Start‐up and enrichment of a granular anammox SBR to treat high nitrogen load wastewaters

BACKGROUND: Landfill leachate is characterized by low biodegradable organic matter that presents difficulties for the complete biological nitrogen removal usually performed by conventional biological nitrification/denitrification processes. To achieve this, the anaerobic ammonium oxidation (anammox) process is a promising biological treatment. This paper presents an anammox start‐up and enrichment methodology for treating high nitrogen load wastewaters using sequencing batch reactor (SBR) technology. RESULTS: The methodology is based on the gradual increase of the nitrite‐to‐ammonium molar ratio in the influent (from 0.76 to 1.32 mole NO₂^?‐N mole^?1NH₄⁺‐N) and on the exponential increase of the nitrogen loading rate (NLR, from 0.01 to 1.60 kg N m^?3 d^?1). 60 days after start‐up, anammox organisms were identified by polymerase chain reaction (PCR) technique as Candidatus Brocadia anammoxidans. After one year of operation, NLR had reached a value of 1.60 kg N m^?3 d^?1 with a nitrogen (ammonium plus nitrite) removal efficiency of 99.7%. The anammox biomass activity was verified by nitrogen mass balances with 1.32 ± 0.05 mole of nitrite removed per mole of ammonium removed and 0.23 ± 0.05 mole of nitrate produced per mole of ammonium removed. Also, enrichment of anammox bacteria was quantified by fluorescence in situ hybridization (FISH) analysis as 85.0 ± 1.8%. CONCLUSIONS: This paper provides a methodology for the enrichment of the anammox biomass in a SBR to treat high nitrogen loaded wastewaters. Copyright © 2007 Society of Chemical Industry     

自养脱氮工艺有机物去除段与硝化段精确分离的实现与实时控制

为了实现城市污水处理过程中的节能降耗,提出了三段式城市污水自养脱氮工艺,阐述了除有机物SBR在整套工艺中的重要地位,探讨了不同曝气量与污泥浓度条件下,除有机物SBR中有机物的去除特征与规律。结果表明,在不同的曝气量及污泥浓度条件下,COD降解结束前NO₂^--N与NO₃^--N的浓度均低于0.1 mg·L^-1,反应器进入COD难降解阶段后,NO₂^--N与NO₃^--N的浓度快速提高,可以认为在除有机物SBR内有机物的去除和硝化过程是分步进行的,即先进行有机物的去除,而后进行硝化过程。DO曲线与pH曲线的突越点与除有机物过程的终点始终保持一致,可将其作为实时控制参数监测有机物的去除终点,对好氧曝气过程进行实时控制。     

Increased hydrazine during partial nitritation process in upflow air-lift reactor fed with supernatant of anaerobic digester effluent

The optimal balance of ammonium and nitrite is essential for successful operation of the subsequent anammox process. We conducted a partial nitritation experiment using an upflow air-lift reactor to provide operational parameters for achieving the optimal ratio of ammonium to nitrite, by feeding supernatant of anaerobic digester effluent, highnitrogen containing rejection water. Semi-continuous operation results show that HRT should be set between 15 and 17 hours to achieve the optimum ration of 1.3 of NO₂-N/NH₄-N. In the UAR, nitritation was the dominant reaction due to high concentration of ammonia and low biodegradable organics. The influent contained low concentrations of hydroxylamine and hydrazine. However, hydrazine increased during partial nitritation by ～60–130% although there was no potential anammox activity in the reactor. The partial nitritation process successfully provided the ratio of nitrogen species for the anammox reaction, and relived the nitrite restraint on the anammox activity by increasing hydrazine concentration.     

Simultaneous organic carbon and nitrogen removal in an SBR controlled at low dissolved oxygen concentration

Simultaneous organic carbon and nitrogen removal was studied in a sequencing batch reactor (SBR) fed with synthetic municipal wastewater and controlled at a low dissolved oxygen (DO) level (0.8 mg dm^?3). Experimental results over a long time (120 days) showed that the reactor achieved high treatment capacities (organic and nitrogen loading rates reached as high as 2.4 kg COD m^?3 d^?1 and 0.24 kg NH₃‐N m³ d^?1) and efficiencies (COD, NH₃‐N and total nitrogen removal efficiencies were 95%, 99% and 75%). No filamentous bacteria were found in the sludge even though the reactor had been seeded with filamentous bulking sludge. Instead, granular sludge, which possessed high activity and good settleability, was formed. Furthermore, the sludge production rate under low DO was less than that under high DO. Significant benefits, such as low investment and less operating cost, will be obtained from the new process. © 2001 Society of Chemical Industry     

