Chrcteristion of some South Africn wter tretment residues nd implictions for lnd ppliction LW Titshll* nd JC Hughes Soil Science, School of Environmentl Sciences, University of KwZulu-Ntl, Privte Bg X01, Scottsville 3209, South Afric Abstrct Lnd ppliction of wter tretment residue (WTR) the by-product from the production of potble wter, is becoming the preferred method of disposl, s there re environmentl concerns nd incresingly high costs ssocited with other disposl options. However, before WTR cn be pplied to lnd, considertion needs to be given to their chemicl nd physicl chrcteristics to determine potentil impcts. Six WTR smples were obtined from five South Africn wter tretment fcilities (Fure Wter Tretment Plnt (two smples), Rnd Wter, Umgeni Wter, Amtol Wter nd Midvl Wter Compny). The Rnd Wter WTR ws CO, FeCl 3, long-chin orgnic polymer (LCP) residue with ctivted silic nd CO 2 being dded. The Umgeni nd Amtol Wter WTRs were lime nd LCP residues. The Midvl Wter WTR ws n Al 2.nH 2 0, FeCl 3, lime nd LCP residue nd the Fure WTRs were Fe 2, ctivted chrcol, lime nd LCP residues. These WTR smples were nlysed for some physicl (prticle size distribution, prticle density nd plnt vilble wter) nd chemicl ttributes (ph, electricl conductivity, ction exchnge cpcity, clcium crbonte equivlence, exchngeble cidity, extrctble bses nd metl ctions, totl nd plnt vilble nutrients, totl elementl nlysis nd metl frctiontion) nd minerlogicl properties, nd their potentil for ppliction to lnd considered. The WTRs tended to be neutrl to lkline in ph, with low electricl conductivity. Generlly, mounts of N, P nd K were low, but some of the WTRs showed potentil to supply other plnt nutrients (C, Mg, S, Zn, Cu nd Fe). Their physicl chrcteristics were vrible, showing wide rnge in prticle size distribution s well s plnt vilble wter. Hevy metl concentrtions tended to be low, but Mn ws elevted in some WTRs, especilly in the Fure WTRs, which my led to plnt growth problems. Lnd ppliction of these WTRs ppers to be fesible disposl option, but currently they re regulted by the minimum requirements for disposl of hzrdous wste. Delisting would firstly be required for lnd ppliction nd if then permitted by legisltion, the ppliction rtes would need to be bsed on existing soil conditions, the chrcteristics of prticulr WTR, nd the proposed lnd use. Keywords: Wter tretment residue, lnd ppliction, potble wter, minimum requirements, disposl Introduction Wter tretment residue (WTR) is the by-product from the production of potble wter. It consists minly of the precipitted hydroxides of the tretment chemicls tht re dded to cogulte nd flocculte dissolved nd suspended mteril in the rw wter source nd lso during the residue dewtering process (Elliott et l., 1990b). Types nd dosges of tretment chemicls vry depending on the qulity of the rw wter nd their cost nd vilbility. The chemicls typiclly include Al 2.nH 2 0, FeCl 3, Fe 2, long-chin orgnic polymers (LCP), ctivted chrcol, ctivted silic nd lime. In the pst, WTRs were dischrged into wtercourses (AWWARF, 1969), nd more recently hve been disposed of in lndfills, due to the environmentl concerns over direct river dischrge (Bst, 2000). In mny prts of the world, including South Afric, WTR hs conventionlly been disposed of by lndfilling (Deprtment of Wter Affirs nd Forestry, 1998). Bst (2000), in review pper, hs indicted tht currently lndfill is the most commonly used disposl option, but due to incresed costs, lnd ppliction is becoming the preferred disposl method. In South Afric, the reson for the previous populrity of lndfills ws tht, with environmentl concerns being * To whom ll correspondence should be ddressed. +2733 260-5415; fx: +2733 260-5426; e-mil: Titshll@ukzn.c.z Received 12 Jnury 2004; ccepted in revised form 1 Mrch 2005. of low priority, lndfill constituted convenient method of wste disposl. Since 1994, however, South Afric hs seen the closure of numerous lndfill sites for both socil nd environmentl resons (Deprtment of Wter Affirs nd Forestry, 2003). Interntionl greements since 1994 hve lso put incresing pressure on the South Africn government to improve environmentl policy (Deprtment of Wter Affirs nd Forestry, 2003). As South Africns become more environmentlly wre of the potentil hzrds of lndfills, nd legisltion is mde stricter, lterntives for wste disposl re being sought. Lnd disposl presents n ppeling lterntive to conventionl disposl s it suggests tht wstes cn be ssimilted, without inducing negtive effects on soil qulity. Indeed, there hve lso been reports suggesting tht lnd disposl of WTR my improve soil qulity (Roy nd Couillrd, 1998). Lnd disposl of wste, methodology lso known s lnd ppliction or tretment, hs been described by Overcsh nd Pl (1979) s the intimte mixing or dispersion of wstes into the upper zone of the soil-plnt system, with the objective of microbil stbilistion, dsorption, immobilistion, selective dispersion or crop recovery, leding to n environmentlly cceptble ssimiltion of the wste. Therefore, lnd disposl constitutes n open system offering potentil for wste tretment, s opposed to simply wste disposl such s is ssocited with lndfill. Elliott et l. (1990) nd USEPA (1996) consider some processes nd mngement prctices for lnd disposl to be vible option, while Bst (2000) reviews number of the studies tht hve considered the effects on soil properties nd plnt growth of lnd ppliction of WTR. Most studies report Avilble on website http://www.wrc.org.z ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 299
