waste cells were designed to simulate MSW storage conditions in the early stage. The characteristics of VOCs emissions with different waste compositions were analyzed. The odor concentration (C_O, non-dimensional) method and odor intensity were used for the assessment of odor. Ethanol was the substance with highest emission rate. The release rate of VOCs increased with the growth easily biodegradable waste (EBW). VOCs emissions was reduced by 25% when the proportion of EBW decreased from 60% to 45%. Methyl sulfide, ethanol, dimethyl disulfide and ethyl acetate were identified as typical odorants. The EBW proportion in waste is the main factor significantly influencing odor pollution. The C_O was 244.51 for the 60% EBW condition, which was only 61.46 for 15% EBW condition. These study results provide important information for the implementation of a garbage sorting policy and the monitoring of odor pollution from waste management.

Assessing transfer distances and separation areas of odorous compounds from probability analysis with numerical dispersion modeling

Odor pollution caused by volatile compounds from waste-treatment facilities is a typical nuisance, and assessing its potential impacts is crucial. Challenges in odor-dispersion simulation and impact assessment are attributed to the occasional and fluctuant emissions of odorous compounds and varying meteorological conditions for dispersion. This study established an approach to assessing the transfer distances and determining the separation areas of odor pollution by combining probability analysis and numerical dispersion simulation. With a waste transfer station as a case, we analyzed odorous compounds from 96 samples and performed 2190 simulation rounds with different meteorological parameters throughout an entire year by using a specialized model (ModOdor). Ethanol, dimethyl disulfide, and dimethyl sulfide were identified as typical odorous compounds in terms of source intensity and detection frequency. The concentration distribution, probability of transfer distances in terms of month and year, and separation area determination from cumulative probability were investigated. Under most studied conditions, the compound concentrations rapidly decreased after being released. From the year-round perspective, an ethanol concentration exceeding 1 μg/m³ was in approximately 80% probability limited in the area with a radius of 200 m. With a cutoff of 95% probability, the closest transfer distances towards all orientations can circle the odor separation area. The compound concentrations in the separation area had a probability higher than 5% throughout the year to exceed the assigned reference concentrations. The approach and demonstration can solve the mutability problem of odor pollution from a probability perspective and thus potentially improve odor pollution control in waste management.

Effect of biochemical composition on odor emission potential of biowaste during aerobic biodegradation

This study aimed to identify the individual effect of biochemical composition on odor emission potential of biowaste during aerobic biodegradation. Three kinds of typical mixed wastes, including vegetable-fruit waste, garden waste, and protein-rich waste, were tested for emission quantity of seven common odorous families within 21 days of biodegradation under aerobic conditions. The cumulative odor yields (COY) were as follows: protein-rich waste (2408 μg g^-1 DM) > vegetable-fruit waste (1169 μg g^-1 DM) > garden waste (62 μg g^-1 DM), and their cumulative odor intensity were 16,701, 1888, and 212 g^-1 DM, respectively. The odor emission of vegetable-fruit waste mainly occurred in the first 3 days, accounting for 91.7% COY, and the predominant contributor to odor intensity (PCOI) were terpenes and sulfur compounds. With regard to garden waste, the odor emission rate was the highest on day 1 (22.4 μg g^-1 DM d^-1) and then rapidly decreased, and the PCOI were aldehydes. The odor emission rate of protein-rich waste increased gradually in the initial stage and reached the peak value on day 10 (661.9 μg g^-1 DM d^-1), and its PCOI were sulfur compounds. This study revealed for the first time the relationship between the odor emission potential of biowaste and its characteristic of biochemical composition, then proposed potential application for odor pollution control during aerobic composting.

Malodorous gases production from food wastes decomposition by indigenous microorganisms

Volatile organic compounds (VOCs) produced during the degradation of food wastes may harm to the health of people and create annoyance in adjacent communities. In this work, the VOCs emitted from the decomposition food wastes including fruit, meat and vegetable, and their microbial communities were measured in three individual 57-L reactors for 61 days. Total of 232.8, 373.5, and 191.1 μg·kg^-1·h^-1 VOCs with oxygenated VOCs (57.6%), volatile organic sulfur compounds (VOSCs, 58.6%) and VOSCs (54.9%) as the main group were detected during fruit, meat and vegetable fermentation, respectively. 2-Butanone (55.1%) and ethyl acetate (13.8%) were the two most abundant VOCs from fruit wastes, while dimethyl sulfide (68.0 and 26.6%) and dimethyl disulfide (89.2 and 10.1%) were in vegetable and meat wastes. The predominant Firmicutes represented 93.0-99.9% of the bacterial communities of meat decomposition, while Firmicutes and Proteobacteria were the dominant phyla throughout the fruit digestion process. Proteobacteria (16.9%-83.6%) was the dominant phylum in vegetable wastes, followed by Bacteroidetes, Firmicutes, and Actinobacteria. Malodorous VOCs emissions were highly affected by microbial activity, the abundant Weissella, Leuconostoc and Enterobacteriaceae in vegetable wastes showed correlation with carbon disulfide and dimethyl sulfide, while dominant Peptococcus, Bacteroides, Lactobacillales and Peptoniphilus in meat wastes was related to dimethyl disulfide. Overall, significant differences and correlation between VOCs emission profiles and bacterial communities among different food wastes decomposition were observed. These data contribute to a more comprehensive understanding the relationship between microbial community dynamics and malodorous VOCs emission.

Emission of volatile organic compounds from a small-scale municipal solid waste transfer station: Ozone-formation potential and health risk assessment

Volatile organic compounds (VOCs) are the main precursors of tropospheric ozone and secondary aerosol generation, posing a threat to human health and affecting the environmental climate. A large quantity of VOCs can be produced in the initial decomposition stage of municipal solid waste (MSW). In this study, the atmosphere in an MSW transfer station was monitored for one year. The emission characteristics of VOCs in different seasons and working hours were analyzed, and the ozone-formation potential of VOCs was calculated through the maximum incremental reaction method, and health risks posed by the VOCs in the MSW transfer station were assessed. The results showed that the highest concentration of VOCs appeared in spring and summer, accounting for 70.6% and 26.6% of total VOCs (TVOCs) in peak working periods, respectively. Oxygenated compounds and terpenes contributed most to ozone formation, accounting for 41.0% and 50.6% of total ozone formation, respectively. The carcinogenic risks were above the safe threshold, labeled "probable risks". Tetrachloroethylene and 1,2-dichloroethane were the main contributors to carcinogenic risks. The mean non-carcinogenic risks were within the safe threshold in the MSW transfer station. From the perspective of protecting human health and ecological environmental safety, VOC control needs to be further strengthened in the transfer station.

Dispersion simulation of odorous compounds from waste collection vehicles: Mobile point source simulation with ModOdor

Odour pollution from municipal solid waste is a public nuisance and a threat to the health of residents nearby. Attention and understanding towards odour emissions from waste collection vehicles are insufficient, and dispersion simulation using conventional modelling tools cannot be applied because their special operational characteristics do not conform to either point or linear sources. This study proposes a new dispersion simulation method for mobile point sources with ModOdor, which is a 3D numerical model previously developed by the authors. The 12-month monitoring data show that ethanol, dimethyl disulphide and methylene chloride were identified as typical odorous compounds released from waste collection vehicles. Ethanol dispersion was simulated as a mobile point source for low- and high-speed modes by synchronously changing temporal and spatial grids in high precision. Results revealed the variations in concentration distribution, dispersion distance and impact duration. In general, a diameter of area with odour activity value higher than 0.1 was identified at approximately 30-50 m after stable dispersion. The impact duration varied from approximately 20 s to 40 s along with the tested source intensities, wind directions and speeds with a benchmark of 10 μg·m^-3. This study verified the applicability of the proposed method for the dispersion simulation of mobile point sources and provided useful approach and information for evaluating the odour pollution from waste collection vehicles.

In-situ biodegradation of volatile organic compounds in landfill by sewage sludge modified waste-char

VOCs are the major harmful pollutants released from MSW landfills, which are toxicity to human health. In order to in-situ biodegradation of VOCs released from landfill, two novel laboratory-scale biocovers, including waste-char obtained from MSW pyrolysis (WC), and sewage sludge modified the WC (SWC), are used to degradate VOCs. The removal performances of VOCs as well as the bacterial community in the WC and SWC are investigated in a simulated landfill systems with the contrast experiment of a landfill cover soil (LCS) for 60 days. Meanwhile, the adsorption-biodegradation of VOCs model compounds over the LCS, WC, and SWC are also tested in fixed-bed adsorption reactor and in-situ FTIR. The VOCs removal efficiencies by the SWC are maintained above 85% for a long-term, much higher than that of the LCS and WC. The higher removal efficiencies and long-term stability for VOCs degradation in SWC are attributed to a strongly positive synergistic between adsorption and biodegradation that the gaseous VOCs released from MSW is effectively adsorbed by the SWC due to its higher VOCs adsorption capacity, and then the adsorbed-VOCs is converted into CO₂ and H₂O by the microorganisms that consuming the adsorbed-VOCs as energy and carbon sources. Subsequently, the decrease of the adsorbed-VOCs in SWC would also promote the transformation of the gaseous VOCs into the adsorbed VOCs and accelerate the growth of microorganisms by taking the adsorbed-VOCs as the energy and carbon source, resulted in a higher adsorption rate and degradation rate for VOCs.

Effect of source-classified and mixed collection from residential household waste bins on the emission characteristics of volatile organic compounds

The implementation of domestic waste classification following the principles of reduction, recycling, and harmlessness is an effective method to improve the urban and rural environments and to promote resource recycling. However, in many developing countries, the community residents lack awareness of the benefits of classified collection, which leads to a lack of initiative to classify MSW. To make the people realize the importance of MSW classification and increase the classification dynamics, Suzhou, China was taken as an example in this study, and residential areas were selected as sampling sites for classified and mixed collection of domestic waste. The main components of the odorous volatile organic compounds (VOCs) emitted from the dustbins via different disposal modes were determined by sampling in spring, summer, autumn, and winter. In addition, the ozone formation potential (OFP) and human health risk assessment of the VOCs were analyzed. Halogenated compounds were the major pollutants from the household waste dustbins of the residential areas. However, aromatic compounds contributed the most to the OFP of the VOCs. The OFP of VOCs reached the highest peak in summer, which was 1.02 × 10³ μg/m³. Furthermore, more attention needs to be paid in classifying waste to reduce the concentration of OFP. Although there was a carcinogenic risk in spring and summer, it declined after waste classification. Compared with mixed collection, the source-classified collection of garbage had advantages in terms of controlling the emission of VOCs, ozone formation potential, and human health risk. These results could provide the evidence demonstrating the advantages of waste classification and attract people's attention. Furthermore, the results can also provide impetus to those countries, where separate collection of waste has not yet been implemented, to improve the enthusiasm for classification and the integrity of waste classification system. Residents should be encouraged to classify household waste in residential areas.

