A2O System Research Articles

Temperature-Driven Activated Sludge Bacterial Community Assembly and Carbon Transformation Potential: A Case Study of Industrial Plants in the Yangtze River Delta.

Temperature plays a critical role in the efficiency and stability of industrial wastewater treatment plants (WWTPs). This study focuses on the effects of temperature on activated sludge (AS) communities within the A2O process of 19 industrial WWTPs in the Yangtze River Delta, a key industrial region in China. The investigation aims to understand how temperature influences AS community composition, functional assembly, and carbon transformation processes, including CO2 emission potential. Our findings reveal that increased operating temperatures lead to a decrease in alpha diversity, simplifying community structure and increasing modularity. Dominant species become more prevalent, with significant decreases in the relative abundance of Chloroflexi and Actinobacteria, and increases in Bacteroidetes and Firmicutes. Moreover, higher temperatures enhance the overall carbon conversion potential of AS, particularly boosting CO2 absorption in anaerobic conditions as the potential for CO2 emission during glycolysis and TCA cycles grows and diminishes, respectively. The study highlights that temperature is a major factor affecting microbial community characteristics and CO2 fluxes, with more pronounced effects observed in anaerobic sludge. This study provides valuable insights for maintaining stable A2O system operations, understanding carbon footprints, and improving COD removal efficiency in industrial WWTPs.

Application of a biofilm-enhanced A2O system in the treatment of wastewater from mariculture

Development of environment-friendly and efficient aquaculture effluent treatment system is crucial for sustainable intensification of aquaculture, in the face of the rapidly increasing environmental pressure in the mariculture industry. In this study, mariculture wastewater was treated by the anoxic-anaerobic-oxic biochemical treatment system (A2O system) with traditional activated sludge replaced by nitrifying bacteria, denitrification bacteria and phosphorus accumulating bacteria absorbed on PBS carrier biofilms suitable for saline/brackish water. The results showed that biofilm-enhanced A2O system can effectively remove pollutants from aquaculture wastewater. The removal efficiencies of CODMn, NH4+-N, TN and TP in A2O system were approximately 86.3%-90.8%, 97.7%-99.5%, 94.6%-95.2% and 97.0%-98.1%. The results further showed that CODMn, NH4+-N, and TN were mainly removed in anaerobic tank and anoxic tank, while TP was mainly removed in the anoxic tank and oxic tank. The biofilm-enhanced A2O system by adding nitrifying bacteria and phosphorus accumulating bacteria biofilms using PBS as carriers instead of conventional activated sludge could be applied to the treatment of circulating aquaculture wastewater. This study provides a feasible scheme for enhancing the efficiency of A2O system in the treatment of aquaculture tail water, and provides a reference for the immobilization of microorganisms.

Techno-economic and environmental assessment of different municipal wastewater treatment systems

A comprehensive economic evaluation and environmental assessment of wastewater treatment plants (WWTPs) is a precondition to ensure long-term economic, environmental, and social sustainability. In this study, a techno-economic feasibility analysis for different modern compact municipal wastewater treatment technologies including aerobic granular sludge (AGS), high rate activated sludge (HRAS) coupled with membrane bioreactor (MBR), HRAS + MBR process, was conducted. The findings were comparatively evaluated with the conventional anaerobic/anoxic/aerobic (A2O) process. Capital, operation and maintenance (O&M) costs for each system were investigated in detail. Environmental benefits for each system were assessed and an energy balance for each system was conducted. 21 % lower energy consumption was observed in the AGS system in comparison to the A2O system. This finding might be associated with the absence of mixers, return sludge pumping and recirculation of wastewater for nitrogen removal in AGS system. The unit total cost was found to be 0.113 €/m3, 0.091 €/m3, and 0.195 €/m3 for A2O process, AGS process, and HRAS + MBR process in order. Based on the energy balance and economic analysis, AGS system was found to have lower net energy consumption and total cost compared to A2O process and HRAS + MBR process. The results obtained from this study are of vital importance in the economic evaluation of the projected large new WWTPs.

