Interrelationship of DOC Distribution in Metabolic Network to Growth Yield in Batch Culture

Oxidative assimilation of dissolved organic carbon (DOC) includes the interrelated processes of catabolism and anabolism. It has been demonstrated that energy uncoupling is a dominant characteristic of substrate-sufficient batch culture. However, the interrelationship of DOC distribution between catabolism and anabolism to the observed growth yield (Yobs) has not yet been clear for substrate-sufficient batch cultures. In this study, the DOC distribution between catabolism and anabolism was described using a ratio of the DOC channeled into carbon dioxide (SCO2) to the DOC converted into biomass (Sg). Based on a balanced oxidative reaction of DOC, a SCO2∕Sg-dependent Yobs model was developed for substrate-sufficient batch culture, and was verified with experimental and literature data. The model showed a reducing trend of growth yield an increasing SCO2∕Sg ratio. It appears that the imbalance between catabolism and anabolism induced by substrate excess leads to non-growth-associated DOC consumption, which is responsible for the observed reduction of Yobs under substrate-sufficient conditions.     

Intracellular Polymers in Aerobic Sludge of Sequencing Batch Reactors

The formation and characteristics of intracellular polymers in aerobic sludge of sequencing batch reactors were investigated at ambient temperature under balanced nutrient conditions. Three substrates of different chemical natures, including fatty acid (acetate), carbohydrate (glucose), and aromatic (benzoate), were fed to individual reactors. When substrates were initially in excess, the sludge in all reactors was capable of converting soluble substrates into intracellular polymers under aerobic conditions. Acetate (up to 27%) and benzoate (up to 51%) were converted to poly-β-hydroxybutyrate, whereas glucose (up to 33%) was converted to intracellular carbohydrates. The initial substrate depletion rates were 208–243 mg-C∕g-VSS∕h for acetate, 491–590 mg-C∕g-VSS∕h for benzoate, and 405–558 mg-C∕g-VSS∕h for glucose. When external substrates were absent in the mixed liquor, the intracellular polymers could be consumed by the sludge for endogenous respiration under aerobic conditions or as a carbon source for denitrification under anoxic conditions. These results suggest a dynamic metabolic mechanism in the sequencing batch reactors.     

Methanogenic Characteristics of Formate-Utilizing Sludge

The formate-utilizing sludge was first enriched in a chemostat reactor for over 90 days; at steady state, the sludge yield averaged 0.066 mg volatile suspended solids (VSS)∕mg chemical oxygen demand (COD). The methanogenic characteristics of this sludge were then investigated in three series of batch experiments at 37°C using formate, acetate, and H2∕CO2, individually, as substrates. At pH 6.4–8.0, the formate-degrading rate averaged 0.76 mg∕mg VSS∕h (6.35 mg COD∕mg VSS∕d). At pH 3.0, the sludge completely lost its bioactivity, and required a lengthy recovery period to regain a fraction of its bioactivity after the pH was adjusted to pH 7.1. The sludge was also able to utilize H2∕CO2 as substrate at an average rate of 0.0167 mg H2∕mg VSS∕h (3.21 mg COD∕mg VSS∕d). At pH ≤ 8.0, the sludge degraded acetate at a very low rate of 3.0 μg∕mg VSS∕h (0.077 mg COD∕mg VSS∕d). The sludge exhibited a slight homoacetogenic activity at pH > 8.0 using formate as substrate; the homoacetogenic reaction using H2∕CO2 as substrate was thermodynamically infeasible, according to chemical free energy analysis.     

BTX Biodegradation in Activated Sludge under Multiple Redox Conditions

Activated sludge sequencing batch reactors were used to study BTX biodegradation under anoxic (denitrifying), microaerobic, and aerobic conditions. Toluene and m-xylene were biodegraded under denitrifying conditions, and the loss of these compounds correlated with the activity of reducing enzymes that were capable of oxidizing methyl viologen. Although benzene, p-, and o-xylene were recalcitrant under anoxic treatment, all three were biodegraded under microaerobic [<0.2 mg∕L dissolved oxygen (DO)] and nitrate or nitrite (NOx)-supplemented microaerobic conditions. Methyl viologen oxidation potential decreased under all microaerobic conditions while catechol 1,2-dioxygenase (C12O) and catechol 2,3-dioxygenase (C23O) were induced, indicating that the aromatic hydrocarbons were metabolized by aerobic pathways, even in the presence of NOx and in the absence of measurable DO. The degree of C12O and C23O expression under microaerobic conditions was comparable to levels found under aerobic (DO > 4 mg∕L) conditions. Benzene, p-, and o-xylene were biodegraded twice as fast under NOx-supplemented compared to NOx-free microaerobic conditions, and specific biodegradation rates under aerobic and NOx-supplemented microaerobic conditions were comparable. Oxidation reduction potential successfully differentiated between the various electron acceptor conditions and proved to be a sensitive indicator.     

Simultaneous Wastewater Nutrient Removal by a Novel Hybrid Bioprocess

A combined activated sludge–biofilm bioprocess called TNCU-I was developed by adding a rotating biological contactor to the aerobic zone of a traditional A2O process in order to solve the sludge retention time conflict between nitrifiers and phosphate accumulating organisms (PAOs), and the carbon source competition between denitrifiers and PAO. The TNCU-I process shows excellent carbon, nitrogen, and phosphate removal performance when treating synthetic wastewater. The process also achieved a more stable nitrification performance than the A2O process. The specific nitrification rate, the specific anoxic and aerobic phosphate uptake rates, the specific denitrification rate, and the specific anaerobic phosphate release rate were determined by a series of batch experiments. Such data were further analyzed to optimize the volume ratio of the TNCU-I anaerobic, anoxic, and aerobic tanks. The optimized process was also operated to confirm the performance. In addition, both Nitrosospira and Nitrospira were identified in the activated sludge and the rotating biological contactor biofilm by 16S rDNA based biotechnology.     

Effect of Microaerophilic Conditions on Autothermal Thermophilic Aerobic Digestion Process

A pilot-scale, first-stage, autothermal thermophilic aerobic digestion reactor was used to study the effect of microaerophilic conditions on sludge solids destruction, volatile fatty acids (VFA) production, and phosphorus release. For the aeration rates of 0–100 mL∕min and the reactor sludge volume of 72 L, with a primary to secondary sludge ratio of 35:65, the solids destruction efficiency ranged between 19.5 and 23.8%, as measured by total suspended solids (TSS). The maximum increase in VFA concentration (483 mg∕L as acetic acid) occurred at the low airflow rate of 25 mL∕min. The unit VFA production ranged from 0.009 to 0.183 mg of VFA generated∕mg of TSS destroyed, with the dominance of acetic acid. The milligrams of phosphorus released per milligrams of TSS destroyed was from 0.018 to 0.0312, with the maximum measured when no air (nitrogen) was supplied; but the maximum ratio of VFA to PO4 (equal to 8.2) was measured when the air supply was at 25 mL∕min.     

Temperature and SRT Effects on Aerobic Thermophilic Sludge Treatment

Laboratory-scale experiments were conducted to determine optimum sludge residence time (SRT) and temperature of aerobic thermophilic pretreatment (ATP) of mixed sludge (thickened waste activated sludge and primary sludge) to achieve maximum pathogen reduction and best process performance. 4-L laboratory-scale ATP reactors were operated at SRTs of 0.6, 1.0, and 1.5 days and temperatures of 55, 58, 62, and 65°C. ATP at temperatures ≥62°C and SRT ≥0.6 day reduced the feed sludge fecal coliform density from 107 MPN∕g total solids (TS) to <104 MPN∕g TS. Salmonella in the feed sludge was reduced to <1 MPN∕4 g TS from 2 to 18 MPN∕4 g TS by ATP at temperatures ≥55°C and SRT ≥0.6 day. ATP was able to increase sludge volatile acids concentration by 100–200% over the feed sludge volatile acid concentration and to reduce sludge supernatant chemical oxygen demand from 20,000 to 22,000 mg∕L in the feed to 13,000–17,000 mg∕L in the ATP reactor. Volatile solids reduction by ATP increased from 25 to 40% when SRT was increased from 0.6 to 1.5 days, and a 5% increase in volatile solids reduction was seen at SRTs of 0.6, 1.0, and 1.5 days when ATP temperature was increased from 55 to 65°C.     

