Wastewater, treatment methods

Reverse Osmosis Reverse osmosis (RO) is a filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurised side of the membrane and the pure solvent is allowed to pass to the other side. To be selective, this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely. The reverse osmosis process is used for desalting of brackish water, in the food industry, in maple syrup production and so forth. This technology is not frequently used primarily due to high membrane replacement cost. 

Incineration Incineration is a waste treatment technology that involves the combustion of organic materials and/or substances. Incineration and other high-temperature waste treatment systems are described as thermal treatment The incineration of waste materials converts the waste into incinerator bottom ash, flue gases, particulates and heat, which can in turn be used to generate electric power. The flue gases are cleaned of pollutants before they are dispersed in the atmosphere. 

Wet Oxidation Wet oxidation is a form of hydrothermal treatment. It is the oxidation of dissolved or suspended components in water using oxygen as the oxidiser. It is referred to as wet air oxidation (WAO) when air is used. Oxidation reactions occur in superheated water at a temperature above the normal boiling point of water (100°C), but below the critical point (374°C). The system must be maintained under pressure to avoid excessive evaporation of water. This is done to control energy consumption due to the latent heat of vaporisation. It is also done because liquid water is necessary for most of the oxidation reactions to occur. Compounds that would not oxidise under dry conditions at the same temperature and pressure oxidise under wet oxidation conditions. 

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Generally, wastewater treatment methods can be broadly classified into biological, physical (i.e. mechanical) and chemical [3, 12-14]. Biological... 

The term sonochemistry describes all chemical processes in which ultrasoimd irradiation is involved. The main premise of ultrasound process as wastewater treatment method is generation of free radicals, such as hydrogen and hydroxyl. 

The environmental fate of chemicals describes the processes by which chemicals move and are transformed in the environment. Some of the processes that should be addressed include persistence in air, water, and oil reactivity and degradation migration in ground-water removal from effluents by standard wastewater treatment methods and bioaccumulation in aquatic or terrestrial organisms. 

Bauer R, Fallmann H (1997) The Photo-Fenton Oxidation - A Cheap and Efficient Wastewater Treatment Method, Res. Chem. Intermed. 23, No. 4 341-354. 

The use of catalysts, furthermore, is required in the processes of wastewater purification by reducing treatments. Catalysts also find also application as complementary technologies to other wastewater treatment methods, such as in the control of odour, VOC, N2O and NOx emissions from wet oxidation treatments (for example, in the wet oxidation of industrial sludges), and of odours and VOC emitted from biological processes (aerobic and anaerobic). Although usually commercial catalysts are used in these cases, there are often unpredicted effects in treating complex mixtures and thus more specific catalysts would be preferable. The same is valid for catalysts used to convert stripped VOC from contaminated groundwater. 

Even a combination of primary and secondary wastewater treatment systems will not remove dissolved inoi anic materials such as toxic metal ions, nutrients such as nitrate ions (NO ) or ammonium ions (NH ), or non-biodegradable organic compounds such as chlorinated hydrocarbons. These materials can be removed by a variety of tertiary wastewater treatment methods that are selectively introduced where the nature of the wastewater requires them. One obstacle to tertiary treatment is the initial expense of modifying sewage treatment plants and the ongoing expense of additional treatment. 

Roeleveld et al. (1997) performed an LCA study of different conventional wastewater treatment methods in order to assess the total environmental burden of these systems at a national level and to improve their sustainability. They concluded a priority to minimize the discharge of emissions from effluent and sludge production. They also noted that energy use, construction, and the use of chemicals were less important compared to other activities. 

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