Of Wastewater Treatment Processes

Uncontrolled bacteria in industrial water systems produce an endless variety of problems, including disease, equipment damage, and product damage. Unlike the microbiological problems that can occur in water systems, microbiology can be applied in wastewater treatment as a beneficial science for the destruction of pollutants in wastewater (Kemmer, 1979).

It should be noted that all of the biological processes used for the treatment of wastewater (in particular) are derived or modeled from processes occurring naturally in nature. The processes discussed here are typical examples. It also should be noted, "that by controlling the environment of microorganisms, the decomposition of wastes is speeded up. Regardless of the type of waste, the biological treatment process consists of controlling the environment required for optimum growth of the microorganism involved" (Metcalf & Eddy, 2003).

8.14.1 Aerobic Process

In aerobic treatment processes, organisms use free, elemental oxygen and organic matter together with nutrients (nitrogen, phosphorus) and trace metals (iron, etc.) to produce more organisms and stable dissolved and suspended solids and carbon dioxide (see Figure 8.10)

8.14.2 Anaerobic Process

The anaerobic treatment process consists of two steps, occurs completely in the absence of oxygen, and produces a useable byproduct, methane gas. In the first step of the process, facultative microorganisms use the organic matter as food to produce more organisms; volatile (organic) acids; carbon dioxide, hydrogen sulfide, and other gases; and some stable solids (see Figure 8.11). In the second step, anaerobic microorganisms use the volatile acids as their food source. The process produces more organisms, stable solids, and methane gas that can be used to provide energy for various treatment system components (see Figure 8.12).

Oxygen Bacteria Organic matter Nutrients o

More bacteria Stable solids Settleable solids Carbon dioxide

Figure 8.10 Aerobic decomposition.

Facultative bacteria Organic matter Nutrients o

More bacteria Volatile solids Settleable solids Hydrogen sulfide

Figure 8.11 Anaerobic decomposition, first step.

Anaerobic bacteria Volatile acids Nutrients o

More bacteria Stable solids Settleable solids Methane

Figure 8.12 Anaerobic decomposition, second step.

Nitrate oxygen Bacteria Organic matter Nutrients o

More bacteria Stable solids Settleable solids Nitrogen

Figure 8.13 Anoxic decomposition.

Sun Algae

Carbon dioxide Nutrients

_More algae

V Oxygen

Figure 8.14 Photosynthesis.

8.14.3 Anoxic Process

In the anoxic ("without oxygen") treatment process, microorganisms use the fixed oxygen in nitrate compounds as a source of energy. The process produces more organisms and removes nitrogen from the wastewater by converting it to nitrogen gas, which is released into the air (see Figure 8.13).

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