Sulfide Emissions Research Articles

Field Study of Generation and Emission of Hydrogen Sulfide in a Sanitary Sewer Network Downstream of a Long Forcemain

Field Study of Generation and Emission of Hydrogen Sulfide in a Sanitary Sewer Network Downstream of a Long Forcemain

Characterizing multifaceted environmental risks of oil and gas well leakage through soil and well methane and hydrogen sulfide emissions

Oil and gas wells (OGWs) can lead to soil and well emissions of methane (CH4), a potent greenhouse gas, and hydrogen sulfide (H2S), a highly toxic gas, both of which reduce air quality and can cause explosions when emitted into confined spaces. Developments have been occurring over OGWs, posing larger health and safety risks. However, to our knowledge, previous studies have not conjunctively analyzed well and soil emissions while considering development on or near OGWs. In this paper, we characterize 343 CH4 and H2S emission rate measurements from 67 non-producing (abandoned) and 35 producing (active) OGWs, including 205 measurements from soils surrounding 81 OGWs in Ontario and Quebec. We also provide the first emission rate estimates from an abandoned water and OGW-linked explosion and map OGWs in urban and built-up areas in Ontario and Quebec. We estimate the explosion-linked emissions to be 3,000 g CH4/hour and 7 g H2S/hour. Moreover, we find that 7,264 and 161 OGWs in Ontario and Quebec, respectively, are in urban and built-up areas, with 94% of these wells being abandoned. For the 102 wells we measured, we find OGW emission rate ranges of -16 to 47,000 mg CH4/hour and 0.001 to 3,300 mg H2S/hour, with 9% of the wells having positive detections of H2S. Although soil CH4 emissions at a 1-meter distance from the wells are most correlated with well emissions, the highest soil emission rate was observed at a 3-meter distance, indicating the potential for OGW-related emissions into buildings to occur away from the well. Overall, our multi-faceted measurement dataset provides a basis for conjunctive analysis of the broad range of environmental risks of OGWs to climate, indoor and outdoor air quality, and explosions.

A 20-year (1998–2017) global sea surface dimethyl sulfide gridded dataset with daily resolution

Abstract. The oceanic emission of dimethyl sulfide (DMS) plays a vital role in the Earth's climate system and constitutes a substantial source of uncertainty when evaluating aerosol radiative forcing. Currently, the widely used monthly climatology of sea surface DMS concentration falls short of meeting the requirement for accurately simulating DMS-derived aerosols with chemical transport models. Hence, there is an urgent need for a high-resolution, multi-year global sea surface DMS dataset. Here we develop an artificial neural network ensemble model that uses nine environmental factors as input features and captures the variability of the DMS concentration across different oceanic regions well. Subsequently, a global sea surface DMS concentration and flux dataset (1° × 1°) with daily resolution spanning from 1998 to 2017 is established. According to this dataset, the global annual average concentration was ∼ 1.71 nM, and the annual total emissions were ∼ 17.2 Tg S yr−1, with ∼ 60 % originating from the Southern Hemisphere. While overall seasonal variations are consistent with previous DMS climatologies, notable differences exist in regional-scale spatial distributions. The new dataset enables further investigations into daily and decadal variations. Throughout the period 1998–2017, the global annual average concentration exhibited a slight decrease, while total emissions showed no significant trend. The DMS flux from our dataset showed a stronger correlation with the observed atmospheric methanesulfonic acid concentration compared to those from previous monthly climatologies. Therefore, it can serve as an improved emission inventory of oceanic DMS and has the potential to enhance the simulation of DMS-derived aerosols and associated radiative effects. The new DMS gridded products are available at https://doi.org/10.5281/zenodo.11879900 (Zhou et al., 2024).

