Extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems: a review.

Extraction of extracellular polymers from activated sludge using a cation exchange resin

The enzymatic activity of activated sludge was investigated with special emphasis on the localization of the enzymes in the sludge floc matrix. Activated sludge from an advanced activated-sludge treatment plant, performing biological N and P removal, was used. An enzymatic fingerprint was established using a panel of six different enzymes. The fingerprint revealed peptidase as the most dominating specific enzyme tested. By monitoring sludge bulk enzymatic activity over a 3-month period using fluorescein diacetate as an enzyme substrate, considerable variations in activity were observed even over short periods (a few days). The variation in esterase activity was to some extent correlated to the presence of humic compounds in the sludge, but not to the sludge protein content. Comparison of full sludge enzyme activity to the activity of a batch-grown sludge culture indicated that enzymes accumulated in sludge flocs. A large proportion of the exoenzymes were immobilized in the sludge by adsorption in the extracellular polymeric substances (EPS) matrix. This was demonstrated by extraction of EPS from the activated sludge using cation exchange. Contemporary to the release of EPS a very large fraction of the exoenzymes was released into the water. This showed that the exoenzymes should be considered to be an integrated part of the EPS matrix rather than as direct indicators of the microbial activity or biomass.

Enzymatic activity in the activated-sludge floc matrix

A dynamic model of the clarification-thickening process

The basics of bio-flocs technology: The added value for aquaculture

Il est montre que les agregats de particules se formant au cours des processus par floculation/coagulation, par boues activees et par lits bacteriens possedent des caracteristiques fractales. Plusieurs proprietes morphologiques de ces particules peuvent etre determinees par des dimensions fractales

Fractal geometry of particle aggregates generated in water and wastewater treatment processes

Relatively large activated sludge floes (larger than about 100 microm) were stabilized, using a histological tissue specimen preparation procedure, and then were sliced into sections of 3 to 6 microm thick. The study of these sections, after staining, revealed the internal structure of the activated sludge floes. No uniformity of this structure was found. The distribution of microorganisms and of extracellular polymers (EPs) in the floes varied randomly on the plane of the sections and along the dimension perpendicular to the plane, leaving large water channels and reservoirs in some of the floes. The lack of a characteristic size for the water gaps in the floes and a general self-similar appearance of the sections suggested that the activated sludge floes might be characterized by the fractal concept within a certain size limit. Direct observation of the interior of the floes indicated an abundant presence of extracellular polymers (EPs) in amorphous forms, surrounding microorganisms in most of the floes.

Structure of activated sludge floes.

Stroboscopic determination of settling velocity, size and porosity of activated sludge flocs

Flow through activated sludge flocs

The liquid flow through activated sludge flocs from fullscale conventional treatment plants was evaluated on the basis of the information obtained from settling tests. In the samples of the mixed liquors studied, only a part of the activated sludge flocs was found permeable to fluid drainage. Basically, small flocs were not permeable but all the flocs in the size range from 100- 150 μm showed different degrees of permeability. The permeability of flocs increased with an increase in the dynamic sludge age and decreased with an increase in the shear rate measured as the mean velocity gradient in the aeration tanks. The most sensitive assumption for the estimation of the permeability of the flocs was the size of the primary particles in the aggregates, with the sphericity of the flocs being less important

Da-Hong Li

Papers

Fractal geometry of particle aggregates generated in water and wastewater treatment processes

Structure of activated sludge floes.

Stroboscopic determination of settling velocity, size and porosity of activated sludge flocs

Flow through activated sludge flocs

Advective transport in activated sludge flocs