Disposal of domestic sludge and sludge ash on volcanic soils

of 6

Please download to get full document.

View again

All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
PDF
6 pages
0 downs
2 views
Share
Description
Disposal of domestic sludge and sludge ash on volcanic soils
Tags
Transcript
  Journal of Hazardous Materials B139 (2007) 550–555 Disposal of domestic sludge and sludge ash on volcanic soils Mauricio Escudey a , ∗ , Juan E. F¨orster a , Juan P. Becerra a , Magdalena Quinteros a ,Justo Torres a , Nicolas Arancibia a , Gerardo Galindo a ,Andrew C. Chang b a Facultad de Qu´ımica y Biolog´ıa, Universidad de Santiago de Chile, Av. B. O’Higgins, 3363 Santiago, Chile b  Department of Environmental Sciences, University of California, Riverside, CA, United States Available online 2 May 2006 Abstract Column leaching experiments were conducted to test the ability of Chilean volcanic soils in retaining the mineral constituents and metals insewage sludge and sludge ash that were incorporated into the soils. Small or negligible amounts of the total content of Pb, Fe, Cr, Mn, Cd, andZn (0 to <2%), and more significant amounts of mineral constituents such as Na (7–9%), Ca (7–13%), PO 4  (4–10%), and SO 4  (39–46%) in thesludge and sludge ash were readily soluble. When they were incorporated on the surface layer of the soils and leached with 12 pore volumes of water over a 3 month period of time, less than 0.1% of the total amount of heavy metals and PO 4  in the sludge and sludge ash were collected inthe drainage water. Cation exchange selectivity, specific anion adsorption and solubility are the processes that cause the reduction of leaching. Thevolcanic soils were capable of retaining the mineral constituents, P, and metals in applied sewage sludge and sludge ash and gradually releasedthem as nutrients for plant growth.© 2006 Elsevier B.V. All rights reserved. Keywords:  Sewage sludge; Sludge ash; Column studies; Volcanic soils 1. Introduction Sewage sludge is the inevitable end product of municipalwastewater treatment processes worldwide. As the wastewateris being purified, the impurities removed from the water streamare being concentrated. The sludge stream thus contains manychemical and microbiological constituents usually in concen-trated forms that may become potential sources of pollutantswhen the material is released. No matter how many treatmentsteps it undergoes, at the end, the sludge and/or its derivatives(such as sludge ash), require the ultimate disposal. For disposal,the sewage sludge may be land applied, land filled, incinerated,or ocean dumped. There is not an entirely satisfactory solutionand all of the currently employed disposal options have seriousdraw backs. Land application however is by far the most com-monlyusedmethodaroundtheworld.Approximatelysixmilliondry tons of sewage sludge is produced annually in the UnitedStates [1]. Recent report showed that the annual production of sewage sludge in member countries of the European Union may ∗ Corresponding author. Tel.: +56 2 6819037; fax: +56 2 6812108.  E-mail address:  mescudey@lauca.usach.cl (M. Escudey). reachasmuchas8 × 10 6 tons[2].Significantamountsofsewagesludge produced in the United States and the western Europeannations have been applied on land. Dependent on the regions,24–89% of the sludge produced in the US has been applied onland [1]. Bonnin [2] reported that 65% of the sewage sludge in France was land applied; the situations in other parts of theworld are expected to be similar. Recently, European countriesare studying more restrictive directives to sewage sludge appli-cations on land.As the residue of municipal wastewater treatment, sewagesludge represents the aggregation of organic matter, pathogens,traceelements,toxicorganicchemicals,essentialplantnutrients,and dissolved minerals srcinally dispersed in the wastewaterand are captured and transformed by the wastewater treatmentprocesses.Properlymanaged,thepotentialpollutantsareassimi-latedviathebiochemicalcyclingprocessesofthereceivingsoilsin