Effluent treatment methods

When viewing effluent treatment methods, it is clear that the basic problem of disposing of waste material safety is, in many cases, not so much solved but moved from one place to another. The fundamental problem is that once waste has been created, it cannot be destroyed. The waste can be concentrated or diluted, its physical or chemical form can be changed, but it cannot be destroyed. 

DYES ENVIRONMENTAL CHEMISTRY Effluent Treatment Methods... 

The traditional effluent treatment method in these factories tend to be settlement pits, w here coarse solids are allow ed to settle, sometimes w ith the aid of flocculent addition. Settled solids w ould be periodically dug out of the settlement pits, piled nearby and allow ed to drain back into the pit for further settlement of the runoff w ater. The W ater at the end of the settlement pit w ould then be allow ed to drain to tbul sew er or surface w ater usually w ith mineral acid dosing, to reduce the high pH caused by the lime in the cement, w hich can be as high as pH 13, In extreme, but not that uncommon situations, the w aste w ater is allow ed to flow untreated to surface w aters or allow ed to soak aw ay to the ground, causing immense pollution to the receiving w ater - be it... 

Many of these and other practical aspects of process design and operation, such as appropriate materials of constniction, prevention of crud foimation, effluent treatment methods, and typical process costs, are discussed by Ritcey and Ashbrook. ... 

Let us briefly review the primary treatment methods used. Pretreatment usually starts with phase separation if the effluent is a heterogeneous mixture. 

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Caro s acid is finding increasing appHcation ia hydrometaHurgy, pulp bleaching, effluent treatment, and electronics. There are several appHcations of Caro s acid ia hydrometaHurgy. It is usually made on-site by either the isothermal or the adiabatic process. The latter method is preferred because its capital cost is less and the system is safer due to the fact that the product is used as soon as it is made. 

Gaseous vent streams from the different unit operations may contain traces (or more) of HCl, CO, methane, ethylene, chlorine, and vinyl chloride. These can sometimes be treated chemically, or a specific chemical value can be recovered by scmbbing, sorption, or other method when economically justified. Eor objectionable components in the vent streams, however, the common treatment method is either incineration or catalytic combustion, followed by removal of HCl from the effluent gas. 

Chemical oxidation is a more recent method of effluent treatment, especially chemical effluent. This procedure uses strong oxidi2ing agents like... 

Methods of effluent treatment for dyes may be classified broadly into three main categories physical, chemical, and biological (1). 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

Before powdered carbon can be used commercially or reused for tertiary treatment of sewage effluents, a method of regeneration is required. The use of the fluidized bed for regeneration offers the key advantages of excellent temperature and atmosphere control and the ability to process the powdered solids conveniently and continuously. 

Calculate the mass or weight of chemical in the wastestream being treated by multiplying the concentration (by weight) of the chemical in the wastestream by the flow rate. In most cases, the percent removal compares the treated effluent to the influent for the particular type of wastestream. However, for some treatment methods, such as Incineration or solidification of wastewater, the percent removal of the chemical from the influent wastestream would be reported as 100 percent because the wastestream does not exist in a comparable form after treatment. Some of the treatments (e.g., fuel blending and evaporation) do not destroy, chemically convert, or physically remove the chemical from its wastestream. For these treatment methods, an efficiency of zero must be reported. 

As with the case for water minimization, the graphical methods used for effluent treatment and regeneration have some severe limitations. As before, multiple contaminants are difficult to handle, constraints, piping and sewer costs, multiple treatment processes and retrofit are all difficult to handle. To include all of these complications requires an approach based on the optimization of the superstructure. 

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

For a detailed discussion the reader is referred to a number of recent monographs [9,10,23] and review articles [50,226-231]. The role of electrochemistry in waste water and effluent treatment is still queried, as remarked by Pletcher and Walsh [10]. One answer would be, relatively small since there are many competitive methods which are cheaper on a large scale and use less energy. Principle types of processes used in local-authority sewage works are listed in Table 14. 

Mechanical and biological methods are very effective on a large scale, and physical and chemical methods are used to overcome particular difficulties such as final sterilization, odor removal, removal of inorganic and organic chemicals and breaking oil or fat emulsions. Normally, no electrochemical processes are used [10]. On the other hand, there are particular water and effluent treatment problems where electrochemical solutions are advantageous. Indeed, electrochemistry can be a very attractive idea. It is uniquely clean because (1) electrolysis (reduction/oxidation) takes place via an inert electrode and (2) it uses a mass-free reagent so no additional chemicals are added, which would create secondary streams, which would as it is often the case with conventional procedures, need further treatment, cf. Scheme 10. 

Table 25. Classification of methods of dye and textile effluent treatment [314]...

Constraint control strategies, 20 675-676 Constraint method, in multiobjective optimization, 26 1033 Constructed wetland, defined, 3 759t Constructed wetlands effluent treatment, 9 436 37 Construction... 

Environmental chemistry analytical methods, 9 442 corporate programs, 9 456 457 of Dyes 9 431-463 effluent treatment, 9 432 437 fate of dyes, 9 437-442 pesticide registration requirements for, 18 545-547... 

Many wastewater flows in industry can not be treated by standard aerobic or anaerobic treatment methods due to the presence of relatively low concentration of toxic pollutants. Ozone can be used as a pretreatment step for the selective oxidation of these toxic pollutants. Due to the high costs of ozone it is important to minimise the loss of ozone due to reaction of ozone with non-toxic easily biodegradable compounds, ozone decay and discharge of ozone with the effluent from the ozone reactor. By means of a mathematical model, set up for a plug flow reactor and a continuos flow stirred tank reactor, it is possible to calculate more quantitatively the efficiency of the ozone use, independent of reaction kinetics, mass transfer rates of ozone and reactor type. The model predicts that the oxidation process is most efficiently realised by application of a plug flow reactor instead of a continuous flow stirred tank reactor. 

Scott JS. 1985. An overview of cyanide treatment methods for gold mill effluents. Conf. Cyanide and Environment, Tuscon, AZ, December 1984. Published by Geotechnical Engineering Program, Colorado State University, Fort Collins, CO, 307-330. 

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