Keystone Species and Niche Differentiation Promote Microbial N, P, and COD Removal in Pilot Scale Constructed Wetlands Treating Domestic Sewage

The microbial characteristics related to nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) removal were investigated in three pilot scale constructed wetlands (CWs). Compared to horizontal subsurface flow (HSSF) and surface flow (SF) CWs, the aerobic vertical flow (VF) CW enriched more functional bacteria carrying genes for nitrification (nxrA, amoA), denitrification (nosZ), dephosphorization (phoD), and methane oxidation (mmoX), while the removal of COD, total P, and total N increased by 33.28%, 255.28%, and 299.06%, respectively. The co-occurrence network of functional bacteria in the HSSF CW was complex, with equivalent bacterial cooperation and competition. Both the VF and SF CWs exhibited a simple functional topological structure. The VF CW reduced functional redundancy by forming niche differentiation, which filtered out keystone species that were closely related to each other, thus achieving effective sewage purification. Alternatively, bacterial niche overlap protected a single function in the SF CW. Compared with the construction type, temperature, and plants had less effect on nutrient removal in the CWs from this subtropical region. Partial least-squares path modeling (PLS-PM) suggests that high dissolved oxygen and oxidation-reduction potential promoted a diverse bacterial community and that the nonkeystone bacteria reduced external stress for functional bacteria, thereby indirectly promoting nutrient removal.

[Effect of Anaerobic Plug-flow on Nitrification Denitrifying Phosphorus Removal Aerobic Granular Sludge with Intermittent Aeration]

Actual domestic sewage has a complex composition and relatively low carbon and nitrogen content. Anaerobic plug-flow influent can enhance the utilization of COD by aerobic granular sludge by providing a locally high concentration of substrate. In this study, intermittent aeration was used to cultivate aerobic granular sludge in a sequencing batch reactor (SBR), and actual domestic sewage was used as the feed water to inoculate the sewage plant sludge. In the R1 experiment, rapid anaerobic feeding was adopted, while in R2, anaerobic plug-flow feeding was adopted, to explore the impact of different feeding modes on the aerobic granular sludge system of domestic sewage. Under rapid anaerobic feeding in R1, the particle structure appeared earlier, but particle breakage occurred after 71 days of operation; the particle structure generated in R2 was denser than that of R1, the particle surfaces were smoother, and the denitrifying phosphorous accumulating organisms (DPAO) had a more enriching effect. In the final R1 and R2 reactors, the proportion of DPAO to phosphorous accumulating organisms (PAO) was 14.17% and 22.07%, respectively. The results show that the anaerobic plug-flow feeding mode can enhance the use of influent COD by granular sludge, which is conducive to enriching DPAO, generating denser and more stable particles, realizing "one carbon dual purpose" operation, and removing more nitrogen and phosphorus.

[Aerobic Granular Sludge Operation and Nutrient Removal Mechanism from Domestic Sewage in an Anaerobic/Aerobic Alternating Continuous Flow System]

Mature aerobic granular sludge was inoculated at room temperature in an anaerobic/aerobic alternating continuous flow system. The system consisted of two independent anaerobic and aerobic tanks. Actual domestic sewage was used as the influent to explore the influence of the gas intensity and hydraulic residence time on the continuous flow system. The results revealed that the conditions of a reflux ratio of 2, lower aeration intensity (0.6 mL·min^-1), and proper hydraulic residence time (9 h) were more conducive to the removal of pollutants. Under such conditions, the average removal rate of TP was 80.43%, the average removal rate of TN was 83.6%, the average removal rate of COD was 90.39%, the sludge concentration was approximately 2100 mg·L^-1, the sludge volume index was maintained below 50 mL·g^-1, and the particle size was 700-800 nm. The EEM-PARAFAC model was used to characterize and analyze the EPS at different stages. The results revealed that changing the parameters could change the composition of EPS. The hydraulic residence time had a greater impact on the continuous flow system than the aeration intensity. In addition, a preliminary conceptual reaction process model in the anaerobic/aerobic alternating continuous flow system was built using high-throughput pyrosequencing and phylogenetic assignment. Eleven major functional bacteria related to nitrogen and phosphorus removal were found in the system.

Investigation into the Novel Microalgae Membrane Bioreactor with Internal Circulating Fluidized Bed for Marine Aquaculture Wastewater Treatment

A microalgae membrane bioreactor (MMBR) with internal circulating fluidized bed (ICFB) was constructed at room temperature to study the removal efficiency of marine aquaculture wastewater pollutants and continuously monitor the biomass of microalgae. Within 40 days of operation, the removal efficiency of NO₃⁻–N and NH₄⁺–N in the ICFB-MMBR reached 52% and 85%, respectively, and the removal amount of total nitrogen (TN) reached 16.2 mg/(L·d). In addition, the reactor demonstrated a strong phosphorus removal capacity. The removal efficiency of PO₄³⁻–P reached 80%. With the strengthening of internal circulation, the microalgae could be distributed evenly and enriched quickly. The maximum growth rate and biomass concentration reached 60 mg/(L·d) and 1.4 g/L, respectively. The harvesting of microalgae did not significantly affect the nitrogen and phosphorus removal efficiency of ICFB-MMBR. The membrane fouling of the reactor was investigated by monitoring transmembrane pressure difference (TMP). Overall, the membrane fouling cycle of ICFB-MMBR system was more than 40 days.

