Wastewater Management - Essay Example

Wastewater Management Water is certainly the most valuable natural resource that exists on planet earth. Though over 70% of the Earth’s surface is covered with water, most of the Earth’s water is in the oceans (97 per cent) or locked away as ice. The largest volumes of freshwater are stored underground as groundwater, accounting for about 0.6 per cent of the total. Only a small portion (0.01 per cent) is present as fresh surface water in lakes, streams lochs, reservoirs, ponds, rivers canals, ditches, coastal waters and estuaries (Vale, 2006) . Unfortunately, it is the only proportion which is very important for humans and other terrestrial organisms. With the increase in population, the demand for water has increased drastically over the years. As a matter of fact, besides the water that is locked in the glaciers and icecaps, about 97 % of the fresh water is in the lakes, rivers, streams and ground water. The pollution of these water resources is a serious concern all over the world. As the number of industries is increasing, growing volumes of industrial wastewater are being discharged to surface waters. Due to the lack of funds and proper initiatives, the treatment provided is usually poor to protect the desired uses of the receiving waters. Before getting into the principal steps involved in industrial wastewater treatment, it is important to understand that reducing the generation of waste through proper management of resources could be an easer step than treating the effluents. Thus, through this process the companies will benefit from the reduced input cost or the expenditure on raw materials and also reduces the waste water treatment costs. It also improves the efficiency and the working conditions in the industry. Industries that use large amounts of water for processing have the potential to pollute waterways. Industrial waste consists of both organic and inorganic substances. Organic wastes include pesticide residues, solvents and cleaning fluids, dissolved residue from fruit and vegetables, and lignin from pulp and paper industry. Effluents can also contain inorganic wastes such as salts and heavy metals. When these effluents are released into the water bodies without proper treatment, it can cause serious damage to the ecosystem. Besides, it can also affect the people who use this water for drinking or any other household purposes. It is therefore essential that the industrial effluents are treated to high standards before they are released. Industrial effluents can contain a mixture of contaminants which make them unfit for further use. The most common pollutants and possible methods for their removal are presented in the following table. (Source: Nesaratnam, 81-100) The different types of contamination of wastewater require a variety of strategies to remove the contamination. There are different processes that can be used to clean up wastewaters depending on the type and extent of contamination. Most wastewater is treated in industrial wastewater treatment plants which may include physical, chemical and biological treatment processes. Solids removal: Most solids can be removed using simple sedimentation techniques with the solids recovered as slurry or sludge. Very fine solids and solids with densities can be removed through filtration or ultra-filtration. Alternatively, flocculation may be used using alum salts or the addition of poly-electrolytes Oils and greases: Many oils can be recovered from open water surfaces by skimming devices. However, hydraulic oils and the majority of oils that have degraded to any extent will also have a soluble or emulsified component that will require further treatment to eliminate. Dissolving or emulsifying oil using surfactants or solvents usually exacerbates the problem rather than solving it, producing a very difficult to treat wastewater. Soft organics: Organic material of plant or animal origin is usually possible to treat using extended conventional Sewage treatment processes. Problems can arise if the wastewater is excessively diluted with washing water or is highly concentrated such as neat blood or milk. The presence of cleaning agents, disinfectants, pesticides, or antibiotics can have detrimental impacts on treatment processes. Hard organics: Synthetic organic materials including solvents, paints, pharmaceuticals, pesticides, coking products etc can be very difficult to treat. Treatment methods are often specific to the material being treated. Methods include distillation, adsorption, vitrification, incineration, chemical immobilization or landfill disposal. Some materials such as some detergents may be capable of biological degradation and in such cases, a modified form of Sewage treatment can be used. Acids and alkalis: Acids and alkalis can usually be neutralized under controlled conditions. Neutralization frequently produces a precipitate that will require treatment as a solid residue that may also be toxic. In some cases, gasses may be evolved requiring treatment for the gas stream. Some other forms of treatment are usually required following neutralization. Waste streams rich in hardness ions as from de-ionization processes can readily loose the hardness ions