Bioresource Technology

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1 Bioresource Technology 1 (29) Contents lists vilble t ScienceDirect Bioresource Technology journl homepge: Enhnced solid liquid seprtion of diry mnure with nturl flocculnts M.C. Grci, *, A.A. Szogi b, M.B. Vnotti b, J.P. Chstin c, P.D. Millner d Agriculture Technologicl Institute of Cstill nd Leon (ITACyL), Animl Wste Reserch Line, Crreter de Burgos, Km. 119, 4771-Vlldolid, Spin b USDA-ARS Costl Plins Soil Wter nd Plnt Reserch Center, Florence, SC, USA c Dept. of Agriculturl nd Biologicl Engineering, Clemson University, Clemson, SC, USA d USDA-ARS Sustinble Agriculturl Systems nd Food Sfety Lbs, Beltsville, MD, USA rticle info bstrct Article history: Received 27 June 28 Received in revised form 1 November 28 Accepted 11 November 28 Avilble online 13 December 28 Keywords: Animl wste Biopolymers Chitosn Diry cow wstewter Solid liquid seprtion The im of this study ws to determine the effectiveness of nturl flocculnts to reduce solids nd nutrient lods in diry cow wstewter using solid liquid seprtion; chitosn ws used s model. Its use efficiency nd optimum ppliction rte were determined using flushed diry cow mnure of vried strengths.4%,.8%, 1.6%, nd 3.2% totl solids (TS) content. Tretments consisted of nine rtes of chitosn. The flocculted mnure ws dewtered using 1-mm nd.25-mm screens. Seprtion by screening lone ws not effective; verge efficiencies were bout 6% for totl suspended solids (TSS), 22% for totl Kjeldhl nitrogen (TKN), nd 26% for totl phosphorus (TP). Mixing with chitosn before screening substntilly incresed seprtion. At optimum chitosn rte (.5 g/l for the highest strength effluent), seprtion efficiencies were >95% for TSS, >73% for TKN, nd >54% for TP. The results of this study indicte tht nturl flocculnts such s chitosn re useful for the solid liquid seprtion tretment of livestock wstewter. Ó 28 Elsevier Ltd. All rights reserved. 1. Introduction * Corresponding uthor. Tel.: ; fx: E-mil ddress: GrGonMi@itcyl.es (M.C. Grci). As herd sizes incresed over the lst few decdes, concentrtion of diry mnure hs creted potentil environmentl problems. Most often, the mount of mnure nutrients produced exceeds the ssimiltion cpcity of nerby croplnds (Nennich et l., 23). While utiliztion of diry mnure offers benefits such s increse of soil fertility nd qulity, improper use cn produce ir qulity nd odor concerns nd impir wter qulity. The US Environmentl Protection Agency hs found tht wtersheds with high concentrtion of diry opertions hve the gretest potentil of the mjor frming types for ccelerted eutrophiction of nerby surfce wters becuse of the nonpoint source pollution potentil of the wstewter (USEPA, 22). Thus, there is mjor public interest to develop nd demonstrte best control technologies tht cn lessen or eliminte the disposl problem of lrge mounts of diry wstewter. A simple technology tht hs the potentil to reduce nutrient lods in diry wstewter is solid liquid seprtion. As pre-storge tretment, solid liquid seprtion of diry wstewter yields seprted solids contining orgnic mtter tht cn be used for compost production or energy genertion (Zhng nd Lei, 1998). The remining seprted liquid cn be used in lnd ppliction or reused on the frm s flushing wter. Solid liquid seprtion methods include physicl processes such s sedimenttion, centrifuging, screening, or filtering (Dy nd Funk, 22). Usully, solid liquid seprtion efficiencies of mnure seprtors re in the rnge of bout 2 68% removl (Burton nd Turner, 23; Chstin et l., 21). However, seprtion efficiencies cn be ugmented by chemicl ddition of cogulnts nd flocculnts to bind together the smll prticles of solids into lrger clumps (Sievers et l., 1994; Timby et l., 24; Vnotti nd Hunt, 1999, 22; Zhng nd Lei, 1998). Along