PSI-29 Enhancing growth performance and reducing environmental impact with dietary protease supplementation in growing pigs fed high- and low-density diets

Abstract Exogenous protease has emerged as a promising solution for enhancing protein digestion and utilization in animal diets, offering potential benefits for both animal performance and environmental impact mitigation in pig farming. In a 6-wk trial involving 140 growing pigs [initial body weight (BW) = 24.10 ± 1.66 kg], the effects of dietary protease supplementation on growth performance, nutrient digestibility, and noxious gas emission were investigated. Pigs were randomly assigned to one of four dietary treatments in a 2 x 2 factorial design with two levels of nutrient density and 0 or 125 g/ton supplementation of protease. The pigs were blocked by BW and housed in 28 pens with each pen consisting of 5 pigs (3 barrows and 2 gilts). The experimental design employed a randomized complete block design with 7 replicate pens per treatment. The data were analyzed using two-way ANOVA, with differences between means assessed using Tukey’s test (P < 0.05). Results revealed no significant interaction (P > 0.05) between nutrient density and protease supplementation concerning growth performance, nutrient digestibility, and noxious gas emission. Pigs subjected to high-density diets exhibited greater (P < 0.05) average daily gain (ADG) and gain-to-feed ratio (G:F) compared with those on low-density diets. While protease supplementation did not impact ADG and average daily feed intake (ADFI), there was a tendency towards reduced (P = 0.08) G:F throughout the 6-wk period. Pigs fed high-density diets demonstrated significantly greater (P < 0.05) apparent total tract digestibility (ATTD) of gross energy (GE) compared with their counterparts on low-density diets. Furthermore, the inclusion of protease significantly increased (P < 0.05) ATTD of GE. However, no discernible differences were noted among diets regarding the ATTD of dry matter and nitrogen. Regarding noxious gas emission, protease supplementation did not significantly affect total mercaptans and hydrogen sulfide (H2S) emission. Nonetheless, there was a notable trend towards reduced (P = 0.06) ammonia gas (NH3) emission with protease inclusion. Similarly, nutrient density did not exhibit a significant effect (P > 0.05) on noxious gas emission. In conclusion, the results of the study underscore the importance of nutrient density and protease supplementation in optimizing pig performance and environmental sustainability in swine production systems. Further research is warranted to elucidate the underlying mechanisms and refine strategies for maximizing the benefits of these dietary interventions.

PSVI-26 The benefits of probiotics (L. plantarum and L. acidophilus) supplement in growth performance, egg production, gas emission and gut microbiome diversity in Hy-Line brown laying hens

Abstract During the past few decades, antibiotics have been widely used at subtherapeutic doses to improve growth rates and performance in the poultry industry. However, antibiotics can result in side effects including bacterial resistance; these side effects often have detrimental consequences for human health. Thus, the poultry sector was urged to seek alternative strategies to promote animal performance. One environmentally friendly approach to growth promotion involves the use of probiotics, which have been used in the poultry industry for decades. Therefore, we aimed to investigate the effects of dietary supplementation with Lactobacillus spp. (L. plantarum and L. acidophilus) on growth performance, egg production, gas emission and gut microbiota diversity in laying hens. A total of 192 Hy-Line brown laying hens were randomly divided into four groups and assigned to one of four dietary treatments for 12 wk. The test treatments were basal diet (TRT1), basal + 0.25% antibiotic (TRT2), and basal + 0.1% probiotics (TRT3), and basal + 0.2% probiotics (TRT4). Laying hens fed a diet supplemented with 0.2% probiotics showed increased (P < 0.05) egg production in wk 9, 10, and 12. Moreover, fecal ammonia and hydrogen sulfide emissions were reduced (P < 0.05) in the probiotic groups. Microbiome analysis showed increased (P < 0.05) species richness in the probiotic groups, as indicated by Chao1 and Shannon indices, but a decrease (P < 0.05) in species diversity according to the Simpson index, suggesting a specific microbial community development due to probiotic supplementation. In conclusion, this study provides us with an insight into the potential use Lactobacillus spp. probiotic as a food supplement in the laying hen industry also provides us with a better understanding of the interplay between Lactobacillus spp. and the gut microbiome diversity in laying hens.

High rates of hydrogen sulfide emissions measured from marginal oil wells near Austin and San Antonio, Texas

Marginal oil and gas wells, or wells that produce less than 15 barrels of oil equivalent per day, represent 80% of actively producing wells in the United States, although they produce less than 10% of energy supply. Marginal wells are a disproportionate source of methane (CH4) relative to their production, and they emit harmful air pollutants, such as benzene and other hydrocarbons found in oil and natural gas. We made direct measurements of CH4 and hydrogen sulfide (H2S) emissions from 46 wellheads in the Luling Field, Caldwell County, Texas, just east of the Austin/San Antonio Metroplex. We found that these wells are venting natural gas and are a large source of hydrogen sulfide (H2S), a poisonous air pollutant. Hydrogen sulfide emission rates ranged from 0 to 5 ± 0.5 g H2S hr−1 with an average emission rate of 1.6 ± 0.1 g H2S hr−1. We also found ambient concentrations of H2S at dangerous levels (>100 ppm) near many of the wells. Methane emission rates were in line with previous studies of marginal wells, ranging from 0.0 to 2770 ± 390 g CH4 hr−1, with a skewed distribution and average emission rate of 710 ± 100 g CH4 hr−1. Oil production records from Texas were incomplete: some wells had oil production data from the year of sampling, but many had no production data for several years or decades, although they were actively pumping while we were on site. Interviews with local residents indicate that the closing of the county gas processing plant and subsequent loss of gathering lines may be the cause of gas venting and CH4 and H2S emissions from production sites. This deserves further scrutiny, as marginal wells in this region are a major source of H2S, a health hazard to people living and working nearby.

Assessing sulfate-reducing bacteria influence on oilfield safety: Hydrogen sulfide emission and pipeline corrosion failure

With the further development of oilfield, excessive sulfate-reducing bacteria (SRB) has intensified odors and increased pipeline leakage incidents. Accurate predictive models of H2S emission and pipeline corrosion based on SRB content are essential for safety. This study analyzed the correlation between sulfide content and SRB content at different nodes in the injection-production system of Daqing Oilfield, and characterized the pipeline corrosion products using scanning electron microscopy (SEM), X-ray diffraction (XRD), and stereo microscope. Corrosion rates were investigated through 18 sets of orthogonal experiments, considering factors such as SRB, temperature, pH, liquid flow rate, CO2 partial pressure, and H2S partial pressure, and the main controlling factors of corrosion were identified. Finally, the risk models for H2S emission and corrosion rate based on SRB content were established under on-site operating conditions. The results show that a significantly positive correlated between SRB and sulfide content at different nodes, with the highest levels observed at the settling tank, indicating the highest risk of H2S emission. SRB contributed to corrosion in both water injection and oil collection pipelines, with more serious corrosion in the water injection pipeline. SRB and pH were identified as the main factors influencing corrosion rate. The H2S emission prediction model based on the correlation of SRB and sulfide was reliable, with an accuracy exceeding 90 % compared to the measured results. Additionally, the corrosion rate model for pipelines, related to SRB content, had an error of less than 7 %. To minimize risks, it is recommended to maintain a low risk environment in the injection-production system by sterilization and increasing the pH of water. This study has significant theoretical importance for ensuring the safe operation of injection-production systems.

What kind of corrosion products are “black spots”? —Effects of reduced sulfur compounds on corrosion of bronze artefacts

While deterioration due to the generation of “black spots” is reported, consensus on the specific corrosion products comprising black spots and underlying deterioration mechanisms is lacking. This study investigated the deterioration of copper objects by analysing the black spots that appeared on them and proposes environmental conditions to suppress the appearance of black spots. Bronze artefacts excavated from a marine archaeological site, on which black spots were generated, were closely observed, and investigated. First, X-ray fluorescence and micro-X-ray diffraction analyses were performed on a bronze artefact, from which the black spots were removed, to determine the composition of the artefact. Second, to investigate the composition of the black spots, fine structure analysis of the black spots on the fine fragments of the bronze artefacts was conducted using scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron diffraction (ED) analysis. The results indicate that the black spots were partially composed of metallic copper and a fine particle mixture of Cu2S and CuSO4. These results imply that the transformation of copper sulfide to metallic copper may have played an important role in the initiation and propagation of black spots. In this study, ED analysis was performed on the microscopic area of the black spots; no amorphous phases were detected, and all observed phases were identified as crystalline materials. To determine the sources of gas-phase sulfur compounds that cause black spots, H2S and carbonyl sulfide (COS) emissions from a spherical clay artefact (a cannon ball with gunpowder excavated from an underwater archaeological site) which was exhibited in the same showcase with the bronze artefacts were analysed via gas chromatography. The concentrations of H2S and COS were 0.462 and 8.636 ppb, respectively; these are significantly higher than those in the lower troposphere. These results indicate that deterioration by black spots occurred because of H2S and COS, which were emitted from the spherical clay artefact excavated from an underwater archaeological site in the exhibition case. In addition, it was confirmed that the inclusion of deoxygenating and dehumidifying agents (RP-AN) in the plastic bag in which the spherical clay artefact was inserted resulted in a significant decrease in the concentration of H2S and COS.

Nitrite-dependent microbial utilization for simultaneous removal of sulfide and methane in sewers

Chemicals are commonly dosed in sewer systems to reduce the emission of hydrogen sulfide (H2S) and methane (CH4), incurring high costs and environmental concerns. Nitrite dosing is a promising approach as nitrite can be produced from urine wastewater, which is a feasible integrated water management strategy. However, nitrite dosing usually requires strict conditions, e.g., relatively high nitrite concentration (e.g., ∼200 mg N/L) and acidic environment, to inhibit microorganisms. In contrast to “microbial inhibition”, this study proposes “microbial utilization” concept, i.e., utilizing nitrite as a substrate for H2S and CH4 consumption in sewer. In a laboratory-scale sewer reactor, nitrite at a relatively low concentrations of 25–48 mg N/L was continuously dosed. Two nitrite-dependent microbial utilization processes, i.e., nitrite-dependent anaerobic methane oxidation (n-DAMO) and microbial sulfide oxidation, successfully occurred in conjunction with nitrite reduction. The occurrence of both processes achieved a 58 % reduction in dissolved methane and over 90 % sulfide removal in the sewer reactor, with microbial activities measured as 15.6 mg CH4/(L·h) and 29.4 mg S/(L·h), respectively. High copy numbers of n-DAMO bacteria and sulfide-oxidizing bacteria (SOB) were detected in both sewer biofilms and sediments. Mechanism analysis confirmed that the dosed nitrite at a relatively low level did not cause the inhibition of sulfidogenic process due to the downward migration of activity zones in sewer sediments. Therefore, the proposed “microbial utilization” concept offers a new alternative for simultaneous removal of sulfide and methane in sewers.

Mitigation of ammonia and hydrogen sulfide emissions during aerobic composting of laying hen waste through NaOH-modified biochar

The impact of NaOH-modified biochar on the release of NH3 and H2S from laying hens' manure was examined for 44 days, using a small-scale simulated aerobic composting system. The findings revealed that the NaOH-modified biochar reduced NH3 and H2S emissions by 40.63% and 77.78%, respectively, compared to the control group. Moreover, the emissions of H2S were significantly lower than those of the unmodified biochar group (p < 0.05). The increased specific surface area and microporous structure of the biochar, as well as the higher content of alkaline and oxygenated functional groups, were found to facilitate the adsorption of NH3 and H2S. This enhanced adsorption capability was the primary reason for the significant reduction in NH3 emissions. Furthermore, during the high-temperature phase of composting, there was a notable alteration in the microbial community. The abundance of Limnochordaceae, Savagea, and IMCC26207 increased significantly which aided in the conversion of H2S to stable sulfate. These microorganisms also influenced the abundance of functional genes involved in sulfur metabolism, thereby inhibiting cysteine synthesis, along with the decomposition and conversion of sulfate to sulfite. This led to a significant decrease in H2S emissions. This study provides valuable data for the selection of deodorizers in the composting process of egg-laying hens. The results have significant implications for the application of NaOH-modified biochar for odor reduction in aerobic composting processes.

Assessment of transient hydrogen sulfide peak emissions caused by biogas plant operation

Odor nuisance is a major impediment for public acceptance and wider implementation of biogas plants. Knowledge on composition and dynamics of emissions from these plants is highly needed for development of robust mitigation solutions. In this study, odorant emissions were investigated from two biogas plants of different sizes and capacities. Measurements using proton-transfer-reaction mass spectrometer (PTR-MS) revealed that hydrogen sulfide was the main odorant and constituted 82% and 71% of the odor activity sums (SOAV) at the two studied plants, respectively. Long-term time-resolved measurements furthermore revealed that emissions were highly dynamic with distinct short-term emission peaks. By deploying an array of electrochemical sensors, the main sources of hydrogen sulfide emission were subsequently identified and correlated with operational data to identify the major causes for the highly fluctuating emissions. Addition of biomasses in the form of animal slurry to pre-tanks, were shown to be the major cause of periodic hydrogen sulfide emission within the range of 50–1200 ppm. Such hydrogen sulfide peak emissions could challenge odor abatement from biogas plants and should be taken into account when designing odor abatement technologies for biogas plants.

Research on semi-supervised soft sensor modeling method for sulfur recovery unit based on ISSA-VMD-ESN

Sulfur recovery unit (SRU) in the refining industry can effectively reduce sulfide emissions and achieve efficient use of resources. Predicting sulfide emissions with soft sensors can provide the basis for process optimization and control, to improve SRU’s stability and efficiency. However, due to the dynamicity and nonlinearity of the sulfur recovery process, existing soft sensor models have poor prediction accuracy. Therefore, this paper proposes a semi-supervised soft sensor modeling method based on variational mode decomposition (VMD), echo state network (ESN) and improved sparrow search algorithm (ISSA). Firstly, Reconstructing SRU dataset using semi-supervised fusion method to reduce the impact of dynamicity on prediction results. Secondly, through the ISSA to optimize the VMD parameters and using the optimized VMD to decompose the output sequences into multiple components, to reduce the nonlinearity of sequences. Then, the soft sensor modeling of each component using ESN. Additionally, the ESN parameters are optimized by ISSA to prevent the effect of improper parameter settings on the model’s prediction performance. Afterwards, the predicted values of each component are superimposed to obtain the final prediction. Finally, simulation experiments are conducted based on the SRU dataset of an oil refinery to verify the effectiveness and generalization of the proposed method.

The Impacts of the C/N Ratio on Hydrogen Sulfide Emission and Microbial Community Characteristics during Chicken Manure Composting with Wheat Straw

Wheat straw (WS) has long been subjected to rough treatment by traditional incineration, which not only results in the waste of biomass resources but also poses a risk of atmospheric pollution and is not conducive to the sustainable utilization of natural resources. With great humification potential, WS can be utilized as a valuable composting material. The study optimized the C/N ratio by mixing WS and chicken manure (CM) as composting raw materials, and found that this method could significantly improve the compost quality. In comparison to the conventional poplar woodchip (PW) conditioning, the incorporation of WS resulted in an elevated composting temperature, an extended high-temperature period, a more expeditious lignocellulose degradation, a notable enhancement in the organic matter content, a suppression of hydrogen sulfide production under low C/N ratio, and a promotion of elemental sulfur conversion, collectively contributing to an enhanced overall quality and environmental friendliness of the compost. Correlation analysis of microbial communities and environmental factors demonstrated that the mixed compost facilitated the growth of actinomycetes and sulfur-transforming bacteria. Additionally, structural equation model indicated that parameters such as temperature and pH value played a key role in the composting process.

Natural Marine Precursors Boost Continental New Particle Formation and Production of Cloud Condensation Nuclei.

Marine dimethyl sulfide (DMS) emissions are the dominant source of natural sulfur in the atmosphere. DMS oxidizes to produce low-volatility acids that potentially nucleate to form particles that may grow into climatically important cloud condensation nuclei (CCN). In this work, we utilize the chemistry transport model ADCHEM to demonstrate that DMS emissions are likely to contribute to the majority of CCN during the biological active period (May-August) at three different forest stations in the Nordic countries. DMS increases CCN concentrations by forming nucleation and Aitken mode particles over the ocean and land, which eventually grow into the accumulation mode by condensation of low-volatility organic compounds from continental vegetation. Our findings provide a new understanding of the exchange of marine precursors between the ocean and land, highlighting their influence as one of the dominant sources of CCN particles over the boreal forest.

Sustainable Livestock Production: Screening Analysis and Pilot Implementation of a Biofilm in Piggery Biofilters for Mitigation of Ammonia and Hydrogen Sulfide Emissions

One of the most noticeable problems associated with the close location of piggeries is gaseous compounds emission. Ammonia and hydrogen sulfide emissions affect the quality of life of people living in the vicinity of such facilities. Among the diverse methods for managing and controlling malodorous substances, biological methods, which involve the utilization of microbiological agents, are widely employed. The use of bacterial strains is a relatively simple, low-cost, and ecological method. The study aimed to conduct a preliminary evaluation of the implementation of a novel consortium of deodorizing bacteria. The study involved the selection of bacteria, assessment of the antagonistic properties, implementation of the inoculum in a mesh-filled biofilter, and analysis of ammonia, hydrogen sulfide, and fine dust content in the air before and after passing through the mature biological bed. The results obtained demonstrate the effectiveness of the biofiltration bed in reducing ammonia levels, with a maximum decrease observed at 73.90%. For hydrogen sulfide, a removal efficiency of &gt;72.08% was observed. Reduction in fine dust pollution also decreased from a level of 3.75 mg/m3 to 1.06 mg/m3. The study’s findings demonstrate the promising potential of utilizing a consortium of deodorizing bacteria as an effective approach to mitigating emissions from piggeries.

Risk prediction for hydrogen sulfide emission based on sulfate-reducing bacteria in the water flooding oilfield

The water quality of the injection–production systems deteriorates as the water flooding oilfields are developed more deeply, and the content of sulfate-reducing bacteria (SRB) increases. Accordingly, hydrogen sulfide (H2S) emission related to SRB is intensified, which will arise safety and health problems. In order to investigate the effect of SRB on H2S emission in the water flooding oilfield, the contents of SRB and sulfide of the different nodes of a typical injection–production system of Daqing Oilfield were measured first, and then, H2S emission from water was simulated under different conditions. Consequently, a H2S emission prediction model was established based on Henry coefficient and the correlation between sulfide content and SRB content in the water. The measured sulfide contents were ranging from 0.25 to 6.34 mg/l, and the SRB contents were from 2.5 to 25 000 pcs/ml, and the highest SRB and sulfide contents were found in the settling tank. The correlation between sulfide content and SRB content was much remarkable, and the R2 value of the correlation analysis was 0.94. Henry coefficient of H2S emission was obtained from the simulated experiments under varied conditions such as sulfate content, oil content, and temperature. The established H2S emission prediction model was much reliable for predicting H2S emission for water flooding injection–production system, and the accuracy of the predicted H2S emission of four nodes of the injection–production system was larger than 95% compared to the measured results. This study provides theoretical guidance for predicting H2S emission risks in water flooding injection–production systems.

Mitigation of hazardous ammonia and hydrogen sulphide emissions using carbon based nanometal oxides adsorbents

Mitigation of hazardous ammonia and hydrogen sulphide emissions using carbon based nanometal oxides adsorbents

Thermal Characterization of Crosslinked Polymeric Microspheres Bearing Thiol Groups Studied by TG/FTIR/DSC under Non-Oxidative Conditions.

This paper presents the thermal behavior of polymer microspheres based on glycidyl methacrylate (GMA) and crosslinking agents benzene-1,4-diylbis(2-methylprop-2-enoate) (1,4DMB) and trimethylolpropane trimethacrylate (TRIM) before and after functionalization with thioglycolic acid (TGA). The thermal stability of the polymers was determined using thermogravimetric analysis and differential scanning calorimetry under non-oxidizing conditions. The evolved gases were detected by FTIR and NMR spectroscopy, and the chemical structure of solid residues after preheating was assessed by FTIR/ATR spectroscopy. The post-functionalized microspheres showed higher thermal stability (within 270-290 °C) than the initial copolymers (within 240-250 °C). In this paper, examples of decomposition patterns of polymer microspheres before and after functionalization are presented. The decomposition of the initial microspheres starts with the emission of GMA monomers, acrolein, carbon dioxide, and the formation of unsaturated bonds in the solid residue. In the case of functionalized microspheres, degradation involves the transesterification of ester groups with the -SH groups, resulting in the emission of carbonyl sulfide, acrolein and carbon dioxide. Furthermore, lactone groups are created in the solid residue. The degradation of the functionalized copolymers is a complex process due to their crosslinked structure, rendering the identification of all the degradation products unattainable.

Supplementation of protease and different nutrient density diets in growing-finishing pigs.

This study was conducted to investigate the effects of protease supplementation and different nutrient density of diets in growing-finishing pigs. A total of one hundred-eight crossbred growing pigs ([Landrace × Yorkshire] × Duroc) with an initial body weight (BW; 18.74 ± 3.46 kg) were used for 15 weeks. Pigs were randomly assigned to six dietary treatments with 6 replicates of 3 pigs per pen in a 3 × 2 factorial through the following arrangement: Three groups of protease (1, Basal diets; 2, Protease A: 125 mg/kg protease derived from Streptomyces sps; 3, Protease B: 100 mg/kg protease derived from Bacillus licheniformis) at two different nutrient density diets (1, Basal requirement; 2, 0.94%-0.98% higher than requirement in dietary protein and 50 kcal/kg in energy). High nutrient (HN) diets showed higher average daily gain (ADG) (p < 0.05) and apparent total tract digestibility (ATTD) of crude protein (CP) (p < .0001) compared to basal nutrient (BN) diets during growing periods. Supplementation of protease showed higher BW (p < 0.05) and ADG (p < 0.05) compared to non-supplementation of protease during growing periods. Also, supplementation of protease showed higher ATTD of CP (p < 0.01), ATTD of gross energy (p < 0.05) and decreased blood urea nitrogen (BUN) level (p = 0.001) compared to non-supplementation of protease during finishing periods. Pigs which fed the protease showed decreased ammonia (NH3) emissions (p < 0.05) during experiment periods and decreased hydrogen sulfide (H2S) emissions (p < 0.01) during finishing periods. Interactions between nutrient density and protease were observed, which decreased the feed conversion ratio (p < 0.05) in HN diets without protease compared to BN diets without protease during weeks 4 to 6. Also, interaction between nutrient density and protease was observed, which resulted in improved ATTD of CP (p < 0.01) in response to PTA supplementation with HN diets during the finishing period. In conclusion, supplementation of protease reduces NH3 in feces and BUN in whole blood by increasing the digestibility of CP and improves growth performance. Also, diets with high nutrient density improved growth performance and nutrient digestibility in growing periods.

Sub-dew point claus process for reducing hydrogen sulfide emission from sulfur recovery units

Increasing the efficiency of the sulfur recovery and decreasing the hydrogen sulfide emission are significant from both economic and environmental aspects. The cold bed adsorption (CBA) process is an approach to address the above concerns. The bench scale CBA experiments including adsorption and regeneration stages at temperatures of 140 °C and 280 °C are investigated against an industrial scale modified Claus process by using a commercial Al2O3 catalyst. Implementing CBA increases the H2S conversion of a modified Claus process sulfur recovery unit about 5%, but it is not efficient to convert CS2 and COS to the elemental sulfur. Period times of 12, 7 and 3 h are appropriate for the adsorption, desorption and cooling stages, respectively. After cycles of CBA process, the surface area and pore volume of the commercial Al2O3 Claus catalyst decrease from 385 m2/g and 0.34 cm3/g to 337 m2/g and 0.31 cm3/g, respectively as a result of condensing the elemental sulfur inside its micro- and meso- pores. The proposed CBA process is applicable to reduce the H2S emission, CAPEX and OPEX of sulfur recovery units.