Odorous gas emissions from sewage sludge composting windrows affected by the turning operation and associated health risks

Emerging organic contaminants in sewage sludge: Current status, technological challenges and regulatory perspectives

Sewage sludge is the source and sink of pollutants. It accumulates a large number of organic contaminants such as endocrine disrupting compounds (EDCs), persistent organic pollutants (POPs), microplastics (MPs) and pharmaceuticals and personal care products (PPCPs), thus posing threats to the ecological environment and human health. The harmlessness of sludge provides the possibility to realize the recycling of resources. In this study, the VOSviewer software is used to visualize published papers related to organic contaminants in sewage sludge. The sources and hazards of emerging pollutants in sewage sludge are outlined, as well as the current state of research on composting, hydrothermal treatment, electrochemical technology, and advanced oxidation processes applied to this area. Key challenges facing this field include the low mineralization rate of contaminants, the ecological risks posed by degradation products, reasonableness of regulations, and effectiveness of enforcement. In conclusion, the integration of existing removal technologies, exploration of degradation pathways, and toxicity assessment of degradation products are the key to achieving the harmlessness and resource utilization of sewage sludge. Additionally, it is also necessary to strengthen the international consensus on the prevention and control of emerging organic contaminants in sewage sludge, improve regulatory frameworks, enhance law enforcement, and implement comprehensive management strategies.

Firmicutes primarily drive odor emission profiles in poultry manure treatments

Odor emission during livestock manure treatment poses a threat to the environment and human health. However, the odor emission profiles and related factors of commonly employed poultry manure treatments have rarely been studied. Here, we explored the odor emission profiles of 3 common poultry manure treatments in China, namely, ectopic fermentation beds (EFB), annular composting troughs (ACT) and air-drying rooms (ADR). The results revealed that the total odor concentrations in the EFB, ACT and ADR groups were 2407.67 ± 512.94, 13444.00 ± 1269.92 and 621.33 ± 59.27, respectively. The ACT had the greatest number of odorants (31), followed by the ADR (27) and the EFB (24). Methyl mercaptan, acetic acid, acetaldehyde, hydrogen sulfide, ammonia and acrolein were the key odorous compounds detected in all the treatments. ACT contained the greatest number of key odorants (11) and exhibited an extensive co-occurrence relationship with the bacterial community. The 3 poultry manure treatments exhibited significant differences in the beta diversities of the bacterial community. The phylum of most bacteria associated with key odorants was Firmicutes, and Enterococcus and Oceanobacillus were significantly positively correlated with methyl mercaptan. The bacterial functional groups were enriched in carbohydrate metabolism, amino acid metabolism and energy metabolism, and the functional genes shaped the odor emission patterns in the poultry manure treatments. Redundancy analysis demonstrated that odor emission in the 3 treatments was positively correlated with Firmicutes abundance, pH, electrical conductivity and moisture. Thus, our study provides a good understanding of odor emission profiles in poultry manure treatments and data for precise odor emission control during livestock production.

The production of methyl mercaptan is the main odor source of chicken manure treated with a vertical aerobic fermenter

The process of harmless treatment of livestock manure produces a large amount of odor, which poses a potential threat to human and livestock health. A vertical fermentation tank system is commonly used for the environmentally sound treatment of chicken manure in China, but the composition and concentration of the odor produced and the factors affecting odor emissions remain unclear. In this study, we investigated the types and concentrations of odors produced in the mixing room (MR), vertical fermenter (VF), and aging room (AR) of the system, and analyzed the effects of bacterial communities and metabolic genes on odor production. The results revealed that 34, 26 and 26 odors were detected in the VF, MR and AR, respectively. The total odor concentration in the VF was 66613 ± 10097, which was significantly greater than that in the MR (1157 ± 675) and AR (1143 ± 1005) (P < 0.001), suggesting that the VF was the main source of odor in the vertical fermentation tank system. Methyl mercaptan had the greatest contribution to the odor produced by VF, reaching 47.82%, and the concentration was 0.6145 ± 0.2164 mg/m3. The abundance of metabolic genes did not correlate significantly with odor production, but PICRUSt analysis showed that cysteine and methionine metabolism involved in methyl mercaptan production was significantly more enriched in MR and VF than in AR. Bacillus was the most abundant genus in the VF, with a relative abundance significantly greater than that in the MR (P < 0.05). The RDA results revealed that Bacillus was significantly and positively correlated with methyl mercaptan. The use of large-scale aerobic fermentation systems to treat chicken manure needs to focused on the production of methyl mercaptan.

