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Membrane Filtration Enhances
Landfill Effluent Treatment
Guest article by Greg Johnson, New Logic Research, Inc.
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recent breakthroughs in the membrane filtration industry have now
made it possible for the treatment of some previously difficult
separation applications. New "plate and frame" type
membrane modules can tolerate very high levels of TSS, organics,
and COD. Previous conventional membrane modules with tight feed
channels and limited crossflow capabilities were not able to
effectively handle the high fouling and plugging applications like
Now, with more open high turbulence
membrane modules that are resistant to fouling and plugging,
membranes are becoming a preferred option for treating Landfill
leachate when compared to conventional methods that have been used
for many years.
This article discusses the new
membrane technologies and how they compare to the existing methods
used at municipal landfills in the United States.
The reason for having a landfill is
to contain waste and prevent it from entering into the
environment. In modern landfills, the waste is actually
encapsulated and sealed off to prevent migration of pollutants and
pathogens. The key part of landfill design is the bottom liner on
top of which the solid waste is piled and compressed. The liner is
made of a rugged puncture resistant material like high-density
polyethylene. The liner is also surrounded by compacted clay soil,
geo-fabrics, and other layers of protection.
There are two ways for liquid to
enter into the landfill. One is in the trash itself. Landfills
regulate the moisture content that is allowed when dumping solid
waste. Slump tests and paint filter tests are used to measure
moisture contents. Rainwater also can soak into the landfill and
will result in leachate that must be treated. It is important to
keep the landfill as dry as possible to reduce the amount of
Surface run-off is collected using
ditches and catch basins and is diverted away from the covered
landfill cells. The ditches are either concrete or gravel-lined
and carry water to collection ponds. In the collection ponds,
suspended soil particles are allowed to settle and the water is
tested for leachate chemicals. Once settling has occurred and the
water has passed tests, it is then pumped or allowed to flow
Since the cover of the landfill is
porous, water does leach into the landfill area. The water
percolates through the trash and picks up contaminants along the
way. The decomposition process breaks down the solid waste and the
introduction of water acts as a solvent to dissolve digesting
materials. This water that contains dissolved contaminants is
called landfill leachate and eventually reaches the bottom of the
cell where it starts to accumulate. If the level of leachate
saturating the bottom layer of soil rises, the hydraulic pressure
on the liner also increases. This pressure must be relieved to
prevent leaks and the leachate is pumped out via drainage piping
that is perforated.
Leachate Control Methods
The leachate is directed to a
separate leachate collection pond. Leachate can be pumped to the
collection pond or flow to it by gravity. A leachate collection
pond is designed to catch and isolate the contaminants that can
get into the environment. The leachate in the pond is tested for
acceptable levels of various chemicals (biological and chemical
oxygen demands, organic chemicals, pH, calcium, magnesium, iron,
sulfate and chloride) and allowed to settle. After testing, the
leachate must be treated like any other sewage/wastewater. The
treatment may occur on-site or off-site. The options for treatment
include recirculating the leachate back to the landfill, treating
for sanitary sewer discharge, or treating for local surface water
leachate may contain contaminants from the buried solid waste, it
must be prevented from going outside the landfill boundaries or
down into the groundwater. Through a complex combination of
landfill liners, monitoring wells, piping, pumps, and capping of
the landfill, leachate flow is restricted and captured. The wetter
the climate, the more potential risk there is for leaks and
attenuation of toxic substances. Paint, pesticides, batteries, and
automotive products deposited in landfills contribute to the toxic
contaminant levels in the leachate.
The EPA estimates that 7.1 billion
gallons of wastewater was generated at landfill facilities
domestically in 1992. EPA has proposed to regulate the following
landfill sources of wastewater: leachate, gas collection
condensate, truck/equipment wash water, drained free liquids,
laboratory wastewaters, and contaminated stormwater.
The EPA has published its proposed
regulations for Landfills as part of the Clean Water Act. The new
effluent limitations are based on "Best Available Technology
" (BAT) methods that have been surveyed and reviewed.
Non-hazardous landfills are regulated under Subtitle D and
hazardous landfills are regulated under Subtitle C of the
"Resource Conservation and Recovery Act" (RCRA). The
proposal would also establish pretreatment standards for the
introduction of pollutants into Publicly Owned Treatment Works
(POTWs) associated with the operation of new and existing
Hazardous landfills regulated under Subtitle C of RCRA.
EPA has identified several trends
in the waste disposal industry that may increase the quantity of
leachate produced by landfills. More stringent RCRA regulation and
the restrictions on the management of wastes in general have
increased the amount of waste disposed at landfills as well as the
number of facilities choosing to send wastes off-site to
commercial facilities in lieu of pursuing on-site management
options. This has increased the amount of solid waste and also the
amount of leachate requiring treatment.
The landfills affected by the new
regulation include 158 non-hazardous landfills discharging
wastewater directly into local surface waters. In addition, there
are 6 hazardous landfills that discharge to POTWs that are
affected by the new regulation. Many of the remaining landfills
have their own in-situ wastewater treatment systems and do not
discharge waste to surface waters or to POTWs.
