Impact of COD/N ratio on nitrous oxide emission from microcosm wetlands and their performance in removing nitrogen from wastewater

Constructed wetlands (CWs) are considered to be important sources of nitrous oxide (N₂O). In order to investigate the effect of influent COD/N ratio on N₂O emission and control excess emission from nitrogen removal, free water surface microcosm wetlands were used and fed with different influent. In addition, the transformation of nitrogen was examined for better understanding of the mechanism of N₂O production under different operating COD/N ratios. It was found that N₂O emission and the performance of microcosm wetlands were significantly affected by COD/N ratio of wastewater influent. Strong relationships exist between N₂O production rate and nitrite (r = 0.421, p < 0.01). During denitrification process, DO concentration crucially influences N₂O production rate. An optimal influent COD/N ratio was obtained by adjusting external carbon sources for most effective N₂O emission control and best performance of the CWs in nitrogen removal from wastewater. It is concluded that under the operating condition of COD/N ratio = 5, total N₂O emission is minimum and the microcosm wetland is most effective in wastewater nitrogen removal.     

The Potential of Canna lily for Wastewater Treatment Under Indian Conditions

Low cost treatment of polluted wastewater has become a serious challenge in most of the urban areas of developing countries. The present study was undertaken to investigate the potential of Canna lily towards removal of carbon, nitrogen, and phosphorus from wastewater under sub-tropical conditions. A constructed wetland (CW) cell supporting vegetative layer of Canna lily was used to treat wastewater having high strength of CNP. Removal of biological oxygen demand (BOD₃) and chemical oxygen demand (COD) varied between 69.8–96.4% and 63.6–99.1%, respectively. C. lily could efficiently remove carbon from a difficult to degrade wastewater at COD:BOD ratio of 24.4. Simultaneous reduction in TKN and nitrate pointed to good nitrification rates, and efficient plant assimilation as the dominant nutrient removal mechanism in the present study. Suitable Indian agro-climatic conditions favored plant growth and no evident stress over the Canna plant was observed. High removal rate of 809.8 mg/m²-day for TKN, 15.0 mg/m²-day for nitrate, and 164.2 mg/m²-day for phosphate suggests for a possible use of Canna-based CW for wastewater treatment for small, rural, and remote Indian communities.     

Evaluation of an on-site pilot static granular bed reactor (SGBR) for the treatment of slaughterhouse wastewater

An on-site pilot-scale static granular bed reactor (SGBR) system was evaluated for treating wastewater from a slaughterhouse in Iowa. The study evaluated SGBR reactor suitability for slaughterhose wastewater having high particulate COD concentration (7.9 ± 4.3 g COD/L) at 0.3–1.4 m³/m²/day of the surface loading rates. High organic removal efficiency (over 95% of TSS and VSS removal) was obtained due to the consistent treatability of SGBR system during operation at HRTs of 48, 36, 30, 24, and 20 h. The average effluent TSS, VSS, COD, soluble COD, and BOD₅ concentrations were 84, 71, 301,197, and 87 mg/L, respectively. An effective backwash procedure was performed once every 7–14 days to waste a portion of the accumulated solids in the system. This procedure limited the increase in hydraulic head loss and maintained the system stability. COD removal efficiencies greater than 95% were achieved at organic loading rates ranging from 0.77 to 12.76 kg/m³/day.     

Performance of an anaerobic baffled reactor and hybrid constructed wetland treating high-strength wastewater in Nepal—A model for DEWATS

Centralized wastewater treatment systems require sophisticated technologies and skilled manpower for their operation and maintenance (O&M). These systems have huge construction as well as O&M costs. Therefore, a Decentralized Wastewater Treatment System (DEWATS) rather than a centralized system might be especially beneficial in developing countries. A model for DEWATS is developed in Nepal with Anaerobic Baffled Reactor (ABR) and hybrid Constructed Wetland (CW). The DEWATS treats high-strength wastewater from 80 households (400 PE). This paper summarizes the performance of the DEWATS from July 2006 to August 2007 in the removal efficiencies of TSS, BOD₅, COD, NH₄–N, TP and FC. The ABR is very effective in the removal of organic pollutants and could achieve TSS removal up to 91%, BOD₅ up to 78% and COD up to 77%. The average removal efficiencies of the DEWATS is 96% TSS, 90% BOD₅, 90% COD, 70% NH₄–N, 26% TP and 98% FC.     

