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What is Biological oxygen demand and how does it affect water quality?

Chemicals…oxygen…demand…what do all these words mean and what does it have to do with your water? For a quick look into the world of biochemical oxygen demand just have a look below. Biochemical oxygen demand is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. Natural sources of organic matter include plant decay and leaf fall. However, plant growth and decay may be unnaturally accelerated when nutrients and sunlight are overly abundant due to human influence. Urban runoff carries pet wastes from streets and sidewalks; nutrients from lawn fertilizers; leaves, grass clippings, and paper from residential areas, which increase oxygen demand. Oxygen consumed in the decomposition process robs other aquatic organisms of the oxygen they need to live. Organisms that are more tolerant of lower dissolved oxygen levels may replace a diversity of natural water systems contain bacteria, which need oxygen (aerobic) to survive. Most of them feed on dead algae and other dead organisms and are part of the decomposition cycle. Algae and other producers in the water take up inorganic nutrients and use them in the process of building up their organic tissues.
Consumers like fish and other aquatic animals eat some of the producers, and the nutrients move up the food chain. When these organisms die, bacteria decompose the organic compounds and release into the water inorganic nutrients such as nitrate, phosphate, calcium, and others. Some of these nutrients end up down stream or in sediments, but most of them recycle again and again. Most of the bacteria in the aquatic water column are aerobic. That means that they use oxygen to perform their metabolic activities of decomposition. Remember that we learned in other related exercises that under normal conditions, dissolved oxygen exists in very low concentrations. Natural levels of oxygen in aquatic systems are always somewhat depleted by normal levels of aerobic bacterial activity. In most cases, if dissolved oxygen concentrations drop below 5 parts per million (ppm), fish will be unable to live for very long. All clean water species such as trout or salmon will die well above this level and even low oxygen fish such as catfish and carp will be at risk below 5 ppm.
When abnormally high levels of aerobic bacterial activity takes place, however, the level of dissolved oxygen can drop dramatically. Under what circumstances does this happen? Generally, this occurs when there is some sort of abnormal "pollution" introduced into the system. This can occur in the form of organic pollution for sources such as domestic sewage, septic tank leakage, and fertilizer runoff, or could be in the form of inorganics from domestic or industrial sources. Natural sources of organic compounds can also come into aquatic systems by means of floods, landslides, and erosion.
One of the most important nutrients, which affected BOD in aquatic systems in the recent past is phosphate pollution from American households. It was discovered decades ago that the addition of phosphorous to soaps and detergents made them clean better. By the 1960's, millions of households and businesses were dumping tons and tons of phosphate down the drain. Eventually, much of this important nutrient made its way to the watercourses of America. Because phosphorous is one of the most important limiting factors (necessary nutrients) in aquatic systems, there began numerous and widespread algal blooms. Algal blooms are dramatic population outbursts of growth in which often one or two species of algae suddenly find the conditions right for rapid growth.
Because most unicellular algae reproduce asexually by rapid cell division, it doesn't take long for a species of algae to suddenly and literally turn the water green with billions and billions of new cells. Because the conditions necessary to these algal blooms are sometimes temporary or because the algae exceed the threshold level of some other limiting factor, the blooms are only temporary. They often last only a few days. What happens when the bloom is over? The algal cells don't have enough nutrients and most of them die. At this point, the aerobic bacteria become important and start to decompose the algae. Because there is so much food for them, they also experience a sort of bloom, and they literally suck the oxygen out of the water. When the oxygen is gone, the bacteria and most other aerobic creatures in the aquatic system start to die.
During the 1960's and the 1970's, this phenomenon was widespread with dramatic fish kills and large segments of slow-moving rivers and lakes becoming almost abiotic (lifeless) because of high BOD caused by pollution. The procedures followed in this exercise involve the collection of water and the measurement of dissolved oxygen and pH at the time of the collection. The samples are placed in bottles full to the brim and sealed off by a lid. The sample bottles are covered completely with aluminum foil and placed in a dark place. This limits the photosynthesis, which could happen with captured algae. After five days, the bottles are uncorked and the dissolved oxygen is probed. The difference between the first and the last of the samples is called the BOD. A low number generally means little pollution and/or little aerobic activity. A high BOD means the opposite. 


StarLink Corn: What Happened

Humans and animals have consumed corn for centuries. Corn is one of the world’s most commonly eaten foods. It is no wonder the Aventis Cropscience genetically modified a corn to be resistant to pests.
Aventis Scientists incorporated Cry9C, a protein isolated from a common soil bacteria; Bacillus thuringiensis (Bt) sp. Tolworthi, into StarLink corn. The Cry9C protein is effective against caterpillars because it binds to different sites of the insect gut and destroys the stomach cells. This protein has no effect on other living creatures. StarLink corn was approved by the U.S. Environmental Protection Agency (EPA) for animal feed but not for human food until additional testing was completed.
The controversy began when traces of DNA from StarLink corn were found in taco shells and other corn related products. Although there are several varieties of Bt corns in the market, StarLink was illegal in human food. It was only approved for animal feed. The EPA Scientific Advisory panel considered the protein Cry9C a medium risk potential human allergen. This decision was based upon limited data. The protein was slow to digest, suggesting a possible concern, however the protein’s amino acid sequence was not similar to known allergens therefore the likelihood of allergencity is low. Furthermore, for people to become allergic to a protein they need to be exposed to it multiple times over an extended period of time. Since the Cry9C protein is only a small fraction of corn protein, the probability that the protein would sensitize an individual is low.
The FDA received approximately 34 reports of adverse reaction to corn products which may contain StarLink. Of the 34 reports, 20 were very unlikely a result of an allergenic reaction. The U.S. Center investigated 7 people who experienced symptoms that are consistent with an allergenic reaction. The people showed no reaction to the Cry9C protein. This does not mean people could not develop an allergic reaction in the future.
Aventis submitted a new evaluation of the corn to EPA and requested a temporary approval for human consumption. The new information demonstrated the consumption of corn based foods that contain StarLink would expose consumers to Cry9C many times smaller than needed to cause sensitivity. Subsequently, Aventis voluntarily withdrew registration for StarLink corn. It will no longer be grown.
As a result of this episode, the Aventis Company and others in the biotechnology industry will seek approvals for both human and animal consumption before marketing genetically enhanced seeds.
For more information on biotechnology visit and


Soil formation

One of the most important scientific discoveries was how soil forms spontaneously from rock. Under the influence of physical factors like deformation by heat and cold, assault by wind, rain, hail and ice, and the enormous levering forces of water expanding into ice, solid rock is shattered into smaller pieces (see picture). But however small these fragments, they still have the same properties as the parent rock.
Being formed under high pressure and temperatures, the crystals of the minerals in the rock are somewhat unstable at surface pressure and temperature. Particularly when attacked by acids that etch away the soluble components in the minerals, the crystals fall apart, albeit very slowly. It is called spontaneous weathering, but it is accelerated considerably under the influence of vegetation and its acids (chemical weathering).
During the weathering process, four components are released:
  • minerals in solution (cations and anions), the basis of plant nutrition.
  • oxides of iron and alumina (sesquioxides Al2O3, Fe2O3).
  • various forms of silica (silicon-oxide compounds).
  • stable wastes as very fine silt (mostly fine quartz) and coarser quartz (sand). These have no nutritious value for plants.

Factors in soil formation:

  • parent material

  • time

  • climate

  • atmospheric composition

  • topography

  • organisms

  • Depending on temperature and rainfall, new minerals are formed. The oxides of iron and alumina combine with silica to form clay. In temperate regions a three-layer clay is formed, which is weak, swells under moisture, and clogs. It is able to absorb large amounts of water but is rather heavy on plant roots, blocking the oxygen the soil organisms need. Because clay has a charged surface area, it is able to bind and retain minerals and nutrients (Cation Exchange Capacity). The valuable nutrition for plants won't leach away easily in three-layer clays.
    Two-layer clays are formed in hot, humid tropical regions, producing arable but easily dried soils. These clays are not able to hold much water, or nutrients, but are still very much better than sand.

    Soil's productivity is mainly due to the clays in the soils. Knowing that clay particles are very small (less than 2 microns), one can imagine that this component is easily eroded out of the soil. Its small size prevents it from sedimenting out rapidly in water, resulting in rivers, lakes and ocean water staying turbid for a long time after rains have ended.
    The mix of sand, silt and clay is called a loam. In this diagram, the triangle represents all possible combinations of the three. Soil specialists use names for the various loams, as indicated in the diagram. A loam can be dried and pounded in the laboratory and passed through sieves to separate the mix by particle size. From the diagram, the official composition of 'loam' can be inferred - sand:silt:clay = 40:40:20. (Draw lines parallel to each side and read the left-hand values.)
    Sand is very workable but won't hold water, or nutrients well. Loam is poor in nutrients, reasonably workable, but holds water well. Clay is difficult to work, compacts easily, but holds water and nutrients well, but is reluctant to release these to plants. As the diagram shows, the various loams derived from the three base components, have varying workability, water holding capacity and cation exchange capacity (CEC).

    Not only temperature and moisture affect soil formation but also the level of the groundwater table and the steepness and elevation. As can be seen, soil formation depends on many factors, regional and local, resulting in an almost infinite number of different soils, each having different needs. Nutrients therefore, can vary considerably from patch to patch, requiring careful application and observation.

    Soil profile
    soil profilesWhereas soil is formed from the rock below, it is eroded away from the top. A cover of plant life slows down erosion, allowing the soil layer to build up, but there is more going on.
    Just above the base rock, is the C-horizon, containing the recently weathered and still weathering soil. It is rich in nutrients. The A-horizon is where most plant roots are found and all soil organisms. Its nutrients have been used by plants or leached downward, so it is relatively poor in nutrients, but rich in life. By comparison, the B-horizon is the zone where new material from below and nutrients from above accumulate. Sometimes an impermeable layer or pan is formed above it (podsol), denying plants to access this rejuvenating source of new nutrients. On the surface of the soil, often a thin layer is found, rich in leaf litter and other organic material.

    horizondescription of detailed soil horizons
    Oconsists mainly of organic matter from the vegetation, which accumulates under conditions of free aeration.
    Aeluvial (outwash) horizon consisting mainly of mineral matter mixed with some humified (decomposed) organic matter.
    Estrongly eluviated horizons having much less organic matter and/or iron and/or clay than the horizons underneath. Usually pale coloured and high in quartz.
    Billuvial (inwashed) horizon characterised by concentrations in clay, iron or organic matter. Some lime may accumulate, but if the accumulation is excessive, the horizon is named K.
    Khorizon containing appreciable carbonate, usually mainly lime or calcium carbonate.
    Ggleyed horizons which form under reducing (anoxic) conditions with impeded aeration, reflected in blueish, greenish or greyish colour.
    Cweathered parent material lacking the properties of the solum and resembling more the fresh parent material.
    Rregolith, the unconsolidated bedrock or parent material.
    Soil and top soil are produced naturally at a rate of  1mm in 200-400 years, averaging at about 1 ton/ha/y. A full soil profile develops in 2,000 - 10,000 years, a period which is long for humans but short for the planet. World-wide, agricultural soil is lost at a rate 10-40 times faster than its natural replacement. The USA lost 80mm since farming began, 200 years ago. This amounts to some 18 t/ha/y. China appears to lose 40 t/ha/y. World-wide loss of agricultural land is 6 million ha per year, from a world-wide total of 1200 million ha (0.5%/y). These are compelling reasons for improving the way humans manage their soils.


    Soil Identification & Removal

    Inert Soil

    Soil is any unwanted matter on the surface of an object that one desires to be clean. Cleanliness is an unnatural condition, because all surfaces are constantly being soiled. In order to clean a surface (substrate), it is, therefore, necessary to work against nature, and special care must be taken to ensure that all soil is removed and that it is not redeposited on the substrate. This section deals with classes of soils and the identification of them.
    Soil may be classified as visible and invisible, the latter category being primarily micro-organisms, such as bacteria, yeasts and moulds. Soil is best identified by characteristics that give information on how it may be solubilised, because the object of cleaning is to dissolve or to suspend soil and then to wash it away.
    Visible soil is classified according to its solubility characteristics — whether it is:
    • Soluble in water
    • Soluble in alkali
    • Soluble in acid
    • Soluble in surfactant solution
    • Insoluble in any of the above
    Soils, such as sugar, and some inorganic compounds like ordinary salt can be dissolved and washed away by ordinary water. In addition, the greater part of food soil can either by suspended in water or can simply be removed from a surface by the force of a water spray. Any soils not directly soluble in water will be left behind as a thin film or as a deposit.
    Some of these films and deposits are either solubilised or emulsified by alkaline detergent solutions. Natural fats and oils from plants and animals contain small amounts of free fatty acids. These acids are neutralised by alkaline solutions forming small amounts of soluble soap. This soap can then aid in the emulsification of the fats and oils that are present in many soils or films. Alkalis also react directly with plant and animal fats and oils to form soap, glycerine, and water by a process called saponification. Neutralisation is a much more important reaction than saponification in the removal of greasy films, however, because it is a fast reaction as compared to saponification.

    Protein soils

    Protein soils from milk, eggs, meat etc., can also be solubilised by alkaline solutions. Proteins will hydrate and swell when they come into contact with water which helps alkalis to react with them, forming soluble salts. To a small degree the protein soils may also be broken down into smaller, more soluble molecules by a reaction with alkaline materials which is called peptization. This reaction is slow, however, and therefore, relatively unimportant.


    Milkstone, mineral deposits and other deposits formed by the reaction of minerals with organic substances often are deposited on surfaces where they are not wanted. This type of soil is sometimes very complex, but at least part of it will be solubilised by a reaction with acid. Even if only a part of the soil is removed in this manner, the remainder is often loosened during the reaction so that it is washed away. In those cases where part of the deposit is composed of fat, the acid can be followed by an alkaline wash.

    Lubricating greases and oils

    Lubricating greases and oils are not solubilised by either acids or alkalis. They can sometimes be melted by hot water or steam but even then, a residue is often left behind. Surfactants help emulsify this material by breaking it up into small globules which are soluble in water or which can be suspended in water. Most dust and dirt contains some oily material which makes removal by this method possible.


    Those soils which are insoluble in water, in alkaline solutions, or in acid solutions usually do not cling to most surfaces anyway. Surfactants often allow the detergent solution to wet these soils so that they can be suspended in water or so that they can be flushed from the surface to be cleaned. Examples of such soils are sand, clay and fine metal particles. Charred or carbonised soil is more difficult to remove.
    During the processes in which water is removed from food and in pasteurisation and sterilisation heat is often applied in a manner that chars or carbonises some of the food. The chemistry is often complex, but in ordinary physical terms this is simply burned-on food. A 1% caustic solution applied at 180°F (82.2°C) with brushing will usually solubilise or suspend this type of soil.

    Soil Identification

    Chemicals and basic directions for the identification of most soils....
    It is important (especially when one is not yet completely familiar with soil testing) to perform the tests in the order given here. This will eliminate unnecessary testing and also avoid incorrect soil identification.


    Place a drop or two of phenolphthalein on the soil. If a pink colour appears, the soil is alkaline; if there is no colour change, the soil is neutral or acid. Most alkaline residues are caused by poor rinsing after washing with an alkaline detergent, but sometimes they are caused by alkaline water supplies. The latter case can easily be verified by checking the pH of the raw water. If it is over 9, the cause may very well be the water. The majority of food soils should be neutral or acid in nature.

