Edinburgh Napier University

  Microbial foaming and bulking are among the most frequent and widespread problems in activated sludge (AS) wastewater treatment plants (WWTPs). Bulking has plagued AS plants almost since their inception nearly a century ago, whereas microbial foaming was not documented until around 30 years ago. Both problems are associated with the excessive growth of various filamentous bacteria, although the mechanisms by which they form are not fully understood. Initial attempts to identify these bacteria shifted attention from engineering aspects to the microbiological activities fundamental to the activated sludge process. Subsequently, filament identification keys and abundance scales became routine tools for monitoring filamentous populations in activated sludge. More recently, molecular biological techniques have enabled more detailed and precise study of the diversity and ecology of bacterial communities associated with foaming and bulking.