Combined process of sequencing batch reactor activated sludge process and constructed wetland for do

Vol.9 No. 4Joumal of Chongqing University (English Edition) [ISSN 167 1-8224]December 2010,Article ID: 1671-8224(2010)04-021-07Toche this aticl:; WEI Wu-qiang. HE Qiang, Wisaam S. A-Rekabi. Combined process of sequencing batch reactor actvated sludge process and constucted wetandfordomesic wastewater reatmnent MI. J Chongqing Unv: Eng Ed (SSN 17182241 2010, 94): 201-207.Combined process of sequencing batch reactor activatedsludge process and constructed wetland for domesticwastewater treatment*WEI Wu-qiang 1;2+, HE Qiang 2, Wisaam s. Al-Rekabi 31 Environment Engineeing Research and Design Department, China Raiway Siyuan Survey and Design Group Co, Ltd,Wuhan 430000, P. R. China;2 Key Laboratory of Eco environments in Three Gorges Reservoir Region, Ministry of Education, Chongqing 400030, P. R China;3 Ciwil Engineering Depatment, College of Engineering, Basra University, lraqReceived 21 October 2010; received in revised form 23 November 2010achieve the domestic wastewater treatment. Our purpose was to determine the optimum operating parameters of the combinedprocess. The process involved advantages and shortages of SBR and CW. Under normal temperature, the 3rd cycle (SBR'soperation cycle is 8 h: inflow for 1 h, limnited aeration for 3 h, sediment for I h, outflow for 1 b, and idling for 2 h; CW's hydraulicretention time (HRT) is 24.8 h and hydraulic loading is 24.5 m/m2 d) was the best cyclic mode. The effluents can meet thestandard GB/T18921-2002: "The reuse of urban recycling water: water quality standard for scenic environment use". In the 3rdcycle, the eficiency of CW was the maximum, and energy consumption of SBR was the minimum. Under the condition of lowdissolved oxygen, the removing efficiency of chemical oxygen demand (COD) and ammonia was not affected obviously.Simultaneously, nitrification and denitrification phenomena occured and phosphorus was absorbed obviously.Keywords: sequencing batch reactor activated sludge process ; constructed wetland; energy consumption; low dissolved oxygenCLC number. x5Document code: A1 Introductionthem should be concemed [1].By combining sequencing batch reactor (SBR)As water consumption increases sharply, many areasactivated sludge process and constructed wetland (CW),face water shortage now or in the near future. Tothe domestic wastewater treatment can benefit fromovercome the crisis, many measures have beenboth SBR and CW, such as resistance to shock loading,introduced for the effective use of this valuable naturalsludge bulking prevention, flexible automatic control,resource. In this situation, wastewater could besimple operation, easy maintenance, lower energyconsidered as a water resource. However, conventionalconsumption, lower total investment, more green areas,treatment systems focus on treatment rather than reuse.and other advantages [2]. The two technologies canThus the related issues of what kind of wastewatermake up deficiencies for each other, such as highshould be treated, how to treat, and how to transportenergy consumption of SBR, and covering too largearea and easy blocking of CW. Our purpose was todetermine the optimum operating parameters of thetWEI Wu-qiang (魏武强): wwqhn@ip.q.com.combined process.'Funded by Sustainable Water Management Improves Tomorrow'sCity's Health (SWITCH018530).中国煤化工MYHCNMHG201W. Q. Wei, et al.Wastewater treatment2 Experiment procedurein the reactor was 1/2. Discharge volume of each cycleis equal to 0.5 m'. By using intake pump can cary2.1 Characteritics of infuent wastewaterinfluent (wastewater) from primary sedimentation tank(equalization tank) to SBR tank. Flow capacity wasThe quality of wastewater, resulting from the various35 L/min. The wastewater pump start-up and shutdaily uses in students' dormitory of B campus,down by the water level sensor control in the SBR tank.Chongqing University, fluctuated and is influencedAeration was achieved by an aquarium-type air pumplargely by climate changes. For example, during the(the model