外文原文-卡鲁塞尔氧化沟生活污水处理中同步硝化和反硝化的操作条件的研究.pdf

Study of operational conditions of simultaneous nitrifi cation and denitrifi cation in a Carrousel oxidation ditch for domestic wastewater treatment Yanchen Liu a Hanchang Shia Lan Xiac Huiming Shia Tonggang Shena Zhiqiang Wanga Gan Wang b Yingzhe Wangb aState Key Joint Laboratory of Environment Simulation and Pollution Control Department of Environmental Science and Engineering Tsinghua University Beijing 100084 China bGuozhen Environmental Protection Company Hefei 230088 China cSchool of Chemical and Environmental Engineering China University of Mining and Technology Beijing 100083 China a r t i c l ei n f o Article history Received 7 May 2009 Received in revised form 1 September 2009 Accepted 5 September 2009 Available online 8 October 2009 Keywords Simultaneous nitrifi cation and denitrifi cation Carrousel oxidation ditch Wastewater treatment a b s t r a c t The study on the operational conditions of simultaneous nitrifi cation and denitrifi cation SND in the channel of oxidation ditch OD without the need for a special anoxic tank was carried out based on lab scale and pilot scale experiments using real domestic wastewater The infl uence of sludge loading and component proportion in infl uent temperature hydraulic retention time HRT dissolved oxygen DO and operational mode on SND was investigated The result indicated that the optimal DO ODO of SND occurrence was confi rmed majorly by the sludge loading of infl uent and temperature the high TCOD NH3 N and short HRT can enhance the occurrence of SND A new operational mode was proposed that achieved a higher removal effi ciency of 60 70 for total nitrogen by SND with HRT of 4 6 h and the concentrations of NH3 N and TN in effl uent are less than 5 and 15 mg L respectively 2009 Elsevier Ltd All rights reserved 1 Introduction The removal of nitrogen compounds from wastewater is increasing importance because of the serious eutrophication that has occurred in the surface water bodies of China A new approach for nitrogen removal called SND in time and in space with con stant conditions was reported in recent years Rittman and Lange land 1985 Munch et al 1996 Fuerhacker et al 2000 Holman and Wareham 2005 OD is a situation where SND often has a sig nifi cant impact Hao et al 1997 Gao et al 2006 Usually in the OD the spatial anoxic zones along the ditch are created by adjust ing the aeration at different points and as high internal recycle fl ow subjects mixed liquor to alternating aerobic and anoxic condi tions there exist obvious advantages in performing SND in the ditch The main physical explanation is that SND occurs within micro bial fl ocs as a result of DO concentration gradients arising from dif fusional limitations Puznava et al 2000 In bio fl oc processes the basic concept of SND is to create an oxygen concentration gradient across the micro organism based agglomerates so that both aero bic and anoxic conditions can be established inside a single reactor Under these conditions both the nitrifi ers and denitrifi ers can pre vail in performing their associated biological transformations SND occurs in the micro zones within a biological fl oc in OD and the denitrifi cation should be ascribed to micro anoxic layers in fl ocs Rittman and Langeland 1985 Hao et al 1997 The DO profi les of activated sludge fl oc show that there are anoxic and aerobic zones within the fl oc particles Holley 2003 Li and Bishop 2004 Some previous researches have been conducted to describe the processes of SND inside activated sludge fl oc The concentrations of contaminants in mixed liquor correlate with the oxygen utiliza tion which directly infl uences the oxygen penetration inside the activated sludge fl oc Andreadakis 1993 Holley 2003 Shearing of the fl oc or reducing the fl oc size is believed to be detrimental to the presence of intra particle anoxic zones when reduction in the median fl oc size from 80 to 40lm by high speed blending of the biomass results in a reduction in SND nitrogen removal from 52 to 21 Pochana and Keller 1999 Most previous researches were undertaken to examine the time courses of COD NH3 N and DO during the SND process in SBR Holman and Wareham 2005 and to use those observations to draw inferences about bac terial behavior in the context of microbiological mechanisms in volved in the SND process Helen et al 2003 Panswad et al 2003 Donald et al 2005 However there is an absence of studies on how to create a feasible microenvironment within fl oc for the occurrence of SND in a single OD Many confl icts exist in the conversion activated sludge process of SND such as the consumption of DO in the processes of nitrifi cation and organic substrate metabolism confl ict of requirement of DO concentration of nitrifi cation with denitrifi cation and con sumption of COD in an aerobic zone with the organic substrate re 0960 8524 see front matter 2009 Elsevier Ltd All rights reserved doi 10 1016 j biortech 2009 09 015 Corresponding author Tel 86 10 62773095 fax 86 10 62771472 E mail address hanchang H Shi Bioresource Technology 101 2010 901 906 Contents lists available at ScienceDirect Bioresource Technology journal homepage quired for denitrifi cation The degree of nitrogen removal that can be attributed to anoxic micro zone within fl oc is related to the DO profi le within fl ocs and the transformation of organic substrate across fl ocs vary with the change of the contaminant concentration in mixed liquor The concentration of DO the COD of infl uent total nitrogen loading and HRT are the key factors of change of contam inant concentration in mixed liquor The purpose of this research is to understand the interaction of different control conditions of SND and establish the optimum operational conditions and operational mode for the occurrence of SND to enhance nitrogen removal effi ciency in a single OD reactor A series of experiments was carried out to investigate the infl uence of different control conditions such as DO concentration temperature infl uent sludge loading of ammonia and TCOD HRT and the ratio of TCOD TN on the effi cien cies of nitrogen removal by SND which was intended to determine the conditions and mechanisms affecting SND under the fl uctua tion of infl uent and to pursue the possible technical and new oper ational mode approaches to enhancing nitrogen removal 2 Methods 2 1 Overall performance Two typical Carrousel OD processes are discussed in this study The study on the infl uences of different control conditions on SND was carried out in a lab scale OD The lab scale ditch was built in a laboratory at Tsinghua University the pilot scale ditch was built at WWTP ZhuZJ in Hefei city Fig 1a shows a schematic of the lab scale ditch used in the experiments The lab scale Carrousel OD is a complete mixed reactor with an endless mixed liquor fl ow cir cuit in the channel The horizontal velocity of the fl ow was con trolled at an average 0 06 m s which was previously measured by tracer test in a pure water examination by Particle Doppler Ane mometry Two submerged surface aerators were installed at the ends of the channel The working volume of this lab OD was 102 L length 736 mm width 300 mm depth 350 mm On line detection of DO was done by DO meter YSI 58 the DO regulation was carried out by manual adjustment of rate speed of aerators The feed wastewater was collected from the drainage system of a residential area near Tsinghua University A summary of infl uent is given in Table 1 The pilot scale Carrousel OD was designed to enhance the occurrence of SND under the different inlets of infl uent Fig 1b shows the schematic of the fl ow orientation in the channel and the different mode of infl uent The working volume of this pilot scale Carrousel OD was 117 m3 length 9 5 m width 3 6 m depth 1 1 m On line detection of DO was done by DO meter HACH sc 100 the DO regulation was carried out by manual adjustment of the running scheme and rotating speed of aerators The domestic wastewater was retrieved from the catchment well before pump at Zhu ZJ WWTP in Hefei China The infl uent quantity was relatively constant over a period of a month The characteristics of the waste water are listed in Table 2 The experiment was carried out between September 2006 and December 2007 and the different periods have been characterized by different operating conditions as reported in Table 3 2 2 Analytical methods Sludge samples were immediately centrifuged at 5000 r min for 10 min to remove micro organisms from the liquid medium and tested Daily analyses of COD NH4 N NO3 N NO2 N MLSS MLVSS and sludge volume index SVI were conducted according to the standard methods APHA 1995 Samples for the determina tion of soluble components were immediately fi ltered using 0 45l m fi lter paper and cooled in order to prevent further reaction after sampling The settling ability of the sludge was very good throughout the entire period of operation with the SVI between 54 and 92 ml g This led to a suspended solids concentration in the effl uent of around 4 7 mg L after only 20 min of settling The average MLVSS of the system was 1620 mg L The TCOD removal effi ciency based on the average incoming TCOD concentration of 371 mg L was between 86 and 94 3 Results and discussion 3 1 Infl uence of DO on SND in OD Several studies point out that nitrifi cation and denitrifi cation can occur simultaneously at low DO levels Yoo et al 1999 Jun et al 2003 Trivedi and Heinen 2000 Nitrate produced by nitrifi cation in the aerobic zone can diffuse into the inner anoxic zone along with substrates so that denitrifi cation can occurs within the fl oc depth Of the many factors that are known to affect nitrifi ers DO concentration is one of the most important By contrast the results of different DO concentration in certain loading situations are shown in Fig 2 The results indicated that DO was gradually in creased from 1 0 to 3 0 mg L in lab scale ditch and the effects of DO on nitrifi cation and denitrifi cation were signifi cant The phe nomenon in which the effi ciency of nitrifi cation rapidly increases with the increase of DO in a small range 1 0 1 2 mg L indicated that DO had no effect on the activity of nitrobacteria in the process Hanaki et al 1990a b and the fact that the inhabitation of DO on nitrifi cation was observed may be because of the transformation process of low DO When DO 1 2 mg L the effi ciency of nitrifi ca tion reached almost 100 Although it is reported Wuhrmann 1963 that a DO value of at least 2 0 mg L is essential to maintain complete nitrifi cation in biological wastewater treatment a similar result indicates that a DO value of 1 0 mg L or more appears to be enough for nitrifi cation in the Pasveer OD Hao et al 1997 The observation should be attributed to a low sludge loading The re sult indicates that the fi tting of a low DO range of 1 0 1 2 mg L can ensure the nitrifi cation in OD In general a DO concentration higher than about 0 5 mg L is known to inhibit denitrifi cation Rittman and Langeland 1985 Although the inhibition mechanism is not clear it is well accepted that at a high DO concentration denitrifi ers can switch their elec Nomenclature SND simultaneous nitrifi cation and denitrifi cation HRThydraulic retention time SVIsludge volume index IASL ammonia sludge loading of infl uent ODoxidation ditch ODOoptimal dissolved oxygen LTSLlimit TCOD sludge loading TCODtotal chemical oxygen demand 902Y Liu et al Bioresource Technology 101 2010 901 906 tron acceptors from nitrate to oxygen thereby ceasing to denitrify The effects of DO on the effi ciency of denitrifi cation are shown in Fig 2 The effi ciency of denitrifi cation decreases signifi cantly with the increasing of DO and there is a turning point that indicates the transition of denitrifi cation effi ciency The effi ciency of denitrifi ca tion decreases quickly in the DO range of 1 0 1 2 mg L The result indicated effectively that inhibition of DO on denitrifi cation is more signifi cant in the incomplete nitrifi cation process This phe nomenon should be caused by the higher ratio of degradable COD larger anoxic zone in fl ocs for denitrifi cation in an incomplete nitrifi cation process than in complete nitrifi cation process So range of DO leaded to the incomplete nitrifi cation process is propi tious to occurrence of SND the ODO concentration for the occur rence of SND should be the lowest DO answered for nitrifi cation for which effl uent ammonia concentration can meet the discharge standards Furthermore as lower as possible ODO can enhance the effi ciency of SND due to the confl ict between nitrifi cation and deni trifi cation was smoothed The phenomenon of nitrite accumulation due to incomplete nitrifi cation Hanaki et al 1990a b was not ob served during our experiments 3 2 Infl uence of temperature on SND in OD The effect of the temperature on the effi ciency of nitrifi cation is shown in Fig 3a The results indicated that when the temperature Fig 1 Schematic diagram of Carrousel oxidation ditch a Lab scale and b pilot scale Table 1 Characters of the raw domestic wastewater of the lab scale experiment ParametersRange mg L Typical mg L ParametersRange mg L Typical mg L COD90 500185TP mg L 1 5 6 02 5 BOD535 25080pH6 8 8 37 4 TN15 6035T C 10 2622 NH 4 N 14 5832Alkalinity220 310260 NO 2 N 0 02 1 50 2NO 3 N 0 02 4 51 0 Table 2 Characters of the raw domestic wastewater of the pilot scale experiment ParametersRange mg L Typical mg L ParametersRange mg L Typical mg L COD70 350200TP mg L 0 9 5 03 5 BOD535 18060pH6 7 8 67 6 TN15 4535T C 20 2422 NH 4 N 10 3829Alkalinity210 320260 NO 2 N 0 02 1 20 2NO 3 N 0 02 4 01 6 Table 3 The operation conditions of oxidation ditch ParameterLab scale Pilot scale ParameterLab scale Pilot scale T C 10 2620 24TCOD TN3 114 9 DO mg L 0 5 4 00 2 3 0HRT6 7 9 123 9 5 8 11 7 NH 4 N loading 0 02 0 10 015 0 07MLSS1 42 5 Y Liu et al Bioresource Technology 101 2010 901 906903 slipped below 11 C the nitrifi cation effi ciency decreased sensi tively even the DO is enough to the nitrifi cation In our experi ments it is not implemented still that proposed the high sludge retention time 40 50 d enhance the nitrifi cation capacity at low temperatures Painter 1970 Sharma and Ahlert 1977 Hao et al 1997 Fig 3b shows the effect of temperature 12 C on the ODO of SND and the ODO of SND signifi cantly decreases with the in crease of temperature So the result indicated that the temperature is a key factor on the ODO of SND due to the infl uence of temper ature on the activity of nitrifi es Sharma and Ahlert 1977 That means the relatively high temperatures 12 C can improves the occurrence of SND in a practical OD 3 3 Infl uence of TCOD sludge loading of infl uent on SND in OD As autotrophic nitrifi cation is generally slow in comparison to heterotrophic metabolism so SND requires a degradable organic substrate to provide reducing power for denitrifi cation during the nitrifi cation process Fig 4 shows the infl uence of TCOD sludge loading of infl uent on the nitrifi cation under ODO concentration of SND The result indicated that the effi ciency of nitrifi cation de creases with the increase of TCOD loading especially when the TCOD loading reached the critical value the effi ciency of nitrifi ca tion decreased rapidly This phenomenon could prove the hypoth esis that DO transported from bulk water to the cell of the ammonia oxidizer is excessively consumed by the presence of the crowded cells of heterotrophs which promotes metabolism by the increase of TCOD loading There is a diffusion limitation for the oxygen into the fl oc because of the metabolism of hetero trophs which results in there is a limit TCOD sludge loading LTSL to ensure nitrifi cation following under the ODO following the cer tain ammonia sludge loading of infl uent 3 4 Infl uence of the ammonia sludge loading of infl uent on SND in OD In the aforementioned results the ODO and LTSL to ensure nitri fi cation following the certain ammonia sludge loading of infl uent IASL was shown Fig 5a shows the changes profi le of ODO and LTSL with the IASL The results indicated that the increasing of ODO for SND followed the increasing of the IASL and the ODO in creased with the decreasing of HRT under certain IASL in the ditch The increasing of LTSL for nitrifi cation followed the increasing of IASL and the LTSL increased with the increasing of HRT in the ditch But the ratio of TCOD NH3 N at the condition of LTSL de creased following the increasing of IASL that predicated the decreasing of organic substrate to provide reducing power for denitrifi cation during the SND process These results indicated that the microenvironment of fl ocs which is more suitable for the occurrence of SND would be established depend on the lower IASL in the ditch as the low ODO and high TCOD NH3 N can be achieved in the condition Fig 2 Effect of DO on the effi ciency of SND 99 5 10 10 5 11 11 5 12 12 5 13 13 5 14 0 4 8 12 16 20 24 28 32 NH3 N of effluent removal ratio Temperature C Temperature C NH3 N concentration mg L 0 20 40 60 80 100 removal ratio of NH3 N a b 151923 0 0 0 5 1 0 1 5 2 0 ODO efficiency of nitrification ODO mg L 50 60 70 80 90 100 Efficiency of nitrification Fig 3 Effect of temperature on SND a Effect of temperature on the effi ciency of nitrifi cation and b effect of temperature on the ODO of SND Fig 4 Effect of TCOD sludge loading of infl uent on the nitrifi cation 904Y Liu et al Bioresource Technology 101 2010 901 906 3 5 Infl uence of TCOD NH3 N on SND in OD Fig 5b shows the infl uence of TCOD NH3 N on the effi ciency of denitrifi cation via SND The results indicated that the increased effi ciency of denitrifi cation followed the increasing of TCOD NH3 N when the infl uent TCOD sludge loading was smaller than the LTSL corresponding IASL And the effi ciency of denitrifi cation in lower ammonia loading was higher than in higher ammonia loading at a certain ratio of TCOD NH3 N However the effi ciency of denitrifi cation with shorter HRT w