Autotrophic biological nitrogen removal from saline wastewater under low DO

BACKGROUND: This study was conducted to investigate the feasibility and performance of nitrogen removal through the complete autotrophic nitrogen removal over nitrite (CANON) process for saline wastewater in a continuous reactor, and to characterize microorganisms in the sludge from the reactor using DNA‐based techniques. RESULTS: The nitrogen removal experiment in the reactor was operated over five phases for 286 days treating a synthetic sewage of 1.2% salinity at 21–25 °C. At dissolved oxygen (DO) concentrations of 0.5–1.0 mg L^?1 and in the presence of glucose, NO₂^? was accumulated, indicating the activity of ammonia‐oxidizing bacteria (AOB). At DO concentration of 0.5 mg L^?1 without organic substrate, the anaerobic ammonium oxidation (Anammox) process was the major pathway responsible for nitrogen removal, with a total nitrogen removal of 70% and an ammonium conversion efficiency of 96%. A maximum ammonium removal rate of 0.57 kg‐N m^?3 d^?1 was achieved during the experimental period. The concentrations of AOB and Anammox bacteria were monitored over the operation of reactor using quantitative real‐time polymerase chain reaction (qRT‐PCR). CONCLUSION: In this study, autotrophic nitrogen removal process was achieved under salinity condition in a one‐reactor system. An over 100 fold increase of AOB was found due to the increased supply of ammonium at the beginning, then AOB concentration decreased temporarily in correspondence with the decreased DO, and the AOB resumed their concentration at the last phase. The Anammox bacteria abundance was about 150 fold higher than that at the beginning, indicating the successful enrichment of Anammox bacteria in the reactor. Copyright © 2010 Society of Chemical Industry     

Improvement of the settling properties of Anammox sludge in an SBR

Biological systems for the treatment of wastewater have to provide optimum sludge retention to achieve high removal efficiencies. In the case of slow‐growing micro‐organisms, such as anaerobic ammonia‐oxidizing (Anammox) bacteria, episodes of flotation involving biomass wash‐out are especially critical. In this study a strategy based on the introduction of a mix period in the operational cycle of the Anammox Sequencing Batch Reactor (SBR) was tested for its effects on biomass retention and nitrite removal. Using this new cycle distribution the biomass retention inside the reactor improved as the solids concentration in the effluent of the SBR decreased from 20–45 to 5–10 mg VSS dm^?3 and the biomass concentration inside the reactor increased from 1.30 to 2.53 g VSS dm^?3 in a period of 25 days. A decrease of the sludge volume index (SVI) from 108 to 60 cm³ g VSS^?1 was also observed. Complete depletion of nitrite was achieved in the reactor only with the new cycle distribution treating nitrogen loading rates (g N‐NO₂^? + g N‐NH₄⁺ dm^?3 d^?1) up to 0.60 g N dm^?3 d^?1. Copyright © 2004 Society of Chemical Industry     

Anaerobic digestion of olive mill wastewater in a periodic anaerobic baffled reactor (PABR) followed by further effluent purification via membrane separation technologies

BACKGROUND: The combined treatment of olive mill wastewater (OMWW) by applying the anaerobic digestion process and further treatment in a system consisting of filters and membranes is presented. The anaerobic digestion of the OMWW took place in a high rate system, the periodic anaerobic baffled reactor (PABR). Application of the membrane system aimed at purifying the anaerobic effluent. RESULTS: An increase in the organic loading rate was achieved by increasing the influent chemical oxygen demand (COD) and alternatively by decreasing the hydraulic retention time (HRT). The first option caused process failure, since the volatile fatty acids accumulation resulted in negligible biogas production. In contrast, the second change (decrease in HRT) led to stable operation that permitted the reduction of the HRT to 3.75 d and increase of the organic loading rate to 8.9 g tCOD L^?1 d^?1 with satisfactory total COD removal (72%). Higher total COD removal (up to 80%) was observed at lower organic loading rates (<3.5 g tCOD L^?1 d^?1). Further purification in the membrane units resulted in a final permeate of less than 0.1 g tCOD L^?1. The membrane systems proved to be more efficient on the anaerobic effluent than on the raw OMWW (the final permeate in that case contained 1g tCOD L^?1). CONCLUSIONS: The anaerobic digestion of OMWW in a PABR was stable even at high organic loading rates. Filtering and membrane fractionation of the PABR effluent resulted in a final permeate stream of high quality, suitable for irrigation and/or reuse in the proposed operating scheme for diluting the OMWW prior to anaerobic digestion. Copyright © 2009 Society of Chemical Industry     

