Reactor R1 Research Articles

Response and recovery of nitrifying moving bed biofilm reactor systems exposed to 1°C with varying levels of ammonia starvation

This study investigated the impact of varying total ammonia nitrogen (TAN) feed levels along with water temperature decreases on the performance of nitrifying moving bed biofilm reactor (MBBR) at 1 °C and its recovery at 3 °C. Five MBBR reactors were operated with different TAN concentrations as water temperature decreased from 20 to 3 °C: reactor R1 at 30 mg N/L, reactor R2 at 20 mg N/L, reactor R3 at 15 mg N/L, reactor R4 at 10 mg N/L and reactor R5 at 0 mg N/L. The corresponding biofilm characteristics were also analyzed to understand further nitrifying MBBR under different TAN feeding scenarios. The findings revealed that the higher TAN levels were before reaching 1 °C, the better nitrification performance and the more biomass grew. However, the highest TAN concentration (30 mg N/L) might negatively affect the nitrification performance, the activity of nitrifiers, and the growth of biofilms at 1 °C because of the toxic effects of un-ionized or free ammonia (FA). It was observed that the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were affected by FA concentrations ranging from 0.2 to 0.7 mg N/L at 1 °C, but they could gradually be adapted to such inhibitory environment, with NOB recovering more quickly and robustly than AOB. The study identified 20 mg N/L (67 % of maximum influent TAN at 1 °C in R2 as the optimal TAN feeding concentration, achieving over 90 % TAN removal and a surface area removal rate (SARR) of 0.78 ± 0.02 g N/m2·d at 1 °C. Meanwhile, R2 also exhibited the highest biofilm mass, with total solids at 13.3 mg/carrier and volatile solids at 11.3 mg/carrier. As TAN was removed, nitrite accumulation was observed at 1 °C, and higher influent TAN concentrations prior to 1 °C appeared to delay the accumulation. When water temperature increased from 1 °C to 3 °C, nitrification performance improved significantly in all reactors without nitrite accumulation, and the higher TAN feeding in the previous stage led to faster recovery. Compared with 20 °C, biofilm became thinner and denser at 1 °C and 3 °C. Furthermore, this study revealed significant shifts in microbial community composition and nitrifier abundances in response to changes in water temperature and influent TAN levels. The dominant nitrifiers were identified as Nitrosomonadaceae (AOB) and Nitrospiraceae (NOB). At 1 °C, the nitrifier abundances were significantly correlated with SARRs, FA, and biofilm density. R2, which exhibited the best nitrification performance, maintained higher nitrifier abundances at 1 °C.

Integrating electrochemically-assisted anaerobic reactors with conductive media for enhanced methanation of greywater

The utilization of bioelectrochemical systems is critical for the generation of methane via anaerobic digestion, and the process is influenced by the applied potential. The trajectory of biogas generation in five batch reactors showed important implications for methane production by synergistic effects of electric fields and conductive media allowing for attached growth of microorganisms. Synthetic greywater which is effective water source converts into methane within 5 days of reactor operation. The experiments emphasized that substrate availability enhanced the attached growth of microorganism in anaerobic settings. Reactor R2, with no microorganism-growing surface, produced only 20 % of the methane produced by reactor R3, which contained Polyvinylidene fluoride (PVDF) media. The presence of current (0.5 V) increased CH4 by 1.35 times in case of non-conductive media (R3) and 1.6 times in conductive media higher than without external voltage. The study indicated a direct correlation between applied voltage and methane generation up to 1.0 V. The ratio of CO2/CH4 changed from 1.16 at 0 V (R1) to 0.362, 0.32, 0.267 and 0.296 for R2-R5 at 1.0 V, respectively. Regardless of surface conductivity, the presence of media for attached microbial growth was favorable for the slow growing methanogens. However, high throughput RNA sequencing showed that electrotrophic methanogens were more abundant with conductive media than non-conductive media under electric fields.

