Wetlands and Stabilisation Pond

8/12/2019 Wetlands and Stabilisation Pond

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Feasibility of a constructed wetland and wastewaterstabiiisation pond system as a sew age reciamation |system for agricultural reuse in a decentralised rural |area sBo

J.H.Ham*, C G . Yoon*, J.H. Jeo n and H.C. Kim 8DepartmentofEnvironment Science, Konkuk University, 1Hwayang-dong, Kwangjin-gu, Seoul,Korea 1-(E-mail:[email protected] igResearch Division,Korea EnvironmentInstitute, 613 2Bulgwang-dong, Eunpyeong-gu,Seoul,Korea 9 .8AbstractThe perfom iance of a constru cted wetland (CW ) and wastewa ter stabilisation pond (WS P) system for sewage rclamation and pa ddy rice irrigation in a decen tralised rural area was examined using a feasibiiity Zstudy. The C W was satisfactory for sew age treatment, with g oo d removal efficiency even in the winterperiod, Mbut the effluent concentration was relatively high in the winter period owing to the high influent concentration. ^The C W effluent was further treated in a W S P and the W S P effluent was considered safe for crop irrigation gwith respect to se wage-bcrne pathogens. R eclaimed water irngation did not adversely affect the yield ofrice;o n ithe contrary, it resulted in an approximately 5 0 greater yield Ihan in controls. Tbe chem ical characteristics of 2the soil did not change significantly during the experimental period of irrigation with reclaimed water, In the 9winter, C W effluent could be stored and treated in a W S P until the spring; the water could then be discharged Sor reused for supplemental irrigation dunng the typical Korean spring drough t. Overall, sewag e treatment and Tjagronomic reuse using a CW -W SP system could be a practical integrated sewage management measure for zprotecting receiving water bodies and overcoming water shortages in decentralised ruraf areas. 3TKeywordsAgncultural reuse; CW -W SP system; decentral ised rural area; reclaimed water irr igation; *^sewag e reclamation g

IntroductionIncreases in population density and economic development in Korea have resulted inincreased deinand.s for water and competition among the water demands of agricultural,residential and indu.strial u.ses. Several regions in Korea suffer water stress; while theavera ge prec ipitation in K orea is 1,310 mm /year, it s not evenly distributed spatially ortemporally. Furthermore, available freshwater is not always suitable for its intended usebecause of water quality problems assiiciated with increased pollutant discharges.Increased sewage discharge associated with the growing human population threatens thewater quality of receiving water bodies and rural areas often experience water qualityprtiblems. Because of waler shortages and poor water quality of receiving water bodies,decentralised wastewater management is of great importance in developing long-termstrategies for the management of rural environments. Decentralised wastewater manage-ment involves the collection, treatment, disposal and reuse of wastewater from individualhomes, clusters of homes and isolated communities at or near the point of generation Crites and Tc hob ano glou s, 1998). Cen tralised w astewa ter treatment plants are not feas-ible in rural areas of Korea because of scattered housing patterns and geographical con-straints. Small low-technology wastewater treatment plants are preferred in rural areas


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Pad dy rice culture irrigation is respon sible for mo re than 50 of the total water con -sumption in Korea. Therefore, irrigation of paddy rice fields could be a practical candi-date for treated sewage reuse in terms of both quantity and quality of water. Agronotnicreuse of reclaimed water has been practised for centuries in many parts of the world. Theuse of reclaimed water for irrigation can provide a vital resource to enhance agriculturalproductivity and reduce water pollution problems in receiving water bodies. However,reclaimed water differs from regular irrigation water in many aspects. It contains organicand inorganic components that may affect plant growth, different levels of macronutrientsthat should be taken into consideration as plant nutrients, trace elements that may be pre-sent in excessive levels and residual pathogenic microorganisms that can cause publichealth problems (Metcalf and Eddy, 2003). Therefore, the feasibility of inigation withreclaimed water should be evaluated based on several factors, including toxic chemicals,microorganisms, salinity, and nutrients. The effects of reclaitned water irrigation on riceculture and soil characteristics in experimental plots should be examined. In this study,we examined the feasibility of using a CW-WSP system as a sewage reclamation systemfor agricultural reu.se of water in a decentralised rural area.

Materials and methodsConstructed wetiand CW)An experimental CW was installed and has been working continuously since 1997 on thecampus of Konkuk University in Seoul, Korea. The mean annual rainfall and temperaturefrom 1975-2004 were 1 344mm and 12.2T, respectively. Precipitation primarily occurduring the four summer months, June, July, August and September. The average ambientair temperature in the winter period (December to February) for the last 30 years was- 0 . 2 C and it occasionally dropped below - 10C. The treatment basin (8 m long, 2 mwide, ni deep) was filled with sand, and planted with common reed {Phraf-miies australis Cav. . The walls and bottom of ihe basin were made of concrete, and the bottom slopwa.s 1 tow ards the outlet (Figure 1). The void ratio and specific gravity of the sandused to fill the basin were 0.36 and 2.64, respectively. The hydraulic loading rate andhydrau lic residence time of the system were 6.3 cm /day and 3.5 days, respectiv elyThe CW system operated in a continuous flow without artificial thermal insulation. The.sewage used in the experiment originated from a school building, with toilets being themain source of pollutant discharge. A septic tank had been designed to collect ihe sewiigeand discharge it to the public sewer system after pretreatment. The tank had three

1Paddy ricePiots

1 1^ ^ ^ J Pond 1 Pond


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compartments and the wastewater in the last compartment was pumped into the storagetank and then allowed to flow into the CW system. The average water quality of the sew-age was pH 7.91. 18.80C, 0.40mg/L dis.solved oxygen (DO), 121.96mg/L biologicaloxygen demand over a 5-day period (BO D5), 68.95 mg /L total suspended solids (TSS),13.36mg/L total phosphorus (T-P) and 121.23mg/L total nitrogen (T-N).

Wastewater stabilisation pond WSP)To investigate lhe feasibility of using a WSP for further polishing of CW effluent, twoexperimental WSPs were created from concrete along with the CW (Figure I) . Eachpond measured 2.0 m long. 2.0 m wide and 2.0 m deep. The pond bottoms were 1.5 mbelow the ground surface to minimise temperature effects on the WSP water colimin, andlhe bottom 0.5 m was filled with sand. The iniUient w as introduced up to the 1.9 m levelfrom the bottom of the W SP (water co lumn 1.4 m and sand 0.5 m) . During pha.se 1(December-April) , the WSP was operated with intermittent discharge; it was filled withCW efiluent in winter for further polishing and was dischiirged in the spring. Duringphase-2 (May-November), the WSP was operated with continuous flow; the CW effluentwas introduced into the WSP and the hydraulic loading rate and hydraulic retention timewere 12.5cm/day and II days, respectively. The WSP effluent was used as irrigationwater for the paddy rice culture experiment.

Paddy rice culture with recialmed water irrigationPaddy rice w as grown on plots loca ted next to the W SP and each plot w as 1.0 m long.1.0 m w ide and 1.0 m dee p, w ith a surface area of about Im ~. lUpumbyeo (a Korean ricecultivar) was planted at a rate of one plant per hill and 22 hills per plot on 25 May.Three treatment plots and one control plot were replicated three times, for a total of 12plots. The three treatments were (I) irrigation with WSP effluent and no fertilisation(WENF); (2) irrigation with WSP effluent and half of the conventional fertilisation(WEHF); and (3) irrigation with WSP effluent and conventional fertilisation (WECF).The control plots (CONTROL) were irrigated with potable water, and conventional ferti-l isation was applied. A conventional fertil isation rate of 1 1 0 -7 0 -8 0 kg/ha N -P2 O 3-K 2Oand other standard cultivation practices of the local district were followed. The l-mplots were irrigated with a totai volu me of 430 L of wa ter, in addition to 1.2 X)L of natu-ral preci pitati on (first year 1,401 L, secon d ye ar 98 0L), to maintain the water levelbetween 5 and 10cm for the entire crop season. Th e paddy rice w as harvested on 20October and the yield was measured. Water quality of the irrigation water was analysedusing Stattdard Melbod s for tbe E.xarnina ion if Water and Wastewater (1998) and soilsamples were analysed using the Methods of Soil Analysis (1982).

esults and discussionCW performanceThe CW worked stably in winter without freezing even at temperatures below lO'^C, andwaste removal was still significant. The effluent DO was greater than the influent DO andwas generally above 2.0 mg /L. even w ithout auxiliary aeration. Redu ction of BOD5 andTSS was apparent in ihe CW system over the entire siudy period. Although the effluentBODs level was higher (p 0.05) in mass retention of BOD5


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Table Summary of constnjcted wetland (CW) performanceConstituents CW influent CWeffluent Removai rateGrowing seasonDO (mg/L) 0.3 0.61 2.4 0.97BOD5 (mg/L) 116.2 59.51 20.9 17.98 81.0 12.78TSS {mg/U 62.2 36.05 14.0 11.40 71.6 23.34T-P (mg/L) 13.4 4.03 7.1 3.58 44.0 33.20T-N (mg/L) 121.4 i 39.28 93.9 35.47 20,0 28.00FCM MPN/IOOmL) 693,800 207,299 7,667 3,250 98.9 i 38.34WinterDO (mg/U 1.2 1.04 2.3 0.63BOD5 (mg/L) 150.9 75.37 62.2 48.63 61.8 15.13TSS (mg/L) 102.7 44.61 32.8 19.14 64.8 20.19T-P (mg/L) 13.0 + 4.91 8.5 2,81 26.8 27.15T-N (mg/L) 120.2 46.84 108.0 36.18 7.7 12.91FC^(MPN /100mL) 564,910 i 192,486 5,256 + 2,158 99.1 4 0. 58DO. dissolved oxygen; BOD5, biological oxygen demand over a 5-day period ; TSS, total suspendedsolids; T-P, total phosphorus; T-N, total nitrogen; FC, fecal coiiformFecal coliform measured as the most probable number (MPN)

same range for both winter and the growing season, but the effluent concentraiion in thegrowing season was lower than in winter {p 0.05). The removal of T-N was poor, andthe removal efficiency of T-N in winter was even lower than in the growing season becausethe nitrogen removaJ processes (ammonification, niirificalion and denitrification) were tem-perature-dependent in Ihe CW system (Kadlec and Knight. 1996). The low T-N removalefficiency in this sludy may have been related to the high influent co ncen tration (overlCK) mg/L) and the limited hydraulic residence time (3.5 days) of the experimental CW system. Overall, the CW system produced satisfactory effluent concentrations and performedstably in ihe growing season, The average removal rates of constituents in winter werelower than in the growing season, but winter removal performance was still significant.Generally, the CW system was considered to be adequate for decentralised sewage treat-ment. However, winter performance was a cause for concern and measures for subsequentmanagement of CW effluent should be considered further.

Further po lishing by WSP for crop irrigationCW effluent w a sfurther po lish ed us ing a W S P f orcro p i r r igat ion in th e irr igat ion seaso( M a y - O c t o b e r ) . T h e r e w a s n o difference {p > 0.05) in B O D 5 a n d T S S b e t w e e n C Weffluent a nd W S Pef fluen t because B OD 5 a n d T S S c o n c e n t r a t i o n s i n t h e C W effluenw e r e l o w . T h e a v e ra g e B O D 5 a n d T S S levels in t h e W S Peff luent we re 10.8 mg /L a n9 .9 mg/L, r e spec t ive ly , a n dwere wi thin a n accep tab le r a nge .

The average T - P a n d T - N rem ova l ra te b y W S P w a s a p p r o x i m a t e l y 2 8 a n d 2 5 r e spec t ive ly (Tab le 2) . In thesam e per iod , t h e T - P a n d T - N remova l r a l e b y t h e C W w2 3 a n d 3 1 a n d t h e total T - P a n d T - N rem ova l ra te o f t h e com bine d t r ea tmen t sys t em( C W -f- W S P ) w a sa b o u t 4 6 a n d 5 1 , r e spec t ive ly . Feca l co l i fo rm ( F C ) c o n c e n i r a t i oin C W o r WSP ef f luent a r ecoinm only r educed b y a t least o n e l o gunit , b u t levels belo5 0 0 M P N / I O O n i L a r e difficult to achieve cons i s t en t ly (T anne r a n d S u k i a s , 2 0 0 3


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Table 2Summary of the wastewater stabilisation pond WSP) performance during the irrigation seasonConstituentspHEC dS/m)DO mg/L)BOD5 mg/L)TSS mg/L)T-P mg/L)T-N mg/L)F C MPN/100 mL)

CWeHluent7 2 0 301 18 0 3 653 8 0 478 9 2 19

10 8 4 4 45.7 0.1953.0 2.977,883,3 949,90

WSP effluent7.2 0.811,13 0,3505.3 0,7810.8 2,119.9 1.804.1 0.3438.9 3,27431.7 65.55

Removal rate_--

-28 0 6 5725 1 6 8096 1 1 44

-

CW, constructed wetland; constiluents are as in Table^Fecal coliform measured as the most probable number MPN)

Assessment of redaimed water irrigationAlthough irrigation has been practised ihroughout the world for .iseveral millennia,only in the pa.st century has the importance of the quality of irrigation water beenrecognised. The feasibility of irrigation with reclaimed water was evaluated based onseveral factors, including microorganism concenlrations, salinity and nutrient levels.in rural areas, toxic chemicals normally occur in low concentrations in reclaimedwater and may not cause great health risks. There has been considerable emphasis onthe control of microbiological healrh risks, especially regarding municipal wastewater.Based on the World Health Organisation (WHO) microbiological guidelines tor trea-ted wastewater (WHO. 1989, 2000), paddy rice culture irrigation practices maybelong to category B2, i.e. flood irrigation with restricted application to non-ediblecrops and exp osure to adult work ers only. FC coun ts should be less than 1,000 M PN /lOOmL under these condilions. As indicated in Table 2, the FC levels of CW efflu-ent were still too high for reuse as irrigation water. FC levels were further reducedto less than 500 M PN /iOO inL on average, showing over 95 remov al, in the sub-sequent WSP treatment, and these levels meet the WHO recommended guidelines(WHO. 1989. 2000) .

Excess salinity results in salt accumulation in the crop root zone and poor cropyields. The average salinity of WSP effluent was l.l8dS/ni. Based on the Food andAgriculture Organisation (FAO) irrigation water quality guidelines (FAO. 1985), thedegree of use restriction for this WSP effluent was slight to moderate (0.7-3.0dS/m).The nutrients in reclaimed water can provide fertiliser value for crop production. Themost beneficial nutrient, often present in high concentrations in reclaimed municipalwater, is nitrogen. However, excessive nitrogen may be detrimental to many crops,causing excessive vegetative growth, delayed or uneven maturity, or reduced crop qual-ity. The average T-N concentration of W SP effluent was 53 mg/L, More than 30 mg/Lis considered excessive, even for crops tolerant of excess nitrogen (FAO, 1985). Pro-blems caused by excessive salinity and nitrogen are unlikely to occur in Ihis case, how-ever, because the reclaimed irrigation water m ay be blended with about 900 mm ofprecipitation water, a volume about two or three times greater than that of the irrigationwater during the irrigation season (May-October). To reuse WSP effluent as crop irri-gation water, blending WSP effluent witb other irrigation water keeps salinity undercontrol (


