Environmetal Soil Properties and Behaviour

Environmetal Soil Properties and Behaviour


DisciplinaControle e Remediação da Poluição dos Solos5 materiais18 seguidores
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use light of wavelengths between 300 
and 700 nm. Red tides are indicative of excessive growth of dinoflagellates in 
the sea. The green colour in the body of lakes and rivers is due to the pres-
ence of algae that increase with eutrophication\u2014attributable to the accumu-
lation of nutrients such as fertilizers in the water.
2.8.1.4 Viruses
Although viruses are smaller than bacteria and require a living cell to repro-
duce, their relationship to other organisms is not clear. In order for them 
to replicate, they have to invade various kinds of cells. They consist of one 
strand of DNA and one strand of ribonucleic acid (RNA) within a protein 
coat. A virus can only attack a specific host. For example, those that attack 
bacteria are called bacteriophages.
2.8.2 bacteria
There exist various species of bacteria in soils and sediments\u2014alkalophilic 
and asidophilic bacteria in the ground and barophilic bacteria in sediments. 
They play an important role in soil since (a) they form microcolonies in large 
pores and voids and form biofilms on the walls of large cracks and gaps in 
soil, resulting in bioclogging of pores and changes in the mode of fluid flow 
in soils, and (b) they are thought to have the capability to transform clay 
minerals through mechanisms of weathering (bioweathering) and dissolu-
tion over long time periods. They are prokaryotes that reproduce by binary 
fission by dividing into two cells, in about 20 min. The time it takes for one 
cell to double, however, depends on the temperature and species. For exam-
ple, the optimal doubling time for Bacillus subtilis (37°C) is 24 min and for 
Nitrobacter agilis (27°C) is 20 h.
69Nature of Soils
The broad classification of bacteria is undertaken by the shapes of the bac-
teria: for example, rod-shaped bacillus that have diameters of 0.5 to 1 µm 
and lengths of 3 to 5 µm, spherical-shaped coccus that have spherical cell 
diameters of from 0.2 to 2 µm, and spiral-shaped spirillium that have cell 
diameters ranging from 0.3 to 5 µm and lengths ranging from 6 to 15 µm. 
The cells grow in clusters, chains, or single form and may or may not be 
motile. The substrate of the bacteria must be soluble. Some of the most com-
mon species of bacteria are Pseudomonas, Arthrobacter, Bacillus, Acinetobacter, 
Micrococcus, Vibrio, Achromobacter, Brevibacterium, Flavobacterium, and 
Corynebacterium, and within each species, there will be various strains, with 
each of them behaving differently. Some strains can survive in certain con-
ditions that others cannot, and some species are dependent on other species 
for survival.
The living bodies of bacteria are composed of a variety of elements such 
as C, H, O, N, P, S, and trace elements, and by and large can be chemically 
expressed as [A]CH1.7O0.4N0.2, where A designates P, S, K, Mg, Mn, Ca, Fe, Co, 
Cu, Zn, Ni, Mo, and so forth. Bacteria take these elements in vivo as nutri-
ents, and these elements are used to form (a) the body of bacteria and (b) 
such metabolites as gas and extracellular polysaccharides as well as ATP 
(adenosine triphosphate) that supply the energy required for their growth 
and sustenance. Bacteria that utilize organic substrates for energy are 
called chemoorganotrophs, and those that use organics as a carbon source are 
called heterotrophic bacteria. Bacteria that utilize such inorganic compounds 
such as H2, NH4+, NO2\u2013, S, H2S, and Fe2+ as energy sources and utilize CO2 as 
a carbon source (not organic matter) are called autotrophic bacteria.
Bacteria can also be classified in respect to their requirements for oxygen. 
Those that require molecular oxygen for respiration are aerobes (aerobic 
bacteria), and those that do not require molecular oxygen for respiration are 
anaerobes (anaerobic bacteria). Facultative bacteria grow in both environ-
ments, with and without oxygen. These organisms use molecular oxygen 
when it is present, and when low levels of oxygen are present they utilize 
nitrate or other oxides for their energy source. Energy is obtained from the 
respiration process by the release of hydrogen from a donor enzymatically, 
resulting in oxidation. When the hydrogen atom meets an acceptor, reduc-
tion occurs. Oxygen is the hydrogen acceptor during aerobic respiration. It 
is the best acceptor since the most free energy is released this way. Aerobic 
microbes thus grow faster than anaerobic strains. Water is produced as 
the end product. Carbonate, iron, nitrate, or sulphate ions serve as electron 
acceptors in anaerobic respiration. Methane, ammonia, hydrogen sulphide, 
or a reduced organic compound are the final products, depending on the 
hydrogen acceptor. They live in a wide range of temperatures, that is, 0°C 
to 120°C. The optimum temperature is a range of 25°C\u201350°C for a great 
number of bacteria, although there are some species (thermophilic bacteria) 
that will survive temperatures higher than 100°C, as for example, sulphate 
reducing bacteria. Depending on the species and circumstances, the life 
70 Environmental Soil Properties and Behaviour
span of bacteria is different, that is, from a few days to about 300 days at the 
maximum.
By and large, bacteria live on the surface of solid substances. They form 
colonies and produce biofilms that are composed of the stacks of colonies 
on the surfaces of clay entities such as clay msu and clay masses. A common 
assumption for the mass of bacteria is about 10\u221212 g/cell, with an estimated 
size of bacteria to be about 0.25\u20132.0 \u3bcm. The maximum density obtained 
varies according to the species, for example, 4\u20136×1013 cells/kg-mineral for 
T. ferrooxidans and 2\u20134×1013cells/kg-mineral for T. thiooxidans (Konishi et 
al., 1990, 1995). The mass of bacteria in colonies is assumed to be about 90 
mg/cm3-colony, with the estimated size of colonies to be about 10\u201320 \u3bcm in 
diameter and 5\u201310 \u3bcm thick (Molz et al., 1986), with a maximum thickness 
of 10\u201350 \u3bcm.
The surface of bacteria has a positive charge at an extremely low pH and 
a negative charge at a pH higher than 4 (Marshall, 1976). It is important to 
note that when such biofilms are formed in soil, they will have the ability to 
change the apparent surface charge of the soil particles and msu, depending 
on the pH of the microenvironment. Bacterial growth rate is directly depen-
dent on substrate concentration. The higher the substrate concentration, the 
higher the growth rate. The substrate can be a single compound or a mixture. 
When it is a mixture, the parameters such as biochemical oxygen demand 
(BOD), chemical oxygen demand (COD), total organic carbon (TOC), or total 
petroleum hydrocarbons (TPH) can be used on a mass or liquid basis to indi-
cate the total substrate concentration.
2.8.3 Ecology in Soils
The existence and activities of microorganisms in natural soils and rocks, clay 
buffers, backfills, and host rocks in repository-type environments have been 
reported by many researchers (e.g., Huang and Schnitzer, 1986; Pedersen, 
2000; Wang and Francis, 2005; Yong and Mulligan, 2004). The environmental 
factors that favour optimal activities of microorganisms include tempera-
ture, oxygen availability, presence of water, nutrients, and osmotic pressure. 
Some of the more important chemical factors impacting microbial activity 
include pH, toxicity, heavy metals, molecular structure, and co-metabolism. 
Whilst microorganisms prefer a pH range of between 5.6 and 9.0, there are 
some that can function at higher or lower pH environments than 5 as fungi. 
Sulphur-oxidizing bacteria can produce sulphuric acid, which will lower the 
pH to values below 1 (e.g., H2S + 2O2 \u2192 H2SO4). At neutral pH, generation of 
carbon dioxide by the microorganisms helps to buffer the system and also 
helps to maintain neutral pH.
The three main temperature ranges wherein the various classes of 
microorganisms can grow optimally are as follows: