**5. Effect of landfill and leachate water on microorganisms**

Soil is generally a favorable habitat for the proliferation of microorganisms, with microcolonies developing around soil particles [49]. Bacteria comprise the most abundant group of microorganisms in the soil (3.0× 106 to 5.0× 108 per gram of soil), followed by the actinomycetes (1.0× 106 to 2.0× 107 ), fungi (5.0× 103 to 9.0× 106 ), yeast (1.0× 103 to 1.0 ×106 ), algae and protozoa (1.0× 103 to 5.0× 105 ), and nematodes (50–200 per gram of soil),with wide differences in the relative proportions of individual bacteria genera found in particular soils[50, 51]. In this study, the total coliform bacteria count varied from 2.1 ×105 to 7.4 ×105 in landfill soil.

The number of extant bacterial species is thought to range from 3 × 104 to 3 × 106 [52], of which only a small fraction have been cultured and identified [53,54]. Mayr et al. reported that due to differences in cultivability among soils, the number of cultivable bacteria per ml inoculums ranged from 0.6 ×103 (forest soil) to 7 × 103 (agricultural soil),with significant variability [55]. *E. coli* and thermo tolerant coliform bacteria are widely used as indicators of soil characteristics. However, many microorganisms, including ente rococci, coliphages, and sulfite-reducing clostridial spores, have been suggested as microbial indicators of fecal pollution [56], and anaerobic digestion processes, if operated properly, have long been known to successfully reduce the number of pathogens and indicator organisms [57,58]. In a study by Zhang et al. investigating microorganism concentration in raw sewage, the bacterial indicators total and fecal coliforms were enumerated. The average concentrations of total and fecal coliforms were 2.5 ×107 CFU/100 ml and 9.6×106 CFU/100 ml, respectively [59].

In the last a few years, researchers have reported higher fecal coliform populations, on a dry solids basis, in centrifugally dewatered bio solids compared to digester effluents [60–67]. Therefore, landfill irrigation by leachate water may represent a key process for landfill remediation and rehabilitation.

Tables 4 and 5 show the microbial density at the plots. As shown in Table 4, the density of fecal and total coliforms increased with the use of leachate water, with almost equal amounts between landfill and clean areas, which suggests that leachate water irrigation is an effective method of landfill remediation. The effects of the plants were also examined, as shown in Table 5. The types of plants affected the amount of fecal coliforms, with the highest concentration in the area planted with *A. rosea* (8.6 ×103 ).


Data analyzed using Duncan's multiple range test. *b* maximum value, *ab* intermediate value, *a* minimum value. Alpha = 0.05

**Table 4.** Changes in fecal coliform bacteria and total coliform density in soil for different factors


Data analyzed using Duncan's multiple range test. *b* maximum value; *ab* intermediate value, *a* minimum value. Alpha = 0.05

**Table 5.** Changes in fecal coliform bacterial density in the soil with different plant species
