Environmental chemistry:

“Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places.”

It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science.

Environmental chemistry involves first understanding how the uncontaminated environment works, which chemicals in what concentrations are present naturally, and with what effects. Without this it would be impossible to accurately study the effects humans have on the environment through the release of chemicals.

Environmental chemists draw on a range of concepts from chemistry and various environmental sciences to assist in their study of what is happening to a chemical species in the environment. Important general concepts from chemistry include understanding chemical reactions and equations, solutions, units, sampling, and analytical techniques.

Chemistry in environment:

A large number of people seem to regard chemical industry products as environmental pollutants. Over the last few decades more and more environmentally friendly materials and products have been realsed with considerably lower impact on environment as such. The relationship between industrial processes and environment has been more clearly defined which in turn calls for invention of novel chemical engineering technologies that are less harmful to natural environment.Another evident ecological demand is for updating relevant legislature on national and international level- a process that should go hand in hand with investments in science and technology.

1. Environmental components

The three components of environment are hydrosphere, atmosphere and lithosphere.

1.1. Hydrosphere ( from Greek hydro meaning “water”) comprises all waters contained on the Earth including oceans , seas, rivers ,lakes, dam lakes, swamps glaciers, underground waters and water in the atmosphere. Earth is the only planet in the Solar system on which there is water in liquid state. This water covers 71 % of Earth’s surface (97,5 % of water being saline and 2,5 % — freshwater). About 67,8 % of all fresh water is contained in the glaciers.

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Figure 1: The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere.

1.2. Atmosphere is the gaseous wrapping of our planet’s globe. This term is of Greek origin “atmos” meaning vapour and “sphere” meaning ball. Its function is to protect living organisms by preventing a large portion of ultraviolet rays from falling on them. The gaseous wrapping of the Eareth is called “air” and about 99 % of gasses are nitrogen and oxygen. Atmosphere can be regarded as being made up of five major layers called “spheres”: troposphere, stratosphere, mesosphere, thermosphere and exosphere; their designations being closely related to their location.

Figure 2: Vertical structure of the Earth's Atmosphere

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Earth’s atmosphere is 20000 km in height and at this altitude atmospheric air density equals the density of gases which fill up interplanetary space however, 90 % of its total mass is concentrated within the 15 kilometer overground layer. Atmosphere gradually dissolves in space.With regard to its physical properties atmosphere is not homogeneous and uniform both in vertical and horizontal direction. With greater altitudes its content changes along with some other propereties and parameters.

Air which forms earth’s atmosphere is a mechanical mixture of different gases which do not interact with each other. Air content which is closer to earth’s surface is accurately determined. Apart from the major gases such as nitrogen, oxygen and argon there are some other gaseous admixtures of lower concentration. Nitrogen and oxygen are prevalent within the latitude of 800km. At an altitude above 400 km the content of lighter gasses starts to increase; helium being in the beginning, followed by hydrogen. Above altitude of 800km atmosphere contains mainly hydrogen.

1.3. Lithosphere. Soil. Lithosphere is another term of Greek origin meaning “stone” and “ball”. Lithosphere makes up the uppermost hard cover of our planet. It includes earth’s crust plus the upper layers of the mantle which are located above the asthenosphere. With regard to its physical-mechanical properties, lithosphere is strong, brittle and elastic layer which is able to withstand enourmous pressure up to 1 kbar.

Figure 3: The tectonic plates of the lithosphere on Earth

Figure 4: Earth cutaway from core to crust, the lithosphere comprising the crust and lithospheric mantle

Its thickness varies between 50-120 km reaching 300km at certain places. Lithosphere is severed at narrow elongated zones which, given the present day relief, correspond to the main active tectonic zones. The rest of its substance is unbroken and makes up separate thin blocks some of which are of gigantic dimensions and are referred to as plates. Laterally, and with regard to their physical and mechanical properties these plates are of extreme hardness, they are brittle and posses great strength against shear forces.

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The uppermost layer of lithosphere is referred to as “soil”. It is a complex multiphase structural system at the surface of weatherized crust which posses the property of fertility. Soil is a mixture of minerals, organic matter and water of various content and ratio. It is capable of supporting life of plants on the earth surface. Soil is one of the key components of the chemical cycles occurring in the environment. One of the major cycles taking place in the soil is the ion exchange whereby a number of chemical elements such as K, Ca, Mg and others can reach plants. This property of soil determines its acidity – one of the most important factors behind the development of plants and micro-organisms.

2. Chemistry and environmental protection

The entire biosphere contains substances in concentrations which are variable. Poluution is available whenever these substances exceed predetermined permissible levels of concentration. The Environmental Protection Act defines “environmental pollution” as intrinsic change of its quality due to the impact of physical, chemical and biological factors caused by natural or human agent.

2.1. Air pollution. Atmosphere is regarded as polluted when it contains harmful gases, vapours, liquid or solid particles, including radioactive ones, which have a negative impact on living organisms and plants, bring about changes in climate, decrease visibility and incur material losses.

Figure 5, 6: Indoor & Outdoor Air Pollution

Pollution is a consequence of burning fossil fuels. Exhaust pollutants interact with moisture in atmosphere and form the so called acid rains. Raindrops are slightly acid due to the carbon dioxide in atmosphere, however nitrogen and sulphuric oxides proiduce stronger acids which have an unfavorable impact on plants and animals alike. The greater harm caused by carbon dioxide is seen in global warming, the so called green house effect which is said to be the reason for higher average temperatures on the planet. Another headache is the thinning of ozone layer which allows larger amounts of ultraviolet rays to reach the Earth.

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2.2. Water pollution . Waste and sewer waters are the primary source of water pollution. Since the dawn of industrial revolution factories have been dumping their waste products in the water bodies which is detrimental to the development and growth of local flora and fauna. Households appear to be another big source of pollution as well as agriculture. Fertilizers which boost crops yield and pesticides used in prevention of vermines penetrate from soil into underground waters . Fresh water shortage is on the rise and one third of the world’s population suffer from such shortage

Figure 7,8: Water And Soil Pollution

2.3. Soil pollution. The ecological functions of soil cover are found in its capacity to accumulate water supplies, nutrient elements, active organic substance and the chemical energy related to it; provide life support for plants and micro-organisms; regulate the chemical content of atmosphere, overground and underground waters and sustain geoecosystems.

Soil degradation includes: erosion, dehumification, acidization, salinification, secondary repacking of soils, seasonal overmoisturing, destroyed land surfaces; technogene contamination appears to be one of the major soil damages whereas the other degradation processes are related to different elements of environment. Degradation occurs as a consequence to burning, spraying with pesticides and dumping of industrial and household wastes and watering with polluted waters.

3. Global ecological effects produced by chemical processes in environment

3.1. Global warming (greenhose effect). Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century primarily due to the greenhouse gases released by people burning fossil fuels. Greenhouse effect is a process whereby the infrared radiation of some atmospheric gases warms earth’s surface. Without this effect average temperature would have been -18°C (255 K) instead of 15°C (288 K).

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Such temperature makes it impossible for water to exist in liquid state hence there would be no oceans on Earth. Greenhouse effect is determined by atmospheric transparency in the visible and infrared zone.

Figure 9,10: Greenhouse Effect and Global Warming

Carbon dioxide allows sunrays to reach the surface of the planet but withholds the return of warmth. Other gases which act in the very same way are methane, nitrogen oxide, small quantities of which are obtained in burning fossil fuels and as product of agricultural activity; and freons which are used in sprayers and in air conditioning equipment.

3.2. Nuclear winter. This term designates a hypothetical state of global climate caused in the wake of a nuclear war .it is supposed that due to a large quantity of smoke and soot in the startosphere caused by the explosion of a great number of nuclear war heads, the temperature of our planet will sharply drop to arctic values since sunrays will be reflected by the upper layer of the atmosphere.

3.3. Smog. Smog is the mixture of smoke and fog. Initially, it was mainly a result from burning of enormous quantities of coal which caused oversaturation of air with smoke particles and sulphuric dioxide. Today smog is largely the product of automobile and industrial emissions which interact with sunrays in the atmosphere until the formation of secondary pollutants which in turn remix with the primary pollutants thus forming photochemical smog. It is the chemical reaction of sunlight with the oxides of nitrogen and various organic substances. The resultant mixture contains:

Nitrogen oxides Tropospheric ozone Volatile organic substances such as petrol vapours, pesticides CH3COOONO2 aldehides

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3.4. Acid rain. Energy production based on chemical fuels, mainly coal, is the top polluter of atmosphere. It is found mostly in coal as a remnant of organic matter or is of organic origin. In the organic matter it is found in the form of organic compounds containing sulphur. Hydrogen bisulphide is a product of organic matter decomposition which amounts to 100 million tons.

In atmosphere sulphur is found in the form of compounds such as hydrogen bisulphide, sulphur dioxide, sulphur trioxide. This gas is dissolved in cloud water drops and forms sulfuric acid. That is how acid rains are produced. It is dissolved in the sap thus producing sulphates which are detrimental to living matter. Leaves lose their moisture then their chlorophyll, wither and die. In addition acid rains impair a number of other objects such as cultural assets made of marble and limestone aswell as steel structures.

Figure 11, 12: Process of Acid Rain and Ozone Layer

3.5. Destruction of ozone layer. This is a depletion of steady and sustainable drop by 4% of overall ozone amount in the stratosphere every 10 years which started in the late 70s. It is accompanied by a larger, however seasonal, depletion of ozone in stratosphere over the poles regions. The latter phenomenon is known as ozone hole.

A chemical reaction between substances and the ozone molecules which is the cause for the destruction of the ozone layer. When Antarctic summer is on, the winds forming the barrier around the continent begin to abate and the air which is rich in ozone is transferred to the other side of Antarctica to fill up the depleted ozone layer. In this way the ozone hole usually disappears during November or December. Chlorfluorocarbones

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are found in aerozoles and coolants used in the manufacture of refrigerators and automobile radiators. During the mid 70s of the last century scientists discovered that CFCs are the main cause for ozone layer depletion; moreover CFCs are transferred by air stream thus reaching startosphere.

The full spectrum of UV-B, mainly type UV-B, could harm animal skin including human skin. Sunburn is the most evident and well known result from over-exposure to UV radiation. The latter may cause decolorization of skin, wrinkles and red brownish spots. UV rays type B may even kill the plant by interfering with the photo-synthetic processes. The cause is found in the mutation of important plant cells, interference with respiratory processes and the ability of the plant to absorb СО2 and produce О2.

Chemistry and energy of the future

Energy could be defined as the possibility to carry out work or transfer heat. Two kinds of energy are differentiated: the first is the one we can make use of immediately, e.g. the energy produced by our bodies that enable us to perform various activities and is referred to as kinetic energy. The second kind is the energy stored and is referred to as potential energy; for instance, the stored energy in the torch light batteries or the wound up spring which enables the clockwork to operate in a uniform way. Energy is primarily produced from conventional sources which are:

1.Crude oil (petroleum):

It has been formed over millions of years as a product of sea water flora and fauna. Over time the fossils of these living organisms have been covered by multiple layers of mud deposits. Heat and pressure, which these layers formed upon the fossils buried underneath, have created conditions for these plant and animal remnants to be transformed into crude oil.

2.Coal:

This is one of the first non-renewable sources of energy used by humans. They have been formed out of layers of animal and plant residues blanketed by layers of mud and water in marshy areas of land surface. Heat and pressure produced by mud and water layers enabled these remnants to be transformed into coal such as we know it today.

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3.Natural gas:

It has been formed over millions of years as a product of sea water flora and fauna. Over time the fossils of these living organisms have been covered by multiple layers of mud deposits. Heat and pressure, which these layers formed upon the fossils buried underneath, have created conditions for these plant and animal remnants to be transformed into crude oil.

4.Nuclear energy (uranium):

It is found in the nucleus of an atom. Atoms are tiny particles which make up every object. They consist of electrons, protons and neutrons. The energy that holds atom particles together is actually used by people to turn water into steam which drives turbines producing electricity.

5.Solar energy:

This is the solar radiation that reaches the earth. Our sun is an extremely powerful energy source, however, man has not invented a method of harnessing this colossal amount of energy. On a cloudless day the amount of energy that reaches the earth at our latitude is in the range of 800-1200 W/m2. Therefore, it is possible to utilize solar energy in two ways: as a heat source and as energy source.

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7.Wind power energy:

Wind is air in motion. It is generated by the non-uniform heating of the earth surface. Since it has irregular relief and various water bodies solar radiation is not absorbed uniformly. Whenever the sun shines during the day the air over the ground surface is heated faster as compared to the air over water surfaces. Warm air over the ground surface expands and rises and the colder air over water surface moves in to occupy the place of the warmer air thus generating local winds. During night time winds change directions as the air over ground surface cools down faster than the air over water surface.

8 . Water (hydraulic) energy:

Hydraulic energy is non-polluting, renewable and reliable energy source which converts kinetic energy of falling waters into electricity without consuming more water than its natural availability. This long period has led to many improvements in the way of obtaining energy. Mechanical energy needed to turn an electric generator is obtained by means of directing, harnessing and transferring driving water. The quantity of potential energy of water is determined by its discharge and the height from which it falls.

9. Wave energy:

Waves are formed by the wind blowing above the ocean surface. They contain a colossal amount of energy. The approximate power of waves crushing down at the coast line of the entire territory of our planet amounts to 2-3000000 mega-Watts. One of the possible ways to boost wave energy is through directing a wave into a narrow bay which, consequently, will raise its level. After that the wave is forwarded towards turbines producing electricity.

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8.Biodiesel:

Biodiesel is a liquid fuel made up of fatty acid alkyl esters, fatty acid methyl esters (FAME), or long-chain mono alkyl esters. It is produced from renewable sources such as fresh and used vegetable oils and animal fats and is a cleaner-burning replacement for petroleum-based diesel fuel. It is nontoxic and biodegradable. Biodiesel has physical properties similar to those of petroleum diesel:

Chemistry for clean environment( chemical ways to reduce the waste ):

The problem with waste:

Waste or rubbish is what people throw away because they no longer need it or want it. In the real Nature the word ”waste” does not exist – everything thrown away by a creature or naturally dead could be of huge importance for the lifecycle of another creature. In difference, almost every human activity generates waste. The fact that people produce waste, and get rid of it, matters for the following reasons:

When something is thrown away we lose the natural resources, the energy and the time which have been used to make the product - the majority of resources that we use in manufacturing products and providing services cannot be replaced.

When something is thrown away we are putting pressure on the environment's ability to cope - in terms of the additional environmental impacts associated with extracting the new resources, manufacturing and distributing the goods, and in terms of the environmental impacts associated with getting rid of our rubbish.

When something is thrown away it is lost as possible resource - what is waste to one person may be a possible useful source for another.

Waste can be divided into different types. The most common classification is by their physical, chemical and biological characteristics. One important classification is by their consistency:

Solid wastes are waste materials that contain less than 70% water. This class includes such materials as household garbage, some industrial wastes, some mining wastes, and oilfield wastes such as drill cuttings;

Liquid wastes are usually wastewater's that contain less than 1% solids. Such wastes may contain high concentrations of dissolved salts and metals.

Sludge is a class of waste between liquid and solid. They usually contain between 3% and 25% solids, while the rest of the material is water dissolved materials;

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Gaseous wastes; Waste energy.