Treatment Method Comparisons
There are many methods of treatment
currently being used for landfill leachate. The treatment
technologies include physical/chemical treatment and biological
treatment. Some of these methods include:
- Chemical precipitation
- Aerobic biological
- Anaerobic biological
- Carbon adsorption
- Multimedia filtration
- Reverse osmosis
- Air stripping
- Sludge dewatering
Even though the treatment methods
vary, the most common conventional methods used include various
forms of aerobic biological systems. These include aerated
lagoons, activated sludge systems, and sequential batch reactors.
Biological methods have been successful, but do have some
drawbacks. The retention times are long in order to enhance
performance. The microbiology is sensitive to toxic heavy metals,
loading rates, and temperature variations. In addition, very
often, several treatment technologies must be used in a train of
unit operations in order to meet effluent limits.
With new regulations as part of the
Clean Water Act and with the advent of new technologies to address
this problem, many municipal facilities are re-evaluating their
existing methods. One of the new developments in wastewater
treatment includes the new open channel plate and frame type
polymeric membrane filtration systems. There are several types
including the Disk Tube Module made by Rochem and the VSEP
(Vibratory Shear Enhanced Process) made by New Logic Research of
Reverse Osmosis was previously not
appropriate due to narrow feed channels. Now with this limitation
removed as in the wide channel flow membrane modules, RO membranes
offer an excellent alternative to biological systems. RO membranes
are capable of very selective separations and can achieve filtrate
quality better than any biological system.
These membranes can also be used as
a single unit op to handle the raw leachate flow and produce clean
water in one step. RO membranes can be used in parallel and in
series to handle any flow and produce any water quality needed.
Therefore, they are not subject to the loading rate, toxic metals,
and temperature limitations of biological systems. These plate and
frame type membrane filters are installed in dozens of landfills
worldwide and are becoming more and more accepted as an industry
While Reverse Osmosis is a fairly
mature technology, the use of it for wastewater is a relatively
new advance. First used in the 1950s and 60s, they were primarily
used for seawater desalination and brackish water applications.
The advance of membrane chemistry and especially the invention of
new thin film composite membranes has widened the use of
membranes. These new membranes can tolerate a broader pH range,
higher temperatures, and harsher chemical environments than the
previous Cellulose Acetate membranes. This change has only
occurred as recently as the 1980s.
The driving forces for advancements
in membrane technology are the compelling advantages of RO
membranes over traditional separation technologies. RO membranes
are pressure driven processes and don't involve energy intensive
phase-changes or expensive solvents and adsorbents. The RO process
is inherently simple to design and operate. In one piece of
equipment, simultaneous separation and concentration of both
inorganic and inorganic compounds are possible.
The new Thin Film Composite
membranes are composed of two or more layers of selective polymers
cast onto a porous backing cloth. The top layer is very thin and
is what controls the selectivity and flux through the membrane.
Membranes are formed by a phase inversion or polymer precipitation
process. In the process, polymer precipitates in a polymer rich
solid phase that forms the membrane and a polymer poor liquid
phase that forms the pores. Then cast onto this is another thin
solid film of polymer that forms the membrane surface and is where
diffusion filtration occurs.
Just as membrane chemistry has
evolved, the hardware to deliver the membrane has also advanced.
There have been several generations of membrane module design as
the industry continues to adapt to new applications and demand for
selective membrane filtration. Currently, there are several types
of membrane systems, just as there are several types of biological
systems. As with biological systems, one size does not fit all.
Conventional spiral wound membrane modules are relatively
inexpensive and can be used for polishing of water for discharge
or reuse. However, these have narrow feed channels and are subject
to limitations on the quantity of some chemical components that
can be present in the water. For this reason, the feed water needs
to be pretty clean already and these units are normally associated
with some kind of pretreatment, which may be chemical injection or
pre-filtration by UF or MF membranes.
alleviate the limitations on solids entering a membrane system,
new open channel type plate and frame membrane modules have been
developed. Two leading designs include the Disk Tube Module by
Rochem and the VSEP by New Logic. Rochem's module contains
multiple leaf layers of membranes stacked in a column with spacer
setting the gap between them. Rochem relies on high turbulence and
high crossflow to keep the membrane surface clear of suspended
solids cakes and other formations that would blind the membrane.
New Logic's VSEP, employs the same
stacked column of membrane trays with spacers setting the gap. The
VSEP also utilizes high crossflow and high turbulence to keep the
feed liquid homogenous and evenly concentrated. One main advantage
of VSEP is that it also employs torsional oscillation of the
membrane stack. The membranes are vibrated in resonance at a
frequency of about 50 Hz (times per second) and the membrane
displacement is equal to 3/4" peak to peak at the perimeter.
