High Nitrification Efficiency Research Articles

Enhancing energy and nitrogen removal efficiency through automatic split injection and innovative aeration device: A study of low C/N ratio environments

A new aeration device based on Bernoulli's principle, Jetventrumixer (JVM), was introduced into an aeration tank in denitrification process, which involved an automatic split injection system (ASIS) into two denitrification tanks every 10 minutes. Real-time monitoring of influent water allowed the calculation of the C/N ratio, enhancing the utilization efficiency of internal carbon sources while reducing the need for external carbon. The comparison of the JVM with the conventional air diffuser for 100 days operation showed that the removal efficiency for NH4+-N in both systems was approximately 98 %, but the nitrification efficiencies were 84 % and 80 %, respectively. This indicates that the JVM achieves an high enough removal efficiency and nitrification efficiency compared with conventional air diffuser system with dramatic reduction in energy consumption by 52.1 %. When the influent wastewater was split and injected into duplicate denitrification tanks at ratios of 3:7, 5:5, and 7:3, the total nitrogen (TN) removal efficiencies were 77 %, 73 %, and 72 %, respectively. In contrast, with the implementation of the ASIS, the TN removal efficiency increased up to 82 %. The increase in TN removal indicates that real-time monitoring could stably track changes chemical composition in wastewater influent over 24 h and introducing ASIS facilitate the efficient utilization of internal carbon sources, thereby enhancing denitrification efficiency and improving TN removal efficiency. Finally, the greenhouse gas (GHG) emissions from the JVM and air diffuser were 9.39401 and 19.60488 tCO2eq year-1, respectively, representing a 52% reduction. Therefore, JVM and ASIS successfully reduced energy consumption and enhanced both nitrification and denitrification efficiencies.

Enhancing wastewater treatment efficiency: A hybrid technology perspective with energy-saving strategies

The study aimed to investigate how hybrid technology, combined with various intermittent aeration (IA) strategies, contributes to reducing the energy costs of wastewater treatment while simultaneously ensuring a high treatment efficiency. Even with IA subphases lasting half as long as those without aeration, and oxygen levels reduced from 3.5 to 1.5 mg O2/L, pollutants removal efficiency remains robust, allowing for a 1.41-fold reduction in energy consumption (EO). Hybrid technology led to a 1.34–fold decrease in EO, along with improved denitrification efficiency from 74.05 ± 4.71 to 81.87 ± 2.43 % and enhanced biological phosphorus removal from 35.03 ± 4.25 to 87.32 ± 3.64 %. The high nitrification efficiency may have been attributed to the abundance of Pseudomonas, Acinetobacter, and Rhodococcus, which outcompeted the genera of autotrophic nitrifying bacteria, suggesting that the hybrid system is favorable for the growth of heterotrophic nitrifiers.

Salinity Acclimation Strategies in Nitrifying Bioreactors

Several industries, including aquaculture, produce effluents with high or varying salt concentrations. The treatment of such effluents by the biological nitrification process can be challenging, as the microbes performing this process are sensitive to salinity. In certain cases, such as in recirculating aquaculture systems (RAS), it is essential to maintain high nitrification efficiency during salinity changes to prevent ammonia and nitrite toxicity. Therefore, suitable strategies are required to make nitrifying bioreactors tolerant to salinity variations. Although salinity changes can impact the nitrification performance, it has been shown that nitrifying bioreactors can acclimate to salinity variations over several days. This acclimation can be due to the physiological adaptation of the existing microorganisms or due to selection for microorganisms adapted to that salinity regime. Other factors, such as the biofilm matrix, can also play a role in salinity acclimation. Recent studies have shown that microbial management strategies can be applied to improve the salinity tolerance and reduce the recovery time of nitrifying bioreactors. Here, we discuss the existing knowledge on salinity acclimation in nitrifying systems, and recent advances in strategies to make nitrifying biofilms more tolerant to salinity variations. We also propose directions for future research to improve our understanding of the salinity acclimation mechanisms in nitrifying systems.

