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

A landfill is a land disposal sitefor waste, and its purpose is to protect from environmental pollution andhealth risks. It is a pit that has a protected bottom, which preventscontamination of groundwater, where the trash is buried in layers, compactedand covered. Landfills are constructed to settle waste in compacted layers to decreasethe volume and monitor for the control of liquid and gaseous effluent in orderto protect the environment and human health (Stauffer). Trash and garbage andfecal sludge can also be discharged into landfills.

The U.S. federal regulation(RCRA), which was developed in the 1980s, requires a separate landfill disposalof municipal solid waste and hazardous waste. Most landfills were dumps beforeRCRA.

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These dumps still exist today and continue to pollute the groundwater andsurface water (“Municipal”). Sanitary landfills will fill up fast and aftermany years start to leak. The key components of landfills are a liner, leachatecollection system, leachate detection system, final cap, surface watermanagement system, and a gas collection & management system (Stauffer). Thepurpose of a liner is to minimize leakage of landfill leachate and gas into thesubsurface. It also allows for the collection of leachate for treatment anddisposal.             Theliquid that has been in contact with waste stored in a landfill is calledlandfill leachate.

Landfill leachate will occur when rainwater will get throughthe landfill body. It also arises from the moisture that comes from the wasteitself. Landfill leachate will get caught in the drainage system and has to gothrough special wastewater treatment (“Processes”). The properties of landfillleachate are usually quite cloudy, have a strong smell, and are brown in color.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 landfillholding time increases, the degree of organic pollutants also increases.

Aerobicdecomposition requires oxygen, and due to the limited amount of oxygenavailable buried within refuse and an air transport limitation, aerobicdecomposition is only responsible for a small portion of biologicaldecomposition in the landfill. Leachate is not usually produced at the aerobicdecomposition stage because the refuse has not reached field capacity in thisearly stage. After two to five years, the initially aerobic decompositionprocesses change to anaerobic processes. Anaerobic decomposition consumes onlyshort-chain fatty acids, and the organic compounds entering the leachate arestill somewhat biodegradable (Stauffer).

When the landfill holding timeincreases, anaerobic decomposition progresses to methane production. When thereis little oxygen present when methane concentrations reach 5% to 15%, there islittle danger. When methane gas moves off-site and mixes with the air,explosions can occur (“Leachate”). While there are soluble nitrogen and sulphurcompounds, sulphates and chlorides present, the leachate also contains a highdegree of organic pollutants.             Leachatestarts as rainfall. Rain that falls on top of the landfill is the main contributorto the beginning of leachate.

If untreated leachate enters a body of water, itcan be a hazard to the environment. Within the leachate, there is a list ofsubstances present with low concentrations of “trace contaminants”, which canhave quite strongly contaminating effects. It contains organic and inorganicchemicals, heavy metals as well as pathogens, and can pollute the groundwater, canpollute the soil, and cause health risks. Anything soluble in the wastedisposed will enter the leachate (“Leachate”).

Leachate is becoming lesscontaminated with difficult substances, and public awareness, recycling andincreased legal control over these substances, throughout the industrializedworld, is making leachate less harmful. Municipal wastewater treatment plantsare often not able to process the high organic and nitrogen loads in theleachate. Often, the leachate needs to be treated to the extent that it can bepassed off to the next municipal wastewater treatment plant for furtherprocessing. If treating the leachate to that extent is not possible, it isimportant to treat the leachate up to a quality that will meet the requirementsfor direct discharge (“Processes”). Since the leachate will be treated meetingthe requirements, the remaining contaminant load is so low that the treatedwater can be released into a river, stream, or lake.

Mostlandfills are designed to reduce the amount of leachate they create duringtheir lifetimes. To stop the risks of leachate getting into groundwater,landfills should be properly designed and engineered landfill sites (Kremen). Theproperly designed and engineered landfill sites are constructed on geologicallyimpermeable materials or sites that use impermeable liners made of geotextilesor engineered clay. There aredifferent technologies that are available for the treatment of landfillleachate. The appropriate technology to use for landfill leachate treatmentdepends on the make-up of the leachate (“Processes”). There are three differentways to treat landfill leachate. The first way leachate can be treated is bybiological processes, such as activated sludge.

Another way leachate can betreated is by physico-chemical processes to remove metals, ammonia, anddissolved solids, among other parameters. Reverse osmosis is also another waythat leachate can be treated, and it can produce high quality effluent,including elimination of the dark brown-black tint of leachate. Biologicaltreatment is considered the first step in treatment and is also useful fornitrogen removal. For biological treatment, a moving bed biofilm reactortechnology (MBBR), trickle-flow-reactor (TFR), and activated sludge processescan be used as biological treatment (“Processes”). MBBR technology usesthousands of polyethylene biofilm carriers operating in mixed motion within anaerated wastewater treatment basin. Microorganisms grow inside the biofilms,which consists of immobilized biomass and become established on the surfaces ofthe filing material.

The high-density population of bacteria that grows on thebiofilms achieves high-rate biodegradation within the system. This technologyprovides cost-effective treatment with very little maintenance because MBBRprocesses self-maintain an optimum level of productive biofilm (“Biological”).TFR technology uses a light, small-grain carrier material that is covered by ahighly active mixed population of bacteria that is adapted to the respectiveconditions in days. Since the carrier material bed is not located near a closedbody of water, it can be easily supplied with ample amounts of oxygen. Theconstant inflow of wastewater that trickles down over the bed is aerated by airthat is supplied by a ventilator at a minimum pressure flowing in the oppositedirection (“Biological”).