间歇低氧曝气下CANON工艺处理生活污水的启动

利用序批式反应器（SBR）接种短程硝化和厌氧氨氧化污泥处理实际生活污水,在间歇低氧曝气条件下实现了CANON工艺的启动。同时,保证适宜的温度和污泥浓度对处理效果及系统的稳定也很重要。该运行模式下,可实现对亚硝酸盐氧化菌（NOB）的抑制淘洗,短程硝化和厌氧氨氧化为主导反应,自养脱氮体系稳定。系统稳定运行后污染物去除效果良好：进水总氮和氨氮质量浓度为63.9 mg·L^-1和62.7 mg·L^-1,出水总氮和氨氮质量浓度为12.3 mg·L^-1和7.6 mg·L^-1,总氮和氨氮去除率为77.8%和86.7%,总氮去除负荷达0.16 kg N·（m³·d）^-1。试验研究为间歇低氧曝气运行模式推广应用于城市污水自养脱氮提供了参考。     

Determination of potential methane production capacity of a granular sludge from a pilot‐scale upflow anaerobic sludge blanket reactor using a specific methanogenic activity test

A 450 dm³ pilot‐scale upflow anaerobic sludge blanket (UASB) reactor was used for the treatment of a fermentation‐based pharmaceutical wastewater. The UASB reactor performed well up to an organic loading rate (OLR) of 10.7 kg COD m^?3 d^?1 at which point 94% COD removal efficiency was achieved. This high treatment efficiency did not continue, however and the UASB reactor was then operated at lower OLRs for the remainder of the study. Specific methanogenic activity (SMA) tests were, therefore, carried out to determine the potential loading capacity of the UASB reactor. For this purpose, the SMA tests were carried out at four different initial acetate concentrations, namely 500 mg dm^?3, 1000 mg dm^?3, 1500 mg dm^?3 and 2000 mg dm^?3 so that substrate limitation could not occur. The results showed that the sludge sample taken from the UASB reactor (OLR of 6.1 kg COD m^?3 d^?1) had a potential acetoclastic methane production (PMP) rate of 72 cm³ CH₄ g^?1 VSS d^?1. When the PMP rate was compared with the actual methane production rate (AMP) of 67 cm³ CH₄ g^?1 VSS d^?1 obtained from the UASB reactor, the AMP/PMP ratio was found to be 0.94 which ensured that the UASB reactor was operated using its maximum potential acetoclastic methanogenic capacity. In order to achieve higher OLRs with desired COD removal efficiencies it was recommended that the UASB reactor should be loaded with suitable OLRs pre‐determined by SMA tests. © 2001 Society of Chemical Industry     

Enrichment of Anammox biomass from municipal activated sludge: experimental and modelling results

Anaerobic Ammonia Oxidising (Anammox) biomass was enriched from sludge collected at a municipal wastewater treatment plant, employing a Sequential Batch Reactor (SBR). After 60 days Anammox activity started to be detected, by consumption of stoichiometric amounts of NO₂^? and NH₄⁺ in the system. Fluorescence In Situ Hybridisation analysis confirmed the increase of Anammox bacteria concentration with time. A final concentration of enriched biomass of 3–3.5 gVSS dm^?3 was obtained, showing a Specific Anammox Activity of 0.18 gNH₄⁺‐N gVSS^?1 d^?1 The reactor was able to treat nitrogen loading rates of up to 1.4 kgN m^?3 d^?1, achieving a removal efficiency of 82 %. On the other hand, the start‐up and operation of the Anammox SBR reactor were consequentially modelled with the Activated Sludge Model nr 1, extended for Anammox. The simulations predicted quite well the experimental data in relation to the concentrations of nitrogenous compounds and can be used to estimate the evolution of Anammox and heterotrophic biomass in the reactor. These simulations reveal that heterotrophs still remain in the system after the start‐up of the reactor and can protect the Anammox microorganisms from a negative effect of the oxygen. Copyright © 2004 Society of Chemical Industry     

