Simultaneous Nitrification And Denitrification Research Articles

Enhancing the formation of simultaneous nitrification and denitrification (SND) biofilm and nitrogen removal performance using two-units IFFAS process filled with surface-modified carriers

Moving-bed biofilm reactor (MBBR) and integrated floating-film activated sludge (IFFAS) are considered as well-established technologies for simultaneous nitrification and denitrification (SND). However, SND biofilm formation and nutrient removal performance are generally limited by the innate physico-chemical properties of conventional suspended carriers and/or insufficient carbon source available for denitrification. In this study, novel surface-modified carriers were developed via introducing mixed functional materials (natural zeolite, cationic polyquaternium-10, insoluble biodegradable organic polybutylene succinate/bamboo powder) into polyethylene. The modified carrier revealed enhanced hydrophilicity, positive surface charge, higher surface free energy and carbon source slow release capacity. Biofilm growth feature showed that the surface-modification resulted in more biofilm formation and more polysaccharide and protein in extracellular polymeric substances (EPS), which was structural and functional beneficial for substrate capture, transfer and intercellular interactions between nitrifiers and denitrifiers. IFFAS reactor filled with novel modified carriers was upgraded by dividing into two vertical units, where alternate feeding and aeration was conducted to create an anoxic unit to enhance the utilization of influent carbon source for denitrification as well as an aerobic unit to strengthen nitrification. The two-units IFFAS reactor exhibited highly efficient SND performance with TN removal efficiency of 59.9–65.9%, increased by 12.3–13.5% compared with control group. This study proposed an approach towards enhancement of functional biofilm formation and SND performance, and had fascinating potential in actual applications.

Biodegradation of tetramethylammonium chloride wastewater and inorganic nitrogen removal by a mixed culture

The disposal of wastewater containing tetramethylammonium chloride (TMAC) generated from the semiconductor and photoelectric industries is a challenging problem due to the limited information is available regarding its treatability. This study aims to investigate the feasibility of using biological processes to treat TMAC. An activated sludge collected from a lake near the Southern Taiwan Science Park was used. Various operational parameters, including operating temperature, pH conditions and TMAC dosages were evaluated for the optimal condition. Results showed that the activated sludge could successfully degrade TMAC, and subsequently achieve simultaneous nitrification and denitrification (SND) of the nitrogen-containing intermediates under mild conditions (pH at a range of 3–7 and temperature at a range of 20–40 °C). Besides, more than 60% of the nitrogen-containing intermediates were converted into gaseous nitrogen (N2). TMAC biodegradation was found to follow first-order kinetics. The observed rate constant of TMAC biodegradation increased from 0.64 ╳ 10−4 to 9.57 ╳ 10−4 1/min as the concentration of TMAC decreased. In addition, TMAC demethylation was identified as the rate-limiting step of the entire reaction. Major functional organisms of the activated sludge were identified as Mycobacterium, Ochrobactrum and Arthrobacter species which are aerobic and acidophilic strains. This study can be an important reference for future researches attempting to treatment TMAC wastewater by biological processes.

Comparative Study on Advanced Nitrogen Removal of Landfill Leachate Treated by SBR and SBBR

In order to achieve advanced nitrogen removal from landfill leachate without the addition of external carbon sources, a Sequencing Batch Reactor (SBR) and a Sequencing Biofilm Batch Reactor (SBBR) were proposed for the treatment of actual landfill leachate with ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) concentrations of 1000 ± 100 mg/L and 4000 ± 100 mg/L, respectively. The operating modes of both systems are anaerobic–aerobic–anoxic. After 110 days of start-up and biomass acclimation, the effluent COD and the total nitrogen (TN) of the two systems were 650 ± 50 mg/L and 20 ± 10 mg/L, respectively. The removal rates of COD and total nitrogen could reach around 85% and above 95%, respectively. Therefore, advanced nitrogen removal was implemented in landfill leachate without adding any carbon sources. After the two systems were acclimated, nitrogen removing cycles of SBR and SBBR were 24 h and 20 h, respectively. The nitrogen removing efficiency of SBBR was improved by 16.7% in comparison to SBR. In the typical cycle of the two groups of reactors, the nitrification time of the system was the same, which was 5.5 h, indicating that although the fiber filler occupied part of the reactor space, it had no significant impact on the nitrification performance of the system. At the end of aeration, the internal carbon source content of sludge of SBBR was equivalent to that of the SBR system. However, the total nitrogen concentration of SBBR was only 129 mg/L, which is 33.8% lower than that of SBR at 195 mg/L. The main reason was that biofilm enhanced the simultaneous nitrification and denitrification (SND) effect of the system.