Benefits and drawbacks of integrating a side-stream sludge fermenter into an A2O system under limited COD conditions

The implementation of a side-stream sludge fermenter (SSSF) has been identified as a possible solution to improve the performance of an anaerobic/anoxic/aerobic (A2O) configuration when treating low COD wastewater. This study systematically evaluated the effects of incorporating a SSSF into an A2O configuration (side-stream enhanced biological phosphorus removal, S2EBPR) for P/N/COD removal under a limited influent COD (CODINF) condition. The performance of the S2EBPR (with the SSSF receiving 6% of the recycled activated sludge and operating with a hydraulic retention time (HRT) of 2.4 d) and A2O were compared under the same limited CODINF (350 mg/L) condition. S2EBPR improved the amount of P removed (26.6%) under a low influent COD/P of only 26.3 compared with A2O of 32.6, and enhanced denitrification (11%) without compromising full ammonium and COD removal. However, the PLOAD to the plant increased due to the P-release in SSSF, resulting in higher effluent P concentration. The methane and energy recovery indexes were around 45% lower than those of A2O. Sequencing analysis revealed a high abundance of PAO in accordance to its higher P removal. This study represents a comprehensive evaluation of the S2EBPR configuration and provides an assessment of its suitability.

The relationship analysis and reaction mechanism of carbon, nitrogen, and phosphorus metabolism in sewage treatment in plateau habitat.

The efficiency of pollutant removal in sewage is mainly determined by the structure and abundance of microbial flora, which is essentially represented by the type and abundance of genes and enzymes, and the reaction mechanism is the abundance and degree of reaction of metabolic pathways and metabolic modules. In order to study the mechanism of carbon, nitrogen, and phosphorus metabolism of activated sludge microflora in the A2O process at high altitudes at different temperatures, so as to improve the removal rate of pollutants and reduce the discharge concentration of pollutants. Based on the research environment of high-altitude environmental research, the author used the A2O system as the treatment process and put Illumina MiSeq high-through sequencing technology to comprehensively dissect the reaction relationship of carbon, nitrogen and phosphorus metabolic pathways, and derived the main functional genes and enzymes of carbon, nitrogen, and phosphorus metabolism. It was demonstrated that the abundance of the most metabolic modules and functional genes tended to increase and then decrease with increasing temperature. In particular, the highest abundance and activity and the best pollutant removal efficiency were observed at 20°C. This study will provide a valuable reference for the study of carbon metabolism, nitrogen metabolism, and phosphorus metabolism of microbial flora in sewage treatment under plateau habitats.

Fermentation liquid as a carbon source for wastewater nitrogen removal reduced nitrogenous disinfection byproduct formation potentials of the effluent

Sludge alkaline fermentation liquid (SAFL) is an alternative to sodium acetate (NaAc) in enhancing wastewater nitrogen removal. Upon SAFL addition, dissolved organic nitrogen (DON) can be externally introduced or biologically synthesized during nitrogen removal, which is an important precursor to toxic nitrogenous disinfection by-products (N-DBPs). This study aims to evaluate the effects of different carbon source addition on effluent DON concentration, composition, and N-DBP formation potentials. A lab-scale A2O system treating real municipal wastewater was operated with NaAc or SAFL as external carbon sources. DON molecules and potential N-DBP precursors were identified by Orbitrap mass spectrometry. Subsequently, major microorganisms contributing to DON biosynthesis were suggested based on metagenomics. It was found that effluent DON was higher with SAFL as the carbon source than NaAc (1.51 ± 0.24 v.s. 0.56 ± 0.08 mg N/L, p < 0.05). Nevertheless, dichloroacetonitrile and nitrosamine formation potentials (7.14 ± 1.02 and 1.57 ± 0.07 μg/mg DON-N, respectively) of the effluent with SAFL addition were 42.79 ± 2.42% and 54.89 ± 1.70% lower than those of NaAc. Protein- and lignin-like compounds were the most abundant DON molecules in the effluent, where alanine, glycine and tyrosine were important precursors to N-DBPs. Azonexus and Flavobacterium spp. were positively correlated with these precursors, and possessed key genes involved in precursor synthesis. SAFL is a promising carbon source, not only for achieving efficient inorganic nitrogen and DON removals, but also for reducing N-DBP formation potentials of chlorinated effluent.