is ACO-010, and its largest aerationsummer, temperature and humidity in Chongqing citycapacity is 170 L/min) connected with sintered-sandis very high, which lead to increasing consumption ofdiffusers at the bottom of the SBR tank. The sandwater used by students for various daily purposes. Thediffusers firstly were fixed at the height of 0.3 m fromquantity of wastewater would also increase, therefore.the bottom of the tank, but this height was not benefitHowever, the quantity of water consumed by studentsfor the sludge aeration. Therefore, we changed it todecreased in winter because of the low temperature.0.1 m from the bottom of the SBR tank. It ensured aTable 1 shows the wastewater quality of influent usedgood aeration for the sludge and wastewater treatment.in the experiment. The effluents should meet standardGB/T18921-2002:“The reuse of urban recyclingwater-water quality standard for scenic environment一一To welanduse"[3].Table 1 Wastewater quality of infuent used in theAutomationexperimentIndexRangeRequirementChemical oxygen245 to357 S20demand/(mgL)BOD114 to 208NH;-N/(mg/L)42.4 to 50.2 ;SBR uankAir pumpInfluent pumpTotal nitrogen/(mg/L)58.6to 69.3≤15ValveTotal phosphorus/(mg/L) 4.85 to 6.03 S0.5SedimentalpH6.4 to 7.6Turbidity52 to 64≤5.0-一Iafuent pipe-一Airpipe 一m- - Sludge pipeDischarge pipe一一- Autocontron wine2.2 Experiment processFig. 2 Sequencing batch reactor (SBR) systemFig. 1 shows the experiment process.2.2.2 CW systemInfluentConstructed1 EMuent.SetlingsBRCW consists of three lateral wetlands bed, naturaltankwetlandaeration chutes, and stabilization pond. The paralleldiversion walls divide the CW into S-shaped flowFig. 1 Experiment processgallery. The slope of gallery (corridor) bottom is 1%along the flow direction. The nature aeration chutes in2.2.1 SBR systemthe wetland can improve the dissolved oxygen indomestic wastewater. The CW layout is like a rightSBR reactor consists of SBR tank, intake (influent)triangle (Fig. 3). The three lateral beds are like S- shape.system, aeration system, and decant (discharge) systemOf the first lateral bed (cell), the gallery wide is 0.4 m,(Fig. 2). SBR tank was made of Polyvinylchlorid. Theeffective area is 2.5mr, depth is 0.6 m, volume isshape of base is square with each side of 1.0 m and the1.5 m', and aeration slot width is 0.4 m. Of the secondeffective depth of 1.2 m. In each cycle, the wastewaterlateral bed (cel), the gallery wide is 0.4 m, effectivewas fed to the reactor. The volumetric exchange ratioarea is 2m2. depth is 0.55 m. volume is 1.1 m', and中国煤化工MHCNMHG202J Chongqing Univ. Eng. Ed. [ISSN 1671-8224], 2010, 9(4: 201-207W. Q. Wei, et al.Wastewater treatmentaeration slot width is 0.4 m. Of the third lateral bedSeptember in 2007. The temperature is above 15。C,(ell), the gallery wide is 0.4 m, effective area is 4 m',suitable for living sludge organism. In these conditions,depth is 0.5 m, volume is 2 m', and aeration slot widthSBR operated as 4 cyclic modes as shown in Fig. 4. Inis 0.4m. The last part of CW is a stabilization pondeach cycle, the volume of treated wastewater is 0.5 m'.which is also in S-shape. Its gallery wide is 0.4 m,effctive area is 9.3 m2, depth is 0.45 m, and volume is4.2 m'. Table 2 lists the measurement of CW.21sodReservoirPoint two .Point. throe__InfueatFirst cel)h1hh3h45hih7h8口A[s[o] [口Inflow Aeration Sediment OutflowIdlingCnaveD20-15mmPoint one入Secon'd cllFig. 4 Sequencing batch reactor operate cycleGravelDiS-8mmGrvel STHird oellAeration intensity and aeration time are veryimportant for SBR system, so the dissolved oxygenD8-5mm(DO) concentration of SBR is controlled from0.5 mg/L to 1.0 mg/L [4]. Limited low DO can reducethe energy of SBR.Fig. 3 Constructed wetland plan viewThe wastewater volume treated by CW is 1.5 m'/d,he valid volume of CW is 1.55m3，the HRTTable 2 Constructed wetland's measurement(hydraulic retention time) is 24.8 h, and the hydraulicload rate is 24.5 cm/d.Filter ValidIndexArea/m2 Depth/m Volume/m' volume volume/m'4 Results and discussionFirst cell2.60.65 1.6901.56 0.554.I COD removal under normal