Copper Removal to PPB Residuals via Iron Coagulants and Biosolids Storage Conditioning

Copper removal to residual parts-per-billion (ppb) levels was achieved in an activated sludge system by employing iron bioflocculation and biosolids storage conditioning. Low copper residuals correlated to an increase in extracellular polysaccharides that were produced by microorganisms within activated sludge. In batch bench-scale tests, supernatant copper levels between 15 and 35 ppb were achieved when employing a coagulant dosage of 15 mg∕L (as Fe) and when allowing 18 to 26 h of biosolids storage conditioning to enhance the production of exopolymers. These copper levels were less than half as much as when neither coagulant nor biosolids storage conditioning was employed. Minimum copper residuals occurred in a pH range from 6.5 to 8.8, and when at least half of the biosolids had been stored for a day. Biosolids that were conditioned under a closed-to-oxygen environment yielded the lowest copper residuals among the bench-scale conditions that were tested, and it also produced the largest amounts of extracellular polysaccharides, as determined by a ruthenium red adsorption method and an india ink method.     

Acetate Limitation and Nitrite Accumulation during Denitrification

Nitrite accumulated in denitrifying activated sludge mixed liquor when the carbon and electron source, acetate, was limited. If acetate was added to obtain a carbon-to-nitrogen (C:N) ratio in the range of 2:1 to 3:1, nitrate was completely consumed at the same rate with no nitrite accumulation, indicating that nitrate concentration controlled the respiration rate as long as sufficient substrate was present. However, when acetate was reduced to a C:N ratio of 1:1, while nitrate continued to be consumed, >50% of the initial nitrate-nitrogen accumulated as nitrite and 29% persisted as nitrite throughout an endogenous denitrification period of 8–9 h. While nitrite accumulated during acetate-limited denitrification, the specific nitrate reduction rate increased significantly compared with the rate when excess acetate was provided as follows: 0.034 mg-NO3-N∕mg-mixed liquid volatile suspended solids∕h versus 0.023 mg-NO3-N∕mg-mixed liquid volatile suspended solids∕h, respectively. This may be explained by nitrate respiration out-competing nitrite respiration for limited acetate electrons. Complete restoration of balanced denitrification and elimination of nitrite accumulation during denitrification required several weeks after the C:N ratio was increased back to 2:1.     

Improved Anaerobic Degradation of Phenol with Supplemental Glucose

In this study, phenol degradation was investigated, with and without glucose as a cosubstrate, in batch and continuous studies. The two 2-L lab upflow anaerobic sludge blanket reactors were operated at a constant hydraulic retention time of 12 h with a gradual stepwise increase in phenol concentration from 105 to 1,260 mg∕L. Batch studies showed that a 1,000-mg∕L glucose supplement provided the fastest phenol removal and sludge acclimation. The effect of the glucose supplement was assessed based on microbial acclimation and granulation, phenol degradation, and resistance to shock loading. The reactor with the 1,000-mg∕L glucose supplement had a shorter start-up and granulation period (4 months, compared to 7 months for the reactor without glucose supplement), larger granule size (2.76 mm, compared to 1.77 mm), and higher phenol removal efficiency under steady-state operation at 6-kg phenol-COD∕L?day (98% compared to 88%). The reactor with the glucose supplement also exhibited a higher resistance to shock load or temperature change and faster recovery than the reactor without a glucose supplement.     

Organic Removal of Anaerobically Treated Leachate by Fenton Coagulation

The leachate from a Hong Kong landfill, containing 15,700 mg∕L of chemical oxygen demand (COD) and 2,260 mg∕L of ammonia nitrogen (NH3–N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37°C. The process on average removed 90.4% of COD with 6.6 days of hydraulic retention at an organic loading rate of 2.37 g of COD∕L?day. The UASB effluent was further treated by the Fenton coagulation process using H2O2 and Fe2+. Under the optimal condition of 200 mg of H2O2∕L and 300 mg of Fe2+∕L and an initial pH of 6.0, 70% of residual COD in the UASB effluent was removed, of which 56% was removed by coagulation∕precipitation and only 14% by free radical oxidation. It is obvious that H2O2 and Fe2+ had a strong synergistic effect on coagulation. The average COD in the final effluent was 447 mg∕L. Removing each gram of COD required 0.28 g of Fe2+ and 0.18 g of H2O2.     

