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Abstract: The granulation of activated sludge was investigated using two parallel sequencing batch reactors (SBRs) operated in biological nitrogen and phosphorus removal conditions though the reactor configuration and operating parameters did not favor the granulation. Granules were not observed when the SBR was operated in biological nitrogen removal period for 30d. However, aerobic granules were formed naturally without the increase of aeration intensity when enhanced biological phosphorus removal (EBPR) was achieved. It can be detected that plenty of positive charged particles were formed with the release of phosphorus during the anaerobic period of EBPR. The size of the particles was about 5–20μm and their highest positive ζ potential was about 73mV. These positive charged particles can stimulate the granulation. Based on the experimental results, a hypothesis was proposed to interpret the granulation process of activated sludge in the EBPR process in SBR. Dense and compact subgranules were formed stimulated by the positive charged particles. The subgranules grew gradually by collision, adhesion and attached growth of bacteria. Finally, the extrusion and shear of hydrodynamic shear force would help the maturation of granules. Aerobic granular SBR showed excellent biological phosphorus removal ability. The average phosphorus removal efficiency was over 95% and the phosphorus in the effluent was below 0.50mgL−1 during the operation. [Copyright &y& Elsevier]

Abstract: Limited filamentous bulking caused by low dissolved oxygen (DO) was proposed to establish a low energy consumption wastewater treatment system. This method for energy saving was derived from two full-scale field observations, which showed pollutants removal would be enhanced and energy consumption could be reduced by atleast 10% using limited filamentous bulking. Furthermore, preliminary investigation including the abundance evaluation and the identification of filamentous bacteria demonstrated that the limited filamentous bulking could be repeated steadily in a lab-scale anoxic–oxic reactor fed with domestic wastewater. The sludge loss did not occur in the secondary clarifier, while COD and total nitrogen removal efficiencies were improved by controlling DO for optimal filamentous bacterial population. Suspended solids in effluent were negligible and turbidity was lower than 2 NTU, which were distinctly lower than those under no bulking. Theoretical and experimental results indicated the aeration consumption could be saved by the application of limited filamentous bulking. [Copyright &y& Elsevier]

Abstract: In this study, phosphorus accumulating microbial granules were successfully cultivated in a sequencing batch reactor (SBR) using synthetic wastewater. The average diameter of the granules was 0.74mm and the diameter distribution fitted well with normal distribution with a correlation coefficient of 0.989. Good performance of biological phosphorus removal (BPR) was obtained in the granular system. The average phosphorus removal efficiency was over 94.3% and the level of phosphorus in the effluent was below 0.50mg/L during 300 days of operation. Particle analysis showed that positive charged particles were formed with the release of phosphorus in the anaerobic stage. These particles served as the cores of granules and stimulate the granulation. The maturated granules had a well-formed micro-pore structure with an average pore width between 291.5nm and 446.5nm. The spatial distribution of phosphorus decreased gradually from the surface to the center of the granules. Smaller granules had a higher specific area, pore width and phosphorus removal activity than bigger granules. [Copyright &y& Elsevier]

Abstract: The simultaneous nitrification and denitrification in step-feeding biological nitrogen removal process were investigated under different influent substrate concentrations and aeration flow rates. Biological occurrence of simultaneous nitrification and denitrification was verified in the aspect of nitrogen mass balance and alkalinity. The experimental results also showed that there was a distinct linear relationship between simultaneous nitrification and denitrification and DO concentration under the conditions of low and high aeration flow rate. In each experimental run the floe sizes of activated sludge were also measured and the results showed that simultaneous nitrification and denitrification could occur with very small size of floe. [Copyright &y& Elsevier]

Abstract: An UASB+Anoxic/Oxic (A/O) system was introduced to treat a mature landfill leachate with low carbon-to-nitrogen ratio and high ammonia concentration. To make the best use of the biodegradable COD in the leachate, the denitrification of NOx--N in the recirculation effluent from the clarifier was carried out in the UASB. The results showed that most biodegradable organic matters were removed by the denitrification in the UASB. The NH4+-N loading rate (ALR) of A/O reactor and operational temperature was 0.28–0.60 kg NH4+-N/(m3·d) and 17–29°C during experimental period, respectively. The short-cut nitrification with nitrite accumulation efficiency of 90%–99% was stabilized during the whole experiment. The NH4+-N removal efficiency varied between 90% and 100%. When ALR was less than 0.45 kg NH4+-N/(m3·d), the NH4+-N removal efficiency was more than 98%. With the influent NH4+-N of 1200–1800 mg/L, the effluent NH4+-N was less than 15 mg/L. The shortcut nitrification and denitrification can save 40% carbon source, with a highly efficient denitrification taking place in the UASB. When the ratio of the feed COD to feed NH4+-N was only 2–3, the total inorganic nitrogen (TIN) removal efficiency attained 67%–80%. Besides, the sludge samples from A/O reactor were analyzed using FISH. The FISH analysis revealed that ammonia oxidation bacteria (AOB) accounted for 4% of the total eubacterial population, whereas nitrite oxidation bacteria (NOB) accounted only for 0.2% of the total eubacterial population. [Copyright &y& Elsevier]

Abstract: The aim of this study is to investigate the denitrification potential enhancement by addition of external carbon sources and to estimate the denitrification potential for the predenitrification system using nitrate utilization rate (NUR) batch tests. It is shown that the denitrification potential can be substantially increased with the addition of three external carbon sources, i.e. methanol, ethanol, and acetate, and the denitrification rates of ethanol, acetate, and methanol reached up to 9.6, 12, and 3.2 mgN/(g VSS·h), respectively, while that of starch wastewater was only 0.74 mgN/(g VSS·h). By comparison, ethanol was found to be the best external carbon source. NUR batch tests with starch wastewater and waste ethanol were carried out. The denitrification potential increased from 5.6 to 16.5 mg NO3-N/L owing to waste ethanol addition. By means of NUR tests, the wastewater characteristics and kinetic parameters can be estimated, which are used to determine the denitrification potential of wastewater, to calculate the denitrification potential of the plant and to predict the nitrate effluent quality, as well as provide information for developing carbon dosage control strategy. [Copyright &y& Elsevier]

Abstract: A pilot-scale Orbal oxidation ditch was operated for 17 months to optimize nitrogen removal from domestic wastewater of average COD to total nitrogen ratio of 2.7, with particular concern about the roles of dissolved oxygen (DO), mixed liquor suspended solids (MLSS) and return activated sludge (RAS) recycle ratio. Remarkable simultaneous nitrification and denitrification (SND) was observed and mean total nitrogen (TN) removal efficiency up to 72.1% was steadily achieved, at DO concentration in the out, middle and inner channel of 0.1, 0.4 and 0.7 mg/L, respectively, with an average MLSS of 5.5 g/L and RAS recycle ratio of 150%. Although the out channel took the major role in TN removal, the role of middle channel should never be ignored. The denitrification potential could be fully developed under low DO, high MLSS with adequate RAS ratio. The sludge settleability was amazingly improved under low DO operation mode, and some explanations were tried. In addition, a series of simplified batch tests were done to determine whether novel microorganisms could make substantial contribution to the performance of nitrogen removal. The results indicated that the SND observed in this Orbal oxidation ditch was more likely a physical phenomenon. [Copyright &y& Elsevier]

Abstract: The occurrence of denitrifying phosphate accumulating organisms (DNPAOs) and the contribution of DNPAOs to biological nutrient removal performance were investigated in a bench-scale A2O system. Moreover, the effect of excessive aeration on biological phosphorus removal (BPR) was studied. The experimental results suggested that anoxic phosphorus uptake could occur in the A2O process, as compared with the conventional A2O process. Good COD, phosphorus, ammonia nitrogen and total nitrogen removal efficiency (92.3%, 95.5%, 96% and 79.5% respectively) could be achieved. Furthermore, sludge analysis demonstrated that the ratio of anoxic P uptake rate to aerobic P uptake rate reached 69% in such a system and nitrate concentration in the anoxic phase and different organic substrate introduced into the anaerobic phase had significant effects on the anoxic P uptake. It was also found that if the air supply was not adjusted properly under good anoxic P uptake conditions, excessive aeration of activated sludge at the end of aerobic zone could lead to the deterioration of BPR. [Copyright &y& Elsevier]

This study investigated the effects of denitrification sludge EPS enhanced (DS-EPS CN) by a fluctuating carbon and nitrogen ratio (C/N) cultivation strategy on the properties of Anammox granules under extreme acid or alkaline shock. The results showed that the DS-EPS CN significantly improved the nitrogen removal performance of low-density Anammox granular sludge (Granules- L) and high-density Anammox granular sludge (Granules -H) under extreme acid shock (pH 5.0). The contents of high-molecular-weight substances (such as aromatic proteins and polysaccharides) in the DS-EPS CN rose markedly, contributing to a substantial increase in the flocculation efficiency under acidic conditions and increasing the granule stability. In addition, abundant amounts of N-butyryl- dl -homoserine lactone (C4-HSL) and N-hexanoyl- dl -homoserine lactone (C6-HSL) in the DS-EPS CN promoted the granule activity. However, under extreme alkaline shock (pH 10.5), the flocculation efficiency of the DS-EPS CN was poor, and the addition of DS-EPS CN had no influence on the stability of the granules but improved the activity of the Granules -H. The reason was that the release mechanism of the endogenous acyl-homoserine lactone (AHL) signals in the Granules -H was activated by the exogenous C4-HSL and C6-HSL in the DS-EPS CN under alkaline conditions, leading to increased Granules -H activity. This research provides a novel approach to enhance the resistance of Anammox granular sludge to extreme pH shock. Unlabelled Image • DS-EPS CN enhanced the property of granules -L and granules -H in extreme acid shock. • DS-EPS CN promoted the activity of granules -H under extreme alkaline shock. • Fluctuating C/N ratio cultivation increased the AHLs content in DS-EPS CN. • Fluctuating C/N ratio cultivation improved the flocculation efficiency of DS-EPS CN. [ABSTRACT FROM AUTHOR]

• Zier reactor foremost separates the aeration zone from the upflow sludge bed. • Extremely high upflow velocity > 30 m/h promises treatment and sludge granulation. • CFD proves circulation multipliers > 200 for nitrogen removal > 1.6 kg N/m3/d. • Novel control strategy and operation methods are proposed. The continuous aerobic granular sludge (AGS) process is promising for upgrading existing wastewater treatment facilities. However, this approach is still challenging because of its complicated structure and operation. To address this issue, a novel separate aeration self-circulating technology (abbreviated as Zier) was proposed, which is promising for cultivating AGS by its outstanding upflow velocity and circulation multiplier (more than 30 m/h and 200, respectively). This study elaborated on the Zier reactor's feasibility, optimization, and control strategy through computational fluid dynamics simulations, theoretical calculations, and experiments. An appropriate flow regime for efficient removal of pollutant and granulation of sludge was attained at a superficial gas velocity of 1.3 cm/s. Moreover, optimizing the aeration column diameter to half of the reaction column and increasing the height/diameter ratio to 20 dramatically boosted the nitrogen removal capacity over 1.6 kg N/m3/d. Utilizing a smaller circulation pipe diameter ensured granulation under a consistent flow regime. By judiciously regulating, multiple CSTRs and PFRs seamlessly integrated within the Zier reactor across a broad spectrum of particle sludge. The validity of these findings was further substantiated through experimental and theoretical validations. Drawing from these findings, a multi-scenario control strategy was proposed as Zier's map. With all the superiorities shown by the Zier reactor, this study could offer new insights into an efficient continuous AGS process. [Display omitted] [ABSTRACT FROM AUTHOR]

• A continuous self-circulating up-flow granular sludge bed process was introduced. • Accurate self-circulating multiple times and O 2 supply were driven only by aeration. • High up-flow velocity of 7–16 m/h contributed to particle formation and stability. • HRT of 10 h and DO of 0–0.3 mg/L were optimized for higher OLR and energy savings. • Self-circulation driven by aeration is key factor regulating nitrogen removal. Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20–32 times and an up-flow velocity within the reactor of 7–16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1–0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300–1210 μm, the percentage of mass with particle size distribution < 200 μm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%–0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50–80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage. [Display omitted] [ABSTRACT FROM AUTHOR]

A cost-effective process, consisting of a denitrifying upflow anaerobic sludge blanket (UASB), an oxygen-limited anoxic/aerobic (A/O) process for short-cut nitrification, and an anaerobic reactor (ANR) for anaerobic ammonia oxidation (anammox), followed by an electrochemical oxidation process with a Ti-based SnO 2 –Sb 2 O 5 anode, was developed to remove organics and nitrogen in a sewage diluted leachate. The final chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N) and total nitrogen (TN) of 70, 11.3 and 39 (all in mg/L), respectively, were obtained. TN removal in UASB, A/O and ANR were 24.6%, 49.6% and 16.1%, respectively. According to the water quality and molecular biology analysis, a high degree of anammox besides short-cut nitrification and denitrification occurred in A/O. Counting for 16.1% of TN removal in ANR, at least 43.2–49% of TN was removed via anammox. The anammox bacteria in A/O and ANR, were in respective titers of (2.5–5.9) × 10 9 and 2.01 × 10 10 copy numbers/(g SS). [ABSTRACT FROM AUTHOR]

Highlights: [•] AOB outnumbered AOA with amoA gene ratio varying from 2.56 to 2.41×103 in 8 WWTPs. [•] AOB may play more important role than AOA in the WWTPs studied. [•] Nitrososphaera cluster might be the worldwide distributed AOA species in WWTPs. [•] There may be versatile AOA ecotypes and some AOA may be not obligate autotrophic. [•] Nitrosomonas genus was the most dominant AOB species and showed higher diversity. [ABSTRACT FROM AUTHOR]

Abstract: A lab-scale anaerobic–anoxic–aerobic (A2O) process was operated to investigate denitrifying phosphorus removal and nitritation–denitritation from domestic wastewater, especially regarding the impact of nitrite accumulation caused by nitritation on phosphorus removal. The results showed that mean total nitrogen (TN) removal was only about 47% and phosphorus removal was almost zero without the pre-anoxic zone and additional carbon source. Contrastively, with configuration of pre-anoxic zone, TN and phosphorus removal was increased to 75% and 98%, respectively, as well as denitrifying phosphorus removal of 66–91% occurred in the anoxic zone. Nitritation–denitritation was achieved through a combination of short aerobic actual hydraulic retention time and low dissolved oxygen levels (0.3–0.5mg/L); however, phosphorus removal deteriorated with increase of nitrite accumulation rates. The free nitrous acid (FNA) concentration of 0.002–0.003mg HNO2–N/L in the aerobic zone inhibited phosphorus uptake, which was major cause of phosphorus removal deterioration. Through supplying the carbon sources to enhance denitrification and anaerobic phosphorus release, nitrite and FNA concentrations in the aerobic zone were reduced, and phosphorus removal was improved. Compared with nitrification–denitrification, nitritation–denitritation reduced the carbon requirement by 30% and performed biological nutrients removal well with mean TN and phosphorus removal of 85% and 96%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The contributions of loosely bound extracellular polymeric substances (LB–EPS), tightly bound EPS (TB–EPS), residual sludge (the sludge left after EPS extraction) and functional groups such as amine, carboxyl, phosphate and lipid on aerobic granules on biosorption of four different dyes (Reactive Brilliant Blue KN–R (KN–R), Congo Red (CR), Reactive Brilliant Red K–2G (RBR) and Malachite Green (MG)) were investigated. EPS may be responsible for biosorption of cationic dyes. However, residual sludge always made greater contribution than that of EPS. The biosorption mechanisms were dependent on the functional groups on aerobic granules and dyes’ chemical structures. The lipid and phosphate groups might be the main binding sites for KN–R biosorption. Amine, carboxyl, phosphate and lipid were all responsible for the binding of CR. The lipid fractions played an important role for RBR biosorption. For MG, the phosphate groups gave the largest contribution. [ABSTRACT FROM AUTHOR]

Abstract: With an increase in using seawater, saline sewage is necessarily disposed of to protect the ocean. The objective in this work is to evaluate the effect of influent salinity and inhibition time on short-cut nitrogen removal from real domestic saline sewage, and to detect the performance of nitrifiers in activated sludge in SBR. Microbial tests are used to establish the mechanism of salt inhibition. Dynamic response of salt is recorded during and after the salt inhibition stage. As microbial population tests support that NOB is strongly inhibited below 1% (w/v) salt content, three different salt levels (0.52%, 0.76% and 1.02%) are applied respectively in three parallel SBRs for 60 days. Results reveal that NARs all increase by 95% and keep steady after the 15th, 7th and 2nd day by adding salt. Ammonia is almost totally degraded at the steady state at salt levels below 0.75%; however, it degrades nearly half at 1.02%. After stopping salt addition, the ARE in a 1.02% system reaches 94.3% at the 18th cycle and the SAURs all apparently increase. The NAR in 0.52% and 0.76% systems decreases at the 9th and 20th cycle but still keeps above 95% in the 1.02% system. In order to gain steady shot-cut nitrification in a SBR, conditions of salinity greater than 0.76% and salt inhibition for more than 60 days are very competitive and favorable for application. [Copyright &y& Elsevier]

Abstract: To achieve nitritation from complete-nitrification seed sludge at room temperature of 19±1°C, a lab-scale sequencing batch reactor (SBR) treating domestic wastewater with low C/N ratios was operated to investigate the control and optimization of nitrifying communities. Ammonia oxidizing bacteria (AOB) dominance was enhanced through the combination of low DO concentrations (<1.0mg/L) and preset short-cycle control of aeration time. Nitritation was successfully established with NO2 −-N/NO x −-N over 95%. To avoid the adverse impact of low DO concentrations on AOB activities, DO concentrations were increased to 1–2mg/L. At the normal DO levels and temperatures, on-line control strategy of aerobic durations maintained the stability of nitritation with nitrite accumulation rate over 95% and ammonia removal above 97%. Fluorescence in-situ hybridization (FISH) analysis presented that the maximal percentage of AOB in biomass reached 10.9% and nitrite oxidizing bacteria (NOB) were washed out. [Copyright &y& Elsevier]

Abstract: The characteristics of anaerobic phosphorus release and anoxic phosphorus uptake were investigated in sequencing batch reactors using denitrifying phosphorus removing bacteria (DPB) sludge. The lab-scale experiments were accomplished under conditions of various nitrite concentrations (5.5, 9.5, and 15 mg/L) and mixed liquor suspended solids (MLSS) (1844, 3231, and 6730 mg/L). The results obtained confirmed that nitrite, MLSS, and pH were key factors, which had a significant impact on anaerobic phosphorus release and anoxic phosphorus uptake in the biological phosphorous removal process. The nitrites were able to successfully act as electron acceptors for phosphorous uptake at a limited concentration between 5.5 and 9.5 mg/L. The denitrification and dephosphorous were inhibited when the nitrite concentration reached 15 mg/L. This observation indicated that the nitrite would not inhibit phosphorus uptake before it exceeded a threshold concentration. It was assumed that an increase of MLSS concentration from 1844 mg/L to 6730 mg/L led to the increase of denitrification and anoxic P-uptake rate. On the contrary, the average P-uptake/N denitrifying reduced from 2.10 to 1.57 mg PO43--P/mg NO3--N. Therefore, it could be concluded that increasing MLSS of the DEPHANOX system might shorten the reaction time of phosphorus release and anoxic phosphorus uptake. However, excessive MLSS might reduce the specific denitrifying rate. Meanwhile, a rapid pH increase occurred at the beginning of the anoxic conditions as a result of denitrification and anoxic phosphate uptake. Anaerobic P release rate increased with an increase in pH. Moreover, when pH exceeded a relatively high value of 8.0, the dissolved P concentration decreased in the liquid phase, because of chemical precipitation. This observation suggested that pH should be strictly controlled below 8.0 to avoid chemical precipitation if the biological denitrifying phosphorus removal capability is to be studied accurately. [Copyright &y& Elsevier]