The industrial VSEP machine
contains many sheets of membrane, which are arrayed as parallel
disks separated by gaskets. The disk stack is contained within a
Fiberglass Reinforced Plastic (FRP) cylinder. This entire assembly
is vibrated in torsional oscillation similar to the agitation of a
washing machine. The resulting shear is 150,000 inverse seconds,
which is ten times greater than the shear in crossflow systems.
High shear has been shown to significantly reduce the fouling of
many materials. The resistance to fouling can be enhanced with
membrane selection where virtually any commercially available
membrane materials such as polyamide, polypropylene, polyester,
polysulfone and Teflon can be used.
Each Series i system contains up to
2000 square feet of membrane filtration area. A single VSEP unit
is capable of processing from 5 to 200 U.S. gallons per minute
while producing crystal clear filtrate and a concentrated sludge
in a single pass. This large throughput capability can be
accomplished with a system, which occupies only 20 square feet of
floor space and consumes 15 hp.
Scaling Resilience of VSEP
Torsional oscillation is a very
effective method of colloid repulsion as shear waves from the
membrane surface help to repel oncoming particles. The result is
that suspended solids are held in suspension hovering above the
membrane as a parallel layer where they can be washed away by
tangential crossflow. This washing away process occurs at
equilibrium. Pressure and filtration rate will determine the
thickness and mass of the suspended layer. Particles of suspended
colloids will be washed away by crossflow and at the same time new
particles will arrive. The removal and arrival rate will be
different at first until parody is reached and a state of
equilibrium is reached with respect to the boundary layer.
This layer is permeable and is not
attached to the membrane and is actually suspended above it. In
VSEP, this layer acts as a nucleation site for mineral scaling.
Mineral scale that precipitates will act in just the same way as
any other arriving colloid. If too many of the scale colloids are
formed, more will be removed to maintain the equilibrium of the
diffusion layer. Conventional membrane systems could develop cakes
of colloids that would grow large enough to completely blind the
membrane. In VSEP, no matter how many arriving colloids there are,
and equal number are removed as the diffusion layer is limited in
size due to the gravitational pull (G forces) of the vibrating
One other significant advantage is
that the vibration and oscillation of the membrane surface itself
inhibits crystal formation. Just as a stirred pot won't boil,
lateral displacement of the membrane help to lower the available
surface energy for nucleation. Free energy is available at
perturbations and non-uniform features of liquid/solid interfaces.
With the movement of the membrane back and forth at a speed of 50
times per second, any valleys. Peaks, ridges, or other micro
imperfections become more uniform and less prominent. The smoother
and more uniform a surface, the less free energy is available for
crystallization. Crystals and scale also take time to form. The
moving target of the membrane surface does not allow sufficient
time for proper germination and development. Other stationary
features within VSEP present a much more favorable nucleation
site. Whereas, with conventional membranes that are static, scale
formation on the membrane is possible and has plenty of time to
develop and grow.
VSEP's Reverse Osmosis membrane
module is capable of treating Landfill Leachate Drainage and
providing a filtrate, which is free from suspended solids and low
in COD and Heavy Metals. The VSEP process does not involve any
chemical addition and meets the process engineer's needs for
automated PLC controlled production.
VSEP modules containing about 1900
SF (176m2) of filtration media are modular and can be run in
parallel as needed to meet any process flow requirements. Each
104" VSEP module can produce 40 gpm of clean water from the
leachate pond. Since the units are modular and can be used in
parallel or in series, the number of VSEPs needed can be
calculated based on the amount of material to be processed, (GPD
or GPM). System throughput is a function of the extent to which
the feed is concentrated and will vary from site to site.
The VSEP module is also uniquely
capable of high recovery of filtrate due to its scaling
resistance. Recoveries of up to 96% of the landfill leachate as
clean filtrate are possible. Depending on the concentration of the
leachate, two stages of RO filtration may be required.
Though membranes have experienced
great advances in the past twenty years, their use in leachate
treatment has only been explored recently. With more stringent
regulations placing greater emphasis on leachate treatment, the
industry is seeking new technologies to solve the problem.
Offering economic and operating advantages, VSEP is a leading
technology for treating landfill leachate and will continue to
revolutionize the use of membranes in the industry.
Other Leachate & Groundwater
- Acid Mine Drainage
- Phosphate Cooling Pond Water
- Radioactive Nuclei Removal from
- Arsenic Removal Landfill
- Agricultural run-off
- Produced Water from Oil Drilling
About the Author:
Greg Johnson, Chief Operating
Officer of New Logic Research, has been with the company since
1992 and has a Chemical Engineering background. He is responsible
for engineering and design of the patented VSEP Vibratory Membrane
New Logic is a privately held
corporation located in Emeryville, CA approximately 10 miles from
San Francisco. New Logic markets, engineers, and manufactures a
membrane dewatering and filtration systems used for chemical
processing, waste streams, pulp & paper processing, mining
operations, and drinking water applications.
For more information or to contact
Mr. Greg Johnson
New Logic Research
1295 67th Street
Emeryville, CA 94608
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