Recycling Treated Municipal Wastewater for Industrial Water Use

Section 3: Recycled Wastewater System Components and Costs
Recycling Treated Municipal Wastewater for Industrial Water Use
The tertiary supplies are required for water uses where human contact is likely. Tertiary 1 treatment
processes would be applicable to WWTPs that need to remove phosphorus or hardness and do not need to
remove a significant amount of dissolved salts. The process train consists of conventional chemical
addition, coagulation, flocculation and sedimentation processes, followed by filtration.
The Tertiary 2 supply is based on the use of membrane microfiltration. This technology meets the
regulatory filtration requirements and provides higher pathogen removals than the Base or Tertiary 1
supplies. However, it does not remove hardness as Tertiary 1 treatment does. Similar to Tertiary 1
treatment, Tertiary 2 treatment does not remove dissolved salts. Membrane softening, the key Tertiary 3
treatment process, is required to reduce the dissolved solids, which includes chlorides. For this study,
reverse osmosis was selected as the membrane softening process for the cost analysis. In addition to
removing hardness, reverse osmosis also removes nearly all pathogens, organic and inorganic
compounds. Nanofiltration and electrodialysis are two other potential technologies that could be used to
meet hardness goals, but provide for lower removals and, in the case of electrodialysis, no additional
pathogen removal.
For waters that require very low levels of constituents, advanced processes such as granular activated
carbon, ion exchange, ultraviolet radiation (UV), and UV in combination with oxidants can be used.
These are processes that could be used to treat emerging contaminants of concern that are present at very
low levels. The Tertiary 4 treatment processes are ones that would likely be used by an onsite industry
with its existing water supply. For example, a Tertiary 4 treatment process with ion exchange is a typical
technology used to treat boiler feed water. In this case, the level of treatment provided by a Tertiary 4
process would exceed that provided by a traditional water supply. In some instances, there could be
constituents needing removal that are related to discharges into the sewer system, such as heavy metals
from industry or pharmaceutical-compounds. Tertiary 4 treatment processes could be located at either the
WWTP or industry site depending on the specific attributes of the recycled wastewater application.
An industry sector assessment of treatment needs, presented in Table 3.6, shows the range of options that
an industry would need to evaluate. The variability in WWTP effluent quality and industry water quality
requirements dictates a site-specific evaluation to determine the treatment alternatives. Table 3.6 also lists
the dominant water uses within an industry category and Table 3.7 provides the subcategories for major
industry categories that have a wide range of industry types.
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