more effective but are relatively complex. In the dissolved air flotation cell, air is injected into the oily wastewater as fine bubbles. The oil droplets adhere to the air bubbles and rise to the surface as a froth, which is skimmed off by a motor-driven rake. Some small, suspended particulate contaminants can also be removed in the froth, and others will settle to the bottom of the cell and can be removed as sludge. A coagulant can also be added to aid removal efficiency. If lime is added, for example, it will precipitate some heavy metals and certain anions such as carbonates.
Dissolved air flotation is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter, causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.
Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, and natural gas processing plants and could find use in the oil shale industry.
See also: Settling and Flotation.
Air Pollution
The term air pollution refers to the release of pollutants into the air that are detrimental to human health and the planet as a whole. Air pollution arises from energy use and production and not only from the use of fossil fuels but also from the use of fuels from renewable sources and also from natural events (using volcanoes as the example of a natural event). Air pollution may cause diseases, allergies, and even death to humans as well as cause harm to other living organisms such as animals and food crops, and may damage the environment.
Smog and soot are the most prevalent types of air pollution. The former (smog) occurs when emissions from the combustion of fuels (including biomass and other renewable fuel sources) react with sunlight. Soot (particulate matter) is composed of small (often micron-size) particles of chemicals, soil, smoke, dust, or allergens, in the form of gas or solids, that are carried in the air. Smog can irritate the eyes and throat and also damage the lungs – especially of people who work or exercise outside and is even worse for people who have asthma or allergies – the pollutants only intensify their symptoms and can trigger asthma attacks.
Hazardous air pollutants are either deadly or have severe health risks even in small amounts and most often emitted during gas or combustion of other fossil fuels and fossil fuel products. Polycyclic aromatic hydrocarbon derivatives are toxic components of traffic exhaust and wildfire smoke. In large amounts, they have been linked to eye and lung irritation, blood and liver issues, and even cancer. Dioxin derivatives are also present in small amounts in the air and can affect the liver in the short term and harm the immune, nervous, and endocrine systems, as well as reproductive functions.
Mold and allergens from trees, weeds, and grass are also carried in the air, are exacerbated by climate change, and can be hazardous to health. They are not regulated by the government and are less directly connected to human actions, but they can be considered air pollution. When homes, schools, or businesses are subject to water damage, mold can grow and can produce allergenic airborne pollutants. Exposure to mold can precipitate asthma attacks or an allergic response, and some molds can even produce toxins that would be dangerous for anyone to inhale. Pollen allergies are worsening because of climate change which extends the pollen production season.
See also: Gaseous Pollutants, Greenhouse Gases, Greenhouse Effect.
Alcohol Blended Fuel
Blended fuel usually refers to a mixture composed of automotive gasoline and another liquid, other than a minimal amount of a product such as carburetor detergent or oxidation inhibitor that can be used as a fuel in a motor vehicle.
Alcohol refers to ethyl alcohol (ethanol, C2H5OH), which has a high octane number, RON being 110, and MON 90 and a good antiknock performance. If alcohol contains a certain amount of water, it is favorable to improve its antiknock performance; hence, the enhancement of the compression ratio of the engine occurs when the blended fuel is burned. Meanwhile, an alcohol blend requires no or reduced additive of antiknock substance, which may reduce air pollution caused by lead (Pb). But the effect on increasing of the octane number of blended fuel is not the same when gasoline is mixed with different kinds of alcohol.
The data (Table A-9) show that the change in octane number of blended fuel is in nonlinear correlation with the proportion of alcohol added. A 5 to 20% alcohol blend has a higher mixed octane number. This means that the effect on raising the octane number of blend fuel is more notable. In addition, the lower the octane number of base gasoline is, the more notable the effect on raising the octane number of blended fuel will be.
Table A-9 Octane number (motor method).
| Ethanol, % v/v | Octane number |
|---|---|
| 0 | 72.5 |
| 5 | 74.8 |
| 10 | 76.6 |
| 15 | 78.5 |
| 20 | 80.3 |
| 25 | 81.4 |
| 100 | 90.0 |
Selecting a 15 to 20% blend of alcohol has the advantage of the high antiknock performance of the alcohol. However, if low octane gasoline is used as the base for the blend, without adding any antiknock fluid, not only can the pollution be reduced but the cost of fuel is decreased, thus making the use of mixed fuel on gasoline engine more adaptable.
See also: Blended Fuels.
Alcohol-Diesel Emulsion
Because alcohols have limited solubility in diesel, a stable emulsion must be formed that will allow it to be injected before separation occurs. Numerous techniques have been evaluated to allow for the concurrent use of diesel and ethanol in compression ignition engines. Some of these techniques include alcohol fumigation, dual injection, alcohol-diesel fuel emulsions, and alcohol-diesel fuel blends. Among these approaches, only alcohol-diesel emulsions and blends are compatible with most commercial diesel engines. Since emulsions are difficult to achieve and tend to be unstable, blends—either as micro-emulsions or using co-solvents—are the most common approach as they are stable and can be used in engines with relatively no modifications.
Blends of ethanol with diesel fuel are often referred to as E-Diesel or eDiesel or oxygenated diesel – a term that is not particularly precise since diesel blends containing methyl ester (biodiesel) or any other additive that includes oxygen can be also described as oxygenated diesel. In e-diesel blends, standard diesel fuel (such as US No. 2) is typically blended with up to 15% v/v of ethanol using an additive package