[Microbial Community Structure for Sewage Wastewater Treatment Plants in Winter]

Constructing an effective control strategy for the daily operation of sewage treatment plants daily operation is an important criterion for the removal performances of nutrient stable in winter. To investigate microbial community structure, functional groups, and relationships between population dynamics and effluent variation, activated sludge obtained from 4 plants, which were running stably in a low temperature period (8-15℃) in northern China, were sampled. The high-throughput sequencing results indicated that the microbial community had good richness in the low temperature period during which the abundance of Actinobacteria increased. Nitrosomonas, a key functional ammonia oxidation bacterium, was greatly affected by the decreasing temperature, while Denitrifies, a highly diverse core group with wide distribution, maintained stable abundance indicating less influence of decreasing temperature. The denitrification efficiency was only associated with the mixed liquor reflux ratio. Tetrasphaera was widely present in four processes and played an important role for the removal of biological phosphorus. Sludge bulking phenomena caused by filamentous bacteria overgrowth occurred frequently in winter; however the quality of effluents was slightly influenced.

[Start-up of an Integrated Process of Denitrifying Phosphorus Removal Coupled with Partial Nitritation and Anaerobic Ammonium Oxidation]

An integrated process uses an anaerobic baffled reactor combined with a fully mixed reactor (ABR-CSTR) as a test carrier for low-carbon, high-ammonia nitrogen (NH₄⁺-N ≥ 200 mg·L^-1) wastewater under continuous flow operating conditions; the normal anaerobic sludge in different compartments is subjected to domestication and cultivation to realize denitrifying phosphorus removal, partial nitritation, and anaerobic ammonium oxidation, thereby achieving the coupling effect of the three. Partial nitritation was successfully achieved in the A4 (CSTR) section by the strategy of limited oxygen (dissolved oxygen DO=0.8 mg·L^-1) and intermittent aeration (exposure ratio=30 min:30 min) after 30 days. Subsequently, a strategy of shortening the hydraulic retention time (HRT) was adopted to achieve a stable operation of partial nitritation, and a stable influent substrate of NO₂^--N/NH₄⁺-N 1.0-1.1 was provided for anaerobic ammonium oxidation. The anaerobic ammonium oxidation function was achieved after 154 days in the A5 and A6 compartments. The removal rates of NH₄⁺-N and NO₂^--N were 94% and 97%, respectively, and the NO₃^--N concentration in the effluent was stable at 22 mg·L^-1. The denitrifying phosphorus removal function was successfully achieved in the A1-A3 compartments by using NO_x^--N in the reflux as an electron acceptor. The removal rate of PO₄^3--P was 77%. The integrated process was successfully coupled through 175 days, achieving simultaneous removal of C, N, and P.

[Aerobic Granular Sludge System with Multiple Influent-Aeration Operation Strategy]

SBR reactors R1 and R2 were used to inoculate activated sludge from a sewage treatment plant, and domestic sewage was used as the influent. The operation was carried out using a single and multiple influent-aeration operation strategy, respectively, and the particle size change and removal effect during the operation was studied. The results show that R1 and R2 successfully achieved sludge granulation after 56 days and 39 days of operation, respectively. The concentrations (mg·L^-1) of chemical oxygen demand, total nitrogen, and total phosphorus (TP) in the effluent of R1 and R2 after stable operation were 29.7, 13.7, 0.31, 19.2, 8.1, and 0.37, respectively. The removal rates were respectively 87.7%, 75.6%, 95.1%, and 90.1%, 85.6%, and 94.2%, and the average particle size of the particles reached 740 μm for R1 and 791 μm for R2. The results showed that for the same running time, the effluent NO₃^--N concentration and TP concentration in R2 were lower than those in R1. In the later stage of operation, the ratio of denitrifying phosphorus-accumulating organisms (DPAO) to total phosphorus-accumulating organisms (PAOs) in R1 and R2 increased from an initial 11.17% to 25.47% and 34.08%, respectively. Compared with the one influent-aeration operation strategy, the multiple influent-aeration operation strategy had a lower concentration of NO₃^--N in the initial stage of the startup, the PAOs received less impact, the DPAO enrichment was better, the phosphorus removal performance was better, and it helped to form aerobic granular sludge.

Suitability of SBR for Wastewater Treatment and Reuse: Pilot-Scale Reactor Operated in Different Anoxic Conditions

The present study investigates the performance of a pilot-scale Sequencing Batch Reactor (SBR) process for the treatment of wastewater quality parameters, including turbidity, total suspended solids (TSS), total solids (TS), nitrogen (ammonia (NH₃-N), nitrite (NO₂^-), and nitrate (NO₃^-), phosphate (PO₄^3-), the chemical oxygen demand (COD), and the 5-day biological oxygen demand (BOD₅), from municipal wastewater. Two scenarios, namely, pre-anoxic denitrification and post-anoxic denitrification, were investigated to examine the performance of a pilot-scale SBR on the wastewater quality parameters, particularly the nitrogen removal. The correlation statistic was applied to explain the effects of operational parameters on the performance of the SBR system. The results revealed that the post-anoxic denitrification scenario was more efficient for higher qualify effluent than the first scenario. The effluent concentrations of the targeted wastewater quality parameters obtained for the proposed SBR system were below those of the local standards, while its performance was better than that of the North Sewage Treatment Plant, Dharan, Eastern province, Kingdom of Saudi Arabia (KSA), in terms of the BOD₅, COD, TN, and PO₄^3- treatment efficiencies. These results indicated the suitability of SBR technology for wastewater treatment in remote areas in the KSA, with a high potential of reusability for sustainable wastewater management.

