一篇污水處理英文論文

1、TREATMENT OF DOMESTIC WASTE WATER BY ENHANCEDPRIMARY DECANTATION AND SUBSEQUENT NATURALLYVENTILATED TRICKLING FILTRATIONLINPING KUAI, WIM KERSTENS, NGUYEN PHU CUONGand WILLY VERSTRAETECentre for Environmental Sanitation, Faculty of Agricultural and Applied Biological Sciences,University of Gent, Cou

2、pure links 653, 9000 Gent, Belgiumauthor for correspondence, e-mail: willv.verstgeterua.ac.be)(Received 16 January 1998; accepted 22 June 1998)Abstract. To treat household wastewater, a sequenee of primary decantationtrickling filter percolatior/ was applied in a lab-scale designed treatment system.

3、 Poly-electrolyte was used as coagulant toenhanee the primary treatment and charcoal was used as carrier material in the trickling filters Oxy-gen was supplied to the trickling filters by means of natural ventilation. In the labscale system, theenhanced primary stage removed more than 91% of the sus

4、pended solids (SS), and 79% of the totalchemical oxygen demand (CODt). The subsequent trickling filtration brought a complete nitrificationto the wastewaters at a volumetric loading rate (Bv) of 0.7-1.0 g CODt L-l d-l.Onaverage.theconcentrations of the CODt and SS in the final effluents were about 5

5、5 and 15 mg L-l respectively.With respect to phosphate, physico-chemical removal was the dominant process About 46-62% oftotal P was removed from the tested wastewaters The integrated treatment system also achieved a fairdegree of hygienisation. The numbers of total coliforms, fecal coliforms and fe

6、cal streptococci weredecreased by 2-4 log units The sludge product!on of the entire treatment system was about 1.7%(v/v) of the treated wastewater. Only primary sludge was produced, secondary sludge produced in thetrickling filters was negligible. The cost savings in terms of minimization of sludge

7、production andaeration energy are estimated to be substantial (i.e some 50%) relative to a conventional activatedsludge system.Keywords: charcoal, coagulatior cost evaluation, household wastewater, nitrification, pathogenremoval, poly-electrolyte, sedimentation, small-scale, trickling filter1 Introd

8、uction2.Water pollution in many developing regions causes serious problems Often thepopulation is living in small villages which are scattered in the countryside Theincrease of the population and the imaroveme nt of peoples daily life in these areasresult not only in an in crease of the volume of wa

9、stewater; but also in a changeof the wastewater composition which tends to contain more chemicals such asdetergents. Change of the nightsoil system to the flush toilet brings about 90% ofthe nightsoil into wastewater (Ukita et al., 1993). Direct discharge of n ightsoil into local waters endangers th

10、e hygienic quality. Although no systematic epidemiological studies have been conducted in developi ng coun tries, it is gen erally assumedWater, Air, and Soil Pollution 113: 43-62,1999. 1999 Kluwer Academic Publishers.Printed in the Netherlands.44LINPING KUAI ETAL.that the direct discharge of raw ni

11、ghtsoil is responsible for a high risk of infectiousdisease transmission in many rural regions of the developing countries (Schertenleib, 1995). Water shortage in arid and semi arid areas can necessitate the reuseof wastewater for local irrigation (Mandi et al., 1993). Treatment of this potentialres

12、ource is imperative to avoid sanitary risks before re-use (Hespanhol, 1990).The main objective of wastewater treatment is to dispose the treated effluentwithout causing an adverse impact on the ecosystem of the receiving water body.For this reason sewage treatment always in eludes the reduction of t

13、he concen trationof at least one of the four most important constituents of sewage: (1) suspendedsolids; (2) organic matter; (3) nutrients (notably nitrogen and phosphorus); and(4) pathogenic organisms (Van Haandel and Lettinga, 1994). Up to now, the western model of sewage treatment is the dominant

14、 one leading the environmental tech no logical developme nt over the world However; the tech niq ues which havebee n developed to achieve high levels of N and P removal, might not be applicablein many developing countries because of limited financial and energy resourcesavailable (Larsen and Gujec 1

15、997; Netter et al., 1993). Yet, since agriculture re quires a substa ntial amount of water and n utrient in put, safe reuse of treated sewagein these regions can free high quality water for other purposes and can supplementchemical fertilizers. Efficient use of resources will lead to a minimal in cr