on some of the bsic physicl nd chemicl chrcteristics of WTRs used in ny prticulr study, with some describing specific chrcteristics of the WTR used (Schmitt nd Hll, 1974; Elliott et l., 1990b; Elliott nd Tylor, 2000; Hyde nd Morris, 2000; Dyton nd Bst, 2001). In the context of South Africn legisltion, the responsibility for regulting the finl disposl of wste to lndfill site is ssigned to the Deprtment of Wter Affirs nd Forestry (DWAF), in terms of Section 20 of the Environment Conservtion Act, 1989 (Act 73 of 1989) (ECA). In terms of Section 20, no person my dispose of wste unless under the uthority of permit issued in terms of the ECA (DWAF, 2003). In terms of the Ntionl Wter Act (NWA, Act 36 of 1998), WTR is clssified s wste s follows, wste includes ny solid mteril or mteril tht is suspended, dissolved or trnsported in wter (including sediment) nd which is spilled or deposited on lnd or into wter resource in such volume, composition or mnner s to cuse, or to be resonbly likely to cuse, the wter resource to be polluted. Further, in terms of this Act wter use includes disposing of wste in mnner which my detrimentlly impct on wter resource. This implies tht for regultion of the substnce, wter licence would be needed. This licence would be guided by the Minimum Requirement Series for Wste Disposl tht informs users in terms of wste disposl stndrds, wste clssifiction nd monitoring (DWAF, 1998). However, the NWA is not only concerned with scrificil disposl of wste but llows for generl uthoristion tht does not require licence, but is subject to the relevnt regultions under Section 26 nd conditions imposed under Section 29. These Sections require inter li tht wste stndrds be prescribed, nd tht dequte monitoring nd nlysis be undertken bsed on permissible levels for some or ll of its (the wste) chemicl nd physicl components. However, mjor problem is tht WTR is currently clssified s wste in terms of the definition given bove, i.e. tht it my cuse or be resonbly likely to cuse pollution of wter resource. It is thus considered together with wstewter tretment sludge (sewge sludge or biosolids) nd thus lnd disposl would require, t the very lest, generl uthoristion to be grnted. Although the reserch presented uses the term WTR, in order to stress tht it hs different nture to biosolids, South Africn regultions must lso drw this distinction to llow for more effective hndling nd disposl of WTR. Contminted lnd hs been defined s lnd where substnces re present in concentrtions higher thn those in which they would normlly expect to occur nd where they pose serious thret to public helth nd the environment (Simms, 1988). The work reported here nd elsewhere (Moodley et l., 2004; Hughes et l., 2005) shows tht the clssifiction of WTR s wste mteril tht is resonbly likely to pollute wter resources should be reconsidered nd tht its disposl under generl uthoristion section llowed by the NWA be permitted. This would lrgely remove the present restrictions on its use nd disposl. However, if WTRs re to be pplied to lnd, be it to griculturl, derelict (mined res) or recretionl (prks) lnd, considertion needs to be given to the nture of the WTR to determine ny potentil negtive impcts the mteril my hve. As the source of rw wter (nd tretment process) vries between wter tretment works, properties of WTRs from different res differ drsticlly. While there is n incresing mount of literture describing the rnge of WTRs produced in developed countries, in prticulr the USA, little published literture pertining to South Africn WTRs could be found, with most considering engineering spects (Geldenhuys, 1992; Hodgkinson nd Rencken, 1992; Polsek, 1997;b). This pper describes some of the chemicl nd physicl properties of WTRs from the mjor wter tretment plnts in South Afric s strting point for future developments regrding WTR lnd disposl primrily from n griculturl perspective. In ddition, it should be noted tht this study forms prt of lrger investigtion exmining the effects of pplying WTR on soil chemicl, physicl nd microbiologicl properties. These investigtions hve exmined the effect of pplying different WTRs to different soils from both griculturl nd industril perspectives (Moodley et l., 2004; Hughes et l., 2005). Mterils nd methods Six ir-dried WTR smples were obtined from lrge wter tretment works in South Afric. Three of the WTR smples were from the lrgest bulk wter suppliers, i.e. Rnd Wter, Cpe Metropolitn Council Fure Wter Tretment Plnt (Fure 1 nd 2), nd Umgeni Wter Midmr Wter Tretment Works. The other WTRs were from Amtol Wter (Est London) nd Midvl Wter Compny (Stilfontein). The Rnd Wter WTR ws lime-softening residue with high mounts of CO, s well s FeCl 3, LCP, ctivted silic nd CO 2 being dded. The Midmr nd Amtol Wter WTRs were lime nd LCP residues. The Midvl Wter WTR ws n Al 2.nH 2 0, FeCl 3, lime nd LCP residue nd the Fure WTRs were Fe 2, ctivted chrcol, lime nd LCP residues. The second Fure WTR (Fure 2), obtined from the Fure Wter Tretment Plnt, represented drstic chnge in the rw wter qulity, when lgl blooms cused odour problems. While the tretment chemicls remined the sme s for the Fure 1, there ws chnge in the dosges. Chemicl nd physicl nlyses The ir-dry WTR smples were milled nd pssed through 2 mm sieve. ph ws mesured in distilled wter nd 1 M KCl using Rdiometer PHM210 ph meter with stndrd glss electrode. A WTR: solution rtio of 1:2.5 ws used, nd left to stnd for 45 min with occsionl stirring using glss rod. Electricl conductivity (EC) ws mesured t 25 o C using Rdiometer CDM83 electricl conductivity meter in 1:5 WTR: wter solution (United Sttes Slinity Lbortory Stff, 1954). Extrctble ctions were mesured by sturting