Fate of pharmaceutically active compounds in a pilot-scale A2O integrated fixed-film activated sludge (IFAS) process treating municipal wastewater

The goal of this research was to study the operation of an integrated fixed-film activated sludge system (IFAS), in anaerobic/anoxic/aerobic (A2O) configuration for the elimination of emerging pollutants, in particular of 27 pharmaceutical active compounds (PhACs) (eight anti-inflammatory and/or analgesic pharmaceuticals (AIAPs), six antibiotics, four b-blockers, two antihypertensives/diuretics, three lipid regulators-bezafibrate and four psychiatric medications). Different operational conditions were analyzed in the biological reactor, controlling at all times both the amount of suspended and fixed biomass present. The A2O-IFAS system has obtained similar or higher removal efficiency (RE) in the elimination of organic matter, and especially of nutrients, nitrogen (N) and phosphorous (P), with respect to the conventional A2O system, working however with very low values of the sludge retention time (SRT) (4.0 days) and mix liquid suspended solid (MLSS) in the reactor (1822 mg L-1). In general, conventional activated sludge (CAS) and IFAS processes show the importance of operating at high SRT and MLSS concentration, that give low food/microorganisms (F/M) ratio, to increase the RE of several PhACs. However, the A2O-IFAS system, operating with low mixed liquor SRT and MLSS has achieved similar or better RE of PhACs, obtaining the highest average REs values (>80%) for fenofibrate, acetaminophen, ibuprofen, naproxen, clarithromycin and atenolol. According to the results obtained, due to the affordable cost and well-demonstrated performance, IFAS systems become one of the most promising technology for conventional wastewater treatment plants (WWTP) upgrading.

Potential of aerobic membrane bioreactor for recycling and reuse of domestic wastewater for irrigation

This paper explored the positive attributes of aerobic membrane bioreactor for recycling and reuse of domestic wastewater for irrigation. For this purpose, performances of two different full-scale treatment plants, one designed as aerobic membrane bioreactor (AMBR) equipped with a hollow fiber membrane with a nominal pore size of 0.03 μm, and the other, as a conventional nitrogen removal activated sludge plant with pre-denitrification (A2O) were evaluated and compared. The effluent of the A2O system included an average of 109 mg L−1 chemical oxygen demand (COD), 32 mg L−1 total suspended solids (TSS) and 17 mg L−1 of total nitrogen. The AMBR system was able to reduce the effluent COD level to 24 mg L−1, obviously with lower TSS and turbidity. The effluent quality of the AMBR was in compliance with irrigation water standards; its nitrogen content should be evaluated as an added nutritional value for most plants. Considering the additional profit of the recovered water, the investment and operational costs of A2O and AMBR processes were compatible. The results underlined the merit of AMBR process, especially in low populated areas also requiring resources for irrigation.

A pilot-scale three-dimensional electrochemical reactor combined with anaerobic-anoxic-oxic system for advanced treatment of coking wastewater

Coking wastewater is highly concentrated and extremely toxic, greatly challenging the treatment technologies. Conventional biological technology such as anaerobic-anoxic-oxic (A2O) system is inefficient, since various biological reactions are inhibited by toxicants in coking wastewater. In this work, a pilot-scale three-dimensional electrochemical reactor (3DER) is integrated into the A2O system as a pretreatment unit to improve the treatment efficiency of coking wastewater. The results indicate that 3DER pretreatment increased the biodegradability of coking wastewater, promoting the degradation of coking wastewater in A2O system. The integrated 3DER-A2O system can remove 94.4% of COD and 76.2% of TN from coking wastewater, and the energy consumption was only 0.22 kWh/kg COD and 4.69 kWh/kg TN. The components of coking wastewater were significantly simplified and the acute toxicity was reduced from 99% to 12% after the treatment. The integrated 3DER-A2O system provides a new solution for coking wastewater treatment, showing a promising application potential.