Enhanced reduction of sulfate by iron-carbon microelectrolysis: interaction mechanism between microelectrolysis and microorganisms.

Sulfate wastewater has a wide range of sources and greatly harms water, soil, and plants. Iron-carbon microelectrolysis (IC-ME) is a potentially sustainable strategy to improve the treatment of sulfate (SO42-) wastewater by sulfate-reducing bacteria (SRB). In this study, an iron-carbon mixed micro-electrolysis bioreactor (R1), iron-carbon layered bioreactor (R2), activated carbon bioreactor (R3), and scrap iron filing bioreactor (R4) were constructed by up-flow column experimental device. The performance and mechanism of removing high-concentration sulfate wastewater under different sulfate concentrations, hydraulic retention times (HRT), and chemical oxygen demand (COD)/SO42- were discussed. The results show that the iron-carbon microelectrolysis-enhanced SRB technology can remove high-concentration sulfate wastewater, and the system can still operate normally at low pH. In the high hydraulic loading stage (HRT = 12h, COD/SO42- = 1.4), the SO42- removal rate of the R1 reactor reached 98.08%, and the ORP value was stable between - 350 and - 450mV, providing a good ORP environment for SRB. When HRT = 12h and influent COD/SO42- = 1.4, the R1 reactor sulfate removal rate reached 96.7%. When the influent COD/SO42- = 0.7, the sulfate removal rate was 52.9%, higher than the control group. Biological community analysis showed that the abundance of SRB in the R1 reactor was higher than that in the other three groups, indicating that the IC-ME bioreactor could promote the enrichment of SRB and improve its population competitive advantage. It can be seen that the synergistic effect between IC-ME and biology plays a vital role in the treatment of high-concentration sulfate wastewater and improves the biodegradability of sulfate. It is a promising process for treating high-concentration sulfate wastewater.

Assessment of microbial population in integrated CW-MFC system and investigation of organics and fecal coliform removal pathway

The current study is focused on understanding the operational mechanism of an integrated constructed wetland-microbial fuel cell (CW-MFC) reactor emphasizing fecal coliform (FC) removal. Few studies are available in the literature investigating the inherent mechanisms of pathogen inactivation in a CW-MFC system. Raw domestic wastewater was treated in three vertical reactors, one planted constructed wetland (R1), one planted CW-MFC (R2), and one unplanted CW-MFC (R3). Spatial analysis of treated effluents showed a considerable amount of organics and fecal coliform removal at the vicinity of the anode in R2. Assessment of the microbial population inside all the reactors revealed that EABs (Firmicutes, Bacteroidetes, and Actinobacteria) were more abundant in R2 compared to R1 and R3. During the activity study, biomass obtained from R2 showed a maximum substrate utilization rate of 1.27 mg COD mgVSS−1 d−1. Kinetic batch studies were carried out for FC removal in all the reactors, and the maximum first order FC removal rate was obtained at the anode of R2 as 2.13 d−1 when operated in closed circuit mode. This value was much higher than the natural die-off rate of FCs in raw wastewater which was 1.16 d−1. Simultaneous bioelectricity monitoring inferred that voltage generation can be correlated to faster FC inactivation, which was probably due to EABs outcompeting other exogenous microbes in a preferable anaerobic environment with the presence of an anode. Reactor R2 was found to be functioning as a symbiotic bio-electrochemical mesocosm.

Scaling-up of oxygenic photogranular system in selective-CSTR

The light driven oxygenic photogranule process presents potential aeration free wastewater treatment. Earlier attempts to scale up OPG in larger and deeper sequencing batch reactors were found difficult due to reduced light availability arising from slug entries of turbid wastewater and the accumulation of light-attenuating small biomass. Here, we investigated the use of surface-lit 120 L selective continuous stirred-tank reactors with an internal settler to treat municipal wastewater. The internal settler was deployed to continuously remove small, slow-settling biomass and enhance light availability within the reactor. This continuous-flow OPG system achieved mean effluent TSS of 32 ± 22 mg/L and soluble COD of 31 ± 14 mg/L. A similar reactor operated for 154 days had mean effluent TSS of 28 ± 24 mg/L and soluble COD of 38 ± 17 mg/L. More notably, granulation was maintained and propagated during the operation. Overall, high yields, 0.98 and 0.81 gCOD produced/gCOD consumed were achieved for reactor R1 and R2, respectively.

