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Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

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Front Envir Sci Eng    2013, Vol. 7 Issue (1) : 135-142    https://doi.org/10.1007/s11783-012-0454-3
RESEARCH ARTICLE
Practical consideration for design and optimization of the step feed process
Shijian GE(), Yongzhen PENG(), Congcong LU, Shuying WANG
College of Environmental and Energy Engineering, Key Laboratory of Beijing Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China
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Abstract

Based on the anoxic/oxic (A/O) step feed process, a modified University of Cape Town (UCT) step feed process was developed by adding an anaerobic zone and adjusting sludge return pipeline. Performance evaluation of these two types of processes was investigated by optimizing operational parameters, such as the anaerobic/anoxic/oxic volumes, internal recycle ratios, and sludge retention times, for removal of chemical oxygen demanding (COD), nitrogen, and phosphorus. Results showed high removal efficiencies of COD of (85.0±1.7)%, ammonium of (99.7±0.2)%, total nitrogen (TN) of (85.5±1.7)%, phosphorus of (95.1±3.3)%, as well as excellent sludge settleability with average sludge volume index of (83.7±9.5) L·mg-1 in the modified UCT process. Moreover, (61.5±6.0)% of influent COD was efficiently involved in denitrification or phosphorus release process. As much as 35.3% of TN was eliminated through simultaneous nitrification and denitrification process in aerobic zones. In addition, the presence of denitrifying phosphorus accumulating organisms (DNPAOs), accounting for approximately 39.2% of PAOs, was also greatly beneficial to the nitrogen and phosphorus removal. Consequently, the modified UCT step feed process was more attractive for the wastewater treatment plant, because it had extremely competitive advantages such as higher nutrient removal efficiencies, lower energy and dosages consumption, excellent settling sludge and operational assurance.
Keywords step feed      anoxic/oxic (A/O)      University of Cape Town (UCT)      simultaneous nitrification and denitrification (SND)      denitrifying phosphorus removal      biological nutrient removal (BNR)     
Corresponding Author(s): GE Shijian,Email:geshijian1221@126.com; PENG Yongzhen,Email:pyz@bjut.edu.cn   
Issue Date: 01 February 2013
 Cite this article:   
Shijian GE,Yongzhen PENG,Congcong LU, et al. Practical consideration for design and optimization of the step feed process[J]. Front Envir Sci Eng, 2013, 7(1): 135-142.
 URL:  
https://academic.hep.com.cn/fese/EN/10.1007/s11783-012-0454-3
https://academic.hep.com.cn/fese/EN/Y2013/V7/I1/135
Fig.1  Schematic diagrams of step feed process: (a) A/O step feed process; (b) modified UCT step feed process
Fig.1  Schematic diagrams of step feed process: (a) A/O step feed process; (b) modified UCT step feed process
phase I (days 0-64)The A/O step feed process operated during this period. Effects of sludge retention time (SRT, 15-17 days and 10-12 days) and sludge return ratio (R, 75% and 100%) on nutrient removal were investigated in Runs 1-2.
phase II (days 65-267)During this period it was switched into the modified UCT step feed process. Several operational parameters were optimized in Runs 3-7, such as volume of anaerobic/anoxic/oxic zones (17/119/204 L, 25.5/110.5/204 L and 34/102/204 L), SRT (8, 9 and 10 days) and internal recycle ratio (r, 50%, 75% and 100%)
Tab.1  Experimental approach for two types of step feed process under steady-state conditions
Fig.2  Performance of two types of step feed processes: (a) COD; (b) TN; (c) ; (d)
Fig.2  Performance of two types of step feed processes: (a) COD; (b) TN; (c) ; (d)
Fig.3  Effect of types of step feed process on the pollutants removal pathways along the reactor: (a) COD; (b) ; (c) nitrogen
Fig.3  Effect of types of step feed process on the pollutants removal pathways along the reactor: (a) COD; (b) ; (c) nitrogen
parametersremoval efficiency in phase I/%removal efficiency in phase II/%
Run 1Run 2Run 3Run 4Run 5Run 6Run 7
COD83.1±2.182.5±3.584.7±2.782.1±2.984.1±2.285.0±1.783.5±1.5
NH4+-N99.4±0.499.6±0.499.9±0.399.5±0.499.4±0.399.7±0.299.9±0.5
TN75.4±2.675.3±3.981.5±1.082.3±1.382.4±1.085.5±1.785.6±1.9
PO43--P40.7±7.940.2±4.176.7±1.583.1±1.791.2±3.195.1±3.387.0±2.4
Tab.2  Comparisons of pollutant removal efficiencies in two step feed processes
rundenitrification rate in D1/(mg N·g-1VSS·d-1)denitrification rate in D2/(mg N·g-1VSS·d-1)denitrification rate in D3/(mg N·g-1VSS·d-1)average denitrification rate/ (mg N·g-1VSS·d-1)
138.9±5.664.2±15.987.4±16.763.5
249.5±10.871.7±17.081.3±11.267.5
329.2±3.648.0±11.747.0±11.041.4
430.5±3.131.9±10.474.3±14.545.6
528.6±5.950.0±13.260.9±14.646.5
624.3±4.849.0±11.357.3±15.643.5
725.9±5.945.1±7.578.9±11.949.9
Tab.3  Denitrification rates in three anoxic zones during seven steady-state runs
Fig.4  Comparison between phosphorus release and uptake rates of PAOs and DPAOs under aerobic and anoxic conditions at different sampling days: (a) day 4; (b) day 85; (c) day 220; (d) day 264
Fig.4  Comparison between phosphorus release and uptake rates of PAOs and DPAOs under aerobic and anoxic conditions at different sampling days: (a) day 4; (b) day 85; (c) day 220; (d) day 264
Fig.5  Variations of SVI for the sludge of two types of step feed processes
Fig.5  Variations of SVI for the sludge of two types of step feed processes
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