[Temporal Anaerobic Effect on Aerobic Granular Sludge with Intermittent Influent-Intermittent Aeration]

To initiate the domestic sewage aerobic granular sludge (AGS) process, the experiment is operated by intermittent influent-effluent aeration to reduce the concentration of nitrate and the inhibition of PAO, and realize granulation by phosphate precipitation and positive electricity particles generated during phosphorus removal. The sludge from a sewage treatment plant is inoculated into the SBR reactors R1, R2, R3, and R4, for durations of 30, 60, 90, and 120 min total anaerobic time. This was used to study the effect of anaerobic time on the aerobic granular sludge system in domestic sewage. The experiment shows that reactors R1, R2, R3, and R4 are started successfully with 56, 48, 39, and 35 days, respectively. After 105 days of the operation, the respective average particle sizes reached 750, 764, 791, and 650 μm. During the operational period, at the 43^rd and 47^th day, phosphorus removal performance deteriorated in R1 and R2, and it recovered after the anaerobic time was extended to 90 min. The effect of nitrogen and phosphorus removal in R3 is good; at the 63-77 day the granular sludge in R4 disintegrates, and the effect of nitrogen and phosphorus removal and DPAO enrichment is decreased. During the later stage of operation, the effluent in R1, R2, R3, and R4 reaches the IA standard of the discharge standard of pollutants for municipal wastewater treatment plant. The results show that a long anaerobic time can quickly achieve granulation, however the particles easily disintegrate during a long-term operation. Longer anaerobic time can reduce the inhibition of phosphorus accumulating organisms release phosphorus by nitrate, help enrich DPAO, and obtain a better nitrogen and phosphorus removal effect.

[Simultaneous Short-Cut Nitrification-Denitrification Phosphorus Removal Granules Induced by Phosphorus Removal Granules]

This paper investigated domestic sewage with a low C/N ratio. Mature phosphorus removal granules were inoculated to cultivate granules with a simultaneous short-cut nitrification and denitrification function. The characteristics of nitrogen and phosphorus removal of this process were analyzed. Results show that AOB can be enriched by prolonging the sludge age for 30 days with an aeration intensity of 5 L·(h·L)^-1 and shorter aeration time (140 min), whereas the simultaneous nitrification and denitrification ability could not be improved. The nitrogen loss increased at the aerobic time when aeration intensity was reduced by 3.5 L·(h·L)^-1 and aeration time was prolonged by 200 min. The aeration time was further optimized to restrain the transformation of NO₂^- to NO₃^-, and finally the effluent of TP < 0.5 mg·L^-1 and TN < 15 mg·L^-1. During the process of the system function transformation from phosphorus removal to nitrogen and phosphorus removal, the phosphorus release decreased, however PAOs still played a dominant role (60%) in the process of internal carbon storage. Batch experiments showed that DPAOs that can utilize nitrite as an electron acceptor accounts for 52.43% in the total PAO_S, which alleviated the pressure of the carbon source and improved the simultaneous nitrogen and phosphorus removal.

Casimicrobium huifangae gen. nov., sp. nov., a Ubiquitous "Most-Wanted" Core Bacterial Taxon from Municipal Wastewater Treatment Plants

Microorganisms in wastewater treatment plants (WWTPs) play a key role in the removal of pollutants from municipal and industrial wastewaters. A recent study estimated that activated sludge from global municipal WWTPs harbors 1 × 10⁹ to 2 × 10⁹ microbial species, the majority of which have not yet been cultivated, and 28 core taxa were identified as "most-wanted" ones (L. Wu, D. Ning, B. Zhang, Y. Li, et al., Nat Microbiol 4:1183-1195, 2019, https://doi.org/10.1038/s41564-019-0426-5). Cultivation and characterization of the "most-wanted" core bacteria are critical to understand their genetic, physiological, phylogenetic, and ecological traits, as well as to improve the performance of WWTPs. In this study, we isolated a bacterial strain, designated SJ-1, that represents a novel cluster within Betaproteobacteria and corresponds to OTU_16 within the 28 core taxa in the "most-wanted" list. Strain SJ-1 was identified and nominated as Casimicrobium huifangae gen. nov., sp. nov., of a novel family, Casimicrobiaceae. C. huifangae is ubiquitously distributed and is metabolically versatile. In addition to mineralizing various carbon sources (including carbohydrates, aromatic compounds, and short-chain fatty acids), C. huifangae is capable of nitrate reduction and phosphorus accumulation. The population of C. huifangae accounted for more than 1% of the bacterial population of the activated sludge microbiome from the Qinghe WWTP, which showed seasonal dynamic changes. Cooccurrence analysis suggested that C. huifangae was an important module hub in the bacterial network of Qinghe WWTP.IMPORTANCE The activated sludge process is the most widely applied biotechnology and is one of the best ecosystems to address microbial ecological principles. Yet, the cultivation of core bacteria and the exploration of their physiology and ecology are limited. In this study, the core and novel bacterial taxon C. huifangae was cultivated and characterized. This study revealed that C. huifangae functioned as an important module hub in the activated sludge microbiome, and it potentially plays an important role in municipal wastewater treatment plants.

