Volatile compounds emission and health risk assessment during composting of organic fraction of municipal solid waste

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.

Lifestyle and occupational factors affecting exposure to BTEX in municipal solid waste composting facility workers

Composting facilities workers are potentially exposed to different volatile organic compounds (VOCs). This study aims to investigate the potential exposure to benzene, toluene, ethylbenzene and xylenes (BTEX) compounds among workers of composting facilities by measuring un-metabolized BTEX in urine and to investigate the effect that several lifestyle factors (i.e. smoking and residential traffic), using personal protective equipment, and religious practices such as Ramadan fasting can have on the urinary BTEX concentrations. We assessed concentrations of BTEX in the urine of a composting facility workers. Samples were collected in May 2018. Overall, 25 workers chosen as the exposed group and 20 inhabitants living close to the composting facility as a control group. The urine samples were collected from studied subjects. Identification and quantification of un-metabolized BTEX was performed using a headspace gas chromatography-mass spectrometry (GC-MS). Detailed information of participants was gathered by a comprehensive questionnaire. The geometric mean levels of urinary benzene, toluene, ethylbenzene, m‑p xylene, and o‑xylene in the exposed subjects were 1.27, 2.12, 0.54, 1.22 and 1.51 μg/L, respectively; 1.4 to 3.7-time higher than values in control group (p < 0.05). Post-shift levels were significantly higher than pre-shift for all chemicals (p < 0.05). Smoking habits, exposure to environmental tobacco smoke, and Ramadan fasting predicted urinary BTEX levels. Personal protective equipment which included a simple N95 mask did not protected workers from BTEX emissions. Composting facilities represent a significant source BTEX emissions and exposure for staff. More effective protective strategies are required to minimize exposure and related occupational hazards.

Statistical correlations on the emissions of volatile odorous compounds from the transfer stage of municipal solid waste

Odor pollution from treatment facilities and municipal solid waste (MSW) has caused wide public concern. Odorous compounds released from these facilities possess complex composition. Therefore, identifying typical odorous compounds and using their release rates to estimate those of other compounds may simplify the monitoring and evaluation of odor pollution. This study investigates the correlations of the release data of odorous compounds from a statistical perspective. For 12 months, we conducted in site monitoring in an MSW transfer station once each month to obtain 96 emission samples, and over 100 odorous compounds were quantified for each sample. Oxygenated compounds had considerable high release rates throughout the period, and ethanol was the dominant compound. Ethanol, dimethyl disulfide and methyl mercaptan were the top key compounds that contributed to the odor activity value. Correlation analyses within and across the categories showed that only a few compounds in saturated hydrocarbons and aromatic compounds had strong correlations with release rate. The coefficient of correlation between ethylbenzene and 19 other compounds, which covered only 25% of all the identified compounds in this study, was >0.5. These results show that representative compounds cannot be used in the calculation of release rate during the transfer stage.

An experimental and kinetic study of thermal decomposition of phenanthrene

Polycyclic aromatic hydrocarbons (PAHs) have enormous potential hazards. It is necessary for China to propose more internationally stricter standards for PAHs, in order to improve the country's pollutant prevention and control policy system, and ultimately, provide institutional guarantees for implementing PAH emissions prevention and control. In this study, phenanthrene, a typical PAHs generated during municipal solid waste (MSW) to energy system, was applied as a model compound to study the thermal degradation mechanism during the combustion process. Combustion kinetics for the three major gaseous products, including hydrogen, methane, and carbon dioxide, were determined. Experimental results indicated that hydrogen was promoted compared to methane and carbon dioxide during the combustion of phenanthrene, especially in high oxygen concentrations. The apparent activation energy (E_a) of 8.299-11.51, 13.10-23.07, and 9.368-15.29 kJ/mol, pre-exponential factor (A) of 0.219-1.579, 5.034-10.12, and 6.553-15.51 s^-1, and the reaction order (n) of 1.160-1.234, 1.059-1.305, and 1.636-1.774 were obtained for hydrogen, methane, and carbon dioxide, respectively. Research on combustion behavior of phenanthrene and reaction kinetics provides the theoretical basis for the high-temperature removal of PAHs as byproducts during the combustion of MSW in oxygen-rich atmosphere.

Emission analysis of recycled tire rubber modified asphalt in hot and warm mix conditions

The hazardous emissions of crumb rubber (CR) modified asphalt during construction has been a concern for a long period. This study aims to identify the emission components in the CR modified asphalt in traditional hot mix asphalt (HMA) and with recently developed warm mix asphalt (WMA). The dynamic headspace gas chromatography-mass spectrometry (GCMS) was employed for identifying the emission of asphalt binders at 120°C, 140°C and 160°C. The coupling of gas chromatography and Fourier-transform infrared spectroscopy (GC-FTIR) was used to analyze the emission during the plant mixing for conventional HMA, CR-HMA and CR-WMA. The results showed the emission amount was highly dependent on mixing temperature. The warm mix technology can reduce the emission level significantly and should be encouraged in the asphalt mixture containing CR. Asphalt source and other extra additives in producing CR modified asphalt can also affect the emission significantly. Asphalt mixture containing CR can release toxic emissions such as xylene and toluene significantly higher compared to that without CR. In addition, it was found that the emission amount from the GCMS test for asphalt binder was lower than that in the field test for asphalt mix due to the thin asphalt film of asphalt mix.

Emission characteristics and health risk assessment of volatile organic compounds produced during municipal solid waste composting

Municipal solid waste degradation during composting generates volatile organic compounds (VOCs), which can pose health risks the staff at the composting site and people living nearby. This problem restricts the widespread application of composting techniques. The characteristics of VOCs emitted from different units at a composting plant and the health risks posed were investigated in this study. A total of 44 VOCs (including alkanes, alkenes, aromatic compounds, halogenated compounds, oxygenated compounds, and sulfur-containing compounds) were identified and quantified. The highest VOC concentration (15484.1 ± 785.3 µg/m³) was found in primary fermentation, followed by the tipping unit (10302.1 ± 1334.8 µg/m³), composting product (4693.6 ± 1024.3 µg/m³), secondary fermentation (929.9 ± 105.2 µg/m³), and plant boundary (370.4 ± 75.8 µg/m³). The mean VOC concentration was 6356.0 µg/m³. The main compounds emitted during primary fermentation were oxygenated and those emitted from the tipping unit were alkenes. Health risk assessments indicate that VOCs did not pose unacceptable non-carcinogenic risks i.e., the HR values were <1 and carcinogenic risks (CR) values were <1.0 × 10^-4. These results indicate that VOC emissions do not pose health risks to the staff at the composting site or to people living nearby. However, the cumulative non-carcinogenic and carcinogenic risks posed by the VOC mixture were high, especially for the primary fermentation unit emissions. Therefore, protecting the staff working near the primary fermentation unit should be a priority. Measures should be taken to minimize cumulative non-carcinogenic and carcinogenic risks because people are exposed to a mixture of VOCs mixture rather than to a single type of VOC.

Assessment of the health risks and odor concentration of volatile compounds from a municipal solid waste landfill in China

Municipal solid waste (MSW) landfills are a source of odorous and toxic compounds. In this work, we present an integrated assessment of the odor concentration and human health risks of volatile compounds to evaluate the environmental quality at a MSW landfill. Air samples were collected seasonally from six areas of the landfill with different functions. The total concentrations of the compounds ranged from 204.0 to 7426.7 μg m^-3, and the concentrations in temporarily and permanently capped areas were 50.3 and 83.4% lower than those in the tipping area, respectively. The odor concentration was greatest at the leachate collection tank (1732-6254 ou_E m^-3) and tipping area (1573-4113 ou_E m^-3) and was mainly caused by hydrogen sulfide (57.9 and 49.1%, respectively). Moreover, the odor concentration was positively correlated with the temperature (r = 0.500, p < 0.05, n = 24). Although the non-carcinogenic (HI) and carcinogenic (R) risks of most compounds were largely below the acceptable levels (HI = 1, R = 1.0E-6), HI values of hydrogen sulfide (2.3), trichloropropane (2.0), and naphthalene (1.2) as well as R values of naphthalene (1.3E-4) and trimethylbenzene (1.2E-4) in the waste areas exceeded acceptable levels. Moreover, the cumulative HI (2.5-5.7) and R (1.0E-04 to 3.4E-04) in the waste areas should receive special attention since they were above acceptable levels during all of the seasons. Aromatic and halogenated compounds dominated the cumulative R, accounting for 79 and 21% of the total, on average, while for the cumulative HI, sulfur compounds contributed the most (67%).

