Optimization Of Nitrogen Removal Research Articles

Removal of nitrogen and phosphorus in a combined A 2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter (A 2/O-BAF) combined system was carried out to treat wastewater with lower C/N and C/P ratios. The A 2/O process was operated in a short aerobic sludge retention time (SRT) for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A 2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitrifying phosphate-accumulating organisms (DPAOs). The ratio of DPAOs to phosphorus accumulating organisms (PAOs) could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A 2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A 2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A 2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1–4 mg/L nitrate nitrogen in the anoxic zone effluent of A 2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Novel strategy of nitrogen removal from domestic wastewater using pilot Orbal oxidation ditch

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.

Optimizing Nitrogen Removal in a MBR Under Abnormal Operating Conditions

Optimizing Nitrogen Removal in a MBR Under Abnormal Operating Conditions

Optimizing nitrogen removal in the BioDenitro process

The potential and limits of different configurations of the BioDenitro-alternating process to suit the various design cases that can arise depending on the wastewater characteristics, space necessary and effluent nitrogen requirements were analysed through simulations of the activated sludge model No. 2. The first analysis involved the combination in one cycle of the main phase in the alternating reactors with an aerated phase having the two reactors in aerobic conditions and/or a hydraulic phase using the flow only in the anoxic reactor. This option has been found to have a very high potential for cases with strict requirements concerning effluent total nitrogen, but limited when the requirements are low effluent NH4-N, relatively high effluent total nitrogen and minimum solids and hydraulic retention times. When the latter conditions have to be fulfilled the incorporation of a post-aeration reactor to the alternating reactor was found to be very effective. In addition the configuration is very flexible because multiple combinations of post-aeration reactor volumes and in the duration of the different phases in the alternating reactors can be selected to achieve effluent nitrogen requirements. This flexibility is limited to the use of moderate values in the post-aeration reactor volumes and in the duration of the aerated phase. An experimental trial of the latter configuration was carried out and demonstrated its operational simplicity by achieving the desired nitrogen requirements in the effluent simply by changing the duration of the aerated phase for a given post-aeration reactor volume. From the experimental results an enhanced simultaneous nitrification-denitrification at the start of aeration in the alternating reactors was found and the ASM2 model was shown to have a satisfactory predictive capacity.

Optimization of nitrogen removal from piggery waste by nitrite nitrification

The piggery waste characteristics greatly vary with types of manure collections and the amount of water used. If solids are separated well, the waste strength will be greatly reduced resulting in lower TCOD/TKN ratio of 4 (average). If solids are separated by a mechanical scraper, some solids will remain and the waste strength will be increased with a TCOD/TKN ratio of 7. This study was conducted to find an optimum operating condition for nitrogen removal with these two ratios. Nitrite nitrification was targeted because it could be a short cut process for savings in oxygen for nitrification and carbon requirements for denitrification. The study results indicated that nitrogen loading rate and pH were the most important factors to be considered for stable nitrite nitrification. The applicable nitrogen loads were estimated to be 0.3 to 2.0 kgTKN/oxic m3/d for high TCOD/TKN ratio without pH control. With higher pH > 8, NO2N/NOxN ratios in oxic stages even with lower nitrogen loads were increased. The SBR with low TCOD/TKN ratio less than 4 required additional alkalinity. For a complete denitrification, the influent TCOD/TKN ratio must exceed 6 with oxic/total reactor volume ratio of 0.5. Nitrite nitrification and denitrification could save about 35% in tank volume and 50% in carbon requirement, respectively. However, 9.5% oxygen saving could be expected during the operation with low TCOD/TKN ratio. The elevated temperature due to the heat released from COD removal also enhanced microbial activities for nitrification and denitrification as well as ammonia stripping. However, careful attention must be provided for the reactor temperature not to inhibit the nitrification process.

