**5. Conclusion**

A. Soil containing the beads. Fifty beads were mixed with 50 g of soil (Hyoko, Japan). a. Beads made of alginate gel (0.38 mm in diameter). B. The soil and beads were separated by sieves with mesh sizes between 2.5 mm and 5 mm. B+ and B-. The impassable soil through the 5 mm mesh sieve and the passed soil through the 2.5 mm mesh sieve are

The beads made of alginate gel are most suitable for the LIM method because (1) they can be easily and inexpensively produced at a uniform size, (2) they can immobilize microbial cells

hardness. If it is assumed that the immobilized cell can accumulate lead at 300 mg/g, one bead should be able to absorb 3–30 mg of lead. Additionally, if cells secreting polysaccharides are utilized, each bead may be applied several times for remediation because polysaccharides are not leaked from the beads. Therefore, alginate gel beads can be utilized as a superior absorbent

Figure 5 shows the separation experiment of the beads and soil from the soil and beads mixture (Fig. 4, Step 3). The experiment was performed to examine the separation efficiency of the beads; the absorption by the immobilized cells was not conducted. Fifty beads (0.38 mm in diameter) were mixed with 50 g of soil (Fig. 5A) and separated with 2.5 mm and 5 mm mesh sieves. All beads were collected between 2.5 mm and 5 mm mesh sieves (Fig. 5B) and the soil was eliminated from the 2.5 mm mesh sieve by rinsing with water (Fig. 5C). Heavy metals were extracted by a small amount of nitric acid (Fig. 5D). Following extraction, the beads may be reused in the next remediation because the beads are not broken by the operation and can

), and (3) they have an appropriate

shown. C. The washed soil and beads in water. D. Extraction of lead from the beads by nitric acid.

**Figure 5.** Schematic illustration of the LIM method using alginate gel beads.

262 Advances in Bioremediation of Wastewater and Polluted Soil

at a high density (approximately 100–1, 000 mg dry cells/cm3

be easily separated with small stones (Fig. 5D).

of lead.

A review of the estimated causes of pollution from lead and the following results were discussed. The principal use of lead is due to the production of lead-acid batteries; other uses include inorganic chemicals, solder, tubes, and boards. Following the RoHS Directive, the recycling percentage of lead-acid batteries and crystal glass has gradually increased, and solder, paint, and vinyl chloride containing lead have been converted to lead-free products. Over 80 % of lead is currently recycled in the developed countries. Therefore, serious pollution from lead is low in urban and agricultural areas. However, life-threatening levels of pollution from lead exist in areas containing metallurgy and mining industries in Asia, Africa, and South America due to the dumping of wastes in the rivers and in the air without any posttreatments. The soil in these areas should be promptly remediated.

Next, the author estimated whether phytoextraction is a practical method for remediation. Many native or transgenic plants showing a high accumulation ability to lead were screened or developed, and the ability could be enhanced using EDTA and microorganisms. Therefore, phytoextraction is a promising method for remediation. However, further improvement of the method is necessary due to the long processing time and low capacity (biomass/planted area).

Finally, the author proposed a novel process for remediation using microorganisms. Few microorganisms have been used for the bioremediation of polluted soil by heavy metals because it is often exceedingly difficult to collect the microorganisms from the soil after absorption. The LIM method, which is proposed by the author, is the improved landfarming process which employs beads with immobilized cells. In the LIM method, the processing time is short and the beads may be easily collected from soil with sieves after absorption. Therefore, the LIM method has high potential and may become the ideal process for the remediation of soil contaminated by lead.