Effect of sonication assisted by titanium dioxide and ferrous ions on polyaromatic hydrocarbons (PAHs) and toxicity removals from a petrochemical industry wastewater in Turkey

BACKGROUND: In Izmir (Turkey) polyaromatic hydracarbon (PAH) removal efficiencies are low in petrochemical industry aerobic biological wastewater treatment plants because bacteria are not able to overcome the inhibition of these toxic and refractory organics. In order to increase PAHs removal, sonication process was chosen among other advanced treatment processes include sonication processes. The effects of ambient conditions, increasing sonication time, sonication temperature, TiO₂ and Fe⁺² concentrations on sonication at a petrochemical industry wastewater treatment plant in Izmir (Turkey) was investigated in a 650 W sonicator, at a frequency of 35 kHz and a 500 mL glass reactor. RESULTS: Increasing the temperature improved PAH removal after 150 min sonication at 30 °C and 60 °C. The maximum total PAH removal efficiencies were the same in a reactor containing 20 mg L^?1 TiO₂ and in a TiO₂‐free reactor at 30 °C and 60 °C after 150 min sonication. Maximum 91% and 97% total PAH removals were obtained in a control reactor and a reactor containing 20 mg L^?1 Fe⁺² at 30 °C and 60 °C, respectively, after 150 min sonication. The PAH concentration was toxic to Daphnia magna, so that the EC₅₀ value decreased significantly from 342.56 ng mL^?1 to EC₅₀ = 9.88 ng mL^?1 and to EC₅₀ = 3.35 ng mL^?1, at the lowest TiO₂ (0.1 mg L^?1) and Fe⁺² (2 mg L^?1) concentrations, respectively, after 150 min sonication at 30 °C. CONCLUSION: PAHs and the acute toxicity in a petrochemical industry wastewater were removed efficiently through sonication. Copyright © 2010 Society of Chemical Industry     

Treatment of settled piggery waste by a down‐flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B_V) on the performance of a down‐flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm^?3 d^?1. The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B_V, process failure was not observed. A logarithmic relationship was found to describe the influence of B_V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO₂/CH₄ ratio in the biogas. The effect of the hydraulic volumetric loading rate (H_V) on the flow pattern of the reactor was evaluated. Dispersion number (D_n) was in the range of 0.17–0.37 for the maximum and minimum values of H_V studied, respectively. The ratio between the real and theoretical HRT increased as the H_V decreased. These results demonstrate that axial dispersion increased as the H_V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K_L), microbial decay coefficient (K_d), microbial yield coefficient (Y), maximum microbial growth rate (U_M) and saturation constant (K_S) were found to be: 3.1 (g COD g VSS^?1 d^?1), 3.0 (g COD g VSS^?1 d^?1), 0.062 (d^?1), 0.15 (g VSS g COD removed^?1), 0.39 (d^?1) and 2.6 (g SCOD dm^?3), respectively. Copyright © 2004 Society of Chemical Industry     

Comparative study of nitrification performances of immobilized cell fluidized bed reactor and contact oxidation biofilm reactor in treating high strength ammonia wastewater

BACKGROUND: The immobilized cell fluidized bed reactor and contact oxidation biofilm reactor are two common choices for high strength ammonia wastewater treatment, however, comparative study of the nitrification performance of the two reactors has not been thoroughly studied. The nitrification performance of the two bioreactors when treating strong synthetic ammonia wastewater was investigated and compared. RESULTS: Results demonstrated that the immobilized cell fluidized bed reactor had a shorter acclimation period, and possessed several advantages over the contact oxidation biofilm reactor, in the form of complete oxidation of 150–360 mg L^?1 ammonia wastewater in a shorter time, higher ammonia removal rates (from 9.6 to 4.32 × 10² mgN L^?1 d^?1) over the temperature range 8 to 32 °C, irrespective of organic load. In contrast, a large reduction in ammonia removal was found in the contact oxidation biofilm reactor with chemical oxygen demand (COD) load. The immobilized cell fluidized bed reactor exhibited stable and high rates of nitrification in the long term. CONCLUSION: These facts demonstrated that the immobilized cell fluidized bed reactor is a suitable selection for high strength ammonia wastewater treatment. Copyright © 2007 Society of Chemical Industry     