The activated sludge process uses microorganisms tofeed on organic contaminants in wastewater, producing a high-quality effluent.For activated sludge processes, microorganisms grow and form particles thatclump together. These particles settle to the bottom of the tank, leaving aclear liquid that does not have organic material and suspended solids. Screenedwastewater is mixed with different amounts of recycled liquid which contains ahigh proportion of organisms that is taken from a secondary clarifying tank andbecomes a product called mixed liquor. The mixture is stirred and injected withlarge quantities of air, to provide oxygen and keep solids in suspension. Aftera while, the mixed liquor flows to a clarifier where it settles.

Some of thebacteria are removed as it settles, and the partially cleaned water flows onfor further treatment (“Explaining”). The activated sludge, also known as thesettled solids, is returned to the first tank to begin the process again. Forphysico-chemical treatment technology, chemical precipitation,coagulation-flocculation, activated carbon adsorption, chemical oxidation, andseparation by membranes are all options for treatment for landfill leachate(“Processes”). Chemical precipitation is usually used as a pre-treatment toremove ammonium nitrogen in leachate. This treatment is used because of itscapability, simplicity of the process, and inexpensive equipment. Duringchemical precipitation, dissolved ions in the solution are converted to theinsoluble solid phase by chemical reactions. For the coagulation-flocculationtreatment, it is used for the removal of non-biodegradable organic compoundsand heavy metals from the landfill leachate. The coagulation process minimizescolloidal particles by adding coagulant.

To increase the particle size,coagulation is followed by flocculation of the unstable particles into bulkyfloccules, so they can settle more easily. This treatment removes suspendedsolids and colloid particles from a solution (“Processes”). Thecoagulation-flocculation also has some faults because sludge can be producedand an increase on the concentration of aluminum or iron in the liquid phasemay be observed.

The chemical oxidation treatment contains a mixing chamber tomix influent leachate and the oxidation agent, and then has a chamber withUV-lamps. The flows are circulated continuously to increase elimination ratesof the leachate (Liu). Adsorption is the technique that is used most widely forthe removal of recalcitrant organic compounds from landfill leachate.Adsorption is a mass transfer process by which a substrate is transferred fromthe liquid phase to the surface of a solid and becomes bound by physical orchemical interactions. Activated carbon adsorption provides better reduction inCOD levels than the chemical ways (Liu). The main fault is the need forfrequent regeneration of columns or the high consumption of activated carbon.

For membrane filtration, there are three different membrane filtrationtechniques: microfiltration, ultrafiltration, and nanofiltration. A membrane isdefined as a material that creates a thin barrier capable of selectivelyresisting the move of different components of a fluid and affecting separationof the components. The first technique, microfiltration, is used to catchmicrobial cells, small particles, and large colloidal. For the treatment oflandfill leachate, this method should not be used alone. It is recommended tobe used as a pretreatment process with other membrane processes (Liu). Thesecond technique, ultrafiltration, is used to remove suspended matters bydirect filtration of with biological treatment to replace the sedimentationunit. This technique strongly depends on the kind of material that makes up themembrane. It was reported that high levels for landfill leachate treatment havebeen obtained by using this method (Liu).

The third technique, nanofiltration,removes recalcitrant organic compounds and heavy metals from landfill leachatebecause of its unique properties between ultrafiltration and reverse osmosismembranes (Liu). Nanofiltration also removes heavy metals because of thenegatively charged groups on the membrane. Reverseosmosis removes organic matter and mineral content. It is usually used afteraeration treatment and nanofiltration and removes the nitrate created duringnitrification, which produces a nitrogenous effluent (“The Principle”). Reverseosmosis also removes heavy metals and salts like chloride, sodium, andpotassium, which are found in high concentrations in the leachate. Thistechnique uses properties of semi-permeable membranes, through which watermoves.

In reverse osmosis, energy is used to create a pressure, which reversesthe normal flow across a membrane into a more concentrated solution on theother side of the membrane (“The Principle”). The osmotic pressure is theresult of the water flowing through the semi-permeable membrane from the lessconcentrated compartment to the most concentrated. Asmentioned, landfill leachate is known as all of the water that has been incontact with waste stored in a landfill. Landfill leachate will get caught inthe drainage system and has to go through special wastewater treatment. Thereare three different ways to treat landfill leachate, but each way also hasdifferent techniques to treat the leachate.

For biological treatment, there arethree different techniques to treat leachate: a moving bed biofilm reactortechnology (MBBR), trickle-flow-reactor (TFR), and activated sludge processes.For physico-chemical treatment, there are six different techniques to treatleachate: chemical precipitation, coagulation-flocculation, activated carbonadsorption, chemical oxidation, and separation by membranes. Reverse osmosis isthe last way for treatment of landfill leachate. If landfill leachate is nottreated properly and somehow finds its way into bodies of water, it can causean environmental hazard and health risks. For thebiological treatment, the moving bed biofilm reactor technology seems to be thebest option to treat landfill leachate.

The main advantages of this technologyare that it has higher biomass concentrations, no long sludge-settling periods,lower sensitivity to toxic compounds, and both organic and high ammoniaremovals in a single process. Physico-chemical processes are used along withbiological methods to improve treatment efficiency. For physico-chemicaltreatment, membrane processes are considered the best solution, mainlynanofiltration and reverse osmosis. Nanofiltration and reverse osmosis havebeen proved to be the more efficient, flexible, and crucial means of themembrane processes because it achieves full purification and solve the growingproblem of water pollution.