Simultaneous Nitrogen and Phosphorus Removal Using a Double Sludge Switching Sequencing Batch Reactor

A new process using a sequencing batch reactor (SBR) and two smaller sludge hoppers is proposed for the simultaneous removal of phosphorus and nitrogen from wastewater. In the double sludge switching sequencing batch reactor, denitrifying phosphate accumulating bacteria (DPB) sludge and nitrification sludge are transferred to the SBR at different phases instead of flowing wastewater through different reactors. The process was operated with a cycle time of 10.5?h, consisting of DPB sludge filling phase (0.5?h), anaerobic phase I (2.0?h), settling and changing DPB sludge phase (0.5?h), anaerobic phase II (0.5?h), aerobic phase (4.0?h), settling and changing nitrifying sludge phase (0.5?h), and anoxic phase (3.0?h). Results of stable operation showed that the process was very efficient over a range of temperatures varied from 10?to?28°C. The average effluent concentrations and removal efficiencies were as follows: CODCr 28.0?mg/L, 92.1%; BOD5 7.0?mg/L, 95.1%; NH3–N 0.8?mg/L, 98.0%; TN 9.8?mg/L, 76.7%; and TP 0.5?mg/L, 92.3%.     

Effect of Substrate Nitrogen/Chemical Oxygen Demand Ratio on the Formation of Aerobic Granules

The effect of the substrate nitrogen/chemical oxygen demand (N/COD) (mg/mg) ratio on the formation and characteristics of aerobic granules for simultaneous organic removal and nitrification were studied in four sequencing batch reactors operated at different substrate N/COD ratios ranging from 5/100 to 30/100. Results showed that aerobic granules formed at the substrate N/COD ratios studied, and both nitrifying and heterotrophic activities of aerobic granules were governed by the substrate N/COD ratio. The nitrifying activity was significantly enhanced with the increase of the substrate N/COD ratio, while the heterotrophic activity decreased. By determining elemental compositions of aerobic granules cultivated at different substrate N/COD ratios, it was revealed that the cell hydrophobicity was inversely related to the ratio of cell oxygen content to cell carbon content of aerobic granule. The production of extracellular polysaccharides showed a decreasing trend as the substrate N/COD ratio increased. This is probably due to enriched nitrifying population with the high N/COD ratios. This study clearly demonstrated that an aerobic granule-based sequencing batch reactor would have a great potential for simultaneous organic oxidation and nitrification.     

Immobilized-Cell Membrane Bioreactor for High-Strength Phenol Wastewater

An immobilized-cell membrane bioreactor was fabricated to investigate degradation of phenol at high concentrations using Pseudomonas putida American Type Culture Collection 49451. In the case of suspension cultures, P. putida utilized phenol at concentrations below 1,000 mg∕L, but experienced substrate inhibition at higher concentrations. On the other hand, cells immobilized in 25% by weight polysulfone fibers degraded phenol at concentrations above 1,000 mg∕L. At an initial phenol concentration of 1,200 mg∕L, phenol was fully degraded within 95 h in the immobilized system, whereas no cell growth and phenol degradation were observed in the free suspension system at 1,000 mg∕L phenol. In the immobilized system, it was observed that cells diffused from the membranes when phenol concentrations reached noninhibitory levels in a few experiments. In such cases, the time taken for complete degradation was shorter with cell diffusion because suspension cells were responsible for the rapid phenol degradation. Further biodegradation studies at phenol concentrations of 2,000 and 3,500 mg∕L were also performed to evaluate the effectiveness of cell immobilization for delaying the effects of substrate inhibition. Phenol could be completely degraded at both high concentrations.     

Anoxic Biological Phosphorus Uptake∕Release with High∕Low Intracellular Polymers

This study investigates the denitrification∕phosphate uptake and denitrification∕phosphate release characteristics among denitrifying phosphate accumulating organisms (DNPAO), denitrifier, and nondenitrifying phosphate accumulating organisms (non-DNPAO) in a biological nutrient removal process named TNCU-I, using a series of anoxic batch experiments with and without added acetate under high∕low intracellular polymer conditions. The results showed 47% phosphate uptake in the anoxic tank of the TNCU-I process. Additionally, due to the combined attribution of denitrifier and DNPAO, the experiments with both added acetate and phosphate produced higher denitrification rates than experiments with only acetate added. Furthermore, DNPAO contributed 42% of the denitrification reaction. The sludge exhibited simultaneous phosphate uptake and release under anoxic conditions when acetate was added. When no acetate was added, the specific phosphate uptake rate for the high intracellular polymer level was higher than that found at the low intracellular polymer level. Moreover, the phosphate uptake rate of non-DNPAO was observed to be 2.46 times greater than that of the DNPAO. The phosphate uptake per unit polyhydroxyalkanoates (PHA) consumption (γPO4/PHA) for the non-DNPAO was 1.08 times greater than that of DNPAO. Thus, this study demonstrates that the utilization efficiency of PHA by non-DNPAO is not significantly different with the utilization efficiency of PHA by DNPAO.     

