Page 64 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 47

1.5 INDUSTRY SECTORS WHERE WASTEWATER
TREATMENT, RECYCLING, AND REUSE CAN HAVE
AHIGHIMPACT

The theme of industrial wastewater treatment, recycling, and reuse is
relevant for all chemical and allied industries. It is even more crucial for
some of the sectors where large volumes of wastewater are generated.
The key issues here could be small concentrations but significant health
hazards (metals removal—all industries associated with metal processing),
toxic pollutants/organics and color issues (dyes and textiles), or industries
processing foods where low to high volumes of wastewaters are generated
that can be easily treated, recycled, and reused. In this regard, a brief discus-
sion on the specific aspects in these representative sectors will be highly
useful.

1.5.1 Removal of Metals

The toxic and recalcitrant nature or difficulty in biodegradability of metals
necessitates the utmost importance for their removal from industrial efflu-
ents. High concentrations of metals are undesirable, due to the chronic tox-
icity associated with many metals like Cu, Ni, Cr, Pb, Hg, to name a few.
The main toxic effect of heavy metals can adversely affect mental and learn-
ing abilities in humans, apart from creating other health problems. This
important area therefore attracted attention of a number of researchers
and a good amount of literature exists in this regard. Application of different
physico-chemical methods such as ion exchange (Maturana et al., 2011),
adsorption (Chen et al., 2012), membrane filtration (Mungray et al.,
2012), solvent extraction (Regel-Rosocka et al., 2006), precipitation, and
others have been reported for the removal of metallic species from wastewa-
ter streams. The cost of operation plays major role in deciding the separation
methodology.
Often, heavy metals are removed by the precipitation method (Lewis,
2010) by using caustic soda or lime as the precipitating reagent. The metals
are removed in the form of hydroxides where the pH of the medium plays an
important role. Metals that are of interest in wastewater treatment include
Zn, Cr, Pb, Ni, Cd, Cu, Fe, and Al (Akbal and Camci, 2011). The removal
of Cr and Zn is more effective at a lower pH, below neutral. Cr is a common
pollutant in the plating industry, and it is desirable to reduce hexavalent Cr
to trivalent Cr for effective removal.
Somemetalsthatarerelevanttowastewatertreatmentarebrieflydiscussedin
Table 1.4. (source for discharge limits: (www.cpcb.nic.in/generalstandards.pdf)