with Sr 2+ nd ction exchnge cpcity (CEC) by subsequent replcement with NH 4 + (Hughes nd Girdlestone, 1994). Nitrogen ws determined on <0.5 mm smples by combustion using LECO nitrogen nlyser. Nitrte nd mmoni were extrcted with 2 M KCl (Mynrd nd Klr, 1993) nd solution concentrtions determined colorimetriclly using TRAACS 2000 continuous-flow uto nlyser. Plnt-vilble phosphorus ws extrcted with AMBIC (mmonium bicrbonte) solution nd determined colorimetriclly (The Non-Affilited Soil Anlysis Work Committee, 1990) on Vrin Cry 1E UV-Visible spectrophotometer (UV-Vis). Exchngeble cidity nd exchngeble Al were extrcted ccording to Sims (1996), with Al being mesured by tomic bsorption spectrophotometry (AAS, Vrin SpectrAA-200). Clcium crbonte equivlence (CCE) ws mesured ccording to Jckson (1958). Orgnic crbon (OC) ws digested by potssium dichromte oxidtion nd determined titrimetriclly (Wlkley, 1947). Totl C nd S were nlysed by combustion using LECO CNS 2000 uto nlyser. 300 ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 Avilble on website http://www.wrc.org.z
TABLE 1 Some chemicl properties of six South Africn wter tretment residues Property Rnd Midmr Midvl Amtol Fure 1 Fure 2 ph KCl 8.66 7.78 7.66 6.94 6.19 7.23 H 2 O 9.16 8.00 8.36 7.66 6.56 7.84 Electricl conductivity (ms/m5.10 71.50 31.27 25.33 16.40 40.50 Totl C (g/kg) 82.20 48.80 25.60 23.80 118.90 nd Orgnic crbon (%) 1.23 2.77 1.60 1.96 3.34 10.27 Exchngeble cidity (cmol c /kg) 0.00 0.20 0.10 0.10 0.10 nd Exchngeble luminium (cmol c /kg) 0.07 0.06 0.06 0.07 0.05 nd Clcium crbonte equivlence (%) 109.06 5.92 4.48 4.09 6.94 nd not determined. TABLE 2 Some physicl properties of six South Africn wter tretment residues Property Rnd Midmr Midvl Amtol Fure 1 Fure 2 Prticle Snd (0.053-2 mm) 1.2 91.6 37.5 67.5 91.0 14.4 size Corse silt (0.02-0.053 mm) 1.6 2.4 2.0 1.1 1.3 5.7 distribution Fine silt (0.002-0.02 mm4.3 2.5 31.4 2.1 4.3 61.2 (%) Cly (<0.002mm) 62.9 3.5 29.1 29.3 3.4 18.7 Prticle density (g/cm 3 ) 2.43 2.23 2.09 2.02 2.02 nd Plnt vilble wter (g/kg) 18.17 53.81 40.46 8.66 29.64 197.72 not determined. Prticle size distribution ws determined by the pipette method (Gee nd Buder, 1986) nd prticle density by the method of Blke nd Hrtge (1986). Grvimetric wter content ws determined t -33 nd -1 500 kp using pressure plte pprtus. Plnt vilble wter (PAW) ws considered to be the difference in wter content between -33 nd -1500 kp (Dyton nd Bst, 2001). X-ry diffrction (XRD) nlysis of rndomly oriented powders ws crried out on Philips PW1050 diffrctometer using monochromted Co Kα rdition from 3 o to 75 o 2θ with scnning step of 0.02 o t 1 o per minute. The diffrction dt were cptured by Sietronics 122D utomted micro-processor. The smples were then qulittively nlysed to determine mjor minerlogicl components. Totl elementl concentrtions were mesured by X-ry fluorescence spectrometry nd plnt vilble Cd, Cu, Co, Cr, Mn, Fe, Ni, Pb nd Zn were determined by extrction with DTPA (Ling nd Krmnos, 1993). A five-step frctiontion procedure ws used to determine exchngeble (1 M MgCl 2 ), dilute cid extrctble (1 M NOAc t ph 5), Fe/Mn bound (0.175 M (NH 4 ) 2 C 2 O 4 nd 0.1 M H 2 C 2 O 4 ), orgniclly bound (0.1 M N 4 P 2 O 7 ) nd residul frctions (cid digest, HF, HNO 3 nd HClO 4 ) of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb nd Zn (Elliott et l., 1990b). Elementl solution concentrtions were determined by AAS. Results Chemicl chrcteristics The ph of the WTR smples rnged from 6.19 to 8.66 in KCl nd from 6.56 to 9.16 in wter (Tble 1). In most instnces, the WTR smples were neutrl to lkline, with only the Fure 1 WTR hving slightly cidic ph. Electricl conductivity rnged from 16.4 to 71.5 ms/m. The Fure 1 WTR smple hd the highest mesured totl C concentrtion. The Fure 2 smple probbly hd higher concentrtion, but the C concentrtion exceeded the mesuring prmeters of the instrument used nd so its totl C could not be determined. The other WTRs hd considerbly lower mounts thn the Fure 1 smple, though the Rnd Wter WTR hd modertely high totl C content. Orgnic crbon content rnged from 1.23 to 10.27%. Exchngeble cidity rnged from 0.0 to 0.2 cmol c /kg nd exchngeble Al from 0.05 to 0.07 cmol c /kg. Clcium crbonte equivlence generlly showed low liming potentil for the WTRs (ll <7%), with the exception of Rnd WTR tht hd CCE of 109% due to the high dosing with CO. Physicl chrcteristics The prticle size distribution of the WTR smples ws vrible (Tble 2). Smples tht were esily dispersed tended to hve high mounts of fine silt nd cly (Fure 2, Rnd nd Midvl), while the other, less esily dispersed, WTRs hd higher mounts of snd (Fure 1, Amtol nd Midmr). There ws lso mrked chnge in the prticle size distribution of the Fure WTRs, due to the chnge in rw wter qulity nd tretment processes. To demonstrte the effect of ir-drying on the prticle size chrcteristics of WTR fresh (wet) smple of the Midmr WTR ws nlysed nd found to consist of 6% snd, 4% corse silt, 6% fine silt nd 84% cly. The prticle densities of the dry WTRs rnged from 2.02 to 2.43 g/cm 3. Plnt- vilble wter rnged considerbly from 8.66 to 197.72 g/kg, but ws generlly low. Nutrient concentrtions Nutrient concentrtions were vrible (Tble 3), depending on the source of the residue. Totl S determined by combustion ws generlly quite low, with only the Fure 1 WTR showing n elevted concentrtion. Nitrte-N rnged from 9.7 to 94.2 mg/kg nd NH 4 -N from 26.3 to 358.4 mg/kg. Totl N concentrtions rnged from 200 to 5 200 mg/kg. This indictes tht considerble proportion of the N is bound in less soluble (or less vilble) forms in the WTRs, Avilble on website http://www.wrc.org.z ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 301
