FROTH CONTROL AND PREVENTION STRATEGIES FOR STEP-FEED BNR AT NYC WPCPS

New York City water pollution control plants (NYC WPCP) have been plagued with aeration tanks and secondary clarifier frothing events while operating in step-feed BNR mode at high mean cell residence times (MCRTs). Activated sludge froth has been linked to hydrophobic filamentous organisms such as Nocardiaforms and M. parvicella, among others. (Eikelboom, 1975; Jenkins, et al., 1993). Frothing can pose several operational problems and health hazards such as reduced plant effluent quality, clogged digester gas systems, digester failure and the spread of pathogens in windblown scum. Efforts to combat froth increase operational complexity and increase capital, operational and maintenance costs. Many froth control techniques have been investigated such as employing anoxic selectors; surface and return activated sludge (RAS) chlorination, addition of chemicals such as polymers and surfactants and addition of biological agents such as microorganisms and enzymes; however, their effectiveness for froth control is inconsistent (Gabb et al., 1991). This paper will detail the results obtained via the application of three of the more successful froth control strategies, surface wasting, surface chlorination and RAS chlorination, tested at the PO-55A pilot plant facility located at the NYC 26th Ward WPCP.