[Start-up and Stable Operation of CANON Coupled with Denitrifying Phosphorus Removal]

A process coupled completely autotrophic nitrogen removal over nitrite (CANON)with denitrifying phosphorus removal in a modified anaerobic baffled reactor (ABR) coupled with a membrane bioreactor (MBR), inoculated with ordinary activated sludge, was proposed for treating artificial wastewater with ammonia 200 mg·L^-1 and COD/TN=1. This experiment studied the start-up of the process and its nitrogen and phosphorus removal efficiency by controlling the recycle ratio and increasing it from 50% to 200% step by step, with a temperature of (25±1)℃ and pH of 7.5±0.2. The results showed that the anaerobic part in the ABR consumed 70% COD, and resulted in a quick start-up of partial-nitrification at 21 d under low DO and high ammonia nitrogen. Then, by controlling the intermittent aeration (exposure stop ratio:2 h:2 h, DO 0.3-0.4 mg·L^-1), the start-up of the CANON part in the coupling process was successfully achieved at 132 d, such that the concentration of nitrates in the electron acceptor of the ABR anoxic section increased steadily, and finally the coupling process started successfully at 160 d. With stable operation, the TN removal load in the MBR reached 0.22 kg·(m³·d)^-1, and the average removal efficiency of COD, TN, and PO₄^3--P was 87.0%, 90.4%, and 81.8%, respectively. The batch experiment estimated that the denitrifying phosphate accumulating organisms (DPAOs) using nitrates as electron acceptors in the ABR accounted for 68% of the phosphate accumulating organisms (PAOs). The DPAOs, ammonia-oxidizing bacteria (AOB), and anaerobic ammonium oxidizing bacteria (AnAOB) have been developed in the system and have good simultaneous nitrogen and phosphorus removal efficiency.

Enhanced Simultaneous Nitrogen and Phosphorus Removal in A Denitrifying Biological Filter Using Waterworks Sludge Ceramsite Coupled with Iron-Carbon

In this study, waterworks sludge ceramsite (WSC) was combined with 3% iron-carbon matrix in a denitrifying biological filter (ICWSC-DNBF) to enhance the simultaneous removal of carbon, nitrogen and phosphorus in secondary effluent of wastewater treatment plant (SE-WTP). The chemical oxygen demand (COD) and nitrogen removal, as well as phosphorus removal and the adsorbed forms of phosphorus were measured and the removal mechanism of these pollutants by the ICWSC-DNBF system for treating SE-WTP were investigated. The results showed that the ICWSC-DNBF achieved good removals of COD, NH₄⁺-N, NO₃^--N, total N and total P; effluent concentrations were 17.23 mg/L, 3.72 mg/L, 14.32 mg/L, 17.38 mg/L and 0.82 mg/L, respectively. WSC enhanced the P removal due to its high specific surface area and the high number of adsorption sites. Fe-P and Al-P were the main forms of P adsorbed by WSC, accounting for 78.53% of the total adsorbed P. WSC coupled with Fe and C improved the biodegradability of SE-WTP and promoted the removal of organic matter. The removal of N was attributed to the abundant denitrifying microorganisms in the system and the electrochemical effect produced by the internal electrolysis of Fe and C.

[Effect of Intracellular Carbon Source (PHA) Storage on the Mixed Growth Microbial Community Resistance to Low Temperature]

This study investigated the removal of nitrogen and phosphorous by a biological bio-nutrient removal-carbon regulation and phosphorus recovery (BBNR-CPR) reactor at low temperature. The operating temperature of the BBNR-CPR reactor was continuously reduced, and it was found that the BBNR-CPR reactor could operate steadily at low temperature (<15℃) and low C/N ratio (<4.16). The average removal rates of total phosphorus, ammonia, and total nitrogen were 91.20%, 81.10%, and 58.62%, respectively. With increasing running time and decreasing temperature, the relative abundance of Candidatus_Competibacter, Candidatus_Accumulibacter, Run-SP 154, Thauera, and Candidatus_Nitrotoga increased. These bacteria had the functions of nitrogen and phosphorus removal and the storage of polyhydroxyalkanoate (PHA) in the biofilm of the BBNR-CPR reactor and became the dominant species to tolerate low temperature. It was found that low temperatures reduced the amount of PHA synthesized for a given equal carbon source concentration and reaction time. The amounts of PHA synthesized at 25℃, 15℃, and 8℃ accounted for 16.24%, 11.49%, and 9.01% of the dry weight of the biofilm, respectively. The pre-stored PHA biofilm has the capacity to resist low temperature. At high PHA levels, the phosphorus removal efficiencies at 8℃ and 15℃ were 97.46% and 100%, respectively, and the denitrification efficiencies were 55.15% and 82.55%. At low PHA levels, the phosphorus removal efficiencies at 8℃ and 15℃ were 11.39% and 35.02%, respectively, and the denitrification efficiencies were 0% and 12.10%, respectively.

