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Elements availability in soil fertilized with pelletized fly ash and biosolids
Journal of Environmental Management 159 (2015) 27e36
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Research paper
Elements availability in soil fertilized with pelletized fly ash and biosolids €nnvall a, *, Martin Wolters a, Rolf Sjo € blom a, b, Jurate Kumpiene a Evelina Bra a b
Waste Science & Technology, Luleå University of Technology, 97187 Luleå, Sweden €gen 10, 611 37 Nyko €ping, Sweden Tekedo AB, Spinnarva
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2014 Received in revised form 15 May 2015 Accepted 23 May 2015 Available online 29 May 2015
The aim of the study was to evaluate the impact of combined and pelletized industrial residues on availability and mobility of nutrients and potentially toxic elements in soil, plant growth and element uptake. Plant pot experiments were carried out using soil to which 2% of pelletized residue containing biosolids mixed with either municipal solid waste incineration fly ash (MFA) or biofuel fly ash (BFA) was added. The tests showed that the plant growth did not correspond to the content of available nutrients in fertilised soil. MFA application to soil resulted in elevated concentrations of P (506 mg/kg), As (2.7 mg/ kg), Cd (0.8 mg/kg) and Pb (12.1 mg/kg) in soil, lower plant uptake of Al (25 mg/kg) and Ba (51 mg/kg), but higher accumulation of As (4.3 mg/kg) and Cd (0.3 mg/kg) in plants compared to the unamended soil and soil amended with BFA. On average, the biomass of the plants grown in the soil containing MFA was larger than in other soils. Considering the use of industrial residue mixtures as soil amendments or fertilizers, the amount of added elements should not exceed those taken up by plants, by this preventing the increase of soil background concentrations. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Sequential extraction Rhizosphere Pore water Plant uptake Fly ash Pellets
1. Introduction Currently, the recycling of industrial residues such as biofuel fly ash, an air pollution control residue from combustion of woodbased fuel and municipal sewage sludge (biosolids) to soil as the source of nutrients is encouraged (Swedish Forest Agency, 2008; Swedish EPA, 2002). However, due to a very high alkalinity of fresh ash (pH z 12), a direct application to soil is not recommended. Application of the powdered residue to soil may lead to €nnvall et al., phytotoxic effects and suppressed plant growth (Bra 2014a). Results of this study showed that powdered residues such as fly ash could be toxic to the plants, especially those fly ashes from the municipal solid waste incineration. Taking into account the €nnvall et al., 2014a and results from the previous studies by Bra €nnvall et al., 2014b industrial residue mixtures (biosolids and fly Bra ashes) have been further treated. It is known that processing of the
* Corresponding author. E-mail address: [email protected] (E. Br€ annvall). http://dx.doi.org/10.1016/j.jenvman.2015.05.032 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
residues, e.g. through pelletization, granulation and ageing, might transform the residues into a product that has a lower pH and is easier to handle. Granulated/pelletized residues have a smaller specific surface area compared to powdered ones, which leads to a reduced reactivity and a slower release of constituents (Eriksson, 1998; Larsson and Westling, 1998; Steenari et al., 1998; Nieminen et al., 2005). This is advantageous for the release of potentially toxic elements, which is expected to be smaller than from fresh residues. A slow release of P and N might also reduce the loss of nutrients from the fertilised areas. The aim of this study was to evaluate the impact of combined and pelletized industrial residues containing biosolids mixed with either municipal solid waste incineration fly ash or biofuel fly ash on availability and mobility of nutrients and potentially toxic elements in soil and their uptake by plants. Detail characterisation of raw residues and their mixtures was €nnvall et al., 2014b. Also element performed are presented in Bra availability for plants when powdered i.e. not pelletized fly ash and biosolid mixtures were used and are described in Br€ annvall et al., 2014a. In this paper pelletized residue mixtures as soil fertilizers and element availability for plants is evaluated.
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2. Materials and methods 2.1. Materials 2.1.1. Fly ash Fresh and dry (without added water) biofuel fly ash from combustion of tree bark was collected from a fluidized bed incinerator in Northern Sweden. Municipal solid waste incineration fly ash was collected from a storage pile in a landfill where the ash was transported from a waste incinerator. The fuel comprised household waste, animal by-products, recycled wood chips, sleepers containing creosote and other solid waste. The sampling of this ash was carried out at two separate occasions. 2.1.2. Biosolids Dewatered, anaerobically digested biosolids were collected from a storage pile at a municipal wastewater treatment plant in Northern Sweden. 2.1.3. Soil Forest mineral topsoil (at 10e20 cm depth) collected in Luleå, Sweden, was air dried, homogenized and sieved to a <4 mm fraction prior to the experiment with pelletized residue mixtures. The particle distribution (ISO/TS 17892-4) analysis resulted in 7.1% silt/ clay, 38.9 fine sand, 33.1% course sand and 28% gravel (according to Brady and Weil, 2008). The detail analysis of soil can be found in Nilsson, 2012. 2.2. Preparation of residue mixtures Biosolids (60% of dw (dry weight)) were mixed with either biofuel fly ash or municipal solid waste incineration fly ash (40% of dw), dried at 50 C for 48 h and pelletized, called BFA and MFA, respectively, using a vibrating perforated plate (Van Aarsen type CT 20, No 88732, The Netherlands). The size of pellets is 0.5 mm diameter and ~1.2 mm length. 2.3. Soil fertilization 2.3.1. Soil mixtures 800 g of air-dry soil and soil mixed with 2% pellets (BFA or MFA) were placed in plastic pots (of 1 l volume) in triplicates. Soil without fertilisers (unamended soil) was used as a control. The pots were sown with 1 g of a grass seed mixture composed of 90% grass and 10% herb species and is intended for re-vegetation of sandy, nutrient deficient soils. The detailed composition of the mixture is given in Kumpiene et al. (2007). The pots were placed under artificial light for 12 h one12 h off illumination regime and were kept at a temperature of 14 ± 1 C holding constant soil moisture level by manual irrigation with distilled water. After five weeks, the pots were placed under natural light and kept at ca 23 C in order to promote plant growth. 2.3.2. Soil pore water Soil pore water was collected at the beginning of the experiment (first sampling e 1st) and 7 weeks later just before harvesting the plants (second sampling e 2nd) using the Rhizon soil moisture samplers (Eijkelkamp, the Netherlands) in acid-washed, vacuumed 100 ml glass bottles. The pH and EC were measured immediately after sampling in small aliquots of the samples. The remaining samples were stored refrigerated at 4 C prior to element analysis. 2.3.3. Plants The plant shoots were harvested after 7 weeks for biomass measurements and element concentration analysis. The plants
were washed with double distilled water, dried for 72 h at 60 C, weighed for dry mass determination, then ground using a stainless steel grinder and analysed for chemical elements by the accredited laboratory ALS Scandinavia. 2.4. Evaluation methods 2.4.1. Sequential chemical extraction Bulk soil (Soil B) was carefully separated from the rhizosphere soil (Soil R) and air-dried prior to the sequential extraction. Six steps were applied for element fractionation in 1 g of the bulk and rhizosphere soil samples according to the procedure described in €nnvall et al., 2014b). In brief, the following fractions were (Bra extracted: Fraction (I): Exchangeable, using NH4OAc adjusted to pH 6.5 with acetic acid (HOAc); Fraction (II): Bound to carbonates (acidsoluble), using NaOAc adjusted to pH 5.0; Fraction (III): bound to poorly crystalline Fe(III) oxyhydroxides (reducible), using NH4-oxalate adjusted to pH 3.0; Fraction (IV): bound to crystalline FeeMn oxides (reducible), using NH2OHeHCl in 25% (v/v) HOAc adjusted to pH 2; Fraction (V): bound to organic matter and secondary sulphides (oxidizable), using 30% H2O2; and Fraction (VI): Residual fraction (non-soluble), using aqua regia (HNO3:HCl, 1:3 v/v). 2.4.2. Analytical methods Concentrations of elements in the pore water and extracts were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES, Perkin Elemer Otima 2000 DV). Chloride (Cl), phosphate (PO-4) and sulphate (SO2 4 ) content was determined spectrophotometrically (AACE Quaatro, Bran þ Luebbe, Germany). Total N in solid sample was analysed by the accredited laboratory ALS Scandinavia according to ISO 11261 method. The total element concentration in soil was calculated from the sequential extraction analysis by summing all 6 fractions of each element. The pH and EC of Soil B and Soil R soil was measured in 1:2.5 v:v soil-deionised water suspensions after 30 min equilibration. 2.4.3. Acid neutralization capacity (ANC) ANC was determined by taking 0.5 g of ash suspended in 55 ml of de-ionized water and titrated with 0.1 M HCl, while stirring until the end-point pH 3 was reached. A TitroLab system (Radiometer
Table 1 Properties of pellets made of biofuel fly ash mixture with biosolids (BFA) and MSWI fly ash mixture with biosolids (MFA). BFA TS (%) 77.2 ± 0.5 pH 7.90 ± 0.03 EC (mS/cm) 2.60 ± 0.04 Macronutrients (mg/kg) Ca 62,300 ± 3400 K 13,100 ± 300 Mg 9300 ± 500 N 13,800 P 21,300 ± 600 S 13,000 ± 600 Trace elements (mg/kg) Cr 98.0 ± 4.4 Cu 185 ± 14 Fe 22,000 ± 600 Mn 2968 ± 211 Ni 54 ± 2 Zn 1063 ± 104 Potentially toxic elements (mg/kg) Al 41,700 ± 1400 As 126 ± 13 Cd 5.9 ± 0.4 Pb 42.0 ± 3.6
MFA 74.1 ± 0.3 7.70 ± 0.02 7.30 ± 0.03 76,000 ± 1700 17,800 ± 300 9700 ± 200 16,700 21,500 ± 1500 19,900 ± 800 218 ± 9 854 ± 42 25,100 ± 1000 807 ± 24 66 ± 1 8584 ± 411 51,300 ± 2600 255 ± 5 76.2 ± 2.4 1815 ± 98
€nnvall et al. / Journal of Environmental Management 159 (2015) 27e36 E. Bra
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Analytical S.A., Lyon, France) equipped with an ABU 901 autoburette and TIM900 titration manager with TimTalk9 ver. 2.1 software (LabSoft, Radiometer Analytical S.A.) was used.
2.4.5. Statistics A two-sample t-test procedure (p < 0.05) was applied to discriminate among the sample means at 95% confidence level.
2.4.4. Mineralogical composition The mineralogical composition of samples was determined qualitatively by X-ray diffraction using a Siemens D5000 X-Ray diffractometer at 40 mA current, 40 kV voltage and 30 rpm sample rotation, using CuKa1 radiation, for Bragg-angles (2q) between 5 and 70 , with 0.02 and 3 s steps. The diffraction peak positions and intensity values were compared with reference patterns of known phases in the Powder Diffraction File (PDF).
3. Results 3.1. Composition of fertilizers The pH of both pellets was similar, but BFA had a significantly lower electrical conductivity (EC) as compared to MFA pellets (Table 1). The concentrations of all elements, except for Mn, were higher in MFA than in BFA pellets by up to 98%.
Fig. 1. Soil Pore water composition. I epore water sampled at the beginning of the experiment, and II e pore water sampled at the end of experiment. Soil e unamended soil, Soil þ BFA e soil amended with biofuel fly ash and biosolids mixture pellets, Soil þ MFA e soil amended with municipal solid waste incineration fly ash and biosolids mixture pellets.
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sequence Ca > S > Mg > K > Cl > tot-N > NO3eN > P, while in pore water of soil þ MFA it was as follows: Ca > Cl > S > K > Mg > totN > NO3eN > NH4eN > P. Dissolved P concentrations were the lowest of all the macro-elements, with higher concentrations in soil þ MFA in the end of the experiment as compared to the other samples (Fig. 1). Concentration of total N in the pore water of the unamended soil and NO3eN in the pore water of all soils increased over time, while those of NH4eN, PO4eP and SO2 4 decreased. The highest values for dissolved Cu were found for the unamended soil (Fig. 1). Concentrations of Cl in pore water of soil þ BFA and soil þ MFA decreased over time with 62% and 80%, respectively. Zinc was the most available element among the micronutrients in soil containing MSWI ashes, while Ni was the most available in soil þ BFA. The concentrations of potentially toxic elements in the pore water samples were mostly below instrument detection limits for each element after 7 weeks. Cadmium had the lowest concentrations in soil pore water among the potentially toxic elements in the unamended soil and soil þ BFA, while Pb had the highest concentration in the pore water of the unamended soil as compared to the other samples. Pore water from soil with MFA contained the highest dissolved As (0.09 mg/l) compared to the remaining samples.
Table 2 Concentration of elements in the biomass (n ¼ 3, ±Standard deviation). Elements
Soil
Macronutrients (mg/kg) Ca 6683 ± 201 K 49,567 ± 2155 Mg 3360 ± 195 P 5953 ± 264 Micronutrients (mg/kg) Cr 0.20 ± 0.08 Cu 18.2 ± 0.8 Fe 179 ± 39 Mn 116 ± 12 Na 1313 ± 58 Ni 4.8 ± 0.3 Zn 53.0 ± 2.8 Potentially toxic elements (mg/kg) Al 58 ± 30 As <0.5 Ba 115 ± 24 Cd 0.20 ± 0.03 Pb <0.3
Soil þ BFA
Soil þ MFA
5757 ± 792 49,467 ± 3308 3743 ± 176 5300 ± 376
6423 ± 361 44,967 ± 1050 3527 ± 225 5033 ± 372
0.14 ± 0.04 19 ± 2 159 ± 19 75 ± 7 2440 ± 490 3.8 ± 0.4 48 ± 2
0.07 ± 0.04 16.0 ± 3.7 118 ± 33 80.0 ± 8.5 6470 ± 829 3.3 ± 0.4 47 ± 6
87 ± 23 <0.5 55 ± 10 0.08 ± 0.01 <0.3
25 ± 17 4.3 ± 1.8 51 ± 8 0.3 ± 0.1 <0.3
3.2. Soil pore water composition The pH values in the soil pore water increased in all samples during the time of the experiment (after 7 weeks), while EC showed an opposite pattern. The highest pH was found in the Soil þ BFA, but the largest increase in pH was in pore water of Soil þ MFA (Fig. S1), which also had the largest decrease in EC (ca 93%) over time. The concentrations of all macronutrients, including nitrates, decreased in soil pore water during the time of the second sampling (after 7 weeks), except for K and total N in unamended soil, and S in soil amended with MFA pellets (Fig. 1). Among the micronutrients, concentrations of dissolved Cr, Cu, Fe, Mn and Ni also decreased over time. Lead was the only potentially toxic element for which an increase in the concentration in the pore water was observed in the unamended soil and in soil þ MFA. At the end of the experiment, the most available elements in the pore water of the unamended soil and soil þ BFA followed the
3.3. Plant biomass and elemental composition Soil fertilisation with fly ash and biosolids pellets, in general, did not enhance the biomass production as compared to unfertilised soil, although in some pots a surprisingly notable improvement of plant growth was observed for Soil þ MFA. The biomass increase in each pot of Soil þ MFA was as follows: 0.15, 0.221 and 0.135 g dw/ pot. Soil fertilisation with BFA pellets had a reverse effect on plants i.e. low plant growth, compared to the other soils. The biomass in each pot of Soil þ BFA was as follows: 0.102, 0.141 and 0.109 g dw/ pot. The biomass in unamended soil was: 0.145, 0.158 and 0.147 g dw/pot. Uptake of elements by plants varied in all pots (Table 2). The highest concentrations of Ca, K, P, Cr, Fe, Mn, Ni, Zn and Ba were found in plants from the unamended soil. The concentrations of Mg, Cu and Al were largest in the plants that grew in the pots
Table 3 Total concentration of elements in bulk (B) and rhizosphere (R) soil. Soil B pH 6.68 ± 0.01 EC (mS/cm) 0.230 ± 0.001 Concentration of elements (mg/kg) Al 2841 ± 143 As 2.1 ± 0.1 Ba 22 ± 1 Ca 2760 ± 107 Cd 0.38 ± 0.04 Co 1.9 ± 0.0 Cr 8.3 ± 0.3 Cu 5.1 ± 0.5 Fe 7300 ± 288 Hg 0.003 ± 0.001 K 705 ± 46 Mg 1338 ± 52 Mn 113 ± 4 Mo 0.60 ± 0.02 Ni 9.6 ± 0.2 P 434 ± 15 Pb 3.1 ± 0.2 S 481 ± 104 Si 2210 ± 49 V 16.0 ± 0.6 Zn 125 ± 14
Soil þ BFA B
Soil R 6.69 ± 0.01 0.420 ± 0.001 3193 2.2 27.0 3074 0.39 2.3 9.2 6.9 7386 0.004 795 1585 121 0.70 10.5 444 3.3 542 2448 17.0 155
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
160 0.1 1.3 177 0.04 0.3 0.2 0.8 220 0.001 84 82 6 0.05 0.3 17 0.2 122 112 1.7 57
7.39 ± 0.02 0.400 ± 0.002 2360 1.76 19 2914 0.39 1.7 6.9 4.2 6224 0.0029 653 1269 105 0.61 9.0 389 2.6 510 2085 14.1 123
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
213 0.10 2 174 0.02 0.4 0.6 0.7 379 0.0010 67 77 9 0.10 0.5 38 0.2 107 102 0.7 51
Soil þ BFA R 7.28 ± 0.01 0.900 ± 0.001 2626 1.82 22.0 3308 0.37 1.6 7.4 5.5 6368 0.0027 725 1457 114 0.64 9.1 398 2.6 541 2216 14.6 103
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
89 0.10 0.9 152 0.05 0.1 0.2 0.4 91 0.0010 36 35 6 0.03 0.3 30 0.1 53 76 0.5 24
Soil þ MFA B 7.37 ± 0.01 0.600 ± 0.001 2481 2.7 23 3416 0.8 1.6 7.5 6.7 6277 0.0033 602 1309 107 0.70 8.8 506 12 527 2207 15.5 146
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
123 0.3 1 201 0.1 0.1 0.4 1.1 216 0.0010 44 59 5 0.03 0.3 64 2 45 87 1.2 51
Soil þ MFA R 7.32 ± 0.02 1.4 ± 0.001 2537 2.6 22.0 3657 0.7 1.7 7.9 7.3 6470 0.0035 689 1415 113 0.9 9.6 489 11.0 861 2327 15.0 167
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
86 0.1 0.8 150 0.1 0.1 0.3 1.2 204 0.0010 38 80 5 0.2 0.2 27 1.5 95 101 0.3 38
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containing Soil þ BFA. The highest concentrations of Na, As and Cd were found in plants that grew in the Soil þ MFA. The concentrations of Pb were below the instrument detection limit (<0.3 mg/kg) in all plant samples.
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3.4. Total element concentration in soil The pH of the rhizosphere (R) soil containing fertilisers was slightly lower than of bulk (B) soil (Table 3). No differences were
Fig. 2. Chemical fractionation of macronutrients in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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observed in unamended soil. The EC significantly increased in the rhizosphere soil of all samples (Soil R, Soil þ BFA R and Soil þ MFA R) (Table 3). The concentrations of Al, Ba, Co, Cr, Fe, Hg, K Mg, Mn, Ni, Si and V were highest in the rhizosphere of the unamended soil compared to all other samples (Table 3). Arsenic, Cd, P and Pb were mostly
found in the bulk soil, while Ca, Cu, Mo, S and Zn were predominantly found in the rhizosphere Soil þ MFA. On average, rhizosphere of unamended soil (Soil R) contained the largest concentrations of all elements compared to the bulk soil (Soil B). Rhizosphere soil with BFA (Soil þ BFA R) contained lower concentrations of Cd, Co, Hg, Pb and Zn compared to the bulk soil
Fig. 3. Chemical fractionation of Cr, Co, Cu, Fe and Mn in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
€nnvall et al. / Journal of Environmental Management 159 (2015) 27e36 E. Bra
(Soil þ BFA B), while concentrations of As, Ba, P, Pb and V were lower in the rhizosphere soil amended with MFA (Soil þ MFA R) compared to the bulk soil amended with MFA (Soil þ MFA B) (Table 3).
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3.5. Element fractionation in bulk and rhizosphere soil The fractionation of various elements was determined for the different samples, and the results are shown in Figs. 2e6.
Fig. 4. Chemical fractionation of Mo, Ni, Si, V and Zn in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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In general, Ca was bound mainly to the reducible Fraction (IV) followed by the non-soluble Fraction (VI). The main differences between the samples were found between the rhizosphere and the bulk soil in that the former had a larger fraction of the most soluble Ca (Fraction I). Similarly, amendment MFA slightly increased the exchangeable concentration of Ca. The same soil also contained the largest amount of soluble K. Almost all K fractions were larger in the rhizosphere soil in all pots. Significant amount of K was bound to the carbonates (Fraction II) and the residual fraction (VI) in all samples. No significant difference between the bulk and rhizosphere soil fractionation of Mg was found. Magnesium was predominantly bound to the crystalline FeeMn oxides (Fraction IV) and the nonsoluble fraction (VI). Phosphorus was predominantly bound to poorly crystalline Fe oxyhydroxides (Fraction III) and to crystalline FeeMn oxides (Fraction IV) in all samples. No clear differences between P fractionation in bulk and rhizosphere samples were found. Fractionation of S was more distinct. Sulphur was more soluble in the rhizosphere soil with amendments compared to the unamended soil. However the largest fraction of S was bound to poorly crystalline Fe oxyhydroxides (Fraction III) in all soil samples. Copper, Ni and Mo were predominantly bound to poorly crystalline Fe oxyhydroxides (Fraction III) followed by the crystalline FeeMn oxides (Fraction IV), except for Mo, for which the second predominant fraction was bound to organic matter (Fraction V), especially in rhizosphere soil of Soil þ MFA (Figs. 3e4). Chromium, Fe, Zn, Co and V were mainly bound to reducible Fraction IV followed by the non-soluble fraction, while for Mn, this
order was reverse. Silicon was mostly bound to crystalline FeeMn oxides, followed by oxidizable fraction (V). No significant differences between bulk and rhizosphere soil were found for most of the fractionation of the elements (Fe, Mn, Ni and V). Only Zn in Soil þ MFA pellets had a more distinct fractionation, where a larger fraction of Zn was bound to carbonates in bulk soil compared to rhizosphere soil. Whereas in Soil þ BFA the larger fraction of Zn was exchangeable in rhizosphere soil (Soil þ BFA R) compared to the bulk soil (Soil þ BFA B). Aluminium was predominantly bound to crystalline FeeMn oxides (Fraction IV) and non-soluble Fraction (VI) in all soil samples (Fig. 5). Arsenic was predominantly found in Fraction III, but was also found in a most soluble Fraction I in Soil þ MFA. Significant amount of Ba (ca 35%) was found in the most soluble Fraction I in all samples, followed by fractions IV and VI. Cadmium was mainly bound to the reducible fractions (IV and III) in the unamended soil and Soil þ BFA, while in Soil þ MFA Cd was mainly bound to crystalline FeeMn oxides (Fraction IV) followed by the exchangeable fraction (I), which comprised about 25% of the total Cd concentration. In both bulk and rhizosphere soils amended with MFA, Cd was bound to carbonates (Fraction II) (Fig. 6). Mercury was predominantly bound to organic matter (Fraction V) in all samples (Fig. 6). Only in Soil þ MFA, the second largest fraction of Hg was bound to crystalline FeeMn oxides (Fraction IV). Lead was also mainly found in Fraction IV in all samples. However soil amended with MFA pellets also had significant amounts of Pb in the most soluble fraction (I) and bound to carbonates (Fraction II).
Fig. 5. Chemical fractionation of potentially toxic elements Al, As and Ba in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
€nnvall et al. / Journal of Environmental Management 159 (2015) 27e36 E. Bra
3.6. Acid neutralization capacity Acid neutralization capacity of BFA pellets was higher than those of MFA (Fig. S2). Also BFA pellets were buffering above pH 8 considerably longer and consumed more HCl thus forming a typical plateau likely buffered by carbonates. MFA pellets had lower buffering capacity, but similar ANC to BFA pellets. 3.7. Mineralogical composition of soil Silicon dioxide phase dominated in all soil samples. Other phases with a high certainty could not be identified. 4. Discussion It has been shown that plants with lower biomass can have higher element concentrations than those with higher biomass due to the dilution effect (Fritioff et al., 2005). This was not observed in the present study. For example, concentrations of K, Ni, Al, Zn and P were significantly lower, while those of Cd, As, Fe, were higher in the plants with higher biomass (Table 2). Concentration of PO4eP in soil pore water comprised only 6.1%, 5.6% and 3.8% of the total P in the unamended soil and soil amended with BFA and MFA, respectively. In the beginning of the experiment, plant uptake of P was the largest in the unamended soil, where the concentration of dissolved PO4eP was the highest compared to other pots. In the end of the experiment, concentrations of PO4eP in the unamended soil pore water were the lowest, indicating the P
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uptake by plants or due to the larger biomass compared to amendment soil. Although MFA contained a substantial concentration of Pb (1815 ± 98 mg/kg, Table 1) and a significant amount of Pb was found in the exchangeable fraction of the bulk and rhizosphere soil, plants did not accumulate Pb. Concentration of Pb in plant biomass was below the instrument detection limit (<0.3 mg/kg) likely because Pb was accumulated in roots (Ashraf et al., 2010). Cadmium was also mostly found in exchangeable fraction of Soil þ MFA, but the concentration in plants did not differ from those from unamended soil. Such low Cd accumulation in plants was probably a result of the high salinity of the soil, which might decrease availability of the metals in soil, probably due to the metal complexation with chloride (Greger et al., 1995). High salinity was also shown having an opposite effect on Cd uptake by plants (Smolders and McLaughlin, 1996). Aluminium was mostly accumulated by plants grown in Soil þ BFA, by this decreasing initially the highest concentration of dissolved Al among the samples. Bioavailability of Al is undesirable because of its toxic effect on plants. An excess concentration of Al may lead to reduced uptake of nutrients, such as P, Ca, Mg, K and N by plants (Kabata-Pendias, 2011). However, concentrations of Al in plants were within the range of plant tolerance varying from 7.2 mg/kg to even 3470 mg/ kg (Kabata-Pendias, 2011). Aluminium is pH sensitive, but the pH of soils was above 5, therefore the solubility and toxicity of Al was expected to be low. Concentration of As in pore water of Soil þ MFA was by one order of magnitude higher than in the pore water of the unamended soil at the beginning of the experiment, but
Fig. 6. Chemical fractionation of potentially toxic elements Cd, Hg and Pb in bulk and rhizosphere soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulfides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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significantly decreased before the plant harvesting. Arsenic was the only potentially toxic element that was consistently higher in all measured media, i.e. soil, pore water and biomass, than the samples from unamended soil. It could be explained by the higher concentrations of As in municipal solid waste incineration fly ash added. Application of BFA did not cause any increase in total concentrations of minor nutrients in soil and biomass, although dissolved concentrations were higher than in unamended samples for most of major and minor nutrients. Concentrations of potentially toxic elements, i.e. As, Cd and Pb, in pore water were similar or even lower than in the unamended soil. The pH in all soils increased slightly over time with a half unit (6.2e6.7) in the unamended soil, and up to 1 unit (7.5) in Soil þ BFA. The concentrations of most elements in pore water decreased with time, likely due to depletion caused by the plant uptake. The pH of bulk and rhizosphere soil did not differ significantly. It has been reported that the pH in the bulk soil may differ up to 2 units compared to the rhizosphere soil (Marschner et al., 1989). The differences occur when plant roots take up such ions that affect the pH of the rizosphere without affecting the pH of the bulk soil. When ammonium ions (NHþ 4 ) are absorbed by plant roots, concentration of Hþ ions increase and the pH in the rhizosphere decrease, whereas uptake of NO-3 ions results in an increase of both, OH and pH, in the rhizosphere (Marschner et al., 1991). Indeed, a slightly decreased pH in the rhizosphere soil (Table 3) coincided with the significantly increased centration of available NO-3 and decreased concentration of NHþ 4 in all pots over the time (Fig. 1). Also soil properties, such as buffering capacity, can influence the rootinduced pH changes in the rhizosphere (Heckman and Strick, 1996). The acid neutralization capacity (ANC) of amended residues plays an important role in maintaining soil pH levels. The pH in turn is one of the most important factors governing the solubility of various mineral phases and elements (Chandler et al., 1997). The determined buffering capacity of the used pellets was not high, indicating quite a low resistance of the residues to pH changes in the soil. Although the biomass development was relatively low in all soils during this short period of the experiment, results show that the use of pelletized MFA did not cause a phytotoxic effect on plants, as it was observed in earlier studies where fresh and powdered MFA were used as fertilizers (Br€ annvall et al., 2014a). Pelletized residues were nearly intact in the soil in the end of the experiment, indicating that a full effect of fertilization of soil had not been achieved during the seven-week experiment. 5. Conclusions The difference between the mixtures containing biosolids and either municipal solid waste incineration fly ash (MFA) or those containing biofuel ash (BFA), in terms of the total concentrations of potentially toxic elements, was substantial. MFA contained from two times to two orders of magnitude higher concentrations of As, Cd and Pb than BFA, but the impact on the studied environmental media was not proportional to the total concentrations. Although, applying the same amount of pelletized industrial residue mixtures, MFA contributed higher concentrations of majority of total and soluble elements to soil than BFA, the difference in plant uptake of the elements was small.
Since the plant uptake of the potentially toxic elements was low, the elements might be prone to accumulation in soil top layer with the repeated application of residues to soil. Considering the use of industrial residue mixtures as soil amendments or fertilizers, the amount of added elements should not exceed those taken up by plants, by this preventing the increase of soil background concentrations. Acknowledgements The study was financed by the EU Regional Development Fund Objective 2 project North Waste Infrastructure. Authors thank Nils €m from Luleå Skoglund from Umeå University and Tommy Wikstro University of Technology for the help with the preparation of pellets. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.05.032. References Ashraf, M., Oztürk, M.A., Ahmad, M.S.A., 2010. Plant Adaptation and Phytoremediation. Springer, New York. Brady, N., Weil, R., 2008. The Nature and Properties of Soil, 14th ed. New Jersey, USA. € €blom, R., Skoglund, N., Kumpiene, J., 2014a. Effect of Brannvall, E., Nilsson, M., Sjo industrial residue combinations on plant uptake of elements. J. Environ. Manag. 132, 287e295. €nnvall, E., Belmonte Zamora, C., Sjo €blom, R., Kumpiene, J., 2014b. Effect of inBra dustrial residue combinations on availability of elements. J. Hazard. Mater. 276, 171e181. Chandler, A.J., International Ash Working Group, 1997. Municipal Solid Waste Incinerator Residues. Elsevier, Amsterdam, p. 974. Eriksson, J., 1998. Dissolution of Hardened wood ashes in forest soils: studies in a column experiment. Scand. J. For. Res. (Suppl. 2), 23e32. Fritioff, Å., Kautsky, L., Greger, M., 2005. Influence of temperature and salinity on heavy metal uptake by submersed plants. Environ. Pollut. 133, 265e274. Greger, M., Kautsky, L., Sandberg, T., 1995. A tentative model of Cd uptake in Potamogeton pectinatus in relation to salinity. Environ. Exp. Bot. 35, 215e225. Heckman, J.R., Strick, J.E., 1996. teaching plant-soil relationships with color images of rhizosphere pH. J. Nat. Resour. Life Sci. Educ. http://www.personal.psu.edu/ faculty/j/e/jel5/biofilms/rhizosphere.html. Kabata-Pendias, A., 2011. Trace Elements in Soils and Plants, fourth ed. Taylor &Francis, London, New York. Kumpiene, J., Ore, S., Lagerkvist, A., Maurice, C., 2007. Stabilization of Pb and Cu contaminated soil using coal fly ash and peat. Environ. Pollut. 145, 365e375. Larsson, P.-E., Westling, O., 1998. Leaching of wood ash and lime products: laboratory study. Scand. J. For. Res. 13 (Suppl. 2), 17e22. €mheld, V., 1989. Role of root-induced changes in the Marschner, H., Treeby, M., Ro €hr. Bodenk. rhizosphere for iron acquisition in higher plants. Z. Pflanzenerna 152, 197e204. Marschner, H., H€ aussling, M., George, E., 1991. Ammonium and nitrate uptake rates and rhizosphere pH innon-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.]. Trees-Struct. Funct. 5, 14e21. Nieminen, M., Piirainen, S., Moilanen, M., 2005. Release of mineral nutrients and heavy metals from wood and peat ash fertilizers: Field studies in Finnish forest soils. Scand. J. For. Res. 20, 146e153. Nilsson, 2012. Plant Availability of Phosphorus in Soil Fertilized with Ash and Sludge (in Swedish). Master thesis. Luleå University of Technology, p. 49. Smolders, E., McLaughlin, M.J., 1996. Chloride increases cadmium uptake in Swiss chard in a resin-buffered nutrient solution. Soil Sci. Soc. Am. J. 60, 1443e1447. Steenari, B.M., Marsic, N., Karlsson, L.G., Tomsic, A., Lindqvist, O., 1998. Long-term leaching of stabilized wood ash. Scand. J. For. Res. (Suppl. 2), 3e16. €r Återfo €ring Av Fosfor Ur Avlopp (The Action Swedish, E.P.A., 2002. Aktionsplan Fo Plan for Phosphorus Recycling Form the Wastewater in Swedish). Swedish EPA Rapport 5214. Swedish Forest Agency, 2008. Recommendations on Ash Recycling to the Forest (in Swedish). Report 2:2008.
