| |
Industrial biological wastewater treatment systems are designed
to remove the dissolved organic load from the waters using
microorganisms. The microorganisms used are responsible for
the degradation of the organic matter. The organisms and the
treatment process associated with them can be classified into
aerobic (require oxygen for their metabolism), anaerobic (grow
in absence of oxygen) and facultative (can proliferate either
in absence or presence of oxygen although using different
metabolic processes). One of the major drawbacks of biological
processes for industrial applications is that they are not
easily suited for intermittent operations or high shock loads.
With proper controls and nutrient feed during low loading
periods these systems are successful but with additional costs. |
 |
|
| |
 |
Aerobic
Processes
In these, the reactions occurring can be summarized as:
organic load + oxygen + more cells + CO2 + H2O
In most wastewaters, the need for addition of nutrients (the
most common being nitrogen and phosphorus) seldom appears,
but an adequate provision of oxygen is essential for successful
operation of the systems. The most common aerobic processes
are: activated sludge systems, lagoons, active or trickling
filters and rotating disk contactors. |
|
| |
Anaerobic
Processes
The anaerobic treatment of wastewater proceeds with breakdown
of the organic load to gaseous products (mainly methane and
carbon dioxide) that constitute most of the reaction products
and biomass. Anaerobic treatment is the result of several
reactions: the organic load present in the wastewater is first
converted to soluble organic material which in turn is consumed
by acid-producing bacteria to give volatile fatty acids, plus
carbon dioxide and hydrogen. The methane-producing bacteria
consume these to produce methane and carbon dioxide.
The gas produced by a balanced and well-functioning system
contains 60-70% of methane, the rest being mostly carbon dioxide
and minor amounts of nitrogen and hydrogen.
Anaerobic processes are also sensitive to temperature. This
is why in some cases heating is provided to the digester to
stabilize temperatures to 85°-100°F. In most cases
this can be done in part with the methane gas originating
from the digester. |
 |
|
