A. Azevedo

Application of flocculation–flotation followed by ozonation in vehicle wash wastewater treatment/disinfection and water reclamation

AbstractThis article provides the results of flocculation–flotation followed by sand filtration and ozonation (FFO), applied for the treatment of car wash wastewater in a water reclamation system in Brazil. The assessment of the efficiency of the process in enhancing reclaimed water quality, especially aesthetic, microbiological, and chemical issues is reported. The FFO process provided disinfected (Escherichia coli < 1.8 CFU 100 mL−1) and clarified water (10 NTU), minor foaming (residual surfactants = 1.30 mg L−1MBAS), and no odor-related problems from reclaimed water. Comparative studies were carried out at bench scale; ozone (AOP) and chlorine were applied separately as oxidation procedures and a mass balance was assessed as a function of the number of water cycles. Results revealed that besides higher oxidation of organics and water clarification, both conductivity and dissolved solids concentrations for the ozone-treated water were lower than those obtained with the chlorinated water. A cost–benefit ...

Raw water clarification by flotation with microbubbles and nanobubbles generated with a multiphase pump

Raw water clarification by flotation was studied by injecting air into a centrifugal multiphase pump to generate microbubbles (MBs) and nanobubbles (NBs). Measurements of gas dispersion parameters were performed and optimal conditions were obtained using a pump pressure of 4 bar. Values showed a bubble Sauter diameter of 75 μm, an air holdup of 1.2%, a bubble surface area flux of 34 s-1 and an NB concentration of 1 × 108 NBs mL-1 (measuring 220 nm). Then, a study compared flotation with bubbles formed with the multiphase pump (F-MP) to lamellar settling at the clarification stage of a water treatment plant (WTP), in Brazil. The F-MP showed a higher separation efficiency at high hydraulic loads (9-15 m h-1), even without the use of a polymer, reaching 2 NTU (10-25 NTU raw water feed), which was much lower than the technical goal of the WTP (5 NTU). The results and the technical aspects are discussed, and it is concluded that the employment of MBs and NBs with pumps widens new research lines and applications in modern flotation.

Separation of emulsified crude oil in saline water by flotation with micro- and nanobubbles generated by a multiphase pump

The flocculation-column flotation with hydraulic loading (HL, >10 m h-1) was studied for the treatment of oil-in-water emulsions containing 70-400 mg L-1 (turbidity = 70-226 NTU) of oil and salinity (30 and 100 g L-1). A polyacrylamide (Dismulgan, 20 mg L-1) flocculated the oil droplets, using two floc generator reactors, with rapid and slow mixing stages (head loss = 0.9 to 3.5 bar). Flotation was conducted in two cells (1.5 and 2.5 m) with microbubbles (MBs, 5-80 μm) and nanobubbles (NBs, 50-300 nm diameter, concentration of 108 NBs mL-1). Bubbles were formed using a centrifugal multiphase pump, with optimized parameters and a needle valve. The results showed higher efficiency with the taller column reducing the residual oil content to 4 mg L-1 and turbidity to 7 NTU. At high HL (27.5 m h-1), the residual oil concentrations were below the standard emission (29 mg L-1), reaching 18 mg L-1. The best results were obtained with high concentration of NBs (apart from the bigger bubbles). Mechanisms involved appear to be attachment and entrapment of the NBs onto and inside the flocs. Thus, the aggregates were readily captured, by bigger bubbles (mostly MBs) aiding shear withstanding. Advantages are the small footprint of the cells, low residence time and high processing rate.