Eight Phases Of Landfill Gas Development Environmental Sciences Essay

Landfill gas is generated as a consequence of physical, chemical and microbic procedures taking topographic point within the waste. Owing to the organic nature of the waste, the microbic procedure dictates the gas coevals procedure ( Christensen, 1989- Design-guidelines pg 36 ) . These procedures are sensitive to the environing environment and hence, several natural and unreal conditions will hold a direct impact on the microbic population every bit good as the LFG coevals rate. Short-run surveies performed on life-size landfills utilizing informations from the LFG extraction trials indicate a coevals of about 0.05-0.40 three-dimensional metres ( M3 ) of LFG per kg ( kilogram ) of waste being topographic point into the landfill ( Ham, 1989- Design-guidelines pg 36 ) .

It is of import to underscore that landfill gas coevals takes topographic point in an anaerobiotic status, and therefore any natural or unreal conditions that will drive the procedure to an aerophilic status will impact the LFG coevals. Furthermore, it should be noted that LFG coevals is non instantaneous ; any sum of waste that is disposed in the landfill will undergo a set of procedures as illustrated by the undermentioned figure.

Figure: Eight Phases of Landfill Gas Development ( Beginning: CCRP_3Timone )

Description of the eight stages in the development of landfill gas ( Beginning: CCRP_3Timone ) has been tabulated as follows:

Eight Phases of Landfill Gas Developement

Phase I: Aerobic- This procedure follows waste decomposition in which the residuary O is used up. This stage typically last for a few twenty-four hours to a figure of months, depending on local factors such as temperature and wet handiness.

Phase V: Air intrusion- The rate of methanogenic activity begins to fall as substrate is used up, ensuing in air get downing to come in the waste. Lower rates of gas formation lead to comparatively faster washout of CO2 so that its concentration falls comparative to that of CH4.

Phase II: Acid- In this stage, populations of facultative and fermentative bacteriums develop, bring forthing volatile ( aliphatic ) acids, CO2 and H2, displacing the staying N2 entrained in the waste. This stage may last from hebdomads to old ages, depending on conditions.

Phase VI: CH4 oxidation- In this stage, rates of methanogenesis have now fallen to low degrees, leting the rate of air to increase so that surface beds of waste and the capping now become aerophilic ( oxygen rich ) . Methane concentration in the landfill gas lessenings while that of CO2 additions steadily.

Phase III: Initial methanogenic- During this stage, microbic respiration reduces oxygen concentrations to highly low values, leting populations of methanogenic bacteriums to develop, bring forthing CH4. Concentrations of H2 and CO2 start to worsen.

Phase VII: CO2- Return of aerophilic conditions. At this phase, the rate of landfill gas formation has about ceased because of substrate restriction ; anaerobiotic decomposition becomes inhibited by the immersion of O2 in the air. This allows the aerophilic decomposition of solid organic affair resistant to anaerobic decomposition.

Phase IV: Stable methanogenic- The staying H2 is used in the decrease of CO2 to CH4 and H2O. Phase IV may get down within months to old ages after waste decomposition and last for decennaries. Typical landfill gas collected in this stage consists of 40-65 % by volume of CH4 with most of the balance made up by CO2.

Phase VIII: Soil air- The concluding stage occurs when degradable organic affair has been oxidized and the landfill gas resembles that of typical dirt air.

The continuance of each of these stages is extremely variable. Apart from the initial aerophilic decomposition, which can be completed in yearss to months, the staying stages may hold continuances quantifies in old ages, decennaries or even centuries for the concluding stages

Factors impacting Landfill Gas Generation

Waste composing

The waste composing is the most important factor in measuring the LFG coevals potency and entire output at the landfill site. The maximal possible volume of LFG is dependent on the type and measure of organic content of the waste merchandises ( Environment Canada, 199- Design guidelines pg 39 ) , since decomposition or organic wastes are the primary beginning for all LFG produced. Inorganic and inert wastes will bring forth small or no LFG while organic 1s will be given to bring forth greater sums of LFG.

Age of garbage

In chief, more late buried waste ( & A ; lt ; 10 old ages ) produces more landfill gas through bacterial decomposition, volatilization and chemical reactions than older waste ( & A ; gt ; 10 old ages ) . Peak gas production normally occurs from 5 to 7 old ages after the waste is buried ( Landfill_2001_ch2mod.pdf lfg calc ) .

Moisture content

Moisture presence ( unsaturated conditions ) in the landfill provides the aqueos environment necessary and will by and large increase gas coevals rates as it encourages bacterial decomposition. Moisture may besides advance chemical reactions that will bring forth the landfill gases ( Landfill_2001_ch2mod.pdf lfg calc ) .

Temperature

With temperature rise at the landfill site, bacterial activities besides increase as the latter thrives in high temperature mediums. This will therefore consequence in increased gas formation. Increased temperature can increase volatilization and chemical reaction rates every bit good.

pH and foods

The pH of the waste and leachate nowadays significantly influences the rate of gas production. Generation of methane gas is at its extremum when impersonal pH conditions are present. Furthermore, the bacteriums nowadays in the landfill require assorted foods for growing, chiefly H, N, C and phosphoric. MSW by and large contains the needed foods to back up the bacterial debasement procedure which generates methane gas ( SEPA, 2004- Design guidelines pg 43 )

Some of the composing and features of the different constituents of LFG are shown in Table 1.

Component

% Volume

Characteristic

Methane

45-60

Methane is a of course happening gas. It is colorless and odorless. Landfills are the individual largest beginning of semisynthetic methane emanations.

Carbon Dioxide

35-50

Carbon dioxide is of course found at little concentrations in the ambiance ( 0.03 % ) . It is colorless, odorless and somewhat acidic.

Nitrogen

2-5

Nitrogen comprises about 79 % of the ambiance. It is odorless, tasteless, and colourless

Oxygen

0.1-1

It comprises about 21 % of the ambiance. It is odorless, tasteless, and colourless.

Ammonia

0.1-1

It is a colourless gas with a acrid smell.

Sulfides

0-1

These are of course happening gases that give the landfill gas mixture its rotten-egg odor. Sulfides can do unpleasant smells even at really low concentrations

Carbon Monoxide

0-0.2

It is an odourless, colourless gas.

Hydrogen

0-0.2

It is an odourless, colourless gas.

Potential impacts of LFG

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