Nitrite accumulation followed by denitrification using sequencing batch reactor.

Biological ammonia-nitrogen removal utilizes two distinct processes, nitrification and denitrification. In nitrification, ammonia oxidizes to nitrite then to nitrate. In this study, elimination of nitrite oxidation to nitrate step was attempted in order to directly remove nitrite to nitrogen gas by denitrification. For this study the supernatant from an anaerobic digester was used as an ammonia source and a sequencing batch reactor (SBR) was employed. Emphasis was given to the evaluation of the operational factors affecting nitrite accumulation and the elucidation of kinetics for biological nitrification and denitrification. Accumulation of nitrite in the nitrification process was achieved by suppressing the growth of Nitrobacter, a nitrite oxidizer, by loading high concentration ammonia supernatant immediately after all ammonia in the previous loading was oxidized to nitrite. Nitrite oxidation was taking place as the solid retention time (SRT) was increased from 2.5 days to 3.0 days in a continuously aerated SBR mode with daily feeding. However, nitrite accumulation was achieved even at longer SRT of 5 days when the aeration and non-aeration periods were appropriately combined and the non-aeration period can be used for denitrification of the accumulated nitrite with a carbon source supplied.     

Development of a super high-rate Anammox reactor and in situ analysis of biofilm structure and function.

The anaerobic ammonium oxidation (Anammox) process is a new efficient and cost effective method of ammonium removal from wastewater. Under strictly anoxic condition, ammonium is directly oxidised with nitrite as electron acceptor to dinitrogen gas. However, it is extremely difficult to cultivate Anammox bacteria due to their low growth rate. This suggests that a rapid and efficient start-up of Anammox process is the key to practical applications. To screen appropriate seeding sludge with high Anammox potential, a real-time quantitative PCR assay with newly designed primers has been developed. Thereafter, the seeding sludge with high abundance of Anammox bacteria (1.7 x 10(8) copies/mg-dry weight) was selected and inoculated into an upflow anaerobic biofilters (UABs). The UABs were operated for more than 1 year and the highest nitrogen removal rate of 24.0 kg-N m-3 day(-1) was attained. In addition, the ecophysiology of Anammox bacteria (spatial distribution and in situ activity) in biofilms was analysed by combining a full-cycle 16S rRNA approach and microelectrodes. The microelectrode measurement clearly revealed that a successive vertical zonation of the partial nitrification (NH4+ to NO2-), Anammox reaction and denitrification was developed in the biofilm in the UAB. This result agreed with the spatial distribution of corresponding bacterial populations in the biofilm. We linked the micro-scale information (i.e. single cell and/or biofilm levels) with the macro-scale information (i.e. the reactor level) to understand the details of Anammox reaction occurring in the UABs.     

Nitrogen removal rates at a technical-scale pilot plant with the one-stage partial nitritation/Anammox process.

Traditional nitrification/denitrification is not suitable for nitrogen removal when wastewater contains high concentrations of ammonium nitrogen and low concentrations of biodegradable carbon. Recently, a deammonification process was developed and proposed as a new technology for treatment of such streams. This process relies on a stable interaction between aerobic bacteria Nitrosomonas, that accomplish partial nitritation and anaerobic bacteria Planctomycetales, which conduct the Anammox reaction. Simultaneous performance of these two processes can lead to a complete autotrophic nitrogen removal in one single reactor. The experiments where nitrogen was removed in one reactor were performed at a technical-scale moving-bed pilot plant, filled with Kaldnes rings and supplied with supernatant after dewatering of digested sludge. It was found that a nitrogen removal rate obtained at the pilot plant was 1.9 g m(-2) d(-1). Parallel to the pilot plant run, a series of batch tests were carried out under anoxic and aerobic conditions. Within the batch tests, where the pilot plant's conditions were simulated, removal rates reached up to 3 g N m(-2)d(-1). Moreover, the batch tests with inhibition of Nitrosomonas showed that only the Anammox bacteria (not anoxic removal by Nitrosomonas) are responsible for nitrogen removal.     

Model-based evaluation of COD influence on a partial nitrification-Anammox biofilm (CANON) process.

A model evaluating COD influence on a partial nitrification-Anammox biofilm process is integrated on the basis of heterotrophic growth as described in ASM3, combined with a previously published model for the CANON process. This integrated model can simulate the activities of heterotrophs and autotrophs involved in a biofilm, and interactions between COD oxidation, denitrification, nitrification and Anammox can be evaluated. Simulations indicate that COD in the influent has no important influence on the trends in the partial nitrification-Anammox biofilm process. Besides full COD removal, a total nitrogen removal efficiency of about 90% can be expected for stable biofilm systems. Furthermore, Anammox is a major contributor to the total nitrogen removal in stable biofilm systems and conventional denitrification only takes a share of <20% in the total nitrogen removal.     

Nitrogen removal from sludge digester liquids by nitrification/denitrification or partial nitritation/anammox: environmental and economical considerations.

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this "achievement" turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.     

Biological nitrogen removal in SBR bypassing nitrate generation accomplished by chlorination and aeration time control.

A novel control strategy for biological nitrogen removal with high nitrite built-up through chlorine dosage was studied. In the biological nitrogen removal process operated in a bench-scale sequencing batch reactor, dose of chlorine of 0.2 mg/l in the form of sodium hypochlorite was applied after the COD was depleted. The aerobic phase switched to an anoxic phase shortly after the ammonium was completely biotically oxidized. Nitrite accumulation was stably achieved which was attributed to the chlorination and the lag-time of nitrification. With the time control, stable 100% conversion of nitrite could also be sustained even under the absence of chlorine for at least 20 days. The nitrite oxidizer should have been killed rather than been suppressed in this study. For engineering applications, the advantages of the nitrification/denitrification via nitrite can compensate the cost of chlorine dosage. Combined with the aeration time control, it is feasible to apply chlorination in a biological nitrogen removal process in SBRs.     

Model experiments on improving nitrogen removal in laboratory scale subsurface constructed wetlands by enhancing the anaerobic ammonia oxidation.

Anaerobic ammonia oxidation (Anammox) has been identified as a new general process-strategy for nitrogen removal in wastewater treatment. In order to evaluate the role and effects of the Anammox process in wetlands, laboratory-scale model experiments were performed with planted fixed bed reactors. A reactor (planted with Juncus effusus) was fed with synthetic wastewater containing 150-200 mg L(-1) NH4+ and 75-480 mg L(-1) NO2(-). Under these operating conditions, the plants were affected by the high ammonia and nitrite concentrations and the nitrogen removal rate fell within the same range of 45-49 mg N d(-1) (equivalent to 0.64-0.70 g Nm(-2)d(-1)) as already reported by other authors. In order to stimulate the rate of nitrogen conversion, the planted reactor was inoculated with Anammox biomass. As a result, the rate of nitrogen removal was increased 4-5-fold and the toxic effects on the plants also disappeared. The results show that, in principle, subsurface flow wetlands can also function as an "Anammox bioreactor". However, the design of a complete process for the treatment of waters with a high ammonia load and, in particular, the realisation of simple technical solutions for partial nitrification have still to be developed.     

Nitrogen removal in a fluidized bed bioreactor by using mixed culture under oxygen-limited conditions.

Nitrogen removal involving nitrification and denitrification was investigated in a fluidized bed bioreactor by using mixed culture sludge under oxygen-limited conditions. Methane was used as a sole carbon source for denitrification. In this study, optimal nitrification and denitrification rates were examined by varying methane and oxygen gas dissolution flow rates, 90 ml/min, 400 ml/min and 650 ml/min, in each. Simultaneously nitrification and denitrification was achieved. The total nitrogen removal rate was 15-mg N/g VSS. d, 21-mg N/g VSS. d and 26.4-mg N/g VSS. d at gas dissolution flow rate 90 ml/min, 400 ml/min and 650 ml/min, respectively. No significant accumulation of nitrite was found in this experiment. Nitrogen removal rates depend on gas dissolution flow rates. DO concentration was at 0.5-2 mg/L.     

A novel wastewater treatment process: simultaneous nitrification, denitrification and phosphorus removal.

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen concentration (DO, 0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHA), accompanied with phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to less than 0.5 mg/L at the end of the cycle. Ammonia was also oxidised during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis found that the final denitrification product was mainly nitrous oxide (N2O) not N2. Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms rather than denitrifying polyphosphate-accumulating organisms were responsible for the denitrification activity.     

The presence of ammonium facilitates nitrite reduction under PHB driven simultaneous nitrification and denitrification.

For economic and efficient nitrogen removal from wastewater treatment plants via simultaneous nitrification and denitrification the nitrification process should stop at the level of nitrite such that nitrite rather than nitrate becomes the substrate for denitrification. This study aims to contribute to the understanding of the conditions that are necessary to improve nitrite reduction over nitrite oxidation. Laboratory sequencing batch reactors (SBRs) were operated with synthetic wastewater containing acetate as COD and ammonium as the nitrogen source. Computer controlled operation of the reactors allowed reproducible simultaneous nitrification and denitrification (SND). The oxygen supply was kept precisely at a low level of 0.5 mgL(-1) and bacterial PHB was the only electron donor available for denitrification. During SND little nitrite or nitrate accumulated (< 20% total N), indicating that the reducing processes were almost as fast as the production of nitrite and nitrate from nitrification. Nitrite spiking tests were performed to investigate the fate of nitrite under different oxidation (0.1-1.5 mgL(-1) of dissolved oxygen) and reduction conditions. High levels of reducing power were provided by allowing the cells to build up to 2.5 mM of PHB. Nitrite added was preferentially oxidised to nitrate rather than reduced even when dissolved oxygen was low and reducing power (PHB) was excessively high. However, the presence of ammonium enabled significant reduction of nitrite under low oxygen conditions. This is consistent with previous observations in SBR where aerobic nitrite and nitrate reduction occurred only as long as ammonium was present. As soon as ammonium was depleted, the rate of denitrification decreased significantly. The significance of the observed strongly stimulating effect of ammonium on nitrite reduction under SND conditions is discussed and potential consequences for SBR operation are suggested.     

Nitrogen removal from pharmaceutical manufacturing wastewater with high concentration of ammonia and free ammonia via partial nitrification and denitrification.

In this study, laboratory-scale experiments were conducted applying a Sequencing Batch Reactor (SBR) activated sludge process to a wastewater stream from a pharmaceutical factory. Nitrogen removal can be achieved via partial nitrification and denitrification and the efficiency was above 99% at 23 degrees C+/-1. The experimental results indicated that the nitrite oxidizers were more sensitive than ammonia oxidizers to the free ammonia in the wastewater. The average accumulation rate of nitrite was much higher than that of nitrate. During nitrogen removal via the nitrite pathway, the end of nitrification and denitrification can be exactly decided by monitoring the variation of pH. Consequently, on-line control for nitrogen removal from the pharmaceutical manufacturing wastewater can be achieved and the cost of operation can be reduced.     

不同电子受体的反硝化除磷效果对比研究

反硝化除磷作用可以明显节省脱氮除磷过程的碳源需求和能耗。为研究不同电子受体下的反硝化除磷效果,利用一体化活性污泥工艺中污泥经过厌氧释磷后在不同电子受体下进行反硝化除磷试验,结果表明NO3-—N和NO2-—N均能参与反硝化除磷过程,在NO2-—N初始浓度高达30mg/L的条件下,除磷率仍在93%以上,未对反硝化除磷过程产生毒害作用。在工程应用中应加强短程硝化反硝化与反硝化除磷作用的耦合,在提高脱氮除磷效率的同时,取得明显的节能效果。     

Strong nitrogenous and agro-wastewater: current technological overview and future direction.

Nitrogen input to our environment has increased tremendously during the last four decades. It has been recognized that most of the nitrogenous wastes are produced from animal farms and agro-industries, which discharge a large amount of nitrogen as well as organics. Various biological and physico-chemical means are considered or applied for nitrogen removal. Particularly, biological nitrite nitrification and denitrification, and struvite precipitation have received more attention as applicable processes for strong nitrogenous waste treatment. The advanced oxidation process appears to be more attractive than activated carbon adsorption in terms of the removal of refractory organics when a further treatment of biologically treated effluent is required. Technologies using membrane bioreactors were very effective for solids separation, while reverse osmosis was found to be efficient for water reuse purpose with sufficient removal of refractory organics and nitrogen along with biological treatment. Reuse or recycling of strong nitrogenous wastes and agro-wastewater will be a desirable direction for the future in order to prevent the nitrogenous and organic pollution.     

High strength nitrogen removal from nightsoil and piggery wastes.

Nightsoil and piggery wastes generally present high strength organics and nitrogen. This study evaluated the nitrogen removal characteristics with the existing and modified nightsoil and piggery waste treatment plants. The existing conventional plants showed 20 to 40% nitrogen removal, but the modification with SBR or MLE process could remove effectively both nitrogen and organics with the minimum COD/TN and alkalinity/TN ratios of 6 and 3.6, respectively. Nitrite nitrification and denitrification rates obtainable at higher nitrogen loads were faster than the rates of nitrate nitrification and denitrification resulting in less reactor volume requirement. However, the higher nitrogen loads increased the organic loads resulting in the reactor temperature inhibiting nitrification. Thus, a combined treatment with anaerobic digestion with the adjustment of influent bypass rates was proposed to reduce the reactor temperature and the external carbon requirement. The biological treatment could discharge about 1,100 mg/L soluble COD and 50 mg/L soluble nitrogen, respectively.     