Perspectives of intracellular polymers in functional evaluation of the microbes for EBPR

Abstract To substantiate and interpret the performance of the Enhanced Biological Phosphorus Removal (EBPR) processes with simultaneous nitrogen removal in five full-scale sequencing batch reactors (SBR) systems (with or without pre-anoxic/anaerobic selector) across India, conventional microscopic examinations were performed. Regular examining and cyclic behavior evaluation studies specified that these systems worked for EBPR with effectiveness depending on the wastewater quality and operational steadiness. Treatment with Neisser stain for identifying polyphosphates (poly-P) and Sudan black B stain for observing poly-β-hydroxybutyrates (PHB) granules showed that the enriched biomass of the SBR plants was very diverse concerning morphology, residing populations of traditional rod-shaped PAOs, tetrad (or Sarcina-like cells) forming organisms (submitted as TFOs instead of GAOs), diplococci-shaped cells, and staphylococci-like clustered populations (CC), including few filaments which correlate well with biochemical processes undergoing in SBR plants. SBR plants with readily biodegradable chemical oxygen demand (rbCOD) fraction in COD > 16% and rbCOD/TP ∼10–20 in Varanasi, Mumbai, and Gurgaon, respectively, have performed for >20% EBPR (∼77.8%, ∼76.6%, and ∼84.8% TP removal, respectively) as well as >85% Simultaneous Nitrification and Denitrification (SND). This study can open novel dimensions for optimization by relating microscopic observations (qualitative examination) with the processes undergoing in the plants under varied physicochemical parameters.

Simultaneous nitrification, denitrification and electricity recovery of Halomonas strains in single chamber microbial fuel cells for seawater sewage treatment

Simultaneous nitrification and denitrification (SND) by microbial fuel cell (MFC) holds great promise in the nitrogen removal from seawater sewage due to the harvest of electricity and low organic carbon requirement. However, this remains very difficult owing to the inhibition of microbial growth and metabolism by the high salinity. In this work, a halophilic bacterium Halomonas sp. B01 with both exoelectrogenic and SND capability in hypersaline environment was reported. Halomonas sp. B01 was screened from several Halomonas species considering their growth and electricity production abilities. Halomonas sp. B01 generated a high power density of 24.2 mW/m2 (0.61 W/m3) and efficient N removal rate of 93.8% in single chamber MFCs on seawater substrate. The nitrogen removal pathway of Halomonas sp. B01 was demonstrated to include (1) nitrification process coupled with electron-donating to the anode, and (2) denitrification process coupled with electron-accepting from the cathode. The present work represents a successful attempt to accomplish simultaneous SND and electricity production in MFCs by a single halophilic strain, which provides a theoretical and method support for the convenient treatment of seawater sewage.

Pilot-scale study of a structured bed reactor for nitrogen and organic matter removal from sanitary sewage: advances and design challenges

Simultaneous nitrification and denitrification (SND) is a process that can remove both nitrogen and organic matter in a single unit. Several bench-scale studies show that the structured bed reactors (STBR) subjected to recirculation and intermittent aeration have achieved a good performance for SND treating different types of wastewater. Thus, this study took a step forward and evaluated the efficiency and stability of treating domestic sewage in a pilot-scale STBR. COD removal efficiencies higher than 87% were achieved in the whole experimental period. The highest Total-N removal efficiency was approximately 74 ± 7% by adopting a hydraulic retention time (HRT) of 47.2 h and intermittent aeration (2 h aerated and 1 h non-aerated). The setup of the aeration system was an important mechanism to ensure the optimal balance between nitrification and denitrification in a pilot-scale system.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: a nonconventional nitrogen removal pathway in wastewater treatment.