Development and performance assessment of an integrated vermifiltration based treatment system for the treatment of feedlot runoff

The objective of this study was to treat feedlot runoff by developing an ecologically sustainable, affordable, and resilient treatment system having a relatively long life span. Three horizontal flow soil biofilters were utilized in this study: 1) without earthworms and plants (Biofilter (BF)), 2) with earthworms only (Vermifilter (VF)), and 3) with earthworms and plants (Macrophyte Assisted Vermifilter (MAVF)). The experiments were conducted with a hydraulic retention time of four days using Lumbricus terestrris earthworms and Carex frankii wetland plants. The average COD removal from the BF, VF, and MAVF were 23.2–30.4%, 61.4–69.1%, and 68.3–78.1%, respectively. Average TN removal efficiencies for BF, VF, and MAVF were 15.5–21.4%, 34.4–38.8%, and 39.1–44.0%, respectively. Additionally, average TP removals for BF, VF, and MAVF were 31.9–40.8%, 48.0–54.0%, and 51.1–58.3%, respectively. Comparison of results with literature indicate that the developed system can facilitate more nitrogen removal. Plant roots, along with earthworms, create an aerobic ecosystem within the treatment filter, leading to high organics oxidation and nitrification efficiency among BF, VF, and MAVF. Observational analysis indicates the system with earthworms is prone to clogging while the system with earthworms and plants was less prone to clogging. Thus, it can be concluded that if modularized, the application of MAVF systems can treat feedlot runoffs with higher removal efficiency and expanded life span.

Enhanced nitrogen removal in an anoxic-oxic-anoxic process treating low COD/N tropical wastewater: Low-dissolved oxygen nitrification and utilization of slowly-biodegradable COD for denitrification

Many wastewater treatment plants (WWTPs) operating in biological nitrogen removal activated sludge process in the tropics are facing the pressure of increasingly stringent effluent standards while seeking solutions to reduce the plants' energy consumption and operating cost. This study investigated the feasibility of applying low-dissolved oxygen (low-DO) nitrification and utilizing slowly-biodegradable chemical oxygen demand (sbCOD) for denitrification, which helps to reduce energy usage and operating cost in treating low soluble COD-to-nitrogen tropical wastewater. The tropical wastewater was first characterized using wastewater fractionation and respirometry batch tests. Then, a lab-scale sequencing batch reactor (SBR) was operated to evaluate the long-term stability of low-DO nitrification and utilizing sbCOD for denitrification in an anoxic-oxic (AO) process treating tropical wastewater. The wastewater fractionation experiment revealed that particulate settleable solids (PSS) in the wastewater provided slowly-biodegradable COD (sbCOD), which made up the major part (51 ± 10%) of the total COD. The PSS hydrolysis rate constant at tropical temperature (30 °C) was 2.5 times higher than that at 20 °C, suggesting that sbCOD may be utilized for denitrification. During the SBR operation, high nitrification efficiency (93 ± 6%) was attained at low-DO condition (0.9 ± 0.1 mg O2/L). Utilizing sbCOD for post-anoxic denitrification in the SBR reduced the effluent nitrate concentration. Quantitative polymerase chain reaction, 16S rRNA amplicon sequencing and fluorescence in-situ hybridization revealed that the genus Nitrospira was a dominant nitrifier. 16S rRNA amplicon sequencing result suggested that 50% of the Nitrospira-related operational taxonomic units were affiliated with comammox, which may imply that the low-DO condition and the warm wastewater promoted their growth. The nitrogen removal in a tropical AO process was enhanced by incorporating low-DO nitrification and utilizing sbCOD for post-anoxic denitrification, which contributes to an improved energy sustainability of WWTPs.

