Agronomic Properties of Waste Water Sludge Biochar and Bio Availability of Metals

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Chemosphere 78 (2010) 1167–1171 Contents lists available at ScienceDirect Chemosphere journal homepage: Technical Note Agronomic properties of wastewater sludge biochar and bioavailability of metals in production of cherry tomato (Lycopersicon esculentum) Mustafa K. Hossain a, Vladimir Strezov a,*, K. Yin Chan b, Peter F. Nelson a a b Graduate School of the Environment, Faculty of Science, Macquarie University, NSW 2109, Australia NSW Department of Primar
  Technical Note Agronomic properties of wastewater sludge biochar and bioavailability of metalsin production of cherry tomato ( Lycopersicon esculentum ) Mustafa K. Hossain a , Vladimir Strezov a, * , K. Yin Chan b , Peter F. Nelson a a Graduate School of the Environment, Faculty of Science, Macquarie University, NSW 2109, Australia b NSW Department of Primary Industries, Locked Bag 4, Richmond, NSW 2753, Australia a r t i c l e i n f o  Article history: Received 31 October 2009Received in revised form 7 January 2010Accepted 8 January 2010 Keywords: BiocharChromosol soilPyrolysisWastewater sludge a b s t r a c t Thisworkpresents agronomic values of abiocharproducedfromwastewater sludgethroughpyrolysis ata temperature of 550 ° C. In order to investigate and quantify effects of wastewater sludge biochar on soilquality, growth, yield and bioavailability of metals in cherry tomatoes, pot experiments were carried outin a temperature controlled environment and under four different treatments consisting of control soil,soil with biochar; soil with biochar and fertiliser, and soil with fertiliser only. The soil used was chromo-sol and the applied wastewater sludge biochar was 10tha À 1 . The results showed that the application of biochar improves the production of cherry tomatoes by 64% above the control soil conditions. The abilityof biochar to increase the yield was attributed to the combined effect of increased nutrient availability (Pand N) and improved soil chemical conditions upon amendment. The yield of cherry tomato productionwasfoundtobeatitsmaximumwhenbiocharwasappliedincombinationwiththefertiliser.Applicationof biochar was also found to significantly increase the soil electrical conductivity as well as phosphorusandnitrogen contents. Bioavailability of metals present in the biochar was found to be belowthe Austra-lian maximum permitted concentrations for food. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Sludgewastesproducedduringwastewatertreatmentaresomeof the most difficult waste materials to manage due to the increas-ing quantities produced and the pathogenic organisms and metalcontents present in the sludge. Approximately 190000t of bioso-lids are produced each year at wastewater treatment plants inthe Sydney basin alone (Bamforth et al., 2004). The safe and bene-ficial use of wastewater sludge is a subject of considerable interestfor the society. Application of unprocessed wastewater sludge andwastewater sludge compost have been previously trialled asorganic fertilisers with some success (Singh and Agrawal, 2007;Roca-Perez et al., 2009). Thermal processing of wastewater sludgeprovides an additional option to manage this waste and for itsupgrading to bio-gas, bio-oil and biochar (Werther and Ogada,1999; Inguanzo et al., 2002; Hossain et al., 2009). The biochar isparticularly attracting international attention for the followingtwo reasons. Firstly, biochars can be used as soil amendments forimproving soil properties and crop yield and secondly, storingbiochars in soils is regarded as means for permanently sequester-ing carbon (Glaser et al., 2002a,b; Lehmann et al., 2003, 2006).The conversion of wastes by pyrolysis to produce biochar haspotential to increase conventional agricultural