Coagulation and flotation

Tsai et al. (2007) investigated flotation for CMP wastewater treatment at both the lab and pilot scale. The CMP wastewater had a pH of 9.4, total solids of 8200 mg/L, total Si of 4(X)0 mg/L, turbidity of550 NTU, zeta potential of —50 mV, and a mean particle size of 106 nm. Following screening of alternative coagulants and surfactants, they used a 2k factorial design to evaluate removal efficiency for total solids, dissolved silica, and mrbidity as a function of four operating variables PACl concentration, sodium oleate concentration, hydraulic residence time, and recycle ratio. Optimal 

The current efficiency, rji, for electrocoagulation can be defined in terms of the acmal mass of metal liberated from the anode relative to the theoretical mass liberated for every mole of electrons (Den et al., 2006)  

MW = molecular weight of metal released from anode z = valence number (i.e., 2 for Fe ) 

2 Particle removal during biological wastewater treatment 

Biological treatment would seldom be selected as the primary means of treating a CMP wastewater, but it is useful to consider the fate and potential impacts of alumina, ceria, and silica particles in a biological wastewater treatment process. At many fabs, waste-water is pretreated and discharged to a municipal wastewater treatment system where dilute industrial waste effluents are combined with municipal sewage flows and treated in a biological wastewater treatment process. Some fabs have an onsite biological wastewater treatment process, but they are believed to be in the minority. 

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Some Water-Technological Considerations in Coagulation and Flotation... 

Simple multivalent cations such as Mg2+ and Al + are ineffective in charge reversal for coagulation (62) experiments and in activation for froth flotation (35). The related positive hydroxo complexes do function as coagulants and flotation activators and hence must be specifically adsorbed. By knowing the appropriate hydrolysis constants and the most effective species (in flotation systems apparently M+z(OH)Vi and in coagulation, polynuclear complexes), one can predict the pH range in which each cation can be expected to adsorb strongly. 

This facility produces 110 m2/h of enameled steel and operates 4000 h/yr. It uses 0.0042 m3 water/m2 of product in coating operations. Average process water flow is 1.69 m3/h for coating operations and 0.466 m3/h for metal preparation. The primary in-place treatment is chemical coagulation and clarification. Clarification can be either settling or dissolved air flotation. 

Different technologies have been developed in recent years to treat the wastewaters contaminated with heavy metals. Chemical precipitation, coagulation-flocculation, flotation, ion exchange, and membrane filtration can be employed to remove heavy metals from contaminated wastewater.6 However, they have inherent limitations in application mainly due to the lack of economical feasibility for the treatment of large volumes of water with a low metal concentration. Furthermore, the major disadvantage of conventional technologies is the production of sludge.9... 

DAF is usually designed by pumping compressed air bubbles to remove fine SS and FOG. The wastewater is first stored in an air-pressured closed tank and then enters the flotation tank through pressure-reduction valves. Due to a sudden reduction in pressure, air bubbles form and rise to the surface in the tank. SS and FOG adhere to the fine air bubbles and are carried upward. Both dosages of coagulant and pH are important in the removal of BOD5, COD, FOG, and SS. Other important... 

With a chapter on particle-particle interaction (coagulation) the characteristics of particles and colloids as chemical reactants are discussed. Since charge, and in turn the surface potential of the colloids is important in coagulation, it is illustrated how in simple cases the modelling of surface complex formation permits the calculation of surface charge and potential. The role of particle-particle interaction in natural water and soil systems and in water technology (coagulation, filtration, flotation) is exemplified. 

Suarez S, Lema JM, Omil F (2009) Pre-treatment of hospital wastewater by coagulation-flocculation and flotation. Bioresour Technol 100 2138-2146... 

SOME WATER-TECHNOLOGICAL CONSIDERATIONS IN COAGULATION, FILTRATION, AND FLOTATION... 

Agefloc [CPS] Quaternary anunonium salt flocculant and coagulant, dewatering aids m centrifugation, filtration, and flotation both industrial and municipal waste sludges, potable water treatment... 

Orthokinetic coagulation and differential sedimentation play an important role in such processes as flotation, water treatment, dust entrapment and natural precipitation from the atmosphere. 

Until recently, the standard method for treatment of these wastes consisted of lime coagulation and flocculation with clarification by dissolved air flotation. Subsequently, the underflow is polished with sand or diatomaceous earth filtration. Finally, the sludge is dewatered by vacuum filtration. The effluent quality is variable and does not always meet discharge standards. 

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