Page 151 - Sustainability in the Process Industry Integration and Optimization

128 Cha p te r S i x

Freshwater main Process water main Wastewater main

Temperature water users water users
Process
Process

Overflow

Water quality

- Water source
- Water demand/sink
FIGURE 6.4 Two-dimensional diagram of a water quality network (after
Savulescu and Kim, 2008).

compared with operations when only water minimization is
performed). This case study clearly demonstrated the necessity of a
holistic approach to designing water and energy systems, since there
are significant benefits to simultaneous integration.
6.3.2 Oxygen-Water Pinch Analysis

The link between Water Pinch Analysis and Oxygen Pinch Analysis
is the use of COD as the concentration variable in Water Pinch
Analysis. Here two configurations of wastewater treatment are
investigated, centralized and distributed. The analyzed system
includes the centralized biological treatment unit and several
satellite factories (sites) in the surrounding area that send some
portion of their wastes to the centralized treatment unit. The
variables of interest when analyzing wastewater treatment are the
quantity of wastewater treated and the quantity of oxygen required.
The quantity of treated wastewater gives an indication of how
much freshwater is used and thus of the water management level.
The quantity of required oxygen gives an indication not only of the
wastewater quality but also of the energy required by the wastewater
treatment process. Both the quantity and the quality of the
wastewater treated are related to the cost of the treatment process.