Phytoremediation of Mixed Contaminated Soils: Enhancement with Biochar and Compost Amendments

Transcription

1 IFCEE215, San Antonio, TX, March 17-21, 215 Phytoremediation of Mixed Contaminated Soils: Enhancement with Biochar and Compost Amendments Reshma A. Chirakkara 1, S.M. ASCE and Krishna R. Reddy 2, F. ASCE, P.E., D.GE 1 Graduate Research Assistant, University of Illinois at Chicago, Department of Civil and Material Engineering, 842 West Taylor Street, Chicago, Illinois 667, USA; rac2@uic.edu 2 Professor, University of Illinois at Chicago, Department of Civil and Material Engineering, 842 West Taylor Street, Chicago, Illinois 667, USA; kreddy@uic.edu ABSTRACT: Pot experiments were conducted to study the effects of biochar and compost amendment on phytoremediation of mixed contaminated soil using sunflower plant, oat plant and rye grass. Mixed contaminated soil was prepared by mixing the soil with 5 mg/kg naphthalene, 1 mg/kg phenanthrene, 5 mg/kg Pb, 5 mg/kg Cd, and 2 mg/kg Cr. One set of experiments with the soil amended with 5 g/kg biochar and another set of experiments with soil amended with 2 g/kg compost were conducted. The amended soils were filled in pots and plants were grown in them for 61 days. Plants grown in uncontaminated-unamended soil and contaminated-unamended soil were taken as controls. The change in growth characteristics of oat plant and rye grass by amendments was not significant. Sunflower had better germination and growth characteristics in amended soil compared to unamended soil. The germination and growth characteristic and biomass of the plants were better in compost-amended soil compared to biochar-amended soils in sunflower plants. Cd and Pb removal from the soil was better for all the plants in the presence of amendments, but Cr removal was unaffected by addition of amendments. In planted soils, PAH concentrations were reduced by the presence of amendments. The results suggest that biochar and compost amendments can improve the plant growth characteristics and enhance phytoremediation of mixed contaminated soils. INTRODUCTION Many sites worldwide are contaminated with a mixture of organic contaminants and heavy metals. Since most of the available remediation technologies aim to degrade or immobilize only a particular type of contaminant, remediation of sites cocontaminated with organic and heavy metal contaminants can be a difficult task. Even though there are methods available for remediating mixed contaminated soils, many of them are energy intensive or expensive. For large sites with shallow and moderate Page 1

2 IFCEE215, San Antonio, TX, March 17-21, 215 contamination, phytoremediation is a green and sustainable option to remediate mixed contaminants (Reddy and Chirakkara, 213). In phytoremediation, suitable plants are grown in the contaminated area to degrade, extract, contain or immobilize contaminants from soil and water (Sharma and Reddy, 24). This technology has been studied and implemented lately as an innovative, cost effective and sustainable alternative to more established treatment methods at various contaminated sites (USEPA, 2). Aesthetic nature of planted sites is another factor which makes phytoremediation an attractive and socially acceptable remediation method (ITRC 29). Capability of the plants to uptake the contaminants, ability of the plants to survive in the contaminated soil and bio availability of the contaminants in the soil are some of the limiting factors which influences phytoremediation efficiency. Phytoremediation can be enhanced either by increasing the capability of contaminant uptake of the plant or by amending the soil to increase the bio availability of the contaminants. Plant uptake of contaminants can be increased by the use of transgenic plants (Bhargava and Srivastava, 214) or by the inoculation of engineered endophytic bacteria (Bell et al. 214). Some studies aim at enhancement of phytoremediation by improving the contaminant mobility and bioavailability in soils by adding suitable chelating agents or surfactants. But in such cases, there is a possibility of contamination of the soil and ground water by the chemicals used for mobilizing the contaminants. Also, the mobilized contaminants can migrate to the ground water, thus by contaminating the ground water and also spreading the contamination. Biomass improvement is another way of improving phytoremediation. By improving the growth, the water and nutrient uptake of the plants will be increased and this leads to increased contaminant uptake. Biochar and compost amendments can be used as a way to improve the soil texture and biomass of the plants grown in soil. Biochar can immobilize heavy metals in the soil, by surface sorption of the metals on biochar. It can also improve the biological activity in the soil (Paz-Ferreiro et al. 214). Addition of compost to the soil can improve plant growth and also increase soil microbial activity (Ghanem et al. 213). Compost is also expected to immobilize the heavy metal contaminants in the soil (Alvarenga et al. 214). Considering its benefits on improving the soil, several researches have been conducted lately to combine the use of biochar or compost with phytoremediation of soils. But these studies discuss soils contaminated with either heavy metals or organic contaminants. This study describes the performance of three plant species in mixed contaminated soil in the presence of biochar or compost amendments. Naphthalene, phenanthrene, lead (Pb), cadmium (Cd), and chromium (Cr) the common contaminants observed at many mixed contaminated sites were considered for the study. EXPERIMENTAL METHODS Soil Selected Gray silty clay, which represents typical Chicago glacial till, was selected for performing the pot experiments. Important physical properties of the soil used in the study are presented in Table 1. Page 2

3 IFCEE215, San Antonio, TX, March 17-21, 215 Table 1. Important Properties of Soil Used for the Experiments Soil organic content 2.4% Specific gravity 2.7% Liquid limit 32.7% Plastic limit 19.1% Plasticity index 13.6% Clay (<.2mm) 41% Silt (.2 -.5mm) 43% Sand (.5 2 mm) 14.2% USCS Classification CL USDA Classification Silty clay Soil Spiking Procedure Clean control soil required for the pot experiment was prepared by mixing the soil with 15% of water. Mixed contaminated soil was prepared by spiking the soil with naphthalene, phenanthrene, Pb, Cd & Cr. For that, measured amount of naphthalene and phenanthrene were dissolved in hexane using magnetic stirrer. The hexane with dissolved naphthalene and phenanthrene was mixed in measured quantity of soil to get a final concentration of 5 mg/kg naphthalene and 1 mg/kg phenanthrene in the soil. The mixed soil was kept in fume hood for 3 to 4 days for drying. To ensure uniformity, soil was mixed once every day during drying. After that, PbCl 2, K 2 Cr 2 O 7 and CdCl 2. ½ H 2 O were measured aiming at a final concentration of 5 mg/kg Pb, 2 mg/kg Cr and 5 mg/kg Cd in soil. These chemicals were mixed in water (to get approximate water content of 15% in soil) for one hour using magnetic stirrer. This solution containing dissolved Pb, Cd, and Cr was added to the soil, previously spiked with naphthalene and phenanthrene. The soil was mixed well to ensure that the contaminant distribution was uniform. A part of this mixed contaminated soil was mixed with biochar (5 g/kg soil) and one part of the mixed contaminated soil was mixed with yard waste compost (2 g/kg soil). Measured properties of the contaminated and uncontaminated soil at the time of seeding are presented in Table 2. Selected Plant Species The plant species for the study were selected based on biomass and capability of survival based on some previous results (Chirakkara and Reddy, 213). The plants selected were Avena sativa (oat plant), Lolium perenne (rye grass), and Helianthus annuus (sunflower). Numbers of seeds sown in each pot were ten for oat plant and sunflower and twenty for rye grass. Pots Setup and Monitoring Prepared soil was filled in pots of 8cm diameter and 9 cm height for seeding the three plant species. Two replicates were prepared with control uncontaminated soil for each plant. Numbers of contaminated unamended pots were ten for oat plant & Page 3

4 IFCEE215, San Antonio, TX, March 17-21, 215 sunflower, and six for rye grass. Three sets of contaminated pots were prepared with each amendment (biochar and compost) for each plant species. The seeds were placed in the pots approximately a half inch below the soil surface. Each pot was kept on separate trays to ensure that the leachate does not get mixed up. The pots were placed under grow lights (metal halide lamps; average light intensity of 4 μmols/m 2 /s) hung ~ 12 inches above the plants to obtain the desired light intensity. A timer was set to provide 16 hours of light per day. The hanging height was adjusted as the plants started growing taller to reduce the heat stress caused by the hanging lamps to the plants. The temperature below the grow lights, at the height of the plants was measured as 25 C. Fans were used to control the temperatures of the grow lights. The plants were grown for 61 days and the growth was monitored. Pots were watered every day. The locations of the pots were rotated periodically to ensure uniform light intensity to all the pots. Weekly monitoring was done by counting the number of plants in each pot and measuring the plant height. Photographs were also taken every week to record the plant growth and biomass production. Soil samples were taken at the beginning and end of the plant growth period to test for ph, electrical conductivity, oxidation reduction potential, and metals and organic contaminants concentrations. At the end of the plant growth period, roots of the plants were separated out from shoots and washed in deionized water. The roots, shoots, and soil were dried in oven at 6 C for 6 days (until it attained constant weight). The dry weights of roots and shoots are recorded as root biomass and shoot biomass. Table 2. Properties of Soil at the Time of Seeding Property Soil Type Clean soil Contaminated unamended soil Contaminated soil with biochar Contaminated soil with compost ph Oxidation reduction potential (mv) Electrical conductivity (ms/cm) Analytical Testing Testing of physical properties of the soil viz. water content (ASTM D2216), organic content (ASTM D2974), ph (ASTM D4972), and grain size (ASTM D422) were analyzed as per standards. For conducting the heavy metal analysis, acid digestion of the soil samples was done as per EPA method 35B. The digested and filtered liquid was analyzed with Flame Atomic Absorption (FLAA) spectroscopy for Pb, Cd and Cr. The organic contaminants were analyzed by solvent extraction and analysis using Gas Chromatography, following EPA method SW827C. Page 4

5 IFCEE215, San Antonio, TX, March 17-21, 215 RESULTS AND DISCUSSION Germination percentages of the plants in contaminated and uncontaminated (control) soils are plotted in Figure 1. Here, germination is interpreted as the appearance of a green shoot/leaf above the soil. It can be noticed that the plants in contaminated unamended soil have very low germination rates compared to the plants in clean soil. The worst effect was observed for sunflower, whose germination rate was reduced by 77% due to contamination. Plant germination in contaminated soil improved with addition of amendments Contaminated, biochar amended Conatminated, compost amended Clean, unamended Contaminated, unamended 12 1 Germination (%) Sunflower Oat plant Rye grass FIG. 1. Germination of studied plants in clean soil vs contaminated soils. Figure 2 shows the percentage survival of all the selected plants in clean soil and contaminated soils. Here, survival is expressed as the presence of green/live plant in the pot at the end of the test period. Percentage survival is the number of surviving plants as percentage of the number of seeds germinated. Survival rates of all the plants in contaminated soil improved with addition of amendments, and the improvement was considerable for sunflower and rye grass. The final (after 61 days) heights of the studied plants are presented in Figure 3. All the plants had lesser maximum plant heights in contaminated soils than in control (clean) soil. The maximum plant heights improved for sunflower in amended soils, but this trend was not observed for oat plant and rye grass. Average root and shoot biomass of plants in clean soil and contaminated soils are summarized in Table 3. The biomasses of the plants in all contaminated soils were less that found in clean soil. Addition of biochar and compost improved the biomass of sunflower plants. But for oat plant and rye grass, biomass of plants in contaminated soils did not improve by the addition of amendments. Page 5

6 IFCEE215, San Antonio, TX, March 17-21, Contaminated, biochar amended Conatminated, compost amended Clean, unamended Contaminated, unamended 12 1 Survival (%) Sunflower Oat plant Rye grass FIG. 2. Survival of studied plants in clean soil vs contaminated soils. 7 Contaminated, biochar amended Conatminated, compost amended Clean, unamended Contaminated, unamended 7 Maximum Plant Height (cm) Sunflower Oat plant Rye grass FIG. 3. Final maximum plant height for clean soil vs contaminated soils. The phytotoxicity of plants in the contaminated soil is expected to be mainly due to the heavy metals present in the soil (Chirakkara and Reddy, 214). Cr is an essential micronutrient for plants, but in high concentrations, it can be detrimental to plant growth (Kranner and Colville, 211). Pb and Cd are non-essential heavy metals, which are not known to have any metabolic function in plants, and are toxic to plants at high concentrations (Pahlsson 1989). Plant growth in amended soil is expected to be better than that of unamended soil due to the metal immobilization by biochar and compost. Mobilized metals due to soluble complex formation with organic ligands may be the reason of reduced biomass of oat plant and rye grass in amended soil (McLean and Bledsoe 1992). Page 6