Another classification is based on the toxic waste influence on the human health – according to this principle wastes are divided into two classes: hazardous and non-hazardous. The largest waste classification is by the source of generation – for example inert waste, kitchen waste, litter organic waste, medical waste, municipal solid waste, packaging waste, electronic waste, farm waste, food waste, green waste, commercial waste, construction and demolition waste etc.

The most important classification of waste is based on the possibility for recycling and divides waste into recyclable (plastics, paper, glass, metal etc.) and non-recyclable.

Waste management conceptions. There are various conceptions about waste management. Conception of “3Rs” classifys waste management strategies according to their desirability in terms of waste minimization ("Waste Hierarchy")

R1 - reduce - reduce the amount of produced waste; R2 - reuse - using things again instead of throwing them away after you have

finished with them. R3 – recovery (recycle materials or recover energy) - includes recycling,

composting and energy recovery.

The last option of the hierarchy is “disposal “- via landfill or landraise.

Fig.1. Waste hierarchy

According to this hierarchy the best way and the most desirable option of managing waste is not to produce it (waste prevention) or to reduce the amount of produced waste (fig.1). Then there may be an option to reuse the material. The waste hierarchy specifies the following order of preference for dealing with the wastes: with those towards the top of the list more desirable than those towards the bottom (disposal).

In most cases a combination of options for managing the different wastes produced at home and at work is needed. The challenge is to change our attitudes and our practices so

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that much more of generated waste is dealt with by options towards the top of the hierarchy. Another waste management conceptions are:

- Extended producer responsibility is a strategy designed to promote the integration of all costs associated with products throughout their life cycle (including end-of-life disposal costs) into the market price of the product. This means that firms which manufacture, import and/or sell products are required to be responsible for the products after their useful life as well as during manufacture.

- Polluter pays principle - the Polluter Pays Principle is a principle where the polluting party pays for the impact caused to the environment. This generally refers to the requirement for a waste generator to pay for appropriate disposal of the waste.

Waste management alternatives. Different managing alternatives can be applied to waste, depending mainly on its characteristics. Between the most important waste treatments are sorting and recycling (mechanical and chemical), energy recovery (incineration), biodegradation and finally - landfilling.

Sorting and Mechanical recycling . Sorting and mechanical recycling allows the recovery of raw materials, which can be later used to manufacture new products. Sorting could be done by consumers (by collecting waste separately) or at sorting units. Two types of mixed solid waste are accepted at the sorting units:

Household solid waste: packaging (glass, plastic, aluminium, cardboard and steel) as well as newpapers and magazine etc.;

Commercial and industrial waste: card, paper, wood, metal, plastic, building site waste etc.

Once the mixed waste arrives at the sorting unit, it takes place an initial pre-sorting and a first phase of mechanical sorting (fig.2). After that, a manual process is applied and material is separated in two different groups: recyclable material and non-recyclable material. The last one is normally sent to incinerating facilities or to landfill.

Fig.2. Waste sorting Fig.3. Waste baler

Mechanical recycling combines methods for waste treatment without chemical braking. Recyclable material is mechanically treated for size reduction (if necessary) using

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shredders, cutters, crushers), packed with compactors and balers (fig.3) and sent either to recycling facilities or they are supplied to industry for reuse (for example, card for the paper industry, plastics, metals, glass etc).

Chemical recycling . Waste chemical recycling is based mostly on thermal decomposition of treated materials by breaking of chemical bonds at high temperature.Pyrolysis and gasification are thermal processes which break down waste, containing carbon such as paper, petroleumbased wastes (plastics), and organic materials such as food scraps, using high temperatures. Pyrolysis involves heating waste in the absence of oxygen at temperatures of 400-800°C. The heat alone breaks down complex molecules and the resultant gases are then passed into a combustion chamber where they are burned (in the presence of oxygen) at temperatures around 1250°C. Gasification involves heating wastes in a low-oxygen atmosphere to produce a gas with a low energy content. This gas can then be burned in a turbine or engine. The resulting product is synthetic gas (syngas) consisting of mainly carbon monoxide CO and hydrogen H2 (nearly 85%), ad small amounts of carbon dioxide and methane. Syngas has a high calorific value, so it can be used as a fuel to generate electricity or steam, or used as a basic chemical in the petrochemical and refining industries. Other by-products include liquids (mainly water, used for washing the gas clean) and solid residues – ash or char. Typical gasification and pyrolysis processes have the following steps (fig.4):

Pre-treating the waste - usually involves separating out some of the materials which have no calorific value or are recyclable (glass, grit and metal etc.);

Heating the remaining waste, mainly organic pulp, to produce gas, oils and char (ash);

Cleaning the gas to remove some of the particulates, hydrocarbons and soluble matter (scrubbing);

Application of the cleaned gas to generate electricity or heat.

Fig 4. Schematic view of waste pyrolysis process

A good approach to generate energy from waste is the combination of pyrolysis with gasification process as a second stage: the pyrolysis process degrades waste to produce char (or ash), pyrolysis oil and synthetic gas at the first stage; the gasification process then breaks down the hydrocarbons left into syngas using a controlled amount of oxygen.

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Energy recovery (Incineration). Incineration allows obtaining energy and, at the same time, reducing the volume of landfilled waste. The high combustion temperature makes it possible to recover energy from the waste and use it for heating, industrial applications and electricity production. Main technologies for the incineration of waste are:

Mass Burn This is the simplest and most common form of incineration. Mixed wastes are fed into a hopper and then fall onto a sloping grate which agitates and moves the waste through the combustion chamber. Energy is recovered from the hot combustion gases, which is used to generate electricity; Fluidised Bed Combustion - Before the waste is incinerated, non-combustible components are removed and the waste shredded to produce coarse refuse derived fuel which has a higher calorific value than the untreated waste. This fuel is fed into a bed made up of a mixture of sand and dolomite mineral. Air is pumped through the base so that the solid waste and minerals resemble a bubbling liquid. This ‘fluidisation’ improves the combustion efficiency, hence reducing pollution and generating more energy per tonne of waste.

Three different kind of waste are usually used in the incineration facilities: household waste, non-hazardous industrial waste and rejects from sorting plants. In the incineration process, waste collection vehicles dump the waste in vast trenches where it is mixed and transferred to an oven. Burning waste at extremely high temperatures also destroys chemical compounds and disease-causing bacteria.State-of-the-art technical decisions of incineration process prevent the environmental pollution and allow incinerators to be situated even in the very central zone of cities without risk for the human health (fig.5).

Fig 5,6. Hundertwasser Spittelau Incinerator (Austria,Vienna), biodegradation

Biodegradation: Biodegradation is a process of chemical breakdown of materials by environment. Organic material can be degraded aerobically with oxygen, or anaerobically, without oxygen. Biodegradable matter is generally organic material such as plant and animal matter, substances originating from living organisms, artificial materials that are similar enough to plant and animal matter to be put to use by

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microorganisms.

Aerobic biodegradation: The process of aerobic biodegradation of organic mater is also known as composting. Composting is a process that has always existed in its natural state. Today, with modern technologies, this process can be accelerated and monitored efficiently. In general, composting is the process of controlled aerobic decomposition of biodegradable organic matter. During composting, microorganisms break down organic matter into carbon dioxide, water, heat, and compost.

Organic matter +O2 → compost + CO2+H2O+NO3- +SO42- + heat

There are a large number of biodegradable materials suitable for composting: food and drink industry waste; paper, card, timber and other cellulose-based biodegradable waste; household waste; organic sludge including sewage; agricultural waste. Some waste biodegradable materials should not be used in household compost because they attract unwanted vermin and do not appropriately decompose in the time required: meat, diary products, eggs.

