污水處理外文翻譯--提高塔式復(fù)合人工濕地處理農(nóng)村生活污水的脫氮效率（英文）

1、Ecological Engineering 35 (2009) 1043–1050Contents lists available at ScienceDirectEcological Engineeringjournal homepage: www.elsevier.com/locate/ecolengEnhancement of nitrogen removal in towery hybrid constructed wetla

2、nd to treat domestic wastewater for small rural communitiesFenxia Ye ?, Ying LiDepartment of Chemical Engineering, Ningbo University of Technology, 20 Houhe Lane, Ningbo 315016, PR Chinaa r t i c l e i n f oArticle histo

3、ry:Received 11 September 2008Received in revised form 6 January 2009Accepted 23 March 2009Keywords:Constructed wetlandsNitrificationDenitrificationDomestic wastewaterNitrogen removalNitrifying bacteriaDenitrifying bacter

4、iaa b s t r a c tEfforts to protect watercourses, especially sources of drinking water, particularly in rural areas, are nowunderway in China. Nitrogen present in wastewater, due to its role in eutrophication and potenti

5、al toxicityto aquatic species, is a focus of primary concern. Constructed wetlands (CWs), a simpler, less costly treat-ment alternative, have been used to treat domestic wastewater for small communities. Although showing

6、great promise for removing carbonaceous materials from wastewater, wetland systems have not been suc-cessful in removing nitrogen mainly due to lack of dissolved oxygen (DO). To enhance nitrogen removal,a novel CW config

7、uration with three stages, towery hybrid constructed wetland (THCW), was designed.The first and third stages were rectangle subsurface horizontal flow CWs, and the second stage was a cir-cular three-layer free-water flow

8、 CW. Increased DO by passive aeration of a tower type cascade overflowfrom the upper layer into the lower layer in the second stage of the wetland enhanced nitrification rates.Denitrification rates were also improved by

9、additional organic matter supplied as a result of bypass influ-ent directly into the second stage. Evergreen tree Pond Cypress (Taxodium ascendens), industrial plantsMat Rush (Schoenoplectus trigueter) and Wild Rice shoo

10、ts (Zizania aquatica), ornamental floriferous plantsPygmy Waterlily (Nymphaea tetragona) and Narrow-leaved Cattail (Typha angustifolia) were planted in thewetland. The average percentage of removal was 89%, 85%, 83%, 83%

11、 and 64% for total suspended solid,chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus, respectively. Therewas no significant difference (p < 0.05) at low and high hydraulic loads (16 cm/d an

12、d 32 cm/d) for perfor-mance of THCW. Nitrifying and denitrifying bacteria as well as potential nitrification activity and potentialdenitrification rates measured have shown that nitrification–denitrification is the main

13、mechanism fornitrogen removal in the wetland. THCW also provided additional aesthetic benefits.© 2009 Elsevier B.V. All rights reserved.1. IntroductionWidespread demands for improved receiving water quality,especial

14、ly drinking water are currently driving the implementa-tion of advanced wastewater treatment techniques. In rural areasof China, the domestic sewage was discharged directly into water-courses, lakes, rivers, soil or sea.

15、 This discharge of poorly treatedsewage is responsible for many watercourses, reservoirs and lakesnot meeting their quality objectives. Many small communitieslocated in rural areas of China lack adequate domestic wastewa

16、-ter treatment facilities. Wastewater collection and treatment areproblematic in these areas due to mountainous terrain, dispersedpopulation, and a lower economic base. In order for resource-scarce, economically developi

17、ng rural areas to adopt wastewatertreatment, the treatment technologies must be cost-effective? Corresponding author. Tel.: +86 574 87081702; fax: +86 574 87080072.E-mail addresses: yefenxia@hotmail.com, fenxiaye@126.com

18、 (F. Ye).and easy to adopt, require less energy input and maintenancecosts, and be capable of meeting effluent discharge standards.The centralized wastewater treatment plants based on activatedsludge or bacterial beds pr

19、ocesses which are utilized in largeand small cities are not economically adaptable for such ruralareas, mainly due to the construction costs of sewage collec-tors.On the other hand, the nitrogen content of many watercour

20、ses,reservoirs and lakes in China does not meet the standards ofnational and local governments. It now seems clear that in manylakes, most estuaries, and almost all coastal waters, nitrogen alsoplays a major role in eutr

21、ophication. Therefore, national regula-tions have recently been issued; the project is called “new countryconstruction”. The regulations stipulate that the domestic wastew-ater in rural areas must be treated before being

22、 discharged into awatercourse or soil.Constructed wetlands (CWs) have been scientifically tested andconstructed for on-site treatment in rural areas for small units andsmall villages. Simple construction, large buffering

23、 capacity, little0925-8574/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.ecoleng.2009.03.009F. Ye, Y. Li / Ecological Engineering 35 (2009) 1043–1050 1045Fig. 1. Flow diagram of towery

24、hybrid constructed wetland: 1, first stage; 2, second towery stage; 3, third stage (discharge); 4, wetland plants; 5, bottom circular cell; 6,middle circular cell; 7, upper circular cell; 8, cascade.and an air temperatur

25、e annual average of 16.2 ?C. Extremes varybetween ?4.2 ?C at the lowest and 38.8 ?C at the highest. The coldperiod represents about 3 months from December to February andduring this period the effluent mean temperature w

