Odorous Gases Research Articles

Long-term effective remediation of black-odorous water via regulating calcium nitrate sustained-release.

Nitrate addition is reported as a cost-effective method for remediating black-odorous water, which is mainly induced by the deficiency of electron acceptor. However, excessive release of nitrate and lack of long-term effectiveness significantly limited the application of direct nitrate dosing technology. Herein, for remediating black-odorous water, we constructed a nitrate sustained-release ecological concrete (ecoN-concrete), in which calcium nitrate (Ca(NO3)2) was dosed into concrete block to regulate the release of nitrate. The results showed that chemical oxygen demand (COD), turbidity, ammonia, phosphate, and sulfate were significantly removed in an ecoN-concrete-contained reactor fed with black-odorous water, and its removal efficiency was largely dependent on Ca(NO3)2 dosage. Meanwhile, the released nitrate was lower than 25% of its total dosage and nitrite was lower than 1.5mg/L during 14days remediation. After three recycles, the removal efficiencies of COD and turbidity by using ecoN-concrete were still more than 85%, indicating an excellent nitrate sustained-release performance of ecoN-concrete, which can be applied for preventing water re-blackening and re-stinking. Further investigation illustrated that the ecoN-concrete (1) decreased the abundance of Desulfovibrio, Desulfomonile, and Desulforhabdus in the phylum of Desulfobacterota to alleviate the odorous gas production and (2) significantly increased the abundance of Bacillus and Thermomonas, which utilized the released-nitrate for consuming organic matters and ammonia. This study provided an artful Ca(NO3)2 dosing strategy and long-term effective method for black-odorous water remediation.

Synthetic microbial consortia to enhance the biodegradation of compost odor by biotrickling filter

Composting generates odorous gases, including ammonia (NH3), hydrogen sulfide (H2S), and volatile organic compounds (VOCs). The Biological Trickling Filter (BTF) is effective for odor treatment, but it may have limitations with hydrophobic VOCs. In this study, a strain of Bacillus subtilis with ammonia-reducing ability, a strain of Bacillus cereus with desulfurization ability and a strain of Schizophyllum commune with the ability to degrade dimethyl disulfide were isolated and screened. The three strains were combined to create synthetic microbial consortia for enhancing odor treatment in the BTF. Compared to the activated sludge control, the BTF with synthetic microbial consortia removed 92.43% ammonia, 92.75% hydrogen sulfide. Furthermore, it demonstrated a significant improvement in the removal rates of p-methyl mercaptan, methyl sulfide, and dimethyl disulfide. High-throughput sequencing was conducted on the fillers of the synthetic microbial consortia-inoculated BTF to analyze the microbial community composition.

Optimum factors of a renewable energy plant from poultry organic waste

The article presents the parameters of the device for renewable energy from poultry organic waste. The authors describe the experimental device for the anaerobic processing of poultry organic waste and the results of the implementation of the device. Broad considerations about obtaining alternative energy sources if the dilution mode is used for the first time in the device for obtaining biogas from poultry organic waste are given. Anaerobic treatment of poultry organic waste in a bioreactor was used to absorb odorous gases and to analyze the production of biogas at different temperature regimes by the method of dilution.

Effect of extrusion on the structural and flavor properties of oat flours

As widely consumed functional grain worldwide, oats have received increasing attention due to numerous health benefits. Compared to the traditional multistep baking methods (saturated steam and kiln drying), extrusion offered economic and practical advantages in time and energy savings, as well as consumer product quality. With the purpose of discovering potentially new products, this study investigated the impact of extrusion on starch structural and flavor profiles (volatile and non-volatile) in oat flour. The high temperature, high pressure, and high shear in the extrusion process changed the intimate texture of the oat flour into irregular, spongy texture, which forms V-type crystal structure. Extruded oat flour's gelatinization temperature was significantly lower than unextruded. Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry demonstrated significant increases in aldehydes and heterocycles after extrusion of oat flours. The odorants in raw oat flours, identified by gas chromatography-olfactometry and odor activity value changed from green to pleasant nutty, grass and bean fragrance in extruded flours. Furthermore, umami amino acid contents increased, while bitter amino acid contents decreased significantly. This study identified the structural and flavor differences in extruded oat flours and provided clues that could improve potential in the development of ready-to-eat cereals and snack foods.