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other micro-organisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

Selection and synthesization of multi–carbon source composites to enhance simultaneous nitrification–denitrification in treating low C/N wastewater

Low carbon/nitrogen ratio (C/N) wastewater is widespread and difficult to treat. To find a resolution to this issue, this study systematically evaluated the constituents of composite solid carbon (i.e., skeletons, carbon sources and crosslinking agents), and proposed a new multi-carbon source composite S1 (MCSC.S1). The effects on nitrogen removal were further determined through a sequencing batch moving bed biofilm reactor (SBMBBR). The results showed that MCSC.S1, which was composed of polyvinyl alcohol-sodium alginate (PVA-SA), corncob + poly (R-β-hydroxybutyrate) (CC + PHB), and H3BO3-4% CaCl2+Na2SO4 had high stability and absorption. With MCSC.S1, total nitrification removal was enhanced by more than 48.56% through releasing carbon and absorbing the attached denitrifying bacteria. In addition, it was found that MCSC.S1 can simulate the simultaneous nitrification and denitrification (SND) process and contribute to 29.85% of the total nitrogen removal. 16S gene-based analysis attributed this supplementary nitrogen removal to the enrichment of nitrification (i.e., Proteobacteria, Actinobacteria and Chloroflexi), denitrification of associated bacteria (i.e., Nitrospirota) in MCSC.S1 added reactor, and the increase in nitrogen recycling associated genes. These findings collectively demonstrate that the new MCSC.S1 could effectively enhance nitrogen removal efficiency in low C/N ratio wastewater.

Study on nitrogen removal mechanism of the micro-pressure double-cycle reactor

To explore the reasons for the excellent denitrification performance of the Micro-pressure double-cycle reactor (MPDR), the nitrogen removal mechanism of the reactor in the treatment of municipal wastewater was studied. Through analysis of flow simulation and dissolved oxygen (DO) distribution, it was determined that the reactor had a macroscopic biochemical reaction environment for simultaneous nitrification and denitrification (SND) because of the special structure of reactor. The result of sewage treatment showed that the average removal rates of COD, NH4+-N, TN, TP were 92.29%, 96.64%, 73.6% and 91.66% respectively, and the SND rate was 60.9%. Dechloromonas, Thermomonas, Micropruina, Tetrasphaera, etc. for nitrogen and phosphorus removal existed in the reactor at the same time to explain the excellent performance of the system. PICRUSt2 showed that the metabolic pathways related to nutrient degradation in the reactor were highly active and the abundance of denitrification functional genes was higher in the central zone and lower in the peripheral zone. The research results not only perfected the basic theory of the reactor, but more importantly, provided theoretical and technical support for the further application of the reactor.

Denitrification performance and mechanism of sequencing batch reactor with a novel iron-polyurethane foam composite carrier

Simultaneous nitrification and denitrification (SND) is a promising denitrification method. But so far, there have been few reports on the SND and denitrification mechanism of the coupled system with sponge iron (SI). In this paper, the denitrification performance of the mono-sludge system (only activated sludge), mono-carrier system (activated sludge + polyurethane foam) and coupled system (activated sludge + polyurethane foam and SI) was investigated. The study found that compared with the mono-sludge system, the TN removal efficiencies of the mono-carrier system and coupled system increased by 24% and 29.2%, respectively. The change of dissolved oxygen in the carrier of the coupled system showed that the time of forming anoxic and anaerobic micro-environment in one cycle decreased continuously until it reached zero. The nitrate-dependent ferric oxidizing bacteria Acidovorax and Aquabacterium appeared in the coupled system. In addition, it was found that the intervention of SI significantly increased the activity of membrane nitrate reductase (NAR). This study provides practical and useful technology for the treatment of domestic sewage.

Simultaneous nitrification and denitrification of hypersaline wastewater by a robust bacterium Halomonas salifodinae from a repeated-batch acclimation

Biotreatment of hypersaline wastewater requires robust strains with high resistance to activity inhibition and even bacterium death, which remains a worldwide challenge. Here Halomonas salifodinae, a simultaneous nitrification and denitrification (SND) bacterium, was isolated by performing repeated-batch acclimation, showing efficient nitrogen removal at 0–15% salinity and low activity inhibition prominently superior to that of other strains such as Pseudomonas sp. and Acinetobacter sp. Community analysis as well as comparison of microbial activity at different salinities revealed an increased relative abundance of halotolerant populations by stimulating their salt tolerance during the repeated-batch process. For single or mixed nitrogen sources at 15% salinity, the SND efficiencies of the isolated strain reached above 95%. The high activities were attributed to the key enzymes AMO and HAO for nitrification as well as NAP and NIR for denitrification. The findings provide a promising acclimation pathway to obtain robust bacteria for biotreatment of hypersaline wastewater.

