Biomedical subjects

K Keiding

Publications and source records attributed to K Keiding.

6 recordsLinked to original sources

PubMed2001

Remember the water--a comment on EPS colligative properties.

The relationship between water and activated sludge components was examined. Reevaluation of published data on freezing point depression, drying rates and dewatering has been performed. The basis of this has been the assumption that the water/sludge relationship is considered to be a colligative effect. Since the results indicate this to be the case, we suggest that the published concepts of "pools of water" are false. Data on swelling properties of EPS as a function of pH suggests that the colligative properties are largely determined by the counterions of charged polymers and surfaces.

Biopolymers↗

PubMed2001

Monitoring and troubleshooting of non-filamentous settling and dewatering problems in an industrial activated sludge treatment plant.

A large industrial activated sludge wastewater treatment plant had temporary problems with settling and dewatering of the sludge. Microscopical investigations revealed that the poor settling properties were not due to presence of filamentous bacteria, but poor floc properties. In order to characterise the changes in floc properties that led to settling and dewatering problems and to find reasons for this taking place, a comprehensive monitoring program was conducted during more than one year. The monitoring program included various measurements of floc settleability, floc strength and sludge dewaterability. The monitoring program revealed that a deterioration of the floc strength and the settling properties in the process tanks was closely connected to downstream dewatering problems and poor effluent quality. Particularly severe problems were observed a few weeks after the production at the factory had started after summer closedown. Possible reasons for the changes in floc properties in the process tanks were found by a) analysing change in wastewater composition by evaluating the different production lines in the industrial plant, b) evaluating the operation of the plant, and c) performing short-term laboratory experiments testing factors that could potentially affect floc properties (absence of oxygen, presence of sulphide, detergents, etc). Among several measured parameters, the use of floc strength measurements in particular proved useful to monitor the activated sludge floc properties at this industrial plant. The described strategy can be useful in general to find and solve many solid/liquid separation problems in activated sludge wastewater treatment plants.

Bacteria↗

PubMed2001

Effects of solids concentration on activated sludge deflocculation, conditioning and dewatering.

Optimum conditioning of activated sludge in terms of minimum CST was shown to correspond to the complete removal of turbidity, and the increase in turbidity with shear due to e.g. pumping is therefore expected to affect conditioning. The optimum polymer dosage was directly related to the turbidity of activated sludge after two minutes shear, and was considerably lower than the dosage required for charge neutralisation. The turbidity produced by shear increased more than is proportional with solids concentration and was directly related to the apparent viscosity. It is suggested that increasing solids concentration causes increased surface erosion when network structures are broken, and this causes increases in turbidity and required polymer dosage per solids mass. For Aby activated sludge, optimum polymer dosage per solids mass increased by 52% when the solids concentration was increased from 8.2 to 13.7 g SS/l. Modelling of the effect of solids concentration predicts even higher increases in required polymer dosage for higher solids concentrations. This means that reduced thickening prior to pumping and conditioning may be desirable when the hydraulic capacity of the dewatering device is sufficient. Similar trends were observed for an anaerobically digested sludge. For this sludge, reduction of turbidity with FeCl3 reduced the polymer demand.

Flocculation↗

PubMed1997

Role of Hydrophobicity in Adhesion of the Dissimilatory Fe(III)-Reducing Bacterium Shewanella alga to Amorphous Fe(III) Oxide.

The mechanisms by which the dissimilatory Fe(III)-reducing bacterium Shewanella alga adheres to amorphous Fe(III) oxide were examined through comparative analysis of S. alga BrY and an adhesion-deficient strain of this species, S. alga RAD20. Approximately 100% of S. alga BrY cells typically adhered to amorphous Fe(III) oxide, while less than 50% of S. alga RAD20 cells adhered. Bulk chemical analysis, isoelectric point analysis, and cell surface analysis by time-of-flight secondary-ion mass spectrometry and electron spectroscopy for chemical analysis demonstrated that the surfaces of S. alga BrY cells were predominantly protein but that the surfaces of S. alga RAD20 cells were predominantly exopolysaccharide. Physicochemical analyses and hydrophobic interaction assays demonstrated that S. alga BrY cells were more hydrophobic than S. alga RAD20 cells. This study represents the first quantitative analysis of the adhesion of a dissimilatory Fe(III)-reducing bacterium to amorphous Fe(III) oxide, and the results collectively suggest that hydrophobic interactions are a factor in controlling the adhesion of this bacterium to amorphous Fe(III) oxide. Despite having a reduced ability to adhere, S. alga RAD20 reduced Fe(III) oxide at a rate identical to that of S. alga BrY. This result contrasts with results of previous studies by demonstrating that irreversible cell adhesion is not requisite for microbial reduction of amorphous Fe(III) oxide. These results suggest that the interaction between dissimilatory Fe(III)-reducing bacteria and amorphous Fe(III) oxide is more complex than previously believed.

Journal Article↗

PubMed1996

Changes in the composition of extracellular polymeric substances in activated sludge during anaerobic storage.

Changes in the chemical composition of organic compounds in total activated sludge, activated sludge extracellular polymeric substances (EPS), and sludge bulk water during anaerobic storage (12 days) were studied. The background for the study was that anaerobic storage of activated sludge, which often takes place at wastewater treatment plants before dewatering, causes a deterioration of the dewaterability. The reasons are not known at present, but may be related to changes in exopolymer composition of the flocs. The results showed that a fast decrease in total sludge protein and carbohydrate took place within 3 days of anaerobic storage as a result of degradation processes, which accounted for approximately 20% of the organic fraction. The amount of uronic acids and humic compounds remained almost constant in the sludge. The EPS were extracted from the floc matrix using a cation-exchange resin. In the EPS matrix a similar initial (2-3 days) degradation of proteins and carbohydrate took place, whereas the content of DNA and uronic acids showed minor changes. The extractability of humic compounds increased during the first 3 days of storage. No changes in extractability of the carbohydrate were observed. A fraction of the EPS protein was found to be difficult to extract but was observed to be degraded during the anaerobic storage. The EPS composition was further characterized by high-performance size-exclusion chromatography analysis obtained by on-line UV detection and post-column detