A wastewater treatment (“Processes”). The properties of landfill

A landfill is a land disposal site
for waste, and its purpose is to protect from environmental pollution and
health risks. It is a pit that has a protected bottom, which prevents
contamination of groundwater, where the trash is buried in layers, compacted
and covered. Landfills are constructed to settle waste in compacted layers to decrease
the volume and monitor for the control of liquid and gaseous effluent in order
to protect the environment and human health (Stauffer). Trash and garbage and
fecal sludge can also be discharged into landfills. The U.S. federal regulation
(RCRA), which was developed in the 1980s, requires a separate landfill disposal
of municipal solid waste and hazardous waste. Most landfills were dumps before
RCRA. These dumps still exist today and continue to pollute the groundwater and
surface water (“Municipal”). Sanitary landfills will fill up fast and after
many years start to leak. The key components of landfills are a liner, leachate
collection system, leachate detection system, final cap, surface water
management system, and a gas collection & management system (Stauffer). The
purpose of a liner is to minimize leakage of landfill leachate and gas into the
subsurface. It also allows for the collection of leachate for treatment and
disposal.

            The
liquid that has been in contact with waste stored in a landfill is called
landfill leachate. Landfill leachate will occur when rainwater will get through
the landfill body. It also arises from the moisture that comes from the waste
itself. Landfill leachate will get caught in the drainage system and has to go
through special wastewater treatment (“Processes”). The properties of landfill
leachate are usually quite cloudy, have a strong smell, and are brown in color.

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The make-up of landfill leachate differs depending on the type of waste stored,
the weather and the holding time in the landfill body. While the landfill
holding time increases, the degree of organic pollutants also increases. Aerobic
decomposition requires oxygen, and due to the limited amount of oxygen
available buried within refuse and an air transport limitation, aerobic
decomposition is only responsible for a small portion of biological
decomposition in the landfill. Leachate is not usually produced at the aerobic
decomposition stage because the refuse has not reached field capacity in this
early stage. After two to five years, the initially aerobic decomposition
processes change to anaerobic processes. Anaerobic decomposition consumes only
short-chain fatty acids, and the organic compounds entering the leachate are
still somewhat biodegradable (Stauffer). When the landfill holding time
increases, anaerobic decomposition progresses to methane production. When there
is little oxygen present when methane concentrations reach 5% to 15%, there is
little danger. When methane gas moves off-site and mixes with the air,
explosions can occur (“Leachate”). While there are soluble nitrogen and sulphur
compounds, sulphates and chlorides present, the leachate also contains a high
degree of organic pollutants.

            Leachate
starts as rainfall. Rain that falls on top of the landfill is the main contributor
to the beginning of leachate. If untreated leachate enters a body of water, it
can be a hazard to the environment. Within the leachate, there is a list of
substances present with low concentrations of “trace contaminants”, which can
have quite strongly contaminating effects. It contains organic and inorganic
chemicals, heavy metals as well as pathogens, and can pollute the groundwater, can
pollute the soil, and cause health risks. Anything soluble in the waste
disposed will enter the leachate (“Leachate”). Leachate is becoming less
contaminated with difficult substances, and public awareness, recycling and
increased legal control over these substances, throughout the industrialized
world, is making leachate less harmful. Municipal wastewater treatment plants
are often not able to process the high organic and nitrogen loads in the
leachate. Often, the leachate needs to be treated to the extent that it can be
passed off to the next municipal wastewater treatment plant for further
processing. If treating the leachate to that extent is not possible, it is
important to treat the leachate up to a quality that will meet the requirements
for direct discharge (“Processes”). Since the leachate will be treated meeting
the requirements, the remaining contaminant load is so low that the treated
water can be released into a river, stream, or lake.

Most
landfills are designed to reduce the amount of leachate they create during
their lifetimes. To stop the risks of leachate getting into groundwater,
landfills should be properly designed and engineered landfill sites (Kremen). The
properly designed and engineered landfill sites are constructed on geologically
impermeable materials or sites that use impermeable liners made of geotextiles
or engineered clay.

There are
different technologies that are available for the treatment of landfill
leachate. The appropriate technology to use for landfill leachate treatment
depends on the make-up of the leachate (“Processes”). There are three different
ways to treat landfill leachate. The first way leachate can be treated is by
biological processes, such as activated sludge. Another way leachate can be
treated is by physico-chemical processes to remove metals, ammonia, and
dissolved solids, among other parameters. Reverse osmosis is also another way
that leachate can be treated, and it can produce high quality effluent,
including elimination of the dark brown-black tint of leachate.

Biological
treatment is considered the first step in treatment and is also useful for
nitrogen removal. For biological treatment, a moving bed biofilm reactor
technology (MBBR), trickle-flow-reactor (TFR), and activated sludge processes
can be used as biological treatment (“Processes”). MBBR technology uses
thousands of polyethylene biofilm carriers operating in mixed motion within an
aerated wastewater treatment basin. Microorganisms grow inside the biofilms,
which consists of immobilized biomass and become established on the surfaces of
the filing material. The high-density population of bacteria that grows on the
biofilms achieves high-rate biodegradation within the system. This technology
provides cost-effective treatment with very little maintenance because MBBR
processes self-maintain an optimum level of productive biofilm (“Biological”).

TFR technology uses a light, small-grain carrier material that is covered by a
highly active mixed population of bacteria that is adapted to the respective
conditions in days. Since the carrier material bed is not located near a closed
body of water, it can be easily supplied with ample amounts of oxygen. The
constant inflow of wastewater that trickles down over the bed is aerated by air
that is supplied by a ventilator at a minimum pressure flowing in the opposite
direction (“Biological”). The activated sludge process uses microorganisms to
feed on organic contaminants in wastewater, producing a high-quality effluent.

For activated sludge processes, microorganisms grow and form particles that
clump together. These particles settle to the bottom of the tank, leaving a
clear liquid that does not have organic material and suspended solids. Screened
wastewater is mixed with different amounts of recycled liquid which contains a
high proportion of organisms that is taken from a secondary clarifying tank and
becomes a product called mixed liquor. The mixture is stirred and injected with
large quantities of air, to provide oxygen and keep solids in suspension. After
a while, the mixed liquor flows to a clarifier where it settles. Some of the
bacteria are removed as it settles, and the partially cleaned water flows on
for further treatment (“Explaining”). The activated sludge, also known as the
settled solids, is returned to the first tank to begin the process again.

For
physico-chemical treatment technology, chemical precipitation,
coagulation-flocculation, activated carbon adsorption, chemical oxidation, and
separation by membranes are all options for treatment for landfill leachate
(“Processes”). Chemical precipitation is usually used as a pre-treatment to
remove ammonium nitrogen in leachate. This treatment is used because of its
capability, simplicity of the process, and inexpensive equipment. During
chemical precipitation, dissolved ions in the solution are converted to the
insoluble solid phase by chemical reactions. For the coagulation-flocculation
treatment, it is used for the removal of non-biodegradable organic compounds
and heavy metals from the landfill leachate. The coagulation process minimizes
colloidal particles by adding coagulant. To increase the particle size,
coagulation is followed by flocculation of the unstable particles into bulky
floccules, so they can settle more easily. This treatment removes suspended
solids and colloid particles from a solution (“Processes”). The
coagulation-flocculation also has some faults because sludge can be produced
and an increase on the concentration of aluminum or iron in the liquid phase
may be observed. The chemical oxidation treatment contains a mixing chamber to
mix influent leachate and the oxidation agent, and then has a chamber with
UV-lamps. The flows are circulated continuously to increase elimination rates
of the leachate (Liu). Adsorption is the technique that is used most widely for
the removal of recalcitrant organic compounds from landfill leachate.

Adsorption is a mass transfer process by which a substrate is transferred from
the liquid phase to the surface of a solid and becomes bound by physical or
chemical interactions. Activated carbon adsorption provides better reduction in
COD levels than the chemical ways (Liu). The main fault is the need for
frequent regeneration of columns or the high consumption of activated carbon.

For membrane filtration, there are three different membrane filtration
techniques: microfiltration, ultrafiltration, and nanofiltration. A membrane is
defined as a material that creates a thin barrier capable of selectively
resisting the move of different components of a fluid and affecting separation
of the components. The first technique, microfiltration, is used to catch
microbial cells, small particles, and large colloidal. For the treatment of
landfill leachate, this method should not be used alone. It is recommended to
be used as a pretreatment process with other membrane processes (Liu). The
second technique, ultrafiltration, is used to remove suspended matters by
direct filtration of with biological treatment to replace the sedimentation
unit. This technique strongly depends on the kind of material that makes up the
membrane. It was reported that high levels for landfill leachate treatment have
been obtained by using this method (Liu). The third technique, nanofiltration,
removes recalcitrant organic compounds and heavy metals from landfill leachate
because of its unique properties between ultrafiltration and reverse osmosis
membranes (Liu). Nanofiltration also removes heavy metals because of the
negatively charged groups on the membrane.

Reverse
osmosis removes organic matter and mineral content. It is usually used after
aeration treatment and nanofiltration and removes the nitrate created during
nitrification, which produces a nitrogenous effluent (“The Principle”). Reverse
osmosis also removes heavy metals and salts like chloride, sodium, and
potassium, which are found in high concentrations in the leachate. This
technique uses properties of semi-permeable membranes, through which water
moves. In reverse osmosis, energy is used to create a pressure, which reverses
the normal flow across a membrane into a more concentrated solution on the
other side of the membrane (“The Principle”). The osmotic pressure is the
result of the water flowing through the semi-permeable membrane from the less
concentrated compartment to the most concentrated.

As
mentioned, landfill leachate is known as all of the water that has been in
contact with waste stored in a landfill. Landfill leachate will get caught in
the drainage system and has to go through special wastewater treatment. There
are three different ways to treat landfill leachate, but each way also has
different techniques to treat the leachate. For biological treatment, there are
three different techniques to treat leachate: a moving bed biofilm reactor
technology (MBBR), trickle-flow-reactor (TFR), and activated sludge processes.

For physico-chemical treatment, there are six different techniques to treat
leachate: chemical precipitation, coagulation-flocculation, activated carbon
adsorption, chemical oxidation, and separation by membranes. Reverse osmosis is
the last way for treatment of landfill leachate. If landfill leachate is not
treated properly and somehow finds its way into bodies of water, it can cause
an environmental hazard and health risks.

For the
biological treatment, the moving bed biofilm reactor technology seems to be the
best option to treat landfill leachate. The main advantages of this technology
are that it has higher biomass concentrations, no long sludge-settling periods,
lower sensitivity to toxic compounds, and both organic and high ammonia
removals in a single process. Physico-chemical processes are used along with
biological methods to improve treatment efficiency. For physico-chemical
treatment, membrane processes are considered the best solution, mainly
nanofiltration and reverse osmosis. Nanofiltration and reverse osmosis have
been proved to be the more efficient, flexible, and crucial means of the
membrane processes because it achieves full purification and solve the growing
problem of water pollution.