PH and Oxidation–Reduction Potential Control Strategy for Optimization of Nitrogen Removal in an Alternating Aerobic–Anoxic System

An alternating aerobic and anoxic (AAA) system is a continuous-flow, activated-sludge process in which the environmental conditions necessary to meet the specific requirements for aerobic nitrification and anoxic denitrification are created. Because of stricter regulations on wastewater effluent and concerns on energy consumption, the process control of the system is now becoming more important. A bench-scale AAA system with different fixed aeration ratios was operated for more than 8 months to evaluate effects of the total cycle time and aeration ratio on the system performance and to develop a feasible control scheme. With supplemental organic addition, the system shows removal efficiencies of 85 to 90% and 78 to 82% for chemical oxygen demand and total nitrogen, respectively. The oxidation-reduction potential (ORP) and pH profiles indicate that the aerobic cycle can be controlled by a control point (ammonia valley) on the pH profile indicating the end of nitrification and the anoxic cycle controlled by another point (nitrate knee) on the ORP profile signifying the end of denitrification. Thus, a dual control strategy with the pH and ORP control points was used for terminating aerobic-anoxic and initiating anoxic-aerobic cycles in an AAA system. The performance of the online control system is excellent, with a significant energy saving (average aeration ratio, fa = 0.23) as compared to the fixed time systems (fa = 0.33 to approximately 0.5).

Nitrogen removal from synthetic wastewater by simultaneous nitrification and denitrification (SND) via nitrite in an intermittently-aerated reactor

An intermittently aerated and decanted single-reactor process was proposed and some key control parameters investigated for nitrogen removal from wastewater by simultaneous nitrification and denitrification (SND) via nitrite. Two types of synthetic wastewater with acetate as the main carbon source, and chemical oxygen demand (COD):nitrogen (N) ratios of approximately 5:1 and 10:1 were used. For both types of wastewater the average COD removal efficiency reached above 95%, and under optimal conditions nitrogen removal efficiency also reached above 90%. This process consisted of 72 min aeration, 48 min settling and 24 min effluent decanting. Influent wastewater was fed from the bottom of the reactor, and did not require a separate mixing phase. In this process, nitritation (1st step of nitrification) was induced but nitratation (2nd step of nitrification) was effectively suppressed and denitrification was carried out using nitrite. Most important parameters for effective SND via nitrite in the proposed process were: (1) the increase rate and the minimum and maximum dissolved oxygen (DO) concentration during the aeration period, (2) length of one cycle, and of aeration per cycle, taking advantage of the lag-time of nitrite-oxidizers behind ammonia-oxidizers when adjusting from anoxic/anaerobic to aerobic condition, and (3) close contact between the mixed liquor suspended solids (MLSS) in the reactor and the influent wastewater under anoxic/anaerobic condition. During the aeration period, DO concentration dropped initially reaching the minimum value after several minutes, and then rose in 2nd-order fashion. The optimal maximum DO concentration (at the end of the aeration period) for nitrogen removal was determined to be around 2.0–2.5 mg/l in this proposed process.

The Development of Nutrient‐Removal Processes (Abridged)

AbstractThe earliest references to the loss of nitrogen and phosphorus in activated‐sludge systems indicated an awareness, but no particular interest, in the use of biological processes for the removal of nutrients. The development of extended‐aeration processes in general, and of channel systems in particular, intensified the interest in denitrification as a means of reducing nitrogen in an effluent. Observations of simultaneous nitrification and denitrification led to the proposal of separate anoxic zones for optimal nitrogen removal. The discovery that biological nitrogen and phosphorus removal could be synergistic, led to an explosion of processes, differing in all but the basic underlying biochemistry, for the removal of both nitrogen and phosphorus. The development of computer models, to accurately describe the complex and inter‐related reactions, makes it possible to fully exploit biological systems to achieve cost‐effective nutrient removal.

