Page 40 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 23

streams also emerge from regeneration of adsorption/ion exchange pro-
cesses. The recovery of valuable products from wastewaters can be
attractive propositions in terms of value addition to the existing process
and increasing economic feasibility of wastewater treatment operations.
7. Plant-/process-specific measures: Reduction and recycling of waste are
inevitably site and plant specific. A number of recommendations have
been made in the literature in this regard that include installing
closed-loop systems, recycling on site for reuse, recycling off site for
reuse, and exchanging wastes for further application.

1.4 SEPARATION PROCESSES AND CONVENTIONAL
METHODS OF WASTEWATER TREATMENT

A number of separation processes have been well established in the area of
chemical engineering separations and in wastewater treatment. The drive is
to improve:
- Purity or lower impurities level by removing selected component(s)
- Energy efficiency by using most appropriate separation technology
- Environmental safety and compatibility for meeting regulations
- Economic viability by not putting strain on the process and profitability
- Sustainability (recycling and reuse) of the industry, in general.
In the area of wastewater treatment, typically the operations are classified as
primary, secondary, and tertiary based on the nature of separation processes
selected and outcome of the process. As a general rule, primary treatments
are size-based separations using physical methods such as sedimentation/fil-
tration for basic cleanup. The secondary treatment mainly involves physico-
chemical methods and/or biological methods and is capable of removing
85–95% of BOD/COD and TSS from the wastewaters. Tertiary treatment
involves the final polishing of the effluent by removing toxic/harmful pol-
lutants to desired levels; more than 99% removal can be achieved at the end
of tertiary treatment.
The primary processes produce wastewaters that are not suitable for dis-
charge or for recycling and reuse, the main objective being to produce water
quality suitable for treatment involved in secondary and tertiary separations.
The primary processes mainly have a mandate for protecting processes and
materials that are to be used in secondary/tertiary treatments in order to
avoid process failure. A prominent example of this is pH modifications/
filtration/clarification before sending the stream for membrane separa-
tions/adsorption/ion exchange. The separation processes that are typically