extraction-structural-extracellular-polymeric-substances-from-aerobic

Extraction of Structural Extracellular Polymeric Substances from Aerobic Granular Sludge

To evaluate and develop methodologies for the extraction of gel-forming extracellular polymeric substances (EPS), EPS from aerobic granular sludge (AGS) ...

Delft University of Technology

The Monod equation for microbial growth is purely empirical, and the theoretical basis of this model stays unclear. Similar to any chemical reactions, overall microbial growth process is dependent upon the changes in free energy. This study showed that the Monod equation could be interpreted in a thermodynamic sense very well. It was probably for the first time demonstrated that the Monod constant ( K(s)) was inversely related to the equilibrium constant of the overall microbial growth process.

A thermodynamic interpretation of the Monod equation.

The individual and joint effects of copper and zinc on the growth kinetics of activated sludge microorganisms were studied in batch reactors fed with glucose as sole carbon source. The observed specific growth rate, substrate utilization rate and removal efficiency were determined at different concentrations of individual and joint Cu and Zn. Activated sludge microorganisms showed different kinetic responses to Cu and Zn, and the Haldane model seemed applicable for the inhibitory effect of Zn, while a first-order kinetics for Cu. Compared to Zn, Cu exhibited high toxicity to activated sludge microorganisms even at a very low concentration of 1.0 mg/dm3. However, Zn concentrations less than 40 mg/dm3 would stimulate the growth of activated sludge microorganism, and Zn acted as inhibitory chemical only at concentrations above this value. The combined effect of Cu and Zn could be regarded as neither synergistic nor antagonistic action.

Kinetic responses of activated sludge microorganisms to individual and joint copper and zinc.

To explore bacterial alginates role in aerobic granules' formation, the alginate was extracted from aerobic granules and identified. Its aggregation property in 50 mg x L(-1) CaCl2 solution was investigated by the atomic force microscopy (AFM). Bacterial alginates amounted to 35.1% +/- 1.9% of granules' dry mass. With the concentration increased from 10 mg x L(-1) to 500 mg x L(-1) in 50 mg x L(-1) CaCl2, the extracted alginates tended to form ordered aggregations, with the shape changed from randomly distributed globules, to rod-like and flower-shaped aggregations, and finally to weblike networks due to their supramolecular self-assembly property. The three dimensional alginate-metal gel is the structural polymer of aerobic granules, and the alginates-Ca2+ gel formation plays an important role in granules' formation and structure stabilization.

[Self-aggregation property of bacterial alginates extracted from aerobic granules].

To evaluate the potential use of the bacterial alginate extracted from excess activated sludge as a sustainable copper bioadsorbent, dried alginate-Ca made from municipal excess activated sludge was characterized by atomic force microscopy, and tested in a batch system. The alginate-Ca yield from the activated sludge was 103 +/- 15 mg g(-1). The maximum Cu2+ uptake was 41.96 mg g(-1). Accumulation of Cu2+ reached equilibrium within 50 min and followed the Langmuir adsorption isotherm. The solution pH and initial Cu2+ concentration were critical for Cu2+ biosorption. The sludge alginate-Ca bioadsorbent could be regenerated by 100 mmol L(-1) HCl with 82% Cu2+ recovery. Calcium alginate from excess activated sludge was proved to be a good bioadsorbent for heavy metal elimination.

Biosorption of copper by calcium alginate from excess activated sludge.

The biosorption characteristic of copper ions onto dried Ca-alginate made of bacterial alginate extracted from aerobic granules was investigated in batch system. The biosorption rate of Cu2+ onto the alginate, effects of pH and alginate dosage on Cu2+ biosorption capacity and adsorption isotherm were analyzed. The biosorption of Cu2+ onto the dried Ca-alginate was a rapid process. The maximum Cu2+ uptake was 67.67 mg/g at pH 4, initial Cu2+ concentration of 100 mg/L, dried Ca-alginate dosage 0.7 g/L. Accumulation of Cu2+ followed Langmuir and Freundlich adsorption isotherm. Cu2+ adsorption was accompanied by Ca2+ releasing from the dried Ca-alginate and H+ uptake, indicating that the ion exchange between Cu2+ and Ca2+ requires H+ for charge balance. FT-IR secondary derivative spectra and atomic force microscopy analysis gave proof that, the reaction of MG blocks in dried Ca-alginate with Cu2+ and Ca+ were different. Cu2+ may form complex with MG blocks, leading to a much more ordered structure on the surface of the dried Ca-alginate. The dried Ca-alginate bio-adsorbent was regenerated by 100 mmol/L HCI with 91% Cu2+ recovery.

Yue Mei Lin

Department of Biotechnology

Delft University of Technology

Extraction of Structural Extracellular Polymeric Substances from Aerobic Granular Sludge