Page 33 - Industrial Wastewater Treatment, Recycling and Reuse

16 Industrial Wastewater Treatment, Recycling, and Reuse

times also include oxygen demand of other components, it is higher than
TOC. It is also important to identify volatile organic carbons and the pres-
ence of specific priority pollutants, in addition to the total organic content,
to facilitate effluent treatment strategy.
Although for any wastewater treatment, complete characterization
is desirable for devising treatment methodology, many times, only a few
of the parameters are measured and monitored. The description of all the
parameters and analytical procedures is beyond the scope of this review,
details of which are available elsewhere in the literature (Rice et al.,
2012). Hence, only important parameters for industrial wastewaters are dis-
cussed here. The most common parameters to be monitored for nontoxic
wastewaters are BOD, COD, and ammoniacal nitrogen. If there are any spe-
cific pollutants such as heavy metals or priority chemicals that are harmful,
these have to be removed to well below the statutory limits prescribed by the
government for those specific chemicals. For industrial wastewaters in India,
BOD and COD limits of 10–30 mg/L and 250 mg/L respectively are usu-
ally considered as satisfactory for discharge. The limit for the ammoniacal
nitrogen is generally less than 50 mg/L. Thus, measurement of these param-
eters and monitoring is essential for safe discharge of water. For water recy-
cling and reuse, further stringent limits will be required depending on the
nature of the process and plant. Alternatively, treated wastewaters can also
be used for other agricultural purposes.
For industrial purposes, COD is considered to be a reliable parameter
that can be monitored conveniently. The measurement of COD by ordinary
laboratory procedures requires digestion of the sample for 2 h and titration/
spectroscopic measurement. It does not require the use of expensive chemi-
cals in most cases. The COD value is very important from the point of view
of selection of treatment methodology. The chemical industry by virtue of
its diverse nature generates wastewaters with CODs ranging from a few
hundred to several thousands. As a general rule, the higher the COD of
wastewater, the more difficult it can become to treat it. However, measure-
ment of BOD can help in deciding if the wastewater can be treated biolog-
ically, chemically, or by employing both methods. This is indicated by the
ratio of BOD to COD. The ratio keeps on changing depending on the bio-
degradation process, which has a definite rate even under normal conditions.
As the biodegradation progresses, the BOD goes on decreasing; ideally,
it should become zero when biodegradation is complete.
In contrast to COD measurement, acceptable standard BOD measure-
ment practices require 5 days for incubation. The 5-day period is set as