Efficiency and microbial diversity of aeration solid-phase denitrification process bioaugmented with HN-AD bacteria for the treatment of low C/N wastewater

To evaluate the simultaneous nitrification and denitrification (SND) performance of the aeration solid-phase denitrification (SPD) process and improve the operating efficiency, aeration SPD process using polybutanediol succinate as carbon source was optimized and the process was bioaugmented with heterotrophic nitrification-aerobic denitrification bacteria for the treatment of real wastewater. The results showed that after bioaugmentation, the total nitrogen removal efficiency of the aeration SPD process increased by 50.46 % under condition of dissolved oxygen (DO) 3 mg/L. According to Illumina MiSeq sequencing and correlation analyses, the microbial community can perform SND under the conditions of DO 5 mg and HRT 6 h, but is susceptible to DO. Bioaugmentation mainly affected the carbon source metabolic network with heterotrophic bacteria Methyloversatilis, Thiothrix, and norank_Lentimicrobiaceae as nodes to change the community structure, thereby improving the performance of the functional microbial community. Kyoto Encyclopedia of Genes and Genomes analysis suggested that narB, narG, narH, nirK and narI were the key genes involved in the response to bioaugmentation. This work provides new insights for the application of the SPD process in wastewater treatment.

Occurrence of aerobic denitrifying bacteria in integrated fixed film activated sludge system

Denitrification can be enhanced in the Integrated Fixed Film Activated System (IFAS) system by integrating media into the anoxic or aerobic zone. The simultaneous nitrification and denitrification (SND) in the biofilm layers has been reported in the aerobic zone of the IFAS system. In this study, two IFAS systems with Bioweb® media installed in the anoxic or aerobic reactor were operated in parallel to evaluate both anoxic denitrification or aerobic SND in the biofilm layers enhanced by fixed film media at three different nitrite and nitrate recirculation (NR) ratios of 75%, 100%, and 125%. The results revealed that both IFAS systems achieved the same organic and nitrogen removal efficiencies without statistically significant difference. The NR ratio of 125% enhanced slightly the denitrification in the anoxic zones of both systems. The media increased the anoxic denitrification at the NR ratio of 100%. The SND in the biofilm was found insignificant in both systems. It was evident that suspended-growth microorganisms stored substrates internally in the cells under anoxic conditions due to insufficient retention time. The aerobic denitrifiers including Chryseobacterium sp., Klebsiella pneumonia, and Pseudomonas aeruginosa were abundant in both IFAS systems providing aerobic denitrification with storage products as carbon sources. In summary, the denitrification in the anoxic zone and SND in the biofilm of the aerobic zone, both were enhanced by the fixed film media, did not contribute significantly to the IFAS system for the biological nitrogen removal because of microbial storage products and aerobic denitrification of several aerobic denitrifiers.

Enhancing stability of aerobic granules by microbial selection pressure using height-adjustable influent strategy

Optimizing granules size distribution is critical for both reactor performance and stability. In this research, an optimal size range of 1800 to 3000 μm was proposed regarding mass transfer and granules stability based on granules developed at DO around 8.0 mg L−1 with the feed COD:N:P at 100:5:1. A height-adjustable influent strategy was applied to facilitate the nutrient storage of granules at optimum size range via microbial selective pressure. Results suggested insufficient hydraulic shear stress led to overgrowth of granules size. High abundance of filamentous bacteria (Thiothrix sp.) was observed in oversized granules, which detached and affected the remaining granules, resulting in severe sludge bulking. Strong hydraulic shear stress suppressed uncontrolled growth of granules. However, fewer abundance of simultaneous nitrification and denitrification (SND) bacterium was acquired, which led to unfavored SND effect and total nitrogen (TN) removal efficiency. The height-adjustable influent strategy facilitated the poly-β-hydroxybutyrate (PHB) storage of granules at optimum size range, while limiting the overgrowth of granules size. Additionally, more than 87.51% of total granules situated in optimal sizes range, which led to higher abundance of SND bacterium and higher TN removal efficiency.

