Microporous Aeration Research Articles

Nitrogen reducing mechanism by microporous aeration based on microbial population characteristics: water temperature factor

ABSTRACT The formation of black odour water is primarily attributed to the elevated concentration of organic pollutants, along with an excessive amount of nitrogen and phosphorus, ultimately leading to an anoxic aquatic environment. The water temperature influence mechanism on black-odorous water restoration by microporous aeration is still lacking depth study. This paper selected (15–18) ℃ (spring and autumn), (22–25) ℃ (summer), (8–11) ℃ (winter) as temperature conditions, and investigated temperature influence on nitrogen reduction. Researches showed that: (1) The removal rates of COD, NH4 +-N and TN were significantly positively correlated with temperature (r = 0.99, 0.96, 0.97), the lowest removal rates were 83.16%, 95.68%, 58.7% ((8–11) ℃), the highest values were 92.67%, 98.27%, 70.96% ((22–25) ℃), respectively. (2) At a temperature range of 22–25°C, the microbial community exhibited the highest levels of abundance, diversity, and uniformity. Notably, Proteobacteria dominated this temperature range with a relative abundance of 79.72%. Furthermore, temperature positively correlated with the majority of dominant bacterial species, suggesting that conditions at 22–25°C are highly conducive to the growth of most bacterial communities. Among these, Limnohabitans, Alsobacter, and Candidatus_Aquirestis, which possess key functions in denitrification and nitrogen removal, displayed significantly higher abundances. It explains the positive correlation between temperature and removal rates of COD, TN and NH4 +-N from microbial population’s perspective. Thus, the best temperature for repairing black-smelly water is (22–25) ℃. This study provides technical reference for mechanism research and practical application of microporous aeration.

Investigation on aeration efficiency and energy efficiency optimization in recirculating aquaculture coupling CFD with Euler-Euler and species transport model

Aeration plays a crucial role in maintaining the overall health and sustainability of the recirculating aquaculture system. Conventional aeration operates continuous and consumes 35.06 % of equipment energy consumption. How to optimize aeration while ensuring normal fish growth remains a great challenge. To address these challenges, this research paper established a coupled model of computational fluid dynamics and species transport model (CFD-STM). Aeration tests were carried out in a 33.3 m3 culture tank using a 0.31 m diameter aerator to find out the impacts of operating variables (aeration flow rate, bubble diameter, inlet velocity, and aerator position) on oxygen transfer using a microporous aeration system. A CFD-STM model was coupled to obtain the optimum values of aeration parameters. Results revealed that the Standard Aeration Efficiency (SAE) reductions by 32.1 % for 50 % larger aeration flow rate and 86.4 % for 50 % larger bubble diameter, as well as SAE achieved 5.67 kg/kWh with an aerator position scale factor equal to 0.48. In addition, the energy consumption of the Roots blower was compared for a single aeration and dissolved oxygen saturation. Results indicated that smaller bubbles microbubbles can effectively improve oxygen transfer coefficient. The energy consumption was reduced by 15.7 % for 50 % larger aeration flow rate and 38.6 % for 50 % lower bubble diameter. Based on the results, this study demonstrated that CFD is a useful tool to optimize the aeration system design and operation in order to enhance aeration efficiency. It provides a theoretical foundation the future optimization of energy conservation through intermittent aeration practices.

Integrated thiosulfate-driven denitrification, partial nitrification and anammox process in membrane-aerated biofilm reactor for low-carbon, energy-efficient biological nitrogen removal

Combining multiple bioprocesses in a single membrane-aerated biofilm reactor (MABR) unit for wastewater treatment is an emerging research focus. This study investigated the feasibility of coupling thiosulfate-driven denitrification (TDD) with partial nitrification and anammox (PNA) in a MABR for the treatment of ammonium-containing wastewater. The integrated bioprocess was tested over a continuous operation period (>130 d) in two MABRs: one with a polyvinylidene fluoride membrane (MABR-1), and the other with micro-porous aeration tubes covered with non-wovenpolyester fabrics (MABR-2). After start-up, the MABR-1 and MABR-2 based on the TDD–PNA process achieved satisfactory total nitrogen removal efficiencies of 63% and 76%, with maximum oxygen utilisation efficiencies of up to 66% and 80% and nitrogen removal fluxes of 1.3 and 4.7 gN/(m2·d), respectively. Predictions from the AQUASIM-model verified the integrated bioprocess. These lab scale findings confirmed the applicability of MABR technology for simultaneous sulfur and nitrogen removal, promising for pilot-scale application.