Effect of solar and artificial lighting on microalgae cultivation and treatment of liquid digestate

A comparative study was carried out to assess the effect of two light sources on microalgae cultivation and the treatment of liquid digestate. The R1 photobioreactor operated with LED lightning allowed to achieve moderate nutrient removal rates whereas soluble COD (Chemical Oxygen Demand) was reduced in 90%. After switching this reactor into sunlight, the removal rate of phosphates increased to 66%. However, the greatest removal rate of both nutrients and sCOD of up to 93% was observed in the R2 photobioreactor operated only under sunlight. Microglena sp. was the dominant algae growing in the R1 reactor, and the main bacteria families detected were Chitinophagaceae, Sphingomonadaceae and Xanthobacteraceae. In contrast, Tetradesmus obliquus dominated in the R2 reactor and Rhodanobacteraceae, Chitinophagaceae and A4b were predominant bacteria in this run. Furthermore, much greater biomass productivity as well as overall biomass density was observed in the R2 photobioreactor cultivated exclusively with solar lightning.

Optimization of Engineering and Process Parameters for Vermicomposting

Urbanization and population rise considerably increase the generation of solid wastes. The recycling of solid wastes through vermicomposting is a sustainable approach. The current study aimed to investigate the effect of earthworm (Eisenia fetida and Eugilius euganiae)-processed/mixed solid waste manure (vermicompost) on the development, productivity, and chemical characteristics of chili and brinjal in different wooden reactors (R). A mixture of palash leaf litter, biogas slurry, food wastes from a hostel kitchen and households, and municipal solid waste (MSW) were used during the study. The effects of different reactors; process parameters; earthworm cultures, such as R1–R9 with different widths and lengths at a constant height (30 cm); pH, salt, and moisture content; temperature; C:N ratios; N, P, K, and pathogen content; and the type of mono/-polyculture on vermicompost were tested with respect to chili and brinjal production. The average net increase in the worms’ zoomass in reactor R1 at different mixed worm densities (E. fetida + E. eugeniae) under optimum conditions was observed. Compared to a monoculture reactor, the yield of both chili and brinjal were significantly greater in the polyculture reactor with vermicompost soil.

Formation of microbial products by activated sludge in the presence of sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs) in long-term operated sequencing batch reactors

Emerging contaminants, sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs), were selected as the target pollutants for this study and using a sequencing batch reactor (SBR), the coexistence effect of antibiotics and nanomaterials on the activated sludge system was investigated. The results showed that the average total nitrogen (TN) removal rates during long-term operation (60 days) for the blank group, the reactor with SMZ, ZnO NPs, and SMZ combined with ZnO NPs were 80.47 %, 78.22 %, 73.77 %, and 72.52 %, respectively, and the average total phosphorous (TP) removal rates were 84.17 %, 82.48 %, 74.69 %, and 76.20 %, respectively. This indicates that ZnO NPs, rather than SMZ, have a negative effect on the treatment efficiency of the system, whereas the coexistence of the two has not yet had a higher effect. Both SMZ and ZnO NPs caused an increase in soluble microbial products (SMP) and extracellular polymers (EPS). High-throughput sequencing results showed that the relative abundance of nitrifying, denitrifying, and phosphorus-polymerizing bacteria was the highest in reactor R1, and the long-term stress of either SMZ or ZnO NPs caused a decrease in these functional bacteria. Finally, the comprehensive mechanism of SMZ and ZnO NPs in activated sludge is discussed.

Rapid Start-Up Characteristics of Anammox under Different Inoculation Conditions

The long multiplication time and extremely demanding enrichment environment requirements of Anammox bacteria (AAOB) have led to difficult reactor start-ups and hindered its practical dissemination. Few feasibility studies have been reported on the recovery of AAOB activity initiation after inlet substrate disconnection caused by an unfavorable condition, and few factors, such as indicators of the recovery process, have been explored. Therefore, in this experiment, two modified expanded granular sludge bed reactors (EGSB) were inoculated with 1.5 L anaerobic granular sludge (AGS) + 1 L Anammox sludge (AMS) (R1) and 2.5 L anaerobic granular sludge (AGS) (R2), respectively. After a long-term (140 days) starvation shock at a high temperature (38 °C), the bacteria population activity recovery experiments were conducted. After 160 days, both reactors were successfully started up, and the total nitrogen removal rates exceeded 87%. Due to the experimental period, the total nitrogen removal rate of R2 was slightly higher than that of R1 in the final stage. However, it is undeniable that R2 had a relatively long activity delay during startup, while R1 had no significant activity delay during startup. The sludge obtained from R1 had a higher specific anammox activity (SAA). Analysis of the extracellular polymer substances (EPS) results showed that the extracellular polymer content in R1 was higher than that in R2 throughout the recovery process, indicating that R1 had higher sludge stability and denitrification performance. Scanning electron microscopy (SEM) analysis showed that more extracellular filamentous bacteria could be seen in the R1 reactor with better morphology of Anammox bacteria. In contrast, the R2 reactor had fewer extracellular hyphae and micropores as a percentage and higher filamentous bacteria content. The results of microbial 16SrDNA analysis showed that R1 used AAOB as inoculum to initiate Anammox, and the reactor was enriched with Anammox bacteria earlier and in much greater abundance than R2. The experimental results indicated that inoculating mixed anaerobic granular sludge and Anammox sludge to initiate an anammox reactor was more effective.

Optimizing the Biochemical Methane Potential (BMP) of Food Waste

Recent advances in anaerobic digestion has resulted in expansion of sustainable methods for use of waste as energy resources. Conventional methods prove to be uneconomical and environmentally impractical. Moreover, the microbial consortia in anaerobic digestion are temperature dependent and therefore requires investigations on temperature optimization. Therefore, the recent experimental study is being undertaken with the objective in order to assess the effect of temperature on anaerobic biodegradation of food wasted from a hostel campus. The effect of temperature on methane generation rate has also been investigated. The anaerobic digestion study under psychrophilic, mesophilic and thermophilic temperature conditions has been carried out and compared in order to assess the optimum methane production conditions. All the experimental study for anaerobic digestion of food waste has been carried out at optimum F/M (food to mass) ratio of 0.75. The cumulative highest methane production is observed to be 33, 50 and 65 mL of CH4 in reactor R1, R2 and R3 with initial food waste COD dosage of 100, 150 and 200 mg, respectively under mesophilic temperature conditions. The highest biochemical methane potential (BMP) value of 0.94, 0.95 and 0.93 gCH4-COD/gCOD fed in reactor R1, R2 and R3 respectively, under mesophilic temperature conditions. It been observed that for maximum methane generation rate constant of 0.62 d-1 were observed under thermophilic conditions thus has to be highly accelerative process but overall conversion of organic matter to methane is less as compared to mesophilic temperature conditions, this is because free ammonia concentration increases with increasing temperature, by influencing the equilibrium. However, mesophilic conditions provide a more stable environment for the anaerobic digestion process. This may be due to the fact that temperature fluctuations can disrupt the microbial activity and slow down the process, but mesophilic conditions provide a stable environment for the microorganisms to thrive. Therefore, the mesophilic temperature range provides a balance between high reaction rates, stability, and cost-effectiveness, making it the optimal temperature range for anaerobic digestion of food waste. The obtained results in present study will be helpful in implementing on full-scale anaerobic solid waste digesters for enhancing the methane generation under mesophilic temperature conditions with high organic matter removal. Also, under thermophilic conditions the energy requirement for heating proves to be uneconomical.

Determination of kinetic constants on thermophilic aerobic wastewater treatment of Kraft bleaching cellulose effluent

Recalcitrant compounds found in pulp and paper mill effluents, which are usually generated at high temperatures, have shown the potential for thermophilic treatment. Using bleached kraft pulp mill effluents, this study aims to evaluate the acclimation conditions of mesophilic aerobic sludge to thermophilic conditions and determine the kinetic parameters. Two feeding strategies were used for this purpose: in the first approach, the first reactor R1 was fed with bleached kraft pulp effluent, while in the second strategy the reactor R2 was fed with easily biodegradable synthetic effluent and then the gradual substitution for bleached effluent was performed after sludge acclimation to a thermophilic environment. Both reactors were operated in batch at 55ºC. The second strategy has a slight advantage in COD (chemical oxygen demand) degradation and a considerable higher biomass production. The kinetic parameters (KS, µmax, Y, Kd) for both approaches were obtained using the Monod model. Those values indicated that the approach used for reactor R2 provided higher reaction speed.

Effect of Bio-Electrochemical Treatment of Hydroponic Effluent on the Nutrient Content

This study examined the effect of bio-electrochemical treatment processes on nitrogen and phosphorus removal, but it also evaluated the impact of the treatment processes on the concentration of other nutrients present in hydroponic effluent. A bio-electrochemical reactor (BER) was used in the experiment to treat effluent from the hydroponic cultivation of tomatoes. It was stated that the nitrogen removal efficiency decreased with increasing current density. The study showed that an electric current density of 0.63 A/m2 ensured the lowest effluent nitrate concentration. The nitrogen removal efficiency ranged from 41.6%-R1 (density of 0.63 A/m2) to 8.9%-R4 (density of 5 A/m2). Electric current density higher than 1.25 A/m2 resulted in lower total nitrogen removal efficiency. The total phosphorus removal efficiency increased with increasing electric current density. The phosphorus removal efficiency was the lowest—95.1%—in the R1 reactor, whereas it was the highest in R4—99.1%. The concentration of the other elements in the effluent was determined. The content of molybdenum, boron, sulphates, and potassium did not meet the acceptable norms for discharging hydroponic effluent into the environment. The study showed that bio-electrochemical processes taking place in BER caused secondary contamination of hydroponic wastewater with molybdenum ions.

Fast start-up of ANAMMOX biofilm processes at low temperatures by economical quorum sensing regulation: The importance of endogenous N-acyl-homoserine lactones from enhanced inoculated sludge

The start-up of anaerobic ammonia oxidation (ANAMMOX) processes at low temperatures is quite difficult. In this study, the fast start-up (43 days) of ANAMMOX biofilm processes at 18 ± 3 °C was achieved by adding enhanced ANAMMOX granules (LT-granules) into the inoculated denitrification sludge. The results showed that the addition of LT-granules significantly reduced the duration of the three start-up phases (cell lysis phase, activity lag phase, and activity elevation phase) of reactor R2 compared with the control group R1 without LT-granules. It was demonstrated that LT-granules released high contents of N-hexanoyl-DL-homoserine lactone (C6-HSL), N-octanoyl-DL-homoserine lactone (C8-HSL), and N-3-oxohexanoyl-L-homoserine lactone (3OC6-HSL). The C6-HSL and C8-HSL from LT-granules were strongly positively correlated with the concentrations of polysaccharides (TB-PS) and proteins (TB-PN) in tightly bound extracellular polymeric substances (TB-EPS) in R2 biofilms, respectively. Thus, LT-granules promoted the release of TB-PS and TB-PN from the biofilm in R2 during activity lag and activity elevation phases, improving the biofilm adhesion performance. Furthermore, it was proved that the C6-HSL, C8-HSL, and 3OC6-HSL from LT-granules significantly stimulated the relative abundance of Candidatus Brocadia genus and the expression of functional genes hzo and hzsA in R2 biofilms during activity lag and activity elevation phases. These are the main reasons why adding LT-granules promoted the start-up of reactor R2 at 18 ± 3 °C effectively. This study is the first work to accelerate the start-up of the ANAMMOX biofilm system at the low temperature by the economical quorum sensing (QS) regulation based on endogenous N-acyl-homoserine lactone signals (AHLs) and supply a new way for the rapid start-up of ANAMMOX processes in the low-temperature environment.

Kinetic of nitrogen consumption by Anammox process in membrane biofilm reactors operated in sequential batch

Biological nitrogen removal via Anammox is an advantageous technology in the nitrogen treatment effluents with a low Carbon/Nitrogen ratio, a process that makes this route interesting for the most different types of industries, agribusinesses, and urban effluent treatment plants. Achieving robust Anammox biomass for use in full-scale plants is still a challenge that motivates studies of biomass enrichment and the search for kinetic parameters of substrate consumption rate that help optimize the conduction of reactors. According to the previously mentioned, this work aimed to carry out the kinetic study of nitrogen consumption by the Anammox process in a membrane aerated biofilm reactors operated in sequential batches (MABR-BS). 6 MABR-BS reactors were used, each one of them inoculated with a specific Anammox sludge, obtained from the enrichment of anaerobic and aerobic sludges coming from 3 different sludge sources, namely, a municipal wastewater treatment plant, a landfill leachate treatment plant, and a swine slaughterhouse effluent treatment plant. For the kinetic study, 6 reactors were used, made in glass flasks with a total volume of 1L, with a useful volume of 500 mL, with the 300:200mL ratio between synthetic effluent (with 100mgN-NH4+.L-1) and sludge from the sources: R1 - anaerobic sludge from a UASB reactor for urban sewage treatment; R2 - mixed sludge from a UASB reactor, consisting of waste sludge and supernatant scum; R3 - anaerobic sludge from landfill leachate treatment; R4 - mixed sludge consisting of aerobic and anaerobic sludge from landfill leachate treatment plant; R5 - anaerobic sludge from the swine slaughter effluent treatment plant and R6 - aerobic and anaerobic sludge from the swine slaughter effluent treatment plant. The experimental apparatus had 3 aerators coupled to 3 flowmeters with an air flow regulated at 1.0 L.min-1; 30 cm of silicone membrane in a curved shape with one of the inlets connected to the aerator and flowmeter, the other outlet was immersed in a 75 cm water column, exerting negative pressure on the air inside the tubular silicone membrane, forcing the air to exit through the microporosity of the membrane. Aeration was intermittent, with an interval of 0.16 h between each minute of aeration, the reactors were shaken in a water bath at 30 rpm and temperature of 32°C. The kinetic test had a duration of 24 hours with sampling every 2.5 hours. The nitrogen removal efficiencies (%) determined in the kinetic test were 61.36 (R1); 61.01(R2); 59.03 (R3); 56.70 (R4); 62.77 (R5) and 64.40 (R6). Regarding pH, all reactors had an initial pH above 8.0 and a final pH close to neutral. The specific nitrogen removal rates (in mgN.gVSS-1h-1), were on average 29.43 (R1); 33.50 (R2); 33.62 (R3); 33.42 (R4); 28.90 (R5) and 30.34 (R6). The best performance in the kinetic assay was obtained in the R1 reactor, obtaining a specific activity of maximum nitrogen removal of 57.61 mgN.gVSS-1h-1 and molar generation of residual nitrate with a stoichiometric coefficient of 0.018 mol.

Insight into thiosulfate-driven denitrification and anammox process: Bigger aggregates driving better nitrite utilization on ammonium and nitrate contained wastewater

Recent studies have paid attention to thiosulfate-driven denitrification and anammox (TDDA) process on treating ammonium and nitrate contained wastewater. However, technical challenges still existed in coupling denitratation and reducing denitritation to obtain efficient nitrite supply for anammox. By successfully operated two anoxic sequencing batch reactors (ASBR) with two different sizes of TDDA aggregates, the reactor R1 with smaller aggregates (0.195 mm) achieved 83.38% ammonium removal efficiency and 85.39% total nitrogen removal efficiency. In comparison, the reactor R2 with bigger aggregates (0.554 mm) achieved higher ammonium removal efficiency (92.02%) and total nitrogen removal efficiency (90.05%). Different aggregates showed a similar anammox activity and denitratation activity but varied in denitritation activity (3.47 mg/(L·h) in R1 compared to 1.42 mg/(L·h) in R2), indicating bigger aggregates supplied nitrite to anammox process more efficiently. Annwoodia was the pivotal microorganism involved in nitrite acquisition that outcompeted anammox bacteria in smaller aggregates. Bigger aggregates with the less relative abundance of Annwoodia established a more harmonious microbial community to support effective nitrogen removal. This study provides a novel insight into nitrite utilization of TDDA system and sheds light on the operation of ASBR-based TDDA processes for biological nitrogen removal.

Anaerobic treatment of ultrasound pretreated palm oil mill effluent (POME): microbial diversity and enhancement of biogas production.

In this study, palm oil mill effluent (POME) treated by ultrasonication at optimum conditions (sonication power: 0.88W/mL, sonication duration: 16.2min and total solids: 6% w/v) obtained from a previous study was anaerobically digested at different hydraulic retention times (HRTs). The reactor biomass was subjected to metagenomic study to investigate the impact on the anaerobic community dynamics. Experiments were conducted in two 5 L continuously stirred fill-and-draw reactors R1 and R2 operated at 30 ± 2°C. Reactor R1 serving as control reactor was fed with unsonicated POME with HRT of 15 and 20days (R1-15 and R1-20), whereas reactor R2 was fed with sonicated POME with the same HRTs (R2-15 and R2-20). The most distinct archaea community shift was observed among Methanosaeta (R1-15: 26.6%, R2-15: 34.4%) and Methanobacterium (R1-15: 7.4%, R2-15: 3.2%). The genus Methanosaeta was identified from all reactors with the highest abundance from the reactors R2. Mean daily biogas production was 6.79 L from R2-15 and 4.5 L from R1-15, with relative methane gas abundance of 85% and 73%, respectively. Knowledge of anaerobic community dynamics allows process optimization for maximum biogas production.

Effects of Carriers on ANAMMOX Sludge Activity Recovery and Microbial Flora Characteristics

In order to realize the rapid recovery of ANAMMOX sludge bacterial activity after long-term room temperature storage, three groups of reactors were added to ANAMMOX sludge that had been stored without substrate at room temperature (15-30℃) for 9 months. Among the three groups of reactors, comet fiber carrier and K3 carrier were added to R2 and R3 reactors, respectively, as biological carriers. The effects of different carriers on the recovery rate of ANAMMOX sludge bacterial activity were investigated. The results showed that ANAMMOX reactions in the R2 and R3 reactors began taking place on the 8th and 10th day, respectively, with respective TIN removal rates of 82.25% and 80.92%, which were significantly improved compared with that in the R1 reactor, in which no carrier was added (ANAMMOX reaction started occurring on the 15th day with a TIN removal rate of 80.26%). After 42 days with influent, ρ(NH4+-N) and ρ(NO2--N) respectively increased to 300 mg·L-1 and 396 mg·L-1, and the TIN removal rates of the three groups of reactors were respectively 78.96%, 84.92%, and 84.66%. Microbial community structure analysis showed that the relative abundances of ANAMMOX bacteria in the R2 and R3 reactor were respectively 6.85% and 6.06%, two to four times that in the R1 reactor. The predominant ANAMMOX bacteria in the sludge was Candidatus Jettenia, whose relative abundances in the three groups of reactors were respectively 1.62%, 5.74%, and 5.21%. The results show that ANAMMOX biofilm-granular sludge complex systems constructed by adding carriers can considerably shorten the time for recovering ANAMMOX sludge bacterial activity after long-term room temperature storage without substrate. The carriers effectively promoted the relative abundances of ANAMMOX bacteria in the reactors, whereas the promoting effect of comet fiber carrier was slightly more significant than that of the K3 carrier.

Coagulants put phosphate-accumulating organisms at a competitive disadvantage with glycogen-accumulating organisms in enhanced biological phosphorus removal system

Enhanced biological phosphorus removal (EBPR) process is susceptible to the changed operation condition, which results in an unstable treatment performance. In this work, long-term effect of coagulants addition, aluminum salt for the reactor R1 and iron salt for the reactor R2, on EBPR systems was comprehensively evaluated. Results showed that during the initial 30 days’ coagulant addition, effluent chemical oxygen demand and phosphorus can be reduced below 25 and 0.5 mg·L-1, respectively. Further supply of metal salts would stimulate microbial extracellular polymeric substance excretion and induce reactive oxygen species accumulation, which destroyed the cell membrane integrity and deteriorated the phosphorus removal performance. Moreover, coagulants would decrease the relative abundance of Candidatus Accumulibacter while increase the relative abundance of Candidatus Competibacter, leading phosphors accumulating organisms in a disadvantage position. The results of this work might be valuable for the operation of chemical assisted biological phosphorus removal bioreactor.

How anammox process resists the multi-antibiotic stress: Resistance gene accumulation and microbial community evolution

The effects of multiple antibiotics on the anaerobic ammonia oxidation (anammox) process were investigated. The resistance of the anammox system to high-concentration antibiotics was also demonstrated through gradual acclimation experiments. Inhibition of the anammox process (R1) occurred when the concentrations of erythromycin (ERY), sulfamethoxazole (SMX) and tetracycline (TC) were 0.1, 5.0 and 0.1 mg L−1, respectively. The nitrogen removal efficiency (NRE) of R1 was reduced from 97.2% to 60.7% within 12 days and then recovered to 88.9 ± 9.5% when the nitrogen loading declined from 4.52 ± 0.69 to 2.11 ± 0.58 kg N m−3 d−1. Even when the concentrations of ERY, SMX and TC were as high as 1.0, 15.0 and 1.0 mg L−1, respectively, R1 maintained stable operation. The increases in the abundance of antibiotic resistance genes (ARGs) and in extracellular polymeric substances (EPS) content showed that the anammox process alleviated stress from multiple antibiotics mainly by producing ARGs and secreting EPS. The molecular docking simulation results illustrated the potential binding sites between ammonium transporter and different antibiotics. The upregulation of functional gene expression and the stable abundance of Candidatus Kuenenia in R1 compared with that in the control suggested that the R1 reactor generally maintained more stable long-term operation. This work provides a new understanding of the application of the anammox process to treat wastewater containing multiple antibiotics.

Methanogen and nitrifying genes dynamics in immersed membrane bioreactors during anaerobic co-digestion of different organic loading rates food waste

This work was aimed to evaluate the distinctive food waste (FW) organic loading rates (OLR) on methanogen and nitrifying genes dynamics and its correlation with identified relative abundance of bacterial dynamics during the anaerobic digestion. This experiment were carried out in the digesters at high OLR of food wastes at (4 to 8 g volatile solids/liter/day reactor R1) and (6 to 10 g volatile solids/liter/day reactor R2). The results shown that the relative abundance of mcrA, mcrB and mcrG genes were richest in the first day of both R1 and R2. In addition, the most of nitrifying genes were greater in after 34 days digestion in R2, while these genes did not show the specific regularity in R1. Finally, the correlation figure shows that Clostridium and Lactobacillus genera were significantly correlated with the different organic acids and methanogen and nitrifying genes dynamics.