Microorganisms are key to composting. According to the oxygen consuming microorganisms could be divided in aerobic (use oxygen for their metabolism) and anaerobic (they are active in environment without oxygen). The process has three stages: active (thermophilic) biodegradation, cooling and maturation. Temperature is a key parameter determining the success of composting process. During the first stage the temperature reaches 55-65°C, and during the second one - 35 - 45°C. Heat is produced as a by-product of the microbial breakdown of organic material. Temperatures t< 25°C could end of the composting process. Temperatures t > 70°C could kill also bacteria responsible for composting process. Moisture is the second important for the microorganisms metabolism factor – the optimal moisture level is 50 – 60%. Carbon C, nitrogen N, phosphorus P and sulfur S are elements naturally existing in biomass. Carbon-to-nitrogen, carbon-to-phosphorus and carbon-to-sulfur balanced ratios are also important for the process. The value of pH changes during the composting process also – it decreases during the first stage because of CO2 generation, but increases during the second stage up to 8-9 because of ammonia NH3 generation.

According to the process conditions there are two types of aerobic composting: active (hot) and passive (cold) composting. The passive composting is more slow than the hot one and is preferred for domestic composting. According to the technical performance composting could be performed as enclosed (home container composting or industrial in vessel composting and composting in exposed piles (home composting in pile and industrial windrow composting (fig.6).

There are many benefits from home composting. The ready compost can be used in gardening and agriculture as a soil amendment for erosion control, land/stream reclamation, wetland construction, as landfill cover or as a seed starting medium.

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(Home composting) (Industrial in-vessel composting) (Industrial Windrow composting)

Fig. 7. Composting techniques

Anaerobic digestion. Anaerobic digestion is a biological process conducted in the absence of oxygen in which micro-organisms degrade the organic fraction of a feedstock, yielding a product gas (biogas) of principally methane and carbon dioxide and with some trace gases such as H2S, N2, NH4, etc.

In the anaerobic digestion process, the organic portion of the waste is separated to remove plastic, glass and metals and then placed in a sealed reactor. Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen, used for industrial or domestic purposes to manage waste and/or to release energy. There are four key biological and chemical stages of anaerobic digestion (fig.8):

Fig 8. Anaerobic digestion process

Hydrolysis: the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids by enzymes;

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Acidogenesis (Fermentation): the biological process of acidogenesis is where there is further breakdown of the remaining components by acidogenic (fermentative) bacteria; here volatile fatty acids are created along with ammonia, carbon dioxide and hydrogen sulfide as well as other by-products;

Acetogenesis: molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid as well as carbon dioxide and hydrogen;

Methanogenesis: methanogens utilise the intermediate products of the preceding stages and convert them into methane, carbon dioxide and water.

A simplified generic chemical equation for the overall processes outlined above is as follows: C6H12O6 → 3CO2 + 3CH4

Anaerobic digestion degrades organic matter and makes the resultant residue more stable; this protects the environment from the uncontrolled degradation of the waste. Thus, it reduces the potential for the production of atmospheric methane and leachate. It also reduces the impacts from environmental aspects such as odour, flies and vermin and helps to reduce the plant and animal pathogens that can be spread by wastes. The biogas yielded by the process can be used for various applications. An efficient option is to use the biogas in a combined heat and power (CHP) plant, in which heat and electricity are generated simultaneously

Landfill. Waste that can neither be reused nor receive special processing is stored in landfills. Beforehand, some waste may need to be stabilised to prevent pollution leakage.

A landfill requires high technical standards and must conform to strong safety norms in order to protect the environment and local communities. It is very important taking into account:

The location for the landfill and the surrounding land The design of modular compartments The protection of groundwater The collection, treatment and elimination of leachates The capture, treatment and recovery of biogas The construction of a cover, in order to minimise rainwater penetration

Waste is monitored and weighed as it enters the site. Waste with high pollution levels and toxic waste is redirected to a special site. Waste is stored in isolated independent cells and then covered with geological screens in the form of layers of impermeable materials (eg. clay) topped with watertight and drainage systems. By this way all contact between the waste and the natural environment is prevented. Finally, with the view of revegetation it is added a layer of topsoil. Over time, waste, which decomposes produces landfill gas or biogas, a mixture of carbon dioxide and methane. Biogas is collected and then used in co-generation processes, which produce energy and heat. Apart from biogas, the decomposition of landfilled waste, along with rainwater infiltration, produces a liquid known as "landfill leachate". Leachates contain heavy metals, salts, nitrogenous compounds and various types of organic matter. Due to its high polluting potential it is

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needed that this leachate is collected and treated to avoid environment contamination. Modern landfills are well-engineered facilities that are located, designed, operated, and monitored to ensure compliance with European regulations.

Chemistry and the environment: help or hindrance?

Environmental issues such as climate change, water pollution and renewable energy make the news headlines and have become increasingly important in every day life. Many people perceive chemistry and the chemical industry as harmful to the environment. However, many new advances and scientific researches in the field of chemistry are helping us to develop more environment friendly materials and applications, while preserving the quality and the lifestyle we expect.

Over the years, the industry and wider public have become aware of the damaging effects of some past practices and the need to protect the environment. In the past, few were aware of the potentially negative effects our modern lifestyle might have on the environment, and rather saw only the positive potential for creating new, useful materials and products.

Research in biological sciences and chemistry has revealed that industrial processes in chemistry and petrochemistry could play a role in developing solutions to environmental problems such as climate change, waste management, recycling, energy efficiency – just to name a few. Without chemists, we might never have truly understood these problems. Profound changes have been made – and still are being made - to provide alternative solutions.

Industry has also developed a number of voluntary initiatives such as the ‘Responsible Care’ programme, to raise the standards in dealing with health and environment issues and establish safe and sustainable transport systems in full accordance with regulation. As part of its Responsible Care programme the industry publishes guidelines for the distribution and handling of chemical substances that require appropriate precautions. All these efforts combined with the new European chemicals legislation (called REACH) guarantees that chemistry is carried out in a safer and more environmentally friendly way.

In parallel, chemists and petrochemists are now researching new methods that are more sustainable and environmentally friendly while maintaining the development of our economy and our industry. Examples include:

Biofuels: transportation fuel derived from biomass. A wide range of biomass products such as sugar cane, rapeseed, corn, straw, wood, animal and agriculture residues and waste can be transformed into fuels for transport;

Bioplastics: production of plastic materials using natural sources such as plants, which are then biodegradable;

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Insulation: enhanced insulating materials to enable more energy-efficient homes and buildings;

Lightweight plastic composites which help reduce cars and airplanes’ fuel consumption;

Fuel cells: when used to power cars or motorbikes, hydrogen fuel cells produce water vapour instead of exhaust gases;

New lighting technologies (such as Organic Light Emitting Diodes - OLEDS)  which produce more light with less electricity;

Wind turbines and solar panelling: both rely on materials produced by the chemical industry. The metal blades of wind turbines have largely been replaced by blades made of fibreglass-reinforced polyester to stand up to the severest weather.

Society tends to consider every man-made chemical as bad and everything natural as good. Just because something is natural does not automatically make it good for the health or the environment – or unsafe if it’s a man-made chemical. What looks more natural than burning wood in on open fire for instance? In reality, smoke from open burning can be harmful to both human health and the environment like other combustion processes.

Also, the whole life cycle of a product (from its creation through to its disposal) needs to be taken into account when considering its impact. Did you ever realize that the impact of cotton culture on the environment can be higher than making synthetic fibers such as polyester? The reason for this is that cotton requires the use of enormous quantities of water, fertilizers and pesticides.

Strengthening the science of chemistry through research and development is necessary to allow us maintaining a comfortable life in harmony with the environment and nature. It illustrates the greatest challenge of all disciplines of modern science, and most especially with those that pertain to the environment - the integration of technology, nature and human beings.

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