Risk-oriented source apportionment and implications for mitigation strategies of VOCs in industrial parks: Insights from odor pollution and health risks

A typical industrial park in the upper reaches of the Yangtze River Economic Belt, which is 70 km from the Chongqing urban center, was used to investigate the occurrence and exposure of harmful volatile organic compounds (VOCs). An exposure risk method and a risk-oriented source apportionment approach were performed to assess the inhalation risks and apportion VOC sources, respectively. The quantitative relationships between risk factors and pollution sources were established, identifying key pathogenic and odorous VOCs. The quantitative emission reduction strategies were developed based on risk thresholds. Residents within the industrial parks face potential health risks due to pathogenic VOCs and nuisance odors, and workers in specific sectors experience two to six times higher risks than those in residential areas. Six risk sources were identified in the industrial park, ranked according to their contribution to VOC concentrations as follows: industrial sewage treatment (IST) (32.59 %), natural gas chemical industry (NGCI) (27.77 %), diesel vehicle exhaust (DVE) (12.04 %), pharmaceutical manufacturing industry (PMI) (11.14 %), chemical raw materials manufacturing (CRMM) (9.96 %), and iron and steel industry (ISI) (6.5 %). Among these, NGCI, IST, and CRMM were the top contributors to pathogenic risks, with contributions of 32.13 %, 29.71 %, and 21.71 % to non-carcinogenic risks, and 18.15 %, 19.87 %, and 27.99 % to carcinogenic risks, respectively. DVE produced significantly higher odor pollution compared to other sources, with intensities that were 3 to 10 times greater. The key pathogenic and odorous VOCs differ by source, resulting in varying control priorities for different VOC species. Reducing emissions from these six sources for 20 high-risk species (e.g., acrolein, 2-chlorotoluene, 1,2-dibromoethane, dichloromethane, and p-diethylbenzene) will simultaneously lower pathogenic and odor risks, with cumulative reduction rates ranging from 4.11 % to 93.75 %. This study provides quantitative control targets for VOCs from a health risk perspective, offering valuable guidance for developing risk management policies in industrial parks.

Innovative hyper-thermophilic aerobic submerged membrane distillation bioreactor for wastewater reclamation

For the first time, a hyper-thermophilic aerobic (>60 °C) bioreactor has been integrated with direct submerged membrane distillation (MD), highlighting its potential as an advanced wastewater treatment solution. The hyper-thermophilic aerobic bioreactor, operating up to 65 °C, is tailored for high organic removal, while MD efficiently produces clean water. Throughout the study, high removal rates of 99.5% for organic matter, 96.4% for ammonia, and 100% for phosphorus underscored the impressive adaptability of microorganisms to challenging hyper-thermophilic conditions and a successful combination with the MD process. Despite the extreme temperatures and substantial salinity accumulation reaching up to 12,532 μS/cm, the biomass of microorganisms increased by 1.6 times over a 92-day period, representing their remarkable resilience. The distillation flux ranged from 6.15 LMH to 8.25 LMH, benefiting from the temperature gradient in the hyper-thermophilic setting and the design of the tubular submerged MD membrane module. The system also excels in pH control, utilizing fewer alkali and nutritional resources than conventional systems. Meiothermus, Firmicutes, and Bacteroidetes, the three dominant species, played a crucial role, showcasing their significance in adapting to high salinity and decomposing organic matter.

Advances in understanding bioaerosol release characteristics and potential hazards during aerobic composting

Bioaerosol emissions and their associated risks are attracting increasing attention. Bioaerosols are generated during the pretreatment, fermentation, and screening of mature compost when processing various types of solid waste at composting plants (e.g., municipal sludge and animal manure). In this review, we summarize research into bioaerosols at different types of composting plants by focusing on the methods used for sampling bioaerosols, stages when emissions potentially occur, major components of bioaerosols, survival and diffusion factors, and possible control strategies. The six-stage Andersen impactor is the main method used for sampling bioaerosols in composting plants. In addition, different composting management methods mainly affect bioaerosol emissions from composting plants. Studies of the components of bioaerosols produced by composting plants mainly focused on bacteria and fungi, whereas few considered others such as endotoxin. The survival and diffusion of bioaerosols are influenced by seasonal effects due to changes in environmental factors, such as temperature and relative humidity. Finally, three potential strategies have been proposed for controlling bioaerosols in composting plants. Improved policies are required for regulating bioaerosol emissions, as well as bioaerosol concentration diffusion models and measures to protect human health.