Evaluation of heterotrophic nitrite removal by a sulphide and acetate oxidizing mixed culture originated from an oil reservoir

BACKGROUND: Shortcut biological nitrogen removal (SBNR) has attracted much attention in recent years due to lower aeration and chemical oxygen demand (COD) requirements, shorter residence time and smaller biomass production. In this work an oil reservoir denitrifying culture, with the ability to function under autotrophic and heterotrophic conditions was used for heterotrophic denitritation. Using freely suspended cells, effects of nitrite concentration (10–50 mmol L^?1) and temperature (15–35 °C) on the kinetics of denitritation were investigated and a kinetic model was developed. Potential for enhancement of nitrite removal rate, and impacts of nitrite concentration and loading rate were investigated in a continuous biofilm reactor. RESULTS: Nitrite did not impose any inhibitory effect, even at the highest applied concentration of 50 mmol L^?1. Increase of temperature in the range 15–35 °C enhanced the reduction rate significantly. Fitting the experimental data into the model developed, values of biokinetic coefficients (µ_max?NO2, K_S?NO2, Y_X?NO2, Y_X?Ace?NO2 and Eµ‐_NO2) were determined. In the biofilm reactor increases in nitrite loading rate (through flow rate or feed nitrite concentration) led to a linear increase of nitrite removal rate, with the highest removal rate of 140.6 mmol L^?1 h^?1 achieved with a residence time of 0.19 h. CONCLUSION: The enrichment culture used in this study is not only a superior biocatalyst for simultaneous removal of sulphide, nitrate and BOD, it could also be used effectively in the denitritation step of an SBNR process. The kinetic model developed would certainly have beneficial applications in the design, operation and control of the SBNR process. Copyright © 2011 Society of Chemical Industry     

Batch treatment of saline wastewater by Halanaerobium lacusrosei in an anaerobic packed bed reactor

BACKGROUND: This study considers batch treatment of saline wastewater in an upflow anaerobic packed bed reactor by salt tolerant anaerobic organisms Halanaerobium lacusrosei . RESULTS: The effects of initial chemical oxygen demand (COD) concentration (COD₀ = 1880–9570 mg L^?1), salt concentration ([NaCl] = 30–100 g L^?1) and liquid upflow velocity (V_up = 1.0–8.5 m h^?1) on COD removal from salt (NaCl)‐containing synthetic wastewater were investigated. The results indicated that initial COD concentration significantly affects the effluent COD concentration and removal efficiency. COD removal was around 87% at about COD₀ = 1880 mg L^?1, and efficiency decreased to 43% on increasing COD₀ to 9570 mg L^?1 at 20 g L^?1 salt concentration. COD removal was in the range 50–60% for [NaCl] = 30–60 g L^?1 at COD₀ = 5200 ± .100 mg L^?1. However, removal efficiency dropped to 10% when salt concentration was increased to 100 g L^?1. Increasing liquid upflow velocity from V_up = 1.0 m h^?1 to 8.5 m h^?1 provided a substantial improvement in COD removal. COD concentration decreased from 4343 mg L^?1 to 321 mg L^?1 at V_up = 8.5 m h^?1, resulting in over 92% COD removal at 30 g L^?1 salt‐containing synthetic wastewater. CONCLUSION: The experimental results showed that anaerobic treatment of saline wastewater is possible and could result in efficient COD removal by the utilization of halophilic anaerobic bacteria. Copyright © 2008 Society of Chemical Industry     

Performance and sludge characteristics of anammox process at moderate and low temperatures