    Alkaline Soil

    The preceding test may have indicated alkalinity by turning phenolphthalein pink. This test will tell whether an alkaline soil can be removed completely by acid. Add a few drops of acid as indicated in the directions, allow to stand for at least two minutes, and then rinse with water. If the soil is completely removed from the spot, an acid product will remove the soil. If only part of the soil is removed, other treatment is required.

    Acid Soil

    Add a few drops of caustic to the soil, allow to stand for at least two minutes, and rinse with water. If the soil has been removed, an alkaline product can be recommended. If only a part of the soil was removed, further testing and treatment is necessary.

    Protein Soil

    Add a few drops of caustic and drop of two of Hi Tech Detergents XY-13 (Sodium Hypochlorite) to the soil. Allow to stand for at least two minutes and rinse with water. If this test removes soil that was only partially removed in the last test, a chlorinated alkaline cleaner is required.

    Silica Film

    If the tests for alkaline, acid and protein soils do not remove the film or soil, then and only then should the test for silica film be run. Place a few drops of silica reagent on the soil and allow it to stand for at least two minutes before rinsing it off. If soil is removed that could not be removed by any other test, there is a possibility that there is a silica film. A special acid treatment is needed to remove it, but this treatment is dangerous and should never be used without the authorisation of your supervisor.
    The foregoing tests with their recommendations will help in solving many cleaning problems even if the approach to testing has been over simplified. The examples given here illustrate the manner in which these tests can be combined for the solution of some complex as well as some simple soil problems.

    Example Results

    A series of tests have been run on a soil with the following results....
    AcidNo reaction
    CausticSome reaction after two minutes
    This indicates a neutral or acid type soil, such as fat, protein, or both. A longer test with caustic should be run to see if the soil can be completely removed or if further testing is required. Product selection should be made after that.
    In another example, the test results were as follows:
    AcidSlight reaction
    CausticRemoval of part soil. When tried on the same spot as the acid test, complete removal of soil.
    This indicates that there is fat, protein, or both in the soil as well as a slight mineral deposit. The way the tests were run indicates that an acid wash followed by an alkaline product would be effective in removing the soil. It may be possible to reverse the order for the same result.
    Quite often, a soil that is slowly, but completely removed by caustic alone will be removed much faster by caustic and chlorine. The technician must take time difference into account when choosing between an alkaline and a chlorinated alkaline product.
    A special note on the test for silica film is necessary here to avoid the unnecessary use of this special reagent.
    • silica film is quite rare.
    • this reagent will remove almost any soil.
    • this reagent is dangerous to handle — extremely so.
    Only if one is absolutely positive that no other means are available for the removal of a soil, should one request this chemical.

    Table of Films and Deposits

    The soil chart which follows lists some common films and deposits, their causes, their removal and their prevention.
    A well designed cleaning system should have trouble-free operation as one of its goals, and if it is maintained properly, it should function for long periods of time without problems. However, any given system may have a flaw in it; part of the cleaning procedure may be omitted at times; the equipment may break down; the water supply may change; etc. Any of these "errors" or changes may lead to the formation of a film or a deposit. The table lists and describes some films and deposits, their probable causes, and some methods for their removal. The prevention of further problems will be obtained by adhering to proper cleaning and maintenance procedures.
    Film or Deposit IdentificationDescriptionProbable CausesProcedure for Removal
    Protein FilmA blue or rainbow coloured film having a varnish-like appearance similar to dried apple sauce.Use of a non-chlorinated cleaner. Inadequate pre-rinse. Periodic instead of regular cleaning.Make a paste with equal parts of chlorinated cleaner, alkaline cleaner and water, and apply this to the soil. Allow to soak and then wash with water.
    Fat, Grease, or Oil FilmA greasy, oily, sometimes white film on which water forms into beads.Use of an acid product for washing. Low wash temperature. Oil from equipment.Wash with hot, alkaline surfactant solution.
    Factory SoilA black and/or greasy film.Oil and dirt from the manufacturing process. Grease or oil coating for protection during storage.Wash with hot, foamy, alkaline detergent solution. If rusty, wash with and acid product.
    Surfactant FilmA blue film.Poor rinsing.Wash with a hot detergent solution. Brushing may be necessary.
    Food Stabiliser FilmA white, sandy deposit.Adherence of food stabilisers from foods such as cheese, ice-cream, convenience foods, etc., when only alkaline cleaners are used.Wash with an acid solution.
    Rubber FilmBlack streaks or a film which may be sticky.Reaction of rubber with a chlorinated product or ageing of rubber.Wash with an acid solution and replace rubber parts that are sticky or that still have black streaks.
    Silica Film(very rare)A white or grey glaze.Silica from a water supply when there is poor rinsing or when mechanical cleaning is used where manual cleaning is specified.Clean with a special acid wash (This acid is very dangerous and cannot be used without the proper approval).
    Mineral DepositA white, grey or yellow deposit such as milkstone, beerstone, waterstone etc.Minerals in water settling out or reacting with substances in milk, beer, meat, fruit and then settling out.Wash with an acid product. In breweries a solution of EDTA in water is often used to remove beerstone.
    Iron DepositA red, brown or black deposit.High iron content in the water supply or iron from system components and a lack of iron removal equipment.Wash with an acid product or with a 5% citric acid solution.
    CorrosionA rusty or pitted surface.Migrating metal particles or excessive contact time with a sanitising rinse.Wash with an acid product and brushing to remove rust. Repolish and passivate pitted surface.
    CorrosionA black residue or deposit.Contact of two different metals such as two types of stainless steel. Chemical action of alkaline cleaner or aluminium.Wash with an acid product.
    CorrosionA blue to black film on stainless steel in high temperature equipment.Oxidation through foaming or aeration under conditions of high alkalinity and high temperature.Treat with potassium permanganate and phosphoric acid
    EtchingPitting, usually with a white deposit on the pits.Use of improper chemicals or failure to use chemicals correctly.Repolish and passivate pitted surface.
    The conditions listed below pertain to plastic materials, usually tubing, that are ordinarily clear and colourless. All of them can be prevented or postponed by careful adherence to good cleaning procedures. However, all plastic must be replaced eventually.
    Opaque conditionPlastic is no longer clear and may appear white.Absorption of moisture due to poor drainage or a lack of drying.Expose to heat and light (sunlight). Forced air drying may be necessary.
    YellowingGradual formation of yellow discoloration.Ageing of plastic or improper use of an iodophor.Cannot be removed. Replace the plastic.
    Brown or Black FilmBrown or black deposit may appear as specs, steaks or film may appear suddenly or gradually.Migration of rubber particles or carbon particles from motors.Wash with acid solution. Replace the plastic if washing does not remove the film.
    Red StainBacterial pigment.Pigment from the organism Serratia marcescens.No procedure is known for the removal of this stain.
    Pink or Purple StainBacterial pigment.Pigment from the organism, Streptococcus rubrireticuli.Wash with a highly alkaline solution.

    Surfactants: Surface Active Agents

    The information on the properties of water previously, provides background for a discussion of the properties of surfactants. A surfactant is briefly defined as a material that can greatly reduce the surface tension of water when used in very low concentrations. Table Two shows that Softanol 90 reduces the surface tension of water from 73 to 30 dynes per centimetre when used at a concentration of 0.005 percent. Ethanol when used at a concentration of 20 percent, however, only reduced tension of water to 38 dynes per centimetre.

    Relationship of Surface Tension and Concentration

    Table Two
    Percent Concentration required to reduce the surface tension of water to indicated values
    Surface tension, dynes per cm7350403022
    Softanol 9000.0030.00080.0050---

    A particular type of molecular structure performs as a surfactant. This molecule is made up of a water soluble (hydrophilic) and a water insoluble (hydrophobic) component (Figure Two).
    Figure Two Schematic Sketch of Surfactant Molecule

    The hydrophobe is usually the equivalent of an 8 to 18 carbon hydrocarbon, and can be aliphatic, aromatic, or a mixture of both. The sources of hydrophobes are normally natural fats and oils, petroleum fractions, relatively short synthetic polymers, or relatively high molecular weight synthetic alcohols. The hydrophilic groups give the primary classification to surfactants, and are anionic, cationic and nonionic in nature. The anionic hydrophiles are the carboxylates (soaps), sulphates, sulphonates and phosphates. The cationic hydrophiles are some form of an amine product. The nonionic hydrophiles associate with water at the ether oxygens of apolyethylene glycol chain polyethylene glycol chain (Figure Three). In each case, the hydrophilic end of the surfactant is strongly attracted to the water molecules and the force of attraction between the hydrophobe and water is only slight. As a result, the surfactant molecules align themselves at the surface and Schematic Sketch of Surfactant Molecules in Waterinternally so that the hydrophile end is toward the water and the hydrophobe is squeezed away from the water (Figure Four).
    Figure Three Polyethylene Glycol Chain

    Figure Four Schematic Sketch of Surfactant Molecules in Water
    This internal group of surfactant molecules is referred to as a micelle (m).

    Because of this characteristic behaviour of surfactants to orient at surfaces and to form micelles, all surfactants perform certain basic functions. However, each surfactant excels in certain functions and has others in which it is deficient.
    Foaming agents, emulsifiers, and dispersants are surfactants which suspend respectively, a gas, an immiscible liquid, or a solid in water or some other liquid. Although there is similarity in these functions, in practice the surfactants required to perform these functions differ widely. In emulsification, as an example - the selection of surfactant or surfactant system will depend on the materials to be used and the properties desired in the end product. An emulsion can be either oil droplets suspended in water, an oil in water (O/W) emulsion, water suspended in a continuous oil phase, water in oil (W/O) emulsion, or a mixed emulsion. Selection of surfactants, orders of addition and relative amounts of the two phases determine the class of emulsion.
    Each of these three functions is related to the surfactant absorbing at a surface, either gas, liquid or solid with the hydrophilic ends of the molecules oriented to the water phase. The surfactants form what amounts to a protective coating around the suspended material, and these hydrophilic ends associate with the neighbouring water molecules. In addition to surfactant effects the stability of these suspensions is related to the particle size and density of the suspended material.
    Solubilisation is a function closely related to emulsification. As the size of the emulsified droplet becomes smaller, a condition is reached where this droplet and the surfactant micelle are the same size.
    At this stage, an oil droplet can be imagined as being in solution in the hydrophobic tails of the surfactant and the term solubilisation is used. Emulsions are milky in appearance and solubilised oils, for example - are clear to the eye.

    The Function of Detergency

    The function of detergency or cleaning is a complex combination of all the previous functions.Simplified Illustration of Detergency The surface to be cleaned and the soil to be removed must initially be wet and the soils suspended, solubilised, dissolved or separated in some way so that the soil will not just re-deposit on the surface in question (Figure Five).

    Figure Five Simplified Illustration of Detergency

    Heavy Metal is Bad for You

    Which band are you talking about?
    Not any band, but the fact that although metallic lead itself is not toxic, its compounds often are.
    Lumps of lead are insoluble, but many lead compounds dissolve in water and act as neurotoxins in the body. Lead acetate used to be called 'sugar of lead' because of its sweet taste; it was added to wines as a sweetener! Insoluble lead compounds have been used in paints, including lead chromate for "yellow lines". And, of course, it has been used in petrol.

    Why was lead put in petrol anyway?
    To improve the octane rating.
    What does octane rating mean?
    Petrol is a mixture of compounds of carbon and hydrogen called hydrocarbons; most of the hydrocarbons in petrol are alkanes. In modern car engines, the petrol vapour-air mixture is highly compressed before it is sparked, in order to get the maximum energy from the burning fuel. However, some hydrocarbons tend to ignite under pressure before they are sparked, so that the engine runs roughly; this is known as "knocking". Branched-chain alkanes tend to resist this pre-ignition better than alkanes with unbranched chains. Alkanes and fuel mixtures are given Octane ratings depending on their knocking tendency. 2,2,4-trimethylpentane (which contains 8 carbons and so is an isomer of octane) has an Octane rating of 100; heptane has a rating of 0. The Octane number of a petrol is the % of 2,2,4-trimethylpentane in a mixture with heptane that has the same knocking characteristics as the petrol under test.

    heptane - click for 3D structuretrimethylpentane
    The gasoline fraction from refining crude oil has an octane rating below 60, which is why you can't put it straight into a car (which needs 87 octane for 2-star and 93 octane for 4-star).
    How does lead improve the octane rating?
    In 1922, an American called Thomas Midgely (who also invented CFCs) found that if tetraethyl lead, Pb(CH2CH3)4, was put into petrol, particles of lead and lead oxide PbO are formed on combustion. This helps the petrol to burn more slowly and smoothly, preventing knocking and giving higher Octane ratings. 1,2-dibromoethane is also added to the petrol to remove the lead from the cylinder as PbBr2, which is a vapour and removed from the engine. (This is how lead is released into the environment from leaded fuels). Using higher-Octane leaded petrol meant that more powerful high-compression engines could be built.

    Lead tetraethyl (left) is a lead atom bonded to a tetrahedral arrangment of ethyl groups. Thus, the molecule can be thought of as a metal atom surrounded by a hydrocarbon cage. The C-Pb bond is quite weak, and in the hot environment of an internal combustion engine it fragments producing lead and C2H5 radicals which can help terminate the combustion process by radical reactions.

    So what's the problem?
    There are two problems. First, the lead that's released from car exhausts is dispersed into the environment, and has been linked to a number of health problems. In particular, studies indicated that children living near motorways seemed to have lower IQs than those living in areas with less lead pollution, suggesting that the lead was somehow linked to a lowering of brain function and intelligence in children.
    The second problem is that car exhausts contain environmentally unfriendly gases, such as CO and nitrogen oxides. A catalytic converter can help to remove these gases, but it cannot be used on leaded petrol since the lead 'poisons' the catalyst.
    Are there any alternatives to lead tetraethyl ?
    Yes, there's another additive called MTBE, which stands for methyl tertiary-butyl ether, and it is designed to reduce carbon monoxide and ozone emissions as well as to boost Octane ratings.

    How does it reduce CO levels?
    The toxic gas carbon monoxide is formed by incomplete combustion of petrol. The oxygen atom in MTBE helps provide extra oxygen for complete combustion, and helps give it an Octane rating of 116.
    How is MTBE made?
    By an acid-catalysed addition reaction between methanol and methylpropene. In 1994, MTBE was the 18th most important chemical produced in the USA.
    CH3OH + CH3C(CH3)=CH2 arrow (CH3)3C-O-CH3
    So why is MTBE a problem in the USA?
    Leaking petrol storage tanks and spillage have caused MTBE to get into groundwaters in the USA. Although it is not very toxic, it is not very biodegradable either, and has a strong taste and smell, noticeable at the 15 parts per million level. There is now a strong movement to ban it from petrol, in California in particular.
    What will they use instead?
    Probably another oxygen-containing compound such as ethanol. This is not so toxic, though it will probably increase the cost of the gasoline.
    Is MTBE used in the UK?
    BenzeneTolueneNo, instead of MTBE we have toxic compounds like benzene (left) and toluene (right), with Octane ratings of around 106, added to our petrol !

    If there is no lead in it, surely unleaded petrol is safe?
    There is quite a lot of benzene in unleaded petrol; it makes up 1.4% of normal unleaded (out of 28 % aromatics) and 2.6% in 4 star unleaded (out of 45% aromatics). Not all the hydrocarbons get burned up in the engine so that some gets passed into the air. Benzene is believed to cause cancers, leukaemia and anaemia. Catalytic converters can help reduce hydrocarbon emissions, but not until they are warmed up.



    Industri primer pengolahan hasil hutan merupakan salah satu penyumbang limbah cair yang berbahaya bagi lingkungan. Bagi industri-industri besarsepertiindustri pulp dan kertasteknologi pengolahan limbah cair yang dihasilkannya mungkin sudah memadainamun tidak demikian bagi industri kecil atau sedang.Namun demikianmengingat penting dan besarnya dampak yang ditimbulkan limbah cair bagi lingkunganpenting bagi sektor industri kehutanan untukmemahami dasar-dasar teknologi pengolahan limbah cair.
    Teknologi pengolahan air limbah adalah kunci dalam memelihara kelestarian lingkungan. Apapun macam teknologi pengolahan air limbah domestik maupunindustri yang dibangun harus dapat dioperasikan dan dipelihara oleh masyarakat setempat. Jadi teknologi pengolahan yang dipilih harus sesuai dengankemampuan teknologi masyarakat yang bersangkutan. 
    Berbagai teknik pengolahan air buangan untuk menyisihkan bahan polutannya telah dicoba dan dikembangkan selama ini.  Teknik-teknik pengolahan air buanganyang telah dikembangkan tersebut secara umum terbagi menjadi 3 metode pengolahan:
    1.    pengolahan secara fisika
    2.    pengolahan secara kimia
    3.    pengolahan secara biologi
    Untuk suatu jenis air buangan tertentuketiga metode pengolahan tersebut dapat diaplikasikan secara sendiri-sendiri atau secara kombinasi.
    Pengolahan Secara Fisika
    Pada umumnyasebelum dilakukan pengolahan lanjutan terhadap air buangandiinginkan agar bahan-bahan tersuspensi berukuran besar dan yang mudahmengendap atau bahan-bahan yang terapung disisihkan terlebih dahulu. Penyaringan (screeningmerupakan cara yang efisien dan murah untuk menyisihkanbahan tersuspensi yang berukuran besarBahan tersuspensi yang mudah mengendap dapat disisihkan secara mudah dengan proses pengendapan.  Parameterdesain yang utama untuk proses pengendapan ini adalah kecepatan mengendap partikel dan waktu detensi hidrolis di dalam bak pengendap.

    Proses flotasi banyak digunakan untuk menyisihkan bahan-bahan yang mengapung seperti minyak dan lemak agar tidak mengganggu proses pengolahanberikutnyaFlotasi juga dapat digunakan sebagai cara penyisihan bahan-bahan tersuspensi (clarificationatau pemekatan lumpur endapan (sludge thickening)dengan memberikan aliran udara ke atas (air flotation).
    Proses filtrasi di dalam pengolahan air buanganbiasanya dilakukan untuk mendahului proses adsorbsi atau proses reverse osmosis-nyaakan dilaksanakan untukmenyisihkan sebanyak mungkin partikel tersuspensi dari dalam air agar tidak mengganggu proses adsorbsi atau menyumbat membran yang dipergunakan dalamproses osmosa.
    Proses adsorbsibiasanya dengan karbon aktifdilakukan untuk menyisihkan senyawa aromatik (misalnyafenoldan senyawa organik terlarut lainnyaterutamajika diinginkan untuk menggunakan kembali air buangan tersebut.
    Teknologi membran (reverse osmosisbiasanya diaplikasikan untuk unit-unit pengolahan kecilterutama jika pengolahan ditujukan untuk menggunakan kembaliair yang diolah. Biaya instalasi dan operasinya sangat mahal.
    Pengolahan Secara Kimia
    Pengolahan air buangan secara kimia biasanya dilakukan untuk menghilangkan partikel-partikel yang tidak mudah mengendap (koloid), logam-logam berat,senyawa fosfordan zat organik beracundengan membubuhkan bahan kimia tertentu yang diperlukan.  Penyisihan bahan-bahan tersebut pada prinsipnyaberlangsung melalui perubahan sifat bahan-bahan tersebutyaitu dari tak dapat diendapkan menjadi mudah diendapkan (flokulasi-koagulasi), baik dengan atautanpa reaksi oksidasi-reduksidan juga berlangsung sebagai hasil reaksi oksidasi. 

    Pengendapan bahan tersuspensi yang tak mudah larut dilakukan dengan membubuhkan elektrolit yang mempunyai muatan yang berlawanan dengan muatankoloidnya agar terjadi netralisasi muatan koloid tersebutsehingga akhirnya dapat diendapkan. Penyisihan logam berat dan senyawa fosfor dilakukan denganmembubuhkan larutan alkali (air kapur misalnyasehingga terbentuk endapan hidroksida logam-logam tersebut atau endapan hidroksiapatit.  Endapan logamtersebut akan lebih stabil jika pH air > 10,5 dan untuk hidroksiapatit pada pH > 9,5.  Khusus untuk krom heksavalensebelum diendapkan sebagai kromhidroksida [Cr(OH)3], terlebih dahulu direduksi menjadi krom trivalent dengan membubuhkan reduktor (FeSO4, SO2atau Na2S2O5).

    Koagulasi &Flokulasi

    Penyisihan bahan-bahan organik beracun seperti fenol dan sianida pada konsentrasi rendah dapat dilakukan dengan mengoksidasinya dengan klor (Cl2), kalsiumpermanganataerasiozon hidrogen peroksida.
    Pada dasarnya kita dapat memperoleh efisiensi tinggi dengan pengolahan secara kimiaakan tetapi biaya pengolahan menjadi mahal karena memerlukan bahankimia.
    Pengolahan secara biologi
    Semua air buangan yang biodegradable dapat diolah secara biologi. Sebagai pengolahan sekunderpengolahan secara biologi dipandang sebagai pengolahan yang paling murah dan efisien. Dalam beberapa dasawarsa telah berkembang berbagai metode pengolahan biologi dengan segala modifikasinya.
    Pada dasarnyareaktor pengolahan secara biologi dapat dibedakan atas dua jenisyaitu:
    1.    Reaktor pertumbuhan tersuspensi (suspended growth reaktor);
    2.    Reaktor pertumbuhan lekat (attached growth reaktor).
    Di dalam reaktor pertumbuhan tersuspensimikroorganisme tumbuh dan berkembang dalam keadaan tersuspensi.  Proses lumpur aktif yang banyak dikenalberlangsung dalam reaktor jenis iniProses lumpur aktif terus berkembang dengan berbagai modifikasinyaantara lain: oxidation ditch dan kontak-stabilisasi.Dibandingkan dengan proses lumpur aktif konvensionaloxidation ditch mempunyai beberapa kelebihanyaitu efisiensi penurunan BOD dapat mencapai 85%-90% (dibandingkan 80%-85%) dan lumpur yang dihasilkan lebih sedikit.  Selain efisiensi yang lebih tinggi (90%-95%), kontak stabilisasi mempunyai kelebihan yang lain,yaitu waktu detensi hidrolis total lebih pendek (4-6 jam).  Proses kontak-stabilisasi dapat pula menyisihkan BOD tersuspensi melalui proses absorbsi di dalamtangki kontak sehingga tidak diperlukan penyisihan BOD tersuspensi dengan pengolahan pendahuluan.
    Kolam oksidasi dan lagoonbaik yang diaerasi maupun yang tidakjuga termasuk dalam jenis reaktor pertumbuhan tersuspensi. Untuk iklim tropis sepertiIndonesiawaktu detensi hidrolis selama 12-18 hari di dalam kolam oksidasi maupun dalam lagoon yang tidak diaerasicukup untuk mencapai kualitas efluenyang dapat memenuhi standar yang ditetapkan.  Di dalam lagoon yang diaerasi cukup dengan waktu detensi 3-5 hari saja.
    Di dalam reaktor pertumbuhan lekatmikroorganisme tumbuh di atas media pendukung dengan membentuk lapisan film untuk melekatkan dirinya. Berbagaimodifikasi telah banyak dikembangkan selama iniantara lain:
    1.    trickling filter
    2.    cakram biologi
    3.    filter terendam
    4.    reaktor fludisasi
    Seluruh modifikasi ini dapat menghasilkan efisiensi penurunan BOD sekitar 80%-90%.
    Ditinjau dari segi lingkungan dimana berlangsung proses penguraian secara biologiproses ini dapat dibedakan menjadi dua jenis:
    1.        Proses aerob, yang berlangsung dengan hadirnya oksigen;
    2.        Proses anaerob, yang berlangsung tanpa adanya oksigen.
    Apabila BOD air buangan tidak melebihi 400 mg/l, proses aerob masih dapat dianggap lebih ekonomis dari anaerob.  Pada BOD lebih tinggi dari 4000 mg/l, prosesanaerob menjadi lebih ekonomis.


    Dalam prakteknya saat initeknologi pengolahan limbah cair mungkin tidak lagi sesederhana seperti dalam uraian di atas.  Namun pada prinsipnya,semua limbah yang dihasilkan harus melalui beberapa langkah pengolahan sebelum dibuang ke lingkungan atau kembali dimanfaatkan dalam prosesproduksidimana uraian di atas dapat dijadikan sebagai acuan. [DAW] Pencemaran

    Dari Wikipedia Indonesia, ensiklopedia bebas berbahasa Indonesia.

    Pencemaranmenurut SK Menteri Kependudukan Lingkungan Hidup No 02/MENKLH/1988, adalah masuk atau dimasukkannya mahluk hidupzatenergi,dan/atau komponen lain ke dalam air/udara, dan/atau berubahnya tatanan (komposisi) air/udara
     oleh kegiatan manusia dan proses alamsehingga kualitas air/udara menjadi kurang atau tidak dapat berfungsi lagi sesuai dengan peruntukkannya.
    Untuk mencegah terjadinya pencemaran terhadap lingkungan oleh berbagai aktivitas industri dan aktivitas manusiamaka diperlukan pengendalian terhadappencemaran lingkungan dengan menetapkan baku mutu lingkunganBaku mutu lingkungan adalah batas kadar yang diperkenankan bagi zat atau bahanpencemar terdapat di lingkungan dengan tidak menimbulkan gangguan terhadap makhluk hiduptumbuhan atau benda lainnya.
    Pada saat inipencemaran terhadap lingkungan berlangsung di mana-mana dengan laju yang sangat cepat. Sekarang ini beban pencemaran dalam lingkungansudah semakin berat dengan masuknya limbah industri dari berbagai bahan kimia termasuk logam berat.
    Pencemaran lingkungan dapat dikategorikan menjadi: