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

Rapid detection of multiple gas mixtures and evaluation of harmful gas removal efficiency in a deck decompression chamber using dynamic switching mass spectrometry

The multiple gas mixtures in the deck decompression chamber (DDC) serve as a life-sustaining medium for divers to adapt to high-pressure environments and to safely decompress after saturation diving operations. However, due to the complexity of the gas composition and the wide concentration range, there is currently no technique that can rapidly detect all gases in the DDC. In this study, we developed a photoinduced chemical ionization (pCI) and electron impact (EI) dynamic switching mass spectrometry system. This technique was applied to investigate the spatial distribution uniformity of respiratory gases within the DDC at pressures of 0.13 MPa, 0.6 MPa, and 1.5 MPa, as well as the removal efficiency of toxic gases at 1.5 MPa. The switching stability time of pCI/EI dynamic switching mass spectrometry was 30 s per cycle, with optimal detection performance metrics including a detection limit down to 0.58 ppb (H2S), a fastest response time of 2 s (for CO2 and H2S), sensitivity up to 62.97 counts per ppb (H2S), and an overall concentration detection range spanning from 1.0 × 10-9 v/v (1 ppb) to 4.5 × 10-1 v/v (45%), covering the requirements for all target gases. At the three pressure levels, the spatial distribution uniformity of O2 in the DDC was 0.34%, 0.21%, and 0.08%, with the time to reach uniform distribution being 5 min, 3 min, and 1 min, respectively. For CO2, the spatial distribution uniformity was 0.62%, 1.61%, and 1.30%, with uniform distribution achieved in 10 min, 7 min, and 5 min, respectively. The removal efficiencies for harmful gases such as CO2, CH4, NH3, and H2S were 39.57%, 10.75%, 14.29%, and 3.96%, respectively. Under high-pressure conditions, O2 and CO2 rapidly achieved uniform distribution within the DDC. The pCI/EI dynamic switching mass spectrometry technology provides a rapid detection method for multicomponent gases in enclosed chambers like the DDC. This technology holds significant implications for the life support and operational efficiency of personnel involved in shipwreck salvage, underwater construction, and deep-sea exploration of marine resources.

Characterization of three novel dimethyl disulfide degrading bacteria and their potential degradation pathways

Dimethyl disulfide (DMDS) is an odor compound characterized by the lowest olfactory threshold and high toxicity. It is indispensable to explore the bacteria with high resistance and degradation efficiency to DMDS. Acinetobacter lwoffii, Pseudomonas mendocina, and Myroides odoratus were isolated from kitchen waste. After 6 days of individual treatment, the removal rates were 34.22 %, 40.95 %, and 41.94 % respectively. The DMDS metabolic pathways based on metagenomic assays were discovered to be incomplete due to the insufficient annotation of some key genes in the current database. Following 3 days of treatment with bacterial consortia at ratios of 5:1 for A. lwoffii C2/ M. odoratus C7 and 1:1:1 for the three strains achieved 100 % DMDS removal. Additionally, the consortia reduced hydrogen sulfide (H2S) and dimethyl sulfide (DMS).This discovery broadens the spectrum of bacteria exhibiting high tolerance and efficient degradation of DMDS, with significant implications for DMDS removal and odor treatment.

Phosphate, magnesium containing additives and biochar regulate compost maturity and synergistically reduce odor emission in chicken manure composting: Role of physicochemical, bacterial and fungal dynamics

This study explored the odor composition and emission in chicken manure composting process, employing chemical fixatives and biochar to mitigate odors effectively. Compost maturity, ammonia, sulfur-containing odor emissions, as well as the bacterial and fungal community structure were analyzed to assess composting performance and mechanisms. The results indicated that four malodorous substances were identified as major contributors: dimethyl disulfide (Me2S2), hydrogen sulfide (H2S), methyl sulfide (Me2S), and ammonia (NH3). Biochar (BC) augmented compost maturity by enhancing the relative abundance of Thermobifida and Saccharomonospora, while reducing the emission of total malodorous sulfur-containing components by 65.3% by mitigating Halocella and Hydrogenispora, albeit without affecting NH3 emissions. Superphosphate (SP) mitigated malodorous sulfur-containing components by 51.3% through its calcium (Ca) components and associated bacteria (Pseudomonas, Halocella and Hydrogenispora). Notably, magnesium (Mg) emerged as a limiting factor for NH3 fixation by SP. The combination of SP and magnesium sulfate (MS) decreased NH3 emissions by 47.9% via the formation of struvite crystals (MgNH4PO4) and further reduced the emission of malodorous sulfur-containing components by 60.0% by enhancing functional fungi inhibiting malodorous substance production. Ultimately, the combined application of BC, SP, and MS yielded the most significant odor reduction effects, with reductions of 86.8%, 35.3%, 92.8%, and 38.8% observed in Me2S2, H2S, Me2S, and NH3, respectively.

