Effects of free ammonia and dissolved oxygen on nitrification and nitrite accumulation in a biofilm airlift reactor

The purpose of this research is to find out the effects of free ammonia concentration and dissolved oxygen on nitrification and nitrite accumulation in a biofilm airlift reactor. Free ammonia seriously inhibited the activity of nitrite oxidizers at the concentration higher than 0.1 mg NH₃-N/L and it was very effective for nitrite accumulation. Dissolved oxygen limitation in the biofilm also caused nitrite accumulation. Long term inhibition decreased the growth rate for nitrite oxidizers, and ammonia oxidizers were the dominant nitrifiers in the wastewater nitrification. Selective accumulation of ammonia oxidizers in the biofilm could be another reason for nitrite accumulation. Free ammonia inhibited nitrite oxidizers immediately, and adaptation to free ammonia was not observed. Therefore, the optimum control of free ammonia and dissolved oxygen concentration is critical for nitrite accumulation and the strategy can be used for selective accumulation of ammonia oxidizers in a bioreactor system.     

Nitrite accumulation characteristics of high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor

Selective nitrification was carried out to accumulate nitrite from high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor. Nitrification efficiencies and nitrite accumulation characteristics were investigated at various operating conditions such as ammonium load, oxygen supply and free ammonia concentration. The biofilm reactor showed very stable nitrification efficiencies of more than 90% at up to 2 kg NH₄‐N m^?3 d^?1 and the nitrite content was maintained at around 95%. Inhibition by free ammonia on nitrite oxidizers seems to be the major factor for nitrite accumulation. Batch kinetic analyses of ammonium and nitrite oxidation showed that nitrite oxidation activity was selectively inhibited in the presence of free ammonia. However, the activity recovered quickly as the free ammonia concentration decreased below the threshold inhibition concentration. Examination of specific ammonia and nitrite oxidation activities and the most probable number indicated that the number of nitrite‐oxidizing microorganisms in the nitrite‐accumulating system was less than that in the normal nitrification system due to long‐term free ammonia inhibition of the nitrite oxidizers. The reduced population of nitrite oxidizers in the biofilm system was also responsible for the accumulation of nitrite in the biofilm reactor. © 2003 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     

Reclamation of wastewater from a steel-making plant using an airlift submerged biofilm reactor

A bench-scale airlift submerged biofilm reactor was developed to test the possibility of nitrification of the final effluent discharged from a wastewater treatment process of a steel-making plant with an aim of reusing it as irrigation water. Despite the fluctuation of ammonia concentration in the wastewater (55–90 mg NH₃-N dm⁻³), the ammonia was completely converted to nitrate in the hydraulic retention time of 8 h. When decreasing the hydraulic retention time further down to 4 h, the nitrification efficiency decreased to 67·9%. However, the nitrification efficiency could be significantly enhanced by increasing the airflow rate due to an increase in both of the oxygen transfer rate and liquid circulation rate. At the aeration rate of 4 dm³ min⁻¹ and the hydraulic retention time of 4 h, the nitrification efficiency was as high as 92·6% and the nitrification rate was 34·6 mg NH₃-N dm⁻³ bed h⁻¹. © 1998 Society of Chemical Industry     

Treatment of domestic wastewater by subsurface flow constructed wetlands in Jordan

The use of subsurface flow constructed wetlands for treating domestic wastewater in Jordan is described. The objective was to study the performance of subsurface flow constructed wetlands as a low-cost technology for treating domestic wastewater. Results show that subsurface flow constructed wetlands are capable of reducing biochemical oxygen demand (BOD), different forms of nitrogen, total suspended solids (TSS), fecal coliform count (FCC), and total coliform count (TCC). However, removal efficiencies differ from bed to bed and from month to month. Results show that there is strong correlation between BOD₅ removal efficiency and BOD₅ loading in kg/ha, which is defined as BOD₅ loading rate in kg/ha.d multiplied by residence time. The coefficient of determination (R²) for the six beds varied from 0.827 for bed number one to 0.608 for bed number four. Total nitrogen, ammonia nitrogen, and nitrate nitrogen reductions were observed, which suggestthat, nitrification as well as denitrificationtookplace in the beds. TSS reduction was observed in all beds. However, removal efficiency differed from bed to bed and for the same bed from month to month. Total and fecal coliform counts were reduced by one to three logs, because influent was high in total and fecal coliform counts were still high.     

