This study investigated the operating principles of colorimetric freshness indicators, particularly those for relative humidity (RH) and hydrogen sulfide (H2S), and evaluated the applicability of commercially available indicators for food use. The findings not only provide a deeper understanding of how these indicators respond to substances, such as carbon dioxide, volatile basic nitrogen, sulfides, water activity, and ethylene gas, which are produced during quality changes in food, but also pave the way for the development of new food safety technologies. The RH indicator functions by utilizing a dye that undergoes a chemical structural change when reacting with moisture. The H2S indicator uses a dye that changes color upon detecting H2S or volatile basic nitrogen produced when food spoils. Commercial RH indicators effectively indicated changes in the water activity of almonds, pastries, and red pepper powder; however, their ability to predict them diminished during storage. Commercial H2S indicators exhibited a stronger correlation between color change and volatile basic nitrogen levels in exposure to light than without light, as demonstrated when applied to mackerel and clam. Additionally, at the point of spoilage, the degree of color change in the H2S indicators was more distinct in clam than mackerel. Although commercial RH and H2S indicators are available, they must be sensitive, accurate, and irreversibly developed in response to changes in the target food for effective application.

In this study, the hydrogen sulfide removal performance of materials that can be used instead of NaOH was evaluated to reduce the amount of NaOH, a harmful substance used in chemical cleaning methods. Three alternative chemical agents were evaluated: commercially available chemical-based CB, enzyme-based EB, and natural substance-based NB. The hydrogen sulfide removal performance evaluation consisted of three lab tests: the EL608 method, a method using a bag, a method using a sensor and a chamber, and a field test conducted on a scrubber in operation in the actual field. As a result of evaluation by the EL608 Method, CB was 92.3% (±2.9%), EB 60.5% (±5.8%), and NB 88.3% (±3.6%), similar or somewhat similar to NaOH (5%) 99.8% (0.1%). In the evaluation of the hydrogen sulfide removal performance using Bag, the Michaelis-Menten coefficient was CB 4.30 and EB 5.30, lower than NaOH 6.60, and the affinity for hydrogen sulfide was evaluated to be stronger. Even in the method using the sensor and chamber, CB and EB showed similar hydrogen sulfide removal performance of NaOH, but NB showed low treatment performance. In the evaluation using the scrubber in the actual field, the treatment efficiency of CB and EB was higher than that of NaOH under all hydrogen sulfide inlet concentration conditions. If microorganisms grow on the packing material filled inside the scrubber, treatment efficiency may decrease. In order to prevent this phenomenon, the microbial growth inhibitory function of alternative materials was evaluated, and CB, EB, and NB were all superior to NaOH. As a result of this study, it was shown that CB and EB can replace NaOH because they have excellent performance in removing hydrogen sulfide and inhibiting microbial growth.

The germination process is critical for plant growth and development and it is largely affected by environmental stress, especially salinity. Recently, hydrogen sulfide (H2S) is well known to act as a signaling molecule in a defense mechanism against stress conditions but poorly understood regulating seed germination. In this study, the effects of NaHS (the H2S donor) pretreatment on various biochemical (hydrogen peroxide (H2O2) content and amylase and protease activity) and physiological properties (germination rate) during seed germination of oilseed rape (Brassica napus L. cv. Mosa) were examined under salt stress. The seed germination and seedling growth of oilseed rape were inhibited by NaCl treatment but it was alleviated by NaHS pretreatment. The NaCl treatment increased H2O2 content leading to oxidative stress, but NaHS pre-treatments maintained much lower levels of H2O2 in germinating seeds under salt stress. Amylase activity, a starch degradation enzyme, significantly increased over 2-fold in control, NaHS pretreatment, and NaHS pretreatment under NaCl during seed germination compared to NaCl treatment. Protease activity was highly induced in NaHS-pretreated seeds compared to NaCl treatment, accompanied by a decrease in protein content. These results indicate that NaHS pretreatment could improve seed germination under salt stress conditions by decreasing H2O2 accumulation and activating the degradation of protein and starch to support seedling growth.

