Investigation of sodium and potassium ions in relation to bioflocculation of mixed culture microorganisms

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Bioflocculation happens naturally and microorganisms aggregate into flocs during wastewater
treatment. It is critical to understand the mechanisms of bioflocculation and its impact on the
following solid/liquid separation process since seperation by settling is one of the key aspects
that determine the efficiency and the overall economy of activated sludge systems.
Bioflocculation occurs via extracellular polymeric substances (EPS) and cations by creating a
matrix to hold various floc components together so the cations become an important part of
the floc structure.
The main objective of this study is to investigate the effects of monovalent cations
specifically potassium and sodium (K and Na) on the bioflocculation, settleability and
dewaterability of activated sludge. The particular aim is to grow the mixed culture
microorganisms in the presence of specific cation so that the effect of cation on the
stimulation of EPS production can be seen. In order to achieve this aim, semi-continuous
reactors were separately operated at concentrations of 5, 10, and 20 meq/L of each cation with
mixed culture bacteria and fed with synthetic feed medium representing influent to the
activated sludge systems. Also, a control reactor at low cation dose was operated for each
reactor set. The effective volume of the reactors was 2 L with 8 days of sludge residence time
(SRT) and pH was kept at 7.7± 0.3. The activated sludge reactors were operated until the
reactors reached steady state and then related analyses were conducted.
It was found that addition of potassium and sodium ions at increasing concentrations resulted
in increase in total polymer concentration. However, potassium ions promoted the synthesis
of both polysaccharide and protein type polymers whereas sodium ions tended to stimulate
production of protein type polymers and had an affinity to bind more protein within the floc
structure. Sodium sludges had lower hydrophobicity and higher surface charges, so sodium
ions led to deterioration in flocculation of sludges. Addition of both these ions decreased the
dewaterability, sodium ions had more detrimental effect on dewaterability of sludges
compared to potassium ions. The examination of data related to settleability showed that
potassium ions led to no drastic deterioration in settling characteristics of the activated sludge
but the addition of sodium ions deteriorated the settleability. In addition, it was seen that
while the addition of potassium ions to the feed led to a decrease in viscosity, increase in
sodium concentration correlated with an increase in viscosity. Finally, the comparison of
chemical oxygen demand (COD) removal efficiency of these cations showed that sodium is
more efficient in COD removal.

Fadime Kara
Investigation of sodium and potassium ions in relation to bioflocculation of mixed culture microorganisms · 2007 · 178 sayfa.
Danışman: Prof. Dr. F. Dilek Sanin ; Doç. Dr. G. Candan Gürakan