Conversion of sulfur compounds and microbial community in anaerobic treatment of fish and pork waste

Volatile sulfur compounds (VSCs) are not only the main source of malodor in anaerobic treatment of organic waste, but also pose a threat to human health. In this study, VSCs production and microbial community was investigated during the anaerobic degradation of fish and pork waste. The results showed that after the operation of 245 days, 94.5% and 76.2% of sulfur compounds in the fish and pork waste was converted into VSCs. Among the detected VSCs including H₂S, carbon disulfide, methanethiol, ethanethiol, dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide, methanethiol was the major component with the maximum concentration of 4.54% and 3.28% in the fish and pork waste, respectively. The conversion of sulfur compounds including total sulfur, SO₄^2--S, S^2-, methionine and cysteine followed the first-order kinetics. Miseq sequencing analysis showed that Acinetobacter, Clostridium, Proteus, Thiobacillus, Hyphomicrobium and Pseudomonas were the main known sulfur-metabolizing microorganisms in the fish and pork waste. The C/N value had most significant influence on the microbial community in the fish and pork waste. A main conversion of sulfur compounds with CH₃SH as the key intermediate was firstly hypothesized during the anaerobic degradation of fish and pork waste. These findings are helpful to understand the conversion of sulfur compounds and to develop techniques to control ordor pollution in the anaerobic treatment of organic waste.

Volatile organic compounds (VOCs) removal in non-thermal plasma double dielectric barrier discharge reactor

Non-thermal plasma (NTP) an emerging technology to treat volatile organic compounds (VOCs) present in unhygienic point source air streams. In present study, double dielectric barrier discharge (DDBD) reactors were used for the first time to evaluate the removal efficiency of VOCs mixture of different nature at constant experimental conditions (input power 16-65.8 W, VOCs mixture feeding rate 1-6 L/min, 100-101 ppm inlet concentration of individual VOC). Reactor A and B with discharge gap at 6 mm and 3 mm respectively, were used in current study. When treated at an input power of 53.7 W with gas feeding rate of 1 L/min in DDBD reactor A, removal efficiency of the VOCs were: tetrachloroethylene (100%), toluene (100%), trichloroethylene (100%), benzene (100%), ethyl acetate (100%) and carbon disulfide (88.30%); whereas in reactor B, the removal efficiency of all VOCs were 100%. Plasma-catalyst (Pt-Sn/Al₂O₃, BaTiO₃ and HZSM-5) synergistic effect on VOCs removal efficiency was also investigated. Highest removal efficiency i.e 100% was observed for each compound with BaTiO₃ and HZSM-5 at an input power 65.8 W. However, integrating NTP with BaTiO₃ and HZSM-5 leads to enhanced removal performance of VOCs mixture with high activity, increase in energy efficiency and suppression of unwanted byproducts.

Emission potential of volatile sulfur compounds (VSCs) and ammonia from sludge compost with different bio-stability under various oxygen levels

Volatile sulfur compounds (VSCs) and ammonia from biowaste-derived residues is influenced by both the degree of bio-stability and atmosphere of oxygen level (i.e., either anaerobic, aerobic or anoxic conditions). By means of odor emission potential (OEP) test, present study directly examined how these two factors jointly affected the emissions of different odorous compounds from sludge compost. Results reveal that (1) the cumulative amount of ammonia and VSCs ranged from 0.08 to 0.38 mg/g-DM and 1.92 to 6.42 μg-S/g-DM, respectively. (2) High degree of bio-stability and oxygen level decreased the emission rates and cumulative amounts of ammonia, carbonyl sulfide, carbon disulfide, and especially methlymercaptan, who was even extinguished in the late stage. (3) Dimethyl sulfide and dimethyl disulfide showed no decline trend with increasing of bio-stability degree and oxygen level, suggesting their formation was mainly abiotic; cumulative amount of dimethyl disulfide was even higher under an atmosphere of high oxygen level. (4) Methlymercaptan was the dominant contributor to odor nuisance. The olfactory threshold of ammonia, dimethyl sulfide and dimethyl disulfide also exceeded their limited value. Hence, these odor compounds are priority when came to odor management of sludge compost. Overall, high stability degree and oxygen level alleviated the emission of ammonia, carbonyl sulfide, carbon disulfide and methlymercaptan, while the abatement of dimethyl sulfide and dimethyl disulfide should lie in controlling oxygen level in a certain range rather than extremely high oxygen level. Methlymercaptan can be regarded as an alternative indicator of the degree of bio-stability.