Sludge reduction by a micro-aerobic hydrolysis process: A full-scale application and sludge reduction mechanisms

The process performance of a full-scale sludge process reduction activated sludge (SPRAS) system in long-term operation were investigated by inserting a micro-aerobic tank and a clarifier before conventional activated sludge process. The full-scale SPRAS for industrial park wastewater treatment achieved efficient pollutants removal and a low observed sludge yield of 0.074 g SS/g COD. Batch tests showed that influent feeding into the micro-aerobic tank favored sludge reduction, and obtained a sludge decay constant of 0.168 d−1. The SPRAS enriched slow growers and hydrolytic bacteria for sludge reduction, showed high simultaneous nitrification and denitrification efficiency in the micro-aerobic tank with abundant denitrifying bacteria, and improved sludge settleability by enriching floc-forming bacteria. Process configuration of the SPRAS was beneficial to enhance maintenance metabolism, cyclic micro-aerobic and anaerobic uncoupling, and lysis-cryptic growth for sludge reduction. Techno-economic analysis showed that the SPRAS greatly reduced sludge production with small footprint and low cost.

Effect of nitrifiers community on fouling mitigation and nitrification efficiency in a membrane bioreactor

Membrane fouling in membrane bioreactors (MBR) normally depends on the microbial cell density and microbial population structure. A nitrifying-enriched activated sludge (NAS) was obtained in this study through particular ammonium feeding of conventional activated sludge (CAS). Next, the dominance of autotrophic nitrifier population in NAS system was checked and compared with CAS system by its high nitrification efficiency (100% vs. 43%) and low COD removal (9% vs. 65%). Furthermore, the maximum amount of N-NO3− produced from similar concentrations of ammonium in CAS and NAS systems were 6.6 mg/L and 37.5 mg/L, respectively. A filterability test also was done in the cross-flow and simple dead-end filtration systems proportionally employing different amount of NAS and CAS with a constant MLSS concentration of 2000 mg/L. NAS was twice as filterable compared to CAS. Soluble microbial products (SMP) and extracellular polymeric substance (EPS) in CAS were significantly higher than NAS system (2 and 6 mg/L for NAS vs.100 and 36 mg/L for CAS). By increasing the proportion of nitrifying bacteria, the permeation was enhanced remarkably about 2.5 folds and the operation time of MBR was approximately doubled (6–11.5 h). The results indicated that an appropriate C/N ratio can control the microbial population and help the nitrifier significantly mitigate fouling in MBR.

Analysis of the impact of reflux ratio on coupled partial nitrification–anammox for co-treatment of mature landfill leachate and domestic wastewater

A combined system of anaerobic–aerobic techniques was used for deep co-treatment of mature landfill leachate and domestic sewage, mixed at a ratio of 1:5, through partial nitrification–anammox. While ensuring synchronous removal of organic matter and nitrogen, we investigated changes in several factors under different reflux ratios (0%, 100% and 300%). High nitrification efficiency and a relatively high accumulation rate of NO2−-N were achieved, the latter through selective inhibition of bacteria by free ammonia. The results indicated that maintaining the reflux ratio within an optimum range contributes to the enrichment of anammox bacteria. In this study, the optimum ratio, which permitted the highest removal rates of chemical oxygen demand (COD), NH4+-N, and total nitrogen, was 300%. The COD level in the anammox reactor (ANAOR) decreased to lower than 70mg/L, resulting in no inhibitory effect on anammox and maximum enrichment of bacteria.

On‐line monitoring of a BNR process using in situ ammonium and nitrate probes and biomass nitrification‐denitrification rates in an intermittently aerated and pulse fed bioreactor

AbstractBACKGROUNDThe need to monitor and optimize biological nitrogen removal (BNR) processes has led to the use of on‐line instrumentation. In situ located sensors can monitor in a real‐time mode the dynamics of microbial processes, providing the opportunity to understand and optimize process performance.RESULTSA nitrification–denitrification process was monitored on‐line for the first time in an intermittently aerated and pulse fed activated sludge system using in situ located sensors for ammonia and nitrate. Pulse feeding created a reduced C/N ratio gradient across the anoxic phase, resulting in complete denitrification within a period of 20 min. Two denitrification rates were determined, corresponding to nitrate reduction during utilization of the readily biodegradable (0.110–0.246 g g‐1 d‐1) and the slowly (particulate) biodegradable (0.032–0.041 g g‐1 d‐1) COD, respectively. Despite the fact that the initial C/N ratio at both Food/Microorganism ratio (F/M) 0.20 and 0.28 was decreased from 4.8 to 1.8 at the end of the anoxic phase, the C/N ratio decrease was twice as fast at the higher F/M ratio.CONCLUSIONPulse‐feeding resulted in higher C/N ratios at the beginning of the anoxic phase, creating a reduced C/N ratio gradient during the denitrification period. Organic load was mostly consumed during the anoxic phase, resulting in high nitrification efficiency, low oxygen requirement and saving energy. © 2013 Society of Chemical Industry