temperatureAeration0.9groove 1The effect of aeration time on the COD removal wasSecond cell 2.20.60 1.320 1.21 0.39studied at different operation cycle modes under lowdissolved oxygen (0.5 mg/L to 1.0 mg/L) as shown ingroove 1IFig. 4.Third cell 4.5 0.55 2.475 2.25 0.61The COD oxidization is not afected under low DO.COD removal in each SBR operation cyclic mode isgroove II1.6over 75% (Fig. 5), and COD concentration of theSummation 9.35.02 1.55effuent is reduced to a lower concentration. Theremoval of COD mainly occurred in the first hourWe used fllr in three areas in CW as shown in Fig.because of the dilution reactor and the biological3activated sludge adsorption.Taking all the factors into consideration, we choseBecause the SBR performance for COD degradationlocal windmill grass in Chongqing (climate conditionsis high (SBR removal efficiency is high), CW for CODof the Three Gorges reservoir area)， Cyperusremoval will not performed fully (CW removalaltermifolius, and aquatic canna as the experimentalefficiency is low). It means that the performance of CWplants. The wetland plants were used in the experiment.for COD degradation rate depends on the quality ofCOD influent which comes from SBR. When the COD3 Experiment designof the effluent from SBR is in a high concentration, CWfor COD removal efficiency will increaseThe experiment was started from March tocorrespondinglv. On the contrarv. when the COD of the中国煤化工IYHCNMHGJ. Chongqing Univ. Eng. Ed. ISSN 1671-82241 2010,3(4).CU1-2u1203W. Q. Wei, et al.Wastewater treatmenteffluent SBR is in a low concentration, the removalequivalent to a lot of series-wound or shunt-woundefficiency of CW will reduced accordingly.A2/0 unit, which made nitrification and denitrificationoccur simultaneously in the wetland system.Under normal temperature, the combined process0 SBRmade the removal of ammonia nitrogen efficiently. The1 CWdensity of COD in the effluent was less than 5 mg/L.100The water can meet effluent standards.80 tCW treatment efficiency of ammonia nitrogen50 tremoval is as shown in Fig. 6. It can be seen from Fig.40十6 that the 4th operation cyclic mode is the best cyclicmode to meet the standard and it is a cost-effectivemode.OsBRcwCyclic modeFig. 5 Chemical oxygen demand (COD) removal eficiency00 tby combination process of different cyclic modes 1 to 4The COD concentration of different operation cyclic50modes 1 to 4 can meet the standard. In the 4th40-operation cyclic mode, the COD concentration is20 t17 mg/L, which satisfies the urban landscape waterstandards. And energy consumption is the minimum, so24hat the 4th operation cyclic mode will beCyelic moderecommended as the best cyclic mode.Fig. 6 Ammonia removal efficiency by combine process ofdifferent cyclic modes 1 to 44.2 Ammonia removal under normal temperatureSBR reactor operated under limited aeration4.3 Total nitrogen (TN) removal under normal(0.5 mg/L to 1.0 mg/L), and the ammonia oxidationtemperaturewas not significantly affected. The ammoniadegradation process was effected by the CODUnder normal temperature and limited aerationconcentration. The COD removal started firstly, andcircumstances, TN removal in SBR appeared byafter that the ammonia removal began. In the first hournitrification and denitrification simultaneously.of aeration, the COD concentration was high and theIn the process of influent water, TN in the sewagerate of heterotrophic bacteria quickly increased, so thatsharply decreased due to dilution. Because ofCOD degradation was fast, which made self-supportsynchronic nitrfication and denitrification, TN alwaystype of nitrifying bacteria inhibited. Therefore, thedemonstrated the tendency of descent. After dilution,denitrification rate was slow, and the speed of reducingTN was degraded to 15 mg/L to 20 mg/L by theammonia concentration was slower.nitrification and denitrification.Afterh aeration, the CODdegradationIn the CW system, the removal of TN was due to theaccomplished, and the ammonia degradation ratecapacity of oxygen supplied by the plants. The plantsincreased. The ammonia degradation has not beenin CW