Foaming in aerated wastewater treatment plants

Foaming is a common issue that can arise from a range of causes in a biological environment. It is an occurrence associated with both the anaerobic and aerated biological treatment of wastewaters and it will consist of two parts; the liquid phase and the gaseous phase dispersed in the liquid phase, hence causing a foaming layer that can vary in depth. Foaming events can have multiple operational and financial impacts to biological processes depending on the type and duration of the event and hence should be kept under monitor and control when they appear. This article discusses some commonly encountered foam types in aerated processes and some of their causes.

Foaming can occur during the start-up of an aerated biological process due to the young age of the sludge and the balance between dominant cultures in the biomass. Furthermore, and depending on the type of wastewater, surface active compounds might develop or exist in such an environment. Violent agitation and aeration will cause these compounds to activate hence producing intense foaming, which can in extreme events spill out. As the biomass matures in the aerated tank and with the aid of the correct antifoam agent, the foaming event will subside. This might normally appear as a milky white and, sometimes puffy foam, and is generally easy to handle.

Foaming can also become evident in stable aerated process that have a separate denitrification area, where nitrates are eventually converted to gaseous nitrogen forms. The lower aeration rates in those zones and the formation of gaseous compounds can cause foaming due to formed gases mixing with solids and floating sludge layers. This type of foam appears to be generally brown in colour and lumpy, manifesting itself as individual spots of floating sludge and thick microbubbles.

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Foaming can generally stem in wastewater treatment plants due to a range of varying parameters. Most commonly, it can be associated to changes in the feed wastewater pH values, especially when these are higher to the plant design specification, levels of dissolves oxygen and their impact on normal growth of bacteria in the biomass and temperature changes in the process. These variations can cause the formation of filaments, which can spread within the system and impede the optimum plant performance. In the presence of filamentous bacteria, the resulting foam can appear thick and brown to dark brown in color.

A type of foam that can also be mistaken for foaming due to the presence of filaments is the one caused by the lack of necessary nutrients. This is normally a grey to light brown foam in colour, thick and stable foam in structure with a lingering effect even after the application of a defoaming product as its origin is different to the foams described previously. In such cases, the right type of analyses can identify the nature of the deficiency and the correct type and amount of nutrients will be enough to minimise the effect as well as reduce the risk of its reappearance.

OMEX Environmental can supply a range of the right products to address these types of foaming events in aerated wastewater treatment processes. These products are engineered to minimize the effect of an active event and, for processes with the tendency for frequent foaming, these products can offer stable and effective mitigation measures against the reappearance of foaming in the process.

This information has been sourced, reviewed and adapted from materials provided by OMEX Environmental Ltd.

For more information on this source, please visit OMEX Environmental Ltd.

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