Water and Wastewater Engineering

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TECHNOLOGIES

Reverse Osmosis:

Reverse osmosis is a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane is semi permeable, meaning it allows the passage of solvent but not of solute.

DAF

Dissolved air flotation (DAF) 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 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, natural gas processing plants and similar industrial facilities.

Filters

The rapid gravity sand filter is a type of filter used in the purification of water and is commonly used in municipal water treatment facilities.

Rapid gravity sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals - typically salts of Aluminum or Iron. Water and flocculants flows through the filter medium under gravity and the flocculated material are trapped in the sand matrix.

Rapid gravity sand filters must be cleaned frequently, often several times a day, by backwashing, which involves reversing the direction of the water. During backwashing, the bed is fluidized and care must be taken not to wash away the media.

Rapid gravity sand filtration has very little effect on taste and smell unless activated carbon is included in the filter medium.

Ozone

Ozone treatment of drinking water benefits water quality in several ways. It prevents formation of trihalomethanes and other organochlorine compounds by decomposing humic acids. Humic acids react with chlorine to produce this class of substances. It deodorizes drinking water by breaking down two major compounds that contribute to musty smell, geosmine and 2-methylisoborneol, which other processes do not remove. Combined with activated carbon filtration, it serves to remove agricultural chemicals, wastes from high-tech industrial processes and other substances listed in water-quality regulations.

Chlorination

Chlorination is the process of adding the chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water which has been treated with chlorine is effective in preventing the spread of disease.

The chlorination of public drinking supplies was originally met with resistance, as people were concerned about the health effects of the practice. The use of chlorine has greatly reduced the prevalence of waterborne disease as it is effective against almost all bacteria and viruses, as well as amoeba.

Chlorination is also used to the water in swimming pools and as a disinfection stage in sewage treatment. It can also apply to the addition of chlorine to other elements, such as gold in the formation of gold chloride.

Powder Activated Carbon

Adsorption is a physical process where soluble molecules (adsorbate) are removed by attachment to the surface of a solid substrate (absorbent) primarily by van der Waals forces, although chemical or electrical attraction may also be important. Adsorbents must have a very high specific surface area and include activated alumina, clay colloids, hydroxides and adsorbent resins, with the most widely used being activated carbon. To be effective the surface of the adsorbent must be largely free of adsorbed material, which may require the adsorbent to be activated before use (McKay, 1996). Used both for water and wastewater treatment a wide range of organic materials are amenable to removal by adsorption, including detergents. In water treatment it is used to remove taste and odour–causing trace or organic compounds as well as colour and other organic residual especially chlorination disinfection by-products such as THMs. In wastewater treatment it is used to improve settle ability of activated sludge and to remove toxic compounds.

The most widely used adsorbent is activated carbon which can be produced by pyrolytic carbonization using a number of different raw materials including bituminous coal, lignite, peat and wood. Activated carbon has a highly porous structure resulting in specific surface areas of between 600 and 1500m² g^-1. Particles are irregular in shape with a highly porous internal structure providing the large available surface area for adsorption. The rough external surface is ideal for the attachment of micro-organisms which can enhance adsorption by biological removal mechanisms.

Powder activated carbon offers unique design flexibility. It can be added to process water at various stages within the water and wastewater treatment processes. It can also be used on an intermittent basis which is particularly useful in controlling seasonal taste and odour problems in drinking water caused by algae, actinomycetes or fungi. In water treatment PAC is fed directly into the water stream as a slurry either at the rapid mix stage of chemical coagulation or immediately prior to sand filtration. As the PAC must be removed from the treated water its addition at the coagulation stage ensures maximum contact time and mixing to occur with removal of the PAC by sediment and sand filtration.

Granular Activated Carbon

Granulated activated carbon has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Granulated carbons are used for water treatment, deodorisation and separation of components of flow system. GAC can be either in the granular form or extruded.

Biological Activated Carbon

Biological activated Carbon (BAC) filtration is a drinking water treatment process widely applied. BAC removes organic carbon components like pesticides, THM-precursors, colour, taste and odour compounds by the combinations of absorption and biodegradation.

To predict the performance of Granular Activated Carbon (GAC) filters often simulation models are used. However much less experience exists on modeling and understanding BAC, especially on the interaction between the microbial activity and the absorption.