membranes technologies address emerging contaminants...february 25, 2008 p. 13-17. epa/625/r-00/015...
TRANSCRIPT
America’s Authority in Membrane Treatment
Membranes Technologies Address Emerging Contaminants Overview
Research is documenting with
increasing frequency that many
inorganic, organic and microbial
constituents that have not historically
been considered as contaminants are
present in the environment at low
quantities on a global scale. These
“emerging contaminants” are
commonly derived from municipal,
agricultural, and industrial wastewater
sources and pathways. These newly
recognized contaminants represent a
shift in traditional thinking as many are
produced industrially yet are dispersed
to the environment from domestic,
commercial, and industrial uses.
Emerging contaminants will affect
current and future treatment
technologies utilized by the drinking
water community. Membrane processes
will be carefully examined, possibly as
a tool in the tool box, in order to deal
with these contaminant removal
challenges.
What are emerging contaminants
and where did they come from?
Advanced analytical capabilities have
allowed scientists to identify chemicals
in the environment at extremely low
concentrations. Emerging contaminants
(ECs) are those chemicals that recently
have been shown to occur widely in
water resources and identified as being
a potential environmental or public
health risks. ECs are used every day in
our homes, on our gardens, by
agricultural and other businesses and
industry. ECs include detergents,
fragrances, personal care products,
prescription and non- prescription
drugs, disinfectants and disinfection
by-products, pesticides, herbicides and
Nano-materials. The occurrence of
emerging contaminants correlates with
ecological effects and sexual
abnormalities in fish, although a
cause-and-effect relation has not been
confirmed nor links between ECs and
the environment been specifically
established. For example, we
acknowledge that the feminization of
fish and amphibians has been linked to
exposure to compounds that mimic
estrogen activity; however, it has also
been determined that thousands of
compounds have the potential to
interact with components of the
endocrine system altering the natural
action of the hormone. Table 1 presents
a partial listing of emerging
contaminants found in wastewater
effluent and the aquatic environment.
The recent EPA Contaminant
Candidate List (CCL) selected 116
candidates, many of which also fit in
this category.
A study conducted by the U.S.
Geological Survey as part of its’ Toxic
Substances Hydrology Program did,
however, detect 82 chemicals in 80
percent of 139 streams and waterways
tested between 1999 and 2000. The
most common chemicals were steroids
(anti-inflammatory drugs), antibiotics,
nonprescription drugs, caffeine and
insect repellent. Potential water quality
contaminants originated from
wastewater discharges, run-off from
agricultural and industrial land uses and
discharge from individual septic
systems. Emerging chemical
contaminants, such as industrial solvent
stabilizers (1,4-dioxane), fuel
oxygenates (MTBE and TBA),
disinfection byproducts (NDMA),
pharmaceuticals (antibiotics/ drugs),
personal care products (polycyclic
musks), pesticides and herbicides
(1,2,3- trichloropropane), algal toxins,
emerging pathogens, and other
persistent compounds such as flame
retardants (PBDEs) and phthalates,
illustrate many technical and
institutional challenges.
Membrane processes offer promise
for resolving many emerging
contaminant concerns
Conventional wastewater treatment
varies greatly in its ability to eliminate
drug or personal care product residues.
Additional treatment may be required
in the future either at the effluent
discharge location or prior to the
point-of-entry to the drinking water
distribution system. Membranes are
effective for the treatment of organic
precursor matter and show promise for
meeting removal targets for emerging
contaminants.
Although there are several mechanisms
affecting contaminate removal by
membranes, size exclusion is very
significant and can be used to describe
membrane capability. If the
contaminant is too large to pass through
the membrane pore, then it is removed
from permeate or filtrate streams.
Contaminants can be categorized
simply as microbiological (i.e.
pathogens), organic solutes, and
inorganic solutes. Pathogens can be
subdivided into cysts, bacteria and
viruses. Organics can be subdivided
into DBPs and their total organic
carbon (TOC) natural precursors,
synthetic organic compounds (SOCs)
and volatile organic chemicals (VOCs).
Inorganic parameters refer to such
contaminants as total dissolved solids,
total hardness, heavy metals and other
inorganic contaminants.
Reverse osmosis (RO) and
nanofiltration (NF) are pressure driven
membrane processes that can remove
contaminants to 0.0001 µm and 0.001
µm respectively. RO and NF are both
diffusion and size exclusion controlled
processes. However, no process is
capable of absolute removal.
RO and NF processes have the broadest
span of treatment capability but require
the greatest degree of pretreatment.
Ultrafiltration (UF) membranes can
achieve greater than six-log removal of
all pathogens from drinking water
whereas microfiltration (MF) can
achieve greater than six-log removal of
cysts. Consequently, membrane
processes are ideal for removing
|turbidity and microbiological
contaminants, and they are well suited
for treating the majority of drinking
water sources in the United States.
Membrane processes do not remove
dissolved gases such as methane,
carbon dioxide and hydrogen sulfide.
Log rejection will increase as flux
increases and decrease as recovery
increases in diffusion controlled
membrane processes (primarily NF and
RO). No change will occur in size
exclusion controlled processes
(primarily MF and UF). Pathogen
removal by NF or RO is controlled by a
size exclusion mechanism, whereas ion
removal is diffusion controlled.
Removal of organic compounds
exhibits both mechanisms. Diffusion
controlled processes would have the
flexibility of decreasing recovery to
produce a higher water quality if more
feed water could be drawn to meet
demand.
Table 2 presents examples of treatment
effectiveness for NF and RO with
regards to specific endocrine disruptors.
Membranes have distinct treatment
advantages relative to these and other
emerging contaminants. RO or NF
membranes are capable of meeting the
EPA’s DBP maximum contaminant
levels by removing enough total
organic carbon (TOC) or other DBP
precursors such that free chorine can be
used for disinfection without exceeding
regulated levels within the distribution
system. Pressure driven membrane
processes can reject five to six logs of
viruses, bacteria or cysts, exceeding
most if not all treatment capabilities of
any other single process.
RO or NF membranes can reject small
molecular weight pesticides, are used to
meet stringent European standards and
will likely reject the higher molecular
weight pharmaceuticals (PHACs),
endocrine disruptors, algal toxins, and
similar compounds. There are no
significant water quality disadvantages
to membrane utilization.
The significant membrane
disadvantages are well-known cost and
concentrate disposal issues. However,
costs have reduced due to technological
innovation and concentrate disposal is
not a technical but regulatory burden.
Membranes can meet or exceed current
and pending water quality regulations.
The fundamental question that society
will have to answer is “How much are
we willing to pay for actual, or
perceived, water quality treatment
needs.”
Emerging contaminant issues will
continue to evolve
Unregulated and emerging chemical
contaminants present numerous
technical and institutional challenges to
environmental and public health
professionals. Increasingly advanced
analytical techniques have documented
the emergence of newly detected
inorganic, organic and microbial
chemicals in actual or potential sources
of drinking water.
As our ability to detect these agents has
improved, the number of contaminants
that need to be evaluated for potential
health risks has grown dramatically.
Despite these advances, many
contaminants remain unregulated, and
the number of such unregulated
contaminants will continue to increase
in the future. Consequently,
environmental professionals must make
difficult risk management decisions
regarding water resource and water
supply management issues in the face
of considerable regulatory uncertainty.
While some technologies do not
effectively remove many of these
contaminants from water, membrane
technologies have been shown to be
effective in removing many of the ECs
of concern as either stand-alone
processes or when integrated with other
advanced technologies. Risk
management decisions in the future will
require complex assessments of the
vulnerability of a water supply source
to unregulated contaminants and
include an analysis of the appropriate
combination of treatment processes
required to meet both current and future
water quality concerns arising due to
these contaminants. Cost must always
be considered in the final analysis.
Sources utilized in this fact sheet:
Majority of the data for this fact
from a publication by Dr.
Steve Duranceau who is past
President of AMTA, and is one of
the founding members of the SEDA
and SWMOA.
B. Half o rd. “Side Ef fects”
and Engineering News
(C&EN) Vol 86., No. 8,
February 25, 2008 p. 13-17.
EPA/625/R-00/015 Removal of
Endocrine Disruptor Chemicals
Using Drinking Wa ter r tment
ocesses. March 2001. Washington
DC.
George , E and Y. Li “Emerging
Contaminants in Ground & Surface
Waters” NEHA Annual Educational
Conference, Anchorage, Alaska, May
11, 2004
Andaluri, G. et al. “Pharmaceutical
Chemical Contaminants in Surface
Waters and their Aqueous
Destruction Using Ultrasound.”
AWWA Annual Conference,
Toronto, Ontario, Canada;
June 24-28, 2007
J. Oppenheimer and R. Stephenson.
“Emerging Contaminants: Insights to
the most effective EDC and PPCP
Treatment Strategies.” Opflow,
Vol. 34, No. 5, May 2008.
K.A. Reynolds. “Concern of
Pharmaceuticals in Drinking Water.”
Water Conditioning and Purification,
Vol. 50, No. 4, April 2008.
Pontius, F. USEPA EDC Workshop,
Jan. 29-30, 2002; Cincinnati, OH
S. Snyder, P. Westerhoff et al.
Removal of EDCs and
Pharmaceuticals in Drinking and
Reuse Treatment Processes. Denver,
CO: Awwa Research Foundation,
2007.
S. Snyder, B.J. Vanderford et al.
State of Knowledge of Endocrine
Disruptors and Pharmaceuticals in
Drinking Water. Denver, CO: Awwa
Research Foundation, 2008.
Tabe et al. “Occurrence of PPCPs
and EDCs in Detroit River and Their
Removal Using Ozone Processes.”
AWWA Annual Conference,
Toronto, Ontario, Canada;
June 24-28, 2007.
This material has been prepared as an
educational tool by the American Membrane
Technology Association (AMTA). It is
designed for dissemination to the public to
further the understanding of the contribution
that membrane water treatment technologies
can make toward improving the quality of
water supplies in the US and throughout the
world.
For more information, please contact:
American Membrane Technology
Association (AMTA)
2409 SE Dixie Highway
Stuart, Florida 34996
Phone: (772) 463-0820
Fax: (772) 463-0860
Email: [email protected]
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(FS-18) Nov. 2011