Nutrient removal and microbial granulation in an anaerobic process treating inorganic and organic nitrogenous wastewater.

The sustainable anaerobic nitrogen removal and microbial granulation were investigated by using a laboratory anaerobic granular sludge bed reactor, treating synthetic (inorganic and organic) wastewater and piggery waste. From inorganic synthetic wastewater, lithoautotrophic ammonium oxidation to nitrite/nitrate was observed by an addition of hydroxylamine. Also, the results revealed that the Anammox intermediates (particularly, hydrazine) contents in the substrate would be one of the important parameters for success of the anaerobic nitrogen removal process. The results from organic synthetic wastewater show that if the Anammox organism were not great enough in the startup of the process, denitritation and anaerobic ammonification would be a process prior to the Anammox reaction. The anaerobic ammonium removal from the piggery waste was performed successfully, probably due to the Anammox intermediates contained in the substrate. This reactor shows a complex performance including the Anammox reaction and HAP crystallization, as well as having partial denitritation occurring simultaneously. From the activity test, the maximum specific N conversion rate was 0.1 g NH4-N/g VSS/day (0.77 g T-N/g VSS/day), indicating that potential denitritation is quite high. The NO2-N/NH4-N ratio to Anammox is 1.17. The colour of the biomass treating the piggery waste changed from black to dark red. It was also observed that the red-colored granular sludge had a diameter of 1-2 mm. The settleability assessment of the granular sludge revealed that the granular sludge had a good settleability even though it was worse than that of seed granular sludge.     

塔式生物滤池处理城市污水的研究

尽管目前塔式生物滤池在城市污水处理中运用较少 ,但在有可资利用的地形时它可达到少动力或无动力运行 ,有较大的优势。研究了塔式生物滤池的工作参数及其处理特点。     

Energy saving processes for nitrogen removal in organic wastewater from food processing industries in Thailand.

Nitrogen removal from organic wastewater is becoming a demand in developed communities. The use of nitrite as intermediate in the treatment of wastewater has been largely ignored, but is actually a relevant energy saving process compared to conventional nitrification/denitrification using nitrate as intermediate. Full-scale results and pilot-scale results using this process are presented. The process needs some additional process considerations and process control to be utilized. Especially under tropical conditions the nitritation process will round easily, and it must be expected that many AS treatment plants in the food industry already produce NO2-N. This uncontrolled nitrogen conversion can be the main cause for sludge bulking problems. It is expected that sludge bulking problems in many cases can be solved just by changing the process control in order to run a more consequent nitritation. Theoretically this process will decrease the oxygen consumption for oxidation by 25% and the use of carbon source for the reduction will be decreased by 40% compared to the conventional process.     

同步硝化反硝化脱氮研究

在控制SBR反应器保持良好的好氧状态条件下 ,考察进水COD/NH3比值对同步硝化反硝化脱氮效率的影响。同时也对同步硝化反硝化机理进行了初步的探讨。研究表明 ,进水COD/NH3比值越高 ,总氮去除率越高 ,同步硝化反硝化现象越明显。由该试验可以推断活性污泥菌胶团中异养硝化菌和好氧反硝化菌的存在。     

Automatic control strategy for biological nitrogen removal of low C/N wastewater in a sequencing batch reactor.

To establish an automatic control system of external carbon addition in biological nitrogen removal, a bench-scale sequencing batch reactor with real-time control strategy was designed in this study. An oxidation-reduction potential (ORP) profile was used for automatic control of external carbon addition. The mean removal efficiency of total organic carbon was over 98%. Complete denitrification in an anoxic phase and complete denitrification and nitrification in anoxic and oxic phases were accomplished, respectively, because the oxic and anoxic periods were also appropriately controlled with ORP and pH profiles, respectively. Mean removal efficiency of total nitrogen was over 95%. When concentration of influent wastewater was changed, volume of additional carbon was automatically changed with the influent fluctuation, and flexible hydraulic retention time was achieved in this system.     

Anammox brings WWTP closer to energy autarky due to increased biogas production and reduced aeration energy for N-removal.

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2-3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15-20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.