Study of activated sludge separation problems focused on biological foams formation and their suppression
Prof. Ing. Jiří Wanner, DrSc.
This dissertation is focused on biological foam formation and means of its suppression. Biological foam formation is one of the separation problems. Therefore physicochemical parameters connected with the separation properties of activated sludge were determined in the experiments.
The theoretical part summarizes scientific knowledge about bioflocculation process, basic types of activated sludge separation problems and types of foams in activation process. The biological foam theme is more developed in respect with mechanism of its formation and different kinds of tools allowing its control or suppression.
The purpose of the work was to study influence of enzyme additives, defoamers and mixed coagulants on the biological foam production and the separation properties of activated sludge. Than, based on the carried out research, to make decision concerning additive suitability for operational applications. Furthermore to obtain set of values of physicochemical parameters of activated sludge and biological foam enabling to find a correlation between parameters and subsequently to decide, which of these parameters are connected with the biological foam production. In the end, to specify, to which extent is the biological foam creation related to the presence of fatty compounds in wastewater.
The experimental part contains procedures for determination of the particular physicochemical parameters and methodology of microscopic analyses.
The Results and Discussion chapter describes all of realized experiments together with visually observed changes, measured data and their evaluation. The obtained results are discussed and compared with knowledge mentioned in scientific publications. There is also statistical evaluation of measured characteristics and their correlations in this chapter.
The following results ensued from the accomplished observations:
- The influence of enzyme additive I on biological foam formation was positive in one case and rather negative in another one. The system was not influenced by the enzyme additive I in four experiments.
- With respect to the biological foam creation and other monitored parameters enzyme additive II had a negative effect on wastewater treatment plant.
- Defoamer I removed biological foam from surface of aeration tank, but coincidental deterioration of the monitored parameters occurred. Only a short-term effect of defoamer I was observed.
- Semi continual dosage of defoamer II provided short-term suppression of biological foam. However, negative effects appeared in the system during application. This negative influence endured after the end of the dosing.
- Continual injection of mixed coagulant I lead to biological foam suppression together with decrease of total abundance of filamentous microorganisms.
- Improvement of separation properties of activated sludge and decrease of abundance of filamentous microorganisms was observed in certain phases of mixed coagulant II addition. This positive influence was only temporary, with an exception for sludge volume index.
- Scum index is a suitable parameter for description of processes connected with the biological foam formation and for characterization of foaming potential of activated sludge. On the other hand, the hydrophobicity determined by using the MATH test method is not suitable for this purpose.
- Extracelular polymeric substances influence the separation properties of activated sludge to wide extent. The qualitative and quantitative indications of ECP extracted from activated sludge are more informative, with respect to the used method of extraction, its efficiency and number of mechanisms participating in bioflocculation process.
- Dosing of fatty compounds into influent wastewater lead to biological foam creation.