Feasibility study of a cyclic anoxic/aerobic two-stage MBR for treating ABS resin manufacturing wastewater

This study investigated the feasibility and the treatment efficiency of a cyclic anoxic/aerobic two-stage MBR for treating polymeric industrial wastewater. The anoxic/aerobic hybrid MBR was operated without sludge withdrawal except sampling during the study. The results showed that the highest COD organic loading rate of 8.7 kg COD/m³ day from bioreactor was obtained at phase 3. The system achieved 97% BOD₅ and 89% COD removal. It also revealed that 93% of COD removal was contributed by bioreactor at phase 3 and the similar results happened to phases 1 and 2. The highest TN and TKN removals for each phase were 60, 74, 80% and 61, 74, 81%, respectively and limited by nitritation step. SEM images of nascent and fouled membranes were offered to evaluate the cleaning method. The system was operated for 174 days, resulting in high degradation rate, flexibility towards influent fluctuations and limited sludge production.     

Treatment of low strength soluble wastewaters in UASB reactors

Low strength wastewaters can be those with chemical oxygen demand (COD) below 2,000 mg/l. The anaerobic treatment of such wastewaters has not been fully explored so far. The suboptimal reaction rates with low substrate concentrations, and the presence of dissolved oxygen in the influent are regarded as possible constraints. In this study, the treatment of low strength soluble wastewaters containing ethanol or whey was studied in lab-scale upflow anaerobic sludged bed (UASB) reactors at 30°C. The high treatment performance obtained demonstrates that UASB reactors are viable for treating both types of wastewaters at low COD concentrations. The treatment of the ethanol containing wastewater resulted in COD removal efficiencies exceeding 95% at organic loading rates (OLR) between 0.3 to 6.8 g COD/l-d with influent concentrations in the range of 422 to 943 mg COD/l. In the case of the more complex whey containing wastewater, COD removal efficiencies exceeded 86% at OLRs up to 3.9 g COD/l·, as long as the COD influent was above 630 mg/l. Lowering the COD influent resulted in decreased efficiency with sharper decrease at values below 200 mg/l. Acidification instead of methanogenesis was found to be the rate limiting step in the COD removal at low concentrations, which was not the case when treating ethanol. The effect of dissolved oxygen in the influent as a potential danger in anaerobic treatment was investigated in reactors fed with and without dissolved oxygen. Compared with the control reactor, the reactor receiving oxygen showed no detrimental effects in the treatment performance. Thus, the presence of dissolved oxygen in dilute wastewaters is expected to be of minor importance in practice.     

The effect of pH on the efficiency of an SBR processing piggery wastewater

To treat piggery wastewater efficiently, the hydrolysis of urea (mainly derived from swine urine) in piggery wastewater with the change of sewage pH must be considered. Using activated sludge, piggery wastewater was treated in a sequencing batch reactor (SBR), and the effects of influent pH on SBR processing efficiency, sludge settle ability, and sludge activity were investigated. The results showed that a high influent pH value contributed to the improvement of the removal rate of ammonia nitrogen and reduction of the chemical oxygen demand (COD). When the influent pH was between 9.0 and 9.5, the removal rate of ammonia nitrogen was higher than 90%, and the reduction of COD from its original value was 80%. The influent pH had a greater influence on sludge concentration and sludge activity. When the influent pH increased from 7.0 to 9.5, the sludge concentration increased from 2,350 to 3,947 mg/L in the reactor, and the activities of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) first increased and then decreased. When the influent pH was 9.0 and 8.0, the maximum values (0.48 g O₂/(g MLSS/day) and 0.080 g O₂/(g MLSS/day)) were reached, and the sludge settling ratio was nearly steady between 20 and 35% in each reactor.     