Nitrogen-containing malodorous gas pollutants emission characteristics and health risk assessment from an A/O wastewater treatment plant

Unpleasant odorous emitted from wastewater treatment plants (WWTPs) have been of great concern for many years, especially among local communities with high population density. Knowledge about characteristics of odorous gas release from WWTP can assist in developing gas pollution reduction technologies. This study investigated the emission and variation of NH3 and organic amines (CH3NH2, C2H6NH, and C3H9N) at the water-air interface and concentrations of ambient air exposure from different treatment units in a wastewater treatment plant in North China, which uses the anaerobic/oxic (A/O) treatment process. Results demonstrated that NH3 and C2H6NH emission fluxes had followed a descending order of aeration treatment units > non aeration treatment units. NH3 and C2H6NH achieved the highest release concentration throughout the whole wastewater treatment process, where 0.0023 g of NH3 and 0.0018 g of C2H6NH were emitted during the treatment of 1 m3 wastewater, while CH3NH2 and C3H9N had never been detected. The emission of NH3 and C2H6NH from biological aeration tanks account for 98 % and 95 % of the total discharge of wastewater treatment plant, respectively. The odor pollution of NH3 and C2H6NH in the ambient air of different treatment units of WWTP was the most serious in summer. At the sensory level, NH3 dominated the malodorous effect and its exposure concentration posed a certain non carcinogenic risk to workers in wastewater treatment plant.

Biodegradation characteristics of mixed phenol and p-cresol contaminants from a swine farm using bacteria immobilized in calcium alginate beads

Phenol and p-cresol, major odorous gases in swine farms, pose significant health risks and require efficient elimination. This study screened biofilm-derived bacteria from a local swine farm for effective phenol and p-cresol degradation. Isolated bacteria were exposed to 1000 ppm of phenol and p-cresol and cultivated in Mineral salts medium (MSM). Morphology, degradation characteristics, and 16S rRNA analysis were employed for identification. The isolate Proteobacteria and Actinobacteria, completely degraded phenol and p-cresol in water, up to 500 ppm, within 12 h. The mixtures of Proteobacteria and Actinobacteria eliminated 500 ppm of each compound within 28 h. Additionally, immobilized bacteria in calcium alginate beads exhibited reusable degradation activity for at least 5 cycles, with no decline in performance or bacterial loss. and no bacterial loss. This study highlights the potential of these bacterial strains and immobilization technique for effective VOC degradation in swine farm environments, improving odor control and environmental well-being.

Screening of skatole-degrading bacteria and control of human fecal odor by compound bacteria

PurposeThe biodegradation of skatole was used as a starting point in this study, and existing strains of degrading NH3 and H2S in the laboratory were combined to create a composite deodorant. The deodorization effect of the composite deodorant on human feces was investigated in order to provide a foundation for fecal odor gas treatment.MethodsSkatole-degrading bacteria were identified, degradation conditions were optimized, and skatole metabolites were identified using liquid chromatography-mass spectrometry (LC-MS). The skatole-degrading bacteria were combined with the existing strains of degrading NH3 and H2S in the laboratory to make a compound deodorizer, and the deodorizing effect of the compound deodorizer on fresh human feces and old human feces was compared. Liquid chromatography, specific sensors, and gas chromatography were used to determine the contents of skatole, NH3, H2S, and volatile organic compounds, and the microbial diversity was examined.ResultsMicrobial agents H and Y capable of utilizing skatole were screened out under aerobic and facultative anaerobic conditions, respectively. Within 48 h, the degradation rate of skatole by microbial agent Y was 88.52%. Following condition optimization, the optimum temperature for skatole degradation by microbial agent Y was 33 °C, and the optimum pH was 7. The main functional bacteria were Acinetobacter xiamenensis. The metabolites of skatole were determined by liquid chromatography-mass spectrometry (LC–MS), and six possible metabolites were found, including 3-aldehyde indole, 3-carboxyl indole, 1H-indole-2,3-dione, and 3-methyl indole pyruvate. The skatole-degrading bacteria Lactobacillus rhamnosus and Saccharomyces cerevisiae were then combined in proportion to form a composite deodorant. The 5-day degradation rate of skatole in the old manure group was 88.11%, while the 5-day degradation rate in the fresh manure group was 47.56%.ConclusionsThe compound microbial agent developed in this study has a solid deodorizing effect, particularly in the control of the odor of obsolete feces. The use of composite microbial agents can efficiently degrade skatole in human feces, providing a theoretical foundation for the use of microbial remediation in the actual world.Graphical

Bibliometrics and Knowledge Map Analysis of Research Progress on Biological Treatments for Volatile Organic Compounds

The emission of volatile organic compounds (VOCs) has resulted in increasingly severe harm to the environment and human health. In recent years, biological methods have become the preferred technology for VOC removal due to their environmental friendliness and economic advantages. Based on the theory of bibliometrics, this study analyzed research articles and reviews on biological methods for VOC removal published in the Web of Science Core Collection (WOSCC) database from 1966 to 2021. The knowledge map visualization software CiteSpace was utilized to analyze research progress in different countries, co-citation clustering, co-citation bursts, and keyword clustering in the literature data. The results indicated that early research on VOC biological treatment focused on the removal of odorous gases and single components of volatile organic waste gases. Subsequently, benzene contents (BTEX), hydrophobic VOCs, and multi-component VOCs have gradually become the focus of research. In recent years, improving VOC removal efficiency by studying packing materials and microbial communities has become an important research topic both domestically and internationally. Future research should focus on continuously improving the performance of reactors, developing novel reactors, and investigating technologies for treating complex and recalcitrant VOCs.

Research on odor characteristics of typical odorants of railway vehicle products.

Odor annoyance was a kind of environmental air pollution. Compared to other indoor environments, vehicle interior materials were not well studied. Especially, there had been little research on odor character of the railway vehicles. This study applied the OAV method to identify the key odorants of railway vehicle materials and discussed the characteristics of these odorants through Weber Fechner law and a dual variable method. The result showed that for single odorant, Weber Fechner law can be used to estimate the perceived intensity of an odor gas sample at different concentration levels. The odorant with smaller slope had significant tolerance to human. For the mixtures of odorants, the overall intensity of the mixture is generally dominated by the strongest odor intensity of the individual substance in the mixture, and positive interaction effect can be observed in mixtures whose intensities had little difference. But there was a kind of odorants, such as methacrylate, in which a very small variation in the concentration of mixtures can affect its odor intensity largely. Meanwhile, the odor intensity modification coefficient was an effective way to identify and evaluate odor interaction effect. The interaction potential of the studied odorants from strong to weak was methacrylate, dibutyl-amine, nonanal, 2-ethyl hexanol. The odor interaction potential and odor nature should be paying much attention in the improvement of odor in railway vehicle product.

Volatile organic compounds conversion pathways and odor gas emission characteristics in chicken manure composting process

IntroductionComposting is a highly effective method for managing the growing quantity of agricultural waste, promoting nutrient recycling, and advancing sustainable agriculture. However, the significant amounts of volatile inorganic compounds (VICs) and volatile organic compounds (VOCs) generated during the composting process cannot be ignored due to their serious ecological environmental hazards and detrimental impact on human health. The types and pathways of VICs and VOCs produced during the composting process remain not well understood.MethodsIn this study, we investigated the VOCs produced during chicken manure and straw composting using gas chromatography–mass spectrometry (GC/MS). We performed qualitative and quantitative analyses of VOCs in composting emissions gases and their correlation with odor.ResultsOur results showed that 44 VOCs were detected during composting, including 4 oxidation-containing compounds, 2 sulfur-containing organics, 5 alkanes, 19 halogenated compounds, and 14 aromatic compounds. Aromatic compounds were found to be the main component of VOCs, accounting for 59.14% of the total content. The highest VOC content was found in the pre-composting period, and the highest emitting VOC was p-Isopropyl Toluene, which reached 7870.50 μg/m3. We identified eight substances that were highly correlated with odor concentration (p < 0.01) and are the main odor-causing substances that need to be monitored and controlled.DiscussionOur study provides important insights into the transformation of volatile gases during the composting process. It highlights the need for proper management practices to control VOCs emissions and reduce their environmental impact.

