Total Nitrogen Removal Performance Research Articles

Robust biological nitrogen removal by creating multiple tides in a single bed tidal flow constructed wetland

Achieving effective total nitrogen (TN) removal is one of the major challenges faced by constructed wetlands (CWs). To address this issue, multiple “tides” were proposed in a single stage tidal flow constructed wetland (TFCW). With this adoption, exceptional TN removal (85% on average) was achieved under a high nitrogen loading rate (NLR) of around 28gNm−2day−1, which makes the proposed system an adequate option to provide advanced wastewater treatment for peri-urban communities and rural area. It was revealed that the multiple “tides” not only promoted TN removal performance, but also brought more flexibility to TFCWs. Adsorption of NH4+–N onto the wetland medium (during contact period) and regeneration of the adsorption capacity via nitrification (during bed resting) were validated as the key processes for NH4+–N conversion in TFCWs. Moreover, simultaneous nitrification denitrification (SND) was found to be significant during the bed resting period. These findings will provide a new foundation for the design and modeling of nitrogen conversion and oxygen transfer in TFCWs.

Enhanced removal of contaminant using the biological film, anoxic–anaerobic–aerobic and electro-coagulation process applied to high-load sewage treatment

In order to explore a new treatment process applying to decentralized domestic sewage treatment, and enhance removal of total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD), a novel system integrating anoxic–anaerobic–aerobic (reversed A2O) and electro-coagulation (EC) process was studied, and complex biological media (CMB) was used as suspended carrier for biofilm development. In this work, TN, TP and COD removal performance were investigated with consideration of three major factors, hydraulic retention time (HRT), organic loading rate (OLR) and sludge recycle ratio (SRR). Results showed that (1) The optimum HRT was between 8 and 12 h. The removal efficiencies of TN, TP and COD were about 68%, 95% and 95%, respectively. (2) With the increase of OLR, the removal efficiency of TN increased slowly. But it increased first and then declined for COD and TP removal. Their maximum were attained when OLR was 1.8 g(COD)/(L d), and they were 96% and 93%, respectively. (3) The optimum SRR was 75%. The COD, TN and TP removal efficiencies were about 95%, 72% and 98%, respectively. In this system, the maximum TN and COD removal were achieved in anoxic tank, but it was achieved in aerobic tank for TP removal. The EC bed enhanced the effluent quality, especially the efficiency in advanced P removal. From these results, it was concluded that the new process could be a reliable option for providing excellent effluent quality.

Contaminant removal performances on domestic sewage using modified anoxic/anaerobic/oxic process and micro-electrolysis

The objective of this study was to enhance removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) from domestic sewage in a sequencing batch reactor with added new materials. A modified anoxic/anaerobic/oxic (MAAO) process, integrating a micro-electrolysis (ME) bed in an anoxic tank, and complex biological media (CBM) in anoxic, anaerobic and oxic tanks to treat domestic sewage, and their performances were investigated. The MAAO system was operated at controlled hydraulic reTENTion time (HRT) of 8 h and mixed liquor recirculation (MLR) at 75%. The results showed that the MAAO system could effectively remove COD, TN and TP with average rates of 93%, 80% and 94%, respectively, in March, and 94%, 76% and 91%, respectively, in August. In this system, TP was primarily removed from the anoxic tank regardless of the operational conditions; removal contribution ratios to TP of the anoxic tank reached 56% both in March and August, indicating that the ME bed can effectively enhance phosphorus removal. TN was primarily removed from the anoxic and anaerobic tanks; removal contribution ratios to TN of anoxic and anaerobic tanks reached 36–38% and 37–38%, respectively. The oxic tank had the highest share of COD removal (56% both in March and August) in the removal of phosphorus. The outflow concentrations of COD, TN and TP were 3–46, 7–14 and 0.3–0.5 mg/L, respectively, in March, and 26–49, 9–15 and 0.04–0.1 mg/L, respectively, in August. COD and TN removal performances indicated that the innovative materials of the ME bed and CBM can effectively enhance COD and TN removal.

High Rate Nitrogen Removal in an Alum Sludge-Based Intermittent Aeration Constructed Wetland

A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m(-2) d(-1). This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3-6 mg L(-1)) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.

