POWER December 2015 - 58

WATER TREATMENT
Water-Stressed Regions Provide
Proving Grounds for Advanced ZLD
Systems
Zero-liquid discharge (ZLD) water treatment is already required in some parts
of the world, and the experience gained in those areas with new technologies
may help power generators in other regions evaluate their options as
regulations or resource issues make ZLD increasingly important.
John Tracy
I
n water-stressed regions outside the U.S.,
power producers and other industrial water
users are incorporating higher levels of
water reuse, some to the point of zero liquid
discharge (ZLD), due to heightened regulatory
pressures and for economic reasons. In
China, new power plant and chemical plant
project approvals require inclusion of ZLD
water treatment technology as a result of
directives in the Chinese government's 12th
Five Year Plan. In India, based on the successful
implementation of ZLD requirements
on industrial plants in the southern state of
Tamil Nadu, other regions of the country are
introducing water reuse and ZLD requirements
for power producers and refineries. In
both countries, state-led technical agencies
have taken on the role of guiding companies
toward best available technologies to solve
wastewater problems and to develop water
reuse and ZLD capabilities.
The steps taken by China and India provide
examples for U.S. industrial water users,
power producers in particular, to evaluate the
newest methods of high-recovery water treatment
as they plan their paths to compliance
with more stringent water regulations.
China's Focus on Industrial ZLD
As China builds out infrastructure to further
exploit its massive coal reserves, it is incorporating
technologies to curb the increase of
toxic gas and particulate emissions via SOx
and NOx
abatement, and is mandating water
reuse and ZLD processes for new and existing
plants. New and existing coal-fired power
plants, together with coal-to-chemicals
refining facilities, are targets for these ZLD
mandates, and in both sectors the rate of new
plant construction is staggering. A World
Resources Institute report in 2013 detailed
China's plan to construct 363 new coal-fired
power plants, adding more than 550 GW of
capacity to the existing 758 GW of coal pow58
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POWER
| December 2015
er. Additionally, the Financial Times in 2014
reported on 18 coal-to-chemical projects under
construction in China, with a total of 54
in the pipeline for possible construction.
China's water treatment design institutes,
which are consultants and technology decision-makers
on the wastewater process technologies
for these projects, have sought out
best-in-class technologies for reducing the
energy consumption and cost of wastewater
pretreatment, brine concentration, and final
crystallization of salts for disposal or resale.
They have been early adopters of advanced
technologies such as forward osmosis (FO)
for high-recovery treatment of waste streams
at lower capital cost and energy consumption
than traditional, evaporative technologies.
In fact, the treatment trains most commonly
recommended by the design institutes for
adoption in new ZLD projects have used
either multi-effect evaporation for the brine
concentration step or FO for the brine concentration
step, as shown in Figure 1.
In coal power and coal-to-chemical plants
in China the typical wastewater streams treated
to ZLD are flue gas desulfurization (FGD)
1. Common process flows for Chinese coal power and coal-to-chemical
ZLD projects. Courtesy: Oasys Water
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POWER December 2015

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