7 IFCEE215, San Antonio, TX, March 17-21, 215 Table 3: Average Biomass of Plants Soil Plant Contaminated Contaminated Contaminated Clean Unamended with Biochar with Compost Root Biomass (g) Sunflower Oat Plant Rye Grass Shoot Biomass (g) Sunflower Oat Plant Rye Grass Total Biomass (g) Sunflower Oat Plant Rye Grass Table 4 shows the average values of ph, electrical conductivity, and oxidationreduction potential for the soil samples after the plant growth period. According to this, ph value of the soil increased slightly with the addition of both amendments. Magnitude of reduction potential was also higher for amended soil than the unamended soil. Electrical conductivity values were lower for the amended soil than unamended soil. Figure 4 shows the heavy metal concentrations of the soil after plant growth period in planted and unplanted soils. In unamended soil, only sunflower plants could achieve a considerable reduction in Pb concentration compared to unplanted soil. But in biochar and compost amended soil, all the plants were able to reduce the Pb concentration considerably. Similar results were observed for the reduction of Cd concentration by the plants from soil. But the Cr concentration of the soil was not affected considerably by the addition of the amendments. This variation may be due to the difference in bioavailability of different metals in presence of amendments. The bioavailability and mobility of the metal contaminants in soil are dependent on speciation of metals based on complex formation and ph values. At the present ph conditions of the soil, Cr is more bioavailable for extraction by plants. By the addition of organic amendments like biochar and compost, Pb and Cd is expected to have formed soluble complexes with organic ligands (McLean and Bledsoe 1992). Naphthalene concentration of the initial unamended sample was found to be 8.9 mg/kg which is considerably less than the spiked concentration of naphthalene. No naphthalene was detected in initial amended samples and any of the final samples except for the planted samples with sunflower. In final soil samples with sunflower plants, naphthalene concentration was found to be 3 mg/kg. Figure 5 shows the initial and final phenanthrene concentrations in planted and unplanted samples. The expected dissipation mechanisms of the PAHs in soil are either one or a combination of microbial degradation, volatilization, and phytodegradation /accumulation. In some cases, planted pots seems to have higher PAH contents, possibly due to production of Page 7

8 IFCEE215, San Antonio, TX, March 17-21, 215 phytoalexins by the plants, in stressed conditions (Bais et al. 26). Phytoalexins have antimicrobial properties which can inhibit the degradation of organic contaminants. In the case of planted soils, phenanthrene degradation improved when amendments were added to soil. But for unplanted soil, better degradation was observed in unamended soil. Table 4. Average ph, ORP, and EC Soil Plant Contaminated Contaminated Contaminated Clean Unamended with Biochar with Compost ph Sunflower Oat Plant Rye Grass Oxidation Reduction Potential (mv) Sunflower Oat Plant Rye Grass Electrical Conductivity (ms/cm) Sunflower Oat Plant Rye Grass Soil Cd Concentration (mg/kg) Soil Pb Concentration (mg/kg) No plant Sunflower Oat plant Rye grass No plant Sunflower Oat plant Rye grass Soil Cr Concentration (mg/kg) FIG. 4. Heavy Metal Concentrations 5 Biochar amended Compost amended Unamended No plant Sunflower Oat plant Rye grass Page 8

9 IFCEE215, San Antonio, TX, March 17-21, 215 Phenanthrene Concentration (mg/kg) Biochar amended Compost amended Unamended Initial Blank Sunflower Oat plant Rye grass FIG. 5. Phenanthrene Concentrations CONCLUSIONS All plants showed delayed germination, reduced germination and survival rates in mixed contaminated soil compared to the control. The germination, growth, and biomass of sunflower plants were greatly improved by the addition of amendments. There was improvement of germination for oat plant and rye grass in amended soils, but the final biomass seemed to be lesser than that of plants in unamended soil. Sunflower reduced the concentrations of Pb, Cd, and Cr in unamended soil. With addition of amendments, more reduction of Pb and Cd was observed in pots with sunflower. Cr reduction by sunflower plants did not change considerably with the addition of amendments. Oat plant and rye grass did not remove Pb and Cd from unamended soil. But there was a reduction in concentration of Pb and Cd by oat plant and rye grass in biochar and compost amended soils. Cr reduction was achieved by all the plants in unamended soil, and this did not change considerably with the addition of amendments. PAH degradation in planted soils improved by the addition of amendments. The results suggest that biochar and compost amendments provide a promising approach for enhancing phytoremediation of mixed contaminated soils. REFERENCES ASTM D (21). Standard test method for laboratory determination of water (moisture) content of soil, rock, and soil-aggregate mixtures. ASTM International, West Conshohocken/PA. ASTM D (27). Standard test methods for moisture, ash, and organic matter of peat and organic soils. ASTM International, West Conshohocken/PA. ASTM D 422. (27). Standard test method for particle-size analysis of soils. ASTM International, West Conshohocken/PA. ASTM D (27). Standard test method for ph of soils. ASTM International, Page 9

10 IFCEE215, San Antonio, TX, March 17-21, 215 West Conshohocken/PA. Alvarenga, P., de Varennes, A., and Cunha-Queda, A. C. (214). The effect of compost treatments and a plant cover with Agrostis tenuis on the immobilization/mobilization of trace elements in a mine-contaminated soil. International Journal of Phytoremediation, 16(2), Bell, T. H., Joly, S., Pitre, F. E., and Yergeau, E. (214). Increasing phytoremediation efficiency and reliability using novel omics approaches. Trends in Biotechnology. Bhargava, A., and Srivastava, S. (214). Transgenic approaches for phytoextraction of heavy metals. In Improvement of Crops in the Era of Climatic Changes, Springer New York: Chirakkara, R. A., and Reddy, K. R. (213). Investigation of plant species for phytoremediation of mixed contaminants in soils, Proc. 16th Annual Conference & Exhibition, Air & Waste Management Association, Pittsburgh, PA, Chirakkara, R. A., and Reddy, K. R. (214). Synergistic effects of organic and metal contaminants on phytoremediation. Proc., GeoCongress214, ASCE, Reston, Virginia, Ghanem, A., D'Orazio, V., and Senesi, N. (213). Effects of compost addition on pyrene removal from soil cultivated with three selected plant species. CLEAN Soil, Air, Water, 41(12): ITRC (29), Phytotechnology technical and regulatory guidance and decision treesrevised, Washington, D.C. Kranner, I., and Colville, L. (211). Metals and seeds: Biochemical and molecular implications and their significance for seed germination. Environmental and Experimental Botany, 72 (1): McLean, J. E., and Bledsoe, B. E. (1992). Behaviour of metals in soils, ground water issue. US EPA. EPA/54/S-92/18. Pahlsson, A. B. (1989). Toxicity of heavy metals (Zn, Cu, Cd, Pb) to vascular plants. Water, Air and Soil Pollution, 47 (3-4): Paz-Ferreiro, J., Lu, H., Fu, S., Méndez, A., & Gascó, G. (214). Use of phytoremediation and biochar to remediate heavy metal polluted soils: a review. Solid Earth, 5(1): Reddy, K. R., and Chirakkara, R. A. (213). Green and sustainable remedial Strategy for contaminated site: Case study. Geotech. Geol. Eng., 31, Sharma, H. D. and Reddy, K. R. (24). Geoenvironmental Engineering: Site remediation, waste containment, and emerging waste management technologies. John Wiley & Sons, Hoboken, NJ. USEPA (2). Introduction to Phytoremediation. EPA/6/R-99/17, Office of research and development, Washington, D.C. Page 1