Public complaints arising from centralized animal manure treatment plants are increasing due to the odors produced during animal manure treatment. Various physico chemical and biological methods are used to mitigate such odors. Still, many problems exist, such as a lack of fundamental data on odor generation characteristics and design standards for odor mitigation facilities. Therefore, this study evaluated the characteristics of NH3 and H2S gas produced from a centralized animal manure treatment plant. The centralized animal manure treatment plant selected in this study has a treatment capacity of 150 tons (animal manure and food waste) per day. The composting matrix was mechanically turned from 9:00 am to 6:00 pm on weekdays and not turned all day on weekends. The NH3 concentrations measured during the day on weekdays (96.4 ± 7.8 ppmv) were about 14% higher than on weekends (84.9 ± 15.9 ppmv). During the week, the ammonia concentration during the day was about 15% higher than at night, but there was no difference between day and night on weekends. The hydrogen sulfide concentration during the day (4,729 ± 3,687 ppbv) on a weekday was about 4.7 times higher than at night (1,007 ± 466 ppbv). The results of this study provide valuable information that is necessary for the operation of odor mitigation facilities. It is expected that the results will contribute to establishing an operational strategy that can reduce the energy required to collect exhaust gas.

This study evaluated the odor mitigation effect of rice husk biochar addition to the bedded pack dairy barn floor using lab-scale reactors for five days. Rice husk biochar mixed with dairy manure and sawdust mixture at different ratios (5%-addition test unit: adding biochar by 5% of the total solid weight of the mixture, 10%-addition test unit: adding biochar by 10% of the total solid weight of the mixture). Cumulative NH3 and H2S emissions of 10%-addition test unit were reduced by 26% (p< 0.05) and 46% (p = 0.0655), respectively, compared with control. However, 5%-addition test unit did not show NH3 and H2S emission reduction. Further research is needed to determine the appropriate level of biochar addition between 5 and 10%, and to evaluate applicability in the field through economic analysis.

Odor is a type of sensory pollution that can stimulate the human sense of smell when it occurs, causing discomfort and making it difficult to create a pleasant environment. For this reason, there is a high possibility of complaints regarding odors if odors occur in pigsties near residential properties, and the number of such complaints is also increasing. In addition, odors emanating from pigsties around military installations can cause physical and psychological harm, not only to the soldiers living in these type of facilities but also to the families belonging to military personnel living there as well. Because the concentration of odors varies due to diverse factors such as temperature, humidity, wind direction, wind speed, and interaction between causative materials, predicting odors based on only one factor is not proper or appropriate. Therefore, in this work, we sought to construct models that are based on several regression techniques of machine learning using data collected in field. And we selected and utilized the model that has the highest-accuracy in order to notify and warn residents of odors in advance. In this work, 3672 data items were used to train and test the model. The several machine learning algorithms to build the models are polynomial regression, ridge regression, K-nearest neighbor regression (KNN Regression), and random forest. Comparing the performance of models based on each algorithm, the study found that KNN Regression was the most suitable model, and the result obtained from KNN regression was significant.

Two lab-scale trickle-bed type biofilters with a single fungal species (Aspergillus fumigatus, Acidomyces acidophilus, respectively) have been studied to investigate the simultaneous removal of inorganic (hydrogen sulfide) and organic (butyl acetate) compounds. The biofilter with Aspergillus fumigatus treated simultaneously two different compounds with removal capacity of 1,511 mgS/m3/hr and 6,324 mgC/m3/hr; and the biofilter inoculated with Acidomyces acidophilus had the removal capacity of 1,254 mgS/m3/hr and 6,045 mgC/m3/hr. Stable operational performance was observed in both biofilters under an acidic condition of pH 2 to 4. Based on pseudo-first-order removal rates as a function of depth in the biofilter, Aspergillus fumigatus showed a twice faster rate of hydrogen sulfide removal than Acidomyces acidophilus, 15.9% (Aspergillus fumigatus) and 17.9% (Acidomyces acidophilus) of total sulfur removed were oxidized to produce sulfates, and 77.8% (Aspergillus fumigatus) and 79.4% (Acidomyces acidophilus) were accumulated in the form of S0 through the bed in both biofilters, respectively.

This study was performed to investigate the contamination characteristics of water in the scrubber with the aim of stably maintaining the scrubber, and to comprehend the removal characteristics of sulfur compounds, which are odorous substances, when microbubbles were supplied to the circulation water tank of a scrubber. The results of our analysis found that 63 kinds of gas compounds were detected from the scrubber, and thus it could be determined that Sulfur compounds, Ammonia (base compounds), Aldehyde compounds, and Pyrazine compounds were generated from the process for the production of sesame oil. About 93% of ammonia was removed in the scrubber; however, it was hard to remove Sulfur compounds, Aldehyde compounds and Pyrazine compounds using the scrubber. The efficiency of hydrogen sulfide, methylmercaptan and dimethydisulfide removal using only water in the scrubber was 79.8%, 79.7%, and 81.0%, respectively. However, when microbubbles were supplied to the scrubber, the removal efficiency for each was 83.7%, 91.1%, and 96.1%, respectively. Therefore, it was confirmed that the efficiency of sulfur compound removal was improved by supplying microbubbles to the circulation water tank of the scrubber. In addition, the amount of removal that could be achieved by using microbubbles was 1.05- 1.19 times higher than using only water. In terms of supplying microbubbles, it was confirmed that the saturation time required to absorb odorous gases was about 2.8 times longer than the time without microbubbles because the OH radicals generated when the microbubbles are shrinking partly oxidized organic matter. When there was no chemical in the circulation water tank, the conductivity and CODCr concentration were highly correlated. Therefore the system, which can replace circulation water by using real-time conductivity data, can be considered to be applicable.

A lab-scale biofilter with fungal growth has been studied to investigate the removal of gas-phase hydrogen sulfide. The biofilter inoculated initially with the aerobic activated sludge was operated for 100 days under acidic condition, and 0.36 L/d of the buffered nutrient with 0.05 g/L Chloramphenicol and Gentamicin was injected into the biofilter. The critical removal capacity of hydrogen sulfide was up to 22 g/m³/h. The pH of the effluent liquid was stable at pH 1.5-2, corresponding to the volatile suspended solids of 20-50 mg/L. In microbial analysis through the plate count method, it was found that fungi were dominant over bacteria. The fungi isolated from biomass in the bilfilter were identified as Acidomyces acidophilus and Aspergillus fumigatus. Sulfate and thiosulfate were also detected in liquid samples, as a result of the biological sulfur oxidation in the biofilter bed. For the analysis of sulfur mass balance, the accumulated mass of sulfate and thiosulfate reached up to 67.5% of inlet sulfur. Sulfur was also detected on the biomass collected from the biofilter through Scanning electron microscopy/Energy dispersive X-ray spectroscopy.

Acidic and basic mixtures of odorous compounds are commonly emitted from various sources, and, in an absorption process, pH conditions in the liquid phase significantly affect the performance. In this study, the effect of pH on mass transfer in a bubble column reactor was evaluated using hydrogen sulfide and ammonia as a model mixture. Their mass transfer coefficients were then calculated. Furthermore, the total mass transfer coefficients as a function of pH were evaluated, and the experimental data were fitted into an empirical equation using dimensionless numbers. The mass transfer rates of hydrogen sulfide, the non-ionic form, increased dramatically with increasing pHs, while those of ammonia were almost unchanged because of its high solubility. As a result, a favorable pH condition for less soluble compounds must be selected to achieve high absorption capacity. The total mass transfer rates, which took into account pH effects as well as all the non-ionic and ionic constituents together, were found to be from 2.2 to 2.4 × 10−3 min−1 for hydrogen sulfide and ammonia, respectively, and they were almost constant at different pHs. The empirical equations, which were derived to obtain the best fit for the total mass transfer rates, implied that a method to increase diffusivity of each compound should be applied to improve overall mass transfer. In addition, when using the empirical equation, a mass transfer coefficient at a given set of pH and operating conditions can be calculated and used to design a water scrubbing process.

Hydrogen sulfide (H2S) emitted from various sources is a major odorous compound, and non-thermal plasma (NP) has emerged as a promising technique to eliminate H2S. This study was conducted to investigate lab-scale and pilot-scale NP reactors using corona discharge for the removal of H2S, and the effects of relative humidity, applied electrical power on reactor performance and ozone generation were determined. A gas stream containing H2S was injected to the lab-scale NP reactor, and the changes in H2S and ozone concentration were monitored. In the pilotscale NP experiment, the inlet concentration and flow rate were modified to determine the effect of relative humidity and applied power on the NP performance. In the lab-scale NP experiments, H2S removal was found to be the 1st-order reaction in the presence of ozone. On the other hand, when plasma reaction and ozone generation were initiated after H2S was introduced, the H2S oxidation followed the 0th-order kinetics. The ratio of indirect oxidation by ozone to the overall H2S removal was evaluated using two different experimental findings, indicating that approximately 70% of the overall H2S elimination was accounted for by the indirect oxidation. The pilotscale NP experiments showed that H2S introduced to the reactor was completely removed at low flow rates, and approximately 90% of H2S was eliminated at the gas flow rate of 15 m3/min. Furthermore, the elimination capacity of the pilot-scale NP was 3.4 g/m3·min for the removal of H2S at various inlet concentrations. Finally, the experimental results obtained from both the lab-scale and the pilot-scale reactor operations indicated that the H2S mass removal was proportional to the applied electrical power, and average H2S masses removed per unit electrical power were calculated to be 358 and 348 mg-H2S/kW in the lab-scale and the pilot-scale reactors, respectively. To optimize energy efficiency and prevent the generation of excessive ozone, an appropriate operating time of the NP reactor must be determined.

This study has implemented an experiment in which hydrogen sulfide was removed by establishing a two-stage packed tower effector filled with nutritious medium and also filling a tower that was immobilized in ceramic media after isolating and identifying the sulfur oxidizing bacteria from a sewage treatment plant. As a result, strains isolated from the sewage treatment plant were found to be similar, including Bacillus fusiformis, Bacillus anthracis sp., Paenibacillus sp., Serratia marcescens sp., Bacillus thuringiensis. The effector that immobilized isolated strains in the ceramic media achieved an approximately 90% removal rate of hydrogen sulfide, while the sterilized ceramic media not immobilized with isolated strains showed a removal rate of about 65%. In addition, the removal rate of hydrogen sulfide in the primary media packing effector immobilized with sulfur oxidizing bacteria was about 92%, while the secondary effector filled with medium had a hydrogen sulfide removal rate near 100%. In addition, 90% efficiency of removal was shown in conditions of EBCT 60s in the experiment that investigated removal rate of hydrogen sulfide according to residence-time, while the efficiency was rapidly reduced up to 45% in conditions of EBCT 30s. On the other hand, when operating for an extended period time while increasing the concentration of injected hydrogen sulfide, the amount of sulfate was increased from 2 mg/L to 12.7 mg/L, and pH was rapidly reduced to 2.7.

This study has implemented an experiment in which hydrogen sulfide was removed by establishing a two-stage packed tower effector filled with nutritious medium and also filling a tower that was immobilized in ceramic media after isolating and identifying the sulfur oxidizing bacteria from a sewage treatment plant. As a result, strains isolated from the sewage treatment plant were found to be similar, including Bacillus fusiformis, Bacillus anthracis sp., Paenibacillus sp., Serratia marcescens sp., Bacillus thuringiensis. The effector that immobilized isolated strains in the ceramic media achieved an approximately 90% removal rate of hydrogen sulfide, while the sterilized ceramic media not immobilized with isolated strains showed a removal rate of about 65%. In addition, the removal rate of hydrogen sulfide in the primary media packing effector immobilized with sulfur oxidizing bacteria was about 92%, while the secondary effector filled with medium had a hydrogen sulfide removal rate near 100%. In addition, 90% efficiency of removal was shown in conditions of EBCT 60s in the experiment that investigated removal rate of hydrogen sulfide according to residence-time, while the efficiency was rapidly reduced up to 45% in conditions of EBCT 30s. On the other hand, when operating for an extended period time while increasing the concentration of injected hydrogen sulfide, the amount of sulfate was increased from 2 mg/L to 12.7 mg/L, and pH was rapidly reduced to 2.7.

Odor compounds and air-born microorganisms are simultaneously emitted from various aeration processes such as aerobic digestion, food-waste compositing, and carcass decomposition facilities that are biologically-treating wastes with high organic contents. The air streams emitted from these processes commonly contain sulfur-containing odorous compounds such as hydrogen sulfide(H2S) and bacterial bioaerosols. In this study, a wet-plasma method was applied to remove these air-born pollutants and to minimize safety issues. In addition, the effects of a gas retention time and a liquid-gas ratio were evaluated on removal efficiencies in the wet-plasma system. At the gas reaction time of 1.8 seconds and the liquid-gas ratio of 0.05 mLaq/Lg, the removal efficiency of bioaerosol was approximately 75 %, while the removal efficiency of H2S was lower than 20 %, indicating that the gaseous compound was not effectively oxidized by the plasma reaction at the low liquid addition. When the liquid-gas ratio was increased to 0.25 mLaq/Lg, the removal efficiencies of both H2S and bioaerosol increased to greater than 99 %. At the higher liquid-gas ratio, more ozone was generated by the wet-plasma reaction. The ozone generation was significantly affected by the input electrical energy, and it needed to be removed before discharged from the process.

The contents of this paper is to develop a passive sampler for H2S measurement. When the H2S gas exists in the air, AgNO3 solution coated filter of white used phenomenon which is exchanged with black. If the H2S gas concentration increased, the color of AgNO3 solution coated filter is discolored more black. H2S passive sampler measures the H2S gas concentration by changed color of AgNO3 solution coated filter. The reproducibility of the H2S passive sampler is very stable to within an error 5%RSD. The black color of AgNO3 solution coated filter showed a linear relationship with the H2S gas concentrations. In addition, correlation of the developed CDM and CR-10(Minolta, Japan) showed a high correlation to 0.99. Manufactured H2S passive sampler must be kept refrigerated, stability and reactivity was observed for up to 20 days

In this study, the growth kinetics of sulfur oxidizing bacteria, Acidithiobacillus thiooxidans, and the effect of dissolved oxygen were determined in low pH conditions for the effective removal of high concentrations of hydrogen sulfide. A dual growth kinetic was applied to identify the microbial growth rate at different hydrogen sulfide and oxygen concentrations in the liquid. A modified Monod-Gompertz equation was deemed most appropriate to examine the growth kinetic parameters of A. thiooxidans. The half saturation constants of hydrogen sulfide and oxygen for the modified Monod-Gompertz equation were found to be 0.9 and 1.1 mg/L, respectively. In addition, a bioreactor model, where the Monod-Gompertz equation was modified, was applied to simulate dissolved oxygen concentrations required for the removal of hydrogen sulfide. As a result, the dissolved oxygen concentrations were 0.5, 1.0, 1.5, and 3.3 mg/L, which were necessary to remove hydrogen sulfide to less than 10 ppm at the influent concentrations of 100, 500, 1000 and 3000 ppm, respectively. The required minimum dissolved oxygen concentrations under various conditions including reactor volume, gas retention time, and microbial concentrations can be determined using the numerical model developed in this study.