productivity(McHenry, 2009). Understanding of agricultural effects of biocharis very limited and based on few biomass feedstock materials.Previousworkinvestigatedthebeneficialeffectsof biocharpro-duced from green-waste and poultry litter on the yield of agricul-tural crop and properties of soil (Glaser et al., 2002b; Chan et al.,2007, 2008). It was found that biochar from poultry litter signifi-cantly improves the yield of radish crops (Chan et al., 2008) buttheriskof usingpoultryasasoil amendment isstill unknown. Bio-char addition to soils also improved nitrogen fertiliser use effi-ciency through improvement of the chemical properties of chromosol soil. Application of biochar to the soil was found to in-creasesoilcationexchangecapacity(CEC)byupto40%andsoil pHbyuptoone pHunit (MikanandAbrams, 1995). Theapplicationof wastewater sludge biochar as a soil amendment has a potential toprovidea viable optionfor nutrient recovery whenappliedto soils,improve the wastewater sludge management practice and seques-ter carbon in the soils.However, there is currently no published data available onquantificationoftheeffectofwastewatersludgebiochartothesoil,plantnutrientsandthebioavailabilityofmetalsinplant.Thisstudyis focused on the agronomic potential of wastewater sludge bio-char and its impact on soil quality, plant growth, yield and bio-availability of metals in fruit using cherry tomato ( Lycopersiconesculentum ) as anagricultural cropinaglasshousepot experiment. 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.chemosphere.2010.01.009 * Corresponding author. Tel.: +61 2 9850 6959; fax: +61 2 9850 7972. E-mail address: Strezov).Chemosphere 78 (2010) 1167–1171 Contents lists available atScienceDirect Chemosphere journal  2. Materials and methods  2.1. Soils The soil used for this study was collected from the flat paddockat the Centre for Recycled Organic Agriculture site Menangle nearCamden, south-western region of Sydney, Australia. The soil se-lectedwaswithfairagriculturalpropertiesinordertobetterdeter-mine the effect of treatment conditions using biochar on plantgrowth and production. According to the Australian Soil Classifica-tion, the soil collected for this research is classified as chromosol(Isbell, 1996). A composite sample was collected down to 0.1mof the top soil layer, followed by sieving through a 6mm sieve.The chemical properties of the collected surface soil are shown inTable 1. The soil was found to be low in total nitrogen (0.13%),ammonium nitrogen (3.6mgkg À 1 ), phosphorus (15mgkg À 1 ) andwas found to be acidic in nature.  2.2. Biochar preparation The feedstock used for biochar production for this study waswastewater sludge collected from a wastewater treatment plantin Sydney region, Australia. The wastewater sludge was first air-dried and then pyrolysed under controlled conditions to ensureuniform heating and treatment conditions. Biochar productionwas carried out using a fixed bed reactor set at a heating rate of 10 ° Cmin À 1 upto550 ° C.Nitrogengaswasflownthroughthesam-ple at a rate of 100mLmin À 1 to ensure inert heating conditions.Approximately300gofwastewatersludgebiocharwerepyrolysedwith each experiment. The pyrolysis trials were repeated toachieveatotalof 1kgof biocharwhichwasthenusedfor chemicalanalysis and pot experiments. The chemical properties of thewastewater sludge biochar used in this experiment are shown inTable 1.The biochar was found to be alkaline in nature (pH 8.2)and low in total nitrogen (2.3%).  2.3. Pot trial Glasshouse pot trial using L. esculentum as a crop species werecarried out to determine the agronomic properties and the effectof the wastewater sludge biochar on growth, yield and risk of met-als.Thepottrialswerecarriedoutinatemperaturecontrolled(20–26 ° C) glasshouse environment. Cylindrical plastic pots 19cm inheight, 15cm in diameter at the bottom and 20cm in diameterat the top were used for the pot trials. The experimental designwas factorial randomised block design with four treatments andsix replications. The four treatments were: (i) control soil (CP);(ii) soil with biochar (SB); (iii) soil with biochar and fertiliser(SBF) and (iv) soil with fertiliser (SF).In each pot 6kg of air-dried soil was packed and the appliedbiochar was 10tha À 1 . In absence of standards or recommendedapplicationdoseof biocharstosoils, theamount ofbiocharappliedin this research is based on previous investigations conducted byChanetal.(2008)andVanZwietenetal.(2009)whodemonstratedbenefits to soil and plants by application of 10tha À 1 of biocharproduced from papermill sludge and poultry litter, respectively.The fertiliser application used in the current experiment wasequivalent to 120kg of nitrogen; 70kg of phosphorus and 80kgof potassium ha À 1 (Murrison and Huett, 1987).The pots were wetted up to the field capacity using de-ionisedwater. Fiveseeds of tomatoweresownineachpot andgerminatedfor 5–6d. After 15d the germinated seedlings were thinned andthe healthiest plant from each pot was retained. A shallow traywas placed under each pot and the plants were watered approxi-matelyuptothefieldcapacitythroughoutthedurationofthetrial.The pot trials were carried out for a total of 16wk.  2.4. Soil and fruit analysis The soil from each pot was collected and air-dried at a temper-ature of 36 ° C until constant weight. The soils from each pot weremixedand passedthrougha 4mmsieve to separate the plant deb-ris.Sub-sampleswerefurthergroundtopassthrougha2mmsieveand analysed for electrical conductivity (EC), pH, total nitrogen,extractable phosphorus (Colwell), exchangeable cations and CEC.Total N were measured by Dumas combustion method using anElementar vario MAX CN analyser with combustion chamber setat 900 ° C and oxygen flow rate of 125mLmin À 1 . The pH was mea-sured in 0.01M CaCl 2 (1:5) according to method 4B2 of Raymentand Higginson (1992). Available phosphorus (Colwell), mineralnitrogen (KCl extraction and extractable) and micronutrients weremeasured according to methods 9B1, 7C2 and 12A1 of Raymentand Higginson (1992),respectively. Exchangeable cations weredetermined using theGillman and Sumpter (1986)method. Atthe endof the pot experiment the fruits and plants wereharvestedfrom each pot and oven dried at 70 ° C to constant weight beforeweighing to determine the dry matter.Accumulation of metals and trace elements in fruits were ana-lysed by ICP according to the US EPA method 6010. The sampleswerehomogenisedandasub-sample(0.2–0.5g)wasdigestedwithre-distilled nitric acid on a DigiPrep block for 1h until vigorousreaction was complete. Samples were then transferred to a Mile-stone microwave for further digestion. The digested sample wasanalysed for metals and trace elements using ICP-AES.  2.5. Statistical analysis All data were statistically studied by analysis of variance usingGENSTAT 9.1 software (Lawes Agricultural Trust, 2006). The treat-ment means were compared using least significant differences forthe main effect of biochar on plant growth properties. Unlessotherwise stated, the differences were significant at p 6 0.05 level. 3. Results  3.1. Effect of biochar application on soil parameters Table 2shows the changes of chemical properties of the soils of different treatments due to application of biochar. Application of wastewater sludge biochar was found to significantly change mostofthechemicalpropertiesofthesoil.ThebiocharincreasedEC,pH,total nitrogen, extractable phosphorus and CEC of the soil. EC wasfound to have the highest value (0.53dSm À 1 ) in SBF treatmentwhile pH was the highest (pH 4.7) in the SF treatment. SBF treat-  Table 1 Chemical properties of soil and biochar used in pot experiment. Properties Unit Soil BiocharEC dSm À 1 0.09 1.9pH (CaCl 2 ) pH unit 4.6 8.2Total N % 0.13 2.3P (Colwell) mgkg À 1 15 1100Ammonium N (KCl extract) mgkg À 1 3.6 11Nitrate N (KCl extract) mgkg À 1 4.9 0.49 Exchangeable cations Al cmolkg À 1 0.37 <0.03Ca cmolkg À 1 5 33Mg cmolkg À 1 1.5 1.8K cmolkg À 1 0.17 0.24Na cmolkg À 1 0.2 0.5CEC cmolkg À 1 7.2 351168 M.K. Hossain et al./Chemosphere 78 (2010) 1167–1171  mentcontainedthehighestconcentrationoftotalnitrogen(0.22%).The available phosphorus (Cowell) exhibited the highest value(303mgkg À 1 ) in case of the SF treatment but it was not signifi-cantly different to the SBF treatment at 290mgkg À 1 . A significantincrease of mineral nitrogen was detected in the SBF treatment(Table 2). For the exchangeable cations, the biochar application in-creased only the calcium concentration, while the aluminium de-creased in all treatments.  3.2. Effect of biochar on plant height  The height of each plant in all treatments was measured start-ingfromwk5to15.Theresults, asshowninFig. 1, revealedsignif-icant effect of biochar on the height of the plant. However, SBFtreatment conditions showed the highest average performance(69.3cm), followed by SF (64.0cm), SB (57.7cm) and CP(44.5cm). The maximum plant height at the end of 15wk trialwas estimated at 96.8cm for CP, 107.5cm for SB, 113.5cm forSBFand109cmfor SFconditions. The maximumplant growthratewas observed during the 8th wk for SBF (13.0cm), the 9th wk forSF (13.5cm), and 12th wk for SB (15.8cm).  3.3. Effect of biochar on plant dry matter weight  The dry matter weight of cherry tomato plant shoot varied sig-nificantly among the different treatments, as shown inFig. 2a. Theaveragedryweight of shoot productionrangedfrom61.9gplant À 1 for CP to 92gplant À 1 recorded for SBF treatment. There was nosignificant difference between the SB (73.8gplant À 1 ) and SF(79.7gplant À 1 ) treatments. The SBF treatment showed the highestperformance due to the addition of fertiliser in combination withbiochar, which improved the growth of the cherry tomato plant.  3.4. Effect of biochar on the number of produced fruits The cherry tomato fruits produced from the plants for all of theconsidered treatments were harvested during a period of 12–16wk. All plant treatmentsusingbiochar, fertiliser orcombinationof both, exhibited larger number of fruits per plant, comparing toCP condition (Fig. 2b). Plants grown with SBF had the maximumaverage fruit number which was 167% above the CP condition,63% above SB and 122% above SF treatments.  3.5. Effect of biochar on crop yield Biocharincombinationwithfertiliseralsoshowedthemostsig-nificanteffectontheyieldofcherrytomatoproductionfollowedby  Table 2 Changes in soil chemical properties and standard deviation by biochar application. Properties Unit CP SB SBF SF LSDEC dSm À 1 0.05 (±0.00) 0.29 (±0.03) 0.53 (±0.04) 0.33 (±0.04) 0.14pH pH unit 4.3 (±0.01) 4.5 (±0.03) 4.7 (±0.06) 4.7 (±0.06) 0.13Total N % 0.14 (±0.01) 0.18 (±0.01) 0.22 (±0.01) 0.19 (±0.01) 0.02P (Cowell) mgkg À 1 26 (±0.87) 56 (±2.4) 290 (±24.2) 303 (±16.0) 36Ammonium N (KCl extract) mgkg À 1 3.6 (±0.27) 5.1 (±0.57) 102 (±20.1) 88 (±19) 41Nitrate N (KCl extract) mgkg À 1 9.3 (±1.26) 54 (±21.6) 193 (±19.6) 125 (±23.7) 64 Exchangeable cations Al cmolkg À 1 0.38 (±0.01) 0.23 (±0.01) 0.08 (±0.01) 0.09 (±0.01) 0.04Ca cmolkg À 1 4.7 (±0.07) 5.9 (±0.1) 6.5 (±0.11) 6.0 (±0.1) 0.3Mg cmolkg À 1 1.6 (±0.03) 1.6 (±0.02) 1.4 (±0.04) 1.6 (±0.02) 0.1K cmolkg À 1 0.28 (±0.02) 0.25 (±0.09) 1.3 (±0.16) 1.3 (±0.09) 0.35Na cmolkg À 1 0.39 (±0.01) 0.39 (±0.03) 0.29 (±0.03) 0.38 (±0.01) 0.07CEC cmolkg À 1 7.3 (±0.09) 8.5 (±0.14) 9.5 (±0.18) 9.4 (±0.17) 0.45LSD=least significant difference. 0204060801001205 6 7 8 9 10 11 12 13 14 15 weeks    h  e   i  g   h   t   (  c  m   ) CPSBSBFSF Fig. 1. Weekly plant height of cherry tomato. 