Encapsulation of microorganisms for simultaneous nitrification and denitrification in aerobic reactors

A special denitrifying capsule that was designed according to the theory of maldistribution of DO (dissolved oxygen) for simultaneous nitrification and denitrification (SND) in an aerobic reactor was prepared by an encapsulation technique. The morphology of the denitrifying capsule and its SND performance in an aerobic reactor used for treating synthetic low C/N wastewater were systematically investigated. The spherical capsule comprised a porous membrane, denitrifying active sludge and semen litchi powder, which were cohered together by a physical method. Well-shaped pores were distributed in the membrane and the average pore diameter was approximately 0.25 µm. Circular pores were present in the cross section of the membrane, and the thickness of the membrane ranged from 95.0 µm to 120.0 µm. After 7 days of acclimation, the denitrifying capsule showed good SND performance in an aerobic reactor with a DO concentration of 5.09 mg/L. The NH4+-N concentration of 51.09 mg/L was removed completely after 8 h, the effluent dissolved inorganic nitrogen (DIN) concentration decreased to 6.11 mg/L, the SND ratio reached to 91.6% at 6 h, and finally decreased to 2.09 mg/L at 15 h and could also reach 98.91%. The influent of NH4+-N loading had little effect on the nitrogen removal performance. And decreased of air input induced lower hydraulic shearing force compared to reactors with higher DO had a little effect on the diffusion and mass transfer of NO3--N. With this core shell structure denitrifying capsule, it was easy to achieve SND without controlling the DO concentrations at low levels or using intermittent aeration.

Effects of chloramphenicol on the bacterial community structure and simultaneous nitrification and denitrification performance in a sequencing biofilm batch reactor

The effects of chloramphenicol (CAP) on the performance of simultaneous nitrification and denitrification (SND), as well as on the bacterial community, were evaluated in a sequencing biofilm batch reactor (SBBR). The chemical oxygen demand (COD) removal decreased as the CAP concentration increased from 0 to 20 mg/l. But CAP had different effects on nitrification and denitrification: in contrast to continuously inhibiting nitrification, 15 mg/l CAP slightly promoted denitrification. Besides, the specific oxygen utilization rate declined with increasing CAP concentration, and the nitrifying and denitrifying rates initially displayed a trend of decreasing, and then increasing and finally decreasing, with increases in CAP concentration. In addition, the SBBR process exhibited an excellent ability to degrade CAP, especially when its concentration was 20 mg/l. The high-throughput sequencing results indicated that some obvious variations in the bacterial community at different CAP concentrations—in particular relative abundance changes in the dominant bacterial species at the phylum, class and genus levels. Overall, this study reveals that the effects of CAP on the nitrogen (N) removal performance in SBBR, provides a theoretical guide for SBBR treatment of practical wastewater.

Optimizing nitrogen removal in a hybrid oxidation ditch

Wastewater treatment plants are now facing the challenges of high cost, high energy consumption, while effluent quality is relatively poor with total nitrogen concentration exceeding the requirement of reuse. This study investigated the performance of contaminants removal, especially nitrogen by a hybrid oxidation ditch (H-OD) which is based on the theory of integrated fixed-film activated sludge under different control factors. The aeration rate, return ratio and hydraulic loading were controlled at 0.4 m3/h, 100% and 0.55 m3/m3 h, respectively as the optimized control parameter values. Under the optimized conditions, the effluent concentrations of chemical oxygen demand and ammonium were 35.8 mg/L, 1.04 mg/L, respectively, while the suspended solid was below 10 mg/L. The average removal rate of total nitrogen was 72.8%, and simultaneous nitrification and denitrification (SND) was achieved at 42.7%. Besides, when the carbon/nitogen ratio was maintained from 2.12 to 5.56, the complete nitrification and denitrification was obtained. The results showed that the H-OD was suitable for nitrogen removal and SND was very attractive for practical engineering applications.

Heterotrophic nitrification-aerobic denitrification performance in a granular sequencing batch reactor supported by next generation sequencing

Several nitrogen transformation processes occur in wastewater treatment; among them, heterotrophic nitrification-aerobic denitrification (HNAD) has not been adequately quantified. In the present study, a comprehensive analysis of the simultaneous ammonia and organic carbon removal was carried out in an aerobic granular sequencing batch reactor (SBR) operated under feast/famine regime. For this, biological processes, microbial community composition and metabolic pathways were evaluated. Mass balances allowed estimating the ammonia assimilation and simultaneous nitrification and denitrification (SND). Better SND process (55%) was achieved in starvation period involving that denitrification driven by intracellular carbon reserves is more efficiently coupled to the ammonia oxidation with regard to external carbon-driven denitrification. Proton balances and titration monitored the organic carbon and nitrogen removal. High abundance of HNAD bacteria, Diaphorobacter sp. and Flavobacterium sp., and Zoogloea sp. aerobic denitrifier was detected by next generation sequencing (NGS) technology. Bioinformatics analysis predicted enzymes involved in nitrogen transformation pathways present in Phylogenetic investigation PYCRUSt database. Heterotrophic nitrification took place involving detoxification against ammonia. Non-limiting nitrate and high oxygen concentrations were favorable for aerobic denitrifiers. HNAD was the main process responsible for the biological nitrogen removal according to NGS and operational conditions given by high dissolved oxygen and low COD:NO3−-N ratio.

