4 Pollutants Discharged in Wastewater During Paper
Production
Large amount of various chemicals are used in paper production process including
sodium hydroxide, sodium carbonates, sodium sulfide, bisulfites, elemental chlorine
or chlorine dioxide, calcium oxide, hydrochloric acid, etc. resulting in the generation
of huge quantities of wastewater loaded with organic and inorganic salts and toxic
pollutants, which are let out after incomplete treatment. The studies of Fazeli et al.
(1998) showed an increased level of heavy metals accumulated in plant tissues of
paddy crop irrigated with paper mill effluent. Copper is also one of the main
contributors among other heavy metals of acute toxicity in the kraft mill effluent
(Reyes et al. 2009). There are also various compounds such as chlorinated organic
compounds, phenolics, and lignin which are often not removed adequately by
conventional approaches due to their highly toxic nature and low biodegradability
and pose a threat to aquatic receiving environments (Ali and Sreekrishnan 2001).
During the pulping, bleaching, and chemical recovery process, lignin is produced in
wastewater. During paper manufacturing process, it undergoes a variety of reactions
including aryl–alkyl cleavages, strong modification of side chains, and various
ill-defined condensation reactions fragmenting the polymer into small water/alkalisoluble compounds (Chakar and Ragauskas 2004). There are some other phenolic
compounds such as dichlorophenol, trichlorophenol, dichloroguicol,
tetrachloroguicol, and pentachlorophenol which are formed during the papermaking
process and observed as more toxic compounds (Ragunathan and Swaminathan
2004). The study of Savant et al. (2006) reported that the paper mill effluent is
contaminated by about 500 different chlorinated organic compounds. In the aquatic
system, the dark brown color of paper mill effluent blocks the photosynthesis and
decreases the dissolved oxygen (DO) level, which leads to adverse effects on flora
and fauna and poses toxicity to aquatic ecosystem (Latorre et al. 2007; Sponza
2003). The accumulation of toxic pollutants and metals in effluent contaminated soil
causes adverse effect on growing plant system (Kumari et al. 2014; Raj et al. 2014a,
b; Haq et al. 2016b). The characteristics of some pulp and paper mill effluent are
given in Table 14.2. Major pollutants found in wastewater or effluents are briefly
discussed below:
4.1 Organic Pollutants and Suspended Solids
In pulp and paper wastewater, there are many components such as cellulose,
hemicellulose, fugitive fibers, starch, and organic acids which are mainly responsible
for organic pollution. This results in a COD discharge of pulp in the range of
25–125 kg/ton1‒. In the aquatic ecosystem, high concentration of BOD and COD
value is responsible for depletion of dissolve oxygen. There are several toxic
components like fatty acids, resin, and toxic metalloids which are present in pulp
mill wastewater and absorbed by the organic solids. Further, it causes long-term
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I. Haq and A. Raj
Production
Large amount of various chemicals are used in paper production process including
sodium hydroxide, sodium carbonates, sodium sulfide, bisulfites, elemental chlorine
or chlorine dioxide, calcium oxide, hydrochloric acid, etc. resulting in the generation
of huge quantities of wastewater loaded with organic and inorganic salts and toxic
pollutants, which are let out after incomplete treatment. The studies of Fazeli et al.
(1998) showed an increased level of heavy metals accumulated in plant tissues of
paddy crop irrigated with paper mill effluent. Copper is also one of the main
contributors among other heavy metals of acute toxicity in the kraft mill effluent
(Reyes et al. 2009). There are also various compounds such as chlorinated organic
compounds, phenolics, and lignin which are often not removed adequately by
conventional approaches due to their highly toxic nature and low biodegradability
and pose a threat to aquatic receiving environments (Ali and Sreekrishnan 2001).
During the pulping, bleaching, and chemical recovery process, lignin is produced in
wastewater. During paper manufacturing process, it undergoes a variety of reactions
including aryl–alkyl cleavages, strong modification of side chains, and various
ill-defined condensation reactions fragmenting the polymer into small water/alkalisoluble compounds (Chakar and Ragauskas 2004). There are some other phenolic
compounds such as dichlorophenol, trichlorophenol, dichloroguicol,
tetrachloroguicol, and pentachlorophenol which are formed during the papermaking
process and observed as more toxic compounds (Ragunathan and Swaminathan
2004). The study of Savant et al. (2006) reported that the paper mill effluent is
contaminated by about 500 different chlorinated organic compounds. In the aquatic
system, the dark brown color of paper mill effluent blocks the photosynthesis and
decreases the dissolved oxygen (DO) level, which leads to adverse effects on flora
and fauna and poses toxicity to aquatic ecosystem (Latorre et al. 2007; Sponza
2003). The accumulation of toxic pollutants and metals in effluent contaminated soil
causes adverse effect on growing plant system (Kumari et al. 2014; Raj et al. 2014a,
b; Haq et al. 2016b). The characteristics of some pulp and paper mill effluent are
given in Table 14.2. Major pollutants found in wastewater or effluents are briefly
discussed below:
4.1 Organic Pollutants and Suspended Solids
In pulp and paper wastewater, there are many components such as cellulose,
hemicellulose, fugitive fibers, starch, and organic acids which are mainly responsible
for organic pollution. This results in a COD discharge of pulp in the range of
25–125 kg/ton1‒. In the aquatic ecosystem, high concentration of BOD and COD
value is responsible for depletion of dissolve oxygen. There are several toxic
components like fatty acids, resin, and toxic metalloids which are present in pulp
mill wastewater and absorbed by the organic solids. Further, it causes long-term
342
I. Haq and A. Raj