A sequencing batch reactor (SBR) was used to investigate the performance and sludge characteristics of anammox process at moderate and low temperatures. The initial pH was 7.5 and hydraulic retention time (HRT) was 3 h. When temperature was 25-35 °C, nitrogen removal rate (NRR) fluctuated from 1.67 to 1.82 kg/m³·d. However, when temperature dropped to 15 °C, NRR suddenly decreased by 0.48 kg/m³·d. Larger activation energy was acquired at lower temperature, and it was difficult to achieve efficient nitrogen removal under low temperature. When temperature declined to 10 °C, ΔNO ₂ ^? -N/ΔNH ₄ ⁺ -N and ΔNO ₃ ^? -N/ΔNH ₄ ⁺ -N reached 1.02 and 0.27, respectively. Inhibition resulting from low temperature on anammox activity was recoverable, and the modified Boltzmann model was appropriate to analyze recovery feature of anammox process. Low temperature not only led to poor nitrogen removal, but also affected sludge size and feature.     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Biological removal of 17α‐ethinylestradiol (EE2) in an aerated nitrifying fixed bed reactor during ammonium starvation

BACKGROUND: Conventional wastewater treatment plants (WWTPs) tend to partially remove recalcitrant chemicals, such as pharmaceuticals. Among these, the synthetic estrogen 17α‐ethinylestradiol (EE2) is of great environmental concern. In this work a continuously aerated submerged fixed bed bioreactor was used for the biological removal of EE2 at µg L^?1 levels. RESULTS: Removal efficiencies higher than 96% were obtained at a hydraulic retention time (HRT) of 4.3 days and a volumetric loading rate (B_v) of 11 µg EE2 L^?1 d^?1. Increasing the B_v up to 40 and 143 µg EE2 L^?1 d^?1 led to slightly lower removal efficiencies, 81 and 74%, respectively. Nitrification was confirmed to be the main biological mechanism involved in EE2 removal. Most interestingly, the elimination of EE2 was not affected by the absence of ammonium in the feed, suggesting that ammonia‐oxidizing bacteria (AOB) were able to maintain their population density and their activity, even after several months of starvation. CONCLUSION: The concept of an aerated submerged fixed bed bioreactor, capable of removing estrogens in a sustainable and biological way, shows great potential as an effluent polishing step for existing WWTPs. Copyright © 2008 Society of Chemical Industry     

Start up of a pilot scale aerobic granular reactor for organic matter and nitrogen removal

Aerobic granulation is a promising technology for the removal of nutrients in wastewater. Since research to date is mainly focused at laboratory scale, a pilot‐scale sequencing batch reactor (100 L) was operated to obtain granular sludge in aerobic conditions grown on acetate as organic carbon substrate. Selective pressure created by means of decreasing settling time and increasing organic loading rate (OLR) enhanced the formation of aerobic granular sludge. Granules appeared after 6 days and reached an average diameter around 3.5 mm. The settling velocity value should be higher than 11 m h^?1 in order to remove flocculent biomass. The reactor treated OLRs varying between 2.5 and 6.0 g COD L^?1 d^?1 reaching removal efficiencies around 96%, which demonstrates the high activity and the ability of the system to withstand high OLR. Nevertheless, a rapid increase in the OLR produced a loss of biomass in the reactor due to breakage of the granules. Copyright © 2011 Society of Chemical Industry     

Enhancing completely autotrophic nitrogen removal over nitrite by trace NO2 addition to an AUSB reactor

BACKGROUND: Completely autotrophic nitrogen removal over nitrite (CANON) could decrease energy consumption and CO₂ release compared with conventional nitration–denitrification. Trace NO₂ addition could enhance the activities of aerobic and anaerobic ammonium oxidation. RESULTS: An aerated upflow sludge bed (AUSB) reactor inoculated simultaneously with aerobic and anaerobic ammonium oxidizing sludge was operated to cultivate granular sludge capable of carrying out CANON. The results showed that the efficiency and rate of total nitrogen (TN) removal reached 61% and 0.114 kgN, respectively (m^?3 day^?1) for DO = 0.5–0.6 mg L^?1. Batch tests indicated that trace NO₂ addition could increase the CANON activity of sludge. The TN removal rate and efficiency of the reactor was increased to 0.234 kgN m^?3 day^?1 and 63%, respectively, when the reactor was aerated with air containing 2.7–3.3 mmol m^?3 NO₂ and DO was at 0.5–0.8 mg L^?1. CONCLUSIONS: Trace NO₂ addition provides an alternative to increase the capacity of a CANON system at low DO concentration. Copyright © 2009 Society of Chemical Industry