with the solids, solid liquid seprtion combined with floccultion using polycrylmide (PAM) polymer hs been found to seprte 85 88% of orgnic N from the liquid phse (Vnotti et l., 22, 25). Polymer flocculnts re mcromolecules of vrying moleculr weights tht cn hve positive, negtive or neutrl chrges (Sievers et l., 1994). These mcromolecules destbilize suspended chrged prticles by building bridges mong suspended prticles, resulting in newer, lrger prticles (or flocs) tht settle out of the liquid (Vnotti nd Hunt, 1999). Flocculnts cn be divided into three groups: () inorgnic flocculnts such s luminum sulfte (lum) or polyluminum chloride (PAC); (b) orgnic synthetic high-polymer flocculnts such s polycrylmide nd polyethylene imine; nd (c) nturlly occurring flocculnts such s chitosn (No nd Meyers, 1989), gur gum (J.H. Loughrin, personl communiction), sodium lginte (Sievers et l., 1994) nd microbil flocculnts (Slehizdeh nd Shojosdti, 21). Although inorgnic nd orgnic synthetic high-polymer flocculnts hve been most commonly used becuse of their flocculting effectiveness nd low cost, nturl orgnic flocculnts my hve the dvntge over the synthetic ones becuse they cn be produced /$ - see front mtter Ó 28 Elsevier Ltd. All rights reserved. doi:1.116/j.biortech

2 5418 M.C. Grci et l. / Bioresource Technology 1 (29) economiclly in lrge scle nd with lower energy input (Slehizdeh nd Shojosdti, 21). In our study, we tested chitosn s nturl flocculnt to enhnce solid liquid seprtion from diry mnure. Chitosn is nturl, biodegrdble, nontoxic, polyctionic polymer with multiple pplictions in food, griculturl, phrmceuticl, nd chemicl industries (Srkr et l., 26; Selmer-Olsen et l., 1996; Shhidi et l., 1999; Ymmoto et l., 1995). Chitosn is the decetylted form of chitin, polymer found in certin fungi nd the exoskeleton of rthropods (Entsr et l., 23). Commercil chitosn is mostly obtined from chitin found in shrimp nd crb shells. Since shrimp nd crb shell wste hve production of pproximtely metric tons of wste per yer worldwide, chitin is n bundnt nturl mteril for chitosn production (Peter, 1995). Our objective ws to evlute the effect of wstewter strength on seprtion of solids nd nutrients from flushed diry mnure using chitosn s nturl polymer flocculnt. In this work, we determined polymer use efficiencies in flushed mnure of vried strength nd estblished optimum polymer ddition rtes. In ddition, to help reduce nlyticl costs of wstewter mngement nd improve solid liquid seprtion process control, we lso investigted whether turbidity could be used s surrogte of expensive lbortory nlysis of solids nd nutrients. 2. Methods 2.1. Diry wstewter smples Diry mnure smples were collected from the Lemster Diry Center t Clemson University in South Crolin. The fcility included n open-sided freestll, holding re, nd prlor. The freestlls were bedded with modest mounts of orgnic bedding (shvings nd strw), nd the stll nd feed re ccess lleys were flushed once or twice dy. The floors of the holding re nd prlor were lso clened by flushing two or three times dy. All of the rinwter tht fell on the roofs nd the lleys nd the flushed mnure from the niml housing fcilities nd milking center were conveyed to tretment lgoon by grvity using concrete chnnels nd lrge pipe. Four diry mnure smples with different totl solids (TS) content were used to crete rnge of diry mnure strengths typiclly found in diry fcilities throughout the USA. Diry mnure with TS content of.4%,.8%, 1.6%, nd 3.2% ws obtined by mixing solid diry mnure nd lgoon wter. Solid diry mnure ws collected with shovel from the flush lley in the freestll brn. The lgoon wter ws collected from the flush tnk tht receives the liquid from the tretment lgoon. Both mterils were collected seprtely in 2-L plstic continers nd trnsported in lrge coolers filled with ice to the ARS Costl Plins Reserch Center in Florence, SC, nd kept t 4 C until mixed in different proportions nd used in the bench experiments. Chrcteristics of the solid diry mnure nd tretment lgoon re described in Tble 1. Smples of lgoon wter collected in the field were trnsferred into 1-L vessel nd stirred t 15 rpm with high-torque lbortory mixer to obtin homogeneous smples. A peristltic pump (Prts nd , Cole Prmer Instrument Co., Vernon Hills, IL) ws used to trnsfer 8 L of lgoon wter smple from the 1-L mixing vessel into four 2-L vessels used to mix the lgoon wter nd the solid diry mnure. Four different mounts of solid diry mnure were trnsferred to ech 2-L vessel to chieve.4%,.8%, 1.6%, nd 3.2% of TS. Ech 2-L vessel ws stirred with high-torque lbortory mixer nd 2-mL subsmples were trnsferred to 25-mL Erlenmeyer flsks for lbortory experiments. Chrcteristics of the four diry mnure strengths re summrized in Tble 2. Tble 1 Chrcteristics of the diry mnure solids nd lgoon liquid tht were mixed in different proportions to crete the four flushed mnure strengths used in the study. Prmeters Solid mnure (g/kg) b Lgoon wter (g/kg) Totl solids (6.4) 2.31 (.3) Totl Kjeldhl nitrogen 13. (.15).157 (.1) Totl phosphorus 1.7 (.1).49 (.3) Moisture (6.4) (.3) Mens (SE), n = 4. Solid mnure ws collected from the freestll lleys using shovels. Lgoon liquid ws collected from the surfce ( 15-cm depth) of the nerobic lgoon. Solid mnure nd lgoon liquid were mixed in vrious proportions to crete flushed mnures of vrious strength typiclly found in flushing systems for diry (Tble 2). b Grms per kilogrm of wet solid mnure. Concentrtions of TKN nd TP in solid mnure on dry bsis were 16.3 nd 5.8 g/kg, respectively. Tble 2 Chrcteristics of the four diry mnure strengths used for solid liquid seprtion. Diry mnure prmeters Flushed mnure strength 2.2. Screening nd floccultion tretments Low Medium High Very high Totl solids (g/l) 4.6 (.6) 8.3 (.38) 16.3 (.99) 32.2 (2.4) Totl suspended solids (g/l) 2.6 (.14) 5.3 (.22) 11.3 (.5) 28.3 (1.5) Voltile suspended solids (g/l) 1.6 (.13) 3.2 (.14) 6.4 (.34) 13.8 (.4) Chemicl oxygen demnd (g/l) 3.1 (.5) 6.5 (.67) 17.5 (1.5) 29.2 (2.5) Totl Kjeldhl nitrogen (mg/l) (3.2) 33.6 (2.9) (21) (13) Totl phosphorus (mg/l) 7.7 (1.7) 92.7 (1.) (5.23) (7.) Mens (SE), n = 4. Solid mnure nd lgoon wstewter smples (described in Tble 1) were mixed in different proportions to obtin flushed mnure with totl solids (TS) concentrtions of bout.4%,.8%, 1.6%, nd 3.2% (low, medium, high, nd very-high strength, respectively). Retention of suspended solids nd nutrients in flushed diry mnure using screens of vrious sizes without flocculnt ddition ws performed using diry mnure strength of 1.6% TS. Homogenized diry mnure ws pssed through nine screens with mesh sizes between 3.36 nd.25 mm. Screens with mesh sizes of 3.36, 2., 1.,.59,.5,.297, nd.25 mm were ASTM stndrd wire screen sieves tht corresponded with mesh size numbers 6, 1, 18, 3, 35, 5, nd 6, respectively. Screens with mm nd.794-mm opening sizes were stinless steel with round perfortions of 1/16 nd 1/32 in., respectively, commonly used in commercil screen seprtors. After screening, recovered liquid smples were nlyzed for TSS, VSS (voltile suspended solids), TKN (totl Kjeldhl nitrogen), nd TP (totl phosphorus). Amount retined (%) TSS = -9.6 mesh size R 2 =.918 TKN = mesh size R 2 =.527 TP = mesh size R 2 =.59 TSS TKN TP Mesh size (mm) Fig. 1. Retention of suspended solids nd nutrients in flushed diry mnure using screens of vrious sizes. Dt re verge of two replicte tests performed on high strength diry effluent (TS = 1.6%, Tble 2). TSS = totl suspended solids, TKN = totl Kjeldhl nitrogen, TP = totl phosphorus. Initil concentrtions were: TSS = g/ L, TKN = 57.8 mg/l, nd TP = mg/l.

