Recycling Treated Municipal Wastewater for Industrial Water Use

Section 2
Implementation Considerations
Craddock Consulting Engineers
In Association with CDM & James Crook 2-23
TM1-Sec2_0707.doc
Filtration, nitrification, denitrification, and phosphorus removal are processes that are
commonly used at municipal wastewater treatment facilities. In 20 years, Minnesota
regulations will likely be in place that could require these or alternate new processes
to meet discharge limits. Carbon adsorption and UV treatment of NDMA are
processes used to address specific organic contaminant removal. NDMA is a potent
carcinogen produced with use of chlorine or chloramines for disinfection. To address
concerns with NDMA and other trace organics in reclaimed water, several utilities in
California have installed UV/hydrogen peroxide treatment systems for treatment of
reverse osmosis permeate [CDM, 2004].
Carbon adsorption, a process used by potable water supply systems for taste and
odor control or removal of organic contaminants, can be used to reduce the
biodegradable and refractory organic constituents in wastewater effluent. Carbon
adsorption following a secondary treatment and filtration treatment train can produce
an effluent with a BOD of 0.1-5 mg/L, a COD of 3-25 mg/L and a TOC of 1-6 mg/L.
It can also be used to remove several metal ions, particularly cadmium, hexavalent
chromium, silver, and selenium. Activated carbon has also been used to remove
uncharged elements such as arsenic and antimony from an acidic stream. Endocrine
disrupting compounds have also been successfully removed with activated carbon
[Hunter and Long, 2002]. The use of activated carbon for reclaimed water would be a
very industry specific requirement.
Given that filtration is typically required
prior to the carbon adsportion process,
and that most municipal plants in
Minnesota do not have filters, a different
technology, notably membranes, might
be selected to meet organic and metal
removal goals, as well as serve other
process needs.
Membrane processes are moving into the
wastewater treatment arena. They have
been used for water reclamation in much
the same capacity as for potable water
supply treatment. Figure 2.2 shows a
Figure 2.2. Membrane System Used as a
Tertiary Treatment Process.
typical membrane system for tertiary treatment. New technologies are providing the
ability to use membranes in the secondary process train. This advancement provides
flexibility and/or simplification of the process train to meet wastewater process
performance goals and produce the higher quality effluent required for many reuse
applications.
The type of membrane used is dependent on the various quality goals. As an
extension from potable water industry applications, membranes are typically
characterized by the pathogen requirements as shown in Figure 2.3. For industries,
other constituents are targeted to select the proper membrane system. The West Basin
Municipal Water District of Carson, California, produces several grades of reclaimed