Stabilization of tannery sludge by co-treatment with aluminum anodizing sludge and phytotoxicity of end-products

Size: px

Start display at page:

Download "Stabilization of tannery sludge by co-treatment with aluminum anodizing sludge and phytotoxicity of end-products"

Vincent Joseph
6 years ago
Views:

1 Stabilization of tannery sludge by co-treatment with aluminum anodizing sludge and phytotoxicity of end-products E. Pantazopoulou 1, O. Zebiliadou 1, M. Mitrakas 2 and A. Zouboulis 1 * 1 Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece 2 Department of Chemical Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece *Corresponding author: zoubouli@chem.auth.gr, Tel/Fax: Abstract The current global trend towards increasingly stringent environmental standards and the efforts for the efficient utilization and re-use of available by-products and/or wastes, favor the use of low-cost, eventually considered as waste by-products, sorbent materials for the treatment of heavy metalcontaminated solid wastes. In this study, the stabilization of tannery sludge, produced from the physicochemical and biological treatment of tannery wastewaters, was examined by the addition of another waste, aluminum anodizing sludge (ALAS), which is produced during the biological treatment of the wastewater that is generated through the aluminum anodizing process in aluminum industry. The leachates of stabilized waste with ALAS presented decreased concentrations of chromium and dissolved organic carbon (DOC), below the limit values for disposal at landfills for non-hazardous wastes, according to the Council Decision 2003/33/EC. The stabilized products were subjected to phytotoxicity tests, using three different types of seeds, such as Lepidium sativum, Sinapis alba and Sorghum saccharatum, in order to evaluate the potential toxic effect for plants in case of disposal. Keywords: stabilization, tannery sludge, chromium, aluminum anodizing sludge, phytotoxicity 1. INTRODUCTION The process of leather tanning consists of the transformation of animal skin to leather. Chromium salts, specifically the trivalent ones, are the most widely used chemicals in tanneries [1]. Only 60% of the chromium salts, applied during the tanning process, react with the raw materials (animal skin). The rest of chromium remains in the exhaust tanning bath and is subsequently discharged into the wastewater. The dissolved chromium and other spent chemicals, which are present in the wastewater, are mainly removed through the chemical precipitation technique, by ph adjustment usually by lime and the addition of inorganic coagulants before the wastewater is allowed to enter the biological treatment process. The precipitated chromium along with other co-precipitated organic compounds is discharged as sludge [2]. The trivalent chromium level and the organic compounds in the tannery sludge are sufficiently high and their direct landfilling is not allowed, because chromium can cause serious environmental contamination of soil or water. In Greece, it is estimated that the produced tannery sludge is about 3,000 tonnes [3]. Stabilization aims to convert hazardous substances to more stable chemical forms, which are much less soluble, mobile and toxic, using various additives, therefore stabilized wastes can be safely disposed to the environment with minimal risk of leaching toxic substances and polluting surface water or groundwater resources [4]. Various stabilizing agents (amendments), such as cement, hydrated lime, phosphoric compounds, as well as pozzolanic materials, such as fly ash, have been used in stabilization/solidification processes [4, 5, 6]. The higher cost of traditional stabilizing additives prompt the efficient utilization and re-use of available by-products and/or wastes, favor the use of low-cost sorbent materials, especially for the co-treatment of heavy metal-contaminated solid wastes. Specifically, in this study aluminum Proceedings of the 12 th International Conference on Protection and Restoration of the Environment Editors: A. Liakopoulos, A. Kungolos, C. Christodoulatos, A. Koutsopsyros ISBN