Performance evaluation and microbial community succession analysis of co-composting treatment of refinery waste activated sludge

Refinery waste activated sludge (RWAS) is riched in organic matter with energy recovery value, while unique petroleum components in RWAS may pose challenges to the recycling process. Aerobic composting technology is an effective means of organic solid waste resource treatment, which can convert organic solid waste into fertilizer for agriculture. This study explores the effect of petroleum components on the performance of RWAS composting by co-composting it with chicken manure. The results showed that more than 65% of petroleum was removed by aerobic composting. After composting, germination index (GI) exceeded 80%, and a humic acid to fulvic acid ratio (HA/FA) was greater than 1. These results signified that the petroleum components slightly affect the harmless and recycling of RWAS. The microbial community succession found that Firmicutes (54.11-91.96%) and Ascomycota (82.35-97.21%) emerged as the dominant phyla during the thermophilic phase of composting. Thermobifida, norank_f__Limnochordaceae and Kernia were the key microorganism in the degradation of petroleum and the humification of composting, and reduced the phytotoxicity of composting products. Redundancy analysis found that the degradation of petroleum was conducive to the formation of humic acid. These findings indicate that aerobic composting technology can remove petroleum components in RWAS and convert them into composted fertilizers, providing key technical support for managing RWAS in a sustainable and environmentally friendly manner.

Insights into effects of thermotolerant nitrifying and sulfur-oxidizing inoculants on nitrogen-sulfur co-metabolism in sewage sludge composting

In this study, high temperature thermotolerant nitrifying bacteria (TNB) and high temperature thermotolerant sulfide oxidizing bacteria (TSOB) were obtained from compost samples and inoculated into sewage sludge (SS) compost. The effects of inoculation on physical and chemical parameters, ammonia and hydrogen sulfide release, nitrogen form and sulfur compound content change and physical-chemical properties during nitrogen and sulfur conversion were studied. The results showed that inoculation of TNB and TSOB increased the temperature, pH, OM degradation, C/N ratio and germination index (GI) of compost. Compared with the control treatment (CK), the addition of inoculants reduced the release of NH3 and H2S, and transformed them into nitrogen and sulfur compounds, the hydrolysis of polymeric ferrous sulfate was promoted, resulting in relatively high content of sulfite and sulfate. At the same time, the physical and chemical properties of SS have a strong correlation with nitrogen and sulfur compounds.

Effects of thermophilic bacteria inoculation on maturity, gaseous emission and bacterial community succession in hyperthermophilic composting

Hyperthermophilic composting, characterized by temperatures equal to or exceeding 75 °C, offers superior compost maturity and performance. Inoculation with thermophilic bacteria presents a viable approach to achieving hyperthermophilic composting. This study investigates the effects of inoculating thermophilic bacteria, isolated at different temperatures (50 °C, 60 °C, and 70 °C) into compost on maturity, gaseous emissions, and microbial community dynamics during co-composting. Results indicate that the thermophilic bacteria inoculation treatments exhibited peak temperature on Day 3, with the maximum temperature of 75 °C reached two days earlier than the control treatment. Furthermore, these treatments demonstrated increased bacterial richness and diversity, along with elevated relative abundances of Firmicutes and Proteobacteria. They also fostered mutualistic correlations among microbial species, enhancing network connectivity and complexity, thereby facilitating lignocellulose degradation. Specifically, inoculation with thermophilic bacteria at 60 °C increased the relative abundance of Thermobifida and unclassified-f-Thermomonosporaceae (Actinobacteriota), whereas Bacillus, a thermophilic bacterium, was enriched in the 70 °C inoculation treatment. Consequently, the thermophilic bacteria at 60 °C and 70 °C enhanced maturity by 36 %-50 % and reduced NH3 emissions by 1.08 %-27.50 % through the proliferation of thermophilic heterotrophic ammonia-oxidizing bacteria (Corynebacterium). Moreover, all inoculation treatments decreased CH4 emissions by 6 %-27 % through the enrichment of methanotrophic bacteria (Methylococcaceae) and reduced H2S, Me2S, and Me2SS emissions by 1 %-25 %, 47 %-63 %, and 15 %-53 %, respectively. However, the inoculation treatments led to increased N2O emissions through enhanced denitrification, as evidenced by the enrichment of Truepera and Pusillimonas. Overall, thermophilic bacteria inoculation promoted bacteria associated with compost maturity while attenuating the relationship between core bacteria and gaseous emissions during composting.

Analysis of latrine fecal odor release pattern and the deodorization with composited microbial agent

As an important source of malodor, the odor gases emitted from public toilet significantly interfered the air quality of living surroundings, resulting in environmental problem which received little attention before. Thus, this paper explored the odor release pattern of latrine feces and deodorization effect with composited microbial agent in Chengdu, China. The odor release rules were investigated in sealed installations with a working volume of 9 L for 20 days. The odor units (OU), ammonia (NH3), hydrogen sulfide (H2S) and total volatile organic compounds (TVOC) were selected to assess the release of malodorous gases under different temperature and humidity, while the highest malodor release was observed under 45℃, with OU and TVOC concentration was 643.91 ± 2.49 and 7767.33 ± 33.50 mg/m3, respectively. Microbes with deodorization ability were screened and mixed into an agent, which composited of Bacillus amyloliquefaciens, Lactobacillus plantarum, Enterococcus faecalis and Pichia fermentans. The addition of microbial deodorant could significantly suppress the release of malodor gas during a 20-day trial, and the removal efficiency of NH3, H2S, TVOC and OU was 81.50 %, 38.31 %, 64.38 %, and 76.86 %, respectively. The analysis of microbial community structure showed that temperature was the main environmental factor driving the microbial variations in latrine feces, while Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes were the main bacteria phyla involved in the formation and emission of malodorous gases. However, after adding the deodorant, the abundance of Bacteroidetes, Proteobacteria and Actinobacteria were decreased, while the abundance of Firmicutes was increased. Furthermore, P. fermentans successfully colonized in fecal substrates and became the dominant fungus after deodorization. These results expanded the understanding of the odor release from latrine feces, and the composited microbial deodorant provided a valuable basis to the management of odor pollution.

Semi-permeable membrane-covered high-temperature aerobic composting: A review

Semi-permeable membrane-covered high-temperature aerobic composting (SMHC) is a suitable technology for the safe treatment and disposal of organic solid waste as well as for improving the quality of the final compost. This paper presents a comprehensive summary of the impact of semi-permeable membranes centered on expanded polytetrafluoroethylene (e-PTFE) on compost physicochemical properties, carbon and nitrogen transformations, greenhouse gas emission reduction, microbial community succession, antibiotic removal, and antibiotic resistance genes migration. It is worth noting that the semi-permeable membrane can form a micro-positive pressure environment under the membrane, promote the uniform distribution of air in the heap, reduce the proportion of anaerobic area in the heap, improve the decomposition rate of organic matter, accelerate the decomposition of compost and improve the quality of compost. In addition, this paper presents several recommendations for future research areas in the SMHC. This investigation aims to guide for implementation of semi-permeable membranes in high-temperature aerobic fermentation processes by systematically compiling the latest research progress on SMHC.

Contribution of sulfur-containing precursors to release of hydrogen sulfide in sludge composting

Hydrogen sulfide (H2S) production during composting can impact the environment and human health. Especially during the thermophilic phase, H2S is discharged in large quantities. However, in sludge composting, the contributions of different sulfur-containing precursors to H2S fluxes, key functional microorganisms, and key environmental parameters for reducing H2S flux remain unclear. Analysis of cysteine (Cys), methionine (Met), and sulfate (SO42-) concentrations, multiple stepwise regression analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis of metagenomes showed that Cys was the main contributor to the production of H2S and that Met was among the main sources during the first three days of composting, while the SO42- contribution to H2S was negligible. Fifteen functional genera involved in the conversion of precursors to H2S were identified by co-occurrence network analysis. Only Bacillus showed high temperature resistance (>50 °C) and the ability to reduce H2S. Redundancy analysis showed that total carbon (64.0 %) and pH (23.3 %) had significant effects on functional bacteria. H2S had a quadratic relationship with sulfur-containing precursors. All microbial network sulfur-containing precursors metabolism modules showed a highly significant relationship with Cys.

Determining the soil odor control area: A case study of an abandoned organophosphorus pesticide factory in China

Currently, soil odor-active substance screening and evaluation methods for contaminated sites are underdeveloped, with unclear treatment objectives and areas. Consequently, some sites suffer from odor issues during and even after remediation. This study focused on an organophosphorus pesticide factory site in Guangdong Province, China. It established a method of determining the odorant control area using a comprehensive approach combining instrumental and olfactory soil sample analyses. The main odor-active substances identified were ethylbenzene, phenol, m, p-xylene, styrene, toluene, and o-xylene, with odorant control values (the limit of odor-active substance contents) of 35.2, 28.1, 8.0, 11.3, 40.2 and 89.3 mg/kg respectively. Instrumental analysis of soil samples revealed 11 sampling points where the main odor-causing substances exceeded standard levels. Among the substances, ethylbenzene (1.48E+04 mg/kg) had the highest content, exceeding the limit up to 421-fold. Olfactory analysis indicated 14 sampling points with odor intensity surpassing the standard (OI > 2). Based on the instrumental analysis results and the odorant control value, the initial estimated odor control area (area with the risk of odor nuisance) was 5.64E+03 m2. Incorporating the olfactory analysis findings, the control area was adjusted by 1.25E+03 m2, leading to a final calculated soil odor control area of 6.89E+03 m2 for the study site. The comprehensive approach to analyzing soil samples for odor control can help evaluate the extent of soil odor pollution in contaminated sites and provide a scientific basis for effectively removing and managing odor-causing substances in soil.

Addition of exogenous microbial agents increases hydrogen sulfide emissions during aerobic composting of kitchen waste by improving bio-synergistic effects

The effect of microbial agents (MA) on hydrogen sulfide (H₂S) emissions in the compost is still a controversial issue. This study examined the effects and microbial mechanisms of MA on H₂S emissions during the composting of kitchen waste. The results showed that MA addition can promote sulfur conversion to elevate H₂S emissions by approximately 1.6 ∼ 2.8 times. Structural equations demonstrated that microbial community structure was the dominant driver on H₂S emissions. Agents reshaped the compost microbiome, showing more microorganisms participated in sulfur conversion, and enhanced the connection between microorganisms and functional genes. The relative abundance of keystone species associated with H₂S emissions increased after adding MA. Particularly, the sulfite and sulfate reduction processes were intensified, as evidenced by an increasing in the abundance and pathways cooperation of sat and asrA after MA addition. The outcome provides deeper insights into MA on regulating the mitigation of H₂S emissions in compost.

Effects of microbial inoculum on microbial community and enzyme activity involved in nitrogen-sulfur metabolism during sewage sludge composting

The purpose of this study was to access the effects of thermotolerant nitrifying microorganisms and sulfur-oxidizing bacteria on microbial community and enzyme activity involved in nitrogen‑sulfur metabolism during laboratory-scale sewage sludge (SS) composting，and to do a microbial-environmental factor association analysis to promote composting key species for nitrogen‑sulfur transformation in the body. The microbial community structure and the activities variation of six key enzyme involved were detected. The microbial inocula added had little impact on the diversity of the microbial community but changed its succession direction, and the abundance of Actinobacteria was decreased obviously of inoculation treatment (TR). The three dominant genera and indicator species in TR were significantly correlated with the conversion of nitrogen and sulfur. The addition of microbial inocula promoted the conversion of nitrogen and sulfur in SS compost, and increased the activities of the key enzymes and the microbial genera involved in nitrogen‑sulfur conversion. In other words, the nitrification and sulfur oxidation were enhanced simultaneously in the later stage of composting in TR.

Review of inventory data for the biological treatment of sewage sludge

The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions.

Emission of volatile sulphur compounds during swine manure composting: Source identification, odour mitigation and assessment

This study aimed to identify the sources of volatile sulphur compounds (VSCs) and evaluate their mitigation by ferric oxide (Fe₂O₃) during swine manure composting. Four chemicals, including l-cysteine, l-methionine, sodium sulphite, and sodium sulphate, were further added to simulate organic and inorganic sulphur-containing substances in swine manure to track VSC sources during composting. Results show that sulphur simulants induced the emission of six common VSCs, including methyl sulphide (Me₂S), dimethyl sulphide (Me₂SS), carbonyl sulphide (COS), carbon disulphide (CS₂), methyl mercaptan (MeSH), and ethyl mercaptan (EtSH), during swine manure composting. Of them, COS, CS₂, MeSH and Me₂SS were predominantly contributed by the biodegradation of methionine and cysteine, while Me₂S and EtSH were dominated by the reduction of sulphite and sulphate. Further Fe₂O₃ addition at 1.5 % of total wet weight of composting materials immobilized elemental sulphur and inhibited sulphate reduction to reduce the emission of VSCs by 46.7-80.9 %. Furthermore, odour assessment indicated that adding Fe₂O₃ into composting piles significantly reduced the odour intensity level to below 4, the odour value of VSCs by 47.1-81.3 %, and thus the non-carcinogenic risk by 68.4 %.

An Alternative to Vermiculite: Composting on Tropical Islands Using Coral Sand to Enhance Nitrogen Retention during Ventilation

Reducing nitrogen loss during composting with forced ventilation was comprehensively investigated in this study. Coral sand was tailored in the co-composting in the co-composting of sludge and litters. The physicochemical results revealed that forced ventilation prolonged the thermophilic phase and accelerated the substrate decomposition. With the addition of 10% native coral sand, the amount of nitrogen loss decreased by 9.2% compared with the original group. The microbial community evaluation revealed that the effect of forced ventilation on colony abundance was significantly greater than that of adding coral sand. This study demonstrated that when composting on a tropical island, adding coral sand under forced ventilation was a viable solution for realizing sustainable development.

Spatiotemporal footprints of odor compounds in megacity's food waste streams and policy implication

Odor pollution is one of the most critical issues in food waste (FW) recycling and has significant implications for human health. However, knowledge of their occurrence and spatiotemporally dynamic in urban FW streams is limited, making it not conducive to implement targeted odor management. This work followed the occurrence of 81 odor compounds (OCs) in nine FW-air environments along the Shanghai's FW streams for one year. Results showed that NH₃, acetic acid, acetaldehyde, acetone, 2-butanone, and methylene chloride were consistently the predominant OCs, despite the distinct differences in OCs profiles across seasons and treatment sites. Ridge regression and principal coordinate analysis demonstrated that seasons might play a non-negligible role in shaping odor profiles, and ambient temperature and humidity could account for the seasonal variation in OCs levels. Based on the modified fuzzy synthetic evaluation system, the screened priority pollutants in different FW-air environments were found broadly similar and the regulated air pollutants released via FW should be expanded to aldehyde and ketone compounds, especially for acetaldehyde. To our knowledge, this study is the first to track the spatiotemporal footprints of OCs within urban FW streams, and provides new insights into the control policy on FW-derived odor issues for megacities.

Correlation of microbial dynamics to odor production and emission in full-scale sewage sludge composting

Odor is inevitably produced during sewage sludge composting, and the subsequent pollution hinders the further development of composting technologies. Third-generation high-throughput sequencing was used to analyze microbial community succession, and the correlations between odor and microbial communities were evaluated. Hydrogen sulfide (47.5-87.9 %) and ammonia (9.4-49.9 %) contributed majorly to odor emissions, accounting for 93.7-98.5 % of the emissions. Volatile sulfur compounds were mainly produced in the mesophilic and pre-thermophilic phases (43.0-83.4 %), whereas ammonia was mainly produced in the thermophilic phase (52.1-59.4 %). Microorganisms dominant in the mesophilic and thermophilic phases correlated positively with odor production in the following order: Rhodocyclaceae > Clostridiaceae_1 > Hyphomicrobiaceae > Acidimicrobiales > Family_XI, whereas those dominant in the cooling phase showed negative correlations with odor production in the following order: Bacillus > Sphingobacteriaceae > Pseudomonadaceae > DSSF69 > Chitinophagaceae. The back mixing of mature compost is expected to serve as an economical measure for controlling odor during sewage sludge composting.

Mechanism of digestate-derived biochar on odorous gas emissions and humification in composting of digestate from food waste

Emissions of odorous gases and prolonged composting duration are the key concerns in the composting of digestate from food waste (DFW). In this study, different amounts of biochar derived from DFW (BC-DFW) were introduced in the composting process of DFW to decrease the emissions of ammonia (NH₃) and volatile sulfur compounds (VSCs) and composting duration. The addition of BC-DFW increased the temperature and germination index during DFW composting. The group with 25% BC-DFW exhibited a 30% smaller composting duration. Significant amounts of NH₃ and VSCs emissions were observed in the initial phase of DFW composting. Dimethyl disulfide (DMDS) was a prominent contributor to the odor associated with VSCs. The addition of BC-DFW facilitated the adsorption of NH₃ and VSCs, and the corresponding contents decreased by 5-21% and 15-20%, respectively. Moreover,the BC-DFW accelerated the transformation of ammonium-nitrogen (NH₄⁺-N) to nitrate-nitrogen (NO₃^--N), thereby alleviating the NH₃ volatilization. The addition of 25% BC-DFW minimized the NH₃ emission and enhanced the generation of humic-acid-like matter, thereby promoting humification. Therefore, the addition of 25% BC-DFW was optimal for promoting the degradation of organic matter and humification and odor emission reduction (e.g., NH₃, DMDS).

Determination of Odor Air Quality Index (OAQII) Using Gas Sensor Matrix

This article presents a new way to determine odor nuisance based on the proposed odor air quality index (OAQII), using an instrumental method. This indicator relates the most important odor features, such as intensity, hedonic tone and odor concentration. The research was conducted at the compost screening yard of the municipal treatment plant in Central Poland, on which a self-constructed gas sensor array was placed. It consisted of five commercially available gas sensors: three metal oxide semiconductor (MOS) chemical sensors and two electrochemical ones. To calibrate and validate the matrix, odor concentrations were determined within the composting yard using the field olfactometry technique. Five mathematical models (e.g., multiple linear regression and principal component regression) were used as calibration methods. Two methods were used to extract signals from the matrix: maximum signal values from individual sensors and the logarithm of the ratio of the maximum signal to the sensor baseline. The developed models were used to determine the predicted odor concentrations. The selection of the optimal model was based on the compatibility with olfactometric measurements, taking the mean square error as a criterion and their accordance with the proposed OAQII. For the first method of extracting signals from the matrix, the best model was characterized by RMSE equal to 8.092 and consistency in indices at the level of 0.85. In the case of the logarithmic approach, these values were 4.220 and 0.98, respectively. The obtained results allow to conclude that gas sensor arrays can be successfully used for air quality monitoring; however, the key issues are data processing and the selection of an appropriate mathematical model.

Inhibitory Effects of the Addition of KNO3 on Volatile Sulfur Compound Emissions during Sewage Sludge Composting

Odor released from the sewage sludge composting process often has a negative impact on the sewage sludge treatment facility and becomes a hindrance to promoting compost technology. This study investigated the effect of adding KNO₃ on the emissions of volatile sulfur compounds, such as hydrogen sulfide (H₂S), dimethyl sulfide (DMS), and carbon disulfide (CS₂), during sewage sludge composting and on the physicochemical properties of compost products, such as arylsulfatase activity, available sulfur, total sulfur, moisture content, and germination index. The results showed that the addition of KNO₃ could inhibit the emissions of volatile sulfur compounds during composting. KNO₃ can also increase the heating rate and peak temperature of the compost pile and reduce the available sulfur loss. The addition of 4% and 8% KNO₃ had the best effect on H₂S emissions, and it reduced the emissions of H₂S during composting by 19.5% and 20.0%, respectively. The addition of 4% KNO₃ had the best effect on DMS and CS₂ emissions, and it reduced the emissions of DMS and CS₂ by 75.8% and 63.0%, respectively. Furthermore, adding 4% KNO₃ had the best effect from the perspective of improving the germination index of the compost.

