Performance and microbial population dynamics during stable operation and reactivation after extended idle conditions in an aerobic granular sequencing batch reactor

Stability of aerobic granular sludge for treating inorganic wastewater with different nitrogen loading rates

This paper investigated the effect of nitrogen loading rates (NLRs) on the stability of aerobic granular sludge (AGS) for treating simulated ionic rare earth mine wastewater with high ammonia nitrogen and extremely low organic content. Mature AGS from a sequencing batch reactor (SBR) was seeded into five identical SBRs (R1, R2, R3, R4 and R5). The five reactors were operated with different NLRs (0.2, 0.4, 0.8, 1.2 and 1.6 kg/m3·d). After 30 days of operation, R1, R2 and R5 were dominated by broken granules, while most of the granules in R3 and R4 still maintained a complete structure. The properties of granules from R1, R2, R3, R4 and R5 deteriorated to varying degrees, while the granules from R3 and R4 showed better stability than that from R1, R2 and R5. In R1, R2, R3 and R4, the steady-state ammonia nitrogen removal efficiencies were all greater than 90%, and the steady-state removal efficiencies of total inorganic nitrogen (TIN) were approximately 30%. In R5, the removal efficiencies of ammonia nitrogen and TIN were both approximately 70%. The dominant nitrifying and denitrifying bacterial genera of the granules from the five reactors were Nitrosomonas and Thauera, respectively, and their relative abundance was much higher in granules from R3 and R4. The results demonstrated that a relative equilibrium between the growth and metabolism of nitrifying/denitrifying bacteria was achieved when NLR was between 0.8 and 1.2 kg/m3·d, which could provide technical support for the stability maintenance of AGS in the treatment of ionic rare earth mine wastewater.

Effect of in situ ultrasonic wave and influent ammonia nitrogen fluctuation on stability of aerobic granular sludge

This study elucidates the impact of fluctuating influent conditions and in situ ultrasonic wave exposure on the stability of aerobic granular sludge (AGS) in the treatment of simulated wastewater emanating from rare earth mining operations. During a stable influent period spanning from Day 1 to Day 95, the seed granules underwent an initial disintegration followed by a re-granulation phase. The secondary granulation was achieved on Day 80 and Day 40 for the ultrasonic reactor (R1) and the control reactor (R2), respectively. Notably, granules formed in R1 exhibited a more porous structure compared to those generated in R2. Subsequently, when the ammonia nitrogen in the influent oscillated between 100 and 500 mg/L during Days 96-140, both reactors yielded compact and densely structured granules. Nitrogen removal profiles were comparable between the two reactors: the removal efficiencies for ammonia nitrogen and total inorganic nitrogen escalated from 95% and 80%, respectively, during Days 1-95, to 95% and 90%, respectively, post-Day 140. A suite of performance metrics indicated that steady-state granules from R1 outperformed those from R2 across several parameters. Specifically, the nitrification/denitrification rates, and relative abundance of denitrifying bacteria were all higher in granules from R1. Conversely, the relative abundance of nitrifying bacteria was comparable between granules from both reactors. However, R1 granules demonstrated lower sludge concentration and smaller average particle size than their R2 counterparts. In conclusion, the AGS system demonstrated robust resilience to fluctuating ammonia nitrogen, and the application of ultrasonic waves significantly enhanced granular activity while achieving in situ sludge reduction.

Metatranscriptome analysis unveils the mechanisms of zero-valent iron enhancing reactivation of starvation hydrolysis acidification sludge by inducing high-level gene expression

Hydrolysis acidification (HA) is a promising method for wastewater treatment and resource recovery. However, the extended time required for bacterial reactivation after starvation or a change in living conditions often poses a challenge to the efficient operation of the system. Although the addition of zero-valent iron (ZVI) could enhance HA performance, its effects on sludge reactivation in the HA process are not fully understood. In this study, ZVI was employed to accelerate sludge reactivation and its involved genetic mechanisms were unveiled. The results demonstrated that ZVI addition activated the sludge within 35 days with stable HA performance. Sludge characteristics revealed that ZVI improved active biomass, enzyme activity (by 11.4 % ∼ 26.7 %), ETS activity (by 566 %), and cell viability, with a higher concentration of MLVSS, live cells, more microbial byproducts in EPS, and relative abundance of HA bacteria (63.41 %). Moreover, metatranscriptome analysis showed that ZVI upregulated the expression of genes related to key enzymes in carbohydrate degradation metabolism, biosynthesis of electron transfer media such as heme and ubiquinone, and biosynthesis of vital cofactors like vitamin B12 and folate during microbial growth and metabolism. These findings suggest that ZVI enhanced electron transfer, bacterial growth, and metabolism, resulting in effective starch conversion and VFAs generation. Overall, these results deepen our understanding of the mechanism by which ZVI enhanced HA sludge reactivation, providing valuable information for addressing sludge starvation issues in HA systems.

Towards a better understanding of the anaerobic/oxic/anoxic-aerobic granular sludge process (AOA-AGS) for simultaneous low-strength wastewater treatment and in situ sludge reduction from ambient to winter temperatures

The new anaerobic/oxic/anoxic-aerobic granular sludge (AOA-AGS) merits the advantages of effective carbon utilization and low-carbon treatment. However, low temperature poses stressing concerns and the resisting mechanism remains much unknown. Herein, an AOA-AGS process was configured for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) with low-strength wastewater from ambient (>15 °C) to winter temperatures (<15 °C). Results showed that simultaneously advanced nutrients removal, and dramatic in situ sludge reduction (Yobs of 0.093 g MLSS/g COD) were gained regardless of seasonally decreasing temperatures. Winter temperatures even amplified Candidatus Competibacter predominating from 20.11% to 34.74%, which laid the core basis for endogenous denitrification, sludge minimization and temperature resistance. A removal model was thus proposed given the observed functional groups, and doubts were also raised for future investigations. This study would aid a better understanding on the microbial ecology and engineering aspects of the new AOA-AGS process treating low-strength wastewater at low temperatures.