In-situ biodegradation of harmful pollutants in landfill by sludge modified biochar used as biocover

MSW landfill releases a lot of harmful pollutants such as H₂S, NH₃, and VOCs. In this study, two laboratory-scale biocovers such as biochar (BC) derived from agricultural & forestry wastes (AFW) pyrolysis, and sludge modified the biochar (SBC) were designed and used to remove the harmful pollutants. In order to understand in-situ biodegradation mechanism of the harmful pollutants by the SBC, the removal performances of the harmful pollutants together with the bacterial community in the BC and SBC were investigated in simulated landfill systems for 60 days comparing with the contrast experiment of a landfill cover soil (LCS). Meanwhile, the adsorption capacities of representative harmful pollutants (hydrogen sulfide, toluene, acetone and chlorobenzene) in the LCS, BC, and SBC were also tested in a fixed bed reactor. The removal efficiencies of the harmful pollutants by the SBC ranged from 95.43% to 100.00%, which was much higher than that of the LCS. The adsorption capacities of the harmful pollutants in the SBC were 4 times higher than that of the LCS since the SBC exhibited higher BET surface and N-containing functional groups. Meanwhile, the biodegradation rates of the harmful pollutants in the SBC were also much higher than that of the LCS since the populations of the bacterial community in the SBC were more abundant due to its facilitating the growth and activity of microorganisms in the porous structure of the SBC. In addition, a synergistic combination of adsorption and biodegradation in the SBC that enhanced the reproduction rate of microorganisms by consuming the absorbed-pollutants as carbon sources, which also contributed to enhance the biodegradation rates of the harmful pollutants.

Odorant composition of post-consumer LDPE bags originating from different collection systems

The establishment of recycling systems aiming at high-quality recyclates from post-consumer plastic waste are essential to avoid the waste of resources. One main impediment for introducing recyclates into the market is their unwanted odor. For this reason, this study aimed at determining if the collection strategy affects the odor profile of post-consumer LDPE bags. Furthermore, the effect of hot water washing, inspired by the conventional mechanical recycling procedure, on the odor of post-consumer LDPE bags was screened. More than 60 odorants were detected in LDPE bags collected in a separate plastic fraction as well as in LDPE bags from the non-separated collection by means of gas chromatography-olfactometry, and 37 of them were unequivocally identified using two-dimensional gas chromatography-mass spectrometry/olfactometry. The sensory results revealed that the type of collection affects the overall odor intensity, the hedonic tone of the odor and the odor profile. Namely, cheesy and fecal smelling odorants were predominant in the waste that had not been separated at source, whereas odorants with earthy and moldy smells showed mostly higher intensity ratings in the waste separated at source. Short chain carboxylic acids, likely originating from microbial spoilage of organic waste, were found with higher dilution factors in the mixed fraction, and could, accordingly, contribute to the observed differences. Additionally, we could show that the hot washing procedure, applied to the LDPE sample from the separate collection system, significantly reduced the overall odor intensity from 8 to 6.3 (0-10 scale). However, the washed waste still showed high smell intensity ratings.

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.

Odour Emissions of Municipal Waste Biogas Plants—Impact of Technological Factors, Air Temperature and Humidity

Biogas plants processing municipal waste are an important part of a circular economy (energy generation from biogas and organic fertiliser production for the treatment of selectively collected biowaste). However, the technological processes taking place may be associated with odour nuisance. The paper presents the results of pilot research conducted at six municipal waste biogas plants in Poland. It shows the relations between odour intensity and concentration and the occurring meteorological and ambient conditions (air temperature and relative humidity) and technological factors at biogas plants processing municipal waste. The impact of meteorological and ambient conditions was identified by measuring air temperature and relative humidity and observing their changes. The impact of technological factors was identified by measuring odorant concentration (volatile organic compounds and ammonia) and observing their changes between individual measurement series. At most analysed biogas plants, the influence of technological factors on odour emissions took place and was clearly noted. The elements of biogas installations characterised by the highest concentration of these odorants were indicated. Special attention should be paid to the choice of technological solutions and technical and organisational measures to reduce the impact of unfavourable atmospheric conditions on odour emissions.

