Progress in the Quest for a Solution to Emerging Contaminants and Landfill Leachate
21 February 2019
The
search is on for a solution to a problem caused by a growing global
population: more garbage. And it’s not just the volume of trash, but the
fact that it can contain increasing volumes of materials with
contaminants of emerging concern.
Constituents from these materials often make their way into
landfill
leachate, which requires treatment before being released into the
environment. Landfill owners and operators are challenged with
finding a cost-effective and reliable method of managing contaminated
leachate.
The problem becomes more acute as science discovers the potentially
harmful effects of some leachate constituents, some of them from new
sources and some coming from products used for decades. One example of
constituents found in many leachates, which have the potential for
adverse human health impacts, is Per-and Poly-Fluoroalkyl Substances,
collectively known as
PFAS. PFAS are commonly used in products ranging
from breathable outerwear to non-stick cooking pans. When these products
are disposed of, some of their PFAS content can be released and enter
the landfill’s leachate. Other sources of PFAS can include bio-solids
from
wastewater treatment plants (WWTP), industrial wastes, or
contaminated soils that may be disposed of in the landfill.
PFAS pose problems for biological treatment systems which are typically
used for leachate (by onsite facilities or direct discharge to a WWTP)
as these systems are often unable to remove some constituents including
PFAS. Moreover, the treatment of leachate containing PFAS at a
centralized WWTP can generate PFAS concentrated sludge which may be land
applied or disposed of at another landfill, thereby spreading PFAS
contamination. Other treatment processes frequently used in drinking
water or groundwater applications for PFAS (such as granular activated
carbon and ion exchange media) are often not suitable for complex
leachate matrices.
With the limitations of biological and media-based treatment, some
landfills are looking to alternative treatment methods such as reverse
osmosis and evaporation, as well as other developing technologies such
as electro-coagulation (EC) and electro-oxidation (EO). Technologies
developed for other applications such as macro porous polymer extraction
(MPPE) are also being tested for potential PFAS removal. The variability
between different leachates and other site constraints means that the
preferred treatment process may be different from site to site and may
require site-specific treatability testing before full scale
application.
Electrocoagulation and electro-oxidation may be promising for bulk
removal of PFAS where the concentrations of these compounds are
significantly elevated. These technologies may not always reduce
concentrations to sufficiently low levels and may require additional
polishing. Because EC/EO are promising from the standpoint of simplicity
of operation and avoidance of the use of chemical additions, these
technologies continue to be studied for ways to fine-tune the process to
be capable of treating PFAS to lower levels.
In evaporation, the leachate is heated so that the water converts to a
vapor leaving the leachate constituents within a concentrated slurry
stream. Some landfills use the methane produced by decomposing waste to
fuel the evaporator; however, evaporation has its own problems. One is
that constituents such as PFAS may escape into the atmosphere along with
the
water vapor. Another is that using landfill gas this way means it is
not then available to produce electricity, an income source for some
landfills.
Accordingly, one of the more promising leachate-treatment technologies
is reverse osmosis (RO). It uses a pump and high pressures to push
leachate against a series of semi-permeable membranes. Larger molecules
and particles stay behind, while the smaller water molecules pass
through the membrane to the other side. Today, RO is used in drinking
water, wastewater re-use, and industrial applications, as well as
landfill leachate treatment.
One of the main advantages of RO is that it can deal with a wide range
of contaminants, including PFAS and also has a good chance of being able
to treat contaminants that may become of concern in the future.
RO can, in many cases, produce effluent pure enough that it can be
discharged directly to streams and rivers or could be used for onsite
dust control. The concentrated leachate left behind by the RO process,
generally about ten to twenty percent of the original volume, may be
recirculated or used to optimize waste compaction within the landfill
depending on regulations. Recirculation retains the PFAS in the landfill
and minimizes further spreading of contamination to the environment
although also risks generation of higher strength leachate.
Further management of the concentrated brine would be required in cases
where leachate recirculation is not permitted or there are concerns with
contaminant cycle-up. These management steps could include evaporation,
thermal destruction, and/or solidification/stabilization with placement
back in the landfill.
Paste
technology, long used to manage waste materials in mining, could be
incorporated into solidification/stabilization processes for brine or
treatment residual management.
Golder is currently testing the
combinations of concentrated leachate with coal ash to produce an inert
physical mass called “paste,” which hardens to lock the harmful
constituents away long-term.
Many factors including sustainability, site-specific constraints,
capital and operating costs, and an understanding of the latest
advancements are critical to developing the best overall solutions.
Leachate treatment for contaminants of emerging concern such as PFAS can
represent a significant challenge, however new developments and
technology applications are helping to overcome these challenges.
ABOUT THE AUTHOR
Ryan Schipper, PE, is a civil engineer specialized in water treatment. He has designed and provided construction support for bench, pilot, and full-scale treatment systems at sites throughout North America. His experience includes water treatment alternative evaluations, treatability studies, preliminary and detailed design, construction oversight, and start-up support.
Carlo Zaffaroni, PhD, PE, has 25 years’ experience in industrial water-wastewater treatment (including advanced treatment for low discharge limits and/or re-use) and thermal treatment of wastes. His experience ranges from consulting to engineering, design & build, and operations support. Dr. Zaffaroni provides senior technical assistance to industrial clients in Europe, Middle East, North Africa and India.
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