Ozonation of complex industrial park wastewater: effects on the change of wastewater characteristics

BACKGROUND: Ozonation of complex industrial park wastewater was carried out in a semi‐batch reactor. The variation of wastewater characteristics was evaluated based on the analysis of 5‐day biochemical oxygen demand (BOD₅) concentration, BOD₅/chemical oxygen demand (COD) ratio, COD fractionation, and dissolved organic carbon (DOC) molecular size distribution before and after ozonation. RESULTS: The experimental results indicated that low efficiency of COD removal with increasing tendency of BOD₅ concentration generally appeared after ozonation. Also, the BOD₅/COD ratio increased from an initial of 0.27 to a maximum of 0.38. The COD fractionation tests revealed that most of the inert soluble COD was transformed to biodegradable soluble COD at 30 min of reaction time. Additionally, the DOC molecular size distribution tests showed that the fraction larger than 500 kDa was significantly decreased and the fraction smaller than 2 kDa was increased when the reaction time was prolonged to 240 min. CONCLUSION: This study verified that partial oxidation of the complex industrial park wastewater by ozonation could enhance wastewater biodegradability. The biodegradability enhancement was primarily because the inert soluble COD fraction was converted to the biodegradable soluble COD and the high molecular weight fraction of DOC was shifted toward the low molecular weight fraction. Copyright © 2009 Society of Chemical Industry     

Performance evaluation of a modified anaerobic/anoxic/oxic (A/O) process treating low strength wastewater

A full scale modified A²/O process which combined pre-anoxic selector and the staging strategy treating low strength wastewater was investigated. In South China, domestic wastewater is always low in strength due to the high level of groundwater and setting of septic tank at the beginning of wastewater collection system. The results suggested that inadequate denitrification could result in deterioration of phosphorus removal. In addition, influent phosphorus concentration had effect on phosphorus removal. The pre-anoxic selector in modified A²/O process changed the distribution of nitrogen denitrified in different tanks. Characteristics of 3-stage aeration tanks were also studied. The simplified design of rectangular aeration tank could also perform as plug flow as conventional channel aeration tank. In 3-stage aeration tanks, mixed liquid suspended solid (MLSS) increased from one tank to another, while specific oxygen uptake rate (SOUR) of sludge, chemical oxygen demand (COD) and total phosphorus (TP) removal rate decreased, however ammonia nitrogen (NH₃-N) and nitrate nitrogen (NO₃-N) reaction rate remained constant. Furthermore, high MLSS concentration was not suitable for treating low strength wastewater. Waste sludge discharge could improve removal efficiency of COD, NH₃-N, and TP. Without waste sludge discharge, nitrite accumulated in settler.     

Effects of operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor

This study was performed to evaluate the operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor for wastewater treatment. The membrane bioreactor has 5.5 L of effective working volume including a microfiber membrane. The influent wastewater contained 133mg/L of BOD, 195 mg/L COD, 98 mg/L SS, 30 mg/L total nitrogen, and 3.8 mg/L total phosphorous. Operational conditions related to aeration on/off time were 8.8 h HRT, 10 LMH flux, 10 L/min air flow, and 6300 mg/L MLSS. For 2 h/cycle, aeration on/off time was operated for 12 cycles in three variations: 60/60 min, 50/70 min (I), and 40/80 min. Suction on/off time was 10/2 min, 8/2 min, and 8/2 min, respectively, but also 50/70 min (II) when aeration on/off time was operated at 8300 mg/L MLSS. The BOD removal efficiency rate of this process was higher than 97% regardless of the aeration on/off time distribution. To get higher than 82% total nitrogen removal efficiency rate, aeration off time in the reactor needs to be more than 70 min. The specific denitrification rate was 2.68 mgNO₃-N/gMv/h at 40/80 min on/off aeration times, which was 2.6 times more than at 60/60 min, and 1.4 times more than at 50/70 min (I) for 6300 mg/L MLSS. The specific nitrification rate was 1.96 mgNH₄-N/gMv/h at on/off aeration times of 50/70 min, 1.4 times less than at 40/80 min, but was ineffective for nitrification. Microbial activity was affected only a little by variation in aeration on/off time, though oxygen demand was reduced by aeration off time and allowed microbial concentration to increased. EPS (extracellular polymeric substance) per unit of microorganisms increased with aeration off time.     

