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UTILIZATION OF

MUNICIPAL SOLID WASTE

MSW

Jan Nadziakiewicz

MUNICIPAL SOLID WASTE

MSW is a waste generated by human

activity in the place of living in towns,

settlements and in surrounding enterprises

(shops, restaurants, schools, cultural

institutions etc.).

Municipal Solid Waste

composition

Kitchen waste (food waste, vegetables, fruits, etc.),

Natural origin materials (paper, textiles, metals),

Synthetic materials (plastics).

Morphological composition of MSW in Poland:-organic waste 31,7%-fine fraction 21,4%-paper, cardboard 18,6%-glass 7,5%-plastics 4%-metals 3,5%-others 13,3%.

MSW utilization

1. Segregation Recycling

2. Sorting Recycling

3. Komposting

4. Incineration

5. Landfilling

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Segregation and Recycling

The purpose of Segregation:

Reduction of amount of waste generated.

Recovery of products useful after modifications.

The purpose of Recycling:

Recovery and processing (conversion) of substances

and materials present in waste to obtain substances or

materials that can be used in the same process or in

other processes.

Recovery of Energy.

As a result of segregation and recycling the amount of

waste stored on the landfill space (dumping place) is

reduced and the emission to environment is minimized.

Types of recycling

Product recycling (eg. glass bottles).

Material recycling (eg. metal cans, waste paper).

Energy recycling (waste incineration with heat

recovery).

Recycling in EU

In EU countries the MSW recycling level is:

Paper 50-80%,

Scrap steel 80-90%,

Glass 60-80%,

Plastics 40-80%,

Aluminium 70%.

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Waste storage (landfilling)

The place for landfilling should be provided with the

leachate insulation, draining systems, gas insulation, gasutilization systems.

The landfilling place and its surrounding must be constantly monitored.

By landfilling most of materials are lost at the same timethey spoil the environment.

MUNICIPAL SOLID WASTE LANDFILL PLACE

Landfill

The waste to be landfilled must be compacted by special equipment. This prevents the air to enter the material and reduces biological reactions leading to leachating and gas producing.

The harmful products are: leachate, gas, dust.

Gases generated as a result of biological and thermal reactions should be safely removed from the waste layer to prevent explosion.

Maximal thickness of waste layer should not exceed 2m and they should be covered by the insulating layer of inert material of a thickness about 0.2m (sand, slag, debris).

These layers are insulations against gas, odour and dustemission, against small animals.

The foil cover the landfill place prevents dusting and sanitar risk for surrounding place.

Full landfilling place should be recultivated, possibly to the state similar to previous terrain.

Recultivation (reclamation) is made by covering the waste by a soil of a thickness about 1m and planting the grass or bushes for organizing the recreation garden.

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Landfill cross section

A – clay insulation layer, B – new waste, C- waste layer, D, F, G, H – leachate

monitoring and collection, I – ground water monitoring, J – water cleaning

system.

Landfill leachate

Leachate is the product of chemistry and

microorganisms activity in the organic material with the presence of water.

It varies widely in composition regarding the age of the landfill and the type of waste that it contains.

Leachate can be defined as a liquid that passes through a landfill and has extracted dissolved and suspended

matter from it.

Leachate results from precipitation entering the landfill

and from moisture that exists in the waste when it is

composed.

Landfill leachate

When landfill waste degrades and rain rinses the

resulting products out, leachate is formed. The black liquid contains organic and inorganic chemicals, heavy

metals as well as pathogenes;

It can pollute the groundwater and therefore represents a

health risk.

Its composition varies a lot, both from time to time and

from site to site so that it is difficult to treat the liquid in

the right way.

It must be pretreated before sending to the municipal

waste water drainage system and sewage treatment

plant.

Landfill cross section

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Landfill gas safety

The gas is generated mainly in non-oxygen conditions as

a result of organic matter reactions in the presence of microorganisms.

Main components of biogas are: CH4 and CO2 and some NH3, H2S and C2H2. In the presence of air they can

cause explosion.

Biogas should be allowed to go out the waste layer.

The landfill gas is the reason of big Green House Effect (CH4 + CO2)

Landfill degassing

The biogas composition is: average 60% CH4, 40% CO2.

LHV about 18 MJ/m3.

Amount of gas produced is 200 – 300 m3/Mg of waste in

a period of about 20 years.

A big landfill place can produce several hundreds

thousands up to a million cubic meters of gas in a year.

Special systems are installed to collect this amount of

gas, which prevents of greenhouse effect and gives the energy (heat or electricity).

The effective electricity production from gas is for the

landfill of a volume above 200 000 m3.

Phases of biogas production

Phase I – first phase – aerobic decomposition of organic

fractions. Main products: CO2 and H2O. Time about 2 weeks,

ends with complete oxygen consumption in a waste layer.

Phase II – intermediate phase – anaerobic decomposition of

organic fractions. Main product H2.

Phase III – acidic phase – big molecule fractions

(saccharides, fats, organic polimers) are decomposed to

simple compounds. Main products: organic acids, CO2, H2.

Phase IV – methane fermentation – microorganisms produce

CH4, CO2 from acetic acid and hydrogen

Phase V – final phase – production of gas reduces because

of shortage in organic substance in waste layer.

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Typical landfill gas generation curve (generated using

the US EPA’s LandGEM model) Biogas production in time

Landfill gas prodution and quality Landfill degassing system

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Perforated tubes are drilled into the landfill body and interconnected by a

pipework system. Utilizing a blower, the gas is sucked from the landfill,

compressed, dried and fed into the gas engine

For safety reasons, the installation of a gas flare is recommended so that excess

gas can be burned off in the event of excessive gas production

In most cases, the electrical power generated is fed into the public grid

Landfill degassing systemGas well

Landfill reclamationI. Technical reclamation:

Clearance, levelling and compacting of the waste layer.