An investigation into the optimal granular sludge size for simultaneous nitrogen and phosphate removal

An aerobic granular sludge (AGS) pilot plant fed with a mixture of acetate amended centrate and secondary effluent was used to investigate the optimal granule size range for simultaneous nitrification and denitrification (SND) and ortho-phosphate removal. The anaerobic phase was mixed to understand how AGS will perform if integrated with a continuous flow activated sludge system that cannot feed the influent through the settled sludge bed. Five different granule size fractions were taken from the pilot (operated at DO setpoint of 2mgO2/L) and each size was subjected to activity tests in a well-controlled lab-scale AGS reactor at four dissolved oxygen (DO) concentrations of 1, 2, 3, and 4 mgO2/L. The size fractions were: 212 – 600 µm, 600 – 1000 µm, 1000 – 1400 µm, 1400 – 2000 µm, and >2000 µm. The smallest size range (212 – 600 µm) had the highest nitrification and phosphate removal rates at DO setpoints from 1 – 3 mgO2/L, which was attributed to the higher aerobic volume fraction in small granules and hence a higher abundance of phosphorus accumulating organisms (PAO) and ammonia oxidizing bacteria (AOB). In comparison, large granules (>1000 µm) had 1.4 – 4.7 times lower ammonia oxidation rates than the smallest size range, which aligned with their lower AOB abundance relative to granule biomass. The granules with the highest anoxic volume fraction had the highest abundance of nitrite reductase genes (nir gene) but did not show the highest specific nitrogen removal rate. Instead, smaller granules (212 – 600 and 600 – 1000 µm), which had a lower nir gene abundance, had the highest specific nitrogen removal rates (1.2 – 3.1 times higher than larger granules) across all DO values except at 4 mgO2/L. At a DO setpoint of 4 mgO2/L, nitrite production by ammonia oxidation (ammonia monooxygenase) exceeded nitrite reduction by nitrite reductase in granules smaller than 1000 µm, in addition, some denitrifying heterotrophs switched to oxygen utilization in deeper layers hence suppressing denitrification activity. At the DO range of 2 – 4 mg/L, granular size had a greater effect on nutrient removal than DO. Therefore, for AGS developed at an average DO setpoint of 2 mgO2/L, selecting for size fractions in the range of 212 – 1000 µm and avoiding DO values higher than 3 mgO2/L can achieve both a higher nitrogen removal capacity and energy savings. This study is the first to investigate the influence of different DO values on SND and biological phosphorus removal performance of different aerobic granular sludge sizes.

The role of clogging in intermittent sand filter (ISF) performance in treating rural wastewater retention pond effluent

Although biofilm growth caused clogging is often considered detrimental to the performance of intermittent sand filters (ISF), the presence of biofilm in ISF is indispensable for wastewater treatment. In this study, the role of biofilm growth clogging in ISF performance is studied by pilot experiments and biokinetic simulation. Both the pilot experiments and the simulation demonstrate that biofilm growth is significantly enhanced in the top layers of ISF and is dominantly comprised of heterotrophs. The clogging development zone was responsible for the majority of organic carbon and NH4+−N removal. Simultaneous nitrification and denitrification (SND) also occurred in the clogging development zone. The development of clogging can also enhance the organic carbon and NH4+−N removals as well as SND. Monte Carlo analysis indicated the lifetime of an ISF is negatively related to influent strength and hydraulic loading rate (HLR), and is more sensitive to influent strength than HLR. Although biofilm clogging is impacted by wastewater strength, HLR increase can send more biological removal burdens to layers below the clogging development zone, and thus negatively impact effluent quality due to reduced hydraulic retention time (HRT) within the ISF. Conservatively managed HLRscan reduce clogging development and limit biological removal burdens within the clogging development zone due to increased HRT. This study highlights the merit of managed biofilm growth in ISF and calls for research on advanced strategies to balance the positive and negative aspects of biofilm growth clogging in ISFs.