Effects of Primary Substrate Concentration on NDMA Transport during Simulated Aquifer Recharge

N-nitrosodimethylamine (NDMA) is known to be highly carcinogenic and is present in drinking water, wastewater, and a variety of foods. Because of its presence in chloraminated water at nanogram per liter concentrations, NDMA has become an emerging issue for reclaimed water which may be used for aquifer recharge or irrigation. This research investigated the fate of NDMA in two soil column systems used to simulate subsurface transport. One column system was operated under aerobic conditions with increasing primary substrate concentration where the biodegradable organic carbon (BDOC) in reclaimed water was used as the primary substrate. The reclaimed water content in the influent was increased from 0 to 25% in the column to increase the BDOC concentration. Negligible NDMA removal was observed at 0% reclaimed water and increasing the primary substrate in the influent resulted in NDMA removal suggesting that biodegradation of NDMA might be a cometabolic process. The effects of redox conditions on NDMA fate was studied by operating a second column system with 100% reclaimed water under anoxic conditions and then changing the conditions to aerobic. It was observed that NDMA removal was similar under both aerobic and anoxic condition, however, much lower effluent concentrations were observed under aerobic conditions. Under anoxic condition, a normalized mass removal rate of 254 ng NDMA/mg DOC was observed which increased to 273-ng NDMA/mg DOC under aerobic conditions. The majority of NDMA and substrate removal occurred in the first of three columns in series column under both aerobic and anoxic conditions. Normalized mass removal rates of NDMA after the first, second, and third columns were 372, 30, and 20 ng NDMA/mg DOC, respectively. Since the majority of dissolved organic carbon was also removed in the first column, NDMA biodegradation was consistent with cometabolic activity. Batch tests verified the biodegradation removal potential of NDMA. Addition of a methylotrophic substrate, methanol and an aromatic substrate, toluene, did not increase NDMA removal.     

Anaerobic Thermophilic/Mesophilic Dual-Stage Sludge Treatment

Conventional anaerobic mesophilic (AnM) digestion coupled with anaerobic thermophilic (AnT) pretreatment (AnTAnM system) and anaerobic thermophilic posttreatment (AnMAnT system) of mixed sludge (thickened waste activated sludge and primary sludge) was investigated. The main objectives were to investigate the ability of AnTAnM and AnMAnT systems to produce a product sludge that can meet Class A sludge requirements and to enhance sludge treatment in terms of volatile solids (VS) destruction, gas production, sludge supernatant chemical oxygen demand (COD) reduction, and sludge dewaterability. Lab-scale AnTAnM and AnMAnT systems were operated at a system sludge residence time of 15 days and temperature of 62°C in AnTAnM and AnMAnT thermophilic reactors. A lab-scale control anaerobic digester was operated at a system sludge residence time of 15 days and temperature of 37°C. The AnTAnM and AnMAnT systems and control achieved VS reductions of >38% (Class A sludge vector attraction reduction requirement). Average VS reductions by the AnTAnM (61%) and AnMAnT (63%) systems were significantly higher than VS reduction by the control (50%). The fecal coliform densities in the AnTAnM and AnMAnT system product sludges were below 1,000 most probable number (MPN) per gram total solids (TS) (Class A sludge fecal coliform density limit) compared to 106 MPN∕g TS in the control product sludge. The product sludge from the AnTAnM and AnMAnT systems and the control anaerobic digester met the Class A sludge Salmonella density limit (<3 MPN∕4 g TS) when fed with feed sludge containing 2–12 MPN∕g TS. Average methane production by the AnTAnM mesophilic digester (0.66 ± 0.10 m3∕kg VS destroyed) was higher than those of the AnMAnT (0.51 ± 0.06 m3∕kg VS destroyed) and the control anaerobic mesophilic digesters (0.52 ± 0.03 m3∕kg VS destroyed). The average supernatant CODs in the AnTAnM system product sludge (10,500 ± 200 mg∕L) and AnMAnT system product sludge (10,200 ± 150 mg∕L) were approximately the same and were significantly lower than the supernatant COD in the control anaerobic digester (14,100 ± 350 mg∕L). All three systems were fed with feed sludge containing an average supernatant COD of 22,500 mg∕L. Dewaterability of the product sludges, measured as time to filter, was 244 and 207 s for AnTAnM and AnMAnT systems, respectively, whereas it was 364 s for the control anaerobic digester product sludge.     

Aerobic Thermophilic and Anaerobic Mesophilic Treatment of Sludge

The objective of this research was to investigate the effectiveness of aerobic thermophilic treatment in enhancing conventional anaerobic mesophilic digestion in terms of pathogen reduction. vector attraction reduction, volatile solids (VS) reduction, gas production, and product sludge dewaterability. Lab-scale two-stage experiments were conducted with the aerobic thermophilic stage as pretreatment (AerTAnM) or as posttreatment (AnMAerT) to mesophilic anaerobic digestion. The lab-scale AerTAnM and AnMAerT systems were operated at system sludge residence times (SRTs) of 15 and 15.5 days, thermophilic reactor temperature = 62°C, and mesophilic reactor temperature = 37°C. The control anaerobic digester was operated at a system SRT of 15 and 15.5 days and temperature = 37°C. The AerTAnM and AnMAerT systems and control anaerobic digester operated at a system SRT of 15 days were able to achieve VS reductions of >38% (Class A sludge vector attraction reduction requirement). The VS reductions by the AerTAnM and AnMAerT systems (～65%) were higher than the VS reduction in the control (～51%) by 14%. The AerTAnM and AnMAerT systems reduced fecal coliform density in the feed sludge from 108 most probable number (MPN) per gram of total solids (TS) to <103 MPN∕g TS (Class A sludge fecal coliform density limit), whereas the control reduced the same feed sludge fecal coliform density to about 106 MPN∕g TS. The AerTAnM and AnMAerT systems and control can reduce Salmonella density in the feed sludge from 5 to 12 MPN∕4 g TS to <1 MPN∕4 g TS. Average methane gas production by the AerTAnM system anaerobic mesophilic digester (0.61 m3∕kg VS destroyed) was higher than those of the AnMAerT system (0.50 m3∕kg VS destroyed) and control (0.52 m3∕kg VS destroyed) anaerobic mesophilic digesters. Average H2S content of the AerTAnM [133 ppm volume-to-volume ratio (v∕v)] system anaerobic thermophilic digester gas was significantly lower than those in gas from the AnMAerT system (249 ppm v∕v) and control (269 ppm v∕v) anaerobic mesophilic digesters. The dewaterabilities of the product sludge (measured as time-to-filter, s) from the AerTAnM system (237 s) and AnMAerT system (203 s) were significantly better than that of the product sludge from the control (346 s).     

Simultaneous Nitrogen and Phosphorus Removal from High-Strength Industrial Wastewater Using Aerobic Granular Sludge

Aerobic granular sludge technology was applied to the simultaneous nitrogen and phosphorus removal from livestock wastewater that contains high concentrations of nitrogen and phosphorus (TN: 650?mg/L; TP: 125?mg/L). A lab-scale sequencing batch reactor was operated in an alternating anaerobic/oxic/anoxic denitrification mode. Granular sludge was first formed using synthetic wastewater. When livestock wastewater was diluted with tap water, the shape and settleability of aerobic granular sludge were maintained even though livestock wastewater contained suspended solids. Simultaneous nitrification, denitrification, and phosphate uptake were observed under an aerobic condition. However, when nondiluted livestock wastewater was used, the diameter of granular sludge and the denitrification efficiency under an oxic condition decreased. When the concentrations of nitrogen and phosphorus in wastewater increased, hydraulic retention time (HRT) increased resulting in a decrease in selection pressure for granular sludge. Therefore, the sustainment of granular sludge was difficult in livestock wastewater treatment. However, by applying a new excess sludge discharge method based on Stokes’ law, the shape of granular sludge was maintained in spite of the long HRT (7.5?days). To select large granular sludge particles, excess sludge was discharged from the upper part of settled sludge because small particles localized there after settling. Finally, excellent nitrogen and phosphorus removal was accomplished in practical livestock wastewater treatment. The effluent concentrations of NH4–N, NOx–N, and PO4–P were <0.1, 1.4, and 1.2?mg/L, respectively.