Page 30 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 13

1.2 CHARACTERIZATION OF INDUSTRIAL WASTEWATER

Characterization of wastewaters is the first step in the process of finding solu-
tions to their treatment, recycling, and reuse. The next section here deals with
the strategy of wastewater treatment and management. In this section, we
identify the major issues pertaining to such characterization and its importance
in the total methodology of water treatment, recycling, and reuse.
The first starting point in the wastewater characterization is the identifi-
cation of the source of generation. Identifying the source is important so that
corrective action, even if it is from a process point of view, such as process
modificationorincreaseinefficiency,canbetakentoeliminateorreducepol-
lutant levels at that stage. If this is not possible, identifying the nature of the
pollutant can help in the assessment of risk associated with mixing that stream
with other plant effluents. If there are priority pollutants, it is recommended
that those streams be separated from general plant effluents and treated sepa-
rately using an appropriate method. It is absolutely essential that the nontoxic
and reusable water not be allowed to mix with any other polluted stream. It is
also advisable that the segregation of the streams be done in accordance with
the nature of pollutants and priority goals such that recycling and reuse of the
water is facilitated. For example, a stream containing high ammoniacal nitro-
gen can be separated from the streams not containing any appreciable ammo-
niacal nitrogen. Further, it may not be out of place to emphasize proper
sample collection for the effluent. Usually, a chemical plant comprises many
buildings performing specific roles for process reactions and utilities. The
wastewater generated from each section is therefore different, both qualita-
tively and quantitatively, in terms of pollution levels. Proper sampling is
therefore essentialfor accurateidentification of thestreamscontaining pollut-
ants, their volumes, and the differences in nature of effluent streams. This will
assistindevisingasuitablestrategyformanagementofwastestreams,discussed
later in this chapter. Table 1.3 provides a format for identifying the main ele-
ments of industrial or sewage wastewater that would be most useful with the
desired limits, which are set differently depending on place of discharge,
nature of the industry, and government regulations.
Toxic wastewater streams should never be allowed to mix with other
wastewater streams; otherwise, the entire volume will have to be considered
as toxic, which can increase the load on effluent treatment and pollution
control tremendously. Toxicity is generally expressed as toxicity units
(TUs), which is 100 divided by the toxicity measured:
TU¼100/LC 50 or NOEL (no-observed-effect level)