Pilot-scale verification of efficient nitrifier backseeding in a combined activated sludge-biofilm system

Purpose of the paper is to experimentally verify that a downstream nitrifying fixed-film reactor may effectively backseed an activated sludge (AS) system. The experiment was carried out at the Southpest Wastewater Treatment Plant in Budapest, Hungary, with two pilot-scale AS systems connected directly to the preclarified influent and to the stream recirculated from the nitrifying fixed-film reactor of the full-scale plant ensuring both the nitrate and the backwashed biomass recirculation. Effluent NH 4 -N level dropped down to near zero in the experimental systems whereas no significant nitrification occurred in the fullscale plant being operated at lower aeration intensity. Simulation model developed for describing the combined system supported that backseeding was the cause of the high nitrification efficiency having been limited by inadequate oxygen supply in the full scale system.

Exploring Research on Raschig Rings/Ceramic Double-Packed BAF

A BAF double packed with Raschig rings/ceramic media was developed to determine its pollutants removal efficiency with less frequent backwashing as compared with ordinary BAF. Results showed that a stable operation was achieved during the entire test period and the backwashing cycle time could be extended as well. The COD and SS removals of 57% and 52%, respectively, could be achieved by the Raschig rings packed layer. Nitrifying bacteria accounted for as much as 95% in the ceramic packed layer and ensured high nitrification efficiency with a removal rate of 40.2 gNH4+-N/h•m3. With wastewater pretreatment and backwashing of the packed Raschig rings, the operation cycle of double-packed BAF could be extended to 16 days. In addition, the recovery of treatment performance was fairly rapid after backwashing.

High Rate BAF with Filter Media of Large-Size Lightweight Ceramisite for Micro-Polluted Raw Water Pretreatment

On account of micro-polluted raw water, high rate up-flow biological aerated filter (HUBAF) is used to remove the ammonia nitrogen and micro organic pollutants in raw water. Using ceramisite as filtration media, at a diameter of 6mm to 10 mm, a surface density of above 1g/cm3 and a filtration rate of 16 m/h to 20 m/h, ceramisite layer is in a state of micro expansion, which is beneficial to keep a high nitrification efficiency. On account of raw water where NH3-N is below 4mg/L, NH3-N concentration t can be stabilized at less than 0.5 mg/L in HUBAF effluent. Since lack time of biochemical action, the CODMn removal rate by HUBAF is low. As the effluent of BAF carried abundant amounts of microbes and dissolved oxygen, it increased the CODMn removal rate by 11% in final effluent compared to the individual conventional process of “flocculation-sedimentation-filtration-disinfection”. The turbidity removal efficiency is only the 1/3 of ordinary BAF, which reduces the head loss and energy consumption, and multiple filters to share a centralized aeration system is possible. In addition, HUBAF system is aerated by the single-pore aeration filter heads under the filtration board, equipped with both up-flow and down-flow backwash systems and no need for extra grit chamber, HUBAF is convenient for maintaining and administration.

Molecular indicators of Nitrobacter spp. population and growth activity during an induced inhibition event in a bench scale nitrification reactor

