An understanding of wastewater characteristics will be quite handy in design and operation of wastewater treatment system. Wastewater is characterized in terms of physical, chemical and biological constituents. These characteristics are also useful in checking whether the final effluent coming from treatment plant is suitable for reuse and disposal.
i. Physical Characteristics
Important physical characteristics include total solids, odour, temperature, density, turbidity and colour.
Total solids: Information on total solids in wastewater plays a vital role in design and maintenance of wastewater collection system and treatment facilities. The constituents of total solids are floating matter, settle able matter, colloidal matter and matter in solution. The total solids can be determined by evaporation of sample at 103 to 105 degree Celsius. Settle able solids are determined by measuring the solids that will settle to the bottom of a cone shaped container in a 60 minute period. The total solids can further be classified by filtering through a glass fiber microfiltration membrane, as filterable or dissolved solids (which pass through the membrane) and suspended solids (which pass through the membrane). Volatile portions of filterable solids and suspended solids are determined by igniting the solids at around 600 degree Celsius.
Colour and Odour: With passage of time, the chances of anaerobic conditions waste water conveyance system increase. The anaerobic breakdown organic matter in wastewater gives offensive odour as well as changes the colour to black. This is called septic condition. Thus colour and odour indicate the age of waste water.
Density: The density of wastewater is usually same as that of water. It will vary if wastewater contains large amounts of industrial waste.
Turbidity: The turbidity indicates the concentration of suspended solids in wastewater.
Temperature: The waste water temperature is an important parameters because it affects the biochemical reaction in waste water, the soluble limits of gases decreases. Thus dissolved oxygen, which is necessary in aerobic digestion processes, will be less at higher temperatures and needs to be taken care in design of aeration system.
ii. Chemical Characteristics
The chemical characteristics of the effluent can be specified in terms of organic matter content, inorganic matter and gases. The organic matter content is the general way of estimating the strength of wastewater. Biochemical Oxygen Demand(BOD) is the one analytical parameter that is mostly used to measure the strength or organic matter content of wastewater. In dairy plant effluent, the organic matter comprises of butterfat, casein and other milk proteins, lactose and inorganic salts.
These components may be present in solutions or as a colloidal suspension, depending upon the type of process applied to the milk. Inorganic constituents such as alkaline metals, chloride, heavy metals, nitrogen, PH, phosphorous, priority pollutants, sulfur and gases such as hydrogen sulfide, methane and oxygen contribute to the chemical characteristics.
Biological Oxygen Demand : The BOD of wastewater determines the milligrams per liter of oxygen required during stabilization of decomposable organic matter by aerobic bacteria action. Also, the total milligrams of oxygen required over a five- day test period to biologically assimilate the organic contaminants in one liter of wastewater maintained at 20 degrees Centigrade. Another related parameter is Chemical Oxygen Demand (COD) which is the milligrams of oxygen required to chemically oxidize the organic contaminants in one liter of wastewater. This can be determined in hours as compared to days of BOD.
iii. Biological Characteristics
Biological constituents in wastewater include animals, plants and protists. Protists are important because the bacteria and other microorganisms which degrade the organic matter present in wastewater fall into this category. In wastewater treatment processes, not one but many different types of microorganisms coexist to carry out breakdown of organic matter. Knowledge of type of micro organisms present in waste water is essential for design and operation treatment processes. If pathogens (disease causing micro organisms) are present in waste water, they should be killedmbefore the treated waste water is disposed off. Due to presence of large number of different micro organisms, the isolation of pathogens in waste water is difficult and indicator organisms are used. Use of different indicator organisms in water was discussed in Unit 18 and it holds good for wastewater also.
i. Physical Characteristics
Important physical characteristics include total solids, odour, temperature, density, turbidity and colour.
Total solids: Information on total solids in wastewater plays a vital role in design and maintenance of wastewater collection system and treatment facilities. The constituents of total solids are floating matter, settle able matter, colloidal matter and matter in solution. The total solids can be determined by evaporation of sample at 103 to 105 degree Celsius. Settle able solids are determined by measuring the solids that will settle to the bottom of a cone shaped container in a 60 minute period. The total solids can further be classified by filtering through a glass fiber microfiltration membrane, as filterable or dissolved solids (which pass through the membrane) and suspended solids (which pass through the membrane). Volatile portions of filterable solids and suspended solids are determined by igniting the solids at around 600 degree Celsius.
Colour and Odour: With passage of time, the chances of anaerobic conditions waste water conveyance system increase. The anaerobic breakdown organic matter in wastewater gives offensive odour as well as changes the colour to black. This is called septic condition. Thus colour and odour indicate the age of waste water.
Density: The density of wastewater is usually same as that of water. It will vary if wastewater contains large amounts of industrial waste.
Turbidity: The turbidity indicates the concentration of suspended solids in wastewater.
Temperature: The waste water temperature is an important parameters because it affects the biochemical reaction in waste water, the soluble limits of gases decreases. Thus dissolved oxygen, which is necessary in aerobic digestion processes, will be less at higher temperatures and needs to be taken care in design of aeration system.
ii. Chemical Characteristics
The chemical characteristics of the effluent can be specified in terms of organic matter content, inorganic matter and gases. The organic matter content is the general way of estimating the strength of wastewater. Biochemical Oxygen Demand(BOD) is the one analytical parameter that is mostly used to measure the strength or organic matter content of wastewater. In dairy plant effluent, the organic matter comprises of butterfat, casein and other milk proteins, lactose and inorganic salts.
These components may be present in solutions or as a colloidal suspension, depending upon the type of process applied to the milk. Inorganic constituents such as alkaline metals, chloride, heavy metals, nitrogen, PH, phosphorous, priority pollutants, sulfur and gases such as hydrogen sulfide, methane and oxygen contribute to the chemical characteristics.
Biological Oxygen Demand : The BOD of wastewater determines the milligrams per liter of oxygen required during stabilization of decomposable organic matter by aerobic bacteria action. Also, the total milligrams of oxygen required over a five- day test period to biologically assimilate the organic contaminants in one liter of wastewater maintained at 20 degrees Centigrade. Another related parameter is Chemical Oxygen Demand (COD) which is the milligrams of oxygen required to chemically oxidize the organic contaminants in one liter of wastewater. This can be determined in hours as compared to days of BOD.
iii. Biological Characteristics
Biological constituents in wastewater include animals, plants and protists. Protists are important because the bacteria and other microorganisms which degrade the organic matter present in wastewater fall into this category. In wastewater treatment processes, not one but many different types of microorganisms coexist to carry out breakdown of organic matter. Knowledge of type of micro organisms present in waste water is essential for design and operation treatment processes. If pathogens (disease causing micro organisms) are present in waste water, they should be killedmbefore the treated waste water is disposed off. Due to presence of large number of different micro organisms, the isolation of pathogens in waste water is difficult and indicator organisms are used. Use of different indicator organisms in water was discussed in Unit 18 and it holds good for wastewater also.
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