in a build-up of precipitated calcium and magnesium salts. This precipitation process can cause severe furring of pipes and can, in extreme cases, cause the blockage of disposal pipes. A one meter diameter industrial marine discharge pipe serving a major chemicals complex was blocked by such salts in the 1970s. Treatment is by concentration of de-ionization waste waters and disposal to landfill or by careful pH management of the released wastewater. Toxic materials: Toxic materials including many organic materials, metals (such as zinc, silver, cadmium, thallium etc.) acids, alkalis, non-metallic elements (such as arsenic or selenium) are generally resistant to biological processes unless very dilute. Metals can often be precipitated out by changing the pH or by treatment with other chemicals. Many, however, are resistant to treatment or mitigation and may require concentration followed by land filling or recycling (Wikipedia, 2006). Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater. General terms used to describe different degrees of treatment, in order of increasing treatment level, are preliminary, primary, secondary, and tertiary and/or advanced wastewater treatment. The aim of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment units. Preliminary treatment operations typically include coarse screening, grit removal and, in some cases, combinations of large objects. In grit chambers, the velocity of the water through the chamber is maintained sufficiently high, or air is used, so as to prevent the settling of most organic solids. Grit removal is not included as a preliminary treatment step in most small wastewater treatment plants. Comminutors are sometimes adopted to supplement coarse screening and serve to reduce the size of large particles so that they will be removed in the form of sludge in subsequent treatment processes. Flow measurement devices, often standing-wave flumes, are always included at the preliminary treatment stage. The aim of primary treatment is the removal of settleable organic and inorganic solids by sedimentation, and the elimination of materials that will float (scum) by skimming. Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5), 50 to 70% of the total suspended solids, and 65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent. The purpose of secondary treatment is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. In most cases, secondary treatment follows primary treatment and involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes. Aerobic biological treatment is performed in the presence of oxygen by aerobic micro-organisms (mainly bacteria) that metabolize the organic matter in the wastewater, thereby producing more micro-organisms and inorganic end-products (principally CO2, NH3, and H2O). Several aerobic biological processes are used for secondary treatment differing primarily in the manner in which oxygen is supplied to the micro-organisms and in the rate at which organisms metabolize the organic matter. High-rate biological processes are characterized by comparatively small reactor volumes and high concentrations of micro-organisms compared with low rate processes. Consequently, the growth rate of new organisms is much greater in high-rate systems because of the well controlled environment. The micro-organisms must be separated from the treated wastewater by sedimentation to produce clarified secondary effluent. Tertiary and/or advanced wastewater treatment is employed when specific wastewater constituents which cannot be removed by secondary treatment must be removed. Individual treatment processes are necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics, and heavy metals and dissolved solids. Because advanced treatment usually follows high-rate secondary treatment, it is sometimes referred to as tertiary treatment. However, advanced treatment processes are sometimes combined with primary or secondary treatment (e.g., chemical addition to primary clarifiers or aeration basins to remove phosphorus) or used in place of secondary treatment (e.g., overland flow treatment of primary effluent) (Pescod, 1992). The increasing number of industries after the start of industrial revolution has increased the concerns regarding industrial wastes. Water resource being the most precious of all the resources, it is essential to control the pollution of water bodies. Hence industrial waste water treatment is very important both in developed and developing countries. Best way to reduce the generation of waste is by minimizing the unwanted use of water. It is also essential that small and large industries need to follow standardized procedures in water treatment plants to remove hazardous and harmful substances from the effluents in order to maintain sustainability. Work cited Nesaratnam, S. Portable Water Treatment. T 308, Environmental Monitoring, Modeling and Control. 2005 The Open University, Walton Hall, Milton Keynes, UK. 81-100 Pescod, M.B. Wastewater treatment and use in agriculture Food and Agriculture Organization of the United Nations Rome, 1992. March 28, 2006 Vale, J., Water Quality, 2006. The Environment Agency, March 28, 2006, Wikipedia, Industrial wastewater treatment March 28, 2006 Read More