New Developments in Mixing, Coagulation, Flocculation and Flotation for Industrial Wastewater Pretreatment

Solid/liquid separations are a mature technology area and few new developments occurred in seventies and eighties. However, last decade witnessed appearance of a significant number of new innovative systems in this field. (Rubio et al., 2002) This paper describes new developments in mixing, coagulation, flocculation and flotation systems for industrial wastewater treatment. (Ross et al., 2000; Desam et al., 2001; Morse et al., 2001; Morse et al., 2004a; Bratby et al., 2004, Kiuri, 2001, Colic et al., 2005) Case studies and design details will be discussed. New high throughput flocculation and flotation systems have successfully been tested and installed for applications in industrial high strength wastewater pretreatment, municipal sludge thickening (including thickening of combined primary and secondary sludge), agricultural wastewater treatment and drinking water treatment. Recent applications of flotation technology have occurred in pretreatment of water ahead of membrane separation systems or bioreactors. Post treatment of wastewater after aerobic, anaerobic and moving bed biofilm reactors has also been tested and implemented. Suspended solids and fats oil and grease can now be removed from wastewater that is up to 500 times more concentrated in solids and colloidal particles, such as emulsified oils, than municipal wastewater. (Colic et al., 2001, 2005, Ross et al., 2000) We will also discuss advances in mixing of coagulants, flocculants and other treatment chemicals with wastewater contaminants in flotation system. High energy mixing in some novel systems is also used to further reduce size of bubbles in flotation systems. New air handling pumps can introduce air into water much more efficiently, with close to 100% efficiency and pressures up to 120 psig (Ross et al., 2000). Computational fluid dynamics (CFD) is used to optimize fluid flow conditions in flotation tanks for maximum clarification with minimum chemical dosages. (Desam et al., 2001). It is also possible to add flocculants “in – situ” inside flotation aeration and mixing system. This enables nucleation of bubbles and flocs at the same time. (Morse et al., 2004a,b; Colic et al., 2005) Systems that can respond within seconds to changes in wastewater composition and adjust dosage of chemicals needed to treat wastewater have been developed. One of the remaining challenges is to reduce cost of treatment – chemical dosage and energy consumption in flotation systems. More detailed discussion of some of these developments will be presented below.