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research paper
Elements availability in soil fertilized with pelletized fly ash and biosolids €nnvall a, *, Martin Wolters a, Rolf Sjo € blom a, b, Jurate Kumpiene a Evelina Bra a b
Waste Science & Technology, Luleå University of Technology, 97187 Luleå, Sweden €gen 10, 611 37 Nyko €ping, Sweden Tekedo AB, Spinnarva
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2014 Received in revised form 15 May 2015 Accepted 23 May 2015 Available online 29 May 2015
The aim of the study was to evaluate the impact of combined and pelletized industrial residues on availability and mobility of nutrients and potentially toxic elements in soil, plant growth and element uptake. Plant pot experiments were carried out using soil to which 2% of pelletized residue containing biosolids mixed with either municipal solid waste incineration fly ash (MFA) or biofuel fly ash (BFA) was added. The tests showed that the plant growth did not correspond to the content of available nutrients in fertilised soil. MFA application to soil resulted in elevated concentrations of P (506 mg/kg), As (2.7 mg/ kg), Cd (0.8 mg/kg) and Pb (12.1 mg/kg) in soil, lower plant uptake of Al (25 mg/kg) and Ba (51 mg/kg), but higher accumulation of As (4.3 mg/kg) and Cd (0.3 mg/kg) in plants compared to the unamended soil and soil amended with BFA. On average, the biomass of the plants grown in the soil containing MFA was larger than in other soils. Considering the use of industrial residue mixtures as soil amendments or fertilizers, the amount of added elements should not exceed those taken up by plants, by this preventing the increase of soil background concentrations. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Sequential extraction Rhizosphere Pore water Plant uptake Fly ash Pellets
1. Introduction Currently, the recycling of industrial residues such as biofuel fly ash, an air pollution control residue from combustion of woodbased fuel and municipal sewage sludge (biosolids) to soil as the source of nutrients is encouraged (Swedish Forest Agency, 2008; Swedish EPA, 2002). However, due to a very high alkalinity of fresh ash (pH z 12), a direct application to soil is not recommended. Application of the powdered residue to soil may lead to €nnvall et al., phytotoxic effects and suppressed plant growth (Bra 2014a). Results of this study showed that powdered residues such as fly ash could be toxic to the plants, especially those fly ashes from the municipal solid waste incineration. Taking into account the €nnvall et al., 2014a and results from the previous studies by Bra €nnvall et al., 2014b industrial residue mixtures (biosolids and fly Bra ashes) have been further treated. It is known that processing of the
* Corresponding author. E-mail address: [email protected] (E. Br€ annvall). http://dx.doi.org/10.1016/j.jenvman.2015.05.032 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
residues, e.g. through pelletization, granulation and ageing, might transform the residues into a product that has a lower pH and is easier to handle. Granulated/pelletized residues have a smaller specific surface area compared to powdered ones, which leads to a reduced reactivity and a slower release of constituents (Eriksson, 1998; Larsson and Westling, 1998; Steenari et al., 1998; Nieminen et al., 2005). This is advantageous for the release of potentially toxic elements, which is expected to be smaller than from fresh residues. A slow release of P and N might also reduce the loss of nutrients from the fertilised areas. The aim of this study was to evaluate the impact of combined and pelletized industrial residues containing biosolids mixed with either municipal solid waste incineration fly ash or biofuel fly ash on availability and mobility of nutrients and potentially toxic elements in soil and their uptake by plants. Detail characterisation of raw residues and their mixtures was €nnvall et al., 2014b. Also element performed are presented in Bra availability for plants when powdered i.e. not pelletized fly ash and biosolid mixtures were used and are described in Br€ annvall et al., 2014a. In this paper pelletized residue mixtures as soil fertilizers and element availability for plants is evaluated.
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2. Materials and methods 2.1. Materials 2.1.1. Fly ash Fresh and dry (without added water) biofuel fly ash from combustion of tree bark was collected from a fluidized bed incinerator in Northern Sweden. Municipal solid waste incineration fly ash was collected from a storage pile in a landfill where the ash was transported from a waste incinerator. The fuel comprised household waste, animal by-products, recycled wood chips, sleepers containing creosote and other solid waste. The sampling of this ash was carried out at two separate occasions. 2.1.2. Biosolids Dewatered, anaerobically digested biosolids were collected from a storage pile at a municipal wastewater treatment plant in Northern Sweden. 2.1.3. Soil Forest mineral topsoil (at 10e20 cm depth) collected in Luleå, Sweden, was air dried, homogenized and sieved to a <4 mm fraction prior to the experiment with pelletized residue mixtures. The particle distribution (ISO/TS 17892-4) analysis resulted in 7.1% silt/ clay, 38.9 fine sand, 33.1% course sand and 28% gravel (according to Brady and Weil, 2008). The detail analysis of soil can be found in Nilsson, 2012. 2.2. Preparation of residue mixtures Biosolids (60% of dw (dry weight)) were mixed with either biofuel fly ash or municipal solid waste incineration fly ash (40% of dw), dried at 50 C for 48 h and pelletized, called BFA and MFA, respectively, using a vibrating perforated plate (Van Aarsen type CT 20, No 88732, The Netherlands). The size of pellets is 0.5 mm diameter and ~1.2 mm length. 2.3. Soil fertilization 2.3.1. Soil mixtures 800 g of air-dry soil and soil mixed with 2% pellets (BFA or MFA) were placed in plastic pots (of 1 l volume) in triplicates. Soil without fertilisers (unamended soil) was used as a control. The pots were sown with 1 g of a grass seed mixture composed of 90% grass and 10% herb species and is intended for re-vegetation of sandy, nutrient deficient soils. The detailed composition of the mixture is given in Kumpiene et al. (2007). The pots were placed under artificial light for 12 h one12 h off illumination regime and were kept at a temperature of 14 ± 1 C holding constant soil moisture level by manual irrigation with distilled water. After five weeks, the pots were placed under natural light and kept at ca 23 C in order to promote plant growth. 2.3.2. Soil pore water Soil pore water was collected at the beginning of the experiment (first sampling e 1st) and 7 weeks later just before harvesting the plants (second sampling e 2nd) using the Rhizon soil moisture samplers (Eijkelkamp, the Netherlands) in acid-washed, vacuumed 100 ml glass bottles. The pH and EC were measured immediately after sampling in small aliquots of the samples. The remaining samples were stored refrigerated at 4 C prior to element analysis. 2.3.3. Plants The plant shoots were harvested after 7 weeks for biomass measurements and element concentration analysis. The plants
were washed with double distilled water, dried for 72 h at 60 C, weighed for dry mass determination, then ground using a stainless steel grinder and analysed for chemical elements by the accredited laboratory ALS Scandinavia. 2.4. Evaluation methods 2.4.1. Sequential chemical extraction Bulk soil (Soil B) was carefully separated from the rhizosphere soil (Soil R) and air-dried prior to the sequential extraction. Six steps were applied for element fractionation in 1 g of the bulk and rhizosphere soil samples according to the procedure described in €nnvall et al., 2014b). In brief, the following fractions were (Bra extracted: Fraction (I): Exchangeable, using NH4OAc adjusted to pH 6.5 with acetic acid (HOAc); Fraction (II): Bound to carbonates (acidsoluble), using NaOAc adjusted to pH 5.0; Fraction (III): bound to poorly crystalline Fe(III) oxyhydroxides (reducible), using NH4-oxalate adjusted to pH 3.0; Fraction (IV): bound to crystalline FeeMn oxides (reducible), using NH2OHeHCl in 25% (v/v) HOAc adjusted to pH 2; Fraction (V): bound to organic matter and secondary sulphides (oxidizable), using 30% H2O2; and Fraction (VI): Residual fraction (non-soluble), using aqua regia (HNO3:HCl, 1:3 v/v). 2.4.2. Analytical methods Concentrations of elements in the pore water and extracts were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES, Perkin Elemer Otima 2000 DV). Chloride (Cl), phosphate (PO-4) and sulphate (SO2 4 ) content was determined spectrophotometrically (AACE Quaatro, Bran þ Luebbe, Germany). Total N in solid sample was analysed by the accredited laboratory ALS Scandinavia according to ISO 11261 method. The total element concentration in soil was calculated from the sequential extraction analysis by summing all 6 fractions of each element. The pH and EC of Soil B and Soil R soil was measured in 1:2.5 v:v soil-deionised water suspensions after 30 min equilibration. 2.4.3. Acid neutralization capacity (ANC) ANC was determined by taking 0.5 g of ash suspended in 55 ml of de-ionized water and titrated with 0.1 M HCl, while stirring until the end-point pH 3 was reached. A TitroLab system (Radiometer
Table 1 Properties of pellets made of biofuel fly ash mixture with biosolids (BFA) and MSWI fly ash mixture with biosolids (MFA). BFA TS (%) 77.2 ± 0.5 pH 7.90 ± 0.03 EC (mS/cm) 2.60 ± 0.04 Macronutrients (mg/kg) Ca 62,300 ± 3400 K 13,100 ± 300 Mg 9300 ± 500 N 13,800 P 21,300 ± 600 S 13,000 ± 600 Trace elements (mg/kg) Cr 98.0 ± 4.4 Cu 185 ± 14 Fe 22,000 ± 600 Mn 2968 ± 211 Ni 54 ± 2 Zn 1063 ± 104 Potentially toxic elements (mg/kg) Al 41,700 ± 1400 As 126 ± 13 Cd 5.9 ± 0.4 Pb 42.0 ± 3.6
MFA 74.1 ± 0.3 7.70 ± 0.02 7.30 ± 0.03 76,000 ± 1700 17,800 ± 300 9700 ± 200 16,700 21,500 ± 1500 19,900 ± 800 218 ± 9 854 ± 42 25,100 ± 1000 807 ± 24 66 ± 1 8584 ± 411 51,300 ± 2600 255 ± 5 76.2 ± 2.4 1815 ± 98
€nnvall et al. / Journal of Environmental Management 159 (2015) 27e36 E. Bra
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Analytical S.A., Lyon, France) equipped with an ABU 901 autoburette and TIM900 titration manager with TimTalk9 ver. 2.1 software (LabSoft, Radiometer Analytical S.A.) was used.
