Electro-stimulated anaerobic oxidation of methane with synergistic denitrification by adding AQS: Electron transfer mode and mechanism.

Denitrifying anaerobic methane-oxidizing (DAMO) processes, which link anaerobic methane oxidation (AMO) and denitrification, have a promising prospect in anaerobic wastewater treatment. In bioelectrochemical systems (BES), DAMO consortium presented potent metabolic activity. However, the extracellular electron transfer (EET) in BES was poorly understood. This study investigated the EET mechanisms and modes of electron transport in BES dominated by anaerobic methanotrophic bacteria. In the bioreactors with the auxiliary voltage of 0.5 and 1.1 V, named EMN-0.5 and EMN-1.1, respectively, biological voltages of 0.198 and 0.329 V were generated with power densities of 0.6 and 1.20 mW/m2, after removing the voltage. High throughput and metagenome analyses demonstrated that main methanotrophs were DAMO bacteria and Methylocystis sp. The electroactive bacteria detected were Pseudomonas sp., Hypomicrobium sp., Thiobacillus sp, and Rhodococcus sp. The pil, cytochrome c, hdr, and he/fp genes related to EET were present on the electrode surfaces. Carbon 13 isotope tracing and chemicals analysis by GC-MS exhibited that methanol was an intermediate product released to extracellular environment and acted as the electronic carrier to drive the EET in methane oxidation. Extracellular electron transfer was achieved through the collaboration of DAMO bacteria, Methylocystis sp., and Pseudomonas sp. Anthraquinone 2-sulfonic acid ester (AQS) could improve the rate of electron transfer to the extracellular space, especially in the EMN-0.5 reaction system. This study provides a new understanding of AMO consortium metabolism in BES and may provide a scientific basis for developing methane control technology.

Distribution characteristics and potential risks of bacterial aerosol in waste transfer station.

The waste transfer station (WTS) is an important link in the transfer of municipal solid waste (MSW) between the community and disposal terminals. While WTSs facilitate waste collection in communities, odorous gases and bioaerosols can escape from them, thereby negatively affecting their surroundings. In this study, the concentration, particle size distribution, pathogen population, and health risks of bioaerosols were analyzed at different locations in a transfer station. The results showed that the highest viable bacterial aerosol concentration was 10,353 ± 3701 CFU/m3, which was at 5 m from the disposal site. Fifty-three bacterial species, including pathogens, were detected. Of these, 39 were human pathogenic bacteria directly originating from the WTS. Furthermore, health risk assessments indicated unacceptable levels of non-carcinogenic risk for operational workers caused by bacterial aerosols of the WTS work area. In addition, bacterial aerosols may pose a severe health risk to children within a 15 m area of the WTS. The results of this study provide a scientific basis to control and reduce the risk associated with bioaerosol exposure in solid WTSs.

Improving sewage sludge dewaterability via heterogeneous activation of persulfate by Fe-Al layered double hydroxide: Role of generated SO4-•.

In this study, Fe-Al layered double hydroxide (Fe-Al LDH) was prepared and applied to activate persulfate to condition sewage sludge and improve its dewaterability. The results showed that Fe-Al LDH activated persulfate to generate a large amount of free radicals, which attacked extracellular polymeric substances and reduced their content, disrupted microbial cells, released bound water, decreased sludge particle size, increased sludge zeta potential, and improved sludge dewaterability. After sewage sludge was conditioned with Fe-Al LDH (0.20 g/g total solids (TS)) and persulfate (0.10 g/g TS) for 30 min, the capillary suction time of the sludge dropped from 52.0 s to 16.3 s, while the moisture content of the sludge cake decreased from 93.2% to 68.5%. The dominant active free radical produced by the Fe-Al LDH-activated persulfate was SO4-•. The maximum Fe3+ leaching of the conditioned sludge was only 102.67 ± 4.45 mg/L, thus effectively alleviating the secondary pollution of Fe3+. The leaching rate of 2.37% was significantly lower than that of the sludge homogeneously activated with Fe2+ (738.4 ± 26.07 mg/L and 71.00%).

Emission behavior and impact assessment of gaseous volatile compounds in two typical rural domestic waste landfills.

Landfill sites are sources of gaseous volatile compounds. The dumping area (LDA) and leachate storage pool (LSP) of two typical rural domestic waste landfill sites in north China (NLF) and southwest China (SLF) were investigated. We found that 45, 46, 61 and 68 volatile organic compounds (VOC) were present in the air of NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. And there were 27, 29, 35 and 37 kinds of odorous compounds being detected. Oxygenated compounds (>48.88%), chlorinated compounds (>6.85%), and aromatics (>5.46%), such as organic acid, 1-chlorobutane, and benzene, were the most abundant compounds in both landfills. The SLF-LDA had the highest olfactory effect, with a corresponding total odor activity value of 29,635.39. The ozone-formation potential analysis showed that VOCs emitted from SLF landfills had significantly higher potential for ozone formation than those from NLF landfills, with ozone generation potentials of 166.02, 225.86, 2511.82, and 1615.99 mg/m3 for the NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. Higher chronic toxicity and cancer risk of VOCs were found in the SLF according to method of Risk Assessment Information System. Based on the sensitivity analysis by the Monte Carlo method, concentrations of benzene, propylene oxide, propylene, trichloroethylene, and N-nitrosodiethylamine, along with exposure duration, daily exposure time, and annual exposure frequency, significantly impacted the risk levels. We provide a scientific basis, which reflects the need for controlling and reducing gaseous pollutants from landfills, particularly rural residential landfills, which may improve rural sanitation.

Characteristics of microbial aerosol particles dispersed downwind from rural sanitation facilities: Size distribution, source tracking and exposure risk.

Bioaerosols containing pathogens released from waste and wastewater treatment facilities pose potential health risks to workers on-site and residents downwind. In this study, sampling sites were set up at rural garbage stations (GS-1 and GS-2) and sewage treatment station (STS) to investigate the emission and diffusion characteristics of bioaerosols. High-throughput sequencing was utilized to assay the intestinal bacteria population, while the health risks associated with bioaerosols exposure were estimated based on average daily dose rates (DD). Traceability analysis was used to determine the percentages of intestinal bacteria from GS-1, GS-2 and STS. The recorded emission levels of bioaerosols in the air surrounding GS-1, GS-2, and STS were 5053, 6299, and 4795 CFU/m3, containing 1599, 2244, and 2233 CFU/m3 of intestinal bacteria, respectively. Most of the bioaerosols were coarse particles with size larger than 4.7 µm. Methylobacterium, Rhizobium, Pseudomonas, Enterobacteriaceae, and Brucella presented in the air were originally in rural waste and wastewater. STS and GS-2 were potential sources of intestinal bacteria. With increasing distance from the sources, the concentration of bioaerosols decreased gradually. On-site workers and residents were predominantly affected by bioaerosols through inhalation. The exposure risks via inhalation and skin contact for children were much higher than that for adults. The purpose of this study was to provide preliminary data for bioaerosols control and their risks reduction released from rural sanitation facilities.

Analysis of suitable private-secondary-main sewer diameters in rural areas based on cost model and hydraulic calculation.

High cost of sewer systems usually restricts the sewage collection in rural areas. Many rural areas take traditional sewer scheme whose private-secondary-main sewer diameter is 110-200-300 mm without hydraulic calculation and increased the total cost of sewers. The rational utilization of small diameter sewers might contribute to sewer cost reduction. In this study, rural sewer length and cost models were established taking sewer diameter, household number, and length/width ratio of village as parameters to evaluate the cost benefits of using small diameter sewers. Hydraulic calculation of sewers was applied by Storm Water Management Model to ensure the small diameter sewers were feasible. The results indicate that household number and length/width ratio cause obvious impact on sewer length and cost. Main sewer with 200 mm diameter is suitable for the village with less than 1000 households. Using small diameter sewers can reduce the sewer cost by 6-15% compared with traditional sewer scheme and 110-110-200 might be the better scheme to rural areas because of the low cost (including construction cost and operation and maintenance cost) and high tolerance of sewage flow fluctuation. This study provided the suitable diameter of rural sewers based on cost model and hydraulic calculation which might be helpful for the application of rural sewers.

Microbial aerosol particles in four seasons of sanitary landfill site: Molecular approaches, traceability and risk assessment.