Evaluation of a novel oxidation ditch system with dual DO control technology for biological nutrient removal by mass balance analysis

A novel pilot-scale oxidation ditch (OD) system with an anaerobic tank and dual dissolved oxygen (DO) control technology was used to treat raw domestic wastewater during 310 days of operation. Three intensive sampling sessions indicated that the dual DO control technology could create stable aerobic and anoxic zones along the main ditch, even with large influent fluctuations. Dramatic total nitrogen (TN), total COD, and total phosphorus removal efficiencies were achieved within ranges of 78–90%, 83–91%, and 69–82%, respectively. June nitrogen balance results revealed that 60% of influent TN was denitrified and that 92% denitrification occurred in the main OD, demonstrating the advantage of the dual DO controls. In addition, COD balance values showed that 67% of the mineralized COD was due to denitrification, and aerobic oxidation was minimized. With lower influent BOD/N ratios of 4.0–4.7, significant TN removal performances were obtained in this OD system. Maximizing COD for denitrification and minimizing aerobic degradation suggest that this novel OD system shows promise for highly effective sewage treatment with effective COD consumption.

Simultaneous Bioenergy (CH4) Production and Nitrogen Removal in a Combined Upflow Anaerobic Sludge Blanket and Aerobic Membrane Bioreactor

In this study, the effect of the aeration rate on simultaneous methanogenesis and denitrification was investigated in a combined system consisting of an oxygen-limited upflow anaerobic sludge blanket (UASB) and aerobic membrane bioreactor (MBR). Different oxygen concentrations in the UASB were achieved by recycling the mixed liquor of the aerobic MBR into the bottom of the UASB. The dissolved oxygen (DO) of the aerobic MBR mixed liquor was determined by the aeration rate in the aerobic MBR. Quantitative analysis of biogas production and composition and total organic carbon (TOC) and total nitrogen (TN) removal performances at different aeration rates in the aerobic MBR were carried out. Results showed that TOC and TN removal performances were improved in the combined system compared to a strictly anaerobic UASB. TOC removal efficiency up to 98% after membrane filtration was achieved. TN removal efficiency was related to the aeration rate in the aerobic MBR, which was limited by the nitrification efficiency at a low aeration rate and improved at aeration rates above 2.5 L/min. Biogas production and composition were also investigated. Results showed that a low DO concentration and degradation of NO x - -N through the denitrification process did not affect the methane production. A slight increase in methane production because of the improvement in the TOC removal rate and decrease of CO 2 at a low aeration rate was observed. However, methane production and the ratio decreased at a high aeration rate as a result of more nitrogen and CO 2 being produced via the processes of denitrification and oxidation, respectively. In this study, above 50% methane in the biogas and 80% TN and 98% TOC removal efficiencies at the aeration rates between 2.5 and 5.0 L/min in the aerobic MBR could be successfully achieved. On the basis of these results, it was suggested that simultaneous methanogenesis and denitrification could be employed as a bioenergy production technology using a combined UASB and aerobic MBR.

火力発電所復水脱塩装置再生廃水からの生物学的窒素除去

We developed an effective biological treatment process for ammonia-rich inorganic industrial wastewater such as wastewater discharged from demineralizer regenerating process in the power plant. In continuous nitrification experiment with completely mixed three-phase fluidized bed reactor filled with cement ball as carriers, 50 μm thick biofilms composed of nitrifying bacteria were obtained. In addition, nitrification rate was successfully improved mainly due to acclimation of nitrifying bacteria to higher loading by gradual reduction of hydraulic retention time. Final nitrification rate reached 0.33 kg-N/m3/day. In denitrification batch test, the optimum amount of methanol as carbon source for denitrification process was determined to be the C/N ratio of 1.7. Total nitrogen removal performances in the aerobic-anaerobic configuration and the anaerobic-aerobic circulation configuration were compared. As a result, the aerobic-anaerobic configuration showed better nitrogen removal performance, which achieved the effluent T-N below 10g/m3. Finally, 13 kinds of nitrifying bacterial colonies were isolated from the aerobic reactor of aerobic-anaerobic configuration, two of which showed higher nitrification ability.