3 M.C. Grci et l. / Bioresource Technology 1 (29) Floccultion experiments were crried out using diry mnure with.4%,.8%, 1.6%, nd 3.2% TS content. Chitosn (prcticl grde supplied by Sigm Aldrich Inc.) ws dissolved in 2% cetic cid (No nd Meyers, 1989) for finl concentrtion of.45% (ctive polymer ws not reported). Optimum chitosn dosge ws determined using nine polymer rte tretments pplied in increments of 6 mg/l in dosge rnge of 54 mg/l. After polymer ppliction smples were stirred for 1 min nd pssed through 1-mm nd.25-mm mesh size screens, the filtered liquid ws recovered nd nlyzed for solids, nutrients, nd turbidity Anlyticl methods All treted nd untreted liquid smples were nlyzed ccording to Stndrd Methods for the Exmintion of Wter nd Wstewter (APHA, 1998). Solids nlyses of the liquid smples included TS, TSS, nd VSS. Totl solids re the solids remining fter evportion of smple to constnt weight t 15 C nd include TSS nd dissolved solids (DS). Totl suspended solids re the solids portion retined on glss microfibre filter (Whtmn grde 934-AH, Whtmn Inc., Clifton, NJ) fter filtrtion nd drying to constnt weight t 15 C, while VSS is the frction of the TSS tht ws lost on ignition in muffle furnce t 5 C for 15 min. Therefore, the TSS nd VSS re mesurements of the insoluble totl nd voltile solids tht re removble by seprtion. The soluble frction or dissolved solids ws determined by subtrcting the TSS from the TS. Chemicl nlyses consisted of ph, chemicl oxygen demnd (COD), mmoni-n (NH 3 -N), nitrte-n (NO 3 -N), TKN, orthophosphte-p (o-po 4 ), nd TP. For COD we used the closed reflux method (Stndrd Method 522D). The inorgnic o-po 4 frction, lso termed rective P, ws determined by the utomted scorbic cid method (Stndrd Method 45-P F) fter filtrtion through.45-lm membrne filter (Gelmn type Supor-45, Pll Corp., TS, mg/l 9 6 COD, mg/l TSS, mg/l TKN, mg/l VSS, mg/l TP, mg/l % solids.8% solids 1.6% solids 3.2% solids Fig. 2. Removl of solids, COD, nd nutrients from liquid diry mnure of vrious strengths (.4%,.8%, 1.6%, nd 3.2% TS) by chitosn floccultion nd screening (.25-mm size screen). Ech point is the men of two replictes.

4 542 M.C. Grci et l. / Bioresource Technology 1 (29) Ann Arbor, MI). The sme filtrte ws used to mesure NH 3 -N by the utomted phente method (Stndrd Method 45-NH 3 G) nd NO 3 -N by the utomted cdmium reduction method (Stndrd Method 45-NO 3 F). The TP nd TKN were determined using the scorbic cid method nd the phente method, respectively, dpted to digested extrcts (Technicon Instruments Corp., 1977). The orgnic P frction is the difference between TP nd o-po 4 nlyses nd includes condensed nd orgniclly bound phosphtes. The orgnic N frction is the difference between TKN nd NH 3 -N determintions. Turbidity ws mesured in the treted effluent by the nephelometric method (Stndrd Method 213 B) with 21P Hch portble turbidimeter (Hch Co., Lovelnd, CO) fter screening tretment through 1-mm nd.25-mm mesh size screens. Solid mnure smples were nlyzed for moisture content using microwve moisture nlyzer (Omnimrk Instrument Corp., Tempe, AZ). Solids smples were dried t 45 C in forcedir chmber nd nlyzed for TKN nd TP using the cid block digestion of Gllher et l. (1976) nd the utomted methods described before Sttisticl nlyses Tretment performnce ws determined by the difference between the solids, nutrient, nd COD concentrtions in the effluent pssing the screen nd those in the initil smple before chitosn ppliction nd screening. Dt were nlyzed by mens nd stndrd error, nd by nlyses of vrince to evlute chitosn tretment rte effects (SAS Institute, 1988). Liner nd non-liner regression nlyses (Drper nd Smith, 1981) were used to describe the reltionship mong mesured vribles. Non-liner regression nlysis tht included lest squre itertion nd Guss Newton method (Freund nd Littell, 1991) ws used to determine liner-plteu functions to estimte optimum chitosn ppliction rtes nd mximum TSS seprtion. Both prmeters were used to determine TSS removl efficiency nd chitosn use efficiency t vrious diry mnure strengths (Vnotti et l., 22). 3. Results nd discussion 3.1. Removl of solids nd nutrients by screening Homogenized diry mnure smples with TS concentrtion of 1.6% were pssed through nine screens with different mesh sizes (Fig. 1). Effectiveness of the screening tretment ws determined by the difference between the solids nd nutrient concentrtions in the effluent pssing the screen nd in the initil smple before screening. Results shown in Fig. 1 indicte tht screening per se ws not highly effective in removing TSS, TKN, nd TP. Seprtion efficiencies were consistently low mong the vrious mesh sizes (<45% for TSS nd <2% for both TKN nd TP). Severl studies on solid liquid seprtion of diry wstewter looked into the retention of suspended solids nd nutrients using screens without flocculnt ddition. Seprtion efficiencies from our study were lower thn those reported by others. A study from Zhng nd Westermn (1997) reported 49% of TS removl using 1.68-mm screen size nd influent TS content of 4.6%. Fulhge nd Hoehne (1998) obtined removl efficiencies of 45.5% for TS, 17.1% for TKN nd 11.% for TP, using commercil sttionry inclined screen seprtor with 1.5-mm screen size. Using the sme screen size (1.5- mm), Chstin et l. (21) reported seprtion efficiencies of 62.6% for TSS, 49.2% for TKN, nd 53.1% for TP in diry mnure nd influent TS content of 3.8%. Our lower seprtion efficiencies results (28% for TS, 5.8% for TP nd 6% for TKN nd mesh size screen of mm) my be due to the lower TS content of the diry mnure (1.6%) used in our experiment nd the modest mounts of orgnic bedding used in the freestll t the Lemster Diry Center. It hs been reported tht lrge solid prticles ssocited with orgnic bedding nd wsted feed incresed the frction of TSS of the flushed mnure removed by seprtors (Chstin et l., 21). Our results indicte tht simple screening ws rther ineffective in removing solids nd nutrients from diry mnure. Therefore, chemicl floccultion ws needed to highly reduce TSS nd nutrients (N nd P) from diry mnure Enhnced solid liquid seprtion with chitosn Reduction of solids Floccultion experiments were crried out using four different diry mnure strengths:.4%,.8%, 1.6% nd 3.2%, nd chitosn s flocculnt. The effect of chitosn dosge on verge TS, TSS, nd VSS concentrtion t incresing mnure strength using.25-mm size screen is shown in Fig. 2. For ech diry mnure strength, the optimum chitosn rte dosge necessry for high solids removl efficiency incresed with TS content. At optimum dosge, chitosn tretment could remove >96% of TSS nd VSS from ll diry mnure strengths used in this study. The effect of chitosn dosge nd screen size (.25-mm nd 1- mm) on TSS nd VSS removl rtes is shown in Tble 3 for flocculted liquid diry mnure with 3.2% TS concentrtion. The highest removl efficiencies were obtined for both TSS nd VSS (>98%) using.25-mm screening t chitosn rte of 54 g/l. However, t the sme polymer rte of 54 mg/l, these efficiencies were bove 95% nd 92% for TSS nd VSS, respectively, using 1-mm screen size. This outcome indictes tht t optimum chitosn rtes the reduction in screen size results in smll improvement in TSS nd VSS seprtion. Tble 3 Removl of totl nd voltile suspended solids nd nutrients from liquid diry mnure strength by chitosn floccultion nd screening of 3.2% of totl solids concentrtion nd two screens. Removl efficiency (%) b Polymer rte (mg/l) TSS VSS TKN TP.25-mm screen c 64.1 (3.) 67.8 (.69) 8.3 (5.6) 12.1 (3.2) (2.8) 63.9 (.38) 14.8 (3.8) 16.9 (1.9) (3.) 69.2 (1.7) 14. (3.5) 16.3 (1.1) (2.6) 68.5 (1.5) 19.6 (2.2) 22.9 (.6) (2.4) 72.7 (3.8) 27.6 (1.) 28. (1.) (1.5) 75.4 (6.3) 31.3 (.28) 29.6 (.59) (.4) 76.4 (1.1) 4.7 (2.5) 36. (2.5) (1.) 81.7 (6.1) 43.8 (5.6) 37.3 (3.9) (1.5) 96. (.31) 67.9 (1.4) 49.4 (.31) (.3) 98.4 (.17) 72.5 (.7) 53.9 (1.2) 1-mm screen 55.9 (3.4) 34.7 (13) 35.7 (1) 39. (7.8) (.3) 33.3 (7.1) 41.7 (7.6) 42.2 (7.2) (.4) 31.9 (7.3) 43.1 (2.8) 43.6 (3.6) (1.5) 34.2 (5.4) 34.7 (7.) 33.5 (6.3) (4.5) 35.7 (.94) 43.7 (16) 38. (13) (1.3) 44.3 (5.1) 51. (2.8) 45.1 (6.1) (1.8) 57.2 (7.5) 7.8 (6.9) 61. (5.) (4.4) 65.4 (7.1) 67.1 (3.5) 56. (4.9) (1.2) 85.8 (.21) 79.9 (11) 56.4 (9.7) (.2) 92.3 (.41) 86. (8.1) 61.9 (6.9) Dt re mens (SE) of two replicte tests performed on very-high strength wstewter (Tble 2). b Removl efficiency reltive to concentrtion of liquid diry mnure before chitosn tretment nd screening. Initil concentrtions were: TSS = 28.3 g/l, VSS = 13.8 g/l, TKN = mg/l, nd TP = mg/l. c.25-mm nd 1-mm size screens re ASTM stndrd wire screen sieves with mesh size numbers 18 nd 6, respectively.

5 M.C. Grci et l. / Bioresource Technology 1 (29) TP or TKN Removed (%) TKN TP TKN = 1.71 TSS R 2 =.924 TP = 1.7 TSS R 2 = TSS Removed (%) Fig. 3. Reltionship between the removl of nutrients nd removl of totl suspended solids by chitosn tretment nd screening (.25-mm screen size). Dt obtined from the diry effluent of 3.2% strength nd nine chitosn rte tretments Removl of nutrients Chitosn tretment followed by screening significntly decresed verge TKN nd TP concentrtions in the effluent t ll four mnure strengths (Fig. 2). However, reduction of TKN nd TP levels in screened liquid ws not s drmtic s tht observed for TSS nd VSS. For instnce, chitosn ppliction reduced the TKN nd TP concentrtion on the treted effluent to mximum of 72% for TKN nd 54% for TP using.25-mm mesh size screen (Tble 3). Lower removl efficiencies for nutrients thn for suspended solids were lso observed in floccultion of swine mnure when using PAM (Vnotti et l., 22). The inorgnic N nd P frctions, which re mostly soluble components of TKN nd TP, were not ffected by the flocculnt tretment. On the other hnd, PAM ws very effective in the cpture of orgnic nutrients contined in smll prticles. In our study, we found significnt, positive liner reltionships between TSS vs. TKN (R 2 =.924) nd TSS vs. TP (R 2 =.96; Fig. 3) tht cn be explined by the strong ffinity between prticulte mtter nd the insoluble frctions of TKN nd TP Removl of oxygen-demnding substnces The highest removl efficiencies for COD fter chitosn tretment nd screening (.25-mm mesh size) of diry mnure with TS strengths of.4%,.8%, 1.6%, nd 3.2% were bout 85%, 92%, 88%, nd 82%, respectively (Fig. 2). Optimum COD removl efficiencies were lower thn those obtined for TSS nd VSS (Tble 4) possibly due to bckground COD tht ws not ffected by chitosn tretment. Reduced soluble inorgnic compounds such s mmoni probbly contributed to this bckground COD (Vnotti nd Hunt, 1999). Reltionship between effluent COD nd TSS removed (dt not shown) indicted tht 92 99% of COD reduction in the treted effluent ws explined by the TSS removl Polymer use efficiency In order to determine chitosn ppliction rtes nd mximum TSS seprtion, liner-plteu spline function ws fitted to dt obtined from chitosn tretment nd screening through.25-mm screen nd 1-mm screen; regression prmeters re shown in Tble 4. The TSS removl rte incresed with incresing chitosn dosge reching n optimum dosge where further increse of chitosn hd no effect on suspended solids seprtion. There is trend to increse polymer ppliction with the increse of TS concentrtion independently of the type of screen used to seprte solids (Tble 4). The sme trend hs been observed when PAM ws used by Zhng nd Lei (1998) to flocculte both diry nd swine mnure nd Vnotti et l. (22) to flocculte swine mnure. Overll, chitosn use efficiency (g TSS seprted/g chitosn) for both screening tretments (.25-mm nd 1-mm mesh size) ws lmost the sme (Tble 4). On verge for both screen sizes, polymer use efficiency incresed linerly (from 13.7 to 52.9 g TSS seprted/g chitosn) when TSS concentrtion incresed from 4.6 to 32.2 g/l (Pooled polymer efficiency = 1.38TS ; R 2 =.981; n = 8). Optimum polymer rtes nd TSS removl efficiency were very similr with both screens with n optimmum vlue of 519 mg/l of chitosn for mnure TS content of 3.2% (Tble 4). This ppliction rte ws within the rnge of optimum rtes of synthetic polymer used for floccultion of diry mnure. Chstin et l. (21) found n optimum PAM rte of 3 mg/l for diry mnure with 4.18% TS content. Their lower polymer requirement ws probbly becuse bedding mteril prticles contined in diry mnure might hve improved floccultion performnce by trpping smll prticles nd helping floc formtion. However, from the study of Zhng nd Lei (1998), it ws estimted tht synthetic flocculnt optimum rte could be much higher; their optimum rte ws 941 mg/l of PAM for diry mnure with 3.2% TS content. Tble 4 Chnges in polymer use efficiency with wstewter strength. TS conc. (g/l) TSS conc (g/l) Regression equtions R 2b Slope (g/mg) Optimum chitosn rte (mg/l) Mx. TSS removed (g/l) TSS removl efficiency (%) c Polymer use efficiency d (g solids/g polymer) Polymer usge rte e (%) (lb/ton).25-mm screen mm screen Liner-plteu functions: Y = + bx for X < knot, nd Y = plteu for X > knot, where Y = TSS removed (g/l), X = chitosn rte (mg/l), = intercept, b = slope, knot = optimum chitosn rte, nd plteu = mximum TSS removed (bsed on Vnotti et l., 22). b R 2 = coefficient of determintion; ll vlues significnt t the.5 probbility level. c TSS removl efficiency = mx TSS removed/initil TSS concentrtion. d Polymer use efficiency clculted from prmeters of regression equtions (mximum TSS removed/optimum chitosn rte). e Polymer usge rte given both in percent (g chitosn/1 g dry solids seprted) nd lb/ton (lb polymer/2 lb dry solid seprted).

6 5422 M.C. Grci et l. / Bioresource Technology 1 (29) Turbidity (NTU) Turbidity =.91TSS R 2 = TSS (mg/l) Fig. 4. Reltionship between effluent turbidity nd totl suspended solids (TSS) concentrtion fter chitosn tretment nd screening. Dt include four diry wstewter strengths (TS =.4%,.8%, 1.6%, nd 3.2%), seven to nine chitosn rtes ( 54 mg/l), nd two mesh size screens (.25 nd 1 mm). Ech point is the men of two replictes Turbidity reltionships process control The performnce of wstewter tretment plnt cn be determined by suspended solids mesurement, but lbortory nlysis is necessry. An indirect method for suspended solids mesurement is turbidity, which cn be quickly mesured on-site. In our work, floccultion performnce ws lso determined by chnges in turbidity. As Fig. 4 shows, high correltion (R 2 =.965) ws obtined between turbidity nd TSS fter chitosn nd screening tretments (.25-mm nd 1-mm mesh size screens). The reltionship between TSS nd turbidity indictes tht turbidity mesurement cn be used s TSS removl performnce indictor in wide TSS rnge (from.4% to 3.2% TSS content). Sievers et l. (1994) found similr results between turbidity nd VS for diry mnure with 1% TS content, concluding tht turbidity mesurement ws good method to determine mximum solids removl nd optimum chemicl dosges. An dditionl dvntge of using turbidity mesurements to ssess performnce of polymer enhnced solid liquid seprtion is its strong reltionship with effluent nutrient concentrtion such s concentrtion of TP. Fig. 5 shows the reltionship between effluent TP nd effluent turbidity fter polymer nd screening tretment. Turbidity mesurement is cheper nd quicker thn TP nlyses, thus routine estimtion of nutrient concentrtions from turbidity mesurements cn reduce lbortory nlyses cost. Effluent TP (mg/l) TP = -3E-7 (turbidity) turbidity R 2 = Effluent Turbidity (NTU) Fig. 5. Reltionship between effluent totl phosphorus (TP) nd turbidity fter chitosn floccultion nd screening. Dt include four diry wstewter strengths (TS =.4%,.8%, 1.6%, nd 3.2%), seven to nine chitosn rtes ( 54 mg/l), nd two mesh size screens (.25 nd 1 mm). Ech point is the men of two replictes. 4. Conclusions Orgnic nutrients in diry mnure re mostly contined in the solid frction tht cnnot be efficiently seprted by simple mechnicl screening. Since the modern frming trend towrds lrge opertions leds to surplus of nutrients in nerby croplnd, there is need for better distribution of these nutrients. Solid liquid seprtion of livestock effluents enhnced by flocculnt ddition is good option to concentrte these nutrients in the seprted solids nd esily trnsport them for lnd ppliction or other uses such s composting or bioenergy production. Our interest ws to test if nturl flocculnts cn hve role in effective solid liquid seprtion of livestock effluents. We showed tht chitosn, nturl flocculnt, cn gretly improve the efficiency of diry mnure solid liquid seprtion nd improve the wter qulity of the treted effluent. At optimum rte of the flocculnt, removl efficiencies were >95% for totl suspended solids (TSS), >73% for totl Kjeldhl N, nd >54% for totl phosphorus (TP). These removl efficiencies were comprble to those reported in the literture for diry mnure tretment using synthetic polymers. Becuse of incresed cost of energy nd renewed interest on orgnic frming systems, nturl flocculnts such s chitosn hve the potentil to be used s component of niml wste tretment. Nturl flocculnts my hve n importnt role in orgnic frming becuse the mnure solid frction seprted using these flocculnts could be considered n orgnic fertilizer s it does not contin synthetic compounds. Future reserch on nturl flocculnts for use in niml mnure tretment should be focused on: (1) development of new nturl flocculnts nd (2) cost effective production of nturl flocculnts. Acknowledgements This reserch ws prt of USDA-ARS Ntionl Progrm 26: Mnure nd Byproducts Utiliztion; ARS Project D Innovtive Animl Mnure Tretment Technologies for Enhnced Environmentl Qulity. The first uthor, Dr. M.C. Grci, is grteful to Drs. M.B. Vnotti nd A.A. Szogi for providing the opportunity to work s Visiting Scientist in the USDA-ARS, Costl Plins, Soil, Wter nd Plnt Reserch Center t Florence, SC. The uthors re grteful to Aprel Q. Ellison for her help with lbortory nlyses. Mention of trde nme, proprietry product, or vendor does not constitute gurntee or wrrnty of the product by the USDA nd does not imply its pprovl to the exclusion of other products or vendors tht lso my be suitble. References APHA, Stndrd Methods for the Exmintion of Wter nd Wstewter, 2th ed. Americn Public Helth Assocition, Americn Wter Works Assocition, nd Wter Environment Federtion, Wshington, DC. Burton, C.H., Turner, C., 23. Mnure Mngement: Tretment Strtegies for Sustinble Agriculture. 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