Page 352 - Industrial Wastewater Treatment, Recycling and Reuse

324 Industrial Wastewater Treatment, Recycling, and Reuse

and the World Health Organization has established the maximum level of
1
phenol in drinking water allowable as 1 mgL .
In the present chapter, the focus will be mainly on new adsorbent
materials mainly derived from biomass, metal oxides, and application in
the wastewater treatment for removal of three of the most commonly
encountered industrial pollutants, namely, phenol, 4-nitrophenol, and
4-chlorophenol, represented, respectively, by P, 4-NP, and 4-CP hereafter.
Wastewaters containing phenolics are generated from various types of
industrialprocessingproceduresrelatingtotheproductionofthesechemicals,
preparation of intermediates, and industries using these compounds as raw
materials. The prominent industries include petroleum refineries; textiles;
coke ovens; fuel production facilities; wood preserving plants; manufacturers
of plastics, resins, dyes, pesticides, pharmaceuticals; engineering; metallurgy
(Das and Sharma, 1998); and industries producing a host of other chemicals.
Phenols are also found in wastes of synthetic resin and plastics, rubber proof-
ing, cutting-oil, dye manufacturing, and many chemicals (Davi and Gnudi,
1999). The composition and nature of pollutants vary from industry to indus-
try, and treatment is usually complex. It is reported that the release of phenol,
4-CP, and 4-NP for the year 2000 in the United States (www.epa.gov/tri)
was 22.0, 0.046, and 0.007 t/year, respectively.

8.1.1 Technologies for Removal of Phenolic Compounds
from Wastewaters

A number of technologies, both destructive and nondestructive, are avail-
able for the removal of phenolics from industrial wastewaters. The selection
of appropriate treatments for achieving removal and recovery or removal
through destruction to the desired degree with cost effectiveness is in most
cases a challenging and a complex task. The principal types of technologies
available for treatment are briefly discussed in the following sections.

8.1.1.1 Coagulation
Coagulation is a physicochemical process that is often used to remove tur-
bidity and color from materials that are typically colloidal in nature
(1–200 mm). Both inorganic and organic coagulants have been used. The
optimum time for rapid mixing is often achieved in few minutes. Rapid
mixing is frequently followed by flocculation whereby agglomeration of
settled turbid particles into larger flocs takes place. The flocs then settle
and remove the contaminants in the sludge. Coagulation is often carried
out using chemicals such as ferric chloride, ferrous sulfate, ferric sulfate,