2 anodizing sludge (ALAS) was investigated as an alternative material in order to stabilize chromium along with organic substances in tannery sludge with additional benefits, such as the reduced cost of the treatment method and the minimization of anodizing sludge disposal cost. Aluminum anodizing process is an electrochemical method of coating the surface of aluminum products with a thin layer of aluminum oxide (Al 2 O 3 ). Surface treatment, before anodizing, includes basic and acidic cleaning, that produces wastewater rich in aluminum; this wastewater is then neutralized either by NaOH or Ca(OH) 2 and clarified. The supernatant is discharged to a sewer and the sludge is dehydrated using a filter press [7]. ALAS is the final product of this treatment and is mainly consisted of aluminum hydroxide, oxy-hydroxides and sulphates. This sludge is disposed on land as a common practice and the cost of this operation is estimated to be very high [8]. In European Union, the production of ALAS comes up to 100,000 tonnes per year [7]. 2. MATERIALS AND METHODS 2.1 Sample and data collection The tannery sludge is produced in the central wastewater treatment unit of tanneries cluster in the industrial area of Thessaloniki in Northern Greece. The tannery sludge is stored in the plant backyard at large piles, where it is air-dried. The tannery waste has about 10% moisture and mainly contains trivalent chromium, about 8.6% of dry substance and organic matter (about 23% of organic-bounded carbon). The major physico-chemical characteristics of tannery waste and of ALAS are presented in Table 1. Table 1. Physicochemical characteristics of tannery waste along with ALAS. Tannery waste % mg/kg of dry substance Cr Moisture C N Al Ca Mg Na As Ba Cu Mn Ni Pb Zn total ALAS Stabilization of tannery waste with ALAS The stabilization of tannery waste was investigated using different proportions of tannery waste and ALAS (50:50, 80:20 and 70:30). In each case, the two wastes were homogenized in a ball mill. The homogenized mixtures were then subjected to the standard leaching test EN , immediately after mixing, after 7, 15 and 30 days, in order to evaluate the stabilization rate of chromium and organic substances after the aging (maturation) process. The classification of the examined waste was based on the European Decision 2003/33/EC, regarding the acceptance of wastes at landfills [9]. 2.3 Phytotoxicity Test Phytotoxicity of tannery waste stabilized with ALAS was assessed by using three plant species, the dicotyl garden cress, Lepidium sativum, the dicotyl mustard, Sinapis alba and the monocotyl Sorgho, Sorghum saccharatum, according to the commercial toxicity bioassay Phytotoxkit Test [10]. The wastes were sieved using a sieve of 2 mm mesh and were completely water-saturated. Then, ten seeds of each plant were placed at equal distances in a test plate, above the hydrated wastes on a filter paper. The test plates were placed vertically in a holder incubated at 25 o C for 3 days. At the end of the incubation, a digital picture was captured for each of the test plate with the germinated plants. The determination of the root growth was performed using the Image Tool

3 for Windows. The percent inhibition of seed germination and root growth inhibition was calculated using the following formula: (Equation 1) where A: mean seed germination and root length in the control soil and B: mean seed germination and root length in the stabilized mixture [10, 11]. 3. RESULTS AND DISCUSSION The total chromium and dissolved organic carbon (DOC) values of the obtained leachates are presented in Figure 1 for each proportion of tannery sludge with ALAS, i.e. 50:50, 70:30 and 80:20, respectively. The characterization of tannery waste s leachates revealed that this waste cannot be accepted at landfills for hazardous wastes (DOC limit 1000 mg/kg) according to the European Decision 2003/33/EC, because of high DOC values (2400 mg/kg). The trivalent chromium content (13.5 mg/kg) is also above the limit value for wastes acceptable at non-hazardous wastes landfills (limit 10 mg/kg). As it is shown in Figure 1, in all proportions of tannery waste with ALAS, the concentration of total chromium is below the limit value for wastes acceptable at non-hazardous wastes landfills. ALAS seems to be an effective stabilization agent, as it can stabilize chromium, even when it is used in the small proportion of 20%. On the other hand, DOC concentration is under the limit value, regarding wastes acceptable at non-hazardous wastes landfills, only in the case where ALAS was used in the ratio of 50% and after three weeks in contact with tannery waste (Figure 2). Figure 1. Chromium and DOC values at the leachates for each proportion of tannery waste with ALAS respectively. Therefore, mixing with ALAS in a ratio of 50%, resulted in the production of a stabilized tannery waste acceptable in non-hazardous waste landfills, as both chromium and organic compounds leaching potential of tannery waste were highly reduced. ALAS can be used as an absorbent for various organic and inorganic pollutants, such as heavy metals due to the presence of aluminum 560

4 hydroxide [7]. The mechanism of stabilization seems to be the adsorption to the aluminum oxide onto the surface of ALAS. This probably achieved by means of electrostatic interactions between the pollutants and the surface of the adsorbent (ALAS) [12]. (a) (b) Figure 2. Influence of ALAS addition (50:50 ratio) on (a) Cr and (b) DOC leaching from tannery waste. The limit value for Cr at landfills for hazardous wastes is 70 mg/kg. According to Figure 2, it should be mentioned that the content of total chromium in the leachates of stabilized tannery waste with ALAS, after aging for 2 weeks, is even less than that mentioned in the EU Decision for disposal at landfills for inert wastes. As it is shown in Figure 3 the chromium that is leached is below 0.5%, which indicates that the stabilization of chromium occurred in a level above 90% after four weeks aging. The leachates of the tannery sludge are slightly alkaline with ph about , while stabilized tannery waste has ph about ALAS is a product with neutral to slightly alkaline properties (ph ), which enables it to be a good amendment material for stabilization of chromium; ph is the primary factor which controls the leachability of heavy metals in the stabilized wastes. Figure 3. Cr leached from stabilized tannery waste during the time according the blank sample (maximum concentration of Cr that could be leached, considering the 50:50 mixing of both wastes). Conclusively, mixing tannery waste with ALAS resulted in the production of a stabilized tannery waste acceptable in non-hazardous waste landfills, according the EU limit values for total chromium and DOC values. Therefore, the stabilization of tannery sludge with aluminum anodizing 561

by-product can be considered as an easily applicable and environmentally sound solid waste management method. The effect of stabilized tannery waste studied on seed germination and on root growth.

Sorghum Saccharatum was 24% (Figure 4). On root growth, negative effect was observed for all three seeds, as the inhibition was between 90-97%.

Some of these effects in the case of Sinapis Alba and Sorghum Saccharatum are the decrease of root length, the increase of root diameter and root hairs and the reduction of plant height [13].

5 by-product can be considered as an easily applicable and environmentally sound solid waste management method. The effect of stabilized tannery waste studied on seed germination and on root growth. The most negative effect on seed germination in the case of tannery waste was observed in the case of Sinapis Alba and Lepidium Sativum, while the inhibition for seed germination in the case of Sorghum Saccharatum was 24% (Figure 4). On root growth, negative effect was observed for all three seeds, as the inhibition was between 90-97%. The tannery waste leads to changes in the growth and development pattern of the plant. Some of these effects in the case of Sinapis Alba and Sorghum Saccharatum are the decrease of root length, the increase of root diameter and root hairs and the reduction of plant height [13]. Trivalent chromium can easily enter the plant system, if it is organically complexed in the rhizosphere [13]. In the case where the stabilized tannery waste was used, the inhibition effect on seed germination decreased significantly, i.e. less than 23%. As far as the root growth is concerned, the most negative effect was observed in the case of Lepidium Sativum, while the minimum inhibition was in the case of Sorghum Saccharatum (67%). Figure 5 depicts the seed germination of stabilized tannery waste (50:50) for the three seeds. As a result, stabilization of tannery waste with ALAS can significantly increase the seed germination and decrease the inhibition of root growth at the tannery waste. Figure 4. Inhibition of seed germination along with inhibition of root growth of the stabilized tannery waste (50:50 ratio) in comparison with tannery waste and ALAS. 562

CONCLUSIONS In accordance to the EU Decision 2003/33/EC, the mixing of tannery waste with ALAS results in a stabilized product, with both chromium and DOC concentration values in their leachates

It should be mentioned that in the proposed method a solid industrial waste (ALAS) is utilized for the stabilization of another hazardous waste, rich in chromium (from tanneries), contributing

Moreover, tannery waste stabilized with ALAS can decrease the phytotoxicity of initial sludge, as the phytotoxicity tests revealed that the inhibition of root growth is significantly decreased.

Acknowledgement This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the

, Font J, Puig R., Colak S., Celik D., 2011. Chromium recovery from tannery sludge with saponin and oxidative remediation. Journal of Hazardous Materials, 185, 456 462. 2. Swarnalatha S.

6 (a) (b) (c) Figure 5. Inhibition of seed germination along with inhibition of root growth of stabilized tannery waste (50:50 ratio) for (a) Sorghum Saccharatum, (b) Sinapis Alba and (c) Lepidium Sativum. 4. CONCLUSIONS In accordance to the EU Decision 2003/33/EC, the mixing of tannery waste with ALAS results in a stabilized product, with both chromium and DOC concentration values in their leachates below the respective limit values foreseen for disposal at landfills for non-hazardous wastes. The treated waste can be disposed of at landfills designed for non-hazardous wastes. It should be mentioned that in the proposed method a solid industrial waste (ALAS) is utilized for the stabilization of another hazardous waste, rich in chromium (from tanneries), contributing therefore to an integrated management of two waste streams, produced currently in large amounts. Moreover, tannery waste stabilized with ALAS can decrease the phytotoxicity of initial sludge, as the phytotoxicity tests revealed that the inhibition of root growth is significantly decreased. Thus, ALAS could be used as an alternative material for chromium stabilization of tannery waste, presenting additional benefits. Acknowledgement This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES: Reinforcement of the interdisciplinary and/or inter-institutional research and innovation. References 1. Kilic E., Font J, Puig R., Colak S., Celik D., Chromium recovery from tannery sludge with saponin and oxidative remediation. Journal of Hazardous Materials, 185, Swarnalatha S., Arasakumari M., Gnanamani A., Sekaran G., Solidification/stabilization of thermally-treated toxic tannery sludge. Journal of Chemical Technology and Biotechnology, 81, (accessed May 24 th, 2014) 4. Moon D.H., Dermatas D., Arsenic and lead release from fly ash stabilized/solidified soils under modified semi-dynamic leaching conditions. Journal of Hazardous Materials, 141, Jing C., Liu S., Korfiatis G., Meng X., Leaching behavior of Cr(III) in stabilized/solidified soil. Chemosphere, 64, Chrysochoou M., Dermatas D., Grubb G. D., Phosphate application to firing range soils for Pb immobilization: The unclear role of phosphate, Journal of Hazardous Materials, 144,

7 7. Mitrakas M., Bakaloulis A., Gkinis K., Studies on arsenic absorption by the use of aluminum anodizing sludge. Desalination and Water Treatment, 39, Correia A., Chambino T., Goncalves L., Franco A., Goncalves R., Goncalves A., Limpo V., Delmas F., Nogueira C., Bartolomeu F., 2005, Municipal wastewater treatment with anodizing solid waste. Desalination, 185, /33/EC, Council decision of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC. Official Journal of the European Communities, Brussels. 10. Phytotoxkit, Seed germination and early growth microbiotest with higher plants. Standard operation procedure, Phytotoxkit TM Test, Microbiotest Inc. 11. Oleszczuk P., Malara A., Josko I., Lesiuk A., The phytotoxicity changes of sewage sludge amended soils. Water Air Soil Pollution, 223, Flores J., Lima. E., Maubert M., Aduna E., Rivera J.L., Clean-up of wastes from the textile industry using anionic clays. Clays and Clay Minerals, 59, Shanker A.K., Cervantes C., Loza-Taver H., Avudainayagam S., Chromium toxicity in plants. Environment International, 31,

Stabilization of heavy metals using low-grade magnesia, Portland and Sorel cement

Stabilization of heavy metals using low-grade magnesia, Portland and Sorel cement E. Ntinoudi 1, E. Pantazopoulou 1, M. Mitrakas 2, H. Yiannoulakis 3, Th. Zampetakis 3 and A.I. Zouboulis 1, * 1 Laboratory