Treatment of washrack wastewater with water recycling by advanced flocculation-column flotation

A new technique for flocculation and flotation (aerated flocs), called flocculation-column flotation (FCF) was evaluated for the treatment of vehicle (bus) washrack wastewater and water reuse. The system is composed of a compact flocculation-flotation unit, utilizing an in-line flocculator device, a centrifugal multiphase pump which generates microbubbles (Sauter mean diameter, 75 pm), and a column flotation for solid/liquid separation. Design and operating parameters were studied and the efficiency of the FCF was evaluated based on the chemical and physio-chemical quality of the treated water. A tannin derivative was employed as a flocculant and aerated flocs (0.8-1.6 mm diameter; 45-150 m h(-1) rise rates) were rapidly formed (10 s, residence time). Due to the rapid formation of these very light flocs, the FCF system was able to handle a high hydraulic-load capacity (>18 m h(-1)), using a reduced foot print (compact unit), and reduced energy consumption. The data shows that this rapid FCF system appears to have a high potential to treat oily (or non-oily) voluminous wastewater at high flow-rates.