L¹i THÚY HIÒN¹, TRÇN §×NH MÊN¹, §ç THU PH­¬NG¹,
V­¬NG THÞ NGA¹, NGUYÔN §×NH ViÖT¹, LÊ THÞ LÀI²

Chromium and nickel are widely used in metallurgical, electroplate industry and metal equipment production. Wastewater from such industries contains a considerable amount of soluble Cr and Ni, that causes harmful effect to the human health. Cr is commonly found in two inorganic chemical forms in natural environment, Cr³⁺ (chromide) and (chromate). Cr⁴⁺ is very toxic at any dose, causing diseases, such as nervous, digestion disorder, breathing disorder, liver cancer… Persons contacting usually with Ni can easily get hepatitis, nephritis, bronchitis, pneumonia…

Microbial treatment technology returns mobile and toxic contaminants to their stable immobile mineral forms. For instances, Cr and Ni, Zn and Cu, Pb and Fe are removed to form hydroxide, carbonate, sulfide, respectively. In anaerobic condition SRB can decompose organic compound using SO₄^2- as terminal electron acceptor producing H₂S. It reacts with dissolved metal to sulfide precipitation form (1), (2)

2CH₂O + SO₄^2- ® H₂S + 2HCO₃ ^- (1)

H₂S + M²⁺ ® MS¯ + 2H⁺ (M: metal) (2)

Sottnik and Sucha (1999) successfully carried out the field test in the Sobov, Slovakia for acid mine drainage remediation by passive treatment system. After treatment, the content of dissolved elements significantly reduced: Fe from 2260 to 4.1 mg/l, Al from 900 to 0.18 mg/l, Mn from 51 to 23 mg/l, Cu from 4.95 to 0.03 mg/l. Upflow anaerobic sludge blanket (UASB) was used effectively by Yang (Korea, 2002) in copper treatment. Zaluski and Canty [16] confirmed the ability of SRB in heavy metal removal, especially reducing Cr⁶⁺ to Cr³⁺, a much less toxic form of chromium according to the following reaction:

3 HS^- + 6FeSO₄ + 4CrO₄^2- + 13H₂O + OH^- ® 3S^o + 6Fe(OH)₃ + 4Cr(OH)₃ + 6SO₄^2-

V©n Chàng is a well-known village as mechanical and plating equiment production. Large amount of heavy metal contaminated wastewater is drained directly into V©n Chàng river without treatment, causing seriously water pollution.

To demonstrate the efficiency of treating Cr and Ni-containing wastewater by SRB in V©n Chàng, four Cr and Ni models set up according to UASB are presented in this paper.

* Cr- and Ni - contaminated water and mud samples collected from different places in Vân Chàng village, Nam Định.

* The composition and role of substrate and additives in experimental modelling include:

- Straw, sawdust, cobbles, mineral constituting stable substrate for bacterial growth

- Cow shit served as organic carbon source for bacterial growth.

- Crushed limestone providing buffering capacity to increase the pH

* Culture media (g/l):

Desulfobulbus: Na₂SO₄ 3, KH₂PO₄ 0.2, NH₄Cl 0.3, NaCl 1, KCl 0.5, MgCl₂ O.4, CaCl₂.2H₂O 0.15, FeSO₄.7H₂O 0.5, yeast extract 1, vitamins 1, trace element 0.1, water up to 1 liter, pH 7.2-7.4.

Desulfovibrio: KH₂PO₄ 0.5, NH₄Cl 1, NaCl 1, CaSO₄ 1, MgSO₄.7H₂O 2, sodium lactate 3.5, FeSO₄.7H₂O 0.5, yeast extract 1, vitamins 0.1, trace elements 0.1, water up to 1 liter, pH 7.2-7.4.

Thiobacillus ferooxidans: KH₂PO₄ 0.2, (NH₄)₂SO₄ 0.3, KCl 1, Ca(NO₃)₂ 0.02, MgSO₄ 1, FeSO₄ 1, water up to 1 liter, pH 3.5-4.0 .

Thiobacillus thiooxidans: Na₂S₂O₃.5H₂O 5, KH₂PO₄ 3, NH₄Cl 0.1, CaCl₂ 0.25, MgCl₂ 0.1, water up to 1 liter, pH 3.

Thiobacillus thioparus: Na₂S₂O₃. 5H₂O 5, NaHCO₃ 1, Na₂HPO₄ 0.2, MgCl₂ 0.1, NH₄Cl 0.1, FeSO₄ trace, water up to 1 liter, pH 7.4-8.5.

* Morphology of bacteria and the heavy metal inside the cells are observed by optical microscope Laboval 4 (Germany) and electron microscope JEM 1010 (Japan).

* Assessing the growth of heavy metal removal bacteria by most probable number method (MPN)

* Setting up 50 and 100 liter models for removing Cr and Ni in V©n Chàng settlement according to the principle of UASB.

* Concentration of Cr and Ni is analyzed by photometry

By using SRB that have ability to remove dissolved metals isolated from V©n Chàng wastewater, 4 Cr and 3 Ni models were set up in V©n Chàng according to UASB principle.

* Composition of substrate and additived in the model include:

Cow shit and bacteria 3%, straw 1.5%, sawdust 1.5%, cobbles 2%, crushed limestone 2%

First two weeks keep static stage for bacterial growth. After that effluent wastewater was added with 1/10 volume and take out the same volume during the operation process. The samples that operate for a long time, add cow shit after 4 weeks and material after 6-8 weeks in order to maintain stable activity of the model with pH = 6-7, Eh –100 mV.

4 Cr models (three 50 liter models and one 100 liter model) were set up in V©n Chàng with the ratio of inlet wastewater from 10 well water : 1 Cr contaminated water)

Table 1. Bacteria number, pH and Eh in Cr_II-50l model

Table 2. Concentration of elements in Cr_II-50l model

The results (Table 1, 2) have been indicating that the model is effective for Cr removal after 12 week operation. With 10² CFU/ml of SRB that are supported in inlet, Cr concentration greatly reduced from 260 mg/l to 1.4 mg/l (99.46%).

Table 3. Bacteria number, pH and Eh in Cr_IV-100l model

Table 4. Concentration of elements in Cr_IV-100l model

Fig. 1. Chromium wastewater treatment model Fig. 2. Coriander before and after treatment

Results of Cr_IV-100l scale in tables 3, 4 showed that number of SRB is highest up to 10¹⁰ CFU/ml after 4 week- treatment. Cr concentration significantly reduced from 165 mg/l to 0.375 mg/l (90%) after 8 week- operation

3 Ni models (two 50 liter models and one 100 liter model) were set up in V©n Chàng with the ratio of inlet wastewater from 6 well water: 1 Ni contaminated water).

After first two weeks of static stage, SRB from 10² CFU/ml were up to 10⁷ CFU/ml and highest were 10⁸-10⁹ CFU/ml after 4 week-operation. Ni concentration was decreased after 2 static culture weeks. After two week-operation with the addition of 1/10 volume inlet wastewater and taking out the same volume, Ni concentration reduced 96,7% (Tables 5,6).

Table 5. Bacteria number, pH and Eh in Ni_II-50l

Table 6. Concentration of elements in Ni_II-50l

Outlet wastewater is treated continually by aquatic plants such as water hyacinth, coriander. Consequently, the heavy metals reach the B level of Vietnamese standard for industrial wastewater, (TCVN 5945-1995).

Fig.1. Nickel waswater treatment model Fig.2. Coriander before and after treatment

Table 7. Bacteria number, pH and Eh in Ni_III-100l model

Treated water reaches the B level of the Vietnamese standard for industrial wastewater (TCVN 5945-1995).

This paper is a part of the VNM 00/004 Project, which has been supported by the International Bureau of the Ministry of Education and Research in Germany.

The authors would like to thank BMBF, Department of Sciences, Technology and Environment, Nam §Þnh province, the administrative authorities of V©n Chàng village, Nam Giang commune, Nam §Þnh province, Department of Mineral Deposit, Faculty of Natural Sciences, Commenius University, Bratislava, Slovakia and Department of Petroleum Microbiology, Institute of Biotechnology, Hà Nội, Việt Nam.

1. Bigham J. M., Schwertmann U., Pfab G., 1996. Influence of pH on mineral special in bioreactor stimulating acid - mine drainage. Applied Geochemistry, 11: 845 - 849.
2. Brierley CL., 1990. Bioremediation of Metal-contaminated Surface and Groundwater. Geomicrobiol. J., 8: 201-223.
3. Drovak D. H., Medin R. S., Edenborn H. M., and Mantire R. E., 1991. Treatment of metal contaminated water using Sulfate-reducing bacteria: results from pilot-scale reactors. In: Proc. of the 1991 Nat. Meeting of the Amer. Soc. of Sulfate Mining and Reclamation, Princeton, pp: 241-248.
4. Eaton A. D., L. S. Clesseri, and A. E. Greenberg (ed.), 1995. Standard methods for the examination of water and wastewater. Amer. Public Health Assoc., Washington, D.C., p. 368-370
5. Fujita M., M. Ike., 2003. Laboratory-scale continuous reactor for soluble selenium removal using selenate-reducing bacterium, Bacillus sp. SF-1. Ann. Rep. of water sci. and envir. Biotechn., Osaka Univ. 14: 66-71.
6. Hien L. T, K. Q. Hoa, L. T. Binh, L. T. Lai, 2000. Preliminary results on isolation and characterization of Thiobacillus from V©n Chàng wastewater. Intern. workshop on envir. protection community health for sustain. dev. of craft-settlements in Nam §Þnh, pp: 87-94.
7. Kashiwa M., M. Ike., 2003. Removal of soluble selenium by a selenate-reducing bacterium Bacillus sp. SF-1. Ann. Rep. of water sci. and envir. Biotechn., Osaka Univ.. 14:3-7.
8. Lai L. T., J. Kasbohm, J. Eidam, 2000. Assessment of environmental pollution of metal processing villages of Nam Giang (Nam §Þnh). J. of Earth Sci., 22(2): 140-145.
9. Machemer S. D., and Wildeman T. R., 1992. Adsorption compared with sulfide precipitation as metal removal processes from acid mine drainage in a constructed wetland. J. of contaminant hydr., 9: 115-131.
10. Plumer S. M., Updegraff D. M., and Wildeman I. R., 1991. Sulfate reduction versus methanogenesis in substrates designed to treat acid mine drainage: 201st Nat. meeting, Amer. Chem. Soc.
11. Sucha V., Kraus I., Zlocha M., Stresko V., Gasparovikova M., Lintneriva. Uhlik P., 1997. Prejavy a priciny acidiifikacie v obkasti Sobova (Stiavnicke vrchy), Mineralia Slovaca, 29: 407 - 416.
12. Wildeman T. R., 1998. Biogeochemical principles. Dept. of Chem. and Geoch. Colorado School of Mine, pp: 1-14.
13. Wildeman T. R., Updegraff D. M., 1997. Passive Bioremediation of Metals and Inorganic Contaminants. In Perspectives in Envir. Chem., Oxford, 473 - 495.
14. Wildeman T. R., Updergraff D. M., Reynolds J. S., and Bolis S.L., 1994. Passive bioremediation of metals from water using reactors or constructed wetlands. Emerging Techn. for Biorem. of metals, Lewis Publ., Bocaraton, Florida.
15. Yang J. W., Kim S. J., 2002. Application of Brewery UASB Granules to Treatment of Acidic Industrial Wastewater containing Heavy Metals. First ASEM Conf. on Biorem., Hanoi, Vietnam, Sept. 24-27.
16. Zaluski M., M. Canty, J. Trudnowski, 2000. Application of Sulfate-reducing bacteria for passive remediation of water contaminated with metals. MSE Tech. Appl., Inc. 200 Technology Way, Butte, Montana 59701, USA