Effects of different levels of dietary crude protein on the physiological response, reproductive performance, blood profiles, milk composition and odor emission in gestating sows.

This study was conducted to evaluate the effects of crude protein (CP) levels on the physiological response, reproductive performance, blood profiles, milk composition and odor emission in gestating sows. Seventy-two multiparous sows (Yorkshire×Landrace) of average body weight (BW), backfat thickness, and parity were assigned to one of six treatments with 10 or 11 sows per treatment in a completely randomized design. Experimental diets with different CP levels were as follows: i) CP11, corn‒soybean-based diet containing 11% CP; ii) CP12, corn‒soybean-based diet containing 12% CP; iii) CP13, corn‒soybean-based diet containing 13% CP; iv) CP14, corn‒soybean-based diet containing 14% CP; v) CP15, corn‒soybean-based diet containing 15% CP; and vi) CP16: corn‒soybean-based diet containing 16% CP. There was no significant difference in the performance of sow or piglet growth when sows were fed different dietary protein levels. Milk fat (linear, p = 0.05) and total solids (linear, p = 0.04) decreased as dietary CP levels increased. Increasing dietary CP levels in the gestation diet caused a significant increase in creatinine at days 35 and 110 of gestation (linear, p = 0.01; linear, p = 0.01). The total protein in sows also increased as dietary CP levels increased during the gestation period and 24 hours postpartum (linear, p = 0.01; linear, p = 0.01). During the whole experimental period, an increase in urea in sows was observed when sows were fed increasing levels of dietary CP (linear, p = 0.01), and increasing blood urea nitrogen (BUN) concentrations were observed as well. In the blood parameters of piglets, there were linear improvements in creatinine (linear, p = 0.01), total protein (linear, p = 0.01), urea (linear, p = 0.01), and BUN (linear, p = 0.01) with increasing levels of dietary CP as measured 24 hours postpartum. At two measurement points (days 35 and 110) of gestation, the odor gas concentration, including amine, ammonia, and hydrogen sulfide, increased linearly when sows fed diets with increasing levels of dietary CP (linear, p = 0.01). Moreover, as dietary CP levels increased to 16%, the odor gas concentration was increased with a quadratic response (quadratic, p = 0.01). Reducing dietary CP levels from 16% to 11% in a gestating diet did not exert detrimental effects on sow body condition or piglet performance. Moreover, a low protein diet (11% CP) may improve dietary protein utilization and metabolism to reduce odor gas emissions in manure and urine in gestating sows.

‘악핵독종(惡核毒腫)’ 치료에서 ‘치혈지통(治血止痛)’으로

Ruxiang, one of the most commonly imported herbs, has been mentioned in Chinese literature since the Wei and Jin periods. With the growth of overseas trade during the Tang and Song periods, the massive importation of herbs, including Ruxiang, brought about significant changes in the understanding and utilization of Ruxiang. This study examines historical changes in the perception and utilization of Ruxiang in China.
 In the literature of the third century, Ruxiang was mentioned as a “strange item from the south” and understood as a “medicinal herb.” Particularly during the sixth century, TaoHongjing(陶弘景)’s Bencaojingjizhu本草經集注 focused on the therapeutic effects of Ruxiang for treating carbuncles and abscesses, and specific prescriptions that used Ruxiang were related to these ailments. This understanding continued until the early Tang Dynasty, during which Ruxiang was mainly used for treating carbuncles and abscesses or intestinal gas and bad odor.
 The perception of the efficacy of Ruxiang changed in the eighth century. Notably, ChenCangqi(陳藏器) emphasized its efficacy in treating stroke, female infertility, blood circulation, deafness, and diarrhea in Bencaoshiyi本草拾遺. However, there are no records of Ruxiang being used to treat these conditions in formulary books(醫方書) compiled during that time as well as in Waitaimiyao外台祕要.
 By the end of the late Tang and Five Dynasties periods, with the establishment of local governments and the development of overseas trade, the importation of Ruxiang increased considerably, resulting in significant changes in how it was perceived and used. With Rihuazibencao日華子本草 compiled in the southern region in the tenth century, a more advanced understanding of the efficacy of Ruxiang emerged, which included protecting the regularity of Qi(氣), protecting the waist and knees, stopping pain, and promoting skin regeneration. Additionally, Taipingshenghuifang太平聖惠方 compiled during the Song Dynasty included various prescriptions that reflected the changing perception of Ruxiang’s efficacy since the eighth century, including treatments for stroke, female infertility, and diarrhea.
 Bencaotujing本草圖經 from the mid-Northern Song Dynasty emphasized the efficacy of Ruxiang in treating blood and promoting circulation, a fact that was further confirmed in Taipinghuiminhejijufang太平惠民和劑局方 prescriptions added during the Southern Song period. Ruxiang’s effectiveness in ‘boosting the meridian circulation,’ which was particularly mentioned in the added prescriptions during the Southern Song period came to be highlighted by Yishuixuepai易水學派 and medical scholars such as Zhangyuansu張 元素 and Wanghaogu王好古 during the thirteenth century.
 In conclusion, in the sixth century, Ruxiang was understood to be effective at treating carbuncles and abscesses and dispelling negative energy. Such an understanding of Ruxiang’s efficacy shifted toward an emphasis on its ability to invigorate blood circulation and alleviate pain in the eleventh to thirteenth centuries. This evolution reflected an expanded understanding of Ruxiang’s efficacy and the gradual establishment of an increasingly theoretical framework to explain it. Additionally, the expanded understanding of Ruxiang’s efficacy can be observed in the many usages to which it was put in medical books, which expanded significantly from the tenth and eleventh centuries onward, during the time of large-scale Ruxiang importation. The appearance of medical prescriptions that used Ruxiang in the Song Dynasty’s Taipingshenghuifang太平聖惠方 likely resulted from the expanded understanding of Ruxiang’s efficacy and the increased importation of Ruxiang from the late Tang Dynasty to the Five Dynasties periods.

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

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

ガスセンサ・ニオイセンサに向けた酸化スズナノマテリアルの創製

Expectations for the sensing of very small amounts of gases and odors are increasing in many fields such as medicine, healthcare, and mobility. In recent years, nanomaterials with various forms such as needle-like, belt-like, sheet-like, and dendrite-like have been developed. These nanomaterials have been used to detect very small amounts of gas with a semiconductor gas sensor. In addition, detection of various gases and odor molecules has been realized using these gas sensors. In particular, in the field of ceramics, which requires high-temperature firing at several hundred degrees Celsius, the realization of “cold crystallization”, which has been a long-standing issue, has had a great impact. Nanomaterials with high surface area, unique shape, metastable crystal facets, etc. have been developed with cold crystallization of ceramics. These nanomaterials have improved the low-concentration gas detection characteristics of gas sensors and odor sensors. In this review, I would like to introduce the fabrication of new SnO2 nanomaterials and the development of gas and odor sensors using the SnO2 nanomaterials.

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and odor activity value (OAV) to reveal the flavor characteristics of ripened Pu-erh tea by co-fermentation.

Pu-erh tea is a geographical indication product of China. The characteristic flavor compounds produced during the fermentation of ripened Pu-erh tea have an important impact on its quality. Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and odor activity value (OAV) is used for flavor analysis. A total of 135 volatile compounds were annotated, of which the highest content was alcohols (54.26%), followed by esters (16.73%), and methoxybenzenes (12.69%). Alcohols in ripened Pu-erh tea mainly contribute flower and fruit sweet flavors, while methoxybenzenes mainly contribute musty and stale flavors. The ripened Pu-erh tea fermented by Saccharomyces: Rhizopus: Aspergillus niger mixed in the ratio of 1:1:1 presented the remarkable flavor characteristics of flower and fruit sweet flavor, and having better coordination with musty and stale flavor. This study demonstrated the content changes of ripened Pu-erh tea's flavor compounds in the fermentation process, and revealed the optimal fermentation time. This will be helpful to further understand the formation mechanism of the characteristic flavor of ripened Pu-erh tea and guide the optimization of the fermentation process of ripened Pu-erh tea.

