Recycling Treated Municipal Wastewater for Industrial Water Use

Section 2
Implementation Considerations
Craddock Consulting Engineers 2-17
In Association with CDM & James Crook
TM1-Sec2_0707.doc
the release of carbon dioxide, which is a source of corrosion in steam-using
equipment. Silica and aluminum form a hard scale on heat-exchanger surfaces, while
high concentrations of potassium and sodium can cause excessive foaming in the
boiler. Depending on the characteristics of the reclaimed water, lime treatment
(including flocculation, sedimentation, and recarbonation) may be required, possibly
followed by multi-media filtration, carbon adsorption, and nitrogen removal. Highpurity
boiler-feed water for high-pressure boilers might also require treatment by
reverse osmosis or ion exchange [Meyer, 1991]. The considerable treatment and the
relatively small amounts of makeup required make boiler-feed a poor candidate for
reclaimed water.
Process Water. The suitability of reclaimed water for use in industrial processes
depends on the particular use and is highly variable. For example, the electronics
industry requires a very high water quality for washing circuit boards and other
electronic components. On the other hand, the tanning industry can use relatively
low-quality water. Requirements for textiles, pulp and paper, and metal fabricating
are intermediate.
Use of reclaimed water in the paper and pulp industry is a function of the grade of
paper produced. The higher the quality of the paper, the more sensitive it is to water
quality. Impurities found in water, particularly certain metal ions and color bodies,
can cause the paper to change color with age. Biological growth can cause clogging of
equipment and odors and can affect the texture and uniformity of the paper.
Corrosion and scaling of equipment may result from the presence of silica, aluminum,
and hardness. Discoloration of paper may occur due to iron, manganese, or microorganisms.
Suspended solids may decrease the brightness of the paper.
Water used in textile manufacturing must be nonstaining; hence, it should be low in
turbidity, color, iron, and manganese. Hardness causes curds to deposit on the textiles
and causes problems in some of the processes that use soap. Nitrates and nitrites may
cause problems in dyeing.
Recommended Industrial Water Quality
Each industrial use of reclaimed water has unique water quality requirements, and it
is not possible to elaborate on the recommended requirements for the myriad of
possible industrial applications in Minnesota. However, water quality guidelines are
available for some common industrial uses of water, such as cooling water (Table 2.7)
and boiler feed water (Table 2.8). Recommended water quality for several other
industrial applications are listed in Table 2.9.
Tables 2.7-2.9 demonstrate that the water quality requirements vary considerably with
the type of industry and specific processes. Requirements for specific Minnesota
industries will be presented in the project final report as part of Task 2 work activities.