Model and Sensor Based Optimization of Nitrogen Removal at Klagshamn Wastewater Treatment Plant

Optimization of wastewater treatment plants with extensive phosphorus and nitrogen removal is complicated. The Klagshamn wastewater treatment plant in Sweden is operated with pre-precipitation of phosphorus with ferric chloride and denitrification with methanol as carbon source. An activated sludge process, operated with pre-precipitation and denitrification with external carbon source in a compartmentalized plant, requires only small tank volumes but increases the need for proper operation and optimization. On-line nitrogen, ammonia, and TOC sensors are used for a day-to-day control and optimization while mathematical modelling is used for long term strategic planning. The on-line measurements are further used as the basis for the modelling. TOC and ammonia sensors at the influent clearly identify typical and extreme loading variations and nitrate measurements in the activated sludge tanks and the effluent shows the dynamics of the processes. These measurements provide a basis for model calibration. In combination low residuals of nitrogen, phosphorus and organic matter can be achieved.

Optimizing Nitrogen Removal Reactor Configurations by On-Site Calibration of the IAWPRC Activated Sludge Model

This paper describes a modified version of the IAWPRC model and the techniques used to calibrate it on site. Growth rate of autotrophic bacteria and the inert wastewater fractions were measured by simple methods, both in laboratory pilots and on full scale. Model predictions were compared to full scale results in large plants (> 100 000 P E). Measured autotrophic growth rates ranged from 0.3 to 0.65 1/d, depending on wastewater toxicity. Most model constants compared well with original IAWPRC proposals, and several wastewater types were identified. Parameters to establish a suspended solids balance are given. Different configurations of plants for nitrogen removal were investigated, including conventional recirculation, sludge reaeration (RDN) and step feed alternate zone denitrification.

Optimization of Nitrogen Removal in Small Activated Sludge Plants

In France, many small sewage treatment plants are of the activated sludge/extended aeration type and, generally, only receive a part of their nominal organic load. They are mostly equipped with surface aerators whose Standard wire Aeration Efficiency is in the range 1.3-1.9 kg 02 kwh−1. Consequently the sludge age and the supply of oxygen are sufficient to obtain a large elimination of nitrogen from domestic waste water even when the sludge temperature is low. However the concern is with the optimizing of the nitrogen treatment by the nitrification of ammonia in the aeration basin whilst avoiding any parasitic denitrification in the clarifier. Amongst other investigations, 4 small domestic wastewater treatment plants were studied over several months. A number of adjustment modifications were imposed on them in order to optimize the elimination of nitrogen : The final concentrations to be reached were : N-NH4− lower than 5 mg.l−1 and N-NO3− lower than 3 mg.l−1. The daily operating time of the aerators depends on the received load, the sludge concentration and the oxygenation capacity. When the works are under-loaded, the non-operational periods of the aerators should be as long as 1 1/2 and 2 hours in order to achieve the nitrates reduction. When the load is higher, the time required to attain anoxia after the shutdown of the aerators is shorter and the length of the non-operational periods can be reduced. These field experiments have allowed an evaluation of the tolerances around an optimum adjustment of the aeration operation : a reduction of 5 to 10 % of the daily aeration time may bring about an increase in the residual concentration of Kjeldahl nitrogen which reaches 10 rag.1−1. Conversely, sludge losses may take place in the clarifiers if the daily aeration time is increased by 5 to 10 % in the case of completely mixed basins equipped with slow vertical shaft aerators, and more than 15 % in the case of oxidation ditches (better denitrification probably due to the continuation of the current after stopping the rotors). The sludge concentration should be kept within fairly tight limits (± 0.5 g.1−1). It is however essential to rectify the aeration adjustments during the seasons : a rise in the sludge temperature of 10°C generates an increase in the total oxygen demand by 3 to 5 %. The particular case of plants with anoxic zone ahead is finally discussed.

Optimization of Nitrogen Removal in the Single Sludge Activated Sludge Process

Optimal design of nitrification-denitrification (N-D) systems reduces to obtaining maximum denitrification subject to the constraint of efficient nitrification. Under constant flow and load conditions simple approximate highly accurate formulae are developed to describe the N-D system. Selection of the N-D configuration is found to be crucially influenced by the TKN/COD (influent) ratio, µnm, maximum and minimum temperature and sludge age. In terms of these factors design charts are presented which rapidly allow the best configuration and sizes of the anoxic and aerobic reactors to be selected.