Electrochemical pretreatment for stabilization of waste activated sludge: Simultaneously enhancing dewaterability, inactivating pathogens and mitigating hydrogen sulfide

Stabilization of waste activated sludge (WAS) is an essential step for the disposal or reuse. In this study, WAS stabilization via electrochemical pretreatment (EPT) at 0-15V was evaluated for simultaneous dewaterability enhancement, pathogen removal and H₂S mitigation. The mechanism underlying EPT was investigated and discussed based on the changes in the physicochemical (e.g., particle size, zeta potential, hydrophobicity and extracellular polymeric substances) and biological characteristics (i.e. cell morphology, and distribution and percentages of live/dead cells) of WAS with different EPT voltages. The results revealed that EPT disintegrated WAS flocs and disrupted the cell walls leading to a reduction in particle size (by up to 50%), increased release of extracellular and intracellular substances (by up to 4 times) to facilitate WAS stabilization. With EPT at 15V, the capillary suction time of WAS decreased by 42%, and the concentrations of E. coli and indicator pathogens (Salmonella spp. and Streptococcus faecalis) fell by nearly 5 log₁₀ reaching U.S. EPA hygienization levels. Furthermore, EPT at 12V or higher suppressed the amounts of dissolved sulfide and H₂S_(g) produced from the WAS under anaerobic conditions by over 99%. This study demonstrates the feasibility of EPT for simultaneous WAS dewaterability enhancement, pathogen inactivation and H₂S mitigation, providing a one-step alternative for sludge stabilization.

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.

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.

A comparative study of the effects of microbial agents and anaerobic sludge on microalgal biotransformation into organic fertilizer

The effects of Lactobacillus bulgaricus, Rhodopseudomonas palustris, Issatchenkia orientalis and anaerobic sludge on anaerobic digestion of microalgae to organic fertilizer were studied. High-throughput sequencing was used to analyze characteristics of microbial community structure during anaerobic digestion of microalgae using different inocula. Lactobacillales and Saccharomycetales were more likely to become dominant bacteria and eukaryotes. The relative abundance of Lactobacillales was 98.15%, 88.61% and 81.73% of total bacteria at the beginning, middle and end of the experiment, respectively. Meanwhile, the relative abundance of Saccharomycetales was 90.91%, 98.41% and 98.8% of eukaryotes at the beginning, middle and end of the experiment, respectively. At the end of digestion, the microcystin content in the reactor inoculated with Issatchenkia orientalis decreased to 0.71 μg/kg, which met drinking water standards. Rhodopseudomonas palustris did not become a dominant microorganism and had the most negative impact on the atmosphere. Volatile organic compounds were 11.92 mg/kg while the odor concentration reached 97,724 ou/m³. The organic matter content in reactors inoculated with specific groups of microbial agents, which was higher than the standard required for bio-organic fertilizer, occupying over 96% dry weight. In addition, the effective microorganism counts of Issatchenkia orientalis and Lactobacillus bulgaricus in fermentation products reached 1.8E+09 colony-forming units (cfu)/g and 1.6E+09 cfu/g, respectively, which are suitable values for microbial fertilizer.

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.

Field investigation of temporal variation of volatile organic compounds at a landfill in Hangzhou, China

Variation of volatile organic compound (VOC) concentration and composition in an active landfill were monitored by a developed static chamber for 2 years. The landfill gas from 82 sampling points including 70 points on working face, 8 points on geomembrane (GMB), and 4 points on final cover were analyzed for VOCs by GC-MS. Twenty-eight types of VOCs were detected, including terpenes, sulfur compounds, aromatics, hydrocarbon, oxygenated compounds, aldehyde compounds, and halogenated compounds. Terpenes were the dominant VOCs recorded in the spring, autumn, and winter seasons, whereas sulfur compounds dominated in the summer season. Limonene, ethyl alcohol, and acetone were identified as the main VOCs emitted from the waste working face of the landfill. Limonene dominated the terpenes with a maximum concentration of 43.29 μg m^-3 in the autumn season. Limonene was also the dominant VOC escaping from the defects of geomembrane temporary cover reaching an average concentration 38 μg m^-3. The defects of geomembranes can be a great emission source of VOCs. Emission rate of limonene was 2.24 times higher than that on the working face. VOC concentrations on the final cover can be 166 times less than those obtained on the working face. VOC emitted from the landfill did not represent a health threat for human health. However, concentrations of methyl mercaptan and ethanethiol on the working face were 3.4-22.8 times greater than their odor threshold, which were the main compounds responsible for odor nuisance. Results obtained from CALPUFF model indicated that methyl mercaptan and ethanethiol would not be a nuisance for the residents around the landfill. However, these compounds are harmful to the workers on the landfill.