The response and factors of microbial aerosol emission from the sludge bio-drying process

Exposure to high levels of microbial contaminants during waste disposal leads to the development of various diseases, including respiratory symptoms and gastrointestinal infections. In this study, the emissions of airborne bacteria and fungi during the process of sludge bio-drying were investigated. The recorded emission levels of airborne bacteria and fungi were 2398 ± 1307 CFU/m3 and 1963 ± 468 CFU/m3, respectively. Viable bacteria were sized between 1.1 and 3.3 μm, while fungal particles were concentrated between 2.1 and 4.7 μm. High-throughput sequencing was used to conduct a microbial population assay, and correlation analysis was performed to estimate the relationship between key factors and bioaerosol emissions. The main bacteria identified were Bacillus sp., Lysinibacillus sp. YS11, unclassified Enterobacteriaceae, Brevundimonas olei, and Achromobacter sp.; the primary types of fungi were Aspergillus ochraceus, Gibberella intricans, Fusarium concentricum, Aspergillus qinqixianii, and Alternaria sp.; and the dominant opportunistic pathogens were Bacillus anthracis and Aspergillus ochraceus. At lower moisture and temperature levels, airborne bacterial concentrations were higher, especially the release of fine particles. In addition, moisture content had a significant impact on the microbial population in bioaerosols. This study provides insights into strategies for controlling bioaerosols in the exhaust gases of the sludge bio-drying process.

Control of odorants in swine manure and food waste co-composting via zero-valent iron /H2O2 system

Odors have posed challenges to the advancement of aerobic composting. This work aims to identify the primary components responsible for odors and assess the effectiveness and mechanisms of the zero-valent iron/H2O2 system controlling various odorants in aerobic composting. Swine manure and food waste were used as composting materials, with the addition of zero-valent iron and hydrogen peroxide to mitigate odor emissions. Results revealed that odorants included ammonia, hydrogen sulfide, and 22 types of volatile organic compounds (VOCs), with ethyl acetate, heptane, and dimethyl disulfide being predominant. Among the odorants emitted, ammonia accounted for 75.43%, hydrogen sulfide for 0.09%, and identified VOCs for 24.48%. The ZVI/H2O2 system showed a significant reduction in ammonia and VOCs emission, with the reduction of 51% (ammonia) and 41.3% (VOCs) respectively, primarily observed during the thermophilic period. The occurrence of Fenton-like reactions and changes in key microbial populations were the main mechanisms accounting for odor control. The occurrence of Fenton-like reaction was confirmed by X-ray photoelectron spectroscopy and reactive oxygen detection, showing the oxidation of zero-valent iron by H2O2 to higher valence elemental iron, and the simultaneous production of ·OH. Microbial analysis indicated that an enrichment of specific microorganisms with Bacillus contributed to feammonx and Bacillaceae contributed to organic biodegradation. Redundancy analysis highlighted the role of key microbial species (Bacillaceae, Bacillus, and Ureibacillus) in effectively reducing the level of ammonia and volatile organic compounds. These novelty findings illustrated that the potential of this system is promising for controlling the emission of odorants and aerobic composting reinforcement.

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.

Evaluation of different composting systems on an industrial scale as a contribution to the circular economy and its impact on human health

Due to the production of volatile organic compounds (VOCs), large-scale composting can cause air pollution and occupational health issues. Due to this, it is necessary to determine if the amount generated poses a health risk to plant workers, which can be a starting point for those in charge of composting plant facilities. As a result, the goal of this work is to conduct a thorough analysis of both the physicochemical features and the VOC generation of three large-scale systems. For ten weeks, the three different composting plants were monitored weekly, and VOC identification and quantification were performed using GC-MS gas chromatography. It has been observed that the biggest risk related with VOC formation occurs between the fourth and fifth weeks, when microbial activity is at its peak. Similarly, it has been demonstrated that xylenes and toluene are the ones that are produced in the greatest quantity. Finally, after ten weeks of processing, it was discovered that the material obtained complies with the regulations for the sale of an amendment.Implications: The evaluation and monitoring of the composting processes at an industrial scale is very important, due to the implications they bring. VOCs are produced by the operation of composting facilities with substantial amounts of solid waste, such as the companies in this study. These may pose a health risk to those working in the plants; thus, it is critical to understand where the VOCs occur in the process in order to maintain workers' occupational health measures. This form of evaluation is rare or nonexistent in Colombia, which is why conducting this type of study is critical, as it will provide crucial input into determining when the highest levels of VOC generation occur. These are the ones that may pose a risk at some point, but with proper occupational safety planning, said risk may be avoided. This work has evaluated three composting systems, with different types of waste and mixtures. According to reports, while composting systems continue to produce VOCs and their generation is unavoidable, the potential risk exists only within the plant. These findings can pave the way for the implementation of public policies that will improve the design and operation of composting plants. There is no specific legislation in Colombia for the design and execution of this sort of technology, which allows the use of organic waste.

Real-time emission characteristics, health risks, and olfactory effects of VOCs released from soil disturbance during the remediation of an abandoned chemical pesticide industrial site

Volatile organic compounds (VOCs) released along with soil disturbance during the remediation of abandoned industrial sites have attracted great attention due to their possible toxicity and odour. However, the real-time emission characteristics of these VOCs and their subsequent effects on health and olfaction are less understood. In this study, the gaseous VOCs released from soil disturbance by excavators and drilling rigs at an abandoned chemical pesticide plant were monitored online with a laboratory-built single photoionization time-of-flight mass spectrometer (SPI-TOFMS). Twelve main VOCs with total mean concentrations ranging from 2350 to 3410 μg m-3 were observed, with dichloromethane (DCM) having a significant contribution. The total concentrations of the remaining 11 VOCs increased substantially during soil disturbance, with the total mean concentrations increasing from 18.65-39.05 to 37.95-297.94 μg m-3 and those of peak concentrations increasing from 28.46-58.97 to 88.38-839.13 μg m-3. This increase in VOC concentrations during soil disturbance leads to an enhanced heath risk for on-site workers. The distinctive difference between the mean and peak concentrations of VOCs indicates the importance of using mean and peak concentrations, respectively, for risk and olfactory evaluation due to the rapid response of the human nose to odours. As a result, the cumulative noncarcinogenic risk at the relatively high pollutant plot was higher than the occupational safety limit, while the total carcinogenic risks at all monitored scenarios exceeded the acceptable limit. Among the VOCs investigated, DCM and trichloroethylene (TCE) were determined to be crucial pollutants for both noncarcinogenic and carcinogenic risks of VOCs. With regard to olfactory effects, organic sulphides, including dimethyl disulphide (DMDS), dimethyl sulphide (DMS), and dimethyl trisulphide (DMTS) were identified as dominant odour contributors (78.28-92.11%) during soil disturbance.

Measures for Controlling Gaseous Emissions during Composting: A Review

Composting is a promising technology for treating organic solid waste. However, greenhouse gases (methane and nitrous oxide) and odor emissions (ammonia, hydrogen sulfide, etc.) during composting are practically unavoidable, leading to severe environmental problems and poor final compost products. The optimization of composting conditions and the application of additives have been considered to mitigate these problems, but a comprehensive analysis of the influence of these methods on gaseous emissions during composting is lacking. Thus, this review summarizes the influence of composting conditions and different additives on gaseous emissions, and the cost of each measure is approximately evaluated. Aerobic conditions can be achieved by appropriate process conditions, so the contents of CH4 and N2O can subsequently be effectively reduced. Physical additives are effective regulators to control anaerobic gaseous emissions, having a large specific surface area and great adsorption performance. Chemical additives significantly reduce gaseous emissions, but their side effects on compost application must be eliminated. The auxiliary effect of microbial agents is not absolute, but is closely related to the dosage and environmental conditions of compost. Compound additives can reduce gaseous emissions more efficiently than single additives. However, further study is required to assess the economic viability of additives to promote their large-scale utilization during composting.