The Nitrobacter spp. ribosomal RNA gene (rDNA) and transcript (rRNAt) abundance were quantified in a bench scale nitrification reactor during baseline periods of high nitrification efficiency and an intervening staged inhibition event. The transcript to gene ratio (rRNAt/rDNA) was highly sensitive to changes in the reactor nitrite oxidation rate. During high nitrification efficiency, the rRNAt/rDNA metric displayed a range from 0.68 to 2.01 with one-sided (α=0.10) lower and upper prediction intervals of 0.70 and 1.78, respectively. When nitrification was inhibited by disabling the reactor pH control system, this activity metric declined an order of magnitude to ∼0.05, well below the lower prediction interval reflecting high nitrification efficiency. The decline was rapid (2h) and preceded a significant drop in reactor nitrification performance, which occurred as ammonia accumulated. The rRNAt/rDNA ratio remained low (∼0.05) for several days after the pH control system was re-enabled at a setpoint of 8.0, which otherwise induced rapid oxidation of accumulated ammonia and produced high free ammonia concentrations. The timing of a subsequent increase in the rRNAt/rDNA ratio, which transiently exceeded the upper prediction interval established during the baseline period of high nitrification efficiency, was not coincidental with resumption of pH control at 7.2 that lowered free ammonia concentrations to non-inhibitory levels. Rather, nitrite oxidation resumed and the rRNAt/rDNA ratio increased only after oxidation of accumulated ammonia was complete, which was coincidental with reduced reactor oxygen demand. In summary, the Nitrobacter rRNAt/rDNA activity metric reflected timely and easily recognizable changes in nitrite oxidation activity, illustrating that molecular data can be used to diagnose poor biological wastewater treatment performance.

Efficient COD removal and nitrification in an upflow microaerobic sludge blanket reactor for domestic wastewater

The treatment performance of an upflow microaerobic sludge blanket reactor (UMSB) for synthetic domestic wastewater was investigated at two dissolved oxygen (DO) levels, 0.3-0.5 and 0.7-0.9 mg l(-1), focusing on nitrification performance. The higher DO level induced complete nitrification of ammonia nitrogen (NH(3)-N), achieving chemical oxygen demand and NH(3)-N removals of 97 and 92%, respectively. There were consistently significantly higher nitrate nitrogen (NO(3)-N) and nitrite nitrogen (NO(2)-N) levels in the effluent, with ~66% of newly-produced oxidised nitrogen as NO(2)-N. Despite the high nitrification efficiency, only about 23% of the removed NH(3)-N amount from the influent was ultimately transformed into oxidised nitrogen due to the simultaneous nitrification-denitrification. Sludge blanket development and granulation occurred simultaneously in the UMSB.

Treatment of farm dairy effluent with hybrid upflow multilayer bioreactor and activated sludge module

Biological removal of nitrogen and carbon from farm dairy effluent (FDE) was studied with two laboratory-scale systems following nitrification and denitrification processes. Each system consisted of an upflow multilayer bioreactor (UMBR) as a pre-denitrification unit, an aeration tank (AT) as nitrification unit and a secondary clarifier. The optimization of two operational variables, total hydraulic retention time (HRT) and internal recycle (IR) rate with both real-FDE and a synthetic-wastewater were investigated. First, HRTs of 2, 3, 4 and 5 days were tested with synthetic-wastewater at uniform IR rate. The HRT of 4 days proved optimum with high efficiencies for nitrification (>90%), denitrification (>90%) and total chemical oxygen demand (COD) removal ( approximately 90%). The lowest efficiency was recorded at 2 days HRT with 7% nitrification efficiency. This was followed by experimentation with IR rates of 200%, 300% and 400% on both real-FDE and synthetic-wastewater at optimized HRT. The increase in IR to 300% improved the denitrification potential and overall performance with continuous high nitrification efficiency and COD removal whereas IR of 400% retarded the process. The application of combined UMBR and activated sludge system showed good potential for biological removal of nitrogen from FDE.

Nitrogen removal from wastewater using a double-biofilm reactor with a continuous-flow method.

Wastewater microorganisms of nitrification and denitrification were cultivated to compose two biofilm modules, termed the permeable support bioreactor (PSB) and the membrane feeding substrate bioreactor (MFSB). PSB and MFSB were combined in a single tank to develop a double-biofilm reactor, which was used to treat nitrogen contaminants in wastewater. With a membrane supplement of substrates (O(2) and CH(3)OH), the D.O. and COD levels were at a low value in the bulk solution thus inhibitive effects between nitrification and denitrification were minimized. Simultaneous nitrification/denitrification was conducted in the reactor and the double-biofilm reactor achieved high nitrification and denitrification efficiency, of 96.5% and 82%, respectively.