020406080100120    D  r  y  m  a   t   t  e  r   (  g  m   /  p   l  a  n   t   ) 050100150200250    F  r  u   i   t  s  n  u  m   b  e  r   /  p   l  a  n   t 050010001500200025003000CP SB SBF SF Treatments    Y   i  e   l   d   (  g  m   /  p   l  a  n   t   ) abc Fig. 2. Cherry tomato production using different soil treatments: (a) dry matterproduction of cherry tomato per plant; (b) cherry tomato fruit number; (c) cherrytomato yield. M.K. Hossain et al./Chemosphere 78 (2010) 1167–1171 1169  SF and SB treatments, as shown inFig. 2c. The maximum averageyield per plant was harvested from SBF conditions, (2514g) whichwas 20% greater than the case of SF conditions and 97% above theyield produced in SB conditions. CP produced the lowest (776g)yields of cherry tomatoes. The difference in crop yield betweenCP and SB conditions was also significant (Fig. 2c). SB treatmentproduced 64% greater yield compared to control treatment.  3.6. Heavy metal concentrations in fruits Theaccumulationofheavymetals, especiallyarsenic, cadmium,chromium,copper,lead,nickel,seleniumandzinc,areofgreatcon-cern in agricultural product due to potential threat for human andanimal health. The amount of heavy metals present in the appliedbiochar and their bioavailability in fruits are shown inTable 3.There were 16 metals and trace elements measured in the waste-watersludgebiochar.Theresultsoffruitanalysisshowthatallele-ments are uptaken by the fruits but their amounts are notsignificant. The presence of selenium (<0.05), lead (<0.01) and tin(<0.05mgkg À 1 ) are below the detection limit in all treatments.IntheSBFtreatmentthepresenceofarsenic(<0.01)andchromium(<0.05mgkg À 1 ) in the fruit are also below the detection limit. Theaccumulation of cadmium in fruit was estimated at 0.85% for bothSB and SBF treatments, and 1% in case of the SF treatment. Silver(<0.01mgkg À 1 ) is less than detection limit in SB and CP treat-ments. Copper and zinc show the lowest bioavailability in theSBF treatment followed by SB and SF treatments. Availability of theothertraceelementsinthefruitwasestimatedasverylow(Ta-ble 3). Only the concentration of cadmium present in the fruit forSF treatment conditions was found to be equivalent to the Austra-lian maximumpermitted concentration of cadmiumin food. How-ever, the remaining metals, including antimony, arsenic, cadmium,copper, lead, mercury, selenium, tin and zinc, were measured be-low the Australian maximum permitted concentrations for foodproducts (Table 3). 4. Discussion Resultsobtainedfromthepotexperimentsinthisworkindicatethe potential of the application of wastewater sludge biochar to achromosol soil for improvement of the yield of cherry tomato pro-ductionby64%.Thisvalueisofasimilarmagnitudetotheyieldob-served for radish using poultry litter biochar when applied at thesame dose on a similar soil (Chan et al., 2008). The lower agricul-tural properties of the soil used in the pot experiment was dueto the low nutrient availability of the chromosol soil selected forthe study (Table 1). It was observed that the average fruit yieldproduced under the control treatment conditions was lower andplantswerethinnerthanthefruitsandplantsfromtheothertreat-ments. The weight of the dry shoot (Fig. 2a) and the number of fruits (Fig. 2b) produced from CP treatment were also lower thanunder the remaining treatment conditions.It has been already identified that biochar applied to soils im-provestheavailabilityofphosphorus,totalnitrogenandmajorcat-ions (Glaser et al., 2002b; Lehmann et al., 2003). Additionally,biochar has positive liming effect when applied to low pH soils(Van Zwieten et al., 2007), thereby the application of biochar toacidic soils increases the soil pH and thereof improves nutrientuse efficiency. Our study shows significant improvement in thenumber of fruits per plant when biochar was applied at 10tha À 1 to the chromosol with low pH soil (Fig. 2b), suggesting release of additional nutrients from the biochar. The wastewater sludge bio-char used in the current work was high in extractable phosphorus(1100mgkg À 1 ). Presence of phosphorus in soils is particularly fa-vouredforgrowthof atomatoroot systemincreasingfruit produc-tivity (Filgueira, 2000). According toPoulton et al. (2002)soil with high phosphorus content improves vegetative and reproductivetraits of tomato plants, therefore additional phosphorus has animportant role in incremental fruit formation when biochar isadded to the soil. The wastewater sludge biochar produced for thiswork had a higher level of total nitrogen (2.3%) while the mineralnitrogen was low at 0.49%. This suggests that the wastewatersludge biochar might have the ability to increase mineralisationof soil organic nitrogen upon its incorporation into soil as a resultof priming effect (Hamer et al., 2004). Another possibility forimprovement of the nitrogen release is through the mineralisationofwastewatersludgebiocharandthereforereleaseoftheavailablenitrogenafter addition to soil during the pot experiments. The car-bonandnitrogenratioofthebiocharusedinthepottrialswasonly8.7(Table1),thereforemineralisationisexpecteduponitsapplica-tion to soil (Sullivan and Miller, 2001). According toHamer et al. (2004), biochars from maize and rye residues in soils can promotemineralisationof carboncompoundsas well as biochar byenhanc-ing the growth of micro-organisms.Thehighestyieldof cherrytomatointhecurrent workwas har-vested from the combined biochar with fertiliser treatment(2514g plant À 1 ) which was 20% above the yield produced underthe SF treatment. Since the nutrient addition through a fertiliserwas optimal for cherry tomato growth and production, the im-proved yieldobservedin the combinedbiochar and fertiliser treat-ment, when compared to fertiliser only, suggests additionalbeneficial effects of biochar inclusion, which are beyond the solenutrient effect. These additional benefits include improved soilproperties as well as the liming effects. The fertiliser effect of bio-char is additionally supported by increased water retention andCEC of the soil by the large surface area of the biochar (Steinbeisset al., 2009).Biochar produced from wastewater sludge pyrolysis has poten-tial to reduce the quantity of fertiliser requirement for cultivationofagriculturalcrops,howeverapplicationofwastewaterbiocharat10tha À 1 can not fully substitute for the requirement of fertilisers.The composition of sewage sludge is variable and contains toxicmetals (Smith, 1992) which limit the land application due to foodchain contamination (Chaney, 1990).Singh and Agrawal (2007) found increased concentrations of Pb, Cr, Cd, Cu, Zn and Ni in Betavulgaris (leafy vegetables) when grown in a greenhouse environ-  Table 3 Concentration (mg kg À 1 ) of heavy metals and trace elements in wastewater sludgebiochar and their accumulation in fruits of four different treatments comparing toAustralian food standard limitations for heavy metals in food (mg kg À 1 ). Elements Biochar Treatments Present Australian MPC a CP SB SBF SFArsenic 8.8 0.02 0.02 BDL 0.01 1.0Cadmium 4.7 0.03 0.04 0.04 0.05 0.05–2.0Chromium 230 BDL BDL BDL 0.06 –Copper 2100 5.9 6.2 4.6 6.2 10–70Lead 160 BDL BDL BDL BDL 1.5–2.5Nickel 740 8.2 1.2 0.61 0.55 –Selenium 7 BDL BDL BDL BDL 1.0Zinc 3300 18 22 18 22 150Antimony 8 BDL 0.01 BDL BDL 1.5Boron 20 15 15 9.6 15 –Silver 29 BDL BDL 0.01 0.01 –Barium 750 3.6 0.91 0.35 2.9 –Beryllium 1 BDL BDL BDL BDL –Cobalt 21 0.06 0.03 0.3 0.27 –Tin 310 BDL BDL BDL BDL 50Strontium 390 5 3.1 2.6 4.6 –MPC=maximum permitted concentration.BDL belowdetection limit of <0.05mgkg À 1 for As, Cr, Se and Sb, and <0.01mgkg À 1 for Pb, Sb and Be. a Source :Anon (1987).1170 M.K. Hossain et al./Chemosphere 78 (2010) 1167–1171
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