Oxic Process Research Articles

Fates of intracellular and extracellular antibiotic resistance genes during the cattle farm wastewater treatment process

Cattle farm wastewater, as a significant reservoir for antibiotic resistance genes (ARGs), has received wide attention. Intracellular and extracellular ARGs (iARGs and eARGs) were detected during wastewater treatment, including solid–liquid separation, anaerobic regulation, upflow anaerobic sludge blanket (UASB) digestion, an anoxic–oxic-anoxic–oxic (A2O2) process, a membrane bioreactor (MBR), and ozone disinfection. Ten abundant ARGs were chosen as the target ARGs according to metagenomic sequencing. The concentrations of the total target iARGs and eARGs were 6.12 × 107 and 3.24 × 106 copy numbers/mL in raw wastewater, and then 3.79 × 103 and 3.95 × 105 copy numbers/mL in final effluent, because UASB, A2O2, MBR and ozone disinfection can gradually reduce the concentrations of most ARGs. The concentrations of ARGs were positively correlated with almost all wastewater quality indicators. Positive correlation was also observed between iARGs and Bacteroidetes, Firmicutes and Spirochaetes, indicating that the bacteria in these three phyla might be the main hosts of ARGs. Wastewater quality indicators and bacterial community composition affected the distribution and removal of ARGs during cattle wastewater treatment.

Dynamic relationship between dissolved organic matter and soluble microbial products during wastewater treatment

Dynamics of the dissolved organic matter (DOM) and soluble microbial products (SMP) significantly affected the sustainability of wastewater treatment plants and effluent qualities. In this study, the origin, transformation, and seasonal variation of DOM components in the anaerobic/anoxic/oxic (A2O) units were illustrated with fluorescence analysis. Results show that the anaerobic process transformed humic acid-like substances (HA) and SMP into fulvic acid-like substances (FA) and aromatic proteins (AP), which indicated the decomposition of macromolecules. In cold seasons, the anoxic process turned AP to HA, SMP, and FA; but the oxic process reversed the transformation. In warm seasons, 6.0% of AP decreased while 3.1% of HA, 1.8% of SMP, and 1.0% of FA increased during the oxic process. Proteobacteria strains were isolated from the activated sludge to stimulate the SMP generation, it was found higher temperature facilitated the transformation of FA and HA (humics) to SMP and AP (proteins), which resulted more proteins presented in the wastewater DOM. These findings indicated that the treatment efficiency and DOM quality in A2O processes were influenced by influent quality and/or temperature conditions, and highlighted the generation of SMP by sludge microorganisms, based on which the corresponding strategies considering the seasonal DOM/SMP dynamics were recommended for the stringent regulation of effluents and the sustainability of the receiving water bodies. Besides, the overall fluorescence intensity was positively correlated with the quantified biopolymer contents in SMP, implying the potential of using the fluorescence-derived information to indicate more quantified DOM properties.

Bioaugmentation treatment of a novel microbial consortium for degradation of organic pollutants in tannery wastewater under a full-scale oxic process

Tannery wastewater contains a variety of complex organic compounds that is usually refractory for biodegradation. In this study, the research objective was to couple novel beneficial microorganisms to oxic processes to degrade organic pollutants at an industrial-scale tannery wastewater treatment plant. The characteristics of the conversion and biodegradation of organic material are also discussed. Although several negatively influencing factors (e.g., chromium) for the removal of organic material were present in this treatment system, an average chemical oxygen demand (COD) removal efficiency of 95.2% was achieved during the 328-day operation. Moreover, the results of a Fourier transform infrared spectroscopy and three-dimensional excitation and emission matrix fluorescence spectra were consistent, showing that organic pollutants (e.g., protein-like, polysaccharide-like, and humic acid-like materials) showed great conversion and synchronous degradation under biotreatment. Humic acid-like and protein-like organic matter were the main components of the influent and effluent organic material, respectively. This was attributed to inoculation of a special composition of beneficial microorganisms with abundant functional genes related to the degradation of organic material.

Performance and microbial community dynamics relationship within a step-feed anoxic/oxic/anoxic/oxic process (SF-A/O/A/O) for coking wastewater treatment

A step-feed anoxic/oxic/anoxic/oxic (SF-A/O/A/O) was developed and successfully applied to full-scale coking wastewater treatment. The performance and microbial community were evaluated and systematically compared with the anoxic/oxic/oxic (A/O/O) process. SF-A/OA/O process exhibited efficient removal of COD, NH4+-N, TN, phenols, and cyanide with corresponding average effluent concentrations of 317.9, 1.8, 46.2, 1.1, and 0.2 mg·L−1, respectively. In particular, the TN removal efficiency of A/O/O process was only 7.8%, with an effluent concentration of 300.6 mg·L−1. Furthermore, polycyclic aromatic hydrocarbons with high molecular weight were the dominant compounds in raw coking wastewater, which were degraded to a greater extent in SF-A/OA/O. The abundance in Thiobacillus, SM1A02, and Thauera could be the main reason why SF-A/O/A/O was superior to A/O/O in treating TN. The microbial community structure of SF-A/O/A/O was similar among stages in system (P ≥ 0.05, Welch's t-test) and was less affected by environmental factors, which may have been one of the important factors in the system's strong stability.

Modeling a Three-Stage Biological Trickling Filter Based on the A2O Process for Sewage Treatment

Biological trickling filters are widely used for sewage treatment. This study models a biological trickling filter based on an anaerobic–anoxic–oxic process (A2O–BTF), established by a combination of aerobic and anaerobic technology. The performance and operational parameters were analyzed using Sumo, a commercially available wastewater treatment process (WWTP) simulation software. The wastewater treatment performance of the anaerobic–anoxic–oxic process biological trickling filter (A2O–BTF), the conventional three-stage biological trickling filter (Three-Stage–BTF), and the single-stage biological trickling filter (Single–BTF) was compared, which indicated the higher performance of A2O–BTF in terms of COD, TN, NH3-N, and TP removal. The operational parameters of A2O–BTF were optimized by Sumo simulation software, and the results showed that the removal efficiency of pollutants was increased by raising the temperature to the range of 13.94–21.60 °C. The dissolved oxygen (DO) in the aerobic reactor enhanced removal efficiency under a saturation concentration of 2.2–2.6 g O2/m3. In addition, the optimization of the reflux ratio promoted the removal efficiency of the pollutants, indicated by the maximum removal efficiency of COD and TN, achieved at the reflux ratio of 2.25, and that of NH3-N and TP, achieved at a reflux ratio of 0.75. This study provides a proof-in-concept demonstration that software modeling can be a useful tool for assisting the optimization of the design and operation of sewage treatment processes.

Dynamics of dissolved organic matter and dissolved organic nitrogen during anaerobic/anoxic/oxic treatment processes

With Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and fluorescence spectroscopy, this study investigated the transformation of dissolved organic matter (DOM) and nitrogen (DON) during the widely-applied anaerobic/anoxic/oxic (A2O) processes to provide molecular insights into the removal, generation, and reduction of DOM/DON species in different biological treatment units. Results indicated that the anaerobic process decomposed the macromolecules of influent DOM/DON and decreased their mass. The anoxic process denitrified DON and generated DOM, as indicated by the decreased molecule number of CHON and CHONS and the increased CHO and CHOS species, as well as the increased overall DOM intensities. DOM mineralization and ammonia nitrogen-DON conversion occurred in the oxic process. Aromaticity and unsaturation degree increased slightly after the A2O processes, which was correlated with the relative abundance of Proteobacteria (positively) and Bacteroidetes (negatively). The results have strong implications to the understanding of DOM/DON dynamics in wastewater treatment plants.

An Oxic–Hydrolytic–Oxic Process at the Nexus of Sludge Spatial Segmentation, Microbial Functionality, and Pollutants Removal in the Treatment of Coking Wastewater

Toxic inhibition and wash-out of nitrifying bacteria in traditional single-activated sludge processes frequently cause instability of nitrification in industrial wastewater treatment and limit the ...

Nitrous oxide emission in a laboratory anoxic-oxic process at different influent pHs: Generation pathways and the composition and function of bacterial community

This study focused on the nitrous oxide (N2O) generation from the biological nitrogen removal process under different pH levels. To explore a pH optimum, the online N2O emission and the bacterial composition and function in the anoxic–oxic process were investigated. The mean gaseous N2O emission accounted for 0.329%, 0.103%, 0.085%, and 0.793% of the influent total nitrogen at pH of 5, 6, 8, and 9, respectively. Incomplete oxidation in oxic tanks was the primary source of N2O, while N2O in the anoxic tank was mainly generated by nitrifier denitrification. No direct correlations were observed between N2O emission and potential nitrifiers and denitrifiers. The impacts of pH on N2O generation were more likely related to the response of bacterial enzymes and nitrogen compounds, rather than the feedback of bacterial community structure itself. Above all, an influent pH range of 6–8 is recommended for nitrogen removal and N2O mitigation in anoxic–oxic process.

Research on the enhanced biological nitrogen removal of wastewater by the ultrasound-hydrolysis acidification of excess sludge.

To simultaneously improve the removal of nitrogen and phosphorus from wastewater with a low C/N ratio and reduce excess sludge production, in this paper, excess sludge ultrasound-hydrolysis acidification (UHA) pretreatment was coupled with the anaerobic-anoxic-oxic (AAO) process to provide carbon source and enhance biological nitrogen removal performance, and the experimental results can be summarized as follows. First, the total nitrogen (TN) concentrations in the effluent of the system decreased from 16.94mg/L to 5.74mg/L, and the removal rate of TN increased by 25.5%. In addition, the concentrations for ammonia nitrogen (NH3 -N) in the system decreased 12.59mg/L, and the removal rate of this index increased by 29.0%. Furthermore, the specific oxygen uptake rate (SOUR) in the anoxic zone increased significantly because the application of UHA products enhanced the microbial activity, and the addition of UHA products had an effect on the microbial community structure in the system. The amounts of denitrifying bacteria such as Betaproteobacteria and Alphaproteobacteria also increased, which enhanced the nitrogen removal efficiency of wastewater biological treatment. PRACTITIONER POINTS: Treatment of excess sludge in UHA device as an additional carbon source. Nitrogen removal efficiency was greatly improved after adding UHA products. Input of UHA products enhanced microbial activity in AAO system. Denitrifying bacteria increased with the addition of UHA products.

Analysis of municipal sewage pollution and denitrification treatment under low oxygen conditions

Anaerobic–Anoxic–Oxic (AAO) process is widely used in municipal wastewater treatment plants because of its simple structure, rich experience in engineering design, easy operation control and simultaneous nitrogen and phosphorus removal. The energy consumed in the aeration process occupies more than 50% of the total energy consumption of the sewage treatment plant, and reducing aeration is one of the major ways to reduce energy consumption. With the nitrification effect, the sewage treatment equipment controlled the dissolved oxygen (do) concentration in the aeration tank to 2 mg/L or more. The result shows that even nitrification can achieve complete nitrification. In a low oxygen state, the sewage treatment plant is reduced in energy consumption The degradation of pollutants in AAO process under different DO concentration was studied in a pilot-scale test. At the same time, the effects of temperature and carbon source on nitrogen removal in the system at low DO concentration were investigated, and the microflora structure was analyzed, in order to provide a reliable theoretical basis for the actual wastewater treatment plant to achieve stable and efficient nitrification at low DO concentration and save energy consumption. • Complete nitration can be achieved at a lower concentration of dissolved oxygen. • The influencing factors of pollutant degradation were analyzed. • The microflora structure was analyzed. • The influencing factors of nitrogen removal in the system were analyzed.

Occurrence and Removal of Veterinary Antibiotics in Livestock Wastewater Treatment Plants, South Korea

In this study, livestock wastewater treatment plants in South Korea were monitored to determine the characteristics of influent and effluent wastewater, containing four types of veterinary antibiotics (sulfamethazine, sulfathiazole, chlortetracycline, oxytetracycline), and the removal efficiencies of different treatment processes. Chlortetracycline had the highest average influent concentration (483.7 μg/L), followed by sulfamethazine (251.2 μg/L), sulfathiazole (230.8 μg/L) and oxytetracycline (25.7 μg/L), at five livestock wastewater treatment plants. Sulfathiazole had the highest average effluent concentration (28.2 μg/L), followed by sulfamethazine (20.8 μg/L) and chlortetracycline (11.5 μg/L), while no oxytetracycline was detected. For veterinary antibiotics in the wastewater, a removal efficiency of at least 90% was observed with five types of treatment processes, including a bio-ceramic sequencing batch reactor, liquid-phase flotation, membrane bioreactor, bioreactor plus ultrafiltration (BIOSUF) and bio best bacillus systems. Moreover, this study evaluated the removal efficiency via laboratory-scale experiments on the conventional contaminants, such as organic matter, nitrogen, phosphorus and veterinary antibiotics. This was done using the hydraulic retention time (HRT), under three temporal conditions (14 h, 18 h, 27 h), using the anaerobic–anoxic–oxic (A2O) process, in an attempt to assess the combined livestock wastewater treatment process where the livestock wastewater is treated until certain levels of water quality are achieved, and then the effluent is discharged to nearby sewage treatment plants for further treatment. The removal efficiencies of veterinary antibiotics, especially oxytetracycline and chlortetracycline, were 86.5–88.8% and 87.9–90.8%, respectively, exhibiting no significant differences under various HRT conditions. The removal efficiency of sulfamethazine was at least 20% higher at HRT = 27 h than at HRT = 14 h, indicating that sulfamethazine was efficiently removed in the A2O process with increased HRT. This study is expected to promote a comprehensive understanding of the behavior and removal of veterinary antibiotics in the livestock wastewater treatment plants of South Korea.

Excess sludge conditioning with ultrasound/ozone and its effect on the anaerobic anoxic oxic process in a municipal wastewater treatment plant

Impact of ultrasonication and ozonation pre-treatment on the sewage sludge and ultrasonication–ozonation integrated with anaerobic anoxic oxic system were investigated. According to response surface methodology, the optimal conditions were determined for an ozone dosage of 0.14g·O3/g·SS and an ultrasonic intensity of 1.61W/mL, which corresponded to a maximum sludge reduction ratio of 68.1%. When the residence time of broken sludge was 30min and the reflux ratio was 60%, the broken sludge returned to the anaerobic or anoxic zone had little effect on chemical oxygen demand and improved total phosphorus removal rate of the anaerobic anoxic oxic system effluent. The broken sludge was returned to the anoxic zone, the removal rate of total nitrogen in the effluent of the anaerobic anoxic oxic system could be increased by 13.2%. The broken sludge backflow improved the sedimentation performance of the anaerobic anoxic oxic system sludge, which had little to do with reflow methods. The broken sludge reflowed to the anaerobic zone reduced the sludge production of the anaerobic anoxic oxic system by 51.3%.

Occurrence and removal of illicit drugs in different wastewater treatment plants with different treatment techniques

BackgroundAs a class of contaminants of emerging concern (CECs), illicit drugs should be taken into account in the water management because of their social and public health risks. Wastewater treatment plants (WWTPs) are usually considered as the source and sink of contaminants, and drug residues are observed in their effluents due to the inefficient removal of CECs. In this study, wastewater samples were collected from eight WWTPs in Changzhou City for assessment of the abuse of 12 illicit drugs in the city by wastewater-based epidemiology (WBE) method.ResultsDrug concentrations ranged from < LOD-51.62 ng/L to < LOD-22.44 ng/L in influent and effluent samples, respectively. The highest removal rate of drugs was 79.0% in the WWTP which used sequencing batch reactor activated sludge (SBR) process method, while the lowest was found in the WWTP using anoxic oxic (A/O) process (47.0%), indicating that the drug removal rates were closely related to the treatment techniques. WBE method was applied to estimate the population normalized illicit drugs consumption. It demonstrated that methamphetamine (METH) was the most abused drug in Changzhou City, ranging from 0.16 to 20.65 mg/d/1000 inh, while other target drugs ranged from < LOD-1.52 mg/d/1000 inh. Consumption of cocaine (COC) and ecstasy was very low among the samples.ConclusionOverall, this research suggests that drug removal rates varied in different WWTPs and the SBR process is the best for removing illicit drugs. All target drugs were incompletely removed in wastewater treatment plants. WBE can be readily used to monitor the abuse of drugs in those regions, compared with traditional monitoring models.

Distribution and Removal of Pharmaceuticals in Liquid and Solid Phases in the Unit Processes of Sewage Treatment Plants.

In this study, we analyzed 27 pharmaceuticals in liquid and solid phase samples collected from the unit processes of four different sewage treatment plants (STPs) to evaluate their distribution and behavior of the pharmaceuticals. The examination of the relative distributions of various categories of pharmaceuticals in the influent showed that non-steroidal anti-inflammatory drugs (NSAIDs) were the most dominant. While the relative distribution of antibiotics in the influent was not high (i.e., 3%–5%), it increased to 14%–30% in the effluent. In the four STPs, the mass load of the target pharmaceuticals was reduced by 88%–95% mainly in the biological treatment process, whereas the ratio of pharmaceuticals in waste sludge to those in the influent (w/w) was only 2%. In all the STPs, the removal efficiencies for the stimulant caffeine, NSAIDs (acetaminophen, naproxen, and acetylsalicylic acid), and the antibiotic cefradine were high; they were removed mainly by biological processes. Certain compounds, such as the NSAID ketoprofen, contrast agent iopromide, lipid regulator gemfibrozil, and antibiotic sulfamethoxazole, showed varying removal efficiencies depending on the contribution of biodegradation and sludge sorption. In addition, a quantitative meta-analysis was performed to compare the pharmaceutical removal efficiencies of the biological treatment processes in the four STPs, which were a membrane bioreactor (MBR) process, sequencing batch reactor (SBR) process, anaerobic–anoxic–oxic (A2O) process, and moving-bed biofilm reactor (MBBR) process. Among the biological processes, the removal efficiency was in the order of MBR > SBR > A2O > MBBR. Among the tertiary treatment processes investigated, powdered activated carbon showed the highest removal efficiency of 18%–63% for gemfibrozil, ibuprofen, ketoprofen, atenolol, cimetidine, and trimethoprim.

Promising carbon utilization for nitrogen recovery in low strength wastewater treatment: Ammonia nitrogen assimilation, protein production and microbial community structure

Acetic acid and sodium acetate are generally supplied to wastewater treatment plants (WWTPs) in China to improve total nitrogen (TN) and total phosphorus (TP) removal, and the addition of carbon source also facilitates to increase sludge growth rate and further provides material basis for the extraction of proteins and amino acids from activated sludge. To recycle ammonia nitrogen resources, a system that combined adsorption and anaerobic–anoxic–oxic (A/AAO) process for treating low strength wastewater was established. Experimental results showed that by the addition of carbon substrate from a mixture of anaerobically fermented adsorption sludge, the average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen, TN, and TP were 88%, 96.9%, 93.9%, and 92.1%, respectively, and the ratio of nitrogen assimilation to nitrogen dissimilation significantly increased by a factor of 2.5. Through energy analysis (based on adenosine triphosphate, ATP), sludge flocculation capacity and settling property, it was found that the AAO process sludge presented the logarithmic growth characteristics. The respective sludge protein and amino acids contents increased by over 11.4% and 40.3%, and the synthetic products of glutamic acid, alanine and aspartate increased through the assimilation of ammonia nitrogen, thereby indicating that replenishing the carbon substrate could markedly enhance protein and amino acids contents in AAO process sludge. Moreover, the diversity of the microbial community in adsorption process was relatively rich, the diversity in the adsorption process sludge was the highest, while the diversity of the AAO process sludge evidently decreased. The microbial community in each process was similarly based on 16S rDNA gene sequence analysis, microflora was prominent in the AAO process, with Dechloromonas, Flavobacterium, Zoogloea, Unclassified_Rhodocyclaceae and Thauera as the dominant species. Promising carbon utilization facilitates contaminants removal in low strength wastewater treatment and is conducive to protein production through ammonia nitrogen assimilation.

Elimination of typical polycyclic musks in a full-scale membrane bioreactor combined with anaerobic-anoxic-oxic process in municipal wastewater treatment plant.

The objective of this study was to investigate the removal of 11 synthetic polycyclic musks in a municipal wastewater treatment plant located in Jilin, China, by using a membrane bioreactor combined with anaerobic-anoxic-oxic process. The analysis of synthetic polycyclic musks was conducted with gas chromatography/mass spectrometry after solid-phase extraction. The removal efficiency of 11 synthetic polycyclic musks ranged from 65.9% (3-methylcyclopentadecanone) to 84.6% (Galoxolide) in the influent. Along the treatment process, it was observed that the anaerobic tank could remove the synthetic polycyclic musks effectively whereas the role of the membrane was to the musks, which could be ascribed to the relatively strong hydrophobic property of the musks. The sludge-water distribution coefficients (Kd values) as indicator of adsorption propensity for the sludge from anaerobic, anoxic, oxic and membrane tanks were measured. The high value of Kd, above 5.0 litres per gram of suspended solids, showed most of the musks could be removed by sludge through the adsorption process; thus the removal rate from the water phase caused by adsorption in the wastewater treatment plant can be predicted.

In−situ sludge reduction and carbon reuse in an anoxic/oxic process coupled with hydrocyclone breakage

The long−term performance of an anoxic−oxic−hydrocyclone (AOH) process with an in−situ hydrocyclone treatment unit in the mixed liquid return line for sludge reduction and carbon reuse has been observed, in comparison with a conventional anoxic−oxic (AO) process. Three parallel side−stream systems, including one AOH25 system with a 25−mm hydrocyclone, one AOH35 system with a 35−mm hydrocyclone and one AO system, were built and fed with real wastewater for a comparative study in a wastewater treatment plant. The results demonstrate that the hydrocyclone in the AOH process was able to break macro−flocs into smaller flocs. And the desorption of the extracellular polymeric substance from return activated sludge (AS) leaded to an average increase of 62.97% and 36.36% in SCOD in the AOH25 and AOH35 system, respectively. In addition, shear forces, centrifugal forces of revolution and flocs’ rotation in the hydrocyclone were proposed to be the main influence mechanism of hydrocyclone treatment on AS properties. Compared with the AO process, the SCOD concentration in the effluent of the AOH processes presented a decrease of 12.0 mg/L and the TN was reduced by 21.50% owing to the released carbon sources reuse. Moreover, the sludge production was reduced by 36.81% and 35.92% in the AOH25 and AOH35 process, respectively. By contrast, the AOH25 system was better than the AOH35 system.

Operation space design of microbial fuel cells combined anaerobic–anoxic–oxic process based on support vector regression inverse model

Microbial Fuel Cells (MFCs) can produce power at the same time of wastewater treatment, which is a new technique for environmental protection and new energy. An appropriate space design of operation variables is very important to improve the performance of MFC process. This paper presents a space design method based on data-driven model but not the traditional mechanism model, which is easy to accomplish in a fast and cost-effective mode. The support vector regression (SVR) forward and inverse model are deduced with the quadratic kernel function, in which the quadratic kernel function is suitable for the mathematical formula in the inversion stage. And the space design of operation variables are proposed to calculate directly from the inverse model with the effect of confidence interval when the model prediction uncertainty are considered. The proposed design method is verified in the real MFC-A2/O equipment. It is shown that the designated operation space is a narrow and effective region of the knowledge space which brackets the entire fraction of the MFC experiment space. And in general terms, the possible product quality from the designated operation space is more densely concentrated on the desired value compared to the tradition forward model design method.

Removal and fate of polycyclic aromatic hydrocarbons in a hybrid anaerobic–anoxic–oxic process for highly toxic coke wastewater treatment

Elimination of polycyclic aromatic hydrocarbons (PAHs) from coke wastewater is crucial to minimize the PAHs contamination levels to the environment. Knowledge about the characteristics of PAHs removal in biological treatment processes, especially hybrid systems, for real coke wastewater treatment has been very scarce. In this study, a lab-scale hybrid anaerobic–anoxic–oxic (A1/A2/O) process was used to treat highly toxic coke wastewater and operated more than 600 d at total hydraulic retention time (HRT) of 50 h, 40 h, 30 h, 20 h and internal mixed liquor recirculation ratio (R) of 3, 6, 9. Removal performance and behaviors of priority PAHs in the hybrid A1/A2/O system were investigated. The results showed that the appropriate total HRT and R from oxic reactor to anoxic reactor for organics and nitrogen removal was 40 h and 3, respectively. The concentrations of total PAHs were very high (254–488 μg/L) in the raw coke wastewater, and effectively reduced to 4.1–4.5 μg/L in the final effluent by the present system under the optimized operational conditions. Among the three treatment units, anoxic reactor made the largest contribution to the total PAHs removal. Large amounts of PAHs (415–1310 μg/g) were adsorbed to the activated sludge in the anoxic and oxic reactor, leading to a much higher load of PAHs (2535 μg/d) in the excess sludge than that in the treated coke wastewater (93 μg/d) at SRT 60 d. Therefore, the excess sludge was identified as the major emission source of PAHs in coke wastewater during the hybrid A1/A2/O process, and might pose an environmental risk if the excess sludge was not properly treated and disposed.

Treatment of municipal sewage with low carbon-to-nitrogen ratio via a novel integrated process

In this study, a novel integrated process combining simultaneous partial nitrification, anammox, and denitrification (SNAD) with anaerobic hydrolysis and acidification (AnHA) was proposed for the treatment of municipal sewage with low carbon-to-nitrogen ratio (C/N). The average removal efficiencies of chemical oxygen demand (COD) and NH4+-N in AnHA were 27.15% and 1.45%, respectively. Meanwhile, the removal rates of COD and total nitrogen in SNAD were approximately 83.12% and 79.13%, respectively. Fluorescence in situ hybridization results showed that acidogenic bacteria accounted for 92.4% of all bacteria in AnHA. The dominant bacterial group in the aerobic layer of the SNAD biofilm was ammonium-oxidizing bacteria (65.13%), whereas that in the anaerobic layer was anammox (47.17%) and denitrifying (38.91%) bacteria. Compared with the energy consumption of the anaerobic–anoxic–oxic process (100%), the AnHA-SNAD energy consumption was only 53.2%, which indicated an energy-saving alternative process for low C/N municipal sewage treatment.