L¹I THÚY HIÒN¹, TRÇN §×NH MÊN¹, NGUYÔN V¨N LONG¹,
HOÀNG H¶I¹, Lª THÞ LÀI², JOERN KASBOHM³

Environment pollution caused by heavy metal wastewater impacts badly to human health. One of major reasons of heavy metal pollution is metallic equipment pyritic-ore production.

There are some methods that are applied to treat metal pollution over the world, such as chemistry, physic chemistry, biology… Among them, biological method has been used successfully with economic advantages, easy to carry out and safe conditions.

In the early 1980, Hammer studied on aerobic iron treatment by Thiobacillus. Fe is converted to Fe(OH)₃. Some American, Slovak and German authors applied microorganisms to convert metal from toxic to less toxic compounds, from variable to stable mineralized compounds. For example, aluminium, zinc and copper, lead and iron are removed by forming hydroxide, carbonate, sulfide, respectively. In 1987, a Colorado University research group studied on sulfate - reducing bacteria (SRB) role in anaerobic heavy metal removal. Several years later, Brodie used limestone to control pH of metal removal by SRB at the Orphan mine of Montana. Zaluski had success in applying SRB for chromium treatment. After 2 weeks of experiment, 25 ppm of toxic Cr⁶⁺ was converted to Cr³⁺ with the following reaction:

3HS^- + 6FeSO₄ + 4CrO₄^2- + 13H₂O + OH^- ® 3S^o + 6Fe(OH)_3¯ + 4Cr(OH)_3¯ + 6SO₄^2-

Sottnik and Sucha expanded this treatment process to Sobov mine of Bratislava; the metal treatment effect was very high: Cu decreased from 4.9 to 0.03 mg/l, Mn decreased from 51 to 23 mg/l, Fe decreased from 2260 to 4.1 mg/l, Al decreased from 900 to 0.18 mg/l. Cu was treated effectively by using upflow anaerobic sludge blanket (UASB) in China and Korea in 2002.

Water and mud collected from V©n Chàng village, Nam §Þnh province.

Wastewater from plate production in V©n Chàng village.

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.

Additives used in experiment include cow shit, limestone, straw, chip, rubble.

Bacterial morphology are observed by electron microscope JEM 1010 (Japan) and optical microscope Laboval 4 (Germany).

Analysis of metal concentration realized by atomic absorption spectrometry (AAS), ultraviolet (UV-V13), photometry. Eh and pH were measured by Testo (Germany).

V©n Chàng has not had waste collection and classification system. So, the most suitable method for treatment is a mixture metal model. By using metal converting bacteria that was isolated from wastewater, we set up 3 models for minimizing mixture metal (two 50 liter models and one 100 liter model).

Table 1. Set up models

Substrate and additive composition:

• Cow shit and bacteria 3%,
• Limestone 1%,
• Chip 1.5%,
• Straw 1.5%,
• Rubble 2%.

Result of HH_I-50l model operation is shown in the tables 2, 3.

Table 2. Bacteria number, pH and Eh in HH_I-50l model

Previous SRB number was 10³ CFU/ml. They grew well and reached maximum 10⁸ CFU/ml after 4 weeks. Metal concentration reduced significantly after 12 weeks, treated water came up to the Vietnamese standard.

Cr from 131 reduced to 0.165 mg/l, Ni from 500 reduced to 6.75 mg/l, Al from 224 reduced to 1 mg/l, Zn from 7.5 reduced to 0.067 mg/l, Pb from 0.75 reduced to 0.05 mg/l, Cd from 0.2 reduced to 0.05 mg/l, Mn from 6.0 reduced to 1.2 mg/l, Cu from 4.15 reduced to 0.034 mg/l. The treatment process took a long time (12 weeks), therefore we continued to set up an other model, HH_II-50l.

In this model, we supplemented inlet wastewater with 10⁴ CFU/ml of SRB.

SRB number increased to 10⁸ CFU/ml after 2 keeping week and there was good result of metal analysis (tables 4 and 5).

Table 4. Bacteria number, pH and Eh in HH_II-50l model

Figure 1. Metal concentration in HH_I-50l model

Fig. 2. Metal concentration in HH_II-50l model

 Table 5. Chemical analysis of HH_II-50l model

Table 5 showed that model was operated effectively. Cr concentration decreased 88%, Ni concentration decreased 88.3% after 2 keeping week. Supplemented wastewater to inlet and drained from outlet until the fourth week, metal concentration reduced, Cr 97.79% (from 38 to 0.84 mg/l), Ni 97.29% (from 48 to 1.3 mg/l). Ni and Cr concentration in treated water came up to the Vietnamese standard just after 2 week operation.

Base on high effective 50l model process, the HH_III-100l model was set up at V©n Chàng village.

 Table 6. Bacteria number, pH and Eh in HH_III-100l model

After 8 week operation, Cr concentration decreased from 82 to 1.025 mg/l, Ni concentration decreased from 84.4 to 0.175 mg/l. Number of Desulfovibrio and Desulfobulbus was stable at high level, 10⁷-10⁸ CFU/ml. Bacteria growing on Tf, Tp and Tt media was low, approximately 10¹ CFU/ml.

Treated water came up to the Vietnamese standard (1995, level B). That was demonstrated by the growing of water hyacinth and coriander in outlet water. These plants grew well compared. In contrast, they were dead in untreated wastewater.

Table 7. Analysis of metal composition (mg/l)

Fig. 3. Metal concentration in HH_III-100l model

Fig. 4. Microbial wastewater treatment model Fig. 5. Wastewater was tested by water hyacinth

Based on up flow anaerobic sludge blanket principle, the mixture heavy metal treatment process was set up successfully at the V©n Chàng village, Nam §Þnh province. In both 50 liter and 100 liter models, indigenous SRB played an essential role in converting heavy metals. The best result is in 100 liter model, Cr concentration decreased from 82 to 1.025 mg/l, Ni concentration decreased from 84.4 to 0.175 mg/l. Treated water came up to the B level of Vietnamese standard for industrial wastewater. These models were transferred to producers in Vanchang village.

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 Néi, ViÖt Nam.

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