A case study of the performance of pilot scale light weight aggregates (LWA) based hybrid soil filters in Estonia

Two pilot scale experimental hybrid soil filters (SF) filled with light weight aggregates were established during the summer of 2005 for the treatment of different types of wastewater, with the aim of developing compact hybrid constructed wetlands (CW) for use in cold climates. Both SFs are designed on the same principle: a vertical subsurface flow filter followed by a horizontal subsurface flow filter. Six different operational regimes were tested during the experiments. With a decrease in wastewater and pollutant load and the larger re-circulation of wastewater, purification efficiency increased in terms of most water quality indicators. The highest purification efficiencies in the Nõo SF, 99% and 82% for BOD₇ and N_tot removal respectively, were achieved when the re-circulation rate of 300% was applied and in the Rämsi SF, 99% and 87% for BOD₇ and N_tot removal respectively, were achieved, when the re-circulation rate of 300 to 600% was applied. In order to achieve effective organic matter removal, nitrification/denitrification and TSS removal, the re-circulation rate must be from 100 to 300% of the inflowing wastewater. The re-circulation of wastewater in overloaded systems is a good solution for the improvement of the aeration and overall purification efficiency of CWs.     

Sustained nitrite accumulation in a membrane‐assisted bioreactor (MBR) for the treatment of ammonium‐rich wastewater

A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m^?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm³ day^?1 m^?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m^?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO₂‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m^?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m^?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m^?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry     

A comparison of floating and sunken media biological aerated filters for nitrification

The versatility of the biological aerated filter (BAF) has made it an important process in wastewater treatment. These submerged three-phase fixed media reactors have been used in a wide variety of applications in wastewater treatment, such as primary treatment (solids removal), secondary treatment (COD and BOD removal), and tertiary treatment (nitrification). The aim of this work was to investigate the biological start-up of two such reactors to remove suspended solids (SS), total COD (tCOD) and ammonia, one containing a sunken medium (relative density 1·05) and the other containing a floating medium (relative density 0·92), both identical in shape and size. The reactors (0·054 m³ media) were run in parallel in upflow mode using secondary effluent as the process liquid at a flowrate of 0·2 dm³ min⁻¹ and air: liquid ratio of 10:1. Overall, floating media performed better than sunken media for SS, tCOD and ammonia removal, probably due to the compression of the bed due to the buoyancy force of the media and the flow of air and liquid acting upwards. Bed compression improved solids removal and appeared to have promoted the growth of bacteria. Temperature had a greater impact on nitrification than on carbonaceous matter removal. The floating medium reactor was more resistant to low temperature shocks than the sunken medium reactor but the latter showed a faster recovery time as temperature increased. Although the backwashing frequency used was satisfactory, performance may have improved if the backwashing had been carried out only when reactor performance began to decline. Nitrification was shown to follow a reaction rate between zero and half order. Thus, ammonia removal was generally independent of ammonia concentration and more affected by the presence of carbonaceous matter. © 1998 SCI     

Nitrogen compounds removal in a packed bed external loop airlift bioreactor

A packed bed external loop airlift bioreactor (PBELAB) was proposed as an alternative treatment system for wastewater containing ammonia and nitrate compounds. The 60L PBELAB consisted of aeration and non-aeration zones, both of which were packed with plastic bioballs to enhance the surface area for the attachment of bacteria. The system was able to achieve complete removal of all nitrogen compounds with simultaneous nitrification and denitrification, i.e., ammonia was decomposed in the aeration zone and nitrate was biodegraded in the non-aeration zone. At normal operation, the nitrification rate obtained from the system was in the range of 0.14-0.87 gNH₃-N/m²d and the denitrification rate was 0.04 gNO₃-N/m²d. The factors found to have great influence on the system included dissolved oxygen concentration and biofilm thickness. In addition, PBELAB was proven to perform well under nitrate shock load condition.     