flourished heavily, and the developed roots hadcompleted in the SBR to meet standards, so that morelots of fibrous roots [5]. The vascular species of rootstreatment needs to be accomplish by CW. After CWabsorbed the oxygen in the air and transported it intotreatment, the concentration of ammonia ntrogen in thethe wetland bed matrix.effluent fell beyond 5 mg/L. The reason is that oxygenExcept the oxygen supplied by the roots, the DOsupplied by roots and DO of the natural anaerobic bedconcentration of the CW was enhanced by the naturalmade the wetland bed become consecutively aerobic,reoxygenation bed in the experiment. The DOanoxic and anaerobic in the CW system. It wasconcentration of the reoxygenation bed raised along中国煤化工JMHCNMHG204J. Chongaqing Univ. Eng. Ed. [ISSN 1671-8224]. 2u10. (4): 201-207W.Q. Weli,etal.Wastewater reatmentwith the increase of reoxygenation bed length, and theSCReffects of DO mainly depended on the length of the bed.The relaionship between DO andlength of60 treoxygenation bed is positive and linear as shown inFig. 7.. DOCyelie modey= 0.668 3rR'-0.8971Fig. 8 Total nitrogen (TN removal eficiency by combineprocess of dfferent cyclic modes 1to44.4 Total phosphors (TP) removal under normal67temperatureLeagth of reoxygen bed/mFig. 7 Relationship between dsslved oxygen (DO) andAfter 1 h, SBR reactor stling, the percentage oflength of reoxygenation bedsludge contained in the SBR reactor was between 30%and 35%. The sludge was drained 15 L a day in volumeDue to the degradation of ammonia nitrogen andTNfrom the bottom sludge pipe of SBR. The sludge ageby the SBR, the density of TN was almost less thanwas about 20 d.30 mg/L before the CW process.In conditions of low oxygen aeration in the wholeWhen the nitrogen compounds went to the CW, isprocess, the SBR system obviously appeared adegradation process was similar to the sewagephenomenon that the phosphorus was released andtreatment of A7/0 because of the oxygen supplied byabsorbed. The phenomenon of phosphorus releasingthe roots and DO supplied by the natural reoxygenationappeared in the early stage under the circumstance ofbed. CW change ammonia nitrogen in the sewage intocontinuous low oxygen aeration. The averagenitrate nitrogen in the oxidation zone, and the nitrateconcentration of TP under normal temperature waswas deoxidated into NO2^ by the denirifying bacteria5.84 mg/L. After 1 h low oxygen aeration, the averagein the anaerobic zone, finally it was removed byconcentration of TP in the reactor increased todeoxidated into N2 [6]. The nitrate nitrogen was6.73 mg/L. The time of low oxygen aeration lastedremoved in the denitrifying process by the oxidationfrom 3 h to 5 h, and the concentration of phosphorus inzone and anaerobic zone of the cw. Under thethe efluent water decreased to 2.34 mg/L to 3.52 mg/L.circumstances, there was no oxygen but nitrate whichThe percentage of renoval eficiency was betweenwas used by the denitrifying bacteria to breathe. The42% and 56%.oxygen decomposed organic compound so that theThe removal eficiecncy of phosphorus in the CWnitrate would be deoxidated into N2 or N2O[7].system was stable. The phosphorus removal mainlyAfter the action by the deposition, volatile,depended on microorganisms, plant absorption andadsorption, and microbes of the cW, the plantspacked bed physical chemistry of matrix [8]. The plantabsorbed the descend concentration of TN which wasgrowth needed inorganic phosphorus. On one hand,between 15mg[L and 20 mgL. Except the 4thbecause of the impact of absorption and assimilation byoperation cyclic mode, other modes can make theplants, the inorganic phosphorus in the sewage wascontent of TN in the effluent water meet the standards.synthesized into adenosine triphosphate (ATP),The removal efficiency of TN in the combined processdeoxyribonucleic acid (DNA) and ribonucleic acidis as shown in Fig.8.(RNA), and the phosphorus was removed by reapingOn the premise that the efluent water reached theplants. On the other hand, the phosphorus wasstandards, CW treatment was efective for TN removalnormally assimilated by the microorganism andand gave high removal efficiency in the combinedaccumulated by the polyphosphoric bacteria. Therefore,ess operation. The 3rd operation cyclic mode wasthe phosphorus removal in the system depended onprocethe best cyclic mode because it can meet the standardregularly changing of the wetland bed. Theand was a cost-effective mode.中国煤化工MHCNMHGJ. Chongqing Unlv. Eng. Ed (ISSN 1671-82241, 2010. 9(4: 201-207205W.Q. Wei, et al.Wastewater treatmentphotosynthesis and respiration of plants altemated in2h; CW's HRT is 24.8h and hydraulic loading isthe CW. The quantity of oxygen supplied by the roots24.5 m'/m2d) is the best cyclic mode. The effluentscorrespondingly varied with the alternation of the lightcan meet the standard GB/T18921-2002: "The reuse ofintensity, and the wetland bed was different. Aerobicurban recycling water: water quality standard for scenicand anaerobic conditions appeared in the system owingenvironment use". In the 3rd cycle, the efficiency ofto different rate of oxygen in the region, whichCw is the maximum, and energy consumption of SBRfacilitated the release and excessive accumulation ofis the minimum.phosphorus by the microorganism. During theFig.11 shows the relationship of COD, ammonia,dephosphorization process in the CW, the phosphorusTN, and TP in the 3rd cycle of SBR.was removed by the plant and the microorganism.Although they were not the main methods, theyaffected the cycle of phosphorus in the CW [9].12OContribution rate of SBR■Coatribution rate of CWExcept in the 4th operation cyclic mode, the TP瓷100concentration of the effluent water in other three modeswas below 0.5 mg/L, which meet the standard. The0removal efficiency of TP in the combined process is asshown in Fig. 9.40|20 to SBR■Cw100rCODAmmoniaTNTIFig. 10 Removal fficiency of chemical oxygen demand(COD), ammonia, total nitrogen (TN), and total phosphorous30 t(TP) in combined process0t←CODr -AmmoniaE 20300，+NG2502wCyelie mode自200Fig.9 Total phosphorous (TP) removal efficiency byg15combining process of dfferent cyclic modes 1 to410On the premise that the effluent water reached thestandard, CW treatment was effective for TP removalnd gave high removal efficiency in the combinedhprocess operation. The 3rd operation cyclic mode wasTime/hthe best cyclic mode and it was a cost-effective mode.Fig. 11 Relationship of COD (chemical oxygen demand),4.5 Optimum operation under normal temperatureammonia, TN (total nitrogen), TP (total phosphorus) in the3rd cycle of sequencing batch reactorBy statistically analyzing the removal efficiency ofCOD, ammonia nitrogen, TN, and TP in the combined5 Conclusionsprocess (Fig. 10)， it can be found that COD andammonia nitrogen were mainly removed by the SBR,1) Under normal temperature, the 3rd cycle (SBR'sand TN and TP were effectually removed by the CWoperation cycle is 8 h: inflow for 1 b, limited aeration[9].for 3 h, sediment for 1 h, outflow for 1 h, and idling forUnder normal temperature, the 3rd cycle (SBR's2h; CW's HRT is 24.8 h and hydraulic loading isoperation cycle is 8 h: inflow for 1 h, limited aeration24.5 m'/m2 d) is the best cyclic mode. The effluentsfor 3 h, sediment for 1 h, ouflow for 1 b, and idling forcan I中国煤化工202:“The reuse ofTMYHCNMH G206J. Chongqing Univ. Eng. Ed. [ISSN 1671-8224]. 2010, 9(4): 201-207W. Q. Wei, et al.Wastewater treatmenturban recycling water: water quality standard for scenicConstruction of the P. R. China, 2002. (In Chinese).environment use". In the 3rd cycle, the efficiency of中华人民共和国住房和城乡建设部.GB/T18921-CW is the maximum, and energy consumption of SBR2002城市污水再生利用景观环境用水水质[S].北京:is the minimum.中华人民共和国住房和城乡建设部,2002.2) To control the DO concentration between4] Zhu JL. Full-scale study of nitrogen and phosphorus0.5 mg/L and 1.0 mg/L, the aeration concentrationremoval by low DO activated sludge processes [].should be from 1 m’/h to 2 m/h. Under low oxygenWater & Wastewater Engineering, 1997, 23(5): 62-64.condition, the removal efficiency of COD and(In Chinese).ammonia was not affected obviously. 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