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rop yieldThe average rice yield in the WECF treatment, which received reclaimed water irrigationand conventional fertilisation, was about 50% greater than that of the CONTROL(Table 3), indicating that reclaimed water irrigation can increase paddy rice yields. Theyield in plots with reduced fertilisation (WEHF) was also significantly higher than that ofthe CONTROL, and the yield in plots without fertilisation (WENF) was within the same

s_ range as that of the CO NT RO L (Table 3). Thi s implies that nutrients in the reclaimed wate r helped to increase the yield, and mad e up for part of the conv ention al fertilisationI deficit. Th e amo unt of niiirients applied hy fertilisation and reclaim ed wate r irrigationS may partly explain the difference in crop yield. Th e avera ge crop yield for the cxper-^ imental period approximately matched the quantity of nutrient input. As long as the con-

stituent concentrations are not extremely high, reclaimed water irrigation of paddy ricecultures may not be harmful and may even enhance crop yields.Soli characteristicsThe soil characteristics of the experimental plots were analysed to examine the effects ofreclaimed water irrigation (Figure 2). The results are expressed as averages of three repli-cate samples per plot, taken from the root zone after clearing the suriace organic layer(the upper 3-2Ocm of soil) . As paddy culture continued, the soil pH values slightlyincreased in reclaimed water irrigation plots (WENF, WEHF. and WECF). Vazquea-Montiel et a. (1996) reported significant increases in soil pH as a result of wastewaterapplication, Where conditions for nitrification are adequate, plants take up mainly nitrate,even when amm onium fertilisers are applied (Menge and Kirkby, 1987) and when plantstake up nitrate ions the growth medium becomes more alkaline (Vazquea-Montiel et ai1996). In this study, more nilrate may have been absorbed in the reclaimed water irriga-tion plots than in the CONTROL plots owing to the high nitrogen input, and this maypartially explain the increase in soil pH.

Electrical conductivity (EC) increased after the first year of the experiment compared tothe initial conditions, but it decreased after the second year (Figure 2). Continuous irriga-tion with reclaimed water could cause salt accumulation in the soil, but this was notobserved in our study. The possibility of sait accumulation may be lower in paddy ricefields than in upla nds because of different irrigation water m anage me nt pra ctices. W aterdepth w as maintained at 5 - lOc m during the irrigation season in (he paddy rice culture andall of the water in paddy rice fields is usually drained before the harvest. As paddy culturecontinued, the soil SAR values slightly increased in reclaimed water irrigation plots, butthe values were not high enough to cause serious physical soil problems. When the SARrises above 12-15, permeability and aeration problems arise and plants have difficultyabsorbing water (Munshower. 1994). Monitoring of soil structural stability and/or per-meability should be carried out periodically to detect deterioration that may adverselyaffect continu ed reclaim ed w ater irrigation or future land use. The cation e xch ang ecapacity (CEC) increased in all plots, including the CONTROL, as rice culture continued

Table 3Comparison of grain yields in irrigation and fertilisation treatmentsTreatment

Yield (kg /10 a) st yearWENF

588.6WEHF

672.8WECF

799.6CONTROL

524.4LSD (0.05

120.0


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1 5 9 1 5 9 1 ^ year 2 ' 'yearMonth

1 5 9 1 5 9 12 ^yearMonth

1 5 9 1 5 9 11^ 'year 2 '^yearMonth

WENF WEHF WECF CONTROLR g u r e Analysis of soil samples from experimental plots. EC, electrical conductivity; SAR, sodiumadsorption ratio; CEC, cation exchange capacity; T-P, total phosphorus; T-N, total nitrogenduring the study period. There was no difference in CEC between the CONTROL atidolhcr treatments (Figure 2). Total phosphoru.s (T-P) and total nitrogen (T-N) concentrationsremained fairly constant during the study period. The soil nutrient concentrations may belittle affected by reclaimed water, as long as the water is adequately treated.

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Sewage management tn decentra l ised rural areasCW -W SP system s can be properly used for the pnxluctio n of microbiologica l y safereclaimed water for crop irrigation in decentralised rural areas. During the irrigation sea-son, the sewage can first be treated in a CW. and its effluent discharged inlo a WSPdesigned to achieve the required water quality. CWs can function as the primary and sec-ondary treatment and WSPs as the reclamation system. Irrigation with reclaimed watercan not only provide a vital resource for enhancing agricultural productivity, but it canalso help increase crop yields, decrease chemical feriiliser use. enhance water qualily inreceiving water bodies via zero discharge, and allow a greater allocation of freshwatersupplies to urban use (Asano and Levine, 1998).

However, CW effluent can only be used for crop irrigation during the irrigation sea-son. At other times of the year, CW effluent must be discharged into receiving waterbodies. Relatively poor quality CW effiuent may occur during winter (Table I and thisCW effluent would require further treatment to prevent water quality degradation of thereceiving water bodies. WSPs could be used as intennittent discharge ponds during thewinter period to solve this problem. The CW effluent could be stored and treated inWSPs during the winter, and then discharged to the receiving water bodies in the spring.In a previous study (Ham et ai 2004). 3 months of storage in an intermittent dischargepond provided substantial water quality improvement. WSP water could be discharged to


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year-round method for sewage treatment and agronomic reuse in decentralised ruralarea.s. The CW-WSP system can be located in decentralised rural areas and become apart of the rural ecosystem. Theretbre. the ultimate disposal of sewage for agriculturalpurposes and subsequent land treatment may also be available.

Conclusions^ A CW was dem onstrated to be highly effective at treating sewag e in decen tralised ruralX areas durin g the grow ing season, but its effiuent was not clean enou gh for disch arge to^ receiving water bodies. The CW effluent was reclaimed for crop irrigation using a W SP during the growing season. After reclamation with a W SP . the level of FC

( < 5 0 0 MPN/1 0 0 tn L) me t WHO g u id e l in e s 1,000 M PN /lOO niL) for unrestricted irriga-tion. Therefore, WSP effluent may be used for crop irrigation without much concern forinfection by sewage-bome pathogens. Salt and nitrogen concentrations were high in WSPreclaimed water, but were not a limiting factor in this study. Supplemental use ofreclaimed water combined with existing sources of irrigation water is recommended,rather than irrigation using only a single water source. Irrigation of reclaimed water on topaddy rice cultures did not adversely affect the yield of rice. On the contrary, experimen-tal rice plots treated with reclaimed water demonstrated about a 507c greater yield onaverage than control plots. The chemical characteristics of irrigated soil did not varyduring the experimental period. Overall, the CW-WSP was found to be an effective sew-age reclamation system for decentralised rural areas, and reclaimed water could be reusedas a supplemental source of irrigation water for paddy rice culture with little concern foradverse effects. Sewage treatment and agronomic reuse via CW-WSP systems could bepractical integrated sewage management measures in decentralised rural areas for protect-ing the water quality of receiving water bodies and solving water shortages.

cknowledgementsThi s research wa.s supported by a grant (code 4-5-2) from th e Susta inable W aterResources Research Center of the 21st Century Fronlier Research Program in Korea.

ReferencesAsano, T. anJ Levine. D. 19^8). Waslewaier reclamation, recycling, antl reuse: an inirodiiclion. In

Wastewater Reclamation and Reuse Asanii. T. (ed.). Technomic Publishing, Lancaster, PA, USA.pp . 1-56-Crites. R. and Tchobanoglous. G. 1998).Small and DecentralizedWastewaterManagement Sy.>temsMcGraw-Hill. Boston Burr Ridge. IL. USA.

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Kuilkv. R.H. and Knighl. R.L. (1996). Trentment Wetlands. Lewis Publishers. Boca Raton, FT-, USA.Metealf and Bddy. Inc.. (2003).Wastev -aterEngineering Treatmeni and Reu.se. 4th edn. McGraw-Hill,

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Tanner, C C . and Sukias, J.P.S. (2003). Linking pond and wetland treatment: perfonnance of domtistic andfarm systems in New Zealand.V/tit Sei Tech..48(2). 331-3.39.

Vazquea-Montiel. O.. Horan, N.J. and Mara. D.D. (1996). Management of domestic wasiewater for reuse inirrigation. Wat Sd. Tech. 33(ltH I) , 355-362.

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Wetlands and Stabilisation Pond