Microbial community evolution and functional trade-offs of biofilm in odor treatment biofilters

Biofilters inoculated with activated sludge are widely used for odor control in WWTP. In this process, biofilm community evolution plays an important role in the function of reactor and is closely related to reactor performance. However, the trade-offs in biofilm community and bioreactor function during the operation are still unclear. Herein, an artificially constructed biofilter for odorous gas treatment was operated for 105 days to study the trade-offs in the biofilm community and function. Biofilm colonization was found to drive community evolution during the start-up phase (phase 1, days 0–25). Although the removal efficiency of the biofilter was unsatisfactory at this phase, the microbial genera related to quorum sensing and extracellular polymeric substance secretion led to the rapid accumulation of the biofilm (2.3 kg biomass/m3 filter bed /day). During the stable operation phase (phase 2, days 26–80), genera related to target-pollutant degradation showed increases in relative abundance, which accompanied a high removal efficiency and a stable accumulation of biofilm (1.1 kg biomass/m3 filter bed/day). At the clogging phase (phase 3, days 81–105), a sharp decline in the biofilm accumulation rate (0.5 kg biomass/m3 filter bed /day) and fluctuating removal efficiency were observed. The quorum quenching-related genera and quenching genes of signal molecules increased, and competition for resources among species drove the evolution of the community in this phase. The results of this study highlight the trade-offs in biofilm community and functions during the operation of bioreactors, which could help improve bioreactor performance from a biofilm community perspective.

The Construction of Volatile Profiles of Eight Popular Peach Cultivars Produced in Shanghai Using GC-MS and GC-IMS

Peach (Prunus persica L.) is an economically important fruit crop worldwide due to its pleasant flavor. Volatile organic compounds (VOCs) are vital factors for assessing fruit quality. Here, we constructed the VOC profiles for the top eight popular commercial peach cultivars produced in Shanghai by combining gas chromatography-mass spectrometry (GC-MS), odor activity value and gas chromatograph-ion mobility spectrometry (GC-IMS). Seventy VOCs were detected using GC-MS, of which twenty-three were commonly found in eight peach cultivars, including hexanal, nonanal, benzaldehyde, 2-hexenal, butyl acetate, hexyl acetate, (Z)-3-hexen-1-yl acetate, linalool, β-myrcene, D-limonene, 1-hexanol, 3-hexenol, 2-hexenol, 2-ethyl-1-hexanol, γ-octalactone, δ-decalactone, γ-hexalactone, γ-decalactone, γ-dodecalactone, β-ionone, 2-octanone, 2-ethyl furan and 2,4-ditert-butyl phenol. A total of 17 VOCs were screened on the basis of OAV ≥ 1 and the top 5 of this contribution were γ-decalactone, β-ionone, hexanal, 2-hexenal and linalool. Lactones had the highest OAV in HJML and terpenoids had the highest OAV in JC. JXIU had the lowest OAV of lactones and terpenoids. Based on the range of their OAV values, the flavor evaluation standard of Shanghai high-quality peach cultivars can be established, which is also a reference for breeding excellent offspring. Twenty-six VOCs were detected using GC-IMS, and the largest proportion were aldehydes. Principal component analysis (PCA) showed that Hikawa Hakuho (HH) and Jinchun (JC) were distant from the other samples, indicating that their volatiles were more distinct. These results provide a foundation for improving our understanding of aroma compositions in these high-quality peach cultivars, which might also provide a reference for future design breeding to improve fruit flavor.

Flare exhaust: An underestimated pollution source in municipal solid waste landfills

Flares are commonly used in municipal solid waste landfills, and the pollution from flare exhaust is usually underestimated. This study aimed to reveal the odorants, hazardous pollutants, and greenhouse gas emission characteristics of the flare exhaust. Odorants, hazardous pollutants, and greenhouse gases emitted from air-assisted flares and a diffusion flare were analyzed, the priority monitoring pollutants were identified, and the combustion and odorant removal efficiencies of the flares were estimated. The concentrations of most odorants and the sum of odor activity values decreased significantly after combustion, but the odor concentration could still exceed 2,000. The odorants in the flare exhaust were dominated by oxygenated volatile organic compounds (OVOCs), while the major odor contributors were OVOCs and sulfur compounds. Hazardous pollutants, including carcinogens, acute toxic pollutants, endocrine disrupting chemicals, and ozone precursors with the total ozone formation potential up to 75 ppmv, as well as greenhouse gases (methane and nitrous oxide with maximum concentrations of 4,000 and 1.9 ppmv, respectively) were emitted from the flares. Additionally, secondary pollutants, such as acetaldehyde and benzene, were formed during combustion. The combustion performance of the flares varied with landfill gas composition and flare design. The combustion and pollutant removal efficiencies could be lower than 90%, especially for the diffusion flare. Acetaldehyde, benzene, toluene, p-cymene, limonene, hydrogen sulfide, and methane could be priority monitoring pollutants for flare emissions in landfills. Flares are useful for odor and greenhouse gas control in landfills, but they are also potential sources of odor, hazardous pollutants, and greenhouse gases.

Mechanism and process optimization for H2S removal by plant-derived deodorant

Plant-derived deodorant shows exciting prospect for odorous gas control, while controversy still exists on its effect of removing the malodorous substances with the fact that the removal mechanism and parameter optimization of this deodorization technology were rarely reported. Herein, a laboratory-scale bubbling absorption tower was used to conduct orthogonal test designed with three factors of five levels to investigate the efficiency of plant-derived deodorant to remove hydrogen sulfide (H2S). Compared with water, the aqueous solution of plant-derived deodorants could effectively remove H2S with a maximum removal efficiency of 99.99%. In particular, the removal efficiency of deodorant was about 40% higher than that of water at the H2S concentration of 70 mg/m3. After treated by the aqueous solution of plant-derived deodorants, the outlet concentration of H2S could be lower than 0.02 mg/m3, meeting the requirement of the odor pollutant emission standards in many countries, which exhibited the feasibility of using it an effective way to control H2S. Among the parameters including air input, concentration of H2S, and concentration of plant-derived deodorant, concentration of deodorant was the parameter that presented the most significant impact on the deodorization effect. The calculation results of absorption and reaction parameters showed that the removal of H2S by plant-derived deodorants is a process controlled by chemical absorption.

Adsorption enhancement of hazardous odor gas using controlled thermal oxidation of activated carbon

Nitrogen-containing odorous compounds (NOCs) such as ammonia, ethylamine, dimethylamine, and trimethylamine (TMA) have potentially adverse effects on the environment and human health. An efficient and simple strategy for NOC removal is necessary. Herein, thermally dried activated carbon adsorbents (TDACs) were prepared, and their surfaces were subjected to controlled thermal oxidation at 50, 100, and 200 °C. The resulting TDACs exhibited micropore-intensive porous structures with different specific surface areas (SSA) (135–562 m2 g−1) and demonstrated 2–38 times higher NOC-adsorption capacity (12.35–102.92 mg g−1) than that of pristine AC in a fixed-bed breakthrough test. Comprehensive surface characterization revealed a correlation between the thermal oxidation conditions and corresponding SSAs. Density functional theory calculations revealed that multidentate hydrogen bonding potential prevails over proton affinity in determining the NOC-adsorption trend. The fractal-like kinetics of the classical adsorption fitting for the TDACs suggested a heterogeneous adsorption behavior (R2 = 0.9998). A competitive adsorption test for the TDACs using a binary mixture of TMA and benzene demonstrated that TMA is favorably adsorbed over benzene and that the co-adsorption process involves a roll-up effect. This study demonstrates that NOC adsorption on TDACs can be controlled via a thermal oxidation strategy, which affords adsorbents with high reusability and adsorbate selectivity.