Nitrification Utilizing CaCO3 as the Buffering Agent

Nitrification utilizing chalk (calcium carbonate) as the buffering agent was investigated. Three different fluidized bed reactor configurations were examined in order to study the effect of reactor layout on nitrification and concomitant chalk dissolution. The first system consisted of two interconnected columns with high recycle rate, one containing zeolite as the carrier for the nitrifying biomass and the other chalk as the buffering agent. The second reactor system consisted of a single column containing both zeolite and chalk particles. In the third system, nitrification was carried out in a single column where chalk particles were used both as the carrier for the biomass and as the buffer. Results showed that only the reactor with chalk acting as both the buffering agent and the biomass carrier could be operated without external buffer (NaHCO3) addition. This system operated at high ammonium removal rates of up to 2.5 g N l−1 reactor d−1 even though the bulk solution of the reactor had a low pH of 5.5. The high nitrification efficiency at this low pH was probably mainly a result of a favorable microenvironment surrounding the nitrifying biomass attached to the chalk.

生物学的嫌気好気活性汚泥法におけるＮ２Ｏ発生に及ぼすＳＲＴ，ＤＯの影響

Biological anoxic-oxic activated sludge process, which treated domestic wastewater, was investigated to examine the effects of SRT and DO on nitrogen removal and emission of N20, which is causing global warming. The results obtained were as follows: The greater part of N20 emission was observed through nitrification, that amounted to about 4.5 times as that through denitrification. Alternation of SRT or MLSS, to some extent, had no influence on N20 emission through denitrification in anoxic tanks, as far as the nitrogen removal was made effectively under appropriate nitrogen loading. The amount of N20 emitted through nitrification at the run of 10-days SRT reaced about twice as that at the run of 20-days SRT, which led to that enough SRT could suppress N20 emission through nitrification. Besides, keeping high nitrification efficiency was important for suppression of N20 emission. It was clarified that control of carrying DO into the anoxic tank by nitrified water could reduce N20 emission through denitrification in anoxic tanks.

The importance of surface properties in the selection of supports for nitrification in airlift bioreactors

The selection of the supports for biomass immobilisation is of great importance to obtain a stable biofilm leading to a high nitrification efficiency. In this work five type of supports were assayed in external loop air-lift reactors: sand, limestone, basalt, pumice and poraver. The efficiencies of the supports were compared and discussed in terms of their surface-properties: surface free energy of interaction, surface charge, porosity and shape. The results showed that materials leading to low surface free energies of interaction and with less negative surface charges favour bacterial adhesion and the formation of stable biofilms. High porosities are also relevant for bacterial colonisation. However, irregular shaped particles may promote the erosion of attached biomass.

The PEMMC process for land-limited small wastewater-treatment plants

In order to develop a suitable biological-treatment unit component for a prefabricated small wastewater-treatment package plant, a packed-entrapped-mixed microbial cell (PEMMC) process was investigated for settled-screened and anaerobically treated pig wastewaters. It was found that high nitrification efficiency (95–97%) could be achieved at an HRT of 10 h for the anaerobically treated pig wastewater. For settled-screened pig wastewater, an intermittent aeration (1:1 h for aeration and non-aeration) could achieve the removal efficiency of TCOD and T-N of 80·92 ± 3·2% and 89·89 ± 2·2%, respectively, at an HRT of 30 h. The economic analysis indicated that the PEMMC process is comparable with the conventional biological-treatment alternatives for settled domestic sewage. The land cost is lowest for the PEMMC process, but the capital cost is the highest. The net present values for settled domestic sewage (1000 people) and settled-screened pig wastewater (1000 pigs) are US$426114 and US$136248, respectively. Because of its high treatment efficiency for carbon and nitrogen removals and low operation and maintenance costs, the PEMMC process is very suitable for integration into a prefabricated small, packaged plant for wastewater treatment in land-limited applications. Thus, the reuse of treated wastewater from small wastewater-treatment systems may become feasible.