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。     

Application of solar light for degradation of ammonia in petrochemical wastewater by a floating TiO2/LECA photocatalyst

In this study, photocatalytic degradation of ammonia in petrochemical wastewater was investigated by solar light/TiO₂ photocatalysis. The TiO₂ nanoparticles were used as photocatalysts which were immobilized on light expanded clay aggregate (LECA) granules as a new porous and light weight support. Maximum concentration of ammonia (975 mg/L) in petrochemical wastewater was selected, and to optimize the photocatalytic reaction, the effect of pH and catalyst dosage was investigated in two aerated and agitated reactor systems. Also, the morphology and chemical structure properties of the prepared catalysts were characterized by SEM and XRF analyses. The experimental results were shown that the performance of two types of aeration reactor systems was almost the same. Also, the ammonia removal efficiency was increased by increasing the pH value, and after solar light irradiation in three days, the solar reactor system lead degradation of ammonia in pH = 11–96.5%. The floating of photocatalyst can be reused at least three consecutive times with 14% decreases on the ammonia removal efficiency. The results suggest that the photocatalytic purification followed by solar photocatalytic reactor would be a promising method for the purification of chemical wastewater.     

缺氧胁迫影响硝化污泥活性的机理

硝化过程是废水生物脱氮的关键环节。为了研究缺氧胁迫对硝化活性的影响及其机理,采用分批培养法分别测定了经0、12、24 h缺氧滞留处理的污泥硝化活性、过氧化氢酶活性和过氧化物酶活性,以及这些硝化污泥抗氧毒（过氧化氢）性能。经过12、24 h缺氧处理后,污泥平均比氨氧化活性分别从0.894 mg N·(g MLSS)^-1·h^-1降为0.453、0.387 mg N·(g MLSS)^-1·h^-1,下降了46.8％、49.8％,平均比亚硝酸氧化活性也从0.761 mg N·(g MLSS)^-1·h^-1降至0.485、0.459 mg N·(g MLSS)^-1·h^-1,下降了36.3％、39.7％。试验结果证明,缺氧胁迫可降低污泥硝化活性,缺氧胁迫时间越长,硝化活性降幅越大,缺氧胁迫对氨氧化的影响大于亚硝酸氧化。缺氧胁迫可抑制硝化污泥的抗氧化酶活性,POD、CAT活性分别下降了10％、17％（12 h）和24％、21％（24 h）,缺氧胁迫时间越长,抗氧化酶活性越低。缺氧胁迫可削弱硝化细菌的抗氧毒能力,引起硝化活性降低。     

Das Oxitron-System,ein neues biologisches Abwasserreinigungs-Verfahren für den BSB5-Abbau sowie zur Nitrifikation und Denitrifikation

The oxitron system: a new biological sewage treatment process for reducing BOD₅ and for nitrification and denitrification . In the oxitron process, the waste water passes through a fluidized sand bed. As in the case of droplets, a stable biological slime is formed on the sand particles. The particular efficacy of the process can be explained in terms of the high specific surface, of the order of more than 3000 m² per m³ reactor volume. This leads to a particularly effective use of available space. The high content of biomass makes the process largely insensitive to fluctuations in feed rates and toxic effects. The oxitron process is used as a biological purification stage for reducing BOD₅ or as the third purification stage for nitrification and denitrification. The reactor can be operated at particularly high solids concentrations (ca. 20 g/l). The correspondingly high oxygen consumption of this process requires the use of pure oxygen in the aerobic step; over 90% of the oxygen supply is utilized. The special advantages of the oxitron process are: (1) 30% lower capital costs than for conventional processes (operating costs are comparable); (2) space requirements are some 80% lower than for the best conventional technology presently available, facilitating expansion; (3) the mode of operation is extremely simple and is not subject to interference by blockages, etc. Design data and results for large scale test plant are reported.     

