to 95 percent liquid discharge recovery at a fraction of
ZLD's costs.
Coined by Dow, the term MLD might be new, but
the processes on which it is based rely on proven water
filtration technologies such as ultrafiltration, reverse
osmosis (RO), and nanofiltration — with a host of
improvements.
Depending on individual regulatory and environmental
needs and requirements, as well as the capital and operating
budget, MLD can be a good fit for many industrial and
municipal sites. By conducting a water audit to match waste
streams and appropriate water requirements, companies
can better identify how much wastewater requires
processing and the approach that will most economically
and sustainably
match their plant's
needs.
An excellent
example of an
"MLD mindset"
in action can
be found at the
General Motors
( G M ) ve h i c l e
assembly plant in
San Luis Potosi,
Mexico, outside
of Mexico City,
which opened in
2008.
3
The plant,
which employs up
to 1,800 and has
an annual capacity
of 160,000 cars, is
located in an arid,
remote area with
no receiving stream
or municipal sewer available to discharge wastewater.
Yet by using a combination of RO technology, a
proprietary high-rate chemical softening process, and
other technologies, the plant can convert up to 90 percent
of its tertiary wastewater into reusable water, leaving less
than 10 percent of liquid waste for discharge into adjacent
solar ponds for evaporation.
Clearly, GM has determined 90 percent to be the
optimal economic number for its wastewater conversion.
That's what MLD is all about — providing users with a
variety of options to achieve the results most optimal for a
particular plant, based on a variety of factors.
And it's important to point out that an MLD approach
still significantly benefits the environment and surrounding
community.
In arid Casa Grande, AZ, for example, Frito-Lay North
America, a division of PepsiCo, is using a membrane
bioreactor (MBR) and activated carbon/low-pressure RO
system to achieve 70 to 75 percent water recovery, saving
more than 100 million gallons of fresh water annually. The
plant is the first in the U.S. to convert food process water
into drinking water quality for direct reuse in production.
4
It's A Journey, Not A Destination
The big challenge lies in adopting this new mindset of
"We can achieve significant gains without breaking the
bank." More companies must realize they don't have to
wait for the perfect ZLD solution when an MLD strategy
will put them on a path toward higher recovery today.
Traditional water treatment technologies have advanced,
and now companies can achieve a better water footprint
without going to the extreme — all while staying within
their budget. By adopting this mindset and evaluating
current systems for areas of improvement, companies can
take significant steps towards a circular economy without
breaking the bank. We are on a journey to zero, but the
major steps along that path are what can ultimately help
us make significant progress along the way. n
References:
1. http://wallstcheatsheet.com/business/why-water-scarcity-is-such-a-big-
problem-for-big-business.html/?a=viewall#ixzz3SnU1HFxj
2. http://www.unwater.org/worldwaterday/learn/en/
3. www.waterworld.com/articles/2011/01/zero-liquid-discharge-accelerates-
across.html
4. www.greentechmedia.com/articles/read/near-net-zero-at-frito-lays-casa-
grande-facility-in-arizona
38
wateronline.com
n
Water Innovations
INDUSTRIALREUSE
As the global business director for Dow Water & Process
Solutions, Snehal Desai is responsible for implementing
business growth strategy and leading the 1,700 people who
work in the business. He is an expert on key industry and global
issues such as water scarcity, quality, and safety, along with the
interdependencies of water and energy.
About The Authors
Steve Rosenberg is a research fellow for Dow Water & Process
Solutions with more than 30 years of industrial experience
in the development of advanced materials. His main focus is
on developing breakthrough innovations for water treatment
technologies such as ultrafiltration, reverse osmosis, and ion
exchange.
Nanette Hermsen is the global marketing director for reverse
osmosis at Dow Water & Process Solutions. In this role, she is
responsible for setting the marketing strategy for the business
unit, driving regional marketing programs, and working closely
with research to identify market aligned innovation targets for
reverse osmosis.
Traditional water
treatment technologies
have advanced, and
now companies can
achieve a better water
footprint without going
to the extreme — all
while staying within their
budget.