Evaluating the Performance of the A2O System for Removing Nutrients from Municipality Wastewater

Evaluating the Performance of the A2O System for Removing Nutrients from Municipality Wastewater

Linking microbial diversity and population dynamics to the removal efficiency of pharmaceutically active compounds (PhACs) in an anaerobic/anoxic/aerobic (A2O) system

The removal efficiencies (REs) of nineteen pharmaceutically active compounds (PhACs) (six antibiotics-clarithromycin, ofloxacin, sulfadiazine, sulfamethazine, sulfamethoxazole and trimethoprim -, four β-blockers -atenolol, metoprolol, propranolol and sotalol-, two antihypertensives/diuretics -furosemide and hydrochlorothiazide-, three lipid regulators -bezafibrate, fenofibrate and gemfibrozil-, and four psychiatric medications -carbamazepine, diazepam, lorazepam and paroxetine) were ascertained in a pilot-scale anaerobic/anoxic/aerobic (A2O) system treating urban wastewater, long term operated during two experimental phases using different sets of environmental conditions and operating parameters. Illumina MiSeq sequencing was used to investigate the structure, diversity and population dynamics of bacteria, archaea and fungi communities in the activated sludge. The results showed that mixed liquor suspended solids (MLSS) and food-to-microorganisms ratio (F/M) were operational parameters significantly influencing the REs of five of the analyzed PhACs in the A2O system. Biota-environment (BIO-ENV) analysis revealed strong correlations between population shifts of the activated sludge community and the REs of PhACs of the different pharmaceutical families. Increased REs of clarithromycin, furosemide, bezafibrate and gemfibrozil were concomitant to higher relative abundances of bacterial phylotypes classified within the Rhodobacteraceae and Sphingomonadaceae (Alphaproteobacteria), while those of Betaproteobacteria, Chloroflexi and Methanomethylovorans (Euryarchaea) correlated positively with the REs of up to seven PhACs belonging to different therapeutic groups.

Metagenomic analysis of the inhibitory effect of chromium on microbial communities and removal efficiency in A2O sludge.

This is the first study exploring the effects of persistent Cr(VI) treatment on microbial communities and function as well as the process efficiency of an A2O system. The inhibitory effect was clearly higher at a high Cr(VI) concentration than a low Cr(VI) concentration, and different Cr(VI) concentrations had distinct effects on the microbial communities as well as on the performance efficiency of the system. Functional annotation analysis indicated that Cr(VI) stress inhibited most of the metabolic pathway and functional genes of the microbial communities, especially those involved in the denitrification pathway. Network analysis was used to investigate the co-occurrence patterns between denitrification genes and microbial taxa; the results indicated that microorganisms with functional genes had high diversity and were adversely affected by Cr(VI) exposure. This study is the first to establish a relationship between Cr(VI) stress and microbial communities and function as well as to determine the underlying mechanisms and roles of Cr(VI) in A2O sludge.

Black water collected from the septic tank treated with a living machine system: HRT effect and microbial community structure

In this study, the performance of a living machine (LM) system was evaluated for use in the treatment of black water collected from septic tanks with hydraulic retention times (HRTs) of 6, 5, and 4 days. We found that the HRT had little effect on the removal efficiency of chemical oxygen demand (COD). However, the removal rates of total nitrogen (TN) and ammonium nitrogen (NH4+-N) decreased with the reduction of HRT, whereas the removal efficiency of total phosphate (TP) was consistently low because of the long sludge retention time. The working conditions of #1 achieved the highest removal efficiency of COD (85%), NH4+-N (75%), and TN (47%), although the removal efficiency of TP (11%) was slightly lower than that of #2 (12%). The microbial communities in each tank of the LM system were characterized by high-throughput sequencing, which showed that the LM system successfully created more favorable conditions for fermentative bacteria than traditional systems, with relative abundances of 13% (#1), 13% (#2), and 15% (#3) compared to that of the anaerobic/anoxic/oxic (A2O) system (<3%). Smithella was the dominant fermentative bacteria, accounting for 9% (#1), 7% (#2), and 10% (#3) of total bacteria in the LM system. The relative abundances of ammonia oxidizing bacteria (AOB) (12%) and anaerobic ammonium oxidizing bacteria (AnAOB) (7%) in the LM system were much higher than that in the A2O system. Overall, the LM system offered a more sustainable and economical solution for treating black water.

Removal of anti-inflammatory/analgesic pharmaceuticals from urban wastewater in a pilot-scale A2O system: Linking performance and microbial population dynamics to operating variables

In this study, the removal rates of eight anti-inflammatory and/or analgesic pharmaceuticals, AIAPs (acetaminophen, ibuprofen, naproxen, ketoprofen, diclofenac, codeine, indomethacin and propyphenazone) were assessed in a pilot-scale A2O system (including anaerobic/anoxic/aerobic zones), long term operated during two experimental phases using different sets of environmental conditions and operating parameters. qPCR was used to quantify the absolute abundances of total Bacteria, total Archaea, mycolic-acid containing filamentous Actinobacteria (Mycolata) and Fungi within the activated sludge microbial community developed in the system. Multivariate analyses and Spearman correlation coefficients were used in search of significant links among the removal rates of the AIAPs, the abundances of the targeted microbial groups in the activated sludge, and the changes of environmental/operating variables in the A2O system. Improved removal efficiencies of several of the AIAPs analyzed (acetaminophen, ibuprofen, naproxen, ketoprofen) were correlated to higher organic load in the influent water, higher concentration of mixed liquor suspended solids (MLSS), lower temperature and lower food-to-microorganisms ratio (F/M). Removal efficiencies of several pharmaceuticals correlated with increased abundances of Mycolata in the A2O system, pointing at this group of bacteria as candidate key players for AIAPs removal in activated sludge.

Effect of effluent and sludge recirculation ratios on integrated fixed films A2O system nutrients removal efficiency treating sewage

Effect of effluent and sludge recirculation ratios on integrated fixed films A2O system nutrients removal efficiency treating sewage

Effect of influent C/N ratio on N2O emissions from anaerobic/anoxic/oxic biological nitrogen removal processes.

The problem of producing strong greenhouse gas of nitrous oxide (N2O) from biological nitrogen removal (BNR) process in wastewater treatment plants (WWTP) has elicited great concern from various sectors. In this study, three laboratory-scale wastewater treatment systems, with influent C/N ratios of 3.4, 5.4, and 7.5, were set up to study the effect of influent C/N ratio on N2O generation in anaerobic/anoxic/oxic (A2O) process. Results showed, with the increased influent C/N ratio, N2O generation from both nitrification and denitrification process was decreased, and the N2O-N conversion ratio of the process was obviously reduced from 2.23 to 0.05%. Nitrification rate in oxic section was reduced, while denitrification rate in anaerobic and anoxic section was elevated and the removal efficiency of COD, NH4+-N, TN, and TP was enhanced in different extent. As the C/N ratio increased from 3.4 to 7.5, activities of three key denitrifying enzymes of nitrate reductase, nitrite reductase, and nitrous oxide reductase were increased. Moreover, microorganism analysis indicated that the relative abundance of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were positively correlated with N2O generation, which was reduced from (8.42±3.65) to (3.61±1.66)% and (10.38±4.12) to (4.67±1.62)%, respectively. NosZ gene copy numbers of the A2O system were increased from (1.19±0.49)×107 to (2.84±0.54)×108 copies/g MLSS with the influent C/N ratio elevated from 3.4 to 7.5. Hence, appropriate influent C/N condition of A2O process could optimize the microbial community structure that simultaneously improve treatment efficiency and decrease the N2O generation.

Removal characteristics of pharmaceuticals and personal care products: Comparison between membrane bioreactor and various biological treatment processes

We investigated the concentrations of 57 target compounds in the different treatment units of various biological treatment processes in South Korea, including modified biological nutrient removal (BNR), anaerobic-anoxic-aerobic (A2O), and membrane bioreactor (MBR) systems, to elucidate the occurrence and removal fates of PPCPs in WWTPs. Biological treatment processes appeared to be most effective in eliminating most PPCPs, whereas some PPCPs were additionally removed by post-treatment. With the exception of the MBR process, the A2O system was effective for PPCPs removal. As a result, removal mechanisms were evaluated by calculating the mass balances in A2O and a lab-scale MBR process. The comparative study demonstrated that biodegradation was largely responsible for the improved removal performance found in lab-scale MBR (e.g., in removing bezafibrate, ketoprofen, and atenolol). Triclocarban, ciprofloxacin, levofloxacin and tetracycline were adsorbed in large amounts to MBR sludge. Increased biodegradability was also observed in lab-scale MBR, despite the highly adsorbable characteristics. The enhanced biodegradation potential seen in the MBR process thus likely plays a key role in eliminating highly adsorbable compounds as well as non-degradable or persistent PPCPs in other biological treatment processes.

Effect of copper on the performance and bacterial communities of activated sludge using Illumina MiSeq platforms

The anaerobic-anoxic-aerobic (A2O) process is a highly efficient sewage treatment method, which uses complex bacterial communities. However, the effect of copper on this process and the bacterial communities involved remains unknown. In this study, a systematic investigation of the effect of persistent exposure of copper in the A2O wastewater treatment system was performed. An A2O device was designed to examine the effect of copper on the removal efficiency and microbial community compositions of activated sludge that was continuously treated with 10, 20, and 40 mg L−1 copper, respectively. Surprisingly, a decrease in chemical oxygen demand (COD) and ammonia nitrogen (NH4N) removal efficiency was observed, and the toxicity of high copper concentration was significantly greater at 7d than at 1d. Proteobacteria, Bacteroidetes, Acidobacteria, Chlorobi, and Nitrospirae were the dominant bacterial taxa in the A2O system, and significant changes in microbial community were observed during the exposure period. Most of the dominant bacterial groups were easily susceptible to copper toxicity and diversely changed at different copper concentrations. However, not all the bacterial taxa were inhibited by copper treatment. At high copper concentration, many bacterial species were stimulated and their abundance increased. Cluster analysis and principal coordinate analysis (PCoA) based on operational taxonomic units (OTUs) revealed clear differences in the bacterial communities among the samples. These findings indicated that copper severely affected the performance and key microbial populations in the A2O system as well as disturbed the stability of the bacterial communities in the system, thus decreasing the removal efficiency.

Microbial Community Dynamics and Nutrient Removal Performances in A&lt;sup&gt;2&lt;/sup&gt;O System Using Ultrasonic-Disintegrated Sludge Supernatant as Internal Carbon Source

Ultrasonic-disintegrated sludge supernatant was supplemented into A2O system to assess the effects on nutrient removal performances and microbial community changes. In this experiment, easily biodegradable organics accounted for 50.6% of sludge supernatant, indicating its potential for biological nutrient removal. Simultaneously, during two-month operational period, the ammonia nitrogen (NH4+-N) and total phosphorus (TP) removal efficiencies improved to 92.3% and 93.5% from75.6% and 53.4%. Duo to the application of sludge supernatant, two microbial phyla, Proteobacteria and Actinobacteria, were primarily responsible for the biological nutrient removal. In particular, the sludge supernatant was selective for ammonia oxidizing bacteria Comamonas sp. and denitrifying phosphate accumulating organisms Sphingobacterium.

Biotreatment of Azo Dyeing Wastewater Using a Modified Anaerobic-Anoxic-Aerobic Reactor System

Modified anaerobic-anoxic-aerobic (A2O) technology for dye wastewater was studied. The effects of Hydraulic retention times (HRT), sludge retention time (SRT) and carbon source on treatment efficiency were discussed. Scanning electron microscopes (SEM) for different sludge and UV-visible spectrum analysis for influent and effluent were investigated respectively. The results showed that when COD of influent was 600~1200 mg/L and the dye concentration was 20~40 mg/L, HRT had the obvious effect on treatment efficiency of modified A2O system. Total treatment efficiency of the improved system was more than 90% at the optimal HRT (29 h). The dye structure was demonstrated to be changed during the process. Finally, the dye and its intermediates were transformed and mineralized respectively.