Odor assessment of NH3 and volatile sulfide compounds in a full-scale municipal sludge aerobic composting plant

Methods for assessing odors in municipal sewage sludge aerobic composting plants (MSSACPs) have been ineffective. This study identified the emission amount of typical odor-producing compounds, including NH₃ and volatile sulfide compounds from a full-scale MSSACP, and evaluated risks of odor emissions based on odor intensity and odor active value. Results revealed all sampling sites (i.e. sludge stacking yard, composting workshop, and screening workshop) produced serious odors, especially in the composting workshop. In the composting workshop, the amounts of DMDS (174.59 μg·dry kg^-1) and DMS (71.64 μg·dry kg^-1) emitted were far lower than that of NH₃ (6062.56 μg·dry kg^-1). However, DMDS and DMS showed a similar intensity as NH₃ according to odor intensity assessment. Furthermore, both of their odor active values were higher than that of NH₃. Using results from both odor intensity and odor active value were more reliable for the assessment of odors from MSSACPs.

Assessment of the major odor contributors and health risks of volatile compounds in three disposal technologies for municipal solid waste

Gaseous emissions from municipal solid waste (MSW) disposal plants pose serious odor pollution and health risks. In this study, the emission of volatile organic compounds and carbon disulfide was compared in the main processing units of three disposal methods, i.e., landfilling, eco-mechanical biological treatment (EMBT) and anaerobic fermentation in a MSW disposal plant. Among the detected volatile compounds (VCs), the top ten odor compounds were methanethiol, dimethyl sulfide, dimethyl disulfide, carbon disulfide, styrene, m-xylene, 4-ethyltoluene, ethylbenzene, 2-hexyl ketone and n-hexane in the MSW disposal plant. Sulfur compounds were the main source of odor at the majority of sampling sites, and aromatic compounds were the dominant odor substrates at the tipping unit and sorting system of EMBT, while 2-hexanone was the major odor substrate at the tipping unit (AT) and sorting system (AS) of anaerobic fermentation and the landfill working surface. At AS and AT, the lifetime cancer risk values for 1,2-dichloroethane and trichloroethylene exceeded the carcinogenic risk value (>1.0E-04), and the hazard index values of naphthalene, trichloroethylene and acrolein all exceeded the acceptable level (>1). Therefore, special attention should be paid to VC emissions from MSW disposal facilities, and protection measures should be adopted for on-site workers to minimize health risks.

Emission characteristics of VOCs and potential ozone formation from a full-scale sewage sludge composting plant