Landfill sites are regarded as prominent sources of bioaerosols for the surrounding atmosphere. The present study focused on the emission of airborne bacteria and fungi in four seasons of a sanitary landfill site. The main species found in bioaerosols were assayed using high-throughput sequencing. The SourceTracker method was utilized to identify the sources of the bioaerosols present at the boundary of the landfill site. Furthermore, the health consequences of the exposure to bioaerosols were evaluated based on the average daily dose rates. Results showed that the concentrations of airborne bacteria in the operation area (OPA) and the leakage treatment area (LTA) were in the range of (4684 ± 477)-(10883 ± 1395) CFU/m3 and (3179 ± 453)-(9051 ± 738) CFU/m3, respectively. The average emission levels of fungal aerosols were 4026 CFU/m3 for OPA and 1295 CFU/m3 for LTA. The landfill site received the maximum bioaerosol load during summer and the minimum during winter. Approximately 41.39%- 86.24% of the airborne bacteria had a particle size of 1.1 to 4.7 µm, whereas 48.27%- 66.45% of the airborne fungi had a particle size of more than 4.7 µm. Bacillus sp., Brevibacillus sp., and Paenibacillus sp. were abundant in the bacterial population, whereas Penicillium sp. and Aspergillus sp. dominated the fungal population. Bioaerosols released from the working area and treatment of leachate were the two main sources that emerged in the surrounding air of the landfill site boundary. The exposure risks during summer and autumn were higher than those in spring and winter.

Sewers induce changes in the chemical characteristics, bacterial communities, and pathogen distribution of sewage and greywater.

Sewers may affect the characteristics and bacterial communities of wastewater, and need be studied as they may impact treatment facilities and recycling operations. In this study, the wastewater characteristics and bacterial communities from the inflow and outflow of two sewers (sewage and greywater) were analyzed. The chemical oxygen demand was significantly reduced in the sewage and greywater sewer and the greywater sewer generated less sulfide and methane. Proteobacteria, Bacteroidetes, and Firmicutes as the major phyla in sewage and greywater and sewer biofilms. Sewer conveyance caused changes in the distribution and community interaction of suspended bacteria. Greywater contained abundant water-related pathogenic bacteria (WPB) and some WPB (e.g. Aeromonas, Klebsiella and Shigella) number in greywater were not lower than sewage. Sewers could increase the number of Shigella in sewage and decrease the number of Acinetobacter in greywater. Further treatment or disinfection of greywater collected by sewers was necessary and directly reuse of greywater without treatment should be avoided.

Influences of flow conditions on bacterial communities in sewage and greywater small diameter gravity sewer biofilms.

Small diameter gravity sewers (SDGS) have been applied in rural areas to collect sewage or greywater. Flow conditions in rural SDGS are variable and their influences on bacteria in sewer biofilms are still not clear. To investigate the effect of flow conditions on sewage and greywater SDGS biofilms, six sewage SDGS and six greywater SDGS were operated and Illumina HiSeq sequencing was subsequently performed on sewer biofilms. The results indicate that the predominant bacterial phyla in both sewage and greywater SDGS biofilms were Proteobacteria (63.0% ± 9.3%) and Actinobacteria (26.5% ± 8.8%) and co-presence relationship was the main interaction in SDGS biofilm bacterial communities. Compared with stable flow conditions, variable flow conditions altered the bacterial community of SDGS biofilms from the aspect of bacteria compositions and community interactions and the relative abundance of many bacteria showed significant distinctions between stable and variable flow conditions. In sewage SDGS biofilm, the relative abundance of denitrifying, nitrite-oxidizing, and sulfate-reducing bacteria decreased significantly in variable flow conditions while in greywater SDGS biofilms, nitrite-oxidizing and water-related pathogenic bacteria decreased significantly in variable flow conditions. Influences of flow conditions on predicted bacterial functions were also significant in sewage and greywater SDGS biofilms. Variable flow conditions might be conducive to the reduction of H2S generation and water-related pathogenic bacteria in rural SDGS biofilms.

An appropriate technique for treating rural wastewater by a flow step feed system driven by wind-solar hybrid power.

Most rural wastewater treatment facilities require aeration equipment to ensure sufficient dissolved oxygen (DO) during processing. Operation and maintenance are costly, and cannot be met in many areas with poor economic levels. This has led to further deterioration of the rural water environment and aroused much attention. This work reports a plug-flow step feed system utilizing wind and solar hybrid energy for rural wastewater treatment. Under certain climatic conditions, the wind energy and solar energy provided complimentary power generation, and an automatic control system (without batteries) was constructed. The corresponding control logic for multi-energy level operation was developed. Furthermore, the power generation efficiency of the system, the pollutant removal, and its mechanism on the bioreactor were also analyzed. According to the monitoring of meteorological conditions, wind and solar resources at the test site were abundant, and the electricity generated by the power generation was sufficient to meet the operational needs of the equipment. Energy efficiency can reach 80.0%. The characteristics of pollutant removal in each process section were studied on spatial and temporal dimensions. Results showed that the wastewater treatment process reached mean removal efficiencies of chemical oxygen demand (CODcr), NH4+-N, total nitrogen (TN) and total phosphorus (TP) were 90.2%, 94.3%, 61.4% and 63.1%, respectively. Analyses of microbial community richness and group changes in each anoxic/aerobic reaction chamber in the biofilm reactor showed that the population structure was relatively stable and that there were abundant functional bacteria capable of degrading pollutants in each aerobic and anoxic unit. This system can thus be a more sustainable treatment process than traditional techniques used for rural wastewater treatment, providing a new design approach for low-energy consumption and unattended rural wastewater treatment.

