Page 158 - Industrial Wastewater Treatment, Recycling and Reuse

132 Industrial Wastewater Treatment, Recycling, and Reuse

from biomass, for example, modified bagasse, fly ash, clay, rice husk, and
neem leaf powder, are also used for such applications (Ahmaruzzaman
and Gayatri, 2011; Mane et al., 2003, 2006). However, factoring cost con-
siderations in these applications should essentially consider the costs associ-
ated with the entire removal process rather than the cost of adsorbents alone.
Many times, the biomass-derived adsorbent need not be regenerated and can
be destroyed/burnt as fuel. Typically, the most critical techno-economic
elements for consideration in figuring the cost of adsorbents are the nature
of adsorbents, size of adsorbent (pressure drop vs. rates of removal), cost of
regeneration, life of adsorbent, operating range of pH, and temperature for
most satisfactory selection.
The costs of cavitation operations can be substantially reduced when
compared to other methods of effluent treatment and drastically so when
compared to intensive processes such as oxidation. A typical cost calculation
using hydrodynamic cavitation using a vortex diode as a cavitating device is
as follows:

3 N c DPP E
Cost of treatment=m of effluent ¼
36
where N c is number of circulations needed for the treatment, △P is pressure
drop in atm, P E is price of electricity per kWh, and is efficiency of the
pump. For a typical situation in India, taking the price of electricity as
Rs. 10 per kWh, pump efficiency as 0.66, and pressure drop across the diode
3
as 2.4 atm, the cost of treatment comes out at N c Rs./m of effluent. Typ-
ically, 5–10 recycles are adequate; therefore, the cost is about Rs. 5–10/m 3
of effluent.
Overall, coagulation should be used as an essential step in effluent
treatment, not just to get maximum COD removal, but also to reduce
the overall cost of industrial wastewater treatment, because it has limited
goals and affordable cost. Adsorption and ion exchange are defined processes
for specific pollutants and are required to achieve the desired final objectives
of a wastewater treatment process. Here, the cost of material is significant
and needs to be optimized, mainly through the selection of appropriate
materials and process integration. Oxidation processes are again specific pro-
cesses for the removal of refractory pollutants and are generally cost intensive
due to the cost of catalysts and severe process conditions. Membrane pro-
cesses, as a general sieving process, are not cost intensive but physico-
chemical processes, for example facilitated transport, hybrid membranes,
and ion exchange membranes, can substantially add to the process costs,