Nitrogen removal in multi-stage wastewater treatment plants by using a modified post-denitrification system

Systems in which denitrification follows nitrification (post-denitrification) copy the natural sequence of nitrogen removal. The disadvantage of post-denitrification, however, is that an external carbon source must be added to the denitrification reactor. In the concept discussed in this paper, excess sludge from a high loaded activated sludge plant is used as carbon source and as source of denitrifiers in a three-stage system. The sludge is fed into a anoxic reactor placed in between the nitrification reactor (e.g., trickling filter) and the final clarifier. Two different operation methods were investigated at a pilot-scale system set up at the Ingolstadt wastewater treatment plant Low nitrate effluent values were obtained at high sludge feeding rates, but at the expense of a significant increase in turbidity and NH4-N effluent concentrations. This problem could be solved by a reduction of the sludge feeding rate and by applying intermittent feeding. The effluent turbidity was kept at an acceptable level, but denitrification was relatively slow in progress. To achieve both low effluent turbidity and low nitrate discharge, a combination of pre- and post-denitrification is recommended.     

Modelling of biological nitrogen removal during treatment of piggery wastewater.

During this study, a mathematical model simulating piggery wastewater treatment was developed, with the objective of process optimisation. To achieve this, the effect of temperature and free ammonia concentration on the nitrification rate were experimentally studied using respirometry. The maximum growth rates obtained were higher for ammonium-oxidising biomass than for nitrite-oxidising biomass for the temperatures above 20 degrees C; values at 35 degrees C were equal to 1.9 and 1.35 day(-1), respectively. No inhibition of nitrification was observed for free ammonia concentrations up to 50 mgN/L. Using these data with others experimental data obtained from a pilot-scale reactor to treat piggery wastewater, a model based on a modified version of the ASM1 was developed and calibrated. In order to model the nitrite accumulation observed, the ASM1 model was extended with a two-step nitrification and denitrification including nitrite as intermediate. Finally, the produced model called PiWaT1 demonstrated a good fit with the experimental data. In addition to the temperature, oxygen concentration was identified as an important factor influencing the nitrite accumulation during nitrification. Even if some improvements of the model are still necessary, this model can already be used for process improvement.     

Nitrogen removal from piggery waste using the combined SHARON and ANAMMOX process.

Nitrogen removal in piggery waste was investigated with the combined SHARON-ANAMMOX process. The piggery waste was characterized as strong nitrogenous wastewater with very low C/N ratio. For the preceding SHARON reactor, ammonium nitrogen loading and conversion rates were 0.97 kg NH4-N/m3 reactor/day and 0.73 kg NH4-N/m3 reactor/day, respectively. Alkalinity consumption for ammonium conversion was 8.5 gr bicarbonate utilized per gram ammonium nitrogen converted to NO2-N or NO3-N at steady-states operation. The successive ANAMMOX reactor was fed with the effluent from SHARON reactor. Nitrogen loading and conversion rates were 1.36 kg soluble N/m3 reactor/day and 0.72 kg soluble N/m3 reactor/day, respectively. The average NO2-N/NH4-N removal ratio by ANAMMOX reaction was 2.13. It has been observed that Candidatus "Kuenenia stuttgartiensis" were dominated in the ANAMMOX reactor based on FISH analysis.     

Resource recovery and nitrogen removal from piggery waste using the combined anaerobic processes.

The combined ADEPT (Anaerobic Digestion Elutriated Phased Treatment)- SHARON (Single reactor system High Ammonium Removal Over Nitrite)--ANAMMOX (Anaerobic Ammonium Oxidation) processes were operated for the purpose of resource recovery and nitrogen removal from slurry-type piggery waste. The ADEPT operated at acidogenic loading rates of 3.95 gSCOD/L-day, the SCOD elutriation rate and acid production rate were 5.3 gSCOD/L-day and 3.3 gVFAs(as COD)/L-day, respectively. VS reduction and SCOD reduction by hydrolysis were 13% and 0.19 gSCOD(prod.)/gVS(feeding), respectively. Also, the acid production rate was 0.80 gVFAs/gSCOD(production). In the methanogenic reactor, the gas production rate and methane content were 2.8 L/day (0.3 m3CH4/kgCOD(removal)STP) and 77%, respectively. With these operating condition, the removal of nitrogen and phosphorus were 94.1% as NH4-N (86.5% as TKN) and 87.3% as T-P, respectively.     

High strength nitrogen removal from nightsoil and piggery wastes.

Nightsoil and piggery wastes generally present high strength organics and nitrogen. This study evaluated the nitrogen removal characteristics with the existing and modified nightsoil and piggery waste treatment plants. The existing conventional plants showed 20 to 40% nitrogen removal, but the modification with SBR or MLE process could remove effectively both nitrogen and organics with the minimum COD/TN and alkalinity/TN ratios of 6 and 3.6, respectively. Nitrite nitrification and denitrification rates obtainable at higher nitrogen loads were faster than the rates of nitrate nitrification and denitrification resulting in less reactor volume requirement. However, the higher nitrogen loads increased the organic loads resulting in the reactor temperature inhibiting nitrification. Thus, a combined treatment with anaerobic digestion with the adjustment of influent bypass rates was proposed to reduce the reactor temperature and the external carbon requirement. The biological treatment could discharge about 1,100 mg/L soluble COD and 50 mg/L soluble nitrogen, respectively.     

The removal of residual organic matter from biologically treated swine wastewater using membrane bioreactor process with powdered activated carbon.

The objective of this study was to characterize the mechanisms of the COD removal in the membrane bioreactor (MBR) process with powdered activated carbon (PAC) addition and to determine its optimal operation, for the removal of residual organic matters (ROM) from biologically treated swine wastewater. The MBR process with PAC showed higher removal efficiency of chemical oxygen demand (COD(Mn)) than that without PAC. When the average COD(Mn) concentration of the influent was 217 mg/L, the average COD(Mn) concentration of the permeate from the MBR with PAC was about 41.5 mg/L, indicating an approximate removal efficiency of 81%. On the other hand, the average COD(Mn) concentration of the permeate from the MBR without PAC was 172 mg/L. The PAC dosage estimated to obtain the above removal efficiency was about 0.74 g per litre of influent. Among the total residual organics removed by PAC-added MBR, 46.5% was removed by PAC adsorption, 20.8% by biodegradation, 4.4% by membrane separation, and 9.3% by enhanced microorganism activity. From these results, the MBR process with PAC was considered as a very useful treatment process for the reduction of COD(Mn) in biologically treated swine wastewater.     

Treatment of swine wastewater using MLE process and membrane bio-reactor.

The aim of this study was to develop the optimum integrated treatment system for slurry type swine wastewater through field testing. Although composting and liquid composting are the most desirable processes to treat swine wastewater, inadequate composting has been blamed as critical non-point source pollutants. In the area with limited crop land and grass land, the most feasible method to handle slurry type swine wastewater would be that the solids portion from the solids/liquid separation process is treated by composting and then the liquid portion is treated by a series of wastewater treatment processes, including physicochemical treatment system and biological nutrient removal systems such as the modified Ludzack Ettinger (MLE) process and MLE process coupled with a membrane, to satisfy the different effluent criteria. When using the appropriate solids/liquid separation system, the removal efficiency of SS, COD(Cr), and TKN was 92.4%, 73.6%, and 46.0%, respectively and the amount of bulking agent required for composting and organic loading rate for the following wastewater treatment system can be reduced by 94.8% and 84.7%, respectively. When treating the effluent from solids/liquid separation process by MLE process, the optimal volume fraction for denitrification was 20% of total reactor volume and the optimum ratio of F/M and F(N)/M were increased with increase of C/N ratio. Since the effluent quality of MLE process is not enough to discharge, the DAF process was operated with addition of FeCl3 and cationic polyelectrolyte. The effluent from the DAF process was treated in the MLE process coupled with a crossflow ultrafiltration membrane to satisfy more stringent effluent criteria. When external carbon source is added to keep 6.0 of C/N ratio, the efficiency of denitrification is best. The optimum linear velocity and transmembrane pressure for MBR process was 1.8 m/sec and 2.1 atm, respectively. By addition of external carbon source, nitrogen compounds, especially NOx-N, were considerably removed. And by addition of powdered activated carbon, the removal efficiency of COD(Cr) and COD(Mn) and the membrane flux were increased dramatically.     

ANAMMOX and partial denitritation in anaerobic nitrogen removal from piggery waste.

The anaerobic ammonium removal from a piggery waste with high strength (56 g COD/L and 5 g T-N/L) was investigated using a lab-scale upflow anaerobic sludge bed reactor at a mesophilic condition. Based on the nitrogen and carbon balance in the process, the contribution of autotrophic and heterotrophic organisms was also evaluated in terms of the influent NO2-N/NH4-N ratio (1:0.8 and 1:1.2 for Phase 1 and Phase 2, respectively). The result of this research demonstrates that the anaerobic ammonium removal from the piggery waste, using the UASB reactor, can be performed successfully. Furthermore, it appears that by using granular sludge as the seed biomass, the ANAMMOX reaction can start more quickly. Average nitrogen conversion was 0.59 kg T-N/m3 reactor-day (0.06 kg T-N/kg VSS/day) and 0.66 kg T-N/m3 reactor-day (0.08 kg T-N/kg VSS/day) for Phase 1 and Phase 2. The NO2-N/NH4-N removal ratio by the ANAMMOX was 1.48 and 1.79 for Phase 1 and Phase 2. The higher nitrite contents (about 50%) in the substrate resulted in higher nitrite nitrogen removal by the partial denitritation, as well as the ANAMMOX reaction, implying higher potential of partial denitritation. However, the result reveals that the ANAMMOX reaction was influenced less by the degree of partial denitritation, and the ANAMMOX bacteria did not compete with denitritation bacteria. The colour of the biomass at the bottom of the reactor changed from dark gray to dark red, which was accompanied by an increase in cytochrome content. At the end of the experiment, red-coloured granular sludge with diameter of 1-2 mm at the lower part of the reactor was also observed.     

Comparison of nutrient removal efficiency between pre- and post-denitrification wastewater treatments.

A shortage of organic substances (COD) may cause problems for biological nutrient removal, that is, lower influent COD concentration leads to lower nutrient removal rates. Biological phosphorus removal and denitrification are reactions in which COD is indispensable. As for biological simultaneous nitrogen and phosphorus removal systems, a competition problem of COD utilisation between polyphosphate accumulating organisms (PAOs) and non-polyphosphate-accumulating denitrifiers is not avoided. From the viewpoint of effective utilisation of limited influent COD, denitrifying phosphorus-removing organisms (DN-PAOs) can be effective. In this study, DN-PAOs activities in modified UCT (pre-denitrification process) and DEPHANOX (post-denitrification process) wastewater treatments were compared. In conclusion, the post-denitrification systems can use influent COD more effectively and have higher nutrient removal efficiencies than the conventional pre-denitrification systems.     

Combined anaerobic digestion and biological nitrogen removal for piggery wastewater treatment: a modelling approach

In order to deal with the environmental problems associated with animal production industrialization and at the same time considering energy costs increasing, a piggery wastewater treatment process consisting of combined anaerobic digestion and biological nitrogen removal by activated sludge was developed. This contribution presents a modelling framework in order to optimize this process. Modified versions of the well established ASM1 and ADM1 models have been used. The ADM1 was extended with biological denitrification. pH calculation and liquid gas-transfer were modified to take into account the effect of associated components. Finally, two interfaces (ADMtoASM and ASMtoADM) were built in order to combine both models. These interfaces set up the COD, nitrogen, alkalinity and charge fractionation between both models. However, for the mass balances between both models, some hypotheses were considered and might be evaluated.     

Energy saving processes for nitrogen removal in organic wastewater from food processing industries in Thailand.

Nitrogen removal from organic wastewater is becoming a demand in developed communities. The use of nitrite as intermediate in the treatment of wastewater has been largely ignored, but is actually a relevant energy saving process compared to conventional nitrification/denitrification using nitrate as intermediate. Full-scale results and pilot-scale results using this process are presented. The process needs some additional process considerations and process control to be utilized. Especially under tropical conditions the nitritation process will round easily, and it must be expected that many AS treatment plants in the food industry already produce NO2-N. This uncontrolled nitrogen conversion can be the main cause for sludge bulking problems. It is expected that sludge bulking problems in many cases can be solved just by changing the process control in order to run a more consequent nitritation. Theoretically this process will decrease the oxygen consumption for oxidation by 25% and the use of carbon source for the reduction will be decreased by 40% compared to the conventional process.     

Simultaneous removal of organic and strong nitrogen from sewage in a pilot-scale BNR process supplemented with food waste.

As the sewerage system is incomplete, sewage in Korea lacks easily biodegradable organics for nutrient removal. In this country, about 11,400 tons of food waste of high organic materials is produced daily. Therefore, the potential of food waste as an external carbon source was examined in a pilot-scale BNR (biological nutrient removal) process for a half year. It was found that as the supply of the external carbon increased, the average removal efficiencies of T-N (total nitrogen) and T-P (total phosphorus) increased from 53% and 55% to 97% and 93%, respectively. VFAs (volatile fatty acids) concentration of the external carbon source strongly affected denitrification efficiency and EBPR (enhanced biological phosphorus removal) activity. Biological phosphorus removal was increased to 93% when T-N removal efficiency increased from 78% to 97%. In this study, several kinds of PHAs (poly-hydroxyalkanoates) in cells were observed. The observed PHAs was composed of 37% 3HB (poly-3-hydroxybutyrate), 47% 3HV (poly-3-hydroxyvalerate), 9% 3HH (poly-3-hydroxyhexanoate), 5% 3HO (poly-3-hydroxyoctanoate), and 2% 3HD (poly-3-hydroxydecanoate).     

Fuzzy control of nitrogen removal in predenitrification process using ORP.

In order to meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of nitrogen from wastewater have to be implemented. In the past years, numerous studies have been carried out dealing with the application of fuzzy logic to improve the control of the activated sludge process. In this paper, fuzzy control strategies of predenitrification systems are presented that could lead to better effluent quality and, in parallel, to a reduction of chemicals consumption. Extensive experimental investigations on lab scale plant studies have shown that there was excellent correlation between nitrate concentration and ORP value at the end of the anoxic zone. Results indicated that ORP could be used as an on-line fuzzy control parameter of nitrate recirculation and external carbon addition. The optimal value of ORP to control nitrate recirculation and external carbon addition was - 86 +/- 2 mV and - 90 +/- 2 mV, respectively. The results obtained with real wastewater also showed the good performance and stability of the fuzzy controllers independently from external disturbances. The integrated control structure of nitrate recirculation and external carbon addition in the predenitrification system is also presented.     

Ammonium nitrogen removal from slurry-type swine wastewater by pretreatment using struvite crystallization for nitrogen control of anaerobic digestion.

Precipitation of ammonium together with phosphate and magnesium is a possible alternative for lowering the nitrogen content of wastewater. In this study we examine the removal of ammonium nitrogen and phosphorus from slurry-type swine wastewater containing high concentrations of nutrients by the addition of phosphoric acid along with either calcium oxide or magnesium oxide, which leads to the crystallization of insoluble salts such as hydroxyapatite and struvite. The struvite crystallization method showed a high capacity for the removal of nitrogen when magnesium oxide and phosphoric acid were used as the magnesium and phosphate sources, respectively. When it was applied to swine wastewater containing a high concentration of nitrogen, the injection molar ratio of Mg2+:NH4+:PO4(3-) that gave maximum ammonium nitrogen removal was 3.0:1.0:1.5.     

Nitrogen removal from piggery waste with anaerobic pretreatment.

Aerobic degradation of high strength piggery waste elevated the reactor temperature inhibiting nitrification. This study included anaerobic pretreatment with various influent by-pass rates to control the temperature and to minimize the external carbon requirement for denitrification. To find the optimum operating conditions, both lab-scale AnSBR (anaerobic sequencing batch reactor) and Ax/Ox (anoxic/oxic) SBR were operated at 35 degrees C. The heat energy released from Ax/Ox SBR was assumed to be used for heating the AnSBR, with which the Ax/Ox reactor temperature could successfully be controlled below 40 degrees C. The optimum rates of by-pass were 1.0 for winter, 0.4 for spring/fall and 0.2-0.4 for summer, respectively. Applying the correction factors for the measured AUR2 (nitrite nitrification rate) and AUR (nitrate nitrification) at the predicted temperatures, the required oxic HRTs were computed. The required Ax/Ox HRT ratios were respectively 0.5 for COD/TKN>8, 1.0 for COD/TKN ratio of 5.5-8 and 3.5 for below 5.5. The optimum HRTs were 16 days for AnSBR and 17 days for Ax/Ox SBR with the corrected AUR2.     

活性炭填充三维电极电解法处理氨氮废水研究

针对传统城市污水处理厂冬天出水存在氨氮浓度偏高的问题,采用间歇试验法对活性炭填充三维电极深度去除污水中的氨氮进行了研究。考察了氨氮初始浓度,电流密度,氯离子浓度,p H值等因素对氨氮去除效果的影响。结果表明:氨氮去除速率随着电流密度和氯离子浓度增加而增加,单位氨氮去除能耗随着电流增加而增加,随着氯离子浓度增加而减少。p H值在3.0~9.0范围内对三维电极除氨氮过程影响比较小。实际废水在经过2.5h电解后,氨氮浓度从28.0 mg/L下降至0.3 mg/L,去除率高达99%,可以满足国家污水排放标准一级A要求。     

SH-A节能型生物脱氮工艺处理焦化废水工程实例

采用SH-A节能型生物脱氮工艺处理氨氮含量高、有机物可生化性差的焦化废水。工程处理水量为1600m3/d。进水CODCr约2500mg/L,NH3—N约260mg/L。处理后出水各项指标均达到了《污水综合排放标准》(GB8978—1996)一级标准,其中CODCr≤100mg/L,NH3—N≤15mg/L。     

Model-based evaluation of nitrogen removal in a tannery wastewater treatment plant.

Computer modelling has been used in the last 15 years as a powerful tool for understanding the behaviour of activated sludge wastewater treatment systems. However, computer models are mainly applied for domestic wastewater treatment plants (WWTPs). Application of these types of models to industrial wastewater treatment plants requires a different model structure and an accurate estimation of the kinetics and stoichiometry of the model parameters, which may be different from the ones used for domestic wastewater. Most of these parameters are strongly dependent on the wastewater composition. In this study a modified version of the activated sludge model No. 1 (ASM 1) was used to describe a tannery WWTP. Several biological tests and complementary physical-chemical analyses were performed to characterise the wastewater and sludge composition in the context of activated sludge modelling. The proposed model was calibrated under steady-state conditions and validated under dynamic flow conditions. The model was successfully used to obtain insight into the existing plant performance, possible extension and options for process optimisation. The model illustrated the potential capacity of the plant to achieve full denitrification and to handle a higher hydraulic load. Moreover, the use of a mathematical model as an effective tool in decision making was demonstrated.     

人工湿地处理四环素类抗生素废水时有机碳源的影响

研究了以葡萄糖和乙酸钠为碳源的条件下,垂直流人工湿地对四环素(TC)、土霉素(OTC)和金霉素(CTC)等3种四环素类抗生素(TCs)的去除效果。结果表明,在试验条件下,乙酸钠与葡萄糖两种碳源均能有效促进人工湿地系统对3种TCs的去除;在相同碳源条件下COD质量浓度越高,TCs的去除率越高,当COD质量浓度大于400mg/L时,对3种TCs的去除率均达到90%以上;垂直流人工湿地对TCs的去除过程包括2个阶段:前2 h为湿地基质吸附作用下的快速去除阶段,2~24 h为缓慢去除阶段。乙酸钠与葡萄糖两种碳源对TCs去除率的提高,主要发生在2h之后的第二个阶段,分析认为发生了微生物共代谢作用,促进了湿地系统对基质吸附富集之后的TCs的进一步降解。     

Performance evaluation of SBR treatment for nitrogen removal from tannery wastewater.

Performance of SBR treatment for nitrogen removal from tannery is evaluated for a wide range of wastewater temperature between 7 and 30 degrees C. A pilot-scale SBR unit fed with plain-settled wastewater is operated on site for this purpose. Effective nitrogen removal is sustained by adjustment of the sludge age from 28 to 5 days. Concentration profiles of nitrogen compounds within a selected complete SBR cycle during the steady state operation at different wastewater temperatures and sludge ages are evaluated by model simulation. System performance is also interpreted in terms of modeling and stoichiometric calculation. Additional nitrate loss was observed during aerobic period when the aeration intensity was reduced by the factor of 50%.