TABLE 3 Nutrient concentrtions of six South Africn wter tretment residues Property Rnd Midmr Midvl Amtol Fure 1 Fure 2 Totl S (mg/kg) 10 210 130 320 1 200 nd Totl N (mg/kg ) 200 1 000 2 800 2 600 5 200 4 800 NO 3 N (mg/kg) 94.23 16.80 12.76 31.80 9.65 11.53 NH 4 N (mg/kg) 26.33 170.15 358.38 62.40 108.48 32.10 AMBIC P (mg/kg) 4.70 4.46 31.51 0.74 6.33 21.50 Extrctble ctions (cmol c /kg) Ction exchnge cpcity (cmol c /kg) not determined. C 4.54 31.01 38.28 28.49 25.29 37.31 Mg 15.75 9.13 14.33 8.76 13.42 22.12 N 1.37 0.52 0.56 0.88 0.66 0.81 K 0.38 0.51 0.78 0.39 0.30 0.14 15.85 26.59 41.81 25.38 33.47 35.79 TABLE 4 X-ry fluorescence nlysis of six South Africn wter tretment residues Smple SiO 2 Al 2 O 3 Fe 2 O 3 MnO MgO CO N 2 O K 2 O TiO 2 P 2 O 5 Totl LOI Midmr 54.57 22.60 11.95 1.53 1.92 4.20 0.15 1.47 0.86 0.24 99.49 23.91 Midvl 53.07 22.36 14.24 0.41 1.83 4.45 0.33 1.89 0.74 0.47 99.79 27.70 Amtol 52.59 29.06 10.31 0.07 1.82 1.55 0.43 2.98 0.86 0.12 99.79 25.63 Rnd 24.36 9.89 4.85 0.66 5.25 53.19 0.61 0.82 0.31 0.09 100.03 36.93 Fure 1 29.93 8.70 53.80 0.96 0.72 3.15 bd b 0.93 0.78 0.39 99.36 43.07 Fure 2 37.96 17.78 32.13 2.31 1.54 3.35 0.49 1.86 0.62 0.37 98.40 55.28 Smple Cd Co Cr Cu Ni Pb Zn S Sr As V U (%) (mg/kg) Midmr 4.00 39.0 161.0 44.0 53.0 37.0 84.0 720 71.0 17.0 154.0 bd Midvl nd c 32.0 246.6 53.2 117.7 26.0 142.1 2402 66.2 5.0 187.8 0.2 Amtol nd 19.0 134.3 23.0 39.7 36.0 84.5 911 91.4 11.0 175.8 3.8 Rnd nd 3.5 77.3 5.4 22.9 5.8 33.1 700 273.4 1.7 61.1 2.1 Fure 1 nd nd 43.0 bd 21.0 nd 182.0 2500 nd nd 93.0 nd Fure 2 nd nd 70.0 11.0 27.0 nd 124.0 2500 nd nd 134.0 nd Smple Nb Ce Nd Zr Y Sc Th B L Rb G (mg/kg) Midmr 11.0 96.0 25.0 126.0 27.0 33.0 10.0 1007.0 19.0 94.0 20.0 Midvl 7.8 51.0 24.0 101.6 23.1 30.7 7.9 438.7 5.4 109.2 19.0 Amtol 10.6 71.0 38.0 105.1 29.4 30.1 16.1 705.7 30.6 171.5 23.0 Rnd 2.7 5.1 bd 32.2 38.1 13.5 5.0 398.4 bd 38.1 8.9 Fure 1 nd nd nd nd nd nd nd nd 38.0 nd nd Fure 2 nd nd nd nd nd nd nd nd 26.0 nd nd loss on ignition. b below detection. c not determined. except in the Rnd WTR, where NO 3 -N nd NH 4 -N ccounted for bout 60% of the totl nitrogen, even though the totl concentrtion ws low. The AMBIC extrctble P ws generlly very low, except for the Midvl nd Fure 2 WTRs. The CEC of the WTRs rnged from 15.9 to 41.8 cmol c /kg nd, with the exception of the Rnd WTR, ll were bove 25 cmol c /kg. Extrctble C concentrtions were surprisingly low in the Rnd WTR, while the other WTRs showed considerbly higher C concentrtions, the highest being recorded for the Midvl WTR. Mgnesium concentrtions were lower thn the C concentrtions, except for the Rnd WTR. The Rnd WTR hd C: Mg rtio of bout 1:3, whilst the remining WTRs were 2:1 or 3:1. Potssium nd N concentrtions were low for ll WTRs. Other nlyses X-ry diffrction reveled smll mounts of qurtz in ll smples. Except for the Fure nd Amtol WTRs, ll smples contined clcite with most, s expected, in the Rnd WTR. Cly minerls were present in ll smples. Illite nd kolin were observed in ll smples except Rnd (where no clys could be determined due to the lrge mount of clcite) nd Fure 1 (where there ws no cler presence of illite). The Midvl WTR ppered to lso contin smectite nd the Midmr WTR 1.4nm minerl. Aprt from qurtz nd clcite, the other non-cly minerls found were gibbsite (Midmr), nd feldspr (Amtol). Amorphous mteril occurred especilly in the Fure WTRs where it ppered to 302 ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 Avilble on website http://www.wrc.org.z
TABLE 5 DTPA extrctble metls (mg/kg) of six South Africn wter tretment residues Element Rnd Midmr Amtol Midvl Fure 1 Fure 2 Cd 0.66 0.42 0.45 0.50 bd 0.30 Co 0.42 0.63 0.70 1.06 1.82 2.59 Cr 1.16 1.18 1.45 1.86 bd bd Cu 1.76 5.78 1.39 7.16 0.41 0.29 Fe 48.70 87.70 63.30 246 65.00 42.70 Mn 38.80 88.90 13.23 22.10 725 420 Ni 0.56 1.34 0.61 3.39 bd bd Pb 0.20 1.07 2.67 1.43 0.79 1.64 Zn 1.48 3.01 2.04 8.64 10.27 10.89 below detection be the dominnt phse, nd in the Midvl nd Amtol WTRs. The mjor elements (XRF, Tble 4) of the Midvl nd Amtol WTRs were similr to those of the Midmr WTR, lthough trce elements tended to be more vrible. The Rnd nd Fure WTRs showed mrkedly different chrcteristics from the forementioned WTRs nd ech other. A notble point is the very high C nd Mg content of the Rnd WTR when compred to the other WTRs, this possibly contributing to the high CCE. The Fure WTRs hd very high Fe content, in prticulr the Fure 1 WTR. Both the Rnd Wter nd Fure 1 WTRs hd low Al nd Si contents, with the Fure 2 WTR hving slightly higher concentrtions. Generlly, DTPA extrctble metl concentrtions were low (Tble 5), lthough Fe nd Mn concentrtions were elevted in most of the WTRs. The Midvl WTR hd the highest concentrtion of Fe. The Fure WTRs hd exceptionlly high Mn vlues. This ws ttributed to contminnts in the Fe 2 nd brown lime used to tret the rw wter (Flower, 2003). The Midvl nd Fure WTRs lso hd elevted concentrtions of Zn, possibly lso from the Fe-slts used to tret the rw wter. Nickel concentrtions in the Midvl WTR were slightly elevted, gin probbly due to contmintion from the Fe-slt used for wter purifiction. Copper concentrtions were elevted in the Midvl nd Midmr smples. In the five-step frctiontion for selected metls (Tble 6), little ws removed s exchngeble, with the Fe concentrtion of the Midvl nd Fure being notble, probbly due to the use of Fe-slts in their tretment processes. Only smll mounts of Mn were exchngeble, with the Rnd Wter WTR being below detection. As expected, dilute cid extrction removed greter concentrtion of metls, with Fe nd Mn tending to show the gretest increse in concentrtion. Also notble ws the increse in Zn concentrtion of the Fure WTR nd the Pb concentrtion of the Rnd Wter WTR. The chromte extrctble (Fe/Mn oxide bound) frctions tended to show high Fe nd Mn concentrtions, with Zn incresing in concentrtion for the Fure WTR. For ll the WTRs Fe concentrtions were highest in the chromte extrctble frctions (prt from residul concentrtions) ccounting for between 7 nd 27% of the totl Fe content. Mngnese ccounted for high proportion of the Fe/Mn oxide bound frction (2 to 68% of the totl Mn concentrtion). The orgniclly bound frction gin showed moderte levels of Mn nd Fe. Concentrtions of Cr were lso notble in the Midmr, Amtol, Midvl nd Fure Wter WTRs. The residul frction showed shrp increses in ll metl concentrtions for ll WTRs. Discussion The phs of the WTRs re similr to the typicl ph rnge of 5.10 to 8.00 reported by Bst (2000). The very high ph of the Rnd WTR, nd to lesser extent the Midmr WTR give these WTRs modertely high cid neutrlising potentil. The exceptionlly high CCE of the Rnd WTR suggests tht this WTR hs very rective cid neutrlising component, probbly in the form of C nd Mg crbontes. This is supported by the high concentrtions of C nd Mg shown in the XRF dt. The CCE of WTRs exmined by Elliott et l. (1990) rnged from 10 to 20%, lthough they did not include lime WTR. The ECs suggest low to moderte wter solubility of slts in the WTRs, indicting tht these should not present problem for lnd disposl. Dyton nd Bst (2001) similrly report ECs rnging from 22.0 to 110.0 ms/m for 17 Oklhom WTRs. The high totl C reported for the Fure 1 WTR ws expected, s the residue is product of the removl of dissolved orgnics nd the use of ctivted chrcol nd lime during the tretment process. The other residues probbly reflected the mount of lime nd orgnic polymer dded during wter tretment, nd the mount of orgnic mteril removed from the rw wter. Bst (2000) reports vlues from 0.8 to 6.5%, nd Dyton nd Bst (2001) vlues from 1.7 to 14.9%. Elliott et l. (1990) report men totl OC content of 3% for WTRs from seven Pennsylvni wter tretment fcilities. The low exchngeble cidity nd luminium vlues reflect very low cid producing potentil, result of their lime component nd neutrl to lkline phs. The lkline nture, high CCE nd low exchngeble cidity nd luminium of most of the WTRs suggest the potentil for lnd ppliction on vriety of soils or wstes. An exception my be where extreme cidity my render the neutrlising cpcity of the WTR ineffective potentilly relesing metls into tht prticulr environment, but this is lso dependnt on the mounts present in prticulr WTR. It might be expected tht the residues would exhibit high cly nd silt frctions. However, the residues re formed by the cogultion of fine prticles into lrger stble ggregtes, nd my exhibit corse texture once dried, this depending on the strength of the bonds between the prticles (Skene et l., 1995; Ahmed et l., 1997). This is further supported by the difference found in prticle size distribution between the wet nd dry Midmr WTRs. Plnt vilble wter showed considerble Avilble on website http://www.wrc.org.z ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 303
TABLE 6 Five step frctiontion of metls (mg/kg) from wter tretment residues from five of South Afric s wter tretment fcilities. Results from Elliott et l. (1990b) re given for comprtive purposes. Rnd Midmr MgCl 2 Wek Fe/Mn Orgnic Residul MgCl 2 Wek Fe/Mn Orgnic Residul Cd bd 2.9 0.4 8.20 24.0 Cd bd bd bd bd 30.0 Co bd 5.2 bd bd 47.0 Co bd 0.3 bd bd 80.0 Cr bd bd bd 2.60 339.0 Cr bd bd bd 21.4 254.0 Cu 0.1 7.8 9.0 8.80 32.0 Cu bd 4.5 15.2 0.6 58.0 Fe bd 62.6 4 908.8 2 004.4 24 743.0 Fe bd 244.5 14 373.5 4 962.4 5 6450.0 Mn bd 941.8 1 541.4 141.8 1 057.0 Mn 23.3 1 026.7 6 869.6 1 668.4 528.0 Ni 3.6 13.3 bd bd 38.0 Ni 1.17 bd bd bd 62.0 Pb bd 84.8 4.0 bd 340.0 Pb bd 26.4 bd bd 460.0 Zn bd 8.9 0.9 bd 87.6 Zn bd 3.6 bd bd 129.2 Amtol Midvl MgCl 2 Wek Fe/Mn Orgnic Residul MgCl 2 Wek Fe/Mn Orgnic Residul Cd 0.3 bd 0.2 bd 41.0 Cd 0.2 0.3 bd bd 57.0 Co bd 1.3 bd bd 121.0 Co bd 1.9 bd bd 114.0 Cr bd bd bd 26.4 417.0 Cr bd bd 20.0 47.4 352.0 Cu bd 0.3 8.4 bd 41.0 Cu bd 3.3 21.8 3.6 67.0 Fe bd 47.5 4 522.2 2 386.8 58 373.0 Fe 245.9 1 062.2 23 998.2 5 889.6 58 378.0 Mn 4.5 36.3 96.0 bd 248.0 Mn 7.1 426.7 854.2 222.8 275.0 Ni 4.5 1.7 bd bd 63.0 Ni bd 16.2 37.6 4.6 84.0 Pb bd 18.4 bd bd 620.0 Pb bd 12.0 bd bd 740.0 Zn bd 1.3 bd bd 150.5 Zn bd 14.2 27.5 6.3 186.5 Fure 1 Elliott et l. (1990b) b MgCl 2 Wek Fe/Mn Orgnic Residul MgCl 2 Wek Fe/Mn Orgnic Residul Cd 0.1 0.3 1.6 bd 58.0 Cd 5.8 19.0 bd 38.0 38.0 Co bd 1.8 10.0 5.40 138.0 Co nd c nd nd nd nd Cr bd bd 16.0 47.4 225.0 Cr 1.0 2.4 38 10.0 49.0 Cu bd 0.2 7.4 2.6 57.0 Cu 1.0 5.8 32 6.3 55.0 Fe 737.0 1 111.4 91241.8 2 111.6 289850.0 Fe nd nd nd nd nd Mn 5.0 897.1 1 847.0 991.4 3 235.0 Mn nd nd nd nd nd Ni 3.7 6.6 20.6 bd 73.0 Ni 0.6 12.0 31.8 4.5 51.0 Pb bd 11.2 bd bd 830.0 Pb 4.2 2.6 8.4 13.0 72.0 Zn bd 63.3 134.2 44.3 362.8 Zn 0.5 17.0 34 6.0 42.0 below detection. b men vlues reported by Elliott et l. (1990b) using the sme procedure on 7 WTRs. c not determined. rnge, this being similr to Dyton nd Bst (2001) who report rnge from 26 to 416 g/kg. A number of studies hve reported on improved soil physicl properties s result of WTR dditions (Rengsmy et l., 1980; Skene et l., 1995; Ahmed et l., 1997; Moodley, 2001). While not intensively investigted here, some of the WTRs hd high wter-holding cpcity. This my improve wter retention of some soils, while improving infiltrtion of hevy textured soils, if the WTRs re pplied to lnd. However, Moodley (2001) indicted tht if the WTR pplied to soil were to degrde to its constituent frctions (cly nd silt in most instnces) then clogging of soil pores my led to reduced infiltrtion nd wter retention in ffected soils. Furthermore, this my increse the rective sites for relese of potentilly toxic elements from the WTR. 304 ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 Avilble on website http://www.wrc.org.z
