Wastewater generation

Heavy Metals. Heavy metals of particular concern in the treatment of wastewaters include copper, chromium, 2inc, cadmium, mercury, lead, and nickel. They are usually present in the form of organic complexes, especially in wastewaters generated from textiles finishing and dye chemicals manufacture. 

Step 9.3 Reconcile Wastewater Flows. The sum of the wastewater generated from each unit operation should be approximately the same as the input to the process. If its not, then there are possible sources of error in your accounting. The inability to reconcile water flows is a good tip-off to P2 opportunities. To make sure it doesn t miss such an opportunity, the team should focus attention on accurate reconciliation of the inputs and outputs. 

Relaxing the requirement on BFW quality to few ppm s of ammonia and AN. In this case, recycle and interception techniques can be used to significantly reduce the fresh water feed to the boiler and, consequently, the net wastewater generated. 

Wastewaters generated from primary aluminum processing are produced during clarification and precipitation, although much of this water is fed back into the process to be reused. 

Wastewater generation occurs for each basis material (steel, galvanized and aluminum) and for each functional operation (cleaning, conversion coating, and painting). The wastewater generated by the three functional operations may be handled in one of the following ways ... 

Hamilton Standard of the U.S. EPA has reported several coil coating plants wastewater treatment case histories.8,9 A full-scale wastewater treatment plant system has performed well for treatment of the wastewater generated from coil coating steel subcategory operations. The process principles and operational data of the full-scale treatment of a steel subcategory wastewater are summarized herein for the convenience of readers ... 

This section reviews the technologies currently available and used to remove or recover pollutants from the wastewater generated in the metal finishing industry.5 711 Treatment options are presented... 

The wastewaters generated by the adhesive industries contain high concentrations of both carbon and nitrogen compounds. The process chosen to treat these wastewaters will depend on their COD/N ratio. When the COD/N ratio is high, an anaerobic treatment is the best option as it will save costs... 

The deep shaft plant at Ohtsu Paper Co. came on line in 1980. It treats the wastewater generated by a cardboard recycling facility located within 18.3 m (60 ft) of a residential area inside the city of Ohtsu. The plant discharges treated wastewater to a beautiful recreational body of water named Lake Biwa. 

Treatment of wastewater generated in most industries is often achieved in many steps depending on the volume, shape, and nature of constituents of the wastewater. A typical wastewater treatment plant combines water treatment unit operations and processes to achieve different levels of treatment. They include the following. 

Wastewaters generated from manufacturing plants that produce or use inorganic chemicals vary considerably, depending on raw materials, type of process, and the end product, among others. A screening program is often conducted to determine the presence, concentration, and toxicity of metal ions in such wastewaters. The minimum detection limits for the toxic metals are presented in Table 22.1. 

This section describes the major industrial processes of individual inorganic chemicals under the 11 subcategories and the related wastewater generated. It contains the sources of wastewater and typical treatment processes. 

A typical plant production of aluminum fluoride indicating water use and wastewater generation is shown in the flow diagram (Figure 22.2). 

Some innovating treatment technologies may be introduced in the treatment of wastewater generated in the aluminum fluoride industry to make its effluent safer. The ion exchange process can be applied to the clarified solution to remove copper and chromium. At a very low concentration, these two pollutants can be removed by xanthate precipitation.24 A combination of lime and ferric sulfate coagulation will effectively reduce arsenic concentration in the wastewater. 

Flow diagrams of a typical plant production of chlor-alkali indicating water use and wastewater generation are given in Figure 22.4. 

The wastewater generated in the membrane cell and other process wastewaters in the cell are generally treated by neutralization.28 Other pollutants similar to those in mercury and diaphragm cells are treated in the same process stated above. Ion exchange and xanthate precipitation methods can be applied in this process to remove the metal pollutants, while incineration can be applied to eliminate some of the hydrocarbons. The use of modified diaphragms that resist corrosion and degradation will help in reducing the amount of lead, asbestos, and chlorinated hydrocarbon in the wastewater stream from the chlor-alkali industry.28... 

In addition to the heavy metals stated in Table 22.10, ferro- and ferricyanide are also part of the pollutants in the wastewater generated in a chrome pigment plant. These wastes are generally combined and treated through reduction, precipitation, equalization, and neutralization to be followed by clarification and filtration processes. Most of the heavy metals are precipitated using lime or caustic soda at specific pH. Chromium is reduced by S02 to a trivalent form, wherein it is precipitated as chromium hydroxide at specific pH. Sodium bisulfide is also employed to precipitate some of the metals at a low pH. The treated water is recycled for plant use while the sludge is sent to landfills (Figure 22.7). 

Prominent among the heavy metals found in the wastewater generated in the copper sulfate industry are copper, arsenic, cadmium, nickel, antimony, lead, chromium, and zinc (Table 22.11). They are traced to the copper and acids sources used as raw materials. These pollutants are generally removed by precipitation, clarification, gravity separation, centrifugation, and filtration. Alkaline precipitation at pH values between 7 and 10 can eradicate copper, nickel, cadmium, and zinc in the wastewater, while the quantity of arsenic can be reduced through the same process at a higher pH value. 

Wastewater generated in most sodium bisulfite plants is mainly the process water that is used in making slurry of sodium carbonate. Washdowns and general cleanup water are other sources. The... 

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