2.4.5. Statistics A two-sample t-test procedure (p < 0.05) was applied to discriminate among the sample means at 95% confidence level.
2.4.4. Mineralogical composition The mineralogical composition of samples was determined qualitatively by X-ray diffraction using a Siemens D5000 X-Ray diffractometer at 40 mA current, 40 kV voltage and 30 rpm sample rotation, using CuKa1 radiation, for Bragg-angles (2q) between 5 and 70 , with 0.02 and 3 s steps. The diffraction peak positions and intensity values were compared with reference patterns of known phases in the Powder Diffraction File (PDF).
3. Results 3.1. Composition of fertilizers The pH of both pellets was similar, but BFA had a significantly lower electrical conductivity (EC) as compared to MFA pellets (Table 1). The concentrations of all elements, except for Mn, were higher in MFA than in BFA pellets by up to 98%.
Fig. 1. Soil Pore water composition. I epore water sampled at the beginning of the experiment, and II e pore water sampled at the end of experiment. Soil e unamended soil, Soil þ BFA e soil amended with biofuel fly ash and biosolids mixture pellets, Soil þ MFA e soil amended with municipal solid waste incineration fly ash and biosolids mixture pellets.
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sequence Ca > S > Mg > K > Cl > tot-N > NO3eN > P, while in pore water of soil þ MFA it was as follows: Ca > Cl > S > K > Mg > totN > NO3eN > NH4eN > P. Dissolved P concentrations were the lowest of all the macro-elements, with higher concentrations in soil þ MFA in the end of the experiment as compared to the other samples (Fig. 1). Concentration of total N in the pore water of the unamended soil and NO3eN in the pore water of all soils increased over time, while those of NH4eN, PO4eP and SO2 4 decreased. The highest values for dissolved Cu were found for the unamended soil (Fig. 1). Concentrations of Cl in pore water of soil þ BFA and soil þ MFA decreased over time with 62% and 80%, respectively. Zinc was the most available element among the micronutrients in soil containing MSWI ashes, while Ni was the most available in soil þ BFA. The concentrations of potentially toxic elements in the pore water samples were mostly below instrument detection limits for each element after 7 weeks. Cadmium had the lowest concentrations in soil pore water among the potentially toxic elements in the unamended soil and soil þ BFA, while Pb had the highest concentration in the pore water of the unamended soil as compared to the other samples. Pore water from soil with MFA contained the highest dissolved As (0.09 mg/l) compared to the remaining samples.
Table 2 Concentration of elements in the biomass (n ¼ 3, ±Standard deviation). Elements
Soil
Macronutrients (mg/kg) Ca 6683 ± 201 K 49,567 ± 2155 Mg 3360 ± 195 P 5953 ± 264 Micronutrients (mg/kg) Cr 0.20 ± 0.08 Cu 18.2 ± 0.8 Fe 179 ± 39 Mn 116 ± 12 Na 1313 ± 58 Ni 4.8 ± 0.3 Zn 53.0 ± 2.8 Potentially toxic elements (mg/kg) Al 58 ± 30 As <0.5 Ba 115 ± 24 Cd 0.20 ± 0.03 Pb <0.3
Soil þ BFA
Soil þ MFA
5757 ± 792 49,467 ± 3308 3743 ± 176 5300 ± 376
6423 ± 361 44,967 ± 1050 3527 ± 225 5033 ± 372
0.14 ± 0.04 19 ± 2 159 ± 19 75 ± 7 2440 ± 490 3.8 ± 0.4 48 ± 2
0.07 ± 0.04 16.0 ± 3.7 118 ± 33 80.0 ± 8.5 6470 ± 829 3.3 ± 0.4 47 ± 6
87 ± 23 <0.5 55 ± 10 0.08 ± 0.01 <0.3
25 ± 17 4.3 ± 1.8 51 ± 8 0.3 ± 0.1 <0.3
3.2. Soil pore water composition The pH values in the soil pore water increased in all samples during the time of the experiment (after 7 weeks), while EC showed an opposite pattern. The highest pH was found in the Soil þ BFA, but the largest increase in pH was in pore water of Soil þ MFA (Fig. S1), which also had the largest decrease in EC (ca 93%) over time. The concentrations of all macronutrients, including nitrates, decreased in soil pore water during the time of the second sampling (after 7 weeks), except for K and total N in unamended soil, and S in soil amended with MFA pellets (Fig. 1). Among the micronutrients, concentrations of dissolved Cr, Cu, Fe, Mn and Ni also decreased over time. Lead was the only potentially toxic element for which an increase in the concentration in the pore water was observed in the unamended soil and in soil þ MFA. At the end of the experiment, the most available elements in the pore water of the unamended soil and soil þ BFA followed the
3.3. Plant biomass and elemental composition Soil fertilisation with fly ash and biosolids pellets, in general, did not enhance the biomass production as compared to unfertilised soil, although in some pots a surprisingly notable improvement of plant growth was observed for Soil þ MFA. The biomass increase in each pot of Soil þ MFA was as follows: 0.15, 0.221 and 0.135 g dw/ pot. Soil fertilisation with BFA pellets had a reverse effect on plants i.e. low plant growth, compared to the other soils. The biomass in each pot of Soil þ BFA was as follows: 0.102, 0.141 and 0.109 g dw/ pot. The biomass in unamended soil was: 0.145, 0.158 and 0.147 g dw/pot. Uptake of elements by plants varied in all pots (Table 2). The highest concentrations of Ca, K, P, Cr, Fe, Mn, Ni, Zn and Ba were found in plants from the unamended soil. The concentrations of Mg, Cu and Al were largest in the plants that grew in the pots
Table 3 Total concentration of elements in bulk (B) and rhizosphere (R) soil. Soil B pH 6.68 ± 0.01 EC (mS/cm) 0.230 ± 0.001 Concentration of elements (mg/kg) Al 2841 ± 143 As 2.1 ± 0.1 Ba 22 ± 1 Ca 2760 ± 107 Cd 0.38 ± 0.04 Co 1.9 ± 0.0 Cr 8.3 ± 0.3 Cu 5.1 ± 0.5 Fe 7300 ± 288 Hg 0.003 ± 0.001 K 705 ± 46 Mg 1338 ± 52 Mn 113 ± 4 Mo 0.60 ± 0.02 Ni 9.6 ± 0.2 P 434 ± 15 Pb 3.1 ± 0.2 S 481 ± 104 Si 2210 ± 49 V 16.0 ± 0.6 Zn 125 ± 14
Soil þ BFA B
Soil R 6.69 ± 0.01 0.420 ± 0.001 3193 2.2 27.0 3074 0.39 2.3 9.2 6.9 7386 0.004 795 1585 121 0.70 10.5 444 3.3 542 2448 17.0 155
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
160 0.1 1.3 177 0.04 0.3 0.2 0.8 220 0.001 84 82 6 0.05 0.3 17 0.2 122 112 1.7 57
7.39 ± 0.02 0.400 ± 0.002 2360 1.76 19 2914 0.39 1.7 6.9 4.2 6224 0.0029 653 1269 105 0.61 9.0 389 2.6 510 2085 14.1 123
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
213 0.10 2 174 0.02 0.4 0.6 0.7 379 0.0010 67 77 9 0.10 0.5 38 0.2 107 102 0.7 51
Soil þ BFA R 7.28 ± 0.01 0.900 ± 0.001 2626 1.82 22.0 3308 0.37 1.6 7.4 5.5 6368 0.0027 725 1457 114 0.64 9.1 398 2.6 541 2216 14.6 103
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
89 0.10 0.9 152 0.05 0.1 0.2 0.4 91 0.0010 36 35 6 0.03 0.3 30 0.1 53 76 0.5 24
Soil þ MFA B 7.37 ± 0.01 0.600 ± 0.001 2481 2.7 23 3416 0.8 1.6 7.5 6.7 6277 0.0033 602 1309 107 0.70 8.8 506 12 527 2207 15.5 146
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
123 0.3 1 201 0.1 0.1 0.4 1.1 216 0.0010 44 59 5 0.03 0.3 64 2 45 87 1.2 51
Soil þ MFA R 7.32 ± 0.02 1.4 ± 0.001 2537 2.6 22.0 3657 0.7 1.7 7.9 7.3 6470 0.0035 689 1415 113 0.9 9.6 489 11.0 861 2327 15.0 167
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
86 0.1 0.8 150 0.1 0.1 0.3 1.2 204 0.0010 38 80 5 0.2 0.2 27 1.5 95 101 0.3 38
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containing Soil þ BFA. The highest concentrations of Na, As and Cd were found in plants that grew in the Soil þ MFA. The concentrations of Pb were below the instrument detection limit (<0.3 mg/kg) in all plant samples.
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3.4. Total element concentration in soil The pH of the rhizosphere (R) soil containing fertilisers was slightly lower than of bulk (B) soil (Table 3). No differences were
Fig. 2. Chemical fractionation of macronutrients in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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observed in unamended soil. The EC significantly increased in the rhizosphere soil of all samples (Soil R, Soil þ BFA R and Soil þ MFA R) (Table 3). The concentrations of Al, Ba, Co, Cr, Fe, Hg, K Mg, Mn, Ni, Si and V were highest in the rhizosphere of the unamended soil compared to all other samples (Table 3). Arsenic, Cd, P and Pb were mostly
found in the bulk soil, while Ca, Cu, Mo, S and Zn were predominantly found in the rhizosphere Soil þ MFA. On average, rhizosphere of unamended soil (Soil R) contained the largest concentrations of all elements compared to the bulk soil (Soil B). Rhizosphere soil with BFA (Soil þ BFA R) contained lower concentrations of Cd, Co, Hg, Pb and Zn compared to the bulk soil
Fig. 3. Chemical fractionation of Cr, Co, Cu, Fe and Mn in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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(Soil þ BFA B), while concentrations of As, Ba, P, Pb and V were lower in the rhizosphere soil amended with MFA (Soil þ MFA R) compared to the bulk soil amended with MFA (Soil þ MFA B) (Table 3).
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3.5. Element fractionation in bulk and rhizosphere soil The fractionation of various elements was determined for the different samples, and the results are shown in Figs. 2e6.
Fig. 4. Chemical fractionation of Mo, Ni, Si, V and Zn in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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In general, Ca was bound mainly to the reducible Fraction (IV) followed by the non-soluble Fraction (VI). The main differences between the samples were found between the rhizosphere and the bulk soil in that the former had a larger fraction of the most soluble Ca (Fraction I). Similarly, amendment MFA slightly increased the exchangeable concentration of Ca. The same soil also contained the largest amount of soluble K. Almost all K fractions were larger in the rhizosphere soil in all pots. Significant amount of K was bound to the carbonates (Fraction II) and the residual fraction (VI) in all samples. No significant difference between the bulk and rhizosphere soil fractionation of Mg was found. Magnesium was predominantly bound to the crystalline FeeMn oxides (Fraction IV) and the nonsoluble fraction (VI). Phosphorus was predominantly bound to poorly crystalline Fe oxyhydroxides (Fraction III) and to crystalline FeeMn oxides (Fraction IV) in all samples. No clear differences between P fractionation in bulk and rhizosphere samples were found. Fractionation of S was more distinct. Sulphur was more soluble in the rhizosphere soil with amendments compared to the unamended soil. However the largest fraction of S was bound to poorly crystalline Fe oxyhydroxides (Fraction III) in all soil samples. Copper, Ni and Mo were predominantly bound to poorly crystalline Fe oxyhydroxides (Fraction III) followed by the crystalline FeeMn oxides (Fraction IV), except for Mo, for which the second predominant fraction was bound to organic matter (Fraction V), especially in rhizosphere soil of Soil þ MFA (Figs. 3e4). Chromium, Fe, Zn, Co and V were mainly bound to reducible Fraction IV followed by the non-soluble fraction, while for Mn, this
order was reverse. Silicon was mostly bound to crystalline FeeMn oxides, followed by oxidizable fraction (V). No significant differences between bulk and rhizosphere soil were found for most of the fractionation of the elements (Fe, Mn, Ni and V). Only Zn in Soil þ MFA pellets had a more distinct fractionation, where a larger fraction of Zn was bound to carbonates in bulk soil compared to rhizosphere soil. Whereas in Soil þ BFA the larger fraction of Zn was exchangeable in rhizosphere soil (Soil þ BFA R) compared to the bulk soil (Soil þ BFA B). Aluminium was predominantly bound to crystalline FeeMn oxides (Fraction IV) and non-soluble Fraction (VI) in all soil samples (Fig. 5). Arsenic was predominantly found in Fraction III, but was also found in a most soluble Fraction I in Soil þ MFA. Significant amount of Ba (ca 35%) was found in the most soluble Fraction I in all samples, followed by fractions IV and VI. Cadmium was mainly bound to the reducible fractions (IV and III) in the unamended soil and Soil þ BFA, while in Soil þ MFA Cd was mainly bound to crystalline FeeMn oxides (Fraction IV) followed by the exchangeable fraction (I), which comprised about 25% of the total Cd concentration. In both bulk and rhizosphere soils amended with MFA, Cd was bound to carbonates (Fraction II) (Fig. 6). Mercury was predominantly bound to organic matter (Fraction V) in all samples (Fig. 6). Only in Soil þ MFA, the second largest fraction of Hg was bound to crystalline FeeMn oxides (Fraction IV). Lead was also mainly found in Fraction IV in all samples. However soil amended with MFA pellets also had significant amounts of Pb in the most soluble fraction (I) and bound to carbonates (Fraction II).
Fig. 5. Chemical fractionation of potentially toxic elements Al, As and Ba in bulk (B) and rhizosphere (R) soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulphides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
€nnvall et al. / Journal of Environmental Management 159 (2015) 27e36 E. Bra
3.6. Acid neutralization capacity Acid neutralization capacity of BFA pellets was higher than those of MFA (Fig. S2). Also BFA pellets were buffering above pH 8 considerably longer and consumed more HCl thus forming a typical plateau likely buffered by carbonates. MFA pellets had lower buffering capacity, but similar ANC to BFA pellets. 3.7. Mineralogical composition of soil Silicon dioxide phase dominated in all soil samples. Other phases with a high certainty could not be identified. 4. Discussion It has been shown that plants with lower biomass can have higher element concentrations than those with higher biomass due to the dilution effect (Fritioff et al., 2005). This was not observed in the present study. For example, concentrations of K, Ni, Al, Zn and P were significantly lower, while those of Cd, As, Fe, were higher in the plants with higher biomass (Table 2). Concentration of PO4eP in soil pore water comprised only 6.1%, 5.6% and 3.8% of the total P in the unamended soil and soil amended with BFA and MFA, respectively. In the beginning of the experiment, plant uptake of P was the largest in the unamended soil, where the concentration of dissolved PO4eP was the highest compared to other pots. In the end of the experiment, concentrations of PO4eP in the unamended soil pore water were the lowest, indicating the P
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uptake by plants or due to the larger biomass compared to amendment soil. Although MFA contained a substantial concentration of Pb (1815 ± 98 mg/kg, Table 1) and a significant amount of Pb was found in the exchangeable fraction of the bulk and rhizosphere soil, plants did not accumulate Pb. Concentration of Pb in plant biomass was below the instrument detection limit (<0.3 mg/kg) likely because Pb was accumulated in roots (Ashraf et al., 2010). Cadmium was also mostly found in exchangeable fraction of Soil þ MFA, but the concentration in plants did not differ from those from unamended soil. Such low Cd accumulation in plants was probably a result of the high salinity of the soil, which might decrease availability of the metals in soil, probably due to the metal complexation with chloride (Greger et al., 1995). High salinity was also shown having an opposite effect on Cd uptake by plants (Smolders and McLaughlin, 1996). Aluminium was mostly accumulated by plants grown in Soil þ BFA, by this decreasing initially the highest concentration of dissolved Al among the samples. Bioavailability of Al is undesirable because of its toxic effect on plants. An excess concentration of Al may lead to reduced uptake of nutrients, such as P, Ca, Mg, K and N by plants (Kabata-Pendias, 2011). However, concentrations of Al in plants were within the range of plant tolerance varying from 7.2 mg/kg to even 3470 mg/ kg (Kabata-Pendias, 2011). Aluminium is pH sensitive, but the pH of soils was above 5, therefore the solubility and toxicity of Al was expected to be low. Concentration of As in pore water of Soil þ MFA was by one order of magnitude higher than in the pore water of the unamended soil at the beginning of the experiment, but
Fig. 6. Chemical fractionation of potentially toxic elements Cd, Hg and Pb in bulk and rhizosphere soil unamended and amended with BFA and MFA pellets. I e exchangeable, II e bound to carbonates (acid-soluble), III e bound to poorly crystalline Fe(III) oxyhydroxides (reducible), IV e bound to crystalline FeeMn oxides (reducible), V e bound to organic matter and secondary sulfides (oxidisable), VI e residual fraction (non-soluble). See Section 2.4.1.
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significantly decreased before the plant harvesting. Arsenic was the only potentially toxic element that was consistently higher in all measured media, i.e. soil, pore water and biomass, than the samples from unamended soil. It could be explained by the higher concentrations of As in municipal solid waste incineration fly ash added. Application of BFA did not cause any increase in total concentrations of minor nutrients in soil and biomass, although dissolved concentrations were higher than in unamended samples for most of major and minor nutrients. Concentrations of potentially toxic elements, i.e. As, Cd and Pb, in pore water were similar or even lower than in the unamended soil. The pH in all soils increased slightly over time with a half unit (6.2e6.7) in the unamended soil, and up to 1 unit (7.5) in Soil þ BFA. The concentrations of most elements in pore water decreased with time, likely due to depletion caused by the plant uptake. The pH of bulk and rhizosphere soil did not differ significantly. It has been reported that the pH in the bulk soil may differ up to 2 units compared to the rhizosphere soil (Marschner et al., 1989). The differences occur when plant roots take up such ions that affect the pH of the rizosphere without affecting the pH of the bulk soil. When ammonium ions (NHþ 4 ) are absorbed by plant roots, concentration of Hþ ions increase and the pH in the rhizosphere decrease, whereas uptake of NO-3 ions results in an increase of both, OH and pH, in the rhizosphere (Marschner et al., 1991). Indeed, a slightly decreased pH in the rhizosphere soil (Table 3) coincided with the significantly increased centration of available NO-3 and decreased concentration of NHþ 4 in all pots over the time (Fig. 1). Also soil properties, such as buffering capacity, can influence the rootinduced pH changes in the rhizosphere (Heckman and Strick, 1996). The acid neutralization capacity (ANC) of amended residues plays an important role in maintaining soil pH levels. The pH in turn is one of the most important factors governing the solubility of various mineral phases and elements (Chandler et al., 1997). The determined buffering capacity of the used pellets was not high, indicating quite a low resistance of the residues to pH changes in the soil. Although the biomass development was relatively low in all soils during this short period of the experiment, results show that the use of pelletized MFA did not cause a phytotoxic effect on plants, as it was observed in earlier studies where fresh and powdered MFA were used as fertilizers (Br€ annvall et al., 2014a). Pelletized residues were nearly intact in the soil in the end of the experiment, indicating that a full effect of fertilization of soil had not been achieved during the seven-week experiment. 5. Conclusions The difference between the mixtures containing biosolids and either municipal solid waste incineration fly ash (MFA) or those containing biofuel ash (BFA), in terms of the total concentrations of potentially toxic elements, was substantial. MFA contained from two times to two orders of magnitude higher concentrations of As, Cd and Pb than BFA, but the impact on the studied environmental media was not proportional to the total concentrations. Although, applying the same amount of pelletized industrial residue mixtures, MFA contributed higher concentrations of majority of total and soluble elements to soil than BFA, the difference in plant uptake of the elements was small.
Since the plant uptake of the potentially toxic elements was low, the elements might be prone to accumulation in soil top layer with the repeated application of residues to soil. Considering the use of industrial residue mixtures as soil amendments or fertilizers, the amount of added elements should not exceed those taken up by plants, by this preventing the increase of soil background concentrations. Acknowledgements The study was financed by the EU Regional Development Fund Objective 2 project North Waste Infrastructure. Authors thank Nils €m from Luleå Skoglund from Umeå University and Tommy Wikstro University of Technology for the help with the preparation of pellets. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.05.032. References Ashraf, M., Oztürk, M.A., Ahmad, M.S.A., 2010. Plant Adaptation and Phytoremediation. Springer, New York. Brady, N., Weil, R., 2008. The Nature and Properties of Soil, 14th ed. New Jersey, USA. € €blom, R., Skoglund, N., Kumpiene, J., 2014a. Effect of Brannvall, E., Nilsson, M., Sjo industrial residue combinations on plant uptake of elements. J. Environ. Manag. 132, 287e295. €nnvall, E., Belmonte Zamora, C., Sjo €blom, R., Kumpiene, J., 2014b. Effect of inBra dustrial residue combinations on availability of elements. J. Hazard. Mater. 276, 171e181. Chandler, A.J., International Ash Working Group, 1997. Municipal Solid Waste Incinerator Residues. Elsevier, Amsterdam, p. 974. Eriksson, J., 1998. Dissolution of Hardened wood ashes in forest soils: studies in a column experiment. Scand. J. For. Res. (Suppl. 2), 23e32. Fritioff, Å., Kautsky, L., Greger, M., 2005. Influence of temperature and salinity on heavy metal uptake by submersed plants. Environ. Pollut. 133, 265e274. Greger, M., Kautsky, L., Sandberg, T., 1995. A tentative model of Cd uptake in Potamogeton pectinatus in relation to salinity. Environ. Exp. Bot. 35, 215e225. Heckman, J.R., Strick, J.E., 1996. teaching plant-soil relationships with color images of rhizosphere pH. J. Nat. Resour. Life Sci. Educ. http://www.personal.psu.edu/ faculty/j/e/jel5/biofilms/rhizosphere.html. Kabata-Pendias, A., 2011. Trace Elements in Soils and Plants, fourth ed. Taylor &Francis, London, New York. Kumpiene, J., Ore, S., Lagerkvist, A., Maurice, C., 2007. Stabilization of Pb and Cu contaminated soil using coal fly ash and peat. Environ. Pollut. 145, 365e375. Larsson, P.-E., Westling, O., 1998. Leaching of wood ash and lime products: laboratory study. Scand. J. For. Res. 13 (Suppl. 2), 17e22. €mheld, V., 1989. Role of root-induced changes in the Marschner, H., Treeby, M., Ro €hr. Bodenk. rhizosphere for iron acquisition in higher plants. Z. Pflanzenerna 152, 197e204. Marschner, H., H€ aussling, M., George, E., 1991. Ammonium and nitrate uptake rates and rhizosphere pH innon-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.]. Trees-Struct. Funct. 5, 14e21. Nieminen, M., Piirainen, S., Moilanen, M., 2005. Release of mineral nutrients and heavy metals from wood and peat ash fertilizers: Field studies in Finnish forest soils. Scand. J. For. Res. 20, 146e153. Nilsson, 2012. Plant Availability of Phosphorus in Soil Fertilized with Ash and Sludge (in Swedish). Master thesis. Luleå University of Technology, p. 49. Smolders, E., McLaughlin, M.J., 1996. Chloride increases cadmium uptake in Swiss chard in a resin-buffered nutrient solution. Soil Sci. Soc. Am. J. 60, 1443e1447. Steenari, B.M., Marsic, N., Karlsson, L.G., Tomsic, A., Lindqvist, O., 1998. Long-term leaching of stabilized wood ash. Scand. J. For. Res. (Suppl. 2), 3e16. €r Återfo €ring Av Fosfor Ur Avlopp (The Action Swedish, E.P.A., 2002. Aktionsplan Fo Plan for Phosphorus Recycling Form the Wastewater in Swedish). Swedish EPA Rapport 5214. Swedish Forest Agency, 2008. Recommendations on Ash Recycling to the Forest (in Swedish). Report 2:2008.