Greenhouse Gas Emissions From Biofilters for Composting Exhaust Ammonia Removal

Emissions of odorous compounds, such as ammonia (NH₃), from composting have negative agronomic and environmental impacts. A biofilter is widely used for NH₃ removal, with one of its potential detrimental by-products being nitrous oxide (N₂O), which is a higher warming potential greenhouse gas (GHG). The aim of the study was to evaluate the effect of empty bed retention time (EBRT) on GHG emissions from biofilters for removing NH₃ from composting. Composting experimental trials lasted 6 weeks, and composting materials were mixtures of dead pigs and manure. Three groups of biofilters with 1.2 m-height, 0.3 m-inner diameter, and 1.0 m media depth were conducted with EBRT of 30, 60, and 100s, respectively. Each treatment was performed in triplicate, and the gas was monitored using the dynamic emission vessel method. The Spearman’s correlation analysis showed a significantly positive correlation between inlet concentrations (ICs) of NH₃ and increased N₂O concentrations: ρ = 0.707, 0.762, and 0.607 with p ≤ 0.0001 for biofilters with EBRT of 30, 60, and 100s, respectively. The fraction of NH₃-N denitrified into N₂O-N in biofilters with EBRT of 60 and 100s was higher than that with EBRT of 30s. The total global warming potential (GWP) increased by 126%, 162%, and 144% for biofilters with EBRT of 30, 60, and 100s, respectively. These results indicated that biofilters with longer EBRT will lead to higher GWP production. Future research on odorous mitigation for composting with biofilters should focus more on greenhouse gas emissions.

Ethylene dimethacrylate used as an NH3 adsorbent with high adsorption capacity and selectivity

NH₃ molecularly imprinted polymers (NH₃-MIPs) were synthesized that could successfully separate and recover NH₃ during sludge aerobic composting; however, increased toluene usage during the adsorbent preparation incurred a high cost and severe environmental risks. The purpose of this study was to reduce toluene usage by optimizing the reagent composition of NH₃-MIPs, based on maintaining a high NH₃ adsorption capacity and selectivity. Five adsorbent groups, including NH₃-MIPs, and NH₃-Ethylene dimethacrylate adsorbents (NH₃-EGDMA) with 0%, 75%, 90%, and 100% toluene reduction efficiencies, were prepared and tested for their adsorption performance. The results showed that NH₃-EGDMA with 75% toluene reduction not only had a high NH₃ adsorption capacity (104.42 mg g^-1) but also had a high separation factor for NH₃/methyl sulfide (3121) and NH₃/dimethyl disulfide (4597). The adsorption mechanism was identified as a chemical force between NH₃ and NH₃-EGDMA with a 75% toluene reduction using the analysis of the kinetic model. This study significantly reduces NH₃ adsorbent cost as well as harm to the environment during the adsorbent preparation, which was beneficial to the popularization and application of this NH₃ adsorbent.

Analyses of deodorization performance of mixotrophic biotrickling filter reactor using different industrial and agricultural wastes as packing material

In this study, to efficiently remove malodorous gas and reduce secondary pollution under mixotrophic conditions, pine bark, coal cinder, straw and mobile bed biofilm reactor (MBBR) fillers were used as packing materials in a biological trickling filter (BTF) to simultaneously treat high-concentration H₂S and NH₃. The results showed that the removal rate of BTF-A filled with pine bark was the highest, which was 86.31% and 94.06% under the H₂S and NH₃ loading rates of 53.59 g/m³·h while the empty bed residence time (EBRT) was 40.5 s. The theoretical maximum load was obtained by fitting the kinetic curve, and the value were 90.09 g H₂S m^-³·h^-1 and 172.41 g NH₃ m^-³·h^-1. Meanwhile, after treating with 720 ppm of NH₃, the average concentration of NO₃^- in the BTF circulating fluid was only 127.58 mg/L, indicating the better performance of secondary pollutants control. Microbiological analysis showed that Dokdonella, Micropruina, Candidatus_Alysiosphaera, Nakamurella and Thiobacillus possessed high abundance at the genus level, and their entire percentage in four BTF reactors were 62.87%, 46.32%, 47.98%, and 57.35% respectively. It is worthwhile that the genera Comamonas and Trichococcus with heterotrophic nitrification and aerobic denitrification capabilities and proportion of 3.66%, 1.45%, 5.43%, and 3.23% were observed in four reactors.

Preparation of sludge-based activated carbon for adsorption of dimethyl sulfide and dimethyl disulfide during sludge aerobic composting

Emission of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) during sludge aerobic composting has limited the use and development of this economical sludge treatment process. In this study, cheap and easily available sludge was used as raw material for the preparation of adsorbents to eliminate DMS and DMDS. A series of sludge-based activated carbons (SACs) were prepared by acid or base activation, and coconut shell mix was also assessed. The results revealed that SAC preparation by KOH activation without coconut shell mix could significantly enhance the surface area and pore volume of SAC, and showed the maximum adsorption capacity for DMS (53.45 mg g^-1) and DMDS (151.28 mg g^-1). In addition, SAC had a good adsorption effect on a mixture of DMS and DMDS. The SAC adsorbents could efficiently adsorb DMS and DMDS after four cycles of regeneration. Thermodynamic and kinetic analyses demonstrated that adsorption between the SAC and DMS/DMDS was via physical adsorption. The SAC developed in this study utilized waste in a useful way that could significantly reduce the cost of adsorbents and use them for odor elimination during sludge aerobic composting.

Nitrogen transformation and dynamic changes in related functional genes during functional-membrane covered aerobic composting

The effects of functional membrane covering (FMC) on nitrogen transformation and related functional genes during aerobic composting were investigated by performing a comparable experiment. The FMC increased the pile temperature, promoted compost maturity, and decreased nitrogen loss. The FMC reduced NH₃ and N₂O emissions by 7.34% and 26.27%, respectively. The water film and the micro-positive pressure environment under the membrane effectively prevented NH₃ escaping. The FMC up-regulated the amoA gene copy number (promoting NH₃/NH₄⁺ oxidation). The reduction of N₂O emission by the FMC was mainly related to denitrifying genes (nirK, nirS, and nosZ). The FMC down-regulated the nirK and nirS gene copy numbers, but up-regulated the nosZ gene copy number. Pearson correlation analysis indicated that the functional membrane characteristics and differences between the composting pile environments caused by the FMC significantly affected the nitrogen forms and the related functional genes. The FMC strongly decreased nitrogen emissions and therefore conserved nitrogen.

Determination of Dose–Response Relationship to Derive Odor Impact Criteria for a Wastewater Treatment Plant

Municipal wastewater treatment plants (WWTPs) inside cities have been the major complained sources of odor pollution in China, whereas there is little knowledge about the dose–response relationship to describe the resident complaints caused by odor exposure. This study explored a dose–response relationship between the modelled exposure and the annoyance surveyed by questionnaires. Firstly, the time series of odor concentrations were preliminarily simulated by a dispersion model. Secondly, the perception-related odor exposures were further calculated by combining with the peak to mean factors (constant value 4 (Germany) and 2.3 (Italy)), different time periods of “a whole year”, “summer”, and “nighttime of summer”, and two approaches of odor impact criterion (OIC) (“odor-hour” and “odor concentration”). Thirdly, binomial logistic regression models were used to compare kinds of perception-related odor exposures and odor annoyance by odds ratio, goodness of fit and predictive ability. All perception-related odor exposures were positively associated with odor annoyance. The best goodness of fit was found when using “nighttime of summer” in predicting odor-annoyance responses, which highlights the importance of the time of the day and the time of the year weighting. The best predictive performance for odor perception was determined when the OIC was 4 ou/m3 at the 99th percentile for the odor exposure over time periods of nighttime of summer. The study of dose–response relationship could be useful for the odor management and control of WWTP to maximize the satisfaction of air quality for the residents inside city.

Linking the electron transfer capacity with the compositional characteristics of dissolved organic matter during hyperthermophilic composting

Redox-active functional groups in dissolved organic matter (DOM) can mediate reductions in organic pollutants and the passivation of heavy metals, which are related to the humification process of composting. Hyperthermophilic composting (HTC) has been shown to promote changes in the composition and structure of DOM and accelerate humification. However, how HTC affects the redox properties of DOM remains unclear. Here, we fractionated DOM into humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fraction to study their electron transfer capacities (ETC) and the relationship between ETC and compositional characteristics using electrochemical method and excitation-emission matrix-parallel factor analysis. HTC accelerated the formation of component 3 containing quinone-like moieties, which mainly existed in the HA, improving the electron accepting capacity (EAC) of DOM. The rapid degradation of component 4 containing tryptophan-like substances of HA, FA and HyI strengthened the electron donating capacity of DOM in HTC. Partial least squares path model also showed that compositional changes and the stronger ETC of DOM in HTC had a positive effect on the maturity degree, revealing that the EAC of HA could be used as a maturity index for compost. This study advances our understanding of the humification process and the contamination control mechanism of HTC.

Residuals, sludge, and biosolids: Advancements in the field

Advancements in the field of residuals, sludge, and biosolids have been made in 2019. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings throughout 2019 and includes brief summaries from over 125 articles. The review is organized in sections including life cycle and risk assessments; characteristics, quality, and measurement including micropollutants, nanoparticles, pathogens, and metals; sludge treatment technologies including dewatering, digestion, composting, and wetlands; disposal and reuse including adsorbents, land application and agricultural uses, nutrient recovery, and innovative uses; odor and air emissions; and energy issues.