Characteristics of sewer biofilms in aerobic rural small diameter gravity sewers.

Small diameter gravity sewers (SDGS) are extensively used to collect rural sewage as they are low in cost and quick to construct. However, the characteristics of biofilms in rural SDGS are still not clear. In this study, biofilms characteristics of aerobic rural SDGS were investigated using simulations in a lab under different flow conditions and slopes. Results indicated that the average thickness of aerobic rural SDGS biofilms was in the range of 350-650 µm, decreasing at locations with variable flow and high slopes. Protein was the most abundant substance in extracellular polymeric substance of SDGS biofilms. The most abundant bacteria, Proteobacteria, Actinobacteria, and Bacteroidetes, and functional bacteria showed different distributions when analyzed through Illumina HiSeq sequencing of 16S rRNA. The relative abundances of denitrifying bacteria, nitrite-oxidizing bacteria, and sulfate-reducing bacteria (SRB) were lower during variable flow than during stable flow. High slopes (15‰) decreased SRB presence, which could be used to mitigate H2S accumulation in aerobic SDGS. Overall, this study describes the characteristics of aerobic rural SDGS biofilms and provides valuable suggestions for the optimal design of SDGS based on these characteristics.

The identification, health risks and olfactory effects assessment of VOCs released from the wastewater storage tank in a pesticide plant.

Wastewater generated during pesticide synthesis is a potential source of high concentrations of volatile organic compounds (VOCs) emissions, which would cause adverse effects on human health and the environment. Here, we provided a comprehensive study on concentrations, health risks, and olfactory effects of VOCs emitted from a pesticide wastewater storage tank. A total of 21 VOCs were identified, their concentrations ranged from 0.63 to 5023.83 µg/m3. Chlorinated compounds such as trichloroethylene (mean = 2581.29 µg/m3) and dichloromethane (mean = 2309.55 µg/m3) presented the highest concentrations. Both the cumulative chronic toxicities (514) and cancer risks (1.67 × 10-3) of VOCs were up to three orders of magnitude higher than the occupational safety limits. Trichloroethylene contributed the greatest to the cumulative chronic toxicities (88.41%) and cancer risks (74.91%). Benzene was another compound with a high cancer risk of 3.32 × 10-4. Regarding olfactory effects, triethylamine and diethylamine were the dominant contributors with a relative olfactory perception importance of 39.93% and 34.26%, respectively. The results of fuzzy synthetic evaluation revealed that benzene, diethylamine, trichloroethylene, dichloromethane, and triethylamine were the priority compounds caused the overall pollution levels, health risks, and olfactory effects.

Characteristics and exposure risks of potential pathogens and toxic metal(loid)s in aerosols from wastewater treatment plants.

Aerosols from wastewater treatment plants (WWTPs) are considered to be potentially hazardous to on-site employees and surrounding residents. However, their harmful components and their effects remain poorly understood. In this study, the characteristics, responsible factors, sources and exposure risks of potential pathogens and toxic metal(loid)s in aerosols from four WWTPs were investigated. There were 21 potential pathogens and 15 toxic metal(loid)s detected in the aerosols. Arcobacter and Fe were the dominant taxa responsible for the dissimilarity of the potential pathogen population and toxic metal(loid) composition between the aerosols and the wastewater/sludge, respectively. Both meteorological factors and sources affected pathogen and toxic metal(loid) composition. The potential pathogens and toxic metal(loid)s in indoor aerosols mainly originated from wastewater/sludge, while those in outdoor aerosols originated from wastewater/sludge and ambient air. The highest respirable fraction (<3.30 µm) concentrations and proportions were detected at the aeration units. Non-carcinogenic and carcinogenic risks of toxic metal(loid)s for both adults and children were found within and/or around WWTPs, and non-carcinogenic risks of bacteria for children were found at downwind, suggesting the need for active safeguard procedures, such as that employees wear masks and work clothes, covering the main emission sites, and collecting and destroying of aerosols.

State of the art on granular sludge by using bibliometric analysis.

With rapid industrialization and urbanization in the nineteenth century, the activated sludge process (ASP) has experienced significant steps forward in the face of greater awareness of and sensitivity toward water-related environmental problems. Compared with conventional flocculent ASP, the major advantages of granular sludge are characterized by space saving and resource recovery, where the methane and hydrogen recovery in anaerobic granular and 50% more space saving, 30-50% of energy consumption reduction, 75% of footprint cutting, and even alginate recovery in aerobic granular. Numerous engineers and scientists have made great efforts to explore the superiority over the last 40 years. Therefore, a bibliometric analysis was desired to trace the global trends of granular sludge research from 1992 to 2016 indexed in the SCI-EXPANDED. Articles were published in 276 journals across 44 subject categories spanning 1420 institutes across 68 countries. Bioresource Technology (293, 11.9%), Water Research (235, 9.6%), and Applied Microbiology and Biotechnology (127, 5.2%) dominated in top three journals. The Engineering (991, 40.3%), China (906, 36.9%), and Harbin Inst Technol, China (114, 4.6%) were the most productive subject category, country, and institution, respectively. The hotspot is the emerging techniques depended on granular reactors in response to the desired removal requirements and bio-energy production (primarily in anaerobic granular sludge). In view of advanced and novel bio-analytical methods, the characteristics, functions, and mechanisms for microbial granular were further revealed in improving and innovating the granulation techniques. Therefore, a promising technique armed with strengthened treatment efficiency and efficient resource and bio-energy recovery can be achieved.

Probabilistic evaluation of integrating resource recovery into wastewater treatment to improve environmental sustainability.

Global expectations for wastewater service infrastructure have evolved over time, and the standard treatment methods used by wastewater treatment plants (WWTPs) are facing issues related to problem shifting due to the current emphasis on sustainability. A transition in WWTPs toward reuse of wastewater-derived resources is recognized as a promising solution for overcoming these obstacles. However, it remains uncertain whether this approach can reduce the environmental footprint of WWTPs. To test this hypothesis, we conducted a net environmental benefit calculation for several scenarios for more than 50 individual countries over a 20-y time frame. For developed countries, the resource recovery approach resulted in ∼154% net increase in the environmental performance of WWTPs compared with the traditional substance elimination approach, whereas this value decreased to ∼60% for developing countries. Subsequently, we conducted a probabilistic analysis integrating these estimates with national values and determined that, if this transition was attempted for WWTPs in developed countries, it would have a ∼65% probability of attaining net environmental benefits. However, this estimate decreased greatly to ∼10% for developing countries, implying a substantial risk of failure. These results suggest that implementation of this transition for WWTPs should be studied carefully in different temporal and spatial contexts. Developing countries should customize their approach to realizing more sustainable WWTPs, rather than attempting to simply replicate the successful models of developed countries. Results derived from the model forecasting highlight the role of bioenergy generation and reduced use of chemicals in improving the sustainability of WWTPs in developing countries.

Intestinal bacteria in bioaerosols and factors affecting their survival in two oxidation ditch process municipal wastewater treatment plants located in different regions.

Samples from two oxidation ditch process municipal wastewater treatment plants (MWTPs) (HJK and GXQ) in two regions of China were analysed for bacteria, particles, total organic carbon, and water-soluble ions in bioaerosols. Diversity and potential pathogen populations were evaluated by high-throughput sequencing. Bioaerosol sources, factors affecting intestinal bacterial survival, and the relationship between bioaerosols and water were analysed by Source tracker and partial least squares-discriminant, principal component, and canonical correspondence analyses. Culturable bacteria concentrations were 110-846 and 27-579 CFU/m3 at HJK and GXQ, respectively. Intestinal bacteria constituted 6-33% of bacteria. Biochemical reaction tank, sludge dewatering house (SDH), and fine screen samples showed the greatest contribution to bioaerosol contamination. Enterobacter aerogenes was the main intestinal bacteria (> 99.5%) in HJK and detected at each sampling site. Enterobacter aerogenes (98.67% in SDH), Aeromonas sp. (76.3% in biochemical reaction tank), and Acinetobacter baumannii (99.89% in fine screens) were the main intestinal bacteria in GXQ. Total suspended particulate masses in SDH were 229.46 and 141.6 µg/m3 in HJK and GXQ, respectively. Percentages of insoluble compounds in total suspended particulates decreased as height increased. The main soluble ions in bioaerosols were Ca2+, Na+, Cl-, and SO42-, which ranged from 3.8 to 27.55 µg/m3 in the MWTPs. Water was a main source of intestinal bacteria in bioaerosols from the MWTPs. Bioaerosols in HJK but not in GXQ were closely related. Relative humidity and some ions positively influenced intestinal bacteria in bioaerosols, while wind speed and solar illumination had a negative influence.

Investigation on mechanism of phosphate removal on carbonized sludge adsorbent.

For the removal of phosphate (PO43-) from water, an adsorbent was prepared via carbonization of sewage sludge from a wastewater treatment plant: carbonized sludge adsorbent (CSA). The mechanism of phosphate removal was determined after studying the structure and chemical properties of the CSA and its influence on phosphate removal. The results demonstrate that phosphate adsorption by the CSA can be fitted with the pseudo second-order kinetics and Langmuir isotherm models, indicating that the adsorption is single molecular layer adsorption dominated by chemical reaction. The active sites binding phosphate on the surface are composed of mineral particles containing Si/Ca/Al/Fe. The mineral containing Ca, calcite, is the main factor responsible for phosphate removal. The phosphate removal mechanism is a complex process including crystallization via the interaction between Ca2+ and PO43-; formation of precipitates of Ca2+, Al3+, and PO43-; and adsorption of PO43- on some recalcitrant oxides composed of Si/Al/Fe.

Effects of oxygen and water content on microbial distribution in the polyurethane foam cubes of a biofilter for SO2 removal.

The performance of a biofilter for off-gas treatment relies on the activity of microorganisms and adequate O2 and H2O. In present study, a microelectrode was applied to analyze O2 in polyurethane foam cubes (PUFCs) packed in a biofilter for SO2 removal. The O2 distribution varied with the density and water-containing rate (WCR) of PUFCs. The O2 concentration dropped sharply from 10.2 to 0.8mg/L from the surface to the center of a PUFC with 97.20% of WCR. The PUFCs with high WCR presented aerobic-anoxic-aerobic areas. Three-dimensional simulated images demonstrated that the structure of PUFCs with high WCR consisted of an aerobic "shell" and an anoxic "core", with high-density PUFCs featuring a larger anoxic area than low-density PUFCs. Moreover, the H2O distribution in the PUFC was uneven and affected the O2 concentration. Whereas aerobic bacteria were observed in the PUFC surface, facultative anaerobic microorganisms were found at the PUFC core, where the O2 concentration was relatively low. O2 and H2O distributions differed in the PUFCs, and the distribution of microorganisms varied accordingly.

Characterization and source analysis of indoor/outdoor culturable airborne bacteria in a municipal wastewater treatment plant.

The potential health risks of airborne bacteria emission from a wastewater treatment process have been concerned. However, few studies have investigated the differences in community structure between indoor and outdoor bacteria. In this work, the characterization of airborne bacteria was studied in a municipal wastewater treatment plant in Beijing, China. Two indoor (i.e., fine screen room and sludge dewatering house) and two outdoor (i.e., aeration tank and control site) sampling sites were selected. An Andersen six-stage impactor was used for collecting culturable airborne bacteria in the air, and Illumina MiSeq sequencing was conducted to track the emission source of the culturable airborne bacteria. The results indicate that, compared with the outdoor aeration tank site, the concentrations of culturable airborne bacteria in the indoor fine screen room with poor ventilation were more than ten times higher and the particle size was about twice as large. The community structures of indoor and outdoor culturable airborne bacteria were obviously different. Enterobacteriaceae and opportunistic pathogens were detected in indoor culturable airborne bacteria, with wastewater and sludge dewatering machine identified as the primary sources. Conversely, Enterobacteriaceae and opportunistic pathogens were not detected in outdoor culturable airborne bacteria. Outdoor high wind speed might have resulted in rapid dilution and mixing of culturable airborne bacteria generated from the aeration tank with the ambient air. The results of the present research suggest that covering pollution sources, increasing ventilation rates, and using protective measures for personnel should be implemented to decrease the exposure risk to indoor culturable airborne bacteria.

Sulfur dioxide and o-xylene co-treatment in biofilter: Performance, bacterial populations and bioaerosols emissions.

Sulfur dioxide (SO2) and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO2 and o-xylene in the present study. SO2 and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO2 could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria (SOB) and o-xylene-degrading bacteria (XB) thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO2 and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.