[Pollutant Removal Performance and Membrane Fouling Characteristics in Marine Aquaculture Wastewater Treatment by a Microalgae Membrane Reactor]

In order to treat mariculture wastewater, the pollutant removal performance and membrane fouling characteristics of a microalgae membrane reactor were investigated using Platymonas helgolandica tsingtaoensis. After 60 days of operation, the total nitrogen (TN) and total phosphorus (TP) removal efficiency of the reactor were 73.6% and 77.9%, respectively, and the removal rates of TN and TP reached 15 g·(m³·d)^-1 and 2.8 g·(m³·d)^-1. The microalgae in the reactor could be enriched rapidly, with a maximum growth rate of 53.3 mg·(L·d)^-1 and a maximum biomass of 1.4 g·L^-1. The microalgae in the reactor were harvested on day 18 and day 36; harvesting did not affect the nitrogen and phosphorus removal efficiency of the reactor. To some extent, the membrane fouling phenomenon was alleviated. The increase in the microalgae biomass would significantly increase the pollutant content of the membrane. The three-dimensional excitation-emission matrix (EEM) spectra results confirmed that tryptophan-like substances and aromatic proteins had a significant effect on membrane fouling.

[Impact of Actual Domestic Sewage and Simulated Wastewater on an Aerobic Granular Sludge System]

Sludge returned from the secondary sedimentation tank of a sewage treatment plant is inoculated into two sequencing batch reactors (SBR):R1 and R2. Simulated wastewater and actual domestic sewage are used as the influents of R1 and R2, respectively, in order to study the impact of the influent water quality on the formation at normal temperature (20-30℃) and the stable operation of the system when the temperature changes. The results show that both R1 and R2 start successfully with 25 d and 42 d, respectively. The average size of the aerobic granular sludge in R1 and R2 is 1200 μm and 750 μm when the sludge granules stabilize. The average concentrations of COD, TP, and TN in the R1 and R2 effluent are 22.53, 0.48, and 7.70 mg·L^-1 and 49.73, 0.49, and 14.55 mg·L^-1, respectively, with average removal rates of 90.60%, 90.34%, and 87.85% and 79.74%, 88.59%, and 79.25%. When the temperature drops to 5-16℃, the granular sludge in R1 disintegrates, the removal rates of COD and TP are basically unchanged, the average concentration of TN in the effluent increases to 29.03 mg·L^-1, the average removal rate decreases to 48.81%, and the denitrification performance is suppressed. The granular sludge in R2 remains stable; the average concentrations of COD, TP, and TN in the effluent are 14.31, 0.50, and 12.24 mg·L^-1, and the average removal rates are 92.42%, 93.37%, and 86.28% respectively. The effluent reaches the IA standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant". Both the simulated wastewater and actual domestic sewage can cultivate aerobic granular sludge successfully, but the aerobic granular sludge in the domestic sewage is more compact in structure, effectively suppresses the expansion of filamentous bacteria when the temperature drops to 5-16℃, and is more resistant to changes.

Graphene-Modulated Removal Performance of Nitrogen and Phosphorus Pollutants in a Sequencing Batch Chlorella Reactor

In this work, the influence of graphene on nitrogen and phosphorus in a batch Chlorella reactor was studied. The impact of graphene on the removal performance of Chlorella was investigated in a home-built sewage treatment system with seven identical sequencing batch Chlorella reactors with graphene contents of 0 mg/L (T1), 0.05 mg/L (T2), 0.1 mg/L (T3), 0.2 mg/L (T4), 0.4 mg/L (T5), 0.8 mg/L (T6) and 10 mg/L (T7). The influence of graphene concentration and reaction time on the pollutant removal performance was studied. The malondialdehyde (MDA) and total superoxide dismutase (SOD) concentrations in each reactor were measured, and optical microscopy and scanning electron microscopy (SEM) characterizations were performed to determine the related mechanism. The results show that after 168 h, the total nitrogen (TN), ammonia nitrogen (AN) and total phosphorus (TP) removal rates of reactors T1–T7 become stable, and the TN, AN and TP removal rates were gradually reduced with increasing graphene concentration. At 96 h, the concentrations of both MDA and SOD in T1–T7 gradually increased as the graphene concentration increased. In optical microscopy and SEM measurements, it was found that graphene was adsorbed on the surface of Chlorella, and entered Chlorella cells, deforming and reducing Chlorella. Through the blood plate count method, we estimated an average Chlorella reduction of 16%. According to the water quality and microscopic experiments, it can be concluded that the addition of graphene causes oxidative damage to microalgae and destruction of the Chlorella cell wall and cell membrane, inhibiting the nitrogen and phosphorus removal in Chlorella reactors. This study provides theoretical and practical support for the safe use of graphene.