Volatile organic compounds (VOCs) are the major components of the odor emitted from sewage sludge composting plants and are generally associated with odorous nuisances and health risks. However, few studies have considered the potential ozone generation caused by VOCs emitted from sewage sludge composting plants. This study investigated the VOC emissions from a full-scale composting plant. Five major treatment units of the composting plant were chosen as the monitoring locations, including the dewatered room, dewatered sludge, blender room, fermentation workshop, and product units. The fermentation workshop units displayed the highest concentration of VOC emissions at 2595.7 ± 1367.3 μg.m^-3, followed by the blender room, product, dewatered sludge, and dewatered room units, whose emissions ranged from 142.2 ± 86.8 μg.m^-3 to 2107.6 ± 1045.6 μg.m^-3. The detected VOC families included oxygenated compounds, alkanes, alkenes, sulfide compounds, halogenated compounds, and aromatic compounds. Oxygenated compounds, particularly acetone, were the most abundant compounds in all samples. Principal component analysis revealed that the dewatered room and dewatered sludge units clustered closely, as indicated by their similar component emissions. The product units differed from the other sampling units, as their typical compounds were methanethiol, styrene, carbon disulfide, and hexane, all of which were the products of the latter stages of composting. Among the treatment units, the fermentation workshop units had the highest propylene equivalent (propy-equiv) concentration. Dimethyl disulfide and limonene were the major contributors. Limonene had the highest propy-equiv concentration, which contributed to the increased atmospheric reactivity and ozone formation potential in the surrounding air. To control the secondary environmental pollution caused by the VOC emissions during sewage sludge composting, the emission of limonene and dimethyl disulfide must be controlled from the blender room and fermentation workshop units.

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.

The effect of the composting time on the gaseous emissions and the compost stability in a full-scale sewage sludge composting plant

Volatile organic compounds (VOCs) and ammonia are some of the compounds present in gaseous emissions from waste treatment facilities that contribute to odour pollution. In the present work, the effect of the residence time on the biological stability of raw sludge (RS) composted in dynamic windrows and the gaseous emissions generated were studied at a full-scale composting plant, aiming to provide specific pollutant emission factors and to determine their variability depending on the composting time. Waste stability and emissions analysis considered both a first phase where mixed RS and vegetal fraction (RS - VF) is actively composted in dynamic windrows and a second standard curing phase in turned piles, which lasted 31 days. Two windrows were operated at 4 days of composting time while two other windrows were operated simultaneously at 14 days composting time. Increasing the residence time leads to a better waste stabilization in the first composting phase, providing a 50% reduction of the Dynamic Respiration Index. A decrease of the ammonia emission factor was achieved when increasing the composting time (from 168.5 g NH₃·Mg^-1RS - VF d^-1 to 114.3 g NH₃·Mg^-1RS - VF d^-1), whereas the VOCs emission factor was maintained for the same process conditions (between 26.0 and 28.0 g C-VOC·Mg^-1RS - VF d^-1). However, an increase of the emission masses of both pollutants was observed (from 0.16 to 0.39 kg tVOCs·Mg^-1RS - VF and from 1.21 to 1.60 kg NH₃·Mg^-1RS - VF). Finally, ammonia and VOCs emissions generated at the curing piles were nearly avoided when increasing the composting time of the first phase.

Parameter sensitivity to concentrations and transport distance of odorous compounds from solid waste facilities

Treatment facilities dealing with municipal solid waste (MSW) are typical pollution sources of urban odor nuisance which threatens public health and environmental safety. Dispersion simulation with specialized models is an important approach for simulating the concentration distribution and estimating the transport distances of the released odorous compounds. Given that the temporal and spatial distribution are affected by many factors with different variations and functions. This study investigated the influence of key parameters on the dispersion of odor compounds on the basis of a numerical atmospheric dispersion model. The sensitivity analysis was applied to quantitatively identify their influence on the concentration distributions and transport distances. The results reveal that source intensity is a sensitive parameter in the whole domain under the specified dispersion conditions, with the sensitivity ratios around 1 to concentrations and of 1.5-2.5 to transport distances. Wind speed possesses higher sensitivity ratios at the upwind direction than the downwind direction. Horizontal diffusion coefficient is sensitive to concentrations only in the area of a typical radius of 500 m from the source. Degradation reaction constant and wet deposition are not sensitive in either concentration distribution or transport distances. The most sensitive parameters present respective importance to the transport distances when different olfactory thresholds of compounds are applied to determine the protection area of odor pollution. This study thus provides important information to the application of dispersion models and the data collection of the most sensitive parameters in odor pollution evaluation and management.