2013). Effluent emerged from elemental chlorine bleaching process showed reduction in effluent toxicity and also symptomatic changes but not absence of chronic
impacts (Munkittrick and Sandstrom 1997). However, recent studies showed that
effluent emerged from elemental chlorine-free (ECF) or total chlorine-free (TCF)
processing still exhibited acute lethality in their discharges (Sepulveda et al. 2003).
These suggest that there are many other compounds present in paper mill effluent
which are potential to cause toxicity in aquatic organisms. Paper industry having
secondary effluent treatment process had a huge impact on effluent quality. Disappearance of acute effect of paper mill effluent due to process changes and improvement has been observed (Munkittrick and Sandstrom 1997).
6 Wastewater Treatment Process
The Indian pulp and paper industries use conventional primary and secondary
treatment process for the treatment of wastewaters.
6.1 Primary Treatment
Generally, in the primary treatment process, reduction of suspended solids (fibers,
bark particle, filter, coating materials, etc.) has been achieved by the use of screens
and settling tanks. Primary treatment devices are used to remove the large suspended
or floating solids, heavy inorganic solids such as sand and gravel, as well as metal or
glass. These solids consist of pieces of wood, cloth, paper, plastics, garbage, etc.
Primary treatment of effluents consists of two main processes, preliminary treatment
and primary sedimentation. The devices of this treatment system reduce the velocity
and dispense the flow of wastewater. In primary treatment, the velocity of flow is
reduced to 1–2 feet/min‒1 to maintain a quiescent condition so that the material
denser than water will settle out and material less dense than water will float to the
surface. The effluent from primary treatment therefore contains mainly colloidal and
dissolved organic and inorganic solids. This additional removal of organics can be
accomplished by secondary treatment.
6.2 Secondary Treatment
In the secondary treatment process, various types of bioreactors are used for the
mitigation or removal of wastewater contaminants. The most common bioreactors
are activated sludge process (ASP), aerated lagoon (AL), membrane bioreactors
(MBBR), and biofilm process for degradation of organic pollutants by suspended
growth biomass. At present most of the paper industry effluent treatment process is
14 Pulp and Paper Mill Wastewater: Ecotoxicological Effects and. . .
345
impacts (Munkittrick and Sandstrom 1997). However, recent studies showed that
effluent emerged from elemental chlorine-free (ECF) or total chlorine-free (TCF)
processing still exhibited acute lethality in their discharges (Sepulveda et al. 2003).
These suggest that there are many other compounds present in paper mill effluent
which are potential to cause toxicity in aquatic organisms. Paper industry having
secondary effluent treatment process had a huge impact on effluent quality. Disappearance of acute effect of paper mill effluent due to process changes and improvement has been observed (Munkittrick and Sandstrom 1997).
6 Wastewater Treatment Process
The Indian pulp and paper industries use conventional primary and secondary
treatment process for the treatment of wastewaters.
6.1 Primary Treatment
Generally, in the primary treatment process, reduction of suspended solids (fibers,
bark particle, filter, coating materials, etc.) has been achieved by the use of screens
and settling tanks. Primary treatment devices are used to remove the large suspended
or floating solids, heavy inorganic solids such as sand and gravel, as well as metal or
glass. These solids consist of pieces of wood, cloth, paper, plastics, garbage, etc.
Primary treatment of effluents consists of two main processes, preliminary treatment
and primary sedimentation. The devices of this treatment system reduce the velocity
and dispense the flow of wastewater. In primary treatment, the velocity of flow is
reduced to 1–2 feet/min‒1 to maintain a quiescent condition so that the material
denser than water will settle out and material less dense than water will float to the
surface. The effluent from primary treatment therefore contains mainly colloidal and
dissolved organic and inorganic solids. This additional removal of organics can be
accomplished by secondary treatment.
6.2 Secondary Treatment
In the secondary treatment process, various types of bioreactors are used for the
mitigation or removal of wastewater contaminants. The most common bioreactors
are activated sludge process (ASP), aerated lagoon (AL), membrane bioreactors
(MBBR), and biofilm process for degradation of organic pollutants by suspended
growth biomass. At present most of the paper industry effluent treatment process is
14 Pulp and Paper Mill Wastewater: Ecotoxicological Effects and. . .
345