TABLE 7 Summry tble of the cceptble environmentl risk (mg/l) nd disposl llowed (g/h m) for selected metls s outlined by the Minimum requirements for wste disposl. Element Acceptble environmentl risk (mg/l) Disposl llowed (g/h m) Cd 0.031 47 Co 6.9 10 454 Cr 4.7 7121 Cu 0.1 151 Fe 9 13 636 Mn 0.3 454 Ni 1.14 1727 Pb 0.1 151 Zn 0.7 1061 Deprtment of Wter Affirs nd Forestry However, in n investigtion using the field trils reported on by Moodley (2001), dt suggest tht, fter five yers, the physicl properties of Hutton Soil (Soil Clssifiction Working Group, 1991) treted with WTR t ppliction rtes s high s 1 280 Mg/h re returning, fter initilly hving shown incresed wter retention, to similr conditions s the control tretments (Moodley et l. 2004; Personl observtion, 2003). Although some of the WTRs studied hd low nutrient concentrtions, in prticulr N, K nd P, they my be useful to improve conditions for plnt growth in degrded or nutrientpoor soils. The lkline nture of most of the WTRs (in prticulr the Rnd Wter WTR) would enble them to increse the ph of cid soils. Fertiliser dditions my help overcome some of the nutrient deficiencies, possibly with the exception of P. A number of studies hve reported on the high P sorbing cpcity of WTRs nd the potentil of these WTRs to reduce P uptke by plnts grown in either pure WTR or mixtures of soil or potting medi nd WTR (Elliott nd Singer, 1988; Heil nd Brbrick, 1989; Skene et l., 1995; Ahmed et l., 1997; Bst et l., 2000; Codling et l., 2002). However, field experiments hve shown tht plnt uptke of P is pprently not dversely ffected by dditions of WTR (Grbrek nd Krug, 1987; Geertsem et l., 1994; Buyeye, 2003). While totl N ws modertely high for most WTRs, the vilble frction tended to be low. Dyton nd Bst (2001) report much higher rnge in totl N from 1300 to 18 400 mg/ kg, but the concentrtions of NO 3 -N (22 to 140 mg/kg) nd NH 4 - N (3.5 to 123.0 mg/kg) were similrly low. The high vilbility of Mg in the Rnd Wter WTR suggests tht C:Mg imblnce could occur in soils treted with the Rnd Wter WTR. Although the Rnd Wter WTR hd very high concentrtions of totl C (Tble 4), it is cler tht this C is in n unvilble form. Generlly, however, extrctble C nd Mg pper to be t dequte plnt vilble concentrtions, but K my be too low for stisfctory plnt growth. The source of qurtz in the WTRs my be from snd prticles tht re removed from the rw wter, lthough the most likely source is the introduction of snd grins to the WTR during bckwshing of snd filters used during wter tretment. The obvious source of clcite is the lime used in the wter tretment process, nd lthough Rnd Wter uses CO, clcite is formed s result of the use of CO 2 during wter tretment. All the WTRs showed the presence of vrious cly minerls, nd some hd considerble mounts of X-ry morphous mteril. Rengsmy et l. (1980) lso found tht, prt from smll mounts of qurtz in their lum residue, the XRD pttern consisted lrgely of disordered mterils, probbly morphous hydrous oxides of Al, Fe nd Mn, s well s orgnic frctions. As indicted by Schmitt nd Hll (1974), who exmined sediment bsin residue from the Ok-Ridge Wter Tretment Plnt (Tennessee, USA) for 72 elements, Si, C, Mg, K, Fe nd Ti were generlly the most bundnt elements in the WTRs. The concentrtions of these were to some extent dependnt on the tretment chemicls used. In the cse of the Rnd Wter WTR, use of high mounts of CO in the tretment process is reflected in high C concentrtions in the residue produced. A similr sitution exists for the Fure WTRs, where use of n Fe-slt in the tretment process hs resulted in high Fe concentrtion in the residues. The DTPA extrctble metl concentrtions suggest tht generlly these would not be problemtic for plnt uptke, nd in some instnces my supply some trce nutrients (e.g. Zn). Of some concern ws the high Mn concentrtion of the Fure WTRs, which my led to symptoms of toxicity in plnts or perhps cuse ntgonistic effects in the uptke of other elements (C, Mg, Fe). The use of totl element or metl content is poor indictor of the toxicity of wste s it does not reflect the mobile or vilble frction (Tiller, 1989). At most it gives n indiction of the worst potentil toxicity of n element ssuming complete relese of tht element. The five-step frctiontion perhps gives better indiction of how mobile or vilble these metls my be. This showed tht generlly most metls re not redily exchngeble, except for Fe in the Midvl nd Fure 1 WTRs. Extrction with wek cid, however, showed increses in the concentrtion of most metls from ll smples. This indictes tht these elements my become mobile under cid conditions. Gibson nd Frmer (1986, cited by Elliott et l., 1990b) indicte tht the sum of the exchngeble nd dilute cid extrctble frctions represents the mximum vilbility of the metls to plnts. On this bsis, Elliott et l. (1990b) found Cd to be the likely cuse of concern in the WTRs they studied, ccounting for some 25% of the totl Cd concentrtion. In the WTRs exmined here, the Cd frctions ccounted for very smll proportions (0 to 8%) of the totl Cd concentrtion. For these WTRs, high levels of Mn would pper to represent mjor concern, especilly for the Rnd, Midmr, Amtol nd Fure 1 WTRs. In Rnd Wter WTR, Pb nd Ni my lso represent toxicity problems, lthough this ws not reflected in the DTPA extrction. This suggests tht under even slightly cid conditions moderte concentrtions of these elements my be relesed. The Fure 1 WTR lso showed high Zn concentrtion when extrcted with dilute cid. It is likely tht under the recommendtions of the minimum requirements (DWAF, 1998) most of these WTRs would not be delisted s hzrdous mteril. Tble 7 summrises the criteri set by the minimum requirements (DWAF, 1998) for some of the metls mesured in this study. The cceptble environmentl risk vlues refer to the LC 50 x 0.1 nd re compred to the estimted environmentl concentrtion (EEC). The EEC represents the concentrtion of substnce in the qutic environment when introduced under worst cse scenrio conditions, i.e., directly into body of wter. It is used to indicte possible risk, by comprison with the minimum concentrtion estimted to dversely ffect qutic orgnisms or to produce uncceptble concentrtions in biot, wter or sediment (DWAF, 1998). Disposl llowed refers to the cceptble mount of hzrdous wste tht cn be sfely disposed of per hectre per month. The minimum requirements, however, seem excessively stringent for purposes of lnd disposl, s they do not consider existing soil Avilble on website http://www.wrc.org.z ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 305
bckground conditions nd the bility of soil to buffer dditions of hevy metls. When one considers limits set by other environmentl orgnistions, specificlly for soil, then the levels reported here for these WTRs re generlly not excessive, especilly if one considers the effects of dilution when lnd disposing such wste. For exmple the limits set by Environment Cnd for griculturl soils indicte tht for Cd, Co, Cu, Cr, Ni, Pb nd Zn the limits re 1.4, 40, 63, 64, 50, 70 nd 200 mg/kg, respectively (CCME, 1998). One cn ssume the MgCl 2 nd wek cid extrctble frctions (Tble 6) estimte the likely mount of contmintion from the WTRs, s the remining frctions re unlikely to be vilble. Using these dt it cn be seen tht the only elements of probble concern re Cd nd Pb in the Rnd Wter WTR. The relese of the remining frctions of metls would depend lrgely on the rte of WTR brekdown, nd the environmentl conditions (e.g. reducing or cidic environments). The metls in the residul frction re considered unvilble, s they re bound in minerl lttices, re not redily relesed, nd s for the XRF dt, represent the worst cse for toxicity. Conclusions Generlly it ppers tht the WTRs exmined hve potentil for lnd ppliction. Concerns relte to the relese of metls under certin conditions, in prticulr Mn, Cd nd Pb in some instnces. As it is probble tht the source of the Mn is the tretment chemicls, the use of clener cogulnt would reduce the mount of Mn in the WTRs. If the Rnd Wter WTR were to be pplied to lnd then creful considertion would need to be given to the cidity of the soil. This is to ensure tht the ph remins in rnge tht will not cuse excessive relese of some hevy metls, in prticulr those bound in crbonte compounds. Furthermore, for lnd ppliction of WTRs (s with ny other wste) considertion needs to be given to existing bckground soil chrcteristics, s well s the intended purpose of the lnd to be treted with WTR (Elliott et l., 1990). These fctors will influence the rte nd frequency of ppliction to ny given re. In ddition, lthough the WTRs exmined here include the min WTRs produced in South Afric, it would be beneficil to exmine fr greter number of residues from different wter tretment processes nd from other loctions to improve understnding on the rnge of WTRs produced nd their potentil for lnd ppliction under vriety of conditions. Temporl vribility in WTR production tht my ffect both volumes nd qulity of the wste should lso be considered. Acknowledgements The uthors would like to cknowledge funding from the Wter Reserch Commission, this investigtion flling under their Project No K5/1148. Specil thnks to N McNb nd F Ali of Umgeni Wter, P Flower of the Cpe Metropolitn Council, D Smit nd R Fyfe of the Fure Wter Tretment Plnt nd ll the opertions mngers tht rrnged WTR smples for study. A note of thnks lso goes to the Animl Science Discipline nd the Geology Section, University of KwZulu-Ntl nd the Soil Fertility nd Anlyticl Services Lbortory, KZN Deprtment of Agriculture nd Environmentl Affirs, Cedr for the nlyses crried out. References AHMED M, GRANT CD nd OADES JM (1997) Wter Tretment Sludge: Potentil for Use s Soil Ameliornt. Urbn Wter Res. Assoc. of Austrli, Reserch Report No. 106. AWWARF (1969) Disposl of wstes from wter tretment plnts. J. Am. Wter Works Assoc. 61 541-619. BASTA NT (2000) Exmples nd cse studies of beneficil re-use of municipl by-products. In: Power JF nd Dick WA (eds.) Lnd Appliction of Agriculturl, Industril nd Municipl By-Products. ASA, CSSA nd SSSA, Mdison, WI. 492-504. BASTA NT, ZUPANCIC RJ nd DAYTON EA (2000) Evluting soil tests to predict Bermud grss growth in drinking wter tretment residuls with phosphorus fertilizer. J. Environ. Qul. 29 2007-2012. BLAKE GR nd HARTGE KH (1986) Prticle density. In: Klute A (ed.) Methods of Soil Anlysis: Prt I. Physicl nd Minerlogicl Methods (2nd edn.) ASA, CSSA nd SSSA. Mdison, WI. 377-382. BUYEYE M (2003) Personl communiction. Lecturer, Mngosuthu Technikon, Durbn. CCME (1998) Cndin Environmentl Qulity Guidelines Summry Tble: Updte 2002. Environment Cnd. (http://www.ec.gc.c/ ceqg-rcqe/english/ceqg/soil/defult.cfm). Accessed 11 September 2003. CODLING EE, CHANEY RL nd MULCHI