26、as close to 8 ?Cwith 5.5 ?C as the lowest. The first and third stages were 8 m longand 6 m wide with a depth of 1.0 m. The beds were constitutedof three layers, the lowest layer of washed gravel (2–6 cm) with adepth of 2

27、0 cm, the middle layer of fine gravel (0.5–2.0 cm) witha depth of 65 cm, and the upper layer of soil (0.1–0.2 cm) with adepth of 15 cm. The bottom slope was about 1%. The second stageconsisted of three circular cells wit

28、h diameters of 7 m, 5 m and 3 m,respectively, from the bottom cell to the upper cell, each 0.6 mdeep, providing approximately 38.5 m2 of surface area. The over-flow from the upper cell drops into the lower cell immediate

29、lycreating a turbulent cascade, which increases DO and maintainsoxic conditions.The bottom of the wetland was lined with a high-densitypolyethylene liner and the circumference of the wetland was con-structed with approxi

30、mately 5 cm of brick to eliminate seepageand mixing of wastewater with underground water. Seedlingsof Pond Cypress (Taxodium ascendens) purchased from a nurs-ery were planted 0.8 m apart around the circumference of thebo

31、ttom of the whole wetland, and Mat Rush (Schoenoplectustrigueter) was planted in the center of the bottom of the wholewetland in a density of approximately 56 plants per m2 inNovember and harvested in May of the next yea

32、r. Wild Riceshoots (Zizania aquatica) were planted in a density of approx-imately 9 plants per m2 after the Mat Rush was harvested togrow from June to October. In the second stage, the uppercircular cell was planted with

33、 Pygmy Waterlily (Nymphaea tetrag-ona) in a density of approximately 6 plants per m2, and themiddle circular cell was planted with Narrow-leaved Cattail(Typha angustifolia) in a density of approximately 36 plants perm2.8

34、0% of the raw wastewater flowed continuously into the firststage of the wetland. 20% of the raw wastewater was pumpeddirectly into the uppermost circular cell in the second stage of thewetland, and overflowed into the mi

35、ddle circular cell, then over-flowed to the bottom cell. This wastewater together with waterfrom the first stage flowed into the third stage of the wetland, anddischarged from the end of the third stage of the wetland. W

36、aterdepth was controlled with a standpipe. In Phase 1, the THCW wasoperated with a hydraulic loading of 16 cm/d (corresponding to HRTof 5.4 d) for 4 months (from May 2006 to August 2006). In Phase 2,the THCW was operated

37、 with a high hydraulic loading of 32 cm/d(corresponding to HRT of 2.7 d) for 8 months (from September 2006to April 2007). The domestic wastewater was pretreated in a septictank (Table 1).2.2. Analytical procedure2.2.1. C

38、hemical analysisWastewater samples were collected daily (regular working days)from the inlet of the first stage, outlet of the second stage (onlyduring the Phase 2 test) and outlet of the third stage in the THCWwetland,

39、and formed into weekly composite samples that were pre-served and analyzed for total suspended solid (TSS), COD, NH3-N,TN, and total phosphorous (TP). Weekly in situ temperature, pH andDO measurements of each stage and c

40、ell were made using an YSIprobe. TSS, COD, TN, TP and NH3-N were determined according tothe Standard Methods (APHA, 1998).Wild Rice shoots (Z. aquatica) and Mat Rush (S. trigueter) wereharvested (by cutting all visible p

41、ortions above the water surface)in October 2006 and May 2007, respectively. The harvested plantswere washed in distilled water and dried in the sun for 24 h andlater in an oven of 105 ?C for another 24 h. The plants were

42、 weighedbefore and after drying for water content analysis. The dried plantswere powdered and prepared for total Kjeldahl nitrogen (TKN) anal-ysis according to the Standard Methods (APHA, 1998).2.2.2. Measurement of nitr

43、ification and denitrificationThe potential nitrification activity (PNA) was determined onsamples in the upper 5 cm of sediment taken from the frontpart of the third stage of the wetland. The test media used con-tained pe

44、r litre: 0.14 g K2HPO4; 0.027 g KH2PO4; 0.59 g (NH4)2SO4;1.20 g NaHCO3; 0.3 g CaCl2·2H2O; 0.2 g MgSO4; 0.00625 g FeSO4;0.00625 g EDTA; 1.06 g NaClO3; the pH was 7.5. Sodium chlorate wasused to inhibit the oxidation

45、of nitrite to nitrate. 50 mL sedimentslurry samples were added to 100 mL of test media and incubated at25 ?C on a horizontal shaker at 150 rpm. Subsamples were collectedafter 2, 6, 20, and 24 h of incubation. Nitrite con

46、centrations weremeasured colorimetrically. PNA was calculated by angular coeffi-cient assessment of linear regression calculated for hours and theamount of nitrite produced. Results were normalized for volumeloss during

47、sampling, referred to by dry weight (DW) and expressedas nmol of nitrite per gram dry matter per hour.Potential denitrification rate (PDR) was measured using theacetylene inhibition technique. Sediment core samples were

48、col-lected at four locations in the back part of the third stage (twolocated in bulk, two located in rhizome, diameter = 3.5 cm), andimmediately wrapped tightly in aluminium foil to prevent diffu-sion of oxygen into the

49、sediment cores. Each of these four sampleswere put into a 1500 mL Erlenmeyer flask, and incubated in waterenriched with nutrients (15 mg/L NO3-N, 72 mg/L Ca, 10 mg/L Mg,27 mg/L Na, 39 mg/L K and 2.5 mg/L PO4-P). The head