Research progress towards biological foaming of activated sludge in municipal wastewater treatment plants

Abstract:

Biological foaming is one of the most significant problems influencing the activated sludge settlement which determines the long-term stability of waste water treatment plant (WWTP) operation. Biological foaming gives rise to challenges to effluent water quality, work safety and public health. The formation of biological foaming requires three basic elements: air bubbles, surfactants and hydrophobic substances. Usually, Norcardioform filamentous bacteria and Candidatus Microthrix parvicella are enriched in the foam. A variety of environmental factors, including temperature, dissolved oxygen, pH, sludge retention time and especially nutrients type and concentration, have impacts on the growth of these bacteria. According to it, the paper also introduces the current strategies for controlling the growth of the two types of filamentous bacteria, including selectors, kinetics-based growth control, chemical addition and ecological methods, such as, phages to reduce filamentous bacteria concentration in mixed liquid, in order to alleviate biological foaming. This paper discusses, in detail, the causes and types of biological foaming, indexes representing foaming severity, environmental factors affecting the foaming, and advantages and disadvantages of commonly used control strategies, so as to introduce biological foaming problem of activated sludge as comprehensively as possible and provide helpful information for future research.

Key words:Wastewater treatment plants, Activated sludge, Biological foaming, Nocardioform filamentous bacteria, Candidatus Microthrix parvicella