Wastewater Utilization : A Place for Managed Wetlands

Con~mlctcd wc:~laI1~ arc: being \I~c:<i foT rho rcmoval of nunients from livestock Wl\Stewarer. However. narurlll vegetation typically used in constructed wotlands does not have marketable value. As Iln alterlUlrive, ngronomic plnl\ts grown undcr t1oodcd Clr !'nttlT'lltc:d ~il CQI1uition.'i Ihlll promorc dc:nitrific!lrion CR11 be uscd. Snldics on constructcd wctlands for swine wastc:walt:r w~rt: cOf1uUCled in weIland cellI; that conlnined eilht:r ttuLuTlll wcllanu plants or a combination of soybcans and rice f(lr two Y~I1~ with the objective of maximum nitrogen reduction ro mittimizc thc am(l\1I1t (If lalld rc:q\li~ for tcmlinal treatment. 11\ree systems, of TWO 3.6 by 33.S m wetland cells connected in series w~re used; tWO systems tach conIflmed B different combination of emergent wetland vegetation: rush{bulrush (sYStem 1) and bur-reed/cattail (system 2). 111e third system conrail1ed soybean (G/)'cine Inox) in ~tu~tcd-:;oil-c\llrurc (SSC) iT! thc rim ccll. and floodcd ricc (Oryza sativa) in the second ccll. NitrogcfI (N) IClading nlt~ Clf 3 and 10 kg hn"1 Juil w= u."cd ill thc fi~r ~nd $ccond yca~, rcspcctivcly, Thcsc loading ~tc:s wcrc obtained by mixing :.-wino: InglXJn liquid with fr=h watcr beforc it wa., ~pplicd to thc wctJand. Thc I1\1mcnt removal o:fficic:ncy "'~ similar in the rusll/bulnlSh, bur-reed/catrnils and u!,'tutlotnic plllnl ~~l=. MO:l1n ~" rcmoval uf N Wll,; 94% tIC tho: louuil\g r-.lte of 3 kg N ha.1 day' and decreased to 71 % at tl1e higher rare of 10 kg N hll-1 uuy"l. Tho: tWO yef1rs n\eans for above-grouJ1d dry mlOtIcr proouction for ru",h/b\lITU$h~ and bur-rccdfcart:lils was 12 and 33 Mg ha'l, respecTivcly. Floodcd ricc yield was 4.5 Mg \la-I, and ...oybeall grClWIl in !llIt\lT'Scion cu]t\lrc yicldcd 2.8 Mg !la"l. Additionally, rhr:. pcrfonnancc of !'cv"n o:oybcan c\t!tivaro: \l$iI1g SSC in coru.1.ructeU wo:llundl. with !lwine wa."tcwat~r a." thc w:ttcr l'0\1rcc W:1~ cval\llltcd for Cwo YO:IIT'i. Tho: culLivur Young had tile highest yield witl1 4.0 and 2.8 Mg hCl.1 iu eIlch year. Tllis illdiculcd Ihar production of acceptable !io)'bc=.1n yiel~ in COI1StruCted wetlands seems feasible with SSC using swine lagoon liquid, Two mlCrOCOS\11S srudies were established ro furrhcr invcstigatc: thc maTlagc:mc:nt of consmlctro wotlsnds. In thc fi~t microcosm cxpcrimcnt, tho c:ffccts (If !;win~ lagoon liquid on thc growth of wc:tlunu plUf1b; III half (lIbo\lt 175 mg/1 IImmonia) and full strcngth (abO\lt 350 mgJl /lmm(1ttia.) was inv~rigat~u, Tt wu~ cuncluded IIUlt wetla.nd plll1l!S CBn grow wt:11 it! III ]O:IL"t hulf IiLTcngth l!1g~)Qn liquid. Tn Ute secoud lnicrocOSIII experin1enL sequeucing nitrification-wetland TreatmentS was studied. W11en luLrified lilgoon liquid was added in batch applic:lliol1S (48 kg N ha.1 day'l) ro wctland microcosms tho nirrogcn rcmoval rare was four to five rimcs highcr rhan when non-nirrificd 111 goon liquid was utldo:u. Welll1nd mic.-rOCObm,; with plllnlo; wo:rt: mUTO: o:r'r'cctive than those with bur" ,;oil. 11\ese rc ulc; !iuHg"sr that Vo:g~Ulled wellan~ with nitrification pretreatment an: viabl~ ltc:lllmc:nt 1i'Ylil"m~ for removal of large quantifies of nilTo~o:n [ron\ swine lagoon liquid, (A$ian-Au$. J. Anlm. Scl. 1999, Vol. 12, No.4: 629-632) Key Wnrd... : Wetland-", WlI,;to:wuter UlilizaLiolt, COtlSltUcled Wo:lluntl.;


INTRODUCTION
Traditionally, animal wastes havc bccn rccycl~d through Ihe soil environment with little impact on wllter resources.Swinc production in Ihe SI.)ulheasrern Uniled State~ generates large amounts of wast~ mostly in the rOml or liqt)id manure that are treated and stored in anaerobic lagoons prior II.) lilf1d appl1clltitm.Application of liquid manure to land can havc scveral problems, :;uch 11$ t1l1i~nt1ce odor, high solids content, high nutrient concentrations, and limitl:d putnpit1g dis(at1ce~.Allhough a high degree of nutrient rcmoval may not bc ncccssary in fin in'l III wastewater treannent sYSten1S, one of the ways 10 minimize nutrient enrichment or WilIer r~SOt1rces is ro remove nutrients prior to land application.Constructed wetlands hElve received considerable attention a.c; a mcthod of wastcwater treatment that could rcducc ule land requirements by mn.~c; removal of nutrientS (Hunr ct al., 1995. \997).Construcled wedands remove N by both plant Ul'take and denitrification (Hammer. 1989. andHunr er al., 1995).However, "amral vegetation such as carlail and bulrush typically u~ed in constnlcteu weIland!; do not have marketable value.As an alrcmativ~.agronomic plantS such as rice or !;oybean grown in SSC can be \1.c;ed(Nalhanson et al.. 1984).SalurnLecl-.c.oil-cultl1rc with soil conditions rl1at promorc dcnitrification can be created on raised flat beds that are !rurroundcd by furrows.Irrignlion WtUer in lhese furrows is kept at a con!;tnnt lcvcl and below the surface of.thc bcd l(.) provide a thin aerobic surface layer.(Lawn and 8yth, 1989).Soybcan con acclimnte a11d grow wel] under !;uch SSC condirions (Hartley et al., 1993).
This paper summarizcs the studics on swinc lagoon liquid utilization and treatment cond\lcted in wetland cells that conlQined either natural weLland plants or a combination of soybeans and rice with the objecTive of maximum nitrogen reduction to minimize the amount of land necessary for terminal treatment.Additionally, microcosm studies were condllcled to invesligRle rhe IruMENIK ET AL.
effects of swinc lagoon effluent on the growth of wcrland plnnt.~,and to research the renovation of swine wa~r~water by sequencing nitrificanon-werland treatmcnts.

Site characteristics
The rescarch sire is located in Duplin Co., NC.It hils a nursery operation of 2600 pigs (average weight; t 3 kg) that uses a flushing system to recycle lagoon liquid to clean the ho\L'5e and a single-stage lagoon for primary treatment, The average liquid volume of the lagoon is 4,100 m3.On a mOl.~f: basis, lagoon liquid contained only 17% of the N which entered the lagoon (Szogi et 0.1, 1996).Typically, thc lagoon liquid col1[ained 365 tng/1 of total Kjeldahl nin-ogcn(TKN), mo~lly (> 95%) as ammonia, 93 mg/l tota] phosphorus (TP) and 740 lng/I Chcmical Oxygen Dcmand (COD), Thcsc results suggest tl1at consaucted wetlands either with natural wetland or agronomic planl~ are excellent for mnss removal of N from swine lagoon liquid.However, ar the high loadin~ rales nccessary for substantivc mass removal n. }Iigh concentration of nitrogen remains in the eftllient thus, subsequent In.nd application is necessary.Crop lands, vegemcive slrips.and woodl!lnd~ are viable option-,: (or chc final treatments.Tcrnlinal land application docs nor require discharge pernlitS aJ1d monil<.1nng of discharge water qlll1ljry.The capaciry of ma5S N removal by wel!anus can likcl'j be iTlcreH:;cd by pre-wetland trcarmcnc of lagoon liquid such as overland now, or mcwa filtration.
In the IlISt belch application, waslewater enrich cd with nitillte was applicd to the microco~m wetlllnd unit.<; at a rate of 190 kg nitrate-N{ha and a retention time of four days.Differences in removal were nor significant between the wetland plant treatment and the mineral soil + C source.Results showed about 80% removal of nitrate by treatment 1 (wetland plants) and 2 (mineral !;oil + C) comparcd to 14% by treatment 3 (the control with 110 plants).This removal potencial is equivalent, on an annual basis, ro about 14.000 kg NI ha, which is 5.4 rimes higher than the N removal without nitrification prelreiliment.This indicates that the capacity of mass N removal by wetlands can bc !>ignificantly incrcased hy I\itritWLcation pretrcatmcnt.
In conclusion, whcn nitrified wastcwaler W:l-C; adclcd in batch applications to wetland microcosms thc niliogen removnl rate was four to five timc!! higher than when non-nitrified WaStewater wa!! added.WeIland microcosms with plants wore more effective than those with barc soil and no C addition.Thesc result.';suggest that wellands with nitrification pretreatment are viable treatrncnt systerns for rcmoval of large quantities of nitrate-N from swine wastcwRler.Increascd 11itrate removals recordcu for wetland systems with carbon addition indicate wetl3nus may becomc carbon limited for dcnitri!icalio11.

Different nitrogen loadings
Thc objectives of th~ first microcosm study were to dc[ennine thc e1tect of diffcrent swine lagoon liquid strengths 011 a mixed planting of two wetland plant specie.o;,Juncus effu.~us and Scirp!L.~ validu:;, and the effccls of the vegetarion on N removal.nle eJCperiml-"Ulal design was a mndomizcd complete block, 3 x 2 factorial with 3 replications.The three Ireatment variables were full strength lagoon liquid (about 350 mgjl ammotlia).half !Olrength lagoon liquid (about 175 mg/l ammonia), and a freshwaler controlo The vegetation variablc wa.o; a weIland plant treatment of Scirpus validus and Juncus effilSus comparcd with no plants.Each of thc 1 S microcosms had 11 surface area of one m~ (2.0 x 0,5 m).Each microcosm was lined with PVC film, filled with sandy loam topsoil to a depth of 22 cm, and plan red with eighteeon pl!lnts of each species, The lagoon liquid and frcshwater treatments were applicd u.o;ing pumps controlled by timers set to apply Ii [oral of 7 litel'S per day in dlree equal applications.Outflow pipcs were set to maintain a water dcpch of no grcatr;r th:m 10 cm and the outflow was collcctcd in barrels buried at thc end of each microcosm.Thc collection burrel.c;were sampled every two weeks to dctermine watcr voll1me and nutrient concentrations.l1\e hydraulic loading ratc of 7 liters per day of full strength lagoon liquid supp1ied about 30 kg ba'l day" of nitrogen and ?kg haol day-l of pho."phorus.
During the spring (March to mid-May) plant growth was greatest in the full strcngrh treatment.Total above ground biomass harvested on May 18. ]995 was 422 S m2 for (he control, 989 g/m2 for the half strength treatment and 1810 g/m2 for the full strcngLh.The amount of N prcsent in the plant tissue at thc time of harvest was 4.5 gjml (control), 46.9 g/m1 (half strength), and 61,1 gjml (full .c;rrengili).
During most or Ille growing season, there wa!O lLO outflow from The vegctated microcosms receiving eith~r ha1f or full strcngth liquid.With no outflow there was. in effccl.J 00% trcatment.The wetland microcosms were a sink for 15 kg ha"lday" for the half strengrh treatment and 30 kg ha-1t.layOIfor the full strength.Thc hydraulic loading rate wa!O well below optimum for the amotmt of growth that occurred in response to nutrient inputs from the efflucnt.In early June, water rcquitement.o;for groWth in the full strength effluent treatmcnt e)(ceeded th~ ..;upply, rcsul\\1\g in a dic back of the vcgetation.Data [tom the full Sltet\g[h treatmcnt collected after thaI time wcrc tli!:regarded. Conclusions on the cfrect of diffctent nitrogen loading..; on thc growdl of wetland plants wcrc: 1) Scirpus validus and JunCIL~ effi4Sus grew vigorously in !1alf s[T~nglh lagoon liquitl; the effect of the ful1 s[Ten~th lagoon liquid on groWth was inconclusivc bcc~u."r; of confounding cffccts with inadcquate tnoisrure; 2) Scirpu:; validus Wll,-; better adapted to the conditions imposed by [he experiml;1'\t tl1an Juncu:I ~rfu.$us; 3) During pt:rit~-; of maximum plan!growth, watcr use by plants rccciving haIr strength lagoon liquid was twice thllt of treatments
Two miCTocosrns stUdies were estnbli~hcd to further investigate the management of con~'tructcd wetlands.The fiTS! ~Ludy evaluated thc effect of different nitrogen loadings on thc Growth of wetland plants, and the second one the potential of nitrogen r~moval by diffcrcnt nitrification-wetland trea[mt:nts.