Cultivation of autotrophic nitrifying granular sludge for simultaneous removal of ammonia nitrogen and Tl(I)

Autotrophic nitrifying granular sludge (ANGS) was cultivated for the simultaneous removal of ammonia nitrogen and Tl(I) from inorganic wastewater. The chemical oxygen demand (COD) in the influent gradually decreased to approximately zero in four parallel sequencing batch reactors (B1: blank controller, B2: 10 mL of added nitrifying bacteria concentrate in each cycle, B3: 1 mg/L Tl(I) added in each cycle and B4: 10 mL of added nitrifying bacteria concentrate and 1 mg/L Tl(I) in each cycle) within 15 days. The main properties, such as the granulation rate and specific oxygen uptake rate (SOUR) of the ANGS in B1, B2, B3 and B4 tended to be stable within 40, 33, 30 and 33 days, the removal efficiencies of Tl(I) were 59.5%-82.9% and 57.1%-88.6% in B3 and B4 after Day 30, the removal efficiencies of ammonia nitrogen in B1, B2, B3 and B4 were usually above 90% after Day 33, and the total inorganic nitrogen (TIN) in the effluent of B1, B2, B3 and B4 gradually stabilized after Day 36, 32, 32 and 36, indicating that mature ANGS was successfully cultivated in B1, B2, B3 and B4 within 40, 33, 33 and 36 days. The nitrogen degradation kinetic parameters of ANGS indicated that B3 had the strongest ability to remove ammonia and nitrite, suggesting that Tl(I) stress was beneficial to ammonia nitrogen removal and nitrite oxidation. The adsorption of Tl(I) can be described by the Freundlich equation, and the addition of external nitrifying bacteria improved the adsorption ability of ANGS.

Effect and microbial mechanism of suspended sediments particle size on nitrous oxide emission in eutrophic lakes

Suspended sediment (SPS) is an important environmental factor in eutrophic lakes, where they may play a significant role in the microbial nitrogen cycle and thus affect the N2O source and sink function. This study investigated the correlation and corresponding microbial mechanisms between N2O emission fluxes and SPS particle sizes. N2O emission characteristics were investigated in four parallel operated lab-scale microcosmic systems, in which different sizes of SPS particles were inoculated (i.e., <75, 75-150, 150-300, and >300 μm). The results show that, N2O emission fluxes in the eutrophic lakes were exponentially correlated with the lake trophic level index (TLI) (R2 = 0.94, p < 0.01) and the specific surface area of the SPS (R2 = 0.38, p < 0.05). In the microcosmic systems, SPS with 75-150 μm particles had the highest N2O emission rate of 5.94 ± 0.007 μg N/L/d, which was 2.6 times that of the <75 μm particle size system. The microcosmic system with particle size >300 μm had the highest N2O reduction rate (Vmax) of 6.776 μmol/L/h, which was 16-50 times that of the other three groups. Larger particle size SPS have a smaller specific surface area, which could affect the microenvironment on SPS surface and thus affect the microbe functions. The microbial community structure results indicated that the dominant microorganisms on the SPS surface were denitrifying bacteria. The maximum (nirS + nirK)/nosZ ratio was 30.2 for the 75-150 μm system, which was nearly 2 times higher than the other systems. The >300 μm system had the highest nosZ abundance, indicating a strong ability to reduce N2O. The co-occurrence networks analysis indicated that the cooperation and competition among nitrifiers and denitrifiers determined N2O emissions. These results provide fundamental insights into the influence of SPS size on N2O emissions in eutrophic lakes.

Advanced low-strength wastewater treatment, side-stream phosphorus recovery, and in situ sludge reduction with aerobic granular sludge

Modern paradigm has upgraded wastewater treatment plants (WWTPs) to water resources recovery facilities (WRRFs), where aerobic granular sludge (AGS) is a sewage treatment technology with promising phosphorus recovery (PR) potential. Herein, the AGS-based simultaneous nitrification, denitrification, and phosphorus removal coupling side-stream PR process (AGS-SNDPRr) was developed with municipal wastewater. Results revealed that AGS always maintained good structural stability, and pollutant removal was unaffected and effective after 40 days of anaerobic phosphorus-rich liquid extraction (fixed rate of 30%). The AGS-SNDPRr achieved a stable phosphorus recovery efficiency of 63.40%, and the side-stream PR further exaggerated in situ sludge reduction by 7.7-10%. Apart from responses of extracellular polymeric substances (EPS), the Matthew effect of typical denitrifying glycogen accumulating organisms (DGAOs) Candidatus_Competibacter up to 67.40% mainly contributed to enhanced performance of this new process. This study demonstrated a new approach for simultaneous advanced wastewater treatment, phosphorus recovery, and excess sludge minimization.

Performance and Bacterial Characteristics of Aerobic Granular Sludge in Treatment of Ultra-Hypersaline Mustard Tuber Wastewater

Mustard tuber wastewater (MTW) is an ultra-hypersaline high-strength acid organic wastewater. Aerobic granular sludge (AGS) has been demonstrated to have high tolerance to high organic loading rate (OLR), high salinity, and broad pH ranges. However, most studies were conducted under single stress, and the performance of AGS under multiple stresses (high salinity, high OLR, and low pH) was still unclear. Herein, mature AGS was used to try to treat the real MTW at 9% salinity, pH of 4.1–6.7, and OLR of 1.8–7.2 kg COD/m3·d. The OLR was increased, and the results showed that the upper OLR boundary of AGS was 5.4 kg COD/m3·d (pH of 4.2) with relatively compact structure and high removal of TOC (~93.1%), NH4+-N (~88.2%), and TP (~50.6%). Under 7.2 kg COD/m3·d (pH of 4.1), most of the AGS was fragmented, primarily due to the multiple stresses. 16S rRNA sequencing indicated that Halomonas dominated the reactor during the whole process with the presence of unclassified-f-Flavobacteriaceae, Aequorivita, Paracoccus, Bradymonas, and Cryomorpha, which played key roles in the removal of TOC, nitrogen, and phosphorus. This study investigated the performance of AGS under multiple stresses, and also brought a new route for highly-efficient simultaneous nitrification–denitrifying phosphorus removal of real MTW.

Quorum sensing unveils the sludge floccule-assisted stabilization of aerobic granules in granule-dominated sequencing batch reactors

Floccules are another major form of microbial aggregates in aerobic granular sludge systems. Previous studies mainly attributed the persistence of floccules to their relatively faster nutrient uptake and higher growth rate over aerobic granules; however, they failed to unravel the underlying mechanism of the long-term coexistence of these two aggregates. In this work, the existence and function of the floccules in an aerobic granule-dominated sequencing batch reactor were investigated from the view of quorum sensing (QS) and quorum quenching (QQ). The results showed that though the floccules were closely associated with the granules in terms of similar community structures (including the QS- and QQ-related ones), they exhibited a relatively higher QQ-related activity but a lower QS-related activity. A compatible proportion of floccules might be helpful to maintain the QS-related activity and keep the granules stable. In addition, the structure difference was demonstrated to diversify the QS- and QQ-related activities of the floccules and the aerobic granules. These findings could broaden our understanding of the interactions between the coexistent floccules and granules in aerobic granule-dominated systems and would be instructive for the development of the aerobic granular sludge process.

Effect of pistachio shell as a carbon source to regulate C/N on simultaneous removal of nitrogen and phosphorus from wastewater

Acid-pretreated pistachio shells were used as carbon sources to investigate the effects of carbon source dosage on simultaneous nitrogen and phosphorus removal under different carbon/nitrogen (C/N) ratios (7, 9, and 11). Results showed that C/N was positively correlated with mixed liquor suspended solids (MLSS) (R² = 0.998, p < 0.01) and f value (R² = 0.975, p < 0.05). Moreover, it was negatively correlated with the sludge volume index (SVI) (R² =  - 0.959, p < 0.05). C/N was also significantly negatively related to chemical oxygen demand removal rate (R² =  - 0.986, p < 0.05) and positively related to ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) removal rate (p < 0.05), the correlation coefficients were 0.992, 0.990 and 0.994, respectively. In the reactor with C/N of 11, the MLSS concentration and f value were the highest, the SVI was the lowest, and the removal efficiencies of NH₄⁺-N (85.49 % ± 1.96 %), TN (84.19 % ± 1.42 %) and TP (94.10 % ± 1.67 %) were the highest. Furthermore, the relative abundance of denitrifying bacteria was the highest in the reactor. The abundance of nitrifying bacteria and phosphorus-removal bacteria was also relatively high.

Elucidating nitrifying performance, nitrite accumulation and microbial community in a three-stage plug flow moving bed biofilm reactor (PF - MBBR)

A three-stage plug flow moving bed biofilm reactor (PF - MBBR, consisting of three identical chambers of N1, N2 and N3) was proposed for nitrifier enrichment using synthetic wastewater. During the stable operation, the average NH₄⁺-N effluent was 0.67 mg/L and NH₄⁺-N removal was as high as 97.19% with the nitrite accumulation ratio (NAR) of 54.23%, although the biofilm thickness and biomass both presented downward trends from N1 (296 μm, 2280 mg/L), N2 (248 μm, 1850 mg/L) to N3 (198 μm, 1545 mg/L). Particularly, the comparative results of three stages revealed that N2 showed the optimum NH₄⁺-N removal (77.27%) and NAR (75.21%) in the continuous-flow, while NAR of N3 unexpectedly maintained a high level of 65.83% in the batch test, suggesting that ammonia oxidizing bacteria (AOB) accounted for absolute advantage over nitrite oxidizing bacteria (NOB). High-throughput sequencing initially verified different distribution of bacterial community structure, where N2 was far away from N1 and N3 with the lowest community richness and community diversity (operational taxonomic units (OTUs): 454(N2)<527(N3)<621(N1)). Proteobacteria (77.60%-83.09%), Bacteroidetes (1.66%-3.66%), Acidobacteria (2.28%-4.67%), and Planctomycetes (1.19%-6.63%) were the major phyla. At the genus level, AOB (mainly Nitrosomonas) accounted for 5.08% (N1), 20.74% (N2) and 14.24% (N3) while NOB (mainly Nitrospira) increased from 0.14% (N1), 7.06% (N2) to 4.91% (N3) with the total percentages of 5.22%, 27.80% and 19.15%. Finally, the application feasibility of MBBR optimization linked with nitrite (NO₂^--N) accumulation for deep-level nutrient removal was discussed.

