Advanced sludge reduction and phosphorous removal process

Vol.13 No. 3J. CENT. SOUTH UNIV. TECHNOL.Jun.2006Article ID: 1005 - 9784(2006)03 - 0313 - 05Advanced sludge reduction and phosphorous removal processJI Fang-ying(吉芳英), ZUO Ning(左宁)， YANG Sur bo(杨肃博) ,HU Yu-qin(胡玉琴)(Key Laboratory of Three Gorges Reservoir Region's Eco Environment, Ministry of Education,Chongqing University, Chongqing 400030, China)Abstract: An advanced sludge reduction process, i. e. sludge reduction and phosphorous removal process, was de-veloped. The results show that excellent sludge reduction and biological phosphorous removal can be achieved per-fectly in this system. When chemnical oxygen demand p(COD) is 332- 420 mg/L, concentration of ammoniap(NH,-N) is 30 - 40 mg/L and concentration of total phosphorous p(TP) is 6.0-9. 0 mg/L in influent, the systemstill ensures p(COD)<23 mg/L, p(NH3-N)- <3.2 mg/L and p(TP)<0. 72 mg/L in efluent. Besides, when theconcentration of dissolved oxygen p(DO) is around 1. 0 mg/L, sludge production is less than 0.140 g with the con-sumption of 1 g COD, and the phosphorous removal exceeds 91%. Also, 48. 4% of total nitrogen is removed bysimultaneous nitrification and denitrification.Key words: sludge reduction; phosphorous removal; dissolved oxygen; simultaneous nitrification anddenitrificationCLC number: X703. 1Document code: A1 INTRODUCTION2 SLUDGE REDUCTION AND BIOLOGICALPHOSPHOROUS REMOVAL TECHNOLOGYIt is widely known that there exist distinctdisadvantages in the treatment and disposal tech-In order to solve the problem above, an ad-nologies of sludge, e. g. the large capital construcvanced process, i. e. sludge reduction and phos-tion investment (30%- 40% of the total invest-phorous removal ( SRPR) process was developed ,ment) and higher operating cost (30%- 50% of thewhich is based on the following principle: in atotal operating cost)[1.2]. In addition, the final dis-steady system, the relationship between the sludgeposal technologies of sludge such as landuse, land-retention time(tsRr) and the observed sludge yieldfill, incineration etc, are always affected by the in-(7syR) submits inverse ratio, that is, the longerjurants in sludge. So far, a feasible treatmentmethod towards excess sludge, which can integratethe 'sRT, the lower the 7syn[40. However, it is wellvalidity and environmental security perfectly, hasknown that the traditionally biological phosphor-ous removal technology is built on removing phos-not been developed yet.Reducing excess sludge production can not on-phorous accumulating sludge, and also it isly cut down the sludge treatment cost, but alsothought that short tsRT corresponds to high removaleliminate secondary pollution to environment. Irefficiency of phosphorous. Virtually, phosphatethe term of this, the technologies of excess sludge:an be accumulated in anaerobic sewage by phos-reduction emerge along with the development. Butphorous accumulating organisms (PAOs).. There-there is an evident problem among all existingfore, theoretically, chemical means can be used totechnologies of sludge reduction, that is, the re-eliminate phosphorous effectively from anaerobicmoval efficiency of nutriment is low, especially thephosphorous accumulating sewage[), which carphosphorous is much lowerl3. Along with euresolve the contradiction of SRT controlling be-trophication aggravating， nutriment removal, es-tween phosphorous removal and sludge reduction.pecially nitrogen and phosphorus, becomes an imConsequently, this SRPR system can be used toportant mission for municipal sewage treatmentachieve an excellent effect of simultaneous sludgeplant. Therefore, in this study, an advance sludgereduction and phosphorous removal with longerreduction proces i. e. sludge reduction and phos-tsRT.中国煤化工phorous removal was developed.MHCNMHGD Foundation tem; Projet ( 50278101) supported by the National Natural Science Foundation of China; Project(CSTC, 2005AB7030)supported by Chongqing Key Technologies Research and Development ProgramReceived date: 2005 -12-10; Accepted date; 2006 -02 - 15Correspondence:JI Fang-ying, Professor; Tel: +86-23- 65127537; E-mail: jfy@cqu. edu. cnJournal CSUT Vol.13 No.3 2006mg/L; the concentration of total nitrogen p(TN)3 EXPERIMENTAL=34.0-46.4 mg/L; p(TP)=6-9 mg/L; pH=7- 8.3.1 Experimental setting and processCOD was analyzed by HACH-COD instru-The experimental setting of SRPR system isment, the content of DO was measured with anshown in Fig. 1. The virtual volumes of anoxicYSI oxygen meter, and other parameters were ana-tank, anaerobic tank and oxic tank are 3 L, 24 Llyzed according to Ref. [7]. .and 42. 5 L, respectively. And mechanical stirrerswere used to make sludge and sewage of each tankInfluent 。mixed adequately, in which, oxygen was offeredfrom oxic tank by an air pump. In addition, thePhasphorousAnaerobiqretmovalvirtual volumes of No. 1 settling tank and seconda-tankry settling tank are 2.3 L and 12. 8 L, respective-Aerobigly.ChemicalThe influent was divided into two portions,I No.I steeling sludge80% of which flowed into anaerobic tank, wherephosphate could be accumulated in anaerobic sew-age by PAOs. The proportion of anaerobic phos-phorous accumulating sewage entering chemicalReturning ;EMluentphosphorous removal tank was equal to 10%- 30%sludgeof the gross sewage[6]. After phosphorous was re-moved, the effluent from this tank flowed into oxicOxic tanktank, where chemical oxygen demand (COD) andSludge pumpNH3-N could be eliminated ulteriorly. And then,_____ Secondary sttling tankthe mixed liquid which had finished phosphorousrelease flowed into oxic tank, where phosphorouswas absorbed adequately. Besides, the returnedFig. 1 Schematic diagram of SRPR processsludge was pumped into aerobic tank as well as therest 20% of influent for avoiding the effect of ni-RESULTS AND DISCUSSIONtrate from returned sludge on anaerobic phosphor-ous release.4. 1 Holistic treatment effect of SRPR systemWhen SRPR system operates steadily, theIn the course of examination, the concentra-concentration of mixed liquor suspended solidstions of COD, NH3-N and TP in the influent and(MLSS) maintains 6.0-7.0 g/L; concentration ofeffluent were measured once a day for the purposedissolved oxygen(DO) is0.5- 1.5 mg/L; rate ofof monitoring the holistic treatment effect of SRPRthe returned sludge is 40% ; sludge retention timesystem. And the results are shown in Fig. 2.tsRr=50 d. And other operating parameters areFig. 2 indicates that in despite of longer SRTshown in Table 1.(50d) the removal efficiency of COD is stillTable 1 Operating parameter of SRPR system400Hydraulic5CReacting tankretention time/h(L.-I)wWWww.AWNAnoxic tank1.540Anaerobic tank4.0No.1 setling tank6.0105 203|0o &Secondary settling tank1t/WNMyW& 10Note: Influent flux Q=10 L/h3.2 Materials and testing methodsExperimental wastewater was taken from中国煤化工.campus sewage in Chongqing University. Add am-ylum, glucose, milk powder, NH,Cl and KH;PO,Fig.MHIculuval cliClCNMHG.NH3-N and TPto make it close to typical municipal sewage. The1- NH3-N in influent; 2- -NH3-N in efluent;characteristics of the influent are as follows:3- -TP in influent; 4- TP in effluent;p(COD)= 332 - 420 mg/L; p(NHg-N)=30 - 405-COD in effluent; 6- -COD in influentJI Fangying, et al Advanced sludge reduction and phosphorous removal pr●315.consistent with that in short SRT technologies ofbiological phosphorous removal间. When influent。250CODis 332 - 420 mg/L, the efluent value is al-、200y=0.155 2+1.826ways less than 23 mg/L, and the removal rate rea- .R-0.9945ches 95. 37%.150During the two month runtime, when influentNHs-N is 30 - 40 mg/L, the effluent value main-100tains below 3.2 mg/L, and its removal rate is upto 95. 73%.50FMoreover, Fig.2 still shows that SRPR sys-tem whose SRT is longer has better capability than300600900 1200 1500short SRT phosphorous removal processes whichCumulative COD removal/grealize phosphorous removal by removing phos-phorous accumulating sludge. When the content ofFig.3 Rgr of SRPR SystermTP in influent is 6 -9 mg/L, effluent value is low-er than 1.0 mg/L, which can fully meet the de-mand of first-degree standards of GB18918 - 2002.0.34.2 Efficiency of sludge reduction in SRPR process4.2.1 Sludge yieldg°2fMLSS and COD of influent and efluent were0.1measured once a day for the purpose of monitoringTIsyk and efficiency of sludge reduction.0.51.01.52.0253.03.54.04.5The relationship between the cumulativesludge yield and cumulative removal amount ofρ(DO)(mgL7)COD per day is shown in Fig.3. TByR iso.155, ie.sludge yield is 0. 155 g with the consunptionof1 gFig.4 Influence of DO on %srRCOD. Comparing with tesrm (around 0. 4间) of tradi-tional activated sludge process, the eficiency ofsteady level. When DO in oxic tank is about 1. 0sludge reduction in this system exceeds 61%.mg/L, BYR reaches a steady value, which is aboutThe reasons for lower TIsyR can be explained as0.140. Even though DO increases continuously,follows:Bsyr will not reduce any more.1) the system operates under the condition ofFor the strong reduction of the excess sludgelow load and long tst，so that, longer hydraulicin the system under the condition of lower DO, itretention time(HRT) of anaerobic tank can makecan be explained as follows: the low F/M and longuncoupling come true and reduce microbe productskr can intensify endogenesis respiration of mi-crobe.2). The state of low load and long tskr can im-prove the oxidation and decompose of microbe.4.3 Removal efficiency of phosphorus3) Long tsRr is still propitious to forming com-4.3.1 Phosphorus removal rate in SRPR systemplicated bio ecosystem, which can prolong food. In order to study the removal efficiency ofchain. The amount of protozoan increases gradual-phosphorous in SRPR system ulteriorly, influently, and even metazoan appears. Consequently, the .and efluent TP and TP being released in anaerobicpredacity of microbe is strengthened consumedlytank were mensured termly every day. The resultsand sludge production is reduced markedly.are shown in Fig. 5.Fig. 5 indicates that efluent TP is always less4.2.2Influence of DO on efficiency of sludgethan 0.72 mg/L when influent value maintains 6-reduction9 mg/L. Along with runtime increasing, TP beingThere exists a stubborn problem in variousreleased under anaerobic condition increases gradu-technologies of excess sludge reduction, e.g. ifally, finally, the value can be more than 42 mg/L.excess sludge production is less, oxygen demandBecaluce the highoncentration of anaerobicwill increase 0. Therefore, the influence of DO onphos中国煤化工; the proportion ofsludge production was studied. Fig. 4 shows theanaeiYHC N M H Gmical phosphorousresults.remue llaeiuulc sewage drained intoAs shown in Fig. 4, the influence of DO onphosphorous removal tank is just about 12% of thesludge production indicates that, along with DOgross sewage. Obviously, this will reduce consum-increasing, 7syr descends first and then reaches aedly the medicament dosage of phosphorous removal.●316●Journal CSUT Vol.13 No.3 2006of phosphorus increases gradually with DO increas-100ing. When it is around 1. 0 mg/L, the removal ca-pability of phosphorus comes to level off and re-I 80moval rate exceeds 91%. This also makes sure thatlow DO causes low removal rate of phosphorus50during the early runtime.4.4 Simultaneous nitrification and denitrification20A great number of investigations indicate thatsimultaneous nitrification and denitrification(SND)071325“ 39will be promoted when DO is limited1]. BecauseRuntime/dthe concentration of DO maintains low (0. 5-1.0 mg/L) in SRPR system, . it is essential toFig.5 Removal capability of phosphorousstudy the removal rate of nitrogen. And the results1- p(TP) in influent; 2- -p(TP) released;are shown in Fig. 7.3-p(TP) in efluent; 4- Removal rate78From Fig. 5，it can also be found that phos-phorus removal rate is lower and unstable duringthe first running days: in the first 10 d, the aver-45-4.age removal rate is less than 75%，then it increasesand exceeds 91%. Summarizing the experimental35一40data, it is found that during the first 10 d, DO istoo low，which maintains 0. 5 - 0.8 mg/L, and .255+ 20then it rises to 1.0-1.5 mg/L after the 10th day.15t2/v^ rvvrArSo, the reason for low phosphorous removal ratei 357911 131517 19may be the lower DO during the first runningdays.4.3.2 Influence of DO on phosphorus removalFig. 7 Biological nitrogen removalrate1- p(TN) in influent; 2--p(TN) in effluent;In order to testify the conclusion above, varia-3- -Total removal rate; 4- DBanD; 5- -p(TN.)tion of removal rate of phosphorus with DO con-centration was studied. The results show that theTN removal rate by SND can be expressed asrelationship between concentration of DO andfollows:phosphorus removal rate submits typical logarithm(see Fig. 6): n加= 36.6221np(DO)+84. 983, R'=IsND。 [p(TN,)-p(TN.)]-p(TN,)(1)p(TN)0.917.where DISND means TN removal rate by SND,p(TN。) means the concentration of TN enteringoxic tank; p(TN,) means TN in the concentration90of effluent; p(TN,) means the concentration of TN8removed by assimilation; and p(TN) means they=36.622nx+84.983concentration of TN in the influent.R2=0.9073As shown in Fig. 7, effluent TN is9.8- 17.56mg/L，and the average of TN removal rate is69. 15%, while influent TN is 34. 0- 46. 4 mg/L.It can still be concluded that there exists SND48.50.70.9.11.31.in SRPR system. TN removal rate caused by SNDρ (DO)(mg:L7)is higher and the average is 48. 4%，which accounts for 70% of the total removal rate. AboutFig. 6 Relationship between concentration ofassimilation andDO and phosphorous removal ratedenit中国煤化工7gsyr(0.155)，thepropMYHC NM H G by assimilation isFrom Fig. 6, it can be concluded that low DOonly 8% of the total nitrogen removal rate. Thisis the most significant factor for phosphorous re-illuminates ulteriorly that nitrogen removal is real-moval in SRPR system. Within the DO concentra-ized mostly by SND.tion range from0. 5 to 1. 0 mg/L, the removal rateJI Fang-ying, et al; Advanced sludge reduction and phosphorous removal process317●_3] Saby s, Djafer M, ChenG H. Effect of low ORP in5 CONCLUSIONSanoxic sludge zone on excess sludge production in oxicsettling-anoxic activated sludge process[J]. Water Re-search, 2003, 37(1): 11- 20.1) In SRPR process the longer SRT manner of[4] AhnK H, Park K Y, MaengSK, et al. Ozonation ofremoving anaerobic phosphorous accumulatingwastewater sludge for reduction and recycling[J]. Wasewage is adopted to remove phosphorous fromter Science and Technology, 2002, 46(10); 71 - 77.sewage. The results show that the concentration of5] JI Fang ying, LUO Gu-yuan. ERP SBR bio chemicalTP in effluent is less than 0. 72 mg/L, 9syR is lowprocess for nitrogen and phosphorus removal by drai-(0. 155) and the eficiency of sludge reduction ex-ning out anaerobic rich phosphate supernatant [J ].Technology of Water Treatment, 2005, 31(1): 57 -ceeds 61% when tsRr = 50 d. and concentration 。61. (in Chinese)TP in the influent is 6.0- 9.0 mg/L.2) In the SRPR system, anaerobic phosphor-[6] JI Fang-ying, LUO Gu-yuan, YANG Qin, et al. Bio-logical phosphorous removal capability in SBR systemus accumulating sewage drained into chemicalusing exernal recycle of activated sludge[J]. Chinaphosphorous removal tank is only 12% of the grossWater and Wastewater, 2002, 18(5): 1-5. (in Chi-sewage.nese)3) When the concentration of DO is around 1[7] Edit Committee of State Enviromental Protection Ad-mg/L, PBsyR is about 0. 140 and phosphorous reministration of China. Test and analysis methods ofwater and wastewater[M]. 4th ed. Bejing: China En-moval rate exceeds 91 %. Moreover, the relation-viromental Science Press, 2002. (in Chinese)ship between the concentration of DO and phos-[8] Fukase T, Shibata M, Miyaji Y. Role of an anaerobicphorous removal rate submits typical logarithm:stage on biological phosphorus removal[J]. Water Sci-加=36.6221np(DO) +84.983.ence and Technology, 1985, 17(1): 69 - 80.4) Low DO makes SND come true in SRPR[9] Janssen P M J, Rulkens W H, Rensink J H, et al.system. And TN removal rate by SND is aboutPotential for metazoa in biological wastewater treat-48. 4%，which accounts for 70% of the total re-ment[J]. Water Quality International, 1998， (9/10):moval rate. .[10] Low E W, Chase H A, Milner MG, et al. 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