Enhancement of the activated sludge process by activated carbon produced from surplus biological sludge

Surplus biological sludge from wastewater treatment operations was converted into activated carbon and then added to the aerated vessel of an activated sludge process treating phenol and glucose. The addition of activated carbon, either sludge-based or commercial, enhanced phenol removal from 58 to 98.7% and from 87 to 93% for COD with feed concentrations of 100 mg phenol l^–1 and 2500 mg COD l^–1. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based activated carbon in spite of the higher adsorption capacity of the former.     

Treatment of pig manure liquid digestate in horizontal flow constructed wetlands: Effect of aeration

With the rapid development of scaled anaerobic digestion of pig manure, the generation of liquid anaerobic digestate exceeds the farmland loading capacity, causing serious environmental pollution. Three laboratory‐scale horizontal subsurface flow constructed wetlands (CWs; planted + aeration, planted, and unplanted) were set up to investigate the feasibility of liquid digestate treatment in wetlands. Treatment capacity in different wetlands was evaluated under different influent concentrations (chemical oxygen demand [COD], 5 days biochemical oxygen demand [BOD₅], and nitrogen forms). The effect of aeration and effluent recirculation on organic matter and total nitrogen removal was investigated. Results showed that integrating intermittent aeration in CWs significantly improved the oxygen condition (p < 0.01) in the wetland bed and promoted BOD₅ removal to 90% in aerated CWs as compared with <15% in the unaerated CWs. Meanwhile, COD removal between these three wetlands did not show any difference and varied from 52 to 72% under influent concentration of 200–820 mg/L because of the high content of hard‐degradable organic matter in the liquid digestate. Intermittent aeration resulted in high ammonium removal (>98%) although the influent loading varied from 65 to 350 mg/L. However, intermittent aeration caused nitrate accumulation of 300 mg/L and limited total nitrogen (TN) removal of 33%. To intensify the TN removal, we verified effluent recirculation to increase the removal efficiency of TN to 78%. These results not only show the potential application of CWs for treatment of high‐strength liquid anaerobic digested slurry, but also indicate the significance of intermittent aeration on the enhanced removal of organic matter and ammonium.     

Simultaneous carbon and nitrogen removal using an oxic/anoxic-biocathode microbial fuel cells coupled system

A coupled microbial fuel cell (MFC) system comprising of an oxic-biocathode MFC (O-MFC) and an anoxic-biocathode MFC (A-MFC) was implemented for simultaneous removal of carbon and nitrogen from a synthetic wastewater. The chemical oxygen demand (COD) of the influent was mainly reduced at the anodes of the two MFCs; ammonium was oxidized to nitrate in the O-MFC’s cathode, and nitrate was electrochemically denitrified in the A-MFC’s cathode. The coupled MFC system reached power densities of 14 W/m³ net cathodic compartment (NCC) and 7.2 W/m³ NCC for the O-MFC and the A-MFC, respectively. In addition, the MFC system obtained a maximum COD, NH₄⁺-N and TN removal rate of 98.8%, 97.4% and 97.3%, respectively, at an A-MFC external resistance of 5 Ω, a recirculation ratio (recirculated flow to total influent flow) of 2:1, and an influent flow ratio (O-MFC anode flow to A-MFC anode flow) of 1:1.     

Biodegradation of naphthalene in the oil refinery wastewater by enriched activated sludge

The main purpose of this paper is to study naphthalene (NAP) biodegradation by acclimated activated sludge, employing the culture-enrichment method in a continuous flow bioreactor of the wastewater treatment process. The effects of various COD loadings and influent flow rates of an artificial wastewater containing 15 mg l⁻¹ NAP on the biodegradation rates of the activated sludge will be investigated, in order to determine the biodegradation kinetics and minimum mean cell residence time of the activated sludge. From the experimental results, it was found that the resulting enriched activated sludge follows the growth rate of the Monod type and can biodegrade those COD and NAP loadings in the influents efficiently, and its bio-treatment efficiency on NAPs increases with the decrease of influent flow rate. The sludge volume index (SVI) of the resulting enriched activated sludge meets the design value required by the convectional activated sludge process for the treatment of wastewater.     

Bioremediation of Vegetable Oil and Grease from Polluted Wastewater Using a Sand Biofilm System

Pseudomonas sp. (L1), P. diminuta(L2) were among eight bacterial strains isolated from vegetable grease and oil-contaminated industrial wastewater, four of which only were found to have the ability to degrade oil and grease. They were identified and investigated for oil and grease degradation either individually or in combinations in previous unpublished work by the authors. Since the combination M1 (Pseudomonas sp. andP. diminuta) produced the highest degradative activity, it was used in the present study in a biofilm sand filter system for vegetable oil and grease removal. This system was tested either as one unit or two units in sequence where different flow rates (30, 50, 100 ml/h) were applied compared to a control unit(s). Results showed that both biofilm systems reduced oily wastewater, even in cases of high degree of pollution (fat, oil & grease (FOG), 7535 ppm; biochemical oxygen demand (BOD₅), 525 ppm; chemical oxygen demand (COD), 1660 ppm). Results also showed a removal of FOG with efficiency at 100%; BOD₅ at 95.9% and COD at 96%, at 50 ml/h flow rate using one unit of biofilm system. On using two units in sequence, a complete removal of FOG, BOD₅ and COD with efficiency 100%, at flow rate 100 ml/h was achieved. In conclusion, the previous biofilm results indicated the efficiency of such a system in treating oily polluted wastewater (vegetable oil origin) on the basis of bacterial isolates being used, the optimum flow rate, and the number of biofilm units used in sequence to obtain the highest removal capacity of such a system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollution control in pulp and paper industrial effluents using integrated chemical–biological treatment sequences

The main objective of the present study was to improve the quality of pulp and paper industrial wastewater of two local mills RAKTA and El-Ahlia, Alexandria, Egypt, and to bring their pollutant contents to safe discharge levels. Quality improvement was carried out using integrated chemical and biological treatment approaches after their optimization. Chemical treatment (alum, lime, and ferric chloride) was followed by oxidation using hydrogen peroxide and finally biological treatment using activated sludge (90 min for RAKTA and 60 min for El-Ahlia effluents). Chemical coagulation produced low-quality effluents, while pH adjustment during coagulation treatment did not enhance the quality of the effluents. Maximum removal of the tested pollutants was achieved using the integrated treatment and the pollutants recorded residual concentrations (RCs) of 34.67, 17.33, 0.13, and 0.43 mg/l and 15.0, 11.0, 0.0, and 0.13 mg/l for chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), tannin and lignin, and silica in RAKTA and El-Ahlia effluents, respectively, all of which were below their maximum permissible limits (MPLs) for the safe discharge into water courses. Specific oxygen uptake rate (SOUR) and sludge volume index (SVI) values reflect good conditions and healthy activated sludge. Based on the previous results, optimized conditions were applied as bench scale on the raw effluents of RAKTA and El-Ahlia via the batch chemical and the biological treatment sequences proposed. For RAKTA effluents, the sequence was as follows: (1) coagulation with 375 mg/l FeCl₃, (2) oxidation with 50 mg/l hydrogen peroxide, and (3) biological treatment using activated sludge with 2,000 mg/l initial concentration and 90 min hydraulic retention time (HRT), while for El-Ahlia raw effluents, the sequence was (1) coagulation with 250 mg/l FeCl₃, (2) oxidation with 45 mg/l hydrogen peroxide, and (3) biological treatment using activated sludge with 2,000 mg/l initial concentration and 60 min HRT. In conclusion, results confirmed that the application of the proposed sequential treatments removed almost all COD, BOD₅, high molecular weight compounds, and silica from RAKTA and El-Ahlia influents and produced high-quality effluents, thus achieving the main objective of this study.     

Generating “Tide” in Pilot‐Scale Constructed Wetlands to Enhance Agricultural Wastewater Treatment

The operation of tidal flow was studied using a pilot‐scale system treating high strength piggery wastewater. Located on a farm in Staffordshire, UK, the system consisted of five wetland treatment stages vegetated with common reeds of Phragmites australis. Wastewater samples were collected from the inlet and outlet of each stage and analyzed for BOD₅, COD, NH₄‐N, NO₃‐N, NO₂‐N, SS, PO₄‐P and pH. Average hydraulic and organic loadings on the system were 0.12 m³/m² d and 240 g BOD/m² d, respectively, which is considerably higher than the typical loadings on conventional subsurface flow systems. On average, BOD₅ and COD were reduced by 82 % and 80 % from initial concentrations of 2000 mg/L and 2750 mg/L, respectively, across the whole system. The first‐order kinetics constant for BOD₅ removal (K_BOD in m/d) in this tidal flow system is approximately 2.5 times the rate constant obtainable in a typical horizontal flow system, demonstrating a more efficient removal of organic matter in tidal flow wetlands. The overall efficiency of the system was found to increase with time before stabilizing towards the end of a start‐up period. Straight‐line correlations were established between the loading and removal of BOD₅ and COD. Contributions by individual stages to the overall treatment were analyzed. SEM images of wetland media demonstrated the formation of biofilms and microbial activities inside the matrices of the wetland system, which accounted for the degradations of organic pollutants.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Comparison of biological removal via nitrite with real-time control using aerobic granular sludge and flocculent activated sludge

The process of nitrification–denitrification via nitrite for nitrogen removal under real-time control mode was tested in two laboratory-scale sequencing batch reactors (SBRs) with flocculent activated sludge (R1) and aerobic granular sludge (R2) to compare operational performance and real-time control strategies. The results showed that the average ammonia nitrogen, total inorganic nitrogen (TIN), and chemical oxygen demand (COD) removal during aeration phase were 97.6%, 57.0%, and 90.1% in R2 compared with 98.6%, 48.7%, and 88.1% in R1. The TIN removed in both SBRs was partially due to the presence of simultaneous nitrification–denitrification via nitrite, especially in R2. The specific nitrification and denitrification rates in R2 were 0.0416 mgNH₄⁺–N/gSS-min and 0.1889 mgNO_X⁻–N/gSS-min, which were 1.48 times and 1.35 times that of R1. The higher rates for COD removal, nitrification, and denitrification were achieved in R2 than R1 with similar influent quality. Dissolved oxygen (DO), pH, and oxidization reduction potential, corresponding to nutrient variations, were used as diagnostic parameters to control the organic carbon degradation and nitrification–denitrification via nitrite processes in both SBRs. The online control strategy of granular SBR was similar to that of the SBR with flocculent activated sludge. However, a unique U-type pattern on the DO curve in granular SBR was different from SBR with flocculent activated sludge in aerobic phase.     

Enhanced biological nitrogen removal and N<Subscript>2</Subscript>O emission characteristics of the intermittent aeration activated sludge process

Enhanced biological nitrogen removal processes are necessarily required to cope with more stringent wastewater discharging regulations, especially for wastewater with low level of organic carbon to nitrogen ratios. The intermittent aeration activated sludge process has been received comprehensive attention over the past decades, due to its excellent performance in nitrogen removal and remarkable reduction of energy consumption. Recent advances for this technology was reviewed from aspects of characteristics of system, factors affecting nitrogen removal, nitrous oxide (N₂O) emission and its control, and application of the technology and its operation control. Finally, future development was proposed. In the intermittent aeration activated sludge process, aeration duration should be controlled for adequate nitrification and non-aeration duration should be adequate for complete denitrification, and these would benefit both nitrogen removal and N₂O mitigation. The step feed strategy could be applied to enhance the better utilization of influent organic carbon for nitrogen removal. Dissolved oxygen (DO) and aerobic duration both affected nitrogen removal in particular that via nitrite in the intermittent aeration process. Nitrite should be removed efficiently to avoid a high N₂O emission under both anoxic and aerobic conditions. Intermittent aeration activated sludge process has been applied in the treatment of various wastewaters, such as municipal wastewater, swine wastewater, anaerobic effluents and landfill leachate. For practical application, DO, pH and oxidation–reduction potential could be used as indices for controlling nitrogen removal and N₂O mitigation. Microbial ecology in the intermittent aeration activated sludge process should be specifically focused in future studies.     

Biological treatment of high strength wastewater by fed-batch operation

Biological treatment systems for high strength wastewaters are usually operated in continuous mode such as activated sludge systems. When operated at steady-state, continuous systems result in constant effluent standards. However, in the presence of shock loadings and/or toxic compounds in feed wastewater, system performance drops quite significantly as a result of partial loss of microbial activity. In fed-batch operation, wastewater is fed to the aeration tank with a flow rate determined by effluent standards. In this type of operation, wastewater can be fed to biological oxidation unit intermittently or continuously with a low flow rate without any effluent removal. Feed flow rate is adjusted by measuring COD concentration in the effluent. As a result of intermittent addition of wastewater high COD concentrations and toxic compounds are diluted in large volume of aeration tank and inhibition effects of those compounds are reduced. As a result, biological oxidation of these compounds take place at a much higher rate. In order to show the aforementioned advantage of fed-batch operation, a high strength synthetic wastewater consisting of diluted molasses, urea, KH₂PO₄ and MgSO₄ was treated in an biological aeration tank by fed-batch operation. Organisms used were an active and dominant culture of Zooglea ramigera commonly encountered in activated sludge operations. COD removal kinetics was found to be first order and the rate constant was determined.     

Partial nitrification and nutrient removal in intermittently aerated sequencing batch reactors treating separated digestate liquid after anaerobic digestion of pig manure

The performance of an intermittently aerated sequencing batch reactor (IASBR) technology was investigated in achieving partial nitrification, organic matter removal and nitrogen removal from separated digestate liquid after anaerobic digestion of pig manure. The wastewater had chemical oxygen demand (COD) concentrations of 11,540 ± 860 mg/L, 5-day biochemical oxygen demand (BOD₅) concentrations of 2,900 ± 200 mg/L and total nitrogen (TN) concentrations of 4,041 ± 59 mg/L, with low COD:N ratios (2.9) and BOD₅:COD ratios (0.25). Synthetic wastewater, simulating the separated digestate liquid with similar COD and nitrogen concentrations but BOD₅ of 11,500 ± 100 mg/L, was also treated using the IASBR technology. At a mean organic loading rate of 1.15 kg COD/(m³ d) and a nitrogen loading rate of 0.38 kg N/(m³ d), the COD removal efficiency was 89.8% in the IASBR (IASBR-1) treating digestate liquid and 99% in the IASBR (IASBR-2) treating synthetic wastewater. The IASBR-1 effluent COD was mainly due to inert organic matter and can be further reduced to less than 40 mg/L through coagulation. The partial nitrification efficiency of 71–79% was achieved in the two IASBRs and one cause for the stable long-term partial nitrification was the intermittent aeration strategy. Nitrogen removal efficiencies were 76.5 and 97% in IASBR-1 and IASBR-2, respectively. The high nitrogen removal efficiencies show that the IASBR technology is a promising technology for nitrogen removal from low COD:N ratio wastewaters. The nitrogen balance analysis shows that 59.4 and 74.3% of nitrogen removed was via heterotrophic denitrification in the non-aeration periods in IASBR-1 and IASBR-2, respectively.     

Enhanced aerobic granulation and nitrogen removal by the addition of zeolite powder in a sequencing batch reactor

The aim of this study was to evaluate the impact of zeolite powders on feasibility of rapid aerobic granulation in the column-type sequencing batch reactors. After 90 days' operation, aerobic granular sludge was formed in both reactors by altering influent chemical oxygen demand/nitrogen (COD/N) ratios. R1 with zeolite powders had better removal capabilities of COD and total nitrogen than R2, which was without zeolite powders. Mixed liquor volatile suspended solid concentrations of the two reactors were 7.36 and 5.45 g/L, while sludge volume index (SVI₃₀) values were 34.9 and 47.9 mg/L, respectively. The mean diameters of aerobic granular sludge in the above two reactors were 2.5 and 1.5 mm, respectively. Both reactors achieved the largest simultaneous nitrification and denitrification (SND) efficiency at an influent COD/N ratio of 8; however, R1 exhibited more excellent SND efficiency than R2. The obtained results could provide a novel technique for rapid aerobic granulation and N removal simultaneously, especially when treating nitrogen-rich industrial wastewater.