Installation of gas wells,

Building of roads and paths,

Covering of the whole landfill by the mineral layer of a thickness of

0,15 – 0,3 m and insulation foil.

II. Biological reclamation

Covering the Surface by the biological soil of a thickness 2,0 m. and

its thickening.

Cultivation of plants and bushes and recreation equipment.

III. Continuous monitoring

Monitoring of the level of underground water and water parameters

like: pH, electrolytic conduction, heavy metals.

Monitoring of the landfill gas (CH4, CO2, O2).

Landfill place after reclamation

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Anaerobic digestion

In this biological process, microorganisms are used

to break down organic waste in the absence of oxygen.

Temperature, moisture, nutrient contents, and pH of the organic matter are key factors in the process

The biogas from AD consists of 60%-70% methane (CH4), 30%-40% carbon dioxide (CO2), and other

trace chemicals

Biogas can be used to power a gas engine or turbine

or it can be compressed and purified for use as

vehicle fuel

Methane may also be extracted from the biogas for

direct use.

Anaerobic digestion of waste

The overall process can be described by the chemical

reaction, where organic material such as glucose is biochemically digested into carbon dioxide (CO2) and

methane (CH4) by the anaerobic microorganisms.

C6H12O6 → 3CO2 + 3CH4

The anaerobic digestion process occurs

in three steps:

Decomposition of plant or animal substance by

microorganisms and bacteria into molecules

such as sugar;

Conversion of decomposed matter to organic

acids;

Organic acid conversion to methane gas.

Anaerobic process

Anaerobic processes can occur naturally or in a

controlled environment such as a biogas plant.

In controlled environments, organic materials such as

biosolids and other relatively wet organic materials, along with various types of bacteria, are put in an

airtight container called a digester where the process

occurs.

Depending on the waste feedstock and the system

design, biogas is typically 55 to 75 per cent pure

methane.

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The key stages of anaerobic digestion:

Through hydrolysis the complex organic molecules are broken

down into simple sugars, amino acids, and fatty acids.

The biological process of acidogenesis results in further breakdown

of the remaining components by acidogenic (fermentative) bacteria.

Here, VFAs are created, along with ammonia, carbon dioxide, and hydrogen sulfide, as well as other byproducts.

The third stage of anaerobic digestion is acetogenesis. Here,

simple molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid, as well

as carbon dioxide and hydrogen.

The terminal stage of anaerobic digestion is the biological process

of methanogenesis. Here, methanogens use the intermediate products of the preceding stages and convert them into methane,

carbon dioxide, and water.

Typical MSW anaerobic digestion

process system

The stages of anaerobic digestion Anaerobic digestion process system

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Anaerobic digestion process system

The two conventional operational temperature levels for anaerobic

digesters determine the species of methanogens in the digesters: Mesophilic digestion takes place optimally around 30 to 38 °C, or at

ambient temperatures between 20 and 45 °C, where mesophiles are

the primary microorganism present.

Thermophylic digestion takes place optimally around 49 to 57 °C, or

at elevated temperatures up to 70 °C, where thermophiles are the

primary microorganisms present.

Anaerobic digestion

Anaerobic digestion produces a biogas which can be used to

produce electricity, process steam, or in the transportation sector

In this biological process, microorganisms are used to break down organic waste in the absence of oxygen in an enclosed vessel.

Temperature, moisture, nutrient contents, and pH of the organic

matter are key factors in the process

The biogas from AD consists of 60%-70% methane (CH4), 30%-40% carbon dioxide (CO2), and other trace chemicals

Biogas can be used to power a gas engine or turbine or it can be

compressed and purified for use as vehicle fuel

Methane may also be extracted from the biogas for direct use

Typical MSW anaerobic digestion

process system

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Almost any organic material can be processed with anaerobic

digestion; however, if biogas production is the aim, the level of putrescibility is the key factor in its successful application. The more

putrescible (digestible) the material, the higher the gas yields

possible from the system.

Feedstocks can include biodegradable waste materials, such as

waste paper, grass clippings, leftover food, sewage, and animal

waste.

Anaerobic digesters can also be fed with specially grown energy

crops, such as silage, for dedicated biogas production.

Possible is operation using sewage sludge and manures.

AD installation system

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AD agricultural installation AD efficiency

Efficiency of the AD process depends on the form of waste used as

feedstock as well as the vessel used to host the process

AD is used in individual farms to reduce their environmental (waste) footprint. In these cases, the main feedstock for AD has been animal

waste as opposed to MSW

Municipal sewage contains biomass solids, so AD is also used in

wastewater treatment plants to reduce volume of those solids.

Landfill gas (LFG)-to-energy is a less efficient form of AD that uses gas from pre-existing landfills.

The drawbacks of AD technology

Two drawbacks of AD are its by-product and its need to be pre-

treated

In addition to the methane-rich biogas created in the AD process, a

digestate, in either a solid or liquid form (depending on either dry or

wet input) is also created as a by-product. The digestate must be disposed of or composted in solid form or purified and treated in its

liquid form. This treatment process requires expensive, complex

technologies

In order for MSW to be used in this process, it must be inspected

and sorted to remove plastics and other contaminants. This added

cost reduces the efficiency of AD

Electric Generation Technology

Trends for LFG

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Biogas power station in Gliwice