[Efficiency and Mechanism of Nitrogen and Phosphorus Removal in Modified Zeolite Wetland]

To study the efficiency and mechanism of nitrogen and phosphorus removal for decentralized rural sewage in modified zeolite wetland, the modified zeolite was applied as substrate into a combined process composed of anaerobic baffled reactor (ABR) and baffled flow constructed wetland (BFCW), providing a new way for rural sewage treatment in Suzhou City. The study was contrasted with zeolite wetland. The results showed that the modified zeolite wetland had high efficiency and stability of nitrogen and phosphorus removal, and the nitrogen and phosphorus removal quantities of modified zeolite wetland were 1.8% and 1 times higher than those of zeolite wetland during the trial. The modified zeolite wetland mainly removed nitrogen and phosphorus by substrate adsorption, and the main fractions of modified zeolite were Ca-P and Al-P. The oxygen-secretion and absorption of plants stabilized the water quality of the effluent. The substrate adsorption was the main nitrification removal pathway in front of the wetland, and nitrification and denitrification were the main nitrification removal pathways at the end of the wetland. The nitrogen and phosphorus adsorption capacities during the pilot test were much higher than those of the static test. The optimization of phosphorus adsorption capacity for modified zeolite was achieved under the synergy of multiple pathways. The effect of configuration and plant root was the main reason for the difference of nitrogen and phosphorus adsorption quantities. Nitrification intensity led to the seasonal fluctuation of nitrogen removal effect and stability in modified zeolite wetland, and the low nitrification intensity in the front of wetland was related to the strong adsorption of NH₄⁺-N by the modified zeolite.

Joint effect of triclosan and copper nanoparticles on wastewater biological nutrient removal

Triclosan (TCS) is widely used in household and personal care products, and its release into wastewater might have impact on wastewater biological treatment for its antibacterial property. Besides, emerging pollutant such as copper nanoparticles (CuNPs) will also release from nanoparticle-containing products, showing a joint effect with TCS on biological nutrient removal. The TCS of 1 and 10 mg/L inhibited the nitrosification and nitrification stage, and the first step of denitrification was suppressed as well, causing a decline in final TN removal efficiency. Additionally, the phosphorus uptake was inhibited seriously, leading to a remarkable decrease in phosphorus removal efficiency. When they were co-existed, the TCS concentration decreased due to the absorption by CuNPs, and the released Cu²⁺ from CuNPs increased. Further investigation revealed that when 5 mg/L CuNPs and 1 mg/L TCS were immediately added to the activated sludge, the final joint toxicity was similar to the individual effect of 1 mg/L TCS, while 10 mg/L CuNPs contributed to the final stronger toxicity. When TCS was sufficiently reacted with CuNPs in wastewater, their final toxicity to activated sludge was enhanced because the extent of toxicity relief caused by decrease in TCS concentration was less than the degree of deteriorating effect due to the promotion of Cu²⁺ release from CuNPs.

Nitrogen and phosphorus treatment of marine wastewater by a laboratory-scale sequencing batch reactor with eco-friendly marine high-efficiency sediment

We screened and identified a NH₃-N-removing bacterial strain, Bacillus sp. KGN1, and a [Formula: see text] removing strain, Vibrio sp. KGP1, from 960 indigenous marine isolates from seawater and marine sediment from Tongyeong, South Korea. We developed eco-friendly high-efficiency marine sludge (eco-HEMS), and inoculated these marine bacterial strains into the marine sediment. A laboratory-scale sequencing batch reactor (SBR) system using the eco-HEMS for marine wastewater from land-based fish farms improved the treatment performance as indicated by 88.2% removal efficiency (RE) of total nitrogen (initial: 5.6 mg/L) and 90.6% RE of total phosphorus (initial: 1.2 mg/L) under the optimal operation conditions (food and microorganism (F/M) ratio, 0.35 g SCOD_Cr/g mixed liquor volatile suspended solids (MLVSS)·d; dissolved oxygen (DO) 1.0 ± 0.2 mg/L; hydraulic retention time (HRT), 6.6 h; solids retention time (SRT), 12 d). The following kinetic parameters were obtained: cell yield (Y), 0.29 g MLVSS/g SCOD_Cr; specific growth rate (µ), 0.06 d^-1; specific nitrification rate (SNR), 0.49 mg NH₃-N/g MLVSS·h; specific denitrification rate (SDNR), 0.005 mg [Formula: see text]/g MLVSS·h; specific phosphorus uptake rate (SPUR), 0.12 mg [Formula: see text]/g MLVSS·h. The nitrogen- and phosphorus-removing bacterial strains comprised 18.4% of distribution rate in the microbial community of eco-HEMS under the optimal operation conditions. Therefore, eco-HEMS effectively removed nitrogen and phosphorus from highly saline marine wastewater from land-based fish farms with improving SNR, SDNR, and SPUR values in more diverse microbial communities.

ABBREVIATIONS

DO: dissolved oxygen; Eco-HEMS: eco-friendly high efficiency marine sludge; F/M: food and microorganism ratio; HRT: hydraulic retention time; ML(V)SS: mixed liquor (volatile) suspended solids; NCBI: National Center for Biotechnology Information; ND: not determined; qPCR: quantitative real-time polymerase chain reaction; RE: removal efficiency; SBR: sequencing batch reactor; SD: standard deviation; SDNR: specific denitrification rate; SNR: specific nitrification rate; SPUR: specific phosphate uptake rate; SRT: solids retention time; T-N: total nitrogen; T-P: total phosphorus; (V)SS: (volatile) suspended solids; w.w.: wet weight.

Operational and biological analyses of branched water-adjustment and combined treatment of wastewater from a chemical industrial park

The combined biological processes of branched water-adjustment, chemical precipitation, hydrolysis acidification, secondary sedimentation, Anoxic/Oxic and activated carbon treatment were used for chemical industrial wastewater treatment in the Taihu Lake Basin. Full-scale treatment resulted in effluent chemical oxygen demand, total nitrogen, NH₃-N and total phosphorus of 35.1, 5.20, 3.10 and 0.15 mg/L, respectively, with a total removal efficiency of 91.1%, 67.1%, 70.5% and 89.3%, respectively. In this process, short-circuited organic carbon from brewery wastewater was beneficial for denitrification and second-sulfate reduction. The concentration of effluent fluoride was 6.22 mg/L, which also met the primary standard. Gas Chromatography-Mass Spectrometry analysis revealed that many types of refractory compounds were present in the inflow. Microbial community analysis performed in the summer by PCR-denaturing gradient gel electrophoresis and MiSeq demonstrated that certain special functional bacteria, such as denitrificans, phosphorus-accumulating bacteria, sulfate- and perhafnate-reducing bacteria, aromatic compound-degrading bacteria and organic fluoride-degrading bacteria, present in the bio-tanks were responsible for the acceptable specific biological pollutant reduction achieved.

Effect of gradual-increasing aeration mode in an aerobic tank on nutrients' removal and functional microbial communities

Different aeration rates and modes in an aerobic tank of an anaerobic/anoxic/aerobic (A²O) process were investigated to reveal their influence on nitrogen and phosphorus removal efficiency. Meanwhile, Illumina high-throughput sequencing of partial 16S rRNA gene of bacteria was conducted to monitor the abundance and composition of microbial communities. The results showed that higher aeration rate led to better nutrients' removal efficiency. The gradual-increasing aeration mode along the wastewater stream enhanced the contaminants' removal and the system achieved chemical oxygen demand, [Formula: see text]-N, total nitrogen (TN) removal rates of 72%, 96% and 51%, respectively. However, the gradual-decreasing or uniform aeration modes resulted in inefficient removal of TN, especially the ammonia due to low DO in the end parts of A²O. Microbial community analysis indicated that denitrifying phosphorus-accumulating bacteria Acinetobacter spp. were the most dominant groups under the gradual-increasing aeration mode in all tanks of the A²O bioreactor. Moreover, the members of genera Clostridium, Thauera and Dechloromonas also largely existed in the system. The gradual-increasing aeration mode and cooperation of different groups of bacteria made the system stable and high-performance.

[Characteristics and Mechanism of Biological Nitrogen and Phosphorus Removal Granular Sludge Under Carbon Source Stress]

In SBR reactor, the mature granular sludge fed with sodium acetate was gradually cultivated with different carbon sources (sodium acetate/glucose ratio was 1:0, 3:1, 1:1, 1:3 and 0:1, in terms of COD, respectively). During the five stages, the physical, biochemical properties, extracellular polymeric substances (EPS), phosphorus fractions and nitrogen and phosphorus removal efficiency of granular sludge were studied. 705 days' experimental results were showed as follows. At stage Ⅳ, the granular sludge had the smallest diameter of 0.5 mm; moreover the phosphorus release/uptake rate, denitrification rate and the total phosphorus (TP) content were the lowest. While at stages Ⅰ and Ⅱ, the phosphorus release/uptake and denitrification rates were the highest, meanwhile, the TP content reached up to 72.36 mg·g^-1, and the EPS content was about 350 mg·g^-1, as a result, the nitrogen and phosphorus removal efficiencies were both over 94%. Nevertheless at stage Ⅴ, the biochemical rates were slightly slower than values of stages Ⅰ and Ⅱ, simultaneously the TP, glycogen and EPS contents in sludge were maintained at 69.60 mg·g^-1, 224.18 mg·g^-1 and 200 mg·g^-1, respectively, while high nitrogen and phosphorus removal efficiency was obtained. During all stages, Ca-P was the main phosphorus fraction, and inorganic phosphorus(IP) was closely related to phosphorus removal of granular sludge.

[Operational Characteristics of the Simultaneous Nitrogen and Phosphorus Removal and Removal of Phthalate Esters by Three-dimensional Biofilm-electrode Coupled with Iron/Sulfur Reactor]

In order to explore the technological characteristics of the simultaneous removal of phthalate esters (PAEs) as well as nitrogen and phosphorus by the novel technology of three-dimensional biofilm-electrode coupled with iron/sulfur reactor (3DBER-S-Fe), the changes of the total nitrogen (TN),total phosphorus (TP),DBP,DEHP,NO₃^--N, SO₄^2- and pH value were analyzed under the hydraulic retention time (HRT) of 8 h, 6 h and 4 h respectively. The results showed that 3DBER-S-Fe could remove nitrogen, phosphorus and PAEs effectively. Under the HRT of 8 h, 6 h and 4 h, the removal rates of TN were 80.99%, 78.85% and 64.76%; TP were 65.18%, 67.17% and 43.44%; DBP were 96.72%, 97.32% and 96.53%; DEHP were 91.89%, 81.57% and 74.30%, respectively. There were heterotrophic denitrification, hydrogen autotrophic denitrification and sulfur autotrophic denitrification processes in the 3DBER-S-Fe, the elemental sulfur could compensate for the relative shortage of denitrification electron donor caused by the increase of NO₃^--N load in the influent as a result of maintaining a high efficiency of the denitrification system when the HRT was shortened from 8h to 4h; the iron ions produced by the corrosion of the sponge iron filler in the system had a sustainable and efficient function of removing phosphorus by precipitation; the 3DBER-S-Fe process combined the interactions of physical adsorption, biological degradation and electrochemical processes which supported its high removal rates of DBP and DEHP under the different HRT conditions.

[Enhanced Pollutants Removal in a Municipal Wastewater Treatment Plant with Multistage A/O Process]

Removal of conventional pollutants as well as genotoxicity was studied along a multistage A/O process, which was based on the monitoring data in a Municipal Wastewater Treatment Plant (MWWTP) of Yixing City. The results showed that the multistage A/O process removed (67.3±7.0)% of COD, (93.7±1.5)% of NH₄⁺-N, (65.3±7.9)% of TN and (60.0±18.7)% of TP, respectively, which played a dominant role in the removal performance of the whole wastewater treatment process. The multistage A/O process showed significant ability to reduce alkanes, halogenated hydrocarbons and alcohols in the municipal wastewater, while it failed to remove the aromatic proteins which were the main fluorescent substances of this wastewater. Furthermore, the process removed 82.8% genotoxicity from its influent. Low organic load, single-phase influent and undesirable carbon source feeding pattern, which caused the downstream A/O stages being not fully utilized, were considered as the predominant reasons for the relatively low performance of the multistage A/O process. Multi-phase feeding and adjusting carbon source feeding pattern were thereby proposed. The results were considered to be helpful for improving the operational performance of the MWWTP and useful for performance evaluation of MWWTPs with similar process.

Phosphorus removal performance and population structure of phosphorus-accumulating organisms in HA-A/A-MCO sludge reduction process

We developed a new sludge reduction HA-A/A-MCO (Hydrolysis-Acidogenosis-Anaerobic/Anoxic -Multistep Continuous Oxic tank) process, which has improved phosphate (P) and nitrogen (N) removal. Its biological treatment unit uses an A²/O P & N removal process with hydrolysis acidification, multistep continuous aeration, and continuous flow, coupled with sidestream P removal by draining out anaerobic P-bearing wastewater. The process has advanced synchronization of P and N removal and sludge reduction. The improved performance is closely associated with the population structure of P-accumulating organisms (PAOs). This study investigated the relationship between P removal performance and the population structure of PAOs. The results show that the average effluent P content of HA-A/A-MCO process was only 0.44 mg/L, when the influent P concentration was 8∼12 mg/L. The effluent met the A standard set by GB18918-2002. PAOs were able to effectively release 1 mg of P and absorb 2.8 mg of P. The system removed P by draining out anaerobic P-rich wastewater, as P had been reduced in the aerobic absorption process. This reduced the need for excess P uptake ability of the PAOs. The bacterial pure culture method was applied to isolate 5 PAOs with typical P absorption and removel features. 16SrDNA amplification and sequence analysis revealed that Acinetobacter sp. and Lampropedia sp played dominant roles in anaerobic P-releasing process. Moreover, Devosia sp. and Bdellovibrio sp were the primary strains in the aerobic tank, and, they were the major stains for P absorption. Uncultured Bacterium and other uncultured strains were detected in the anoxic tank.

Nitrogen and phosphorus removal in an airlift intermittent circulation membrane bioreactor

A new airlift intermittent circulation integrated bioreactor was developed for simultaneous nitrogen and phosphorus removal of wastewater, in which, circulation of mixed liquid between mixing zone and aeration zone was realized by aeration power, alternately anaerobic/anoxic bio-environment in mixing zone was realized by intermittent circulation and simultaneous nitrogen and phosphorus removal was obtained through strengthened denitrifying phosphorus removal process. Removal performance of the reactor was investigated and pollutant removal and transfer mechanism in one operation circle was analyzed. The experiment results indicated that under the influent condition of chemical oxygen demand (COD) concentration of 642.1 mg/L, total nitrogen (TN) of 87.4 mg/L and PO4(3-)-P of 12.1 mg/L, average removal efficiencies of COD, TN and PO4(3-)-P reached 96.4%, 83.2% and 90.5%, respectively, with the hydraulic residence time of 22 hr and operation circle time of 185 min. Track studies indicated that the separation of aeration and mixing zones and intermittent circulation of mixed liquid between the two zones provided distinct biological environments spatially and temporally, which ensured the occurrence of multifunctional microbial reactions.

Microalgae cultivation using an aquaculture wastewater as growth medium for biomass and biofuel production

Microalgae as a main feedstock has attracted much attention in recent years but is still not economically feasible due to high algal culture cost. The objective of this study was to develop a comprehensive eco-friendly technology for cultivating microalgae Platymonas subcordiformis using aquaculture wastewater as growth medium for biomass and biofuel production. Platymonas subcordiformis was grown in pretreated flounder aquaculture wastewaters taken from different stages. Each of wastewater contained different levels of nutrients. The biomass yield of microalgae and associated nitrogen and phosphorous removal were investigated. The results showed that algal cell density increased 8.9 times than the initial level. Platymonas subcordiformis removed nitrogen and phosphorus from wastewater with an average removal efficiency of 87%-95% for nitrogen and 98%-99% for phosphorus. It was feasible to couple the removal of nitrogen and phosphorus from wastewater to algal biomass and biofuel production. However, further studies are required to make this technologies economically viable for algae biofuel production.