Nitrification by immobilized cells in a micro‐ecological life support system using packed‐bed bioreactors: an engineering study

The nitrifying component of a micro‐ecological life support system alternative (MELISSA) based on microorganisms and higher plants was studied. The MELISSA system consists of an interconnected loop of bioreactors to allow the recycling of the organic wastes generated in a closed environment. Conversion of ammonia into nitrates in such a system was improved by selection of microorganisms, immobilization techniques, reactor type and operation conditions. An axenic mixed culture of Nitrosomonas europaea and Nitrobacter winogradskyi, immobilized by surface attachment on polystyrene beads, was used for nitrification in packed‐bed reactors at both bench and pilot scale. Hydrodynamics, mass transfer and nitrification capacity of the reactors were analysed. Mixing and mass transfer rate were enhanced by recirculation of the liquid phase and aeration flow‐rate, achieving a liquid flow distribution close to a well‐mixed tank and without oxygen limitation for standard operational conditions of the nitrifying unit. Ammonium conversion ranged from 95 to 100% when the oxygen concentration was maintained above 80% of saturation. The maximum surface removal rates were measured as 1.91 gN‐NH₄⁺ m^?2 day^?1 at pilot scale and 1.77 gN‐NH₄⁺ m^?2 day^?1 at bench scale. Successful scale‐up of a packed‐bed bioreactor has been carried out. Good stability and reproducibility were observed for more than 400 days. Copyright © 2004 Society of Chemical Industry     

Using electrocoagulation-electroflotation technology to treat synthetic solution and textile wastewater, two case studies

The purpose of this study was to investigate the effects of the operating parameters, such as pH, initial concentration (C_i), duration of treatment (t), current density (j), interelectrode distance (d) and conductivity (κ) on the treatment of a synthetic wastewater in the batch electrocoagulation (EC)-electroflotation (EF) process. The optimal operating conditions were determined and applied to a textile wastewater. Initially a batch-type EC-EF reactor was operated at various current densities ranging from 11.55 to 91.5 mA/cm² and various electrode gaps (1, 2 and 3 cm). For solutions with 300 mg/L of silica gel, good turbidity removal (89.6%) was obtained without any coagulant when the current density was 11.55 mA/cm², and with initial pH at 7.6, conductivity at 2.1 mS/cm: the treatment time was hold for 10 min and the electrode gap was 1 cm. Application of the optimal operating parameters on a textile wastewater showed a high removal efficiency for the following variables: suspended solid (SS) 85.5%, turbidity 76.2%, biological oxygen demand (BOD₅) 88.9%, chemical oxygen demand (COD) 79.7%, and color over 93%.     

Ammonia oxidation in Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane reactor

Selective oxidation of ammonia to NO was studied in a dense mixed ion electron conducting Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ membrane reactor, which integrates the separation and catalytic reaction process in a single reactive separation unit. The influence of the temperature and feed concentration on the membrane reaction performance were investigated in detail. Under reaction conditions, the oxygen permeation flux through the dense membrane increases with increasing temperature and ammonia flow rate. The lower temperature and ammonia concentration can favor the formation of NO, in which higher catalytic performance is obtained, suggesting that the membrane reactor operation is much beneficial for selective oxidation of ammonia.     

Mathematical modeling of aerobic membrane bioreactor (MBR) using activated sludge model no. 1 (ASM1)

Activated sludge model no. 1 (ASM1) was applied to an aerobic membrane bioreactor (MBR) treating dilute municipal wastewater. The model for the aerobic MBR was calibrated using the data collected from a lab-scale aerobic MBR using AQUASIM 2.0. The performance of MBR process in terms of chemical oxygen demand (COD) removal and ammonia nitrogen (SNH) nitrification was studied at different operating conditions such as hydraulic retention time (HRT), solid retention time (SRT) and mixed liquor suspended solids (MLSS) concentrations. The characteristics of influent wastewater, pre-settled primary effluent from a wastewater treatment plant (City of Elmhurst WWTP, Elmhurst, IL, USA), were determined in the laboratory and used for the calibration of the model. The results from the simulations provided a better understanding of the mechanisms and kinetics of the MBR process including sludge removal.