35    WATER REUSE AND RECYCLING IN INDUSTRY
Menahem Rebhun, Visiting Professor
Department of Civil Engineering, Virginia Polytechnic Institute and State University
Blacksbay, Virginia 24061
PROBLEM STATEMENT
Wastewater reuse is an essential factor in water resources management in many arid, semi-arid and
other water-short regions. Also in water-rich regions, there might be local areas where as a result of
dense population, intensive industrial activity and developments, the high water consumption and
demand may exceed the safe yield of local resources, resulting in a local or subregional deficit. The
industrial consumption in such areas may constitute a significant part of the total; therefore, reuse for
industry and internal recycle in industrial plants should be seriously considered when planning water
supply and resources management.
Reclamation for industrial use has several distinct advantages: due to the proximity of most
industries to large population centers, and thus, to the source of wastewater, the transportation costs
of renovated water are minimal; most industrial consumptions are constant in flow, permanent
throughout the year, therefore, seasonal storage is not required; reclaimed wastewater is a reliable
source of water and the industrial consumer is a reliable recipient; the product value per unit of water
used in industry is often high, enabling economically justifiable advanced treatment processes, contributing to improved water and environmental quality control; and, the advanced purification processes, usually required in reuse schemes, are often similar in nature and equipment to processes used in
industrial water conditioning.
REUSE FOR COOLING SYSTEMS
Cooling systems are major water consumers in many industries and in power stations and excellent
candidates for utilization of renovated wastewater. In water short regions, recirculating cooling water
systems with cooling towers (See Figure 1) are used, rather than once-through systems. As a result of
expansion and development in the large Haifa refinery and petrochemical complex, the cooling water
circulation rate reached 30,000 m3/h (195 mgd) (in a once-through cooling system this would be the
amount required and impossible to supply) with a make-up comsumption of 600 mVh (4 mgd). While
supplying the 4 mgd from fresh water sources posed serious problems in this water short area, a
nearby municipal treatment plant produced 20 mgd of secondary effluent. The reuse of this effluent
has been selected as a source for make-up water to the cooling system (See Figure 2). Water quality
factors were related to three major problems encountered in circulating water cooling systems: scaling, corrosion, and biofouling.
E
EVAPORATION
M,CM     _l
MAKE   UP
R
RECIRCULATION
COOLING  TOWER
EXCHANGER
B.C
B
SLOWDOWN
• CONCENTRATION    CYCLES
Figure  1.    Schematic of recirculating cooling
system.
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