CL (2002) Biomss yield nd phosphorus vilbility to whet grown on high phosphorus soils mended with phosphte inctivting residues. I. Drinking wter residue. Commun. Soil Sci. Plnt Anl. 33 1039-1061. DAYTON EA nd BASTA NT (2001) Chrcteristion of drinking wter tretment residuls for use s soil substitute. Wter Environ. Res. 73 52-59. DEPARTMENT OF WATER AFFAIRS AND FORESTRY (1998) Wste Mngement Series. Minimum Requirements for Wste Disposl by Lndfill. Deprtment of Wter Affirs nd Forestry. Pretori. DEPARTMENT OF WATER AFFAIRS AND FORESTRY (2003) (http://www.dwf.co.z). Accessed 12 December 2003. ELLIOTT HA, DEMPSEY BA, HAMILTON DW nd DEWOLFE JR (1990) Lnd Appliction of Wter Tretment Sludges: Impcts nd Mngement. Am. Wter Works Assoc. (AWWA) Res. Foundtion, Denver, CO. ELLIOTT HA, DEMPSEY BA nd MAILLE PJ (1990b) Contents nd frctiontion of hevy metls in wter tretment sludges. J. Environ. Qul. 19 330-334. ELLIOTT HA nd SINGER LM (1988) Effect of wter tretment sludge on growth nd elementl composition of tomto (Lycopersicom esculentum) shoots. Commun. Soil Sci. Plnt Anl. 19 345-354. ELLIOTT HA nd TAYLOR M (2000) Molybdenum content of wter tretment residuls. J. Environ. Qul. 29 1835-1839. FLOWER P (2003) Personl communiction. Opertions Mnger, Cpe Metropolitn Council. GEE GW nd BAUDER JW (1986) Prticle-size nlysis. In: Klute A (ed.) Methods of Soil Anlysis: Prt 1. Physicl nd Minerlogicl Methods, ASA, CSSA nd SSSA. Mdison, WI. 312-383. GEERTSEMA WS, KNOCKE WR, NOVAK JT nd DOVE D (1994) Long-term effects of sludge ppliction to lnd. J. Am. Wter Works Assoc. 86 64-74. GELDENHUYS JC (1992) Tretment nd disposl of wterworks sludge t the Rnd Wter Bord. Wter Sewge Effl. 12 35-39. GRABAREK RJ nd KRUG EC (1987) Silviculturl ppliction of lum sludge. J. Am. Wter Works Assoc. 79 84-88. HEIL DM nd BARBARICK KA (1989) Wter tretment sludge influence on the growth of Sorghum-Sudngrss. J. Environ. Qul. 18 292-298. HODGKINSON D nd RENCKEN GE (1992) Mngement of wterworks sludges. Wter Sewge Effl. 12 30-34. HUGHES JC nd GIRDLESTONE SJA (1994) The effects of lethery tnnery sludge on the lechtes from soil columns. S. Afr. J. Plnt Soil 11 90-95. 306 ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 Avilble on website http://www.wrc.org.z
HUGHES JC, TITSHALL LW, BUYEYE M, JOHNSTON MA, MOOD- LEY M nd PECKU S (2005) The Effect of Lnd Appliction on Wter Tretment Residue. Wter Reserch Commission Report No 1148/1/05. HYDE JE nd MORRIS TF (2000) Phosphorus vilbility in soils mended with dewtered wter tretment residul nd metl concentrtions with time in residul. J. Environ. Qul. 29 1896-1904. JACKSON ML (1958) Soil Chemicl Anlysis. Constble Compny Limited, London. LIANG J nd KARAMANOS RE (1993) DTPA-extrctble Cu, Fe, Mn nd Zn. In: Crter MR (ed.) Soil Smpling nd Methods of Anlysis. Lewis Publishers, Boc Rton, FL. 87-90. MAYNARD DG nd KALRA YP (1993) Nitrte nd exchngeble mmonium nitrogen. In: Crter MR (ed.) Soil Smpling nd Methods of Anlysis. Lewis Publishers, Boc Rton, FL. 25-38. MOODLEY M (2001) Effects of the Lnd Disposl of Wter Tretment Sludge on Soil Physicl Qulity. Ph.D. Thesis. University of Ntl, Pietermrizburg, South Afric. MOODLEY M, JOHNSTON MA, HUGHES JC nd TITSHALL, LW (2004) Effects of wter tretment residue, lime, gypsum, nd polycrylmide on the wter retention nd hydrulic conductivity of two contrsting soils under field conditions in KwZulu-Ntl, South Afric. Aus. J. Soil Res. 42 273-282. POLASEK P (1997) Tretment process efficiencies of South Africn wterworks - Prt 1. Wter Sewge Effl. 17 52-56. POLASEK P (1997b) Tretment process efficiencies of South Africn wterworks - Prt 2. Wter Sewge Effl. 17 64-69. OVERCASH MR nd PAL D (1979) Design of Lnd Tretment Systems for Industril Wstes Theory nd Prctice. Ann Arbor Science Publishers. Ann Arbor. USA. RENGASAMY P, OADES JM nd HANCOCK TW (1980) Improvement of soil structure nd plnt growth by ddition of lum sludge. Commun. Soil Sci. Plnt Anl. 11 533-545. ROY M nd COUILLARD D (1998) Metl leching following sludge ppliction to deciduous forest soil. Wter Res. 32 1642-1652. SCHMITT CR nd HALL JE (1974) Anlyticl chrcteristion of wter tretment plnt sludge. J. Am. Wter Works Assoc. 5 40-42. SIMMS DL (1988) Led in soil: A Europen s view. In: Dvies BE nd Wixson BG (eds.) Led in Soil: Issues nd Guidelines. Whitstble Litho Printers Ltd., Kent, UK. SIMS JT (1996) Lime requirement. In: Sprks DL (ed.) Methods of Soil Anlysis: Prt 3. Chemicl Methods. ASA, CSSA nd SSSA, Mdison, WI. 491-518. SKENE TM, OADES JM nd KILMORE G (1995) Wter tretment sludge: potentil plnt growth medium. Soil Use Mnge. 11 29-33. SOIL CLASSIFICATION WORKING GROUP (1991) Soil Clssifiction. A Txonomic System for South Afric. Deprtment of Agriculturl Development, Pretori, South Afric. TILLER KG (1989) Hevy metls in soils nd their environmentl significnce. Adv. Soil Sci. 9 113-142. THE NON-AFFILIATED SOIL ANALYSIS WORK COMMITTEE (1990) Hndbook of Stndrd Soil Testing Methods for Advisory Purposes. Soil Science Society of South Afric, Pretori, South Afric. UNITED STATES SALINITY LABORATORY STAFF (1954) Dignosis nd Improvement of Sline nd Alkli Soils. USDA, Wshington DC. USEPA (1996) Technology Trnsfer Mnul: Mngement of Wter Tretment Plnt Residuls. EPA/625/R-95/008. Office of Reserch nd Development. Wshington, D.C. WALKLEY A (1947) A criticl exmintion of rpid method for determining orgnic crbon in soils: Effect of vritions in digestion conditions nd of orgnic soil constituents. Soil Sci. 63 251-263. Avilble on website http://www.wrc.org.z ISSN 0378-4738 = Wter SA Vol. 31 No. 3 July 2005 307
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