Page 35 - Industrial Wastewater Treatment, Recycling and Reuse

18 Industrial Wastewater Treatment, Recycling, and Reuse

combined nitrogen content of 40–60 mg/L, while industrial wastewaters
can have ammoniacal nitrogen up to a few thousand mg/L. Ammoniacal
nitrogen removal can be carried out by biological or physico-chemical
means, or a combination of these methods. Available technologies include
adsorption, chemical precipitation, membrane filtration, reverse osmosis
(RO), ion exchange, air stripping, breakpoint chlorination, and biological
nitrification and denitrification (Metcalf and Eddy, Inc. 1991). Conven-
tional methods such as chlorination, electrodialysis, RO, and distillation,
however, are not efficient and are cost intensive. For wastewaters containing
a large ammoniacal nitrogen content, if other pollutants are satisfactorily
removed, the water can be used as a nitrogenous fertilizer. The fertilizer
effect can be augmented by suitable addition of phosphate, which can sub-
stantially enhance its application directly as a fertilizer for agriculture. Con-
ventionally, stripping/ion exchange or biological processes are used for
removal of ammonia. A pH of 9–10 is required for air-stripping ammonia.
Further, it may result in air pollution. In biological processing, the time
requirement is very high and even sludge of 10 days may not appreciably
oxidize ammonia, indicating lower performance in the biological processes.
Thus, the total volume of wastewater as well as the chemical analyses
indicating the organic and inorganic components along with toxicity eval-
uation is essential for conceptualizing the scheme of overall wastewater
treatment, recycling, and reuse. It would also help in plant design for treating
wastewater once the appropriate methodology is identified based on
the above.

1.3 STRATEGY FOR WASTEWATER MANAGEMENT

Key issues in industrial wastewater treatment, recycling, and reuse in today’s
context can be briefly outlined as follows (Figure 1.8):
1. Can we avoid liquid discharge?
• (Aspire to zero liquid discharge)
2. Can we reuse treated water?
• (At least as cooling water or boiler makeup if not as process water)
3. How do we manage process economics?
• (In terms of money and space)
• Where is the dedicated space for the process plant?
• Treatment cost: Rs X/liter
4. Beyond 3Rs
• (Reduce, recycle, and reuse)