16、ease ofen tropy and will require an active rather than a reactive approach (Larsen andGujer; 1997). It is therefore of importanee in many developing areas to treat sewageto the extend that it can be safely reused on the land. If the wastewater has to bedischarged to the local water-bodies, it should

17、 be treated so that the quality ofthe receiving water can be maintained at a level for safe drinking with no risk ofpathogens, no bad smell, no depletion of 02 and no toxicity from NHC4 or NH3.Henee, removal of pathogens and organic matter, in addition to achieving a highlevel of nitrification are e

18、ssential.Centralized sewage treatment plants are generally not suitable for rural areas.Collection of domestic wastewater and transport to a distant treatment plant isexpensive at low population density (Netter et al.# 1993; Paulsrud and Haraldsen,1993). On-site treatment using small scale wastewate

19、r treatme nt plants is the mostcost-effective alter native The treatme nt tech no logy for small wastewater streamsshould be based on locally available and serviceable materials and equipments thatare simple and economical to operate Those low technical skills needed are the most appropriate ones (0

20、degaardz 1997). A primary settling tank combined witha trickling filter based on n atural materials and n atural ven tilatio n might be an appropriate solution for water pollution control in most rural areas, especially indeveloping countries. The small-scale treatment unit desi gned for in dividual

21、 house holds or small communities can be compact and closed without causing negativeimpact on the landscape and without producing noise or odors It can handle fluctuatio ns in hydraulic and orga nic loads without variati on in removal efficiencies(DAntonio et al.# 1997).TREATMENT OF DOMESTICWASTEWAT

22、ER 45TABLE IThe main characteristics of the two types of wastewater(Average Standard deviation)Parameter UnitThe MHWThe SHW CODtmg L-l 5000376 2865.0王3822 CODs mg L-l 161.042 205.0134 SS mg L-l 673.0425 2555.03103 Total N mg L-l 41.0+13 204.0161 Kj-N mg L-l 41.013 202.0161NHC4 -N mg L-l 30.01063.028

23、 NOx-N mg L-l 0.0 2.03Total Pmg L-l 8.03 26.013 PO3C4 一Pmg L-l 4.03 13.04 pH7.20.4 77土03The purpose of our research was to develop a treatment process that will guarantee the technical asibility in rural areas, taking into con sideratio n factors suchasthe con struct! on and main tena nee costs, the

24、 availability ofc on structio n materialsa nd equipme nt, the limitatio n of land for anindividual household, the productionof noise and odor as well as specialized labor and skills, especially for developingcountries2. Materials and Methods2.1. WASTEWATERTwo types of domestic wastewaters were teste

25、d in the experiments One was amultiple households wastewater (MHW) obtained from a municipal wastewatertreatment plant located in Gent, Belgium. The other was a single household wastewater (SHW) collected from a family living in the rural area of Avelgem, Belgium.The wastewater samples we佗 taken gen

26、erally once a week from the sites andstoredat 4 C in the lab before feeding The main characteristics of the waste waters a regive n in Table I. The SHW was about 3 times more concen trated tha n the MHWbecause the water con sumption of the family was relatively low and rainfall was not entering the

27、wastewater collecting system. In stead of 180 L per in habita ntequivale nt (I.E.) per day, discharged to the municipal wastewater treatment plantthe family only discharged maximally 70 L(I.E.)-ld-lLINPING KUAI ETAL.4646UNPING KLAIET ALFigun L Process scheme for die treainxMit of the tuo types of ho

28、usehold wastewaters, die M1IW aid S1IW.InfluentIntluentInner net columnCharcoalEffluentFigure 2 The structure of the modified inckling filter used for the M1IW ireaunent.Inner nei column D = 5.6 cm Outside column D = 8 cm2.2 EXPERIMENTS2.2.1. Integrated Treatment of the Multiple Households Wastewate

29、rThe process diagram used for the treatment of the MHW is illustrated in Figure l.The lab-scale in tegrated system con sisted of an in flue nt tank of 30 L, a primarysettli ng tank of 6 L and a naturally ventilated trickling filter of 2.5 L To enhancethe natural aeration, as illustrated in Figure 2,

30、 the trickling filter was modified basedTREATMENT OF DOMESTICWASTEWATER 47on a con ventio nal trickling filter by placi ng a net column in side to improve the O2supply. This inner net column was made with PVC and about 80% of the wall areawas holes with 1 cm in diameter.The dimensions of the modifie

31、d trickling filterwere 1.0 m in height, 0.08 m in diameter of the outside PVC colum n and 0.0S6 mof the in side net column. A commercial charcoal (Charb on de bois Epure, S. A.Delhaize, Brussels, Belgium) was used as carrier material, it was grinded toparticles with diameter of about 2 cm before use

32、 Aeration occurred via natural contactwith air entering through the in side net colum n. Suppleme ntal forced aeratio n was not imposed.The raw MHW was batch fed into the in fluent tank once a day. It was pumpedsemi-c ontinu ously from the in flue nt tank into the primary settli ng tank in upwarddir

33、ecti on, i.e. 10 min every 15 min. During the pumping period, the influe nt was si-multa neously mixed by a mixer to avoid accumulatio n of solids in the in flue nt tank.Chemical coagulation was not applied in the primary stage The supernatant fromthe primary settling tank automatically flowed into

34、the subsequent trickling filterby gravity force. It percolated over the carrier in dow nward directi on. Operatio n ofthe trickling filter was started at a low loadi ng rate The loading rate was increasedstep-wise during the first few weeks depending on the removal efficiencies of totalchemical oxyg

35、en dema nd (CODt) and NHC4 N. After an adaptatio n period of 4week$# the flow rate was con trolled aro und 25 L d-1, and the HRTs (hydraulicrete ntion time) of the primary settling tank and the trickling filter were 5.8 and2.4 hr, respective!y. The volumetric loading rate (Bv) of the trickling filte

36、r wasabout 1.0 g COD L-ld-lcorresponding to 0.35 g Kj-N L-ld-l(based on theCODt and Kj-N concentrations of the outflow from the primary settling tank). During the whole experimental period, the integrated treatment system was operated atroom temperature varying around 20 C2.2.2 Integrated Treatment

37、of the Single Household Wastewater2.2.2.1. (a). Primary Coagulation and Sedimentation Tests Before operation ofthe integrated treatment system, a jar test using chemical coagulation and sedimentation to pre-treat the highly concentrated wastewater was carried out. Polyelectrolyte (Praestol BC 611, C

38、hemischeFabrik Stockhausen Gmbh, Krefeld, Germany) was used as the coagulant. Five different dosages of poly-electrolyte, namelyO, 2.5, 5, 7.5, 10 mg L-l, were tested The wastewater sample (800 mL) and theneeded amount of the poly-electrolyte stock solution (1 g L-l) were added intolOOO mL beakers A

39、fter mixing at 250 rpm for 2 min, the mixed liquors wereallowed to settle for 30 min and the super natants were take n for an a lyses The testswere performed twice with samples obtained at two different times.2222(b) Operation of the Integrated Treatment System The process diagramof the integrated s

40、ystem operated for the SHW was similar to the one used for theMHW treatment. However, the in dividual treatment units were slightly different.The volume of the in flue nt tank and the primary settling tank were smaller, only48 LINPING KUAI ET AL.10 and 4 L, respectively. The employed trickling filte

41、r was a conventional tricklingfilter constructed with a PVC column with a total volume of 2 L. 1.0 m in heighta nd 0.05 m in diameter. The detailed structure is dem on strated in Figure 1. Freshcharcoal, grinded and sieved to a particle size of about 2 cm, was used as carriermaterial. On the top of

42、the trickling filter, a layer of 10 cm of crushed stones with0.5 to 1 cm in diameter, was placed in order to improve the in flue nt distribution.About 8 small holes, with 1 cm in diameter each, were scattered on the wall of thePVC column close to the bottom. Aeration occurred via contact with air en

43、teringthrough the aeration holes.Based on the results of the primary coagulation and sedimentation tests, chemical coagulation was applied in the primary treatment stage for this highly concentrated SHW. The raw SHW and about 5 mg L-lof poly-electrolyte (PraestolBC 611) were batch added into the inf

44、luent tank once a day. They were mixed inthe in fluent tank and pumped into the primary settli ng tank in upward di recti o n simulta neously, for 10 min in every IS min. The con sequential treatme nt procedureswere similar to those applied for the MHW treatment. After an adaptation periodof 4 weeks

45、, the flow rate was controlled around 10 L d-1. The Bv of the tricklingfilter fluctuated around 0.7 g CODt L-ld-lwhich was about 30% lower than theone applied for the MHW treatment. The nitrogen loading rate was about 0.3 gKj-N L-ld-1. The HRT was about 9.6 hr in the primary settling tank and 4 8 hr

46、 in the trickling filter. The primary sludge was removed at intervals from the primarysettling tank, e.g. once every two weeks The system was also operated at roomtemperature around 20 C2.3. ANALYSESThe routine analyses were carried out once a week unless stated otherwise Theinfluent and effluert sa

47、mples were collected proporti on ally everyday and stored at4 C until an alyses The parameters of COD, Kj-N (Kjeldahl-N), NHC4 -N, NOx -N.ardPt (total P) were determined in accordance to the Standard Methods (APHAet al.z 1992). Total coliform (TC), fecal coliform (FC) and fecal streptococci (FS)were

48、 enumerated by plate count techniques as described by Kersters et al. (1995).3. ResultsThe treatment performanee of the laboratory integrated systems were monitoredby determining the removal of (1) suspended solid; (2) organic materials (CODt);(3) nutrients (N and P); and (4) pathogenic organisms (T

49、C, FC and FSJ.TREATMENT OF DOMESTICWASTEWATER 49TABLE I IThe results of the jar tests on the raw SHWTREATMENT OF DOMESTIC WASTEWATER49TABLE IIThe results of the jar tests on the raw SHWWastewater sampleCODt (mg L*1) (before treatment)CODt removal (%) (after treatment) (Dosage of poly-elcctroljie, mg

50、 L-i)02.55.07.510Sample I19407389959589Sample 2140023899393913.1. CODt AND SS REMOVAL3.1.1. Primary Jar Tests to Pre-Treat the SHW by Coagulation and SedimentationThe results of the jar tests by coagulation and sedimentation are described in Table II. For the concentrated SHW, simple sedimentation g

51、ave an insufficient andunstable removal of CODt which varied from 23 to 73% The poly-electrolyteshowed to be highly effective to enhance the CODt removal. By adding 5 mg L-lof poly-electrolyte, the removal percentage of CODt increased to 93%3.1.2. The Integrated SystemThe change of the CODt concentr

52、ations during the whole experimental period areshown in Figure 3 The in fluent CODt and SS in both types of wastewaters variedc on siderably. For the SHW, up to 15700 mg L-lof CODt was measured in weekl5 coupled with a high SS concentration of 11200 mg L-l The variation of theMHW was slightly lower

53、because the wastewater was taken after a grjt chamberwhere large particles had already been removed However; as shown in Figure 3,the influent CODt was still often up to 1000 mg L-l, which was 2 times as high asitsmean value.The high CODt mainly resulted from the high SS concentration. The primarytr

54、eatments removed the major part of CODt and SS from both types of wastewaters.As indicated in Table III, although in the treatment of MHW, poly-electrolyte wasnot used in the primary stage, straight-forward sedimentation still removed 79% ofCODt and 91% of SS, leaving a stable CODt con centration in

55、 the efflue nt rangin gfrom 80 to 250 mg L-l. For the SHW combi nation of chemical coagulation andsedimentation could even remove up to 95% of CODt and 99% of SS, respectively.Fluctuation of the loading rates was successfully smoothed. The effluent after theprimary stage had a relatively stable conc

56、entration of CODt, mostly between lOOto 200 mg L-l.The subsequent trickling filters polished the outflows from the primary settlingtanks to a high quality The final effluents of the MHW and SHW contained a lowCODt concentration of 55 and 50 mg L-las well as a low SS concentration of 17andllmgL-lin a

57、verage, respective!y.50 LINPING KUAI ETAL. InfluentA 4 Outflow from the primary decantor Effluent from the trickling filter1600140012001000800600400令200o-0246810121416181000000100000CT 10000E,5 1000 10010Time (weeks)In fluent； $ Outflow from the primary decantor02468 10 12 14 16 18 20 22Time (weeks)

58、Figure 3.The concentration of CODt in the different process stages A) The multiple households wastewater; B) The single household wastewater.In total, the entire processes removed respectively about 98% of CODt and 99%of SS fromthe SHW, and about 89% of CODt and 98% of SS from the MHW.3.2. REMOVAL OF NITROGENThe concentrations of nitrogen compounds in the different treatment processes