Health impact of odor from on-situ sewage sludge aerobic composting throughout different seasons and during anaerobic digestion with hydrolysis pretreatment

Aerobic composting and anaerobic digestion with hydrolysis pretreatment are two mainstream methods used to recycle and reclaim sewage sludge. However, during these sludge treatment processes, many odors are emitted that may cause severe emotional disturbance and health risks to those exposed. This study identified odor pollution (i.e. sensory influence, odor contribution, and human risks) from samples collected during sludge aerobic composting throughout different seasons as well as during anaerobic digestion with hydrolysis pretreatment. Odor intensity, odor active values, and permissible concentration-time weighted averages for ammonia and five volatile sulfur compounds were assessed. The results revealed serious odor pollution from all sampling sites during aerobic composting, especially in winter. Excessively strong odors were identified in the composting workshop, with total odor active values between 997 and 8980 which accounted for 78.45%-96.18% of the total sludge aerobic composting plant. Levels of ammonia and dimethyl disulfide in the ambient air were high enough to harm employees' health. During anaerobic digestion, excessively strong odors were identified in dehydration workshop 2, and the total odor active values of six odors reached 32,268, with ammonia and hydrogen sulfide levels significant enough to harm human health.

Synthesis of ammonia molecularly imprinted adsorbents and ammonia adsorption separation during sludge aerobic composting

Ammonia (NH₃) is the predominant harmful odor emitted from sludge aerobic composting plants, however, this NH₃ could be recycled and used as energy or nitrogen fertilizer. Therefore, the aim of this study was to use molecular imprinting technology to prepare an adsorbent that could separate NH₃ from mixed gases. An NH₃ molecular imprinted polymer (NH₃-MIP) was prepared by precipitation polymerization and optimal synthesis was determined by testing several different ratios of reaction components. NH₃ adsorption capacity of the optimal NH₃-MIP was 1.62 times that of non-imprinted material. NH₃ separation factors increased from 154 (dimethyl sulfides) and 217 (dimethyl disulfides) for non-imprinted material, to 213 (dimethyl sulfides) and 302 (dimethyl disulfides) for the NH₃-MIP. The adsorption mechanism was identified as physical adsorption and hydrogen bonding between H-O on the -COOH in NH₃-MIP and the nitrogen in NH₃. Effective desorption at 150 °C with vacuum maintained over 95% of the NH₃ adsorption capacity.

Insights into the storage stability of ammonia in polyester aluminum bags

A list of gaseous odorants such as ammonia (and hydrogen sulfide) are generally collected using rigid containers or flexible bags for quantitative analysis. The aim of this investigation was to assess the stability of polyester aluminum bags used for gaseous ammonia sampling and storage. To this end, ammonia standards were prepared at two concentration levels of low (7.8 ppm) and high concentrations (39 ppm) and stored in the polyester ammonia bags for durations of 0, 1, 2, 4, and 6 days. These samples were then analyzed at each interval by an impinger-based indophenol method utilizing a spectrophotometer. At each pre-set period, three different mass loadings of ammonia samples were collected from the storage bag to obtain response factors (RF) for comparison between different elapsed times set for the storage. Subsequently, the relative recovery values for each interval were computed by dividing the RF for each sampling day by that of the 0^th day. The relative recovery values for low and high concentration standards decreased with increasing storage time as 82.9% (day 1) to 36% (day 6) and 89.9% (day 1) to 59.7% (day 6), respectively. As such, the potentially superior recovery of ammonia from polyester aluminum bags was demonstrated (e.g., relative to other storage options introduced previously) to support its practical merit as storage media.

Impact of Composting Methods on Nitrogen Retention and Losses during Dairy Manure Composting

Currently, composting is one of the most effective methods for treating fecal waste on large-scale livestock and poultry farms, but the quality effects of different composting methods are different. In this study, we implemented four composting methods, including farmer compost (FC), anaerobic compost (AnC), mixed compost (MC), and aerobic compost (AC), to study the effects of different composting methods on nitrogen (N) losses while composting dairy manure. Our results showed that the germination indexes (GIs) of three of the composting treatments (AnC, MC, and AC) exceeded 80%, which met the maturity requirements for composted products. Ammonia (NH₃) emissions were the main contributor to nitrogen losses, while accumulated nitrous oxide (N₂O) emissions accounted for the lowest proportion of nitrogen losses. The cumulative N losses via the leachate of the AC treatment were the lowest and accounted for 0.38% of the initial total nitrogen (TN). The accumulated N losses of the AC, FC, AnC, and MC treatments accounted for 13.13% 15.98%, 15.08%, and 19.75%, respectively, of the initial TN. Overall, the AC method significantly reduced N losses via leachates, further reducing TN losses. This observation suggests that AC might be an appropriate method for highly efficient nitrogen management during dairy manure composting.