Degradation of dibutyl phthalate by ozonation in the ultrasonic cavitation-rotational flow interaction coupled-field: performance and mechanism.

Dibutyl phthalate (DBP) is present in hydraulic fracturing flowback and produced water. Degradation of DBP in aqueous by means of ozonation in ultrasonic cavitation-rotational flow interaction coupled-field (UC-RF coupled-field) was studied. The effect of ozone dosage, ozone intake flow, operating temperature, initial pH, DBP initial concentration, liquid flow rate, and ultrasonic power on the DBP removal was investigated. Results indicated that the DBP degradation rate was strongly influenced by the liquid flow rate and the ultrasonic power over the range investigated. HCO3- and Cl- revealed an inhibitory effect on the DBP removal. SO42- seemed to have no effect on DBP removal. The ozone utilization efficiencies in the UC-RF coupled-field were 2.77 and 1.13 times higher than those in the conventional microporous aeration (CMA) and rotating-flow microbubble aeration (RFMA), respectively. The DBP degradation rate was diminished in the presence of tert-butyl alcohol. Cavitation bubbles are considered as innumerable microreactors. Degradation of DBP by direct ozonation, hydroxyl radical (·OH) oxidation, high pressure, and high-temperature pyrolysis was demonstrated. Finally, a possible degradation pathway of DBP is obtained on the basis of the main reaction intermediates.

Influence of Aeration Pipe Length on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field.

Improving the gas-liquid mass transfer efficiency in microporous aeration technology is the key to strengthening the restoration effect of black and odorous water bodies. However, the effect of bubble motion characteristics on oxygen mass transfer has not been systematically studied, which limits the efficient and economical application of microporous aeration remediation technology in black and odorous water. The influence under different aeration pipe lengths was analyzed for oxygen mass transfer and bubble movement in microporous aeration technology. The aeration pipe length (0.1-0.5 m) was positively correlated (R = 1.000, R = 0.997) with the number of bubbles and the specific surface area of bubbles and negatively correlated with the time-average velocity of bubbles and Sauter average diameter (R = -0.999, R = -0.997). Moreover, the increase in pipe length weakened the disturbance intensity of plume to water body. The results of oxygen mass transfer showed that the oxygen mass transfer coefficient (K L a) and oxygen utilization rate (E A) increased (K L a from 1.96 to 4.57 h-1, E A from 6.47 to 15.07%) with the increase of pipe length, which was significantly positively correlated (R = 0.985, R = 0.969) with the number of bubbles and bubble specific surface area (S b). This study provided theoretical parameters for the mechanism of oxygen mass transfer during microporous aeration.

Quantitative microbial risk assessment with nasal/oral breathing pattern for S. aureus bioaerosol emission from aeration tanks and residual sludge storage yard in a wastewater treatment plant.

A large number of pathogenic bioaerosols are generated during the treatment process of wastewater treatment plants (WWTPs), and they can pose potential risks to human health. Therefore, this study systematically analyzed the emission characteristics of Staphylococcus aureus bioaerosols released from an inverted umbrella aeration tank, a microporous aeration tank, and a residual sludge storage yard in a WWTP, and quantitatively evaluated the health risks of four kinds of exposed populations with nasal/oral breathing patterns under optimistic and conservative estimations. The results displayed that the bioaerosol concentration in inverted umbrella aeration tank was higher than that in microporous aeration tank and residual sludge storage yard. Aerosolization ratio in residual sludge storage yard was an order of magnitude lower than that in aeration tanks. Sludge workers were at higher health risks than the other three exposed populations. The health risks of nasal breathers (infection risk: 1.62 × 10-5-2.56 × 10-3 pppy; disease burden: 4.24 × 10-8-6.72 × 10-6 DALYs pppy) were 0.61-0.63 times higher than those of oral breathers (infection risk: 9.95 × 10-6-1.59 × 10-3 pppy; disease burden: 2.61 × 10-8-4.18 × 10-6 DALYs pppy). For female field engineers using oral breathing, laboratory technicians, and researchers without personal protective equipment (PPE), infection risk and disease burden had the opposite results, which indicated that satisfying one certain benchmark did not mean absolute safety. In addition, health risks of exposed populations were reduced by an order of magnitude after wearing PPE. This study can provide a reliable theoretical basis for the risk prevention of bioaerosols and supply data support for the strategies of health risk control perspectives for local sewage utilities.

Bioaerosols emission characteristics from wastewater treatment aeration tanks and associated health risk exposure assessment during autumn and winter

Aeration tanks from activated sludge wastewater treatment plants (WWTPs) can release a large amount of bioaerosols that can pose health risks. However, risk characterization of bioaerosols emissions form wastewater treatment plants is currently not systematically carried out and still in its infancy. Therefore, this study investigated emission characteristic of two indicator model bioaerosols Staphylococcus aureus and Escherichia coli, emitted from aeration tanks of a municipal WWTP. Monte Carlo simulation was then used to quantitatively assess microbial risk posed by different aeration modes under optimistic and conservative estimates. Further to this, two different exposure scenarios were considered during 3 days sampling campaign in autumn and winter. Results showed that the bioaerosol concentration from microporous aeration tank (20–262 CFU m−3) was one order of magnitude lower than rotating disc aeration tank. Average aerosolization rate was 7.5 times higher with mechanical aeration mode. Health risks of exposed populations were 0.4 and 9.6 times higher in winter than in autumn for E. coli and S. aureus bioaerosol, respectively. Health risks of staff members were 10 times higher than academic visitors. Interesting results were observed for academic visitors without personal protective equipment (PPE) respectively exposed to S. aureus and E. coli bioaerosol in autumn and winter: while the derived infection risk met the United States Environmental Protection Agency (U.S. EPA) benchmark under optimistic estimation, the disease risk burden was over the World Health Organization (WHO) benchmark under conservative estimation. These revealed that only satisfying one of the two benchmarks didn't mean absolute acceptable health risk. This study could facilitate the development of better understanding of bioaerosol quantitative assessment of risk characterizations and corresponding appropriate risk control strategies for wastewater utilities.

Seasonal variation of quantitative microbial risk assessment for three airborne enteric bacteria from wastewater treatment plant emissions

Airborne E. coli, fecal coliform, and Enterococcus are all related to sewage worker’s syndrome and therefore used as target enteric bioaerosols about researches in wastewater treatment plants (WWTPs). However, most of the studies are often inadequately carried out because they lack systematic studies reports bioaerosols emission characteristics and health risk assessments for these three enteric bacteria during seasonal variation. Therefore, quantitative microbial risk assessment based on Monte Carlo simulation was utilized in this research to assess the seasonal variations of health risks of the three enteric bioaerosols among exposure populations (academic visitors, field engineers, and office staffs) in a WWTP equipped with rotating-disc and microporous aeration modes. The results show that the concentrations of the three airborne bacteria from the rotating-disc aeration mode were 2–7 times higher than the microporous aeration mode. Field engineers had health risks 1.5 times higher than academic visitors due to higher exposure frequency. Health risks of airborne Enterococcus in summer were up to 3 times higher than those in spring and winter. Similarly, health risks associated to E. coli aerosol exposure were 0.3 times higher in summer compared to spring. In contrast, health risks associated with fecal coliform aerosol were between 2 and 19 times lower in summer compared to spring and winter seasons. Data further suggest that wearing of N95 mask could minimize health risks by 1–2 orders of magnitude. This research shed light on seasonal variation of health risks associated with bioaerosol emission from wastewater utilities.

Modelling and controlling dissolved oxygen in recirculating aquaculture systems based on mechanism analysis and an adaptive PID controller

In aquaculture, dissolved oxygen (DO) content is critical to the growth and development of aquatic products, and it must be precisely controlled. Based on the theory of microporous aeration mass transfer and mass conservation equations, this paper analyzed the influence of the four main factors of recirculating water flow, mechanical aeration, surface reaeration and respiration of shrimp on the dynamic changes of DO, and established a DO system dynamics model in the recirculating aquaculture system. Based on the established model, this paper proposed a fuzzy rule-optimized single neuron adaptive PID controller (FL-SN-PID) for precise control of DO. In order to verify the reliability of the established model, several aeration experiments with different aeration flows were conducted in Simulink and actual breeding system. All fitting R2 between simulated data and measured data of the DO response are above 0.94, indicating that the established dynamics model can accurately approximate the actual breeding system and can provide a basis for the design of the controller. In the simulation experiment, the proposed controller was applied to the DO tracking control in three scenarios, and its tracking performance was also compared with the traditional PID controller and the SN-PID controller. In performance analysis, the integral of absolute error (IAE) and the integral of squared error (ISE) of the FL-SN-PID controller are obviously smaller than the other two controllers, indicating this controller has better control accuracy and robustness, and can be competent for precise control of DO in aquaculture.

Estimating acceptable exposure time for bioaerosols emission in a wastewater treatment plant by reverse quantitative microbial risk assessment based on various risk benchmarks.

Populations exposed to bioaerosols over time in wastewater treatment plants (WWTPs) will be infected. Then, the reverse quantitative microbial risk assessment (QMRA) provides a quantitative framework for the estimation of acceptable exposure time to protect people from excessive exposure and then manage their health risk. In this study, the acceptable exposure time for staffs and visiting researchers exposed to S. aureus or E. coli bioaerosols emitted from aeration ponds in WWTPs was estimated and analyzed by Monte Carlo simulation-based reverse QMRA (using the 1E-4 pppy suggested by the US EPA or 1E-6 DALYs pppy suggested by the WHO as benchmarks). The 1E-3 and 1E-2 pppy were selected as a series of loose annual infection risk benchmarks to calculate a practical acceptable exposure time. The results showed that for the acceptable exposure time in each specific exposure scenario, the exposure of females was consistently 0.3-0.4 times longer than that of males; the exposure of staffs was 3.6-3.9 times shorter than that of visiting researchers; the exposures of populations in the rotating-disc aeration mode were consistently 6.3-6.6 and 2.8-3.1 times longer than those in the microporous aeration mode for S. aureus and E. coli bioaerosols, respectively. The acceptable exposure time with the use of personal protective equipment (PPE) was 33.4-35.0 times as long as that without PPE. The US EPA benchmark is stricter than the WHO benchmark with regard to the estimation of the acceptable exposure time of S. aureus or E. coli bioaerosols. The 1E-3 pppy is more appropriate and practical than the US EPA benchmark, but the 1E-2 pppy is notably too loose for health risk management. This research can assist managers of WWTPs to formulate a justified exposure time and develop applicable administrative and personal intervention strategies. The results can enrich the knowledge bases of reverse QMRA to elect a series of loose health-based target risk benchmarks for health risk management.

A self-sufficient electro-Fenton system with enhanced oxygen transfer for decontamination of pharmaceutical wastewater

The need for extra iron catalyst, limited selectivity of the oxygen reduction reaction (ORR) to produce H2O2, and harsh pH applicability still plague the electro-Fenton (EF) process. To alleviate these concerns simultaneously, a novel self-sufficient EF system was constructed, in which the newly fabricated Fe, N and S co-doped cathode was aerated via microporous aeration and a greater number of cathodes was utilized. Results indicated that the prepared cathode achieved a high H2O2 accumulation (15.60 ± 0.16 mg L−1 cm−2) coupled with nearly 90% H2O2 selectivity. The microporous aeration tube, which delivered microbubbles and changed the diffusion direction to supply more O2 to the electrode active sites, is beneficial to the H2O2 formation. Apart from its high H2O2 accumulation, the proposed system was set up to automatically reduce the bulk pH by regulating different current densities on electrodes. The proposed EF system was employed to treat real pharmaceutical wastewater, in which ·OH, 1O2, ·O2− and Fe(IV) were the main active species. Finally, an improvement of BOD5/COD values after EF treatment was a good indicator to confirm the feasibility of the developed system as a pretreatment prior to the subsequent engineering applications.

Application of Flow Field Analysis in the Process Design of Modified Microporous Aeration Oxidation Ditch

According to the environment and water quality factors of the project location, an improved microporous aeration oxidation ditch process is designed, which has the characteristics of biochemical reaction of space division, microporous aeration, infinite water circulation in the ditch, and multiple water inlets; under simplified boundary conditions, based on the CFD method, the SSTK-W model is used to close the RANS equation to simulate the flow field in the hypoxic and aerobic areas. With the optimal equipment configuration and the lowest energy consumption, the flow velocity in the trench is more than 0.3m/s, to ensure high buffering capacity of the process; study the flow field state and the unfavorable flow velocity under the optimized operation state of the flow thruster; the rationality of the design is verified through the commissioning and operation of the sewage treatment plant.

Discussion on the design of solar aerator for fish pond

The solar energy is used as the power of the aerator in the solar aerator for fish pond to provide sufficient oxygen for fishes in pond, which meets the needs of general aquaculture. In this paper, solar energy is used as the power source of aerator, and weak current DC aerator replaces the traditional existing strong alternating aerator. The system comprises of a polycrystalline solar panel square array, solar panel bracket, controller, colloidal battery, DC aeration blower, micro-porous aeration coil, DC-DC regulated adjustable power supply module, DC brushless water spray aerator, etc. The experimental results show that the solar aerator can work for 6.5 hours per day on average. Furthermore, after adding the DC-DC regulated and adjustable power supply module, the voltage and the current of the solar aerator are relatively stable. Therefore, the aerator has a noticeable effect on the dissolved oxygen in the water, and it can effectively and stably provide the necessary oxygen for the fish pond.

