Page 87 - Industrial Wastewater Treatment, Recycling and Reuse

62 Industrial Wastewater Treatment, Recycling, and Reuse

plant ETP- Hussain, 2012; Raymond Textile Kolhapur ETP- Desai and
Kore, 2011; Silk and Dyeing Mill, Shaoxing- Wang et al., 2011; Printing
and dyeing mill, Baijing- Wang et al., 2011). It is evident that for discharge
of wastewaters in surface water bodies such as rivers, often an appropriate
combination of primary and secondary methods is quite adequate. How-
ever, in the case of priority pollutants and for satisfactory water recycling
and reuse, usually tertiary treatments are essential.
It is important to design proper sequencing of different operations to
meet the desired levels of pollutants in the treated water, keeping cost con-
siderations in mind. For example, bioprocesses for ethanol production gen-
erate wastewaters with high BOD amenable for treatment using biological
methods. Here, anaerobic treatment is done first in view of the high organic
load, and then the aerobic process is applied to meet the desired effluent stan-
dards. In the first step, nearly 80–90% of COD is removed, and then the
partially treated wastewater with reduced organic load is sent for aerobic
treatment. This scheme of treatment is more efficient: High-strength waste-
waters are used for gathering energy in the form of biogas, while an aerobic
process is employed to perform the remaining task of getting clear water
without appreciable odor problems (which is otherwise difficult with an
anaerobic process alone). If the treated waters still continue to have odor
problems, a tertiary treatment/polishing is essential.
It is also important that a comparison of two or more methods is required
for techno-economic feasibility analysis of the wastewater treatment. It is
quite possible that both physico-chemical methods and biological methods
may be able to achieve desired effluent goals. In that event, it is necessary to
closely evaluate cost performance of the methods for the selection made. An
example of this is shown in Figure 1.19 for effluent from a steel plant
(Sirajuddin et al., 2010). Two methods have been compared, carbon adsorp-
tion from the class of physico-chemical methods and a biological method. It
can be seen that efficiency of carbon treatment is better in all respects for
BOD and COD removal. Integrated adsorption and biological treatment
methods can provide excellent solutions in removing BOD, COD,
organics, and pharmaceutical and pesticide pollutants apart from inorganics
such as some heavy metals, ammonia, and nitrates (Ferhan, 2011).

1.6.1 Newer Modifications in the Existing Methods
Separation technology is an essential component in most chemical process
operations and is considered to be the most critical component