the land application. The practice provides soils with organicmaterials and offers the possibility of recycling plant nutrients,which in turn, improve the fertility [3] and physico-chemicalproperties of agricultural soils [4]. If not appropriately con-trolled, the potential pollutants released through the land appli-cation may degrade the quality of downstream water bodies, betransferredthroughthefoodchaintoharmtheconsumersofhar- 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2006.02.062   M. Escudey et al. / Journal of Hazardous Materials B139 (2007) 550–555  551 vests, and drastically alter the physical and chemical propertiesof the receiving soils. It is imperative that mass input providesadequateamountsofsubstancesthatareusefultoplantdevelop-ment and the pollutant inputs are controlled to avert detrimentalpublic health and environmental effects. Major countries suchas the US, the European Union [5] and China [6] have enacted regulationsorissuedguidelinesthatlimitedthedisposaloptionsfor a variety of reasons.In Chile, the treatment works are gradually being broughtonline in recent years, before the collected wastewater wasdirectly discharged and sewage sludge did not exist. Withthe commencement of wastewater treatment, sewage sludgeand ash of the incinerated sewage sludge are accumulating inthe metropolitan areas awaiting final disposals. In the sewagesludge used, the levels of heavy metals follow the sequenceZn>Mn>Cu>Cr>Pb>Ni>Mo>Cd (from 1780mg/kg forZn down to 5mg/kg for Cd), being land application one of theprimary options under consideration at this time.The agricultural soils in Central Chile where most of thecountry’s population centers are situated are derived from par-ent material of volcanic srcin, and account for approximately69% of nation’s arable land. The predominant minerals of thesesoils are allophane and ferrihydrite in the Andisols and kaolin-ite, halloysite and iron oxides in Ultisols. These soils are rich iniron oxides and organic matter contents, possess pH-dependentvariable surface charge and high PO 4  accumulation. However,the soils have poor fertility; at the srcinal acidic pH range of 4.5–5.5,theyhavelowcapacityforexchangeablecations(CEC)and a strong selectivity for K and Ca over Mg [7]. Phosphorusis strongly fixed by the minerals, thus is not readily available forplant absorption in these soils. To be productive, they requirefrequent adjustments of soil pH, replenishment of exchangeableMg, and heavy PO 4  applications. When soil pH increases theCECincreases,PfixationdecreasesandKselectivityisreduced.On the other hand, when the soil organic matter increases, the Kselectivity is also reduced [7]. Municipal sewage sludge and ashof the incinerated sewage sludge appear to possess the essentialplant nutrients and dissolved minerals and the buffering capac-ity [8–11]. When land applied, they may replenish the depleting nutrient reservoirs in these soils under cultivations. If the addedconstituents are retained in the soils and absorbed by plants,the risk of contaminating the downstream water bodies may beminimized. In this study, the capacity of volcanic soils to retainchemical constituents in the land applied sewage and sewagesludge ash was investigated. 2. Materials and methods 2.1. Soils The surface 0–25cm depth layers of five volcanic soilslocated in the agricultural regions of the Southern CentralChile were collected. Namely, they were Collipulli, Diguillin,Nueva Braunau, Metrenco, and Ral´un reflecting the localitiesfrom where soils were extracted. The samples were obtainedfrom well drained and regularly cultivated fields. Collipulli andMetrenco are classified as Ultisols and Ral´un, Diguillin, andNuevaBraunauasAndisols.Generalinformationontheclimateand geography of the soils may be found in Escudey et al .  [12].Soil samples were screened in the field to pass a screen with2mm openings and stored at the field moisture content in a 4 ◦ Ccold room until used. 2.2. Experiments Soils were packed to the depth of 25cm into acrylic columnsof30cmlengthand10cmofdiameter,accordingtotheirrespec-tive field bulk densities. A filter paper disk was placed on theperforated plate at the bottom of each column to prevent theloss of solid materials. The sewage sludge was obtained from adomestic water treatment plant located in Santiago (Chile), thesewage sludge ash was obtained by heating the sewage sludgeat 500 ◦ C for 2h. Dependent on the treatment, 30g of air driedsewage sludge or the ash equivalent of 30g of air dried sewagesludge were incorporated into the surface 5cm of the packedcolumns. The experimental controls received neither the sludgenortheashtreatment.Thecolumns,wereplacedinverticalposi-tion, flooded once a week with one pore volume of distilledwater, and drained by gravity from top to bottom, for a period of 12 weeks. In addition, 30g of sludge and the ash equivalent of 30g of sludge were leached in the same manner. The drainagesfrom each weekly leaching cycle were analyzed for pH, electri-cal conductivity, SO 4 , PO 4 , Na, K, Mg, Ca, Zn, Cu, Fe, Al, Ni,Cd, Pb, Mo, and Mn.At the end of the leaching experiment, each soil column wascutopenlengthwiseandtheprofilewassectionedintofiveequallength segments for analysis of the soils’ pH, electrical conduc-tivity,andorganiccarbon,exchangeablecations,andPcontents.A chemical fractionation of heavy metals was carried out insludge and sludge ash, by using the methodology proposed byChang et al. [13]. The sequential extraction with 0.5M KNO 3 ,distilled water, 0.5M NaOH, 0.05M EDTA, and 0.5M HNO 3 allows to estimate the exchangeable, sorbed, organic, carbonateand residual fractions of heavy metals. 2.3. Chemical determinations The bulk density, exchangeable cations, total porosity,and organic carbon content of the soils were determinedby methods outlined in methods of soil analysis (AmericanSociety of Agronomy, Madison, WI). Briefly, the bulk density[14] was determined by the average air dried weight of soilsin undisturbed soil cores of the 0–25cm soil profile in 5cm(diameter) × 5cm (height) brass rings; the exchangeablecations were determined as the concentrations of Na, K, Mg,and Ca in ammonium acetate extracts [15]; and organic carbonwas determined by the Walkley-Black method [16]. The pHand electrical conductivity of soils were measured in soilsuspensions with soil to water ratio of 1:2.5w/v. The totalelementalcontentsofNa,K,Mg,Ca,Zn,Cu,Fe,Al,Ni,Cd,Pb,Mo, Mn, P and S were determined by digesting the soils witha concentrated HNO 3 –HCl–HF mixture in a microwave ovenand measuring the concentrations by ICP–OES spectroscopy(PerkinElmerOptima2000equipment,MECESUPUSA9903).  552  M. Escudey et al. / Journal of Hazardous Materials B139 (2007) 550–555 Table 1Properties of soils, sewage sludge and sludge ashSoil pH Bulk density(gcm − 3 )Pore volume(mL)Organic carbon(%)Electrical conductivity(  Sm − 1 )Exchangeable bases (cmolkg − 1 )Na K Mg CaCollipulli 5.4 1.36 1027 2.3 81 0.1 0.2 1.8 5.9Metrenco 5.5 1.33 1056 1.8 29 0.2 0.3 1.5 4.0Ral´un 4.5 0.90 988 6.2 436 0.1 0.1 0.4 2.5Diguillin 5.9 1.12 830 6.5 94 0.2 0.7 1.1 8.4N. Braunau 5.5 0.82 834 11.0 20 0.1 0.1 0.2 1.1Sludge 7.7 0.46 – 17.8 8520 1.5 2.5 10.7 65.9Sludge ash 7.4 – – <0.1 3890 1.2 1.1 7.4 25.8 Comparable components of the sewage sludge and sludge ashwere determined in the same manner. The concentration of thesame elements in leachates was also determined by ICP–OES;the SO 4  and PO 4  concentrations in the drainage water weremeasured by ion chromatography (Waters 625LC), providedwith a Waters IC Pak anion HR 4.5mm × 75mm column.Theabsorbanceofleachateswasmeasuredat465and665nmin an UV–vis Perkin Elmer Lambda 20 spectrophotometer. 3. Results and discussions 3.1. Soils, sludge, and sludge ash Prior to the sludge and ash treatments, the soils were acidicwith pH varying from 4.5 to 5.9 and low in exchangeable basescontents varying from 1.5 to 10.4cmolkg − 1 (Table 1). In con-trast, the sewage sludge and sludge ash had pH of 7.7 and 7.4,respectively that were 2–3 orders magnitude higher in alkalinitythan those of the soils. The exchangeable base content of thesewage sludge was 80.6cmolkg − 1 , 10–54 times those of thesoils. The Na, K, Mg and Ca in the sludge ash were solublebut not necessary in the exchangeable forms. Judging by theirelectrical conductivities, the soluble mineral contents of sewagesludge and sludge ash were orders of magnitude larger than thesoils, even though the incineration of sewage sludge results inless soluble chemical forms, and consequently presents a lowerelectrical conductivity than sewage sludge. The total elementalcontentsoftheCa,Mg,K,andNainsoilsfollowthesametrendsas those in the exchangeable forms and the concentrations arein the same order of magnitude. The column pore volume wascalculated considering the amount of soil into the column andthe total porosity of each soil (Table 1). 3.2. Releases from sludge and sludge ash Whenthesludgeandsludgeashwereleached,thesolubleNaandSO 4  werereleasedquickly(Fig.1).Judgingfromtheshapesof the break through curves, the soluble Na and SO 4  in sewagesludge were depleted with one pore volume of water used toleach the soils. On the other hand, the soluble Na and SO 4  insewagesludgeasharegraduallyreleasedwith5–8porevolumesof water. Slight differences in the total amounts released fromthesludgeandsludgeashforNa(19mgversus16mg),andSO 4 (342mg versus 319mg), were observed.One main domain is observed in sludge release, which isassociated to highly soluble forms. On the other hand, two maindomains are observed in sewage ash, the first associated to sol-uble forms which is less important than in sludge, and a secondfrom 2 to 5 pore volumes which can be associated to slow equi-libria between solid and water. In both samples the quantitiesreleased were a small fraction of the total amounts.OrganicandinorganicPformsarepresentinsludge,whileinsludgeash,aftercalcination,onlyinorganicPformsarepresent.The P forms in both samples are released slowly and released atconstant rates over time (Fig. 2). In sludge, release is probablycontrolled by slow equilibria between solid organic P forms andsoil solution, and by solubility of inorganic P forms. The releaseof P forms from ash is mainly solubility controlled, which isreflected in the lower slope shown in Fig. 2. Consequently, attheendof12leachingcycles,smallamountsofPO 4  wererecov-ered from drainages of sewage sludge and sludge ash (18 and Fig. 1. Releases of Na and SO 4  from sewage sludge and sludge ash.   M. Escudey et al. / Journal of Hazardous Materials B139 (2007) 550–555  553Fig. 2. Phosphorus release from sewage sludge and sludge ash. 6mg, respectively) compared with their total contents (181 and170mg, respectively).ThepatternsofZnreleasesforthesludgeandsludgeashweresimilar (Fig. 3). However, the amounts released by the sludge,0.8mg, were considerably higher than that of the sludge ash,<0.1mg. Nevertheless, they were far below the total amounts of 53 and 49mg in the sludge and sludge ash, respectively.In all, only small amounts of the Na, SO 4 , P, and Zn werereleased when the sludge and sludge ash were subject to intenseleaching for 12 weeks. Even though Cu and Zn are the mainheavy metals in Chilean sewage sludge, also other heavy metalsof environmental interest, such as Ni, Cd, Cr, Mo and Mn, wereconsidered. 3.3. Soil attenuation ThepHofleachatesincontrolandtreatedsoilsincreasesafter12 pore volumes; the final pH is about 1.5–2.0 units higher thanthe initial pH. The process is controlled by the soil; thus, after12 pore volume the pH of treated soil leachates is only about0.3 pH unit higher than those observed in the control columns.In all the experiments, after 12 pore volume, the leachate pH isbasic, ranging between 7 and 8.The leaching of organic matter was followed by measur-ing the absorbance of leachates after each pore volume at 465and 665nm. Only leachates from Ralun soil columns showed Fig. 3. Zinc release from sewage sludge and