Seasonal fluctuation of aerosolization ratio of bioaerosols and quantitative microbial risk assessment in a wastewater treatment plant.

Wastewater treatment plants (WWTPs) play a vital role in public health because it can emit a large quantity of bioaerosols. Exposure to bioaerosols from WWTPs is a potential health risk to WWTP workers and surrounding residents. In this study, the seasonal fluctuation of aerosolization ratios of several bioaerosols and quantitative health risks of the WWTP workers and the surrounding residents exposed to total coliform, fecal coliform, and enterococcal bioaerosols were analyzed. Results showed that the aerosolization ratio of airborne bacteria was higher in the cold seasons and lower in the warm seasons, whereas the aerosolization ratio of airborne fungi was the highest in summer. The aerosolization ratio of airborne fungi was evidently higher than that of other bioaerosols. Moreover, the aerosolization ratio under the inverted umbrella aerator mode was generally higher than that under the microporous aerator mode. For each exposure scenario, the health risks of males were generally 7.2-26.7% higher than those of females. The health risks of the exposure population exposed to total coliform and enterococcal bioaerosols were generally higher in warm seasons, whereas those of the population exposed to fecal coliform bioaerosol were the highest in winter. Additionally, the health risks of exposure population without masks under the imprudent/conservative estimate all exceeded the benchmarks. However, when equipped with masks, all the exposure populations' health risks decreased 1-2 orders of magnitude and approached acceptable levels. This research methodically provides new scientific data on the aerosolization ratio of microorganism bioaerosols in a WWTP and promotes the comprehension of their quantitative health risks under imprudent/conservative estimates.

Constraining release of pollutants from anoxic bottom sediment via water-lifting aeration in a source water reservoir, East China

Seasonal hypoxia in water bodies can increase levels of reduced chemical species in the hypolimnion as they are released from anoxic bottom sediments. Water-lifting aeration (WLA) is a technology known to solve this problem by elevating near-sediment dissolved oxygen (DO) and increasing mixing in the water column in a canyon reservoir with deep water (>20 m). The influence of WLA in reservoirs with large surface area and small water depth has not been adequately evaluated. For this purpose, the efficiency of an innovative WLA system was reviewed in Zhoucun Reservoir (ZCR), a mildly eutrophic reservoir with a mean depth of 15 m. Three years of field experiment was performed in ZCR. Water and sediment samples were collected before and after the operation of the WLA system to explore the causes for the deterioration of water quality in ZCR, and the efficiency of the innovative WLA system installed in 2015. With the use of a microporous aerator and a kinetic energy dissipator, the new-style WLA system is different from WLA studied before. As a result of thermal stratification and the long duration of anaerobic environment in the hypolimnion, the sediment oxygen consumption rate in ZCR was calculated to be 16.14 mg m−2 h−1, which was much higher than other reservoirs, and the main pollutants in ZCR were ammonia, phosphorus, manganese and sulphide. After the operation of the new WLA system, the anaerobic environment in the bottom water was completely reversed and the DO concentration in the hypolimnion water has been maintained at more than 6 mg L−1. The release of pollutants from sediments, such as ammonia, phosphorus, manganese and sulphide, was inhibited significantly. Ammonia, phosphorus, manganese and sulphide in water decreased by 89%, 84%, 97% and 87%, respectively. The results of this study demonstrate that employing WLA systems to oxygenate and mix stagnant water bodies is a viable and potentially favourable management strategy for reservoirs with large surface area and relatively small water depth.

Influence of Aeration Microporous Aperture on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field

Microporous aeration has been widely used to restore eutrophic water bodies. The gas–liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.

Emission characteristics of bioaerosol and quantitative microbiological risk assessment for equipping individuals with various personal protective equipment in a WWTP

Wastewater treatment plants (WWTPs) are a nonnegligible source of bioaerosols that can pose health risks to workers and nearby residents. Thus, this study systematically investigated the emission characteristics of the size distribution and concentration of Staphylococcus aureus bioaerosol in a WWTP. Then, the research focused on the quantitative microbiological risk assessment (QMRA) of workers and nearby residents for equipping them with various grades personal protective equipment (PPE). Results showed that the peak proportion of the size distributions of bioaerosol particles in the three sources all obtained a size range between 3.3 and 4.7 μm. In the residential building, the peak proportion was larger (>7.0 μm). Referring to the three sources, the average bioaerosol concentrations were in the following sequence: inverted umbrella aerator tank > residual sludge storage yard > microporous aerator tank. The health risks of residents were generally 1–2 orders of magnitude higher than the other two exposure scenarios and were clearly beyond the benchmarks. Meanwhile, the health risks of the field engineer were usually lower than those of the staff at the residual sludge storage yard. In general, equipping workers and residents with PPE could at least decrease the health risks by one order of magnitude, and higher-grade PPE could appropriately promote the reduction of health risks. This research systematically delivered a series of novel data about the emission characteristics of Staphylococcus aureus bioaerosol in a WWTP. It advanced the understanding of the quantitative health risks of equipping individuals with various PPE.

Quantitative microbial risk assessment of bioaerosols in a wastewater treatment plant by using two aeration modes.

Nonnegligible emission of bioaerosols usually occurs during aeration of wastewater in aerator tanks in wastewater treatment plants (WWTPs). Literature had shown that the respiratory and intestinal diseases of workers at WWTPs are related to bioaerosols. Thus, quantitative microbial risk assessment (QMRA) based on Monte Carlo simulation was utilized in this research to assess the health risks of Gram-negative bacteria bioaerosol (GNBB) and Staphylococcus aureus bioaerosol (SAB) among academic visitors and staffs. Results showed that the concentrations of GNBB and SAB in the inverted umbrella aeration mode were consistently higher than those in the microporous aeration mode under all six size distribution ranges of the Anderson six-stage impactor. Thus, GNBB and SAB can be highly threatening to the weasand and first bronchus (or alveoli and third bronchus) for the exposure populations. The health risks (annual probability of infection (Py) and disease burden (DB)) of males were constantly higher than those of females for each certain exposure scenario. The health risks of staffs were higher than those of academic visitors when assessed by Monte Carlo simulation. The wearing of mask is an effective measure to minimize health risks through reducing the bioaerosol concentration intake. Especially, for the academic visitors and staffs exposed to GNBB, all their DB failed to meet the World Health Organization DB benchmark under various credible intervals when they were without a mask on. In a word, the results of health risk assessment in this research can be utilized as an educational tool and policy basis to facilitate the implementation of efficacious prevention measures to protect the public health from bioaerosol health threats in WWTPs.

Start-up and operational performance of the partial nitrification process in a sequencing batch reactor (SBR) coupled with a micro-aeration system

Partial nitrification (PN) of ammonia to nitrite is investigated in a lab-scale sequencing batch reactor (SBR) coupled with both a microporous aeration system and a mechanical agitation system at a moderate temperature of (27 ± 1 °C). The SBR has a high actual oxygen transfer efficiency (AOTE) of 2.0% and dynamical efficiency (DE) of 20.0%. Alkalinity consumption declined with the decreasing ratios of HCO3− to NH4+-N in the influent from 2.57, 1.96, 1.91 to 1.66, while the pH of the effluent is constantly maintained at 7.5 ± 0.1. The SBR is successfully operated for 195 days at a nitrogen loading rate (NLR) of up to 2.82 kg·m−3.d−1, achieving a nitrite accumulation rate (NAR) of over 90%. The high-throughput sequencing shows that the ratio of Nitrosomonas, the dominant species, is up to 29.83%.

Characteristics of MBR Oily Sludge and Its Influence on Membrane Fouling under Two Aeration Modes

A membrane bioreactor (MBR) with ordinary aeration (reactor R1) and a MBR with microporous aeration (reactor R2) are conducted in parallel to investigate the characteristics of oily sludge and its effect on membrane fouling. The results indicate that the order of membrane fouling rate from high to low is: reactor R1 dissolved oxygen (DO) (1 mg/L) > reactor R2 DO (1 mg/L) > reactor R1 DO (4 mg/L) > reactor R2 DO (4 mg/L). Membrane fouling rate is not related to oily sludge concentration but to oily sludge sedimentation performance and the small particle oily sludge is the key factor to affect the membrane fouling. The soluble microbial products (SMP) are examined by three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra. 3DEEM spectra demonstrate that the main organic substances of the SMP in two reactors are tyrosine aromatic protein, fulvic acid-like substances and soluble microbial products under DO are1 mg/L and 4 mg/L, respectively. The proportion sum of fulvic acid-like substances and soluble microbial products is the key factor affecting membrane fouling, and membrane fouling accelerates as the ratio increases.