Page 82 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 59

the removal of colloids to a great extent. The effluent contains dissolved
solids (TDS) mostly in the form of salts/inorganics/heavy metals that can
be removed by processes such as adsorption, ion exchange, chemical precip-
itation, and the more expensive membrane-based methods such as NF, RO,
and electrodialysis. A major part of the pollution load is in the form of
organics (BOD/COD/TOC) that can be removed using oxidations,
adsorption/ion exchange, chemical precipitation, and higher-end mem-
brane separations (e.g., UF/NF and RO), apart from biological processes
(such as aerobic and anaerobic processes). Most of the methods generate sec-
ondary waste streams in the form of sludge or a secondary stream, though on
a much smaller scale compared to the wastewater treated. These secondary
streams have to be disposed of using appropriate means. For industrial waste-
water treatment process engineering, typically the following formats are
most popular.
Primary treatment (Basic clean-up/physical methods)
– Filtration (dual media, carbon, sand filters)
– Screening, grit removal, and sedimentation for sludge/solid
removal
Secondary(removes85–95%ofBOD/CODandTSS;20–40%P;0–50%N)
– Neutralization/stabilization
– Coagulation/clarification
– Biological treatment (aerobic/anaerobic)
– Physico-chemical methods
– Hybrid separations
Tertiary/Polishing treatment (removes >99% of pollutants)
– Adsorption/ion exchange/membranes
– Hybrid separations.
Industrial wastewater process engineering involves identification of process
stages in accordance with the nature and concentration of pollutants and
desired goals for wastewater treatment. Typically, goals for transforming
wastewater to make it suitable for discharge into surface water bodies differ
significantly from those for water recycling and reuse. The cost of operation
and maintenance is of prime importance in process engineering and design.
A brief review of industrial wastewater treatment for some specific industries is
given in Table 1.5, mainly representing textile and dye industry wastewater
treatment (Amaravati ETP- Das, www.fibre2fashion.com/industry-article/
3/215/textile-effluent-treatment-a-case-study-in-home-textile-zone1.asp;
Egypt Textile ETP- Seif and Malak, 2001; Cotton Textile, Mumbai- Babu,
2008; Dye wastewater for recovery of salt- CPCB India, 2007; Arulpuram