sludge ash.Fig. 4. Total amount of Ca and SO 4  leached from sewage sludge and sludge ashtreated soils. absorbance higher than zero, but the amount of organic mat-ter leached was too low to be quantified. No significant lossof organic colloids was observed, because the mass balancedemonstrates that the organic carbon remains constant in allcolumns considering the experimental errors of the Walkley-Black method.Evenwithouttheapplicationsofsludgeorsludgeash,signif-icant amounts of cations and anions such as Ca and SO 4  maybeleached from the soils (Fig. 4) and the amounts collected in thedrainage water were dependent on conditions of soils. Sludgeand sludge ash amendments consistently enhanced the leach-ing of minerals. However, collected amounts were significantlysmaller than the total introduced through the addition of sludgeor sludge ash, and are practically leached in the first 3 or 4 porevolumes of drainage water. Soil incorporation further reducedthemobilityofthechemicalconstituentsinthesludgeandsludgeash (Fig. 5). For P and Zn, the amounts found in the drainagewater (Fig. 5) were 2–3 orders of magnitude lower than theamounts present in the added sludge and sludge ash. As a result,nutrients such as the available P significantly increased with theapplication of sewage sludge and sludge ash for both the Ultisoland Andisol (Fig. 6).Thegeneraltrendinalltheexperimentswasthatonlyasmallfractions of the total amounts incorporated by the addition of sludgeorsludgeashwereleached.Asanexample,thetotalinputfromsludgeandash,thetotalamountleachedfromthem,andthetotal amount collected after 12 pore volumes for Collipulli andNuevaBraunausoils,arepresentedinFig.7.Thetotalamountof heavymetals(Cu,Zn,Ni,Cd,Pb,Mo,Mn)leachedafter12porevolumes was <0.1% of the total input through sewage sludge or  554  M. Escudey et al. / Journal of Hazardous Materials B139 (2007) 550–555 Fig. 5. Total amount of Zn and PO 4  leached from sewage sludge and sludge ashtreated soils.Fig. 6. Available P in the sewage sludge and sludge ash treated Ultisol(Metrenco) and Andisol (Diguillin).Fig. 7. Total amount of selected cations and anions in sewage sludge and theequivalent ash (Total in SS, SA), total amount leached from sewage sludge andsewage ash (leached from SS, SA), and leached from sewage sludge-treatedcolumns and ash-treated columns (leached from ss treated, ash treated), forCollipulli and Nueva Braunau soils. sewage ash (represented by Zn, Cu and Pb in Fig. 7). On theother hand, fractions leached of SO 4  (22–55%), Na (7–15%), K(2–30%), Ca (3–7%), and Mg (2–30%) are more significant.The leaching of exchangeable bases behaves as predicted bycation exchange selectivity previously reported [17]. Phosphateis leached in very low amounts (<0.1%), even though sewagesludge and sludge ash present large P contents; this is due tothe specific PO 4  adsorption, which is a characteristic of Chileanvolcanic soils [12].Fractionationexperimentsdemonstratethat86–99%ofheavymetalchemicalformsinsewagesludgeareassociatedtoorganicmatter complexes, carbonate and residual low soluble com-pounds, and that 95–99% is associated to carbonate and lowsolubility forms in sludge ash. All of them have low mobility,andconsequentlytheirleachingismainlyassociatedtothemoresolublechemicalforms,whicharepresentonlyinverylowcon-centration in both substrates. 4. Conclusions Resultsofcolumnleachingexperimentsshowedthatvolcanicsoils in Chile were capable of retaining the inorganic mineralconstituents, P, and Zn in sewage sludge and sludge ash whenland applied. These constituents are essential inputs to enhancethe productivity of volcanic soils that are frequently low in fer-tility. Cation exchange selectivity, specific anion adsorption andsolubility are the processes that cause the reduction of leach-ing. In this regard, the volcanic soils will attenuate the sewagesludgebornepollutantsandprovidesoilswithnutrientsthatmaybe slowly released for crop production.
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks