Chemistry Reference
In-Depth Information
3.6.1
Enhancement of Organic Carbon Removal by Activated Carbon
The most striking effect of activated carbon in integrated systems is observed in
the case of organic carbon removal that takes place as a result of mechanisms
discussed in Section 3.2. The benefits of enhanced organics removal are observed
directly or indirectly. Direct benefits include mainly the decrease in effluent
concentration, alleviation of toxicity, removal of odor, color, reduction in VOC
emissions, and so on. Furthermore, the decrease in SMP and EPS is related to
enhanced organics removal. Indirect effects include improved nitrification as a
result of enhanced biological removal and/or adsorption of inhibitory or toxic
compounds. Also, improvement in sludge settling and dewaterability is to a cer-
tain extent related to enhanced organics removal.
The enhancement of organic carbon removal in integrated systems is extensively
discussed in Chapters 4 and 5, for the case of small- and full-scale systems,
respectively.
3.6.2
Enhancement of Nitrification by Activated Carbon
Nitrogeneous matter in wastewater, like carbonaceous matter, can be divided into
two categories, nonbiodegradable and biodegradable. The nonbiodegradable frac-
tion is associated with nonbiodegradable organic matter while the biodegradable
fraction contains ammonia and soluble and particulate organic nitrogen. Parti-
culate organic nitrogen is hydrolyzed to soluble organic nitrogen in parallel to the
hydrolysis of slowly biodegradable organic matter. The soluble organic nitrogen
can be converted to ammonia by ammonification [62].
Nitrification is an autotrophic process in which energy for bacterial growth is
derived from the oxidation of ammonia. At neutral pH, most of the nitrogen
is present in the form of the ammonium ion rather than ammonia. Therefore,
equations delineating nitrification involve the ammonium ion as the initial sub-
strate. Nitrification bacteria, or nitrifiers, use inorganic carbon instead of organic
carbon for cell synthesis. Nitrification is a two-step process carried out by
Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB), con-
verting ammonium into nitrite and nitrite into nitrate, respectively. The two steps
of oxidation reactions, which yield the energy required for the synthesis of new
nitrifier cells, are shown as follows.
3
2
O
2
AOB
NH
4
NO
2
þ
2H
þ
þ
þ
!
H
2
O
(3.5)
1
2
O
2
NOB
NO
2
þ
NO
3
!
(3.6)
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