Food waste composting based on patented compost bins: Carbon dioxide and nitrous oxide emissions and the denitrifying community analysis

Mature compost and rice bran were used as bulking agents to perform Food Waste Rapid Composting (FWRC) in a patented composting bin. The characteristics of CO₂ and N₂O emission and the denitrifying community were investigated. The release of CO₂ and N₂O concentrated in the early composting stage and reduced greatly after 28 h, and the N₂O emission peak of the treatment with mature compost was 8.5 times higher than that of rice bran. The high N₂O generation resulted from massive denitrifying bacteria and NO_x^--N in the composting material. The relative abundances of denitrifiers, correspondingly genes of narG and nirK were much higher in the treatment with mature compost, which contributed to the N₂O emission. Moreover, the correlation matrices revealed that N₂O fluxes correlated well with moisture, pH, temperature, and the abundances of nirK and nosZ genes during FWRC.

Metagenomics reveals functional species and microbial mechanisms of an enriched thiosulfate-driven denitratation consortia

In this study, thiosulfate-driven denitratation (TDD) system was successfully established under optimal S/N molar ratio of 1.00, with nitrite accumulation efficiency (NAE) of 82.24 ± 17.09%. This work highlighted that thiosulfate significantly preferred the reduction of nitrate than nitrite. However, after the depletion of thiosulfate, the in-situ formed intermediate product element sulfur (S⁰) served as the main electron donor, and significantly favored the reduction of nitrite than nitrate, which constrained nitrite accumulation and nitrate removal. In addition, metagenomic sequencing revealed that the functional denitratation species might be Thiobacillus_sp._65-29, but the occurrence of Nir-annotated species would decrease nitrite accumulation. Under S/N ratio of 1.00, the decreased abundant Nir-annotated species (e.g., Thiobacillus_sp.), as well as the down-regulated quorum sensing interactions between Nar- and Nir-annotated species were key microbial metabolisms of high NAE in the TDD system. Overall, this work provides new sight into the metagenome-base functional species and metabolic potential of thiosulfate-driven denitratation.

Reactivation of Frozen Stored Microalgal-Bacterial Granular Sludge under Aeration and Non-Aeration Conditions

In this paper, reactivation of microalgal-bacterial granular sludge (MBGS) stored at −20 °C for 6 months was investigated under respective aeration (R1) and non-aeration (R2) conditions. Results showed that the granular activity could be fully recovered within 21 days. The average removal efficiency of ammonia was higher in R1 (92.78%), while R2 showed higher average removal efficiencies of organics (84.97%) and phosphorus (85.28%). It was also found that eukaryotic microalgae growth was stimulated under aeration conditions, whereas prokaryotic microalgae growth and extracellular protein secretion were favored under non-aeration conditions. Sequencing results showed that the microbial community underwent subversive evolution, with Chlorophyta and Proteobacteria being dominant species under both conditions. Consequently, it was reasonable to conclude that the activity and structure of frozen stored MBGS could be recovered under both aeration and non-aeration conditions, of which aeration-free activation was more feasible on account of its energy-saving property. This study provides important information for the storage and transportation of MBGS in wastewater treatment.

The performance of aerobic granular sludge for simulated swine wastewater treatment and the removal mechanism of tetracycline

In this study, aerobic granular sludge (AGS) cultivated in a sequencing batch reactor (SBR) was employed to investigate its ability on the decontamination of tetracycline (TC) from swine wastewater (SWW). The removal mechanism of TC by AGS was studied. Results showed that the AGS process could effectively remove chemical oxygen demand (COD), ammonium nitrogen (NH_{+ 4}-N), total phosphorus (TP), and TC during operation. The removal of TC by AGS was mainly due to adsorption and biodegradation, and the contribution rate of biodegradation increased after AGS adaptation to TC. Twenty-two by-products were detected during biodegradation of TC, and accordingly the degradation pathway of TC was speculated. Compared to the control reactor, the microbe diversity in different levels of classification was richer in the TC fed reactor according to the LefSe analysis. The results revealed that enzymes that participated in the metabolic pathway of microbial biodegradation of polycyclic aromatic compounds were enriched and may have played a key role in the biodegradation of TC.

Performance of a recirculating aquaculture system using biofloc biofilters with convertible water-treatment efficiencies

To achieve high water-treatment efficiencies and simplify the setup of recirculating aquaculture systems (RAS), this study examined the use of suspended growth reactors (R1 and R2) based on biofloc technology (BFT) as water-treatment biofilters. Moreover, the conversion of the heterotrophic R1 biofilter to a nitrifying role was investigated. During RAS operation using heterotrophic BFT biofilters, R1 and R2 simultaneously controlled total ammonium nitrogen, nitrite (NO₂^--N), nitrate (NO₃^--N), soluble reactive phosphate (SRP), and alkalinity, with relevant functional microbes including denitrifying bacteria (DNB), phosphorus accumulating organisms (PAOs), denitrifying PAOs (DNPAOs), glycogen accumulating organisms, ammonia oxidizing bacteria, and nitrite oxidizing bacteria. To achieve low concentrations of nitrogen, phosphorus, and save carbon sources, we were able to quickly convert R1 into a nitrifying BFT biofilter by stopping carbohydrate addition. Although there were dominant relative abundances of DNB, PAOs, and DNPAOs in the converted R1, the lack of carbon sources resulted in continuous rise of NO₃^--N in the effluent, stable NO₂^--N removal efficiency, and absence of SRP removal after 40 h. However, R2 retained the previous NO₃^--N and SRP removal efficiencies with carbohydrate addition. This indicated that this novel RAS using BFT biofilters achieved simultaneous nitrogen and phosphate removal, and that the convertible water-treatment efficiencies of BFT biofilters could be controlled by carbohydrate addition. This approach could simplify the RAS setup and meet real-time water quality demands.

New insights into enhanced anaerobic degradation of coal gasification wastewater (CGW) with the assistance of magnetite nanoparticles

Magnetite nanoparticles (Fe₃O₄ NPs) was firstly used to enhance pollutants removal during coal gasification wastewater (CGW) treatment in anaerobic digestion (AD) system. Bench-scale results revealed that 200 mg/L and 20-40 nm of Fe₃O₄ NPs addition resulted in a maximum removal capacity of total phenol (TPh) at a temperature of 36 °C and hydraulic retention time (HRT) of 36 h. Meanwhile, Fe₃O₄ NPs addition reduced the oxidation reduction potential (ORP) values and biological toxicity, and enhanced the stability of AD system. Pilot-scale results showed that the TPh and chemical oxygen demand (COD) removal efficiency (53% and 49%) were obtained with the optimal dosage of Fe₃O₄ NPs. Moreover, electron nanowires may be established with Fe₃O₄ NPs assisted to perform direct interspecies electron transfer (DIET) among Geobacter, Pseudomonas and Methanosaeta species, and finally enhanced the pollutants removal efficiency.

Nutrient metabolism, mass balance, and microbial structure community in a novel denitrifying phosphorus removal system based on the utilizing rules of acetate and propionate

The effect of acetate (HAc) and propionate (HPr) on denitrifying phosphorus removal (DPR) was evaluated in a novel two-sludge A²/O - MBBR (anaerobic/anoxic/oxic - moving bed biofilm reactor) system. Results showed that it was the carbon source transformation and utilization especially the composition of poly-β-hydroxyalkanoates (PHA) (mainly poly-β-hydroxybutyrate (PHB) and poly-bhydroxyvalerate (PHV)) decided DPR performance, where the co-exist of HAc and HPr promoted the optimal nitrogen (85.77%) and phosphorus (91.37%) removals. It facilitated the balance of PHB and PHV and removing 1 mg NO₃^- (PO₄^3-) consumed 3.04-4.25 (6.84-9.82) mgPHA, where approximately 40-45% carbon source was saved. Mass balance revealed the main metabolic pathways of carbon (M_An,C (consumed amount in anaerobic stage) and M_A-O,C (consumed amount in anoxic and oxic stages): 66.38-76.19%), nitrogen (M_DPR,N (consumed amount in DPR): 57.01-65.75%), and phosphorus (M_WS,P (discharged amount in waste sludge): 81.05-85.82%). Furthermore, the relative abundance and microbial distribution were assessed to elucidate DPR mechanism (e.g. Accumulibacter, Acinetobacter, Dechloromonas, Competibacter, and Defluviicoccus) in the A²/O reactor and nitrification performance (e.g. Nitrosomonas, Nitrosomonadaceae and Nitrospira) in the MBBR. Carbon source was demonstrated as the key point to stimulate the biodiversity and bioactivity related to DPR potential, and the operational strategy of carbon source addition was proposed based on the utilizing rules of HAc and HPr.

Microbial community responses to agricultural biomass addition in aerated constructed wetlands treating low carbon wastewater

Using agricultural biomasses as solid carbon substrates in constructed wetlands (CWs) could be an effective way to achieve sustainable nitrogen removal for carbon-limited wastewater treatments. This study investigated the response of bacteria community in CWs to the addition of agricultural biomasses (wheat straw, walnut shell and apricot pit). Results indicated that the addition of different agricultural biomasses had distinct influence on bacterial communities in CWs. Both wheat straw and walnut shell increased the diversity of microbial communities and optimized the structure of microorganisms. The effect of apricot pit on the richness and evenness of microbial communities was not significant, but the composition of microorganisms was significantly affected at the phylum level, especially the relative abundance of phylum Saccharibacteria. Moreover, the addition of agricultural biomasses in CWs acclimatized more functional bacteria including nitrifier and denitrifier, which were proved to be positively correlated with the high-rate denitrification performance. The obtained results would be beneficial to understand the underlying microbial mechanism of nitrogen removal in CWs with agricultural biomass and provide some guidance on the practical application of CWs.

Bioaugmentation of low C/N ratio wastewater: Effect of acetate and propionate on nutrient removal, substrate transformation, and microbial community behavior

The effect of various acetate/propionate ratios (1:0, 2:1, 1:1, 1:2, and 0:1) in a two-sludge A2/O - MBBR process was investigated. Results showed that the increased propionic/acetic ratios exerted indistinctive impact on COD (91.21-93.44%) and P (92.23-93.87%) removals, but high P content (7.42%) accelerated sludge granulation proved by SEM and EDS. Acetate favored N removal (79.52%-82.92%) with higher PURA (3.53-4.06 mgP/(gVSS·h)), while the removal declined (75.14%) due to lower PHB/PHA ratio (52.3-57.8%) with propionate as sole carbon source. Based on the stoichiometry-based quantifications, PAOs were the major contributors to nutrient removal although certain GAOs and OHO participated. The mixture ratio of 1:1 facilitated microbial diversity (995 OTUs), Rhodobacteraceae (25.63%) was responsible for high-efficient denitrifying phosphorus removal, while Defluviicoccus (15.23%) contributed to nitrite accumulation was the main competitiveness with PAOs. Nitrospira, Nitrosomonas, and Nitrosomonadaceae responsible for nitrification accounted for 7.73%, 27.11%, and 38.76% in MBBR, but the biodiversity decreased owing to the enrichment and purification.

Performance and bacterial community structure of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic municipal wastewater

The performance of a lab-scale integrated anoxic and aerobic inverse fluidized bed bioreactors (IFBBR) for biological nutrient removal from synthetic municipal wastewater was studied at chemical oxygen demand (COD) loading rates of 0.34-2.10 kg COD/(m³-d) and nitrogen loading rates of 0.035-0.213 kg N/(m³-d). Total COD removal efficiencies of >84% were achieved, concomitantly with complete nitrification. The overall nitrogen removal efficiencies were >75%. Low biomass yields of 0.030-0.101 g VSS/g COD were achieved. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less at organic loading rates (OLRs) of 1.02 and 2.10 kg COD/(m³-d). Bacterial community structures of attached and suspended biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs) in the aerobic attached biomass were 0.451% and 0.110%, respectively. COD mass balance in the anoxic zone was closed by consideration of sulfate reduction, which was confirmed by the presence of genus Chlorobium (sulfate-reducing bacteria) in the anoxic attached biofilm with a relative abundance of 0.32%.

Elevated salinity deteriorated enhanced biological phosphorus removal in an aerobic granular sludge sequencing batch reactor performing simultaneous nitrification, denitrification and phosphorus removal

Hypersaline wastewater may pose threats to biological wastewater treatment processes. An aerobic granular sludge-based sequencing batch reactor (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was evaluated with increased salinity from 1 to 2 % (w/v). Nitrogen removal performance was unaffected by salinity up to 20 g/L in terms of reliable and efficient nitrification and denitrification. Enhanced biological phosphorus removal (EBPR) process was completely deteriorated at salinity up to 2 %, in contrast to excellent phosphorus removal at 1 %. Profiles of phosphorus over one cycle demonstrated that higher salinity not only inhibited anaerobic phosphorus release but also impeded aerobic/anoxic phosphorus uptake. Illumina MiSeq sequencing revealed multiple halophilic and non-halophilic bacteria within aerobic granules with family Anaerolineaceae being the predominant potential salt adapter. Besides, ammonia oxidizing bacteria (AOB), glycogen accumulating organisms (GAOs) were more tolerant to salt than nitrite oxidizing bacteria (NOB) and phosphorus accumulating organisms (PAOs) and denitrifying PAOs (DNPAOs). These results deciphered the resilience of aerobic granular sludge-based biological nitrogen and phosphorus removal processes to hypersaline stress.

Evolution of microbial community during dry storage and recovery of aerobic granular sludge

Aerobic granular sludge (AGS) was imbedded in agar and stored at 4 °C for 30 days, and then the stored granules were recovered in a sequencing batch reactor fed real wastewater within 11 days. Variations in microbial community compositions were investigated during dry storage and recovery of AGS, aiming to elucidate the mechanism of granular stability loss and recovery. The storage and recovery of AGS involved microbial community evolution. The dominant bacterial genera of the mature AGS were Zoogloea (relative abundance of 22.39%), Thauera (16.03%) and Clostridium_sensu_stricto (11.17%), and those of the stored granules were Acidovorax (26.79%), Macellibacteroides (12.83%) and Pseudoxanthomonas (5.69%), respectively. However, the dominant genera were Streptococcus (43.64%), Clostridium_sensu_stricto (12.3.6%) and Lactococcus (11.47%) in the recovered AGS. Methanogens were always the dominant archaeal species in mature AGS (93.01%), stored granules (99.99%) and the recovered AGS (94.84%). Facultative anaerobes and anaerobes proliferated and dominated in the stored granules, and their metabolic activities gradually led to granular structure destruction and property deterioration. However, the stored granules served as carriers for the microbes originated from the real septic tank wastewater during recovery. They proliferated rapidly and secreted a large number of extracellular polymeric substances which helped to recover the granular structure in 11 days.

Diversity evolution of functional bacteria and resistance genes (CzcA) in aerobic activated sludge under Cd(II) stress

An activated sludge sequencing batch reactor (SBR) was used to treat divalent cadmium (Cd(II)) wastewater for 60 d to investigate the overall treatment performance, evolution of the bacterial community, and abundance of the Cd(II) resistance gene CzcA and shifts in its potential host bacteria. During stable operation with a Cd(II) concentration of 20 mg/L, the average removal efficiencies of Cd(II) and chemical oxygen demand (COD) were more than 85% and that of total phosphorus was greater than 70%, while the total nitrogen (TN) was only about 45%. The protein (PN) content in the extracellular polymeric substances (EPS) increased significantly after Cd(II) addition, while polysaccharides displayed a decreasing trend (p < 0.05), indicating that EPS prefer to release PN to adsorb Cd(II) and protect bacteria from damage. Three-dimensional fluorescence spectral analysis showed that fulvic acid-like substances were the most abundant chemical components of EPS. The addition of Cd(II) adversely affected most denitrifying bacteria (p < 0.05), which is consistent with the low TN removal. In addition, quantitative polymerase chain reaction analysis revealed that CzcA gene abundance decreased as the Cd(II) concentration increased, possibly because expression of the CzcA gene was inhibited by Cd(II) stress. The majority of CzcA gene sequences were carried by Pseudomonas, making it the dominant genus among Cd(II)-resistant bacteria.

Aerobic granular sludge operation and nutrients removal mechanism in a novel configuration reactor combined sequencing batch reactor and continuous-flow reactor

A novel aerobic granular sludge (AGS) system called SBR (sequencing batch reactor)-CF (continuous-flow) system merging the advantages of sequencing batch reactors (SBRs) and continuous flow (CF) reactors was developed. The AGS was successfully operated in the SBR-CF system which consisted of four same SBRs (each served as settling tank/anaerobic feeding tank/aerobic reacting tank in turn). The effects of aeration intensity and hydraulic retention time (HRT) on the SBR-CF system were studied. The results showed strong aeration intensity (9.74 h^-1 in this study) and appropriate HRT (9 h in this study) were more favorable to the nutrients removal. The EEM-PARAFAC analysis was applied to characterize the LB-EPS, TB-EPS and domestic wastewater, as results TB-EPS was found play an important role in the biosorption in COD removal of the SBR-CF system. In addition, a preliminary conceptual reaction process model in the SBR-CF system was built using high-throughput pyrosequencing and phylogenetic assignment.

The key role of inoculated sludge in fast start-up of sequencing batch reactor for the domestication of aerobic granular sludge

Two types of inoculated sludges, granular sludge that had been stored at -20°C and activated sludge, were investigated for the domestication of aerobic granular sludges (AGSs) in sequencing batch reactors (SBRs). The results showed that using the stored granular sludge as inoculation sludge could effectively shorten the domestication time of AGS and yielded mature granular sludge after 22 days of operation. The AGS domesticated by stored granular sludge had better biomass and sedimentation properties; its MLSS and SVI reached 8.55 g/L and 35.27 mL/g, respectively. The removal efficiencies for chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N) and total phosphorus (TP) reached 90.76%, 97.39% and 96.40%, respectively. By contrast, 54 days were needed to obtain mature granules using activated sludge. The microbial community structure was probed by using scanning electron microscopy (SEM) and high-throughput sequencing. The results showed that the diversity of the microbial community in mature granules was reduced when stored granular sludge rather than activated sludge was employed as inoculation sludge, and the dominant microbes were changed. The dominant species in mature granules domesticated using stored granular sludge were Zoogloea, Acidovorax and Tolumonas at the genus classification level, while the dominant species were Zoogloea and TM7-genera in granules developed from activated sludge.

Probing operational conditions of mixing and oxygen deficiency using HSV color space

In this work, the relationship between sludge color and operational conditions was studied. It was found that the coordinates H and S of the HSV color space well correlated with biological status and the operational conditions of mixing and oxygen deficiency, and a coefficient of variation (CV_H/S) of the ratio of H to S in sludge cake images was derived. A smaller CV_H/S indicated better mixing conditions based on the observations of four laboratory-scale experiments and two full scale WWTPs, which can be used as a promising index for the monitoring of mixing condition. The coordinate oxygen uptake rate (OUR_q) of the respirogram space showed similar trend as CV_H/S, and analysis of microbial community also showed that CV_H/S could indicate changes of biological community including species and richness. These findings suggested that CV_H/S is a biological meaningful index for detecting the effect of changing operational conditions, which gives a key to quantify a large number of empirical rules accumulated in the past. Furthermore, it promotes the Internet of Things (IoT) application to the management of WWTPs, as color is readily available with MEMS (Micro-Electro-Mechanical Systems) sensors such as smart phones.

Impact of carbon to nitrogen ratio on the performance of aerobic granular reactor and microbial population dynamics during aerobic sludge granulation

Carbon to nitrogen (C/N) ratio is one of the most important factor affecting aerobic granular sludge (AGS) growth and pollutant removal in aerobic granular sludge sequencing batch reactor (AGSBR). For stability of sludge granulation process, AGSs were domesticated in five sequence batch reactors (SBRs) with different C/N ratios (6, 7, 8, 9, and 10), which the ammonia nitrogen concentration of influent was 165 mg/L. The effects of C/N ratio on morphology and property of AGS were studied. The results showed that stable AGS was yielded with good settleability, high pollutant removal efficiency and rich microbial diversity when C/N ratio was 8. AGS yielded had stable structure due to higher protein in extracellular polymeric substances (EPS). High throughput 16S rDNA gene analysis revealed the microbial community diversity increased in AGS under the C/N ratio. The dominant microbes changed at the phylum, class and family three levels with the increasing operation time.

Hydrodynamic shear force shaped the microbial community and function in the aerobic granular sequencing batch reactors for low carbon to nitrogen (C/N) municipal wastewater treatment

The lab-scale aerobic granules process was applied for low carbon to nitrogen (C/N < 4) wastewater treatment under different hydrodynamic shear forces. Results revealed that aerobic granules exhibited strong adaptability and stability. The aerobic granules might adopt an extracellular polymeric substances (EPS) regulating mechanism to address the changes in operational conditions, especially through growing secretion of fluorescence protein. The hydrodynamic shear force determinedly shaped and regulated the diversity and structure of dominant microbial community, briefly, reduced aeration intensity with increased time led to higher microbial richness, lower diversity and evenness, and shifts of predominant microorganisms. Phylogenetic classification of the key functional groups including bacteria related to carbon and nutrients removal, EPS production and quorum sensing (QS) presented much more differences among the reactors subject to different conditions. Therefore, the present work adds insight into the comprehensive understanding of the effect of aeration induced hydrodynamic shear force on aerobic granules.

Storage of aerobic granular sludge embedded in agar and its reactivation by real wastewater

Aerobic granular sludge (AGS) was preserved using an agar embedding method to maintain its stability. No obvious damage was imposed on the granular appearance during 30 days of cold and dry storage, but the granular microstructure had an uneven surface with a large number of holes. The results were consistent with the extinction of microbial communities and the monitored consumption of extracellular polymeric substances, in which granular specific oxygen utilization rate and mixed liquor volatile suspended solids/mixed liquor suspended solids ratio, respectively, decreased by 72.4% and 62.5% during storage. A mass conversation calculation indicated that the loss of granular mass was 1.6393 g. An offensive odour was smelled during storage, and the results indicated that a material transformation and mitigation were involved between AGS and the gas phase. Although the granular structure was destroyed to a certain extent, no obvious damage was imposed on the granular skeleton during storage. After it was aerated again after a feeding with real wastewater, the residual skeleton served as a carrier for the rapid proliferation of microorganisms, and good granular properties were obtained after 11 days of reactivation.

Natural sunlight induced rapid formation of water-born algal-bacterial granules in an aerobic bacterial granular photo-sequencing batch reactor

Wastewater treatment by means of algal-bacterial granules has become a hot topic worldwide recently. Rapid granulation of algal-bacterial granules was achieved in an aerobic bacterial granular sequencing batch reactor (SBR) under natural sunlight exposure. Occurrence of abundant filamentous bacteria bridging the water-born algae, and overproduction of extracellular polymeric substances (EPS) (especially polysaccharides (PS), tryptophan & protein-like, and humic acid-like substances) were observed on the first 3 days, while the algae grew into the inner side of the granules and mature granules were obtained on day 7. The growth of the water-born algae slightly decreased the settleability, mean sizes of the granules, but stimulated the bioactivity significantly. Whereas, the biomass retention decreased before day 3, and got stable soon with the maturation period with symbiotic growth of algal-bacterial biomass. Illumina results revealed that the introduction of algae reduced the richness and diversity of bacterial community. Besides, few changes in structure and some compositions shifts in bacterial communities were found, while the predominant algae shifted from Diatomea to green algae Chlorophyceae. The possible mechanism for natural sunlight induced granulation of algal-bacterial granules was thus proposed based on the interactions between algae and bacteria.

Simultaneous nitrification, denitrification and phosphorus removal in aerobic granular sequencing batch reactors with high aeration intensity: Impact of aeration time

A new operating approach by reducing the aeration time while keeping high intensity was evaluated for enhanced nutrients removal and maintenance of granular stability. Three aerobic granular sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) were run at different aeration time (120, 90, and 60 min). Aerobic granules could remain their integrity and stability over long-term operation under high aeration intensity and different time, and shorter aeration time favored the retention of biomass, better settleability, and more production of extracellular polymeric substances (EPS). Besides, efficient and stable reactor performance for carbon and phosphorus were achieved, especially, enhanced nitrogen removal was obtained due to reduction of aeration time. Further exploration revealed that the aeration time shaped the bacterial community in terms of diversity, composition, as well as the distribution of functional groups involving carbon, nitrogen and phosphorus removal.

Qualitative and quantitative spectrometric evaluation of soluble microbial products formation in aerobic granular sludge system treating nitrate wastewater

In present study, the characteristics of soluble microbial products (SMP) were evaluated in aerobic granular sludge system during denitrification process under different chemical oxygen demand/nitrogen (C/N) ratios. Batch experiment showed that the effluent nitrate (NO₃^--N) concentration were 15.24 ± 1.83 and 1.72 ± 1.53 mg/L at C/N ratio of 1 and 6, respectively. For the release of SMP, the protein (PN) and polysaccharide contents increased from 1.23 ± 0.38 and 7.46 ± 1.13 mg/L to 1.80 ± 0.76 and 10.53 ± 1.24 mg/L with increasing C/N ratios, respectively. Excitation-emission matrix identified four peaks in SMP, including aromatic PN-like, tryptophan PN-like, fulvic acid-like and humic acid-like substances. Fluorescence regional integration suggested that biodegradable PN-like substances occupied the percentage between 53.0 and 61.7% in SMP. Synchronous fluorescence spectra coupled with two-dimensional correlation spectroscopy indicated that the release of SMP fractions in the early stage (0-150 min) changed in the following sequences: PN-like fraction > fulvic acid-like fraction.

Optimization of F/M ratio for stability of aerobic granular process via quantitative sludge discharge

Food to microorganisms (F/M) ratio is one of the most important factors affecting microbial growth and pollutant removal in biological wastewater treatment system. For stability of aerobic granular process, optimal range of F/M ratio and a maneuverable F/M ratio control method via quantitative sludge discharge were investigated in this study. Results showed that stable aerobic granules were achieved with good settleability, high pollutant removal efficiency and microbial diversity when F/M ratio was controlled at 0.4-0.5 gCOD/gSS d. In addition, a maneuverable F/M ratio control method via quantitative sludge discharge was developed to verify the feasibility for optimization of F/M ratio. By this method, aerobic granules cultivated with the F/M ratio of 0.4 ± 0.02 gCOD/gSS d had better pollutant removal performance and stable structure with higher protein-like components in EPS. This study further revealed the importance of F/M ratio in the stability of aerobic granular sludge process.

The performance and evolution of bacterial community of activated sludge exposed to trimethoprim in a sequencing batch reactor

The performance and microbial community changes of an activated sludge sequencing batch reactor were evaluated after exposure to trimethoprim for 51days. The average chemical oxygen demand, ammonia nitrogen, phosphorus efficiencies were 88.6%±0.56%, 90.47%±0.29% and 64.25%±1.12%, respectively. The protein and polysaccharide contents increased with increasing trimethoprim concentration to protect the cells from the unfavorable conditions. The chemical composition of extracellular polymeric substances increased. For denitrifying bacteria, the read numbers of Pseudomonas, Flavobacterium and Bacillus were both significantly increased from Day 1 to 25 and sharply decreased by Day 50 (p<0.05), which is consistent with the tendency of Planctomyces (Anammox). The read number of Paracoccus displayed an increasing trend, whereas Nitrospirales, Nitrospira (nitrite oxidizer) and Nitrosomonadaceae (ammonia oxidizer) were significantly decreased (p<0.05). The read number of Rhodocyclaceae (phosphorus oxidizer) was significantly decreased from Day 1 to 25 and sharply increased by Day 50 (p<0.05).