Original Research The Performance of Species Mixtures in Nitrogen and Phosphorus Removal at Different Hydraulic Retention Times

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1 Pol. J. Environ. Stud. Vol. 23, No. 3 (214), Originl Reserch The Performnce of Species Mixtures in Nitrogen nd Phosphorus Removl t Different Hydrulic Retention Times Hi Wng 1, 2, Cheng-Ci Hung 2, Ying Ge 1, Jin zhi Wu 1, Jie Chng 1 * 1 College of Life Sciences, Zhejing University, Hngzhou 3158, PR Chin 2 College of Life Sciences, Shoxing University, Shoxing 312, PR Chin Received: 23 August 213 Accepted: 18 Decemer 213 Astrct The effects of species compositions (two-species mixtures or monocultures) nd hydrulic retention times (HRT; 1, 4, 8, 16, 24, 48 hours) on totl nitrogen (TN) nd totl phosphorus (TP) removl from eutrophic wter were studied in constructed wetlnd. Two species mixtures showed higher efficiency to remove TN nd TP thn monocultures. Averge removl efficiency of TN nd TP ws 49.6% nd 34.%, respectively. A longer HRT enhnced the removl efficiency of TN nd TP, which suggested tht species mixtures, HRT, nd species mixtures HRT interction were useful for incresing the wstewter TN nd TP removl. Keywords: constructed wetlnd, eutrophic wter, plnt mixtures, pollutnt removl, wstewter tretment Introduction Nitrogen (N) nd phosphorus (P) were the two mjor nutrients tht were importnt for the norml functioning of ecosystems, such s plnt growth nd survivl. However, excess influent of N nd P ws the min cuse of eutrophiction [1], which cused wter turidity nd often-unexpected iologicl chnges, such s loss of iodiversity [2, 3]. Enhncing N nd P removl from eutrophic wter ws criticl issue of wstewter tretment. As sustinle technique for nutrient removl from wstewter, ecologicl engineering hs ttrcted extensive ttention [1]. For exmple, constructed wetlnds (CWs) hve een widely used t present [4, 5] to remove excess nutrients nd other pollutnts from sewge in high efficiency [5, 6]. In CWs, N removl ws performed y plnt uptke nd denitrifiction processes [7, 8], nd P removl ws performed y sustrte (medi) sorption nd plnt *e-mil: jchng@zju.edu.cn uptke [9]. Plnts in CWs re functionlly nd morphologiclly different nd my ply oth direct nd indirect roles in nutrient removl [1, 11]. Plnt species richness (numer of plnt species) cn increse microil nd enzyme ctivities nd N removl in CWs [12, 13]. Plnt diversity my ply n importnt role in the functions (plnt iomss ccumultion nd nutrient removl) of wetlnds [14-16]. However, studies using the numer of species lone cnnot descrie community properties dequtely [17]. Furthermore, differences in species compositions were more sensitive thn diversity mesures to detect the influence of mngement on the plnt [18, 19]. The chnge of species compositions ffects the function of the phytoplnkton community in polluted qutic ecosystems [2]. However, the reltionship etween plnt species compositions nd removl efficiency of TN nd TP in CWs hs not yet een sufficiently solved. In CWs, some previous studies hve uilt nd screened out the suitle plnt species [14, 21] or plnt mixtures [13], nd evluted the removl efficiency of the CW t different

2 918 Wng H., et l. hydrulic retention times (HRT) [22]. Mny studies hve suggested tht the performnce of CWs ws generlly function of the HRT [22, 23]. So, for mximum nutrient removl, selection of proper HRT ws required for the ppliction of CW. This study ims to investigte the effects of plnt species composition nd HRT on TN nd TP removl functions in the CW. The results of this study cn e used to suggest mngement choices to improve the removl efficiency of nutrients in CWs. Tle 1. Plnt species nd compositions used in the study. Species compositions No. of the plots Ad, C, Cl, It, Ls, Td 18 C+Cl, C+Td, C+Ad, C+It, C+Ls, Cl+Td, Cl+Ad, Cl+It, Cl+Ls, Td+Ad, Td+It, Td+Ls, Ad+It, Ad+Ls, It+Ls Ad Arundo donx L., C Cyperus lternifolius L., Cl Coix lcrym-joi L., It Iris tectorum Mxim., Ls Lythrum slicri L., nd Td Thli delt. 45 Mterils nd Methods Site Description nd Experimentl Design A susurfce verticl-flow CW (8 m 2 ) ws uilt in 29 t Dongyng City, Zhejing Province, Chin. The structure of CW ( m, length width depth) is outlined in Fig. 1. The CW ws uilt with 3-lyer filter: one lyer of corse 1-2 mm snd (.4 m) t the top followed y 6-12 mm grvel (.2 m) in the middle nd 5-12 mm grvel t the ottom (.5 m). It ws designed to receive mximum tretment cpcity of out 1,5 m 3 dy -1. During the experimentl period (August to Octoer, 212), the sewge ws supplied once every two dys nd the flow ws controlled y wter-level ctivted pump. The CW ws fed with pretreted rel eutrophic wter (verge chemicl oxygen demnd (COD) = 9.6 mg L -1, iochemicl oxygen demnd in five dys (BOD 5 ) = 21.2 mg L -1, totl N = 6.1 mg L -1, nd totl phosphorus = 2.5 mg L -1 ) from Dongyng river. Plots in the CW were 3 3 m, spced.5 m prt. Polyvinyl chloride (PVC) pipes with dischrging holes provided consistent supply of wter to ech plot, ensuring tht ech plnt hd similr growth environment in the down-flow chmers of the CW (Fig. 1). Wter influent ws -3 cm elow the sustrte surfce. Wter effluent ws mixed 5 cm elow the surfce. There ws no physicl rrier to isolte the plots, so the smples were collected in the center of ech plot t depth of 3 cm to void the edge effect. Plnt species were Cyperus lternifolius L. (C), Iris tectorum Mxim. (It), Arundo donx L. (Ad), Thli delt (Td), Coix lcrym-joi L. (Cl), nd Lythrum slicri L. (Ls), which were commonly used in CWs of Chin. All plnted species hd similr length to ensure similr initil iomss nd were trnsplnted eight seedlings per m 2 (Tle 1). We plnted ll the species either in monoculture or with two-species comintion in Mrch 21 (Tle 1). Experimentl species tretments were estlished y independent rndom drws (Fig. 1). Ech tretment ws triplicted with 63 plots in totl (Tle 1). Smple Collection nd Anlysis Fig. 1. The experiment ws crried out in the wetlnd. Schemtic drwing of the verticl structure of the CW ws shown in Fig. 1. The numers in the empty rectngles indicted the numer of species in the plots (). At the surfce of the CW, the smll points on the pipe represented dischrge holes (). We mde 189 PVC pipes with dischrging holes (2 cm dimeter 3 cm deep) to collect sustrte solutions. In the center of ech plot, wter chnnel (2.5 m.3 m.2 m, length width depth) ws dug in August 212. The PVC pipes with dischrging holes were inserted into the wter chnnel t 5 cm. Eight vcuum pumps were used to collect the smples from the pipes. We collected the smples t the time of 1, 4, 8, 16, 24, nd 48 hours fter wstewter irrigtion. Three susmples of ech plot were mixed to form composite smple to estimte the effluent TN nd TP concentrtions. The smples were filtered with.45 μm sh-free filter ppers prior to nlysis. Totl N ws nlyzed using the lkline potssium persulfte digestion ultrviolet spectrophotometric method [24]. Totl P concentrtions were determined on cidified portions of ech smple vi persulfte digestion nd the scoric cid method [24]. Removl efficiency (%) of TN nd TP ws clculted s ((influent-effluent)/influent) 1. Wstewter smples were collected on the 2 August, 2 Septemer, nd 2 Octoer 212.

3 The Performnce of Species Mixtures Tle 2. Men nd stndrd error (SE) vlues of TN nd TP concentrtions in influent nd effluent from 8-2 to 1-2. Dte/month-dy Influent TN Effluent TN Influent TP Effluent TP Removl of TN (%) Removl of TP (%) ± ± ± ± ± ± ± ± ± ± ± ± Removl efficiency of TN nd TP ws clculted s ((influent-effluent)/influent) 1. Hrvesting of plnts ws performed in two prllel nd evenly spced.2 2 m strips in the center of ech plot on 4 Octoer 212. Plnt mterils were divided into oveground nd elowground, nd dried t 7ºC until constnt weight to determine dry mtter (DM) yield (referred to s oveground DM, elowground DM nd totl DM the sum of oveground nd elowground DM). Sttisticl Anlysis Anlysis of vrince (ANOVA) ws performed on the removl efficiency of TN nd TP using SPSS Version 16. (SPSS Inc., Chicgo, IL, USA). The effects of the species compositions nd HRT on the effluent TN nd TP concentrtions nd removl efficiency were tested using ANOVA generl liner models procedure. One-wy ANOVA ws used to evlute the significnce etween different prmeters ccording to species compositions nd the HRT y the Tukey HSD tests. The level of significnce of P =.5 ws ccepted. Significnt P-vlues (P <.5) were in old. The error estimtes given in the text nd error rs in figures re stndrd errors (SE) of mens. Results nd Discussions Both plnt species mixtures nd HRT were two importnt vriles in influencing the removl efficiency of CWs [22, 23]. The concentrtion nd removl efficiency of TN nd TP for the experiment re shown in Tle 2. Effects of Species Mixtures on Removl Efficiency of TN nd TP Species compositions hd significnt effect on TN concentrtions in effluent nd the removl efficiency of TN nd TP (Fig. 2). Removl efficiency of TN nd TP rnged from 47.8 to 51.3%, nd 29.6 to 36.7%, respectively (Tle 2). Effluent TN concentrtions in the plots of two-species mixtures were lower thn those in the monocultures (Fig. 2). However, effluent TP concentrtions in the plots of twospecies mixtures nd monocultures hd no significnt difference (Fig. 2). Removl efficiency of TN nd TP in the plots of two-species mixtures ws higher thn tht in the monocultures (Fig. 2c, d), which my e due to the higher plnt iomss in the mixture plnts community [5, 13]. The greter Effluent TN (mg/l) () Removl of TN (%) (c) Effluent TP (mg/l) () Removl of TP (%) (d) Fig. 2. Totl N nd TP concentrtions in effluent (, ) nd removl efficiency of TN nd TP (c, d) in the plots of monocultures nd two-species mixtures. ANOVA tested for significnt differences mong tretment mens. Vlues were mens ± SE. Removl efficiency of TN nd TP ws clculted s ((influent-effluent)/influent) 1.

4 92 Wng H., et l. plnt iomss, especilly elowground iomss, would increse the plnt N nd P uptke or retention more efficiently through the crossed distriution of roots mong different depths of sustrte [14, 25, 26], leding to decreses in N nd P concentrtions in effluent [22, 23]. On the other hnd, high iomss mixtures my increse oxygen diffusion nd orgnic exudtes in the rhizosphere [7, 16], which my increse N nd P trnsformtion y microes [25, 27], thus led to low TN nd TP concentrtion in effluent of more diverse communities. As result, the two-species mixtures produced the lrger plnt iomss thn tht in the monocultures (Fig. 3), ut hd lower TN nd TP concentrtions in effluent (Fig. 2, ). It showed tht plnt mixtures could increse plnt iomss ccumultion nd TN nd TP removl in CWs. Effects of Hydrulic Retention Time on Removl Efficiency of TN nd TP Hydrulic retention time (HRT) ws one of min fctors influencing the removl efficiency of the CW [22]. Plnt DW (g/m 2 ) Monocultures Two-species mixtures AG DM BG DM Totl DM Fig. 3. Aoveground (AG) dry mtter (DM), elowground (BG) DM, nd totl DM in the tretments of monocultures nd two-species mixtures. ANOVA tested for significnt differences mong tretment mens. Vlues were mens ± SE. In this study, we wnt to know how different HRTs (1, 4, 8, 16, 24, 48 hours) ffect the removl of TN nd TP. Results showed tht the HRT hd significnt effect on TN nd TP concentrtions in effluent, nd removl efficiency of TN nd TP (Fig. 4), showing the importnce of the HRT in TN nd TP removl. Removl efficiency of TN nd TP rnged from 8.3 to 62.1% nd 6.1 to 43.2%, respectively (Fig. 4 c, d). With the HRT incresed (1 to 48 hours), the TN nd TP concentrtions in effluent were decresed (Fig. 4, ), while the removl efficiency of TN nd TP ws incresed (Fig. 4 c, d). The HRT could ffect the durtion of wter within the CWs, flow depth nd sustrte porosity nd plnt growth through the nutrient supply in CWs [23], thus longer HRT my enhnce the removl of pollutnts [23]. Likewise, the study showed tht pollutnt removls depended gretly on the HRT [23]. The longer contct of microorgnisms with pollutnts could improve the removl efficiency of TN nd TP [23], which showed tht the increse of HRT could increse TN nd TP removl in CWs. Effects of Species Compositions nd Hydrulic Retention Time on Removl Efficiency of TN nd TP Across ll plots, we found tht species compositions nd HRT ffect the removl efficiency of TN nd TP (Tle 3). The removl efficiency of TN nd TP ws improved y the species compositions, plus HRT nd their interctions, showing tht the interction mong the species compositions, nd HRT ws lso importnt in influencing TN nd TP removl. Some studies lso found tht NO 3 -N removl ttriuted to the interction of plnt species richness nd HRT [22, 23]. Our findings lso confirmed tht the highest removl efficiency of TP ws in the CWs with two plnt Effluent TN (mg/l) c c d d () (d) c Fig. 4. Totl N nd TP concentrtions of effluent (, ), nd removl efficiency of TN nd TP (c, d) in different hydrulic retention times (HRT; 1, 4, 8, 16, 24, 48 hours). ANOVA tested for significnt differences mong tretment mens. Vlues were mens ± SE. Removl efficiency of TN nd TP ws clculted s ((influent-effluent)/influent) 1. Effluent TP (mg/l) () Removl of TN (%) Removl of TP (%) d c (c)

5 The Performnce of Species Mixtures Tle 3. Effects of species compositions (SC), nd hydrulic retention times (HRT), nd oveground (AG) DM, nd elowground (BG) DM, nd totl DM on the removl efficiency of TN nd TP. Results from ANOVA were included (F-test nd P- vlues). Significnt P-vlues (P <.5) were in old. Removl efficiency of TN nd TP ws clculted s ((influent-effluent)/influent) 1. Source of vrition Species composition (SC) Removl of TN (%) Removl of TP (%) F P F P HRT SC HRT AG DM BG DM Totl DM species t the longest HRT [23]. Plnt uptke ws regrded s n importnt removl pttern of TP. Likewise, this study lso found tht the elowground iomss hd significnt effect on removl efficiency of TN nd TP (Tle 3). Prior ppers lso emphsized the importnce of elowground iomss in nutrient dynmics of wetlnd systems [5, 26]. High diverse plnt mixtures could hve higher elowground iomss nd my increse N nd P comined uptke y plnts nd microes [25, 27]. A longer HRT my cuse longer contct of wstewter with the plnt roots nd microes in the CWs nd improve the removl efficiency of pollutnts [23, 28]. It showed tht species mixtures HRT interctions could increse TN nd TP removl in CWs. Conclusions The study of susurfce verticl-flow CW showed tht verge removl efficiency of TN nd TP ws 49.6% nd 34.%, respectively. The plnt mixtures were more useful for improving wstewter TN nd TP tretment efficiency thn species in monoculture. A longer HRT enhnced the removl efficiency of TN nd TP. Therefore, the results showed tht diverse plnt mixtures, longer HRT, nd species mixtures HRT interction were useful for incresing wstewter N nd P tretment efficiency in CWs. Acknowledgements Our study ws funded y the Ntionl Science Foundtion of Chin (grnt numer nd ) nd the technologicl plnning of deprtment of technology in Zhejing Province (No. 212C224). References 1. LI X. N., SONG H. L., LU X. W., XIE X. F., INAMORI Y. Chrcteristics nd mechnisms of the hydroponic io-filter method for purifiction of eutrophic surfce wter. Ecol. Eng. 35, 1574, SCHEREN P.A.G.M., ZANTING H.A., LEMMENS A.M.C. Estimtion of wter pollution sources in Lke Victori, Est Afric: ppliction nd elortion of the rpid ssessment methodology. J. Environ. Mnge. 58, 235, JIANG J. G., SHEN Y. F. Estimtion of the nturl purifiction rte of eutrophic lke fter pollutnt removl. Ecol. Eng. 28, 166, VYMAZAL J. Removl of nutrients in vrious types of constructed wetlnds. Sci. Totl Environ. 38, 48, WANG H., CHEN Z.X., ZHANG X.Y., ZHU S. X., GE Y., CHANG S.X., ZHANG C.B., HUANG C.X., CHANG J. Plnt species richness incresed elowground plnt iomss nd sustrte nitrogen removl in constructed wetlnd. Clen-Soil, Air, Wter, 41, (7), 657, CHUNG A.K.C., WU Y., TAM N.F.Y., WONG M.H. Nitrogen nd phosphte mss lnce in su-surfce flow constructed wetlnd for treting municipl wstewter. Ecol. Eng. 32, 81, BRIX H. Functions of mcrophytes in constructed wetlnds. Wter Sci. Technol. 29, (4), 71, CAO H.Q., GE Y., LIU D., CHANG S.X., WANG X.Y., CHANG J. Nitrte/mmonium rtios ffect ryegrss growth nd nitrogen ccumultion in hydroponic system. J. Plnt Nutr. 34, 1, GRÜNEBERG B., KERN J. Phosphorus retention cpcity of iron-ore nd lst furnce slg in susurfce flow constructed wetlnds. Wter Sci. Technol. 44, (11-12), 69, CHANG J., LIU D., CAO H.Q., CHANG S.X., WANG X.Y., HUANG C.C., GE Y. NO 3 /NH 4+ rtios ffect the growth nd N removl ility of Acorus clmus nd Iris pseudcorus in hydroponic system. Aqut. Bot. 93, 216, JAMPEETONG A., BRIX H., KANTAWANICHKUL S. Effects of inorgnic nitrogen forms on growth, morphology, nitrogen uptke cpcity nd nutrient lloction of four tropicl qutic mcrophytes (Slvini cucullt, Ipomoe qutic, Cyperus involucrtus nd Vetiveri ziznioides). Aqut. Bot. 97, 1, ZHANG C.B., WANG J., LIU W.L., ZHU S.X., GE H.L., CHANG S.X., CHANG J., GE Y. Effects of plnt diversity on microil iomss nd community metolic profiles in full-scle constructed wetlnd. Ecol. Eng. 36, 62, ZHU S.X., GE H.L., GE Y., CAO H.Q., LIU D., CHANG J., ZHANG C.B., GU B.J., CHANG S.X. Effects of plnt diversity on iomss production nd sustrte nitrogen in susurfce verticl flow constructed wetlnd. Ecol. Eng. 36, 137, ENGELHARDT K.A.M., RITCHIE M.E. The effect of qutic plnt species richness on wetlnd ecosystem processes. Ecology 83, 2911, CALLAWAY J.C., SULLIVAN G., ZEDLER J.B. Speciesrich plntings increse iomss nd nitrogen ccumultion in wetlnd restortion experiment. Ecol. Appl. 13, 1626, LIANG M.Q., ZHANG C.F., PENG C.L., LAI Z.L., CHEN D.F., CHEN Z.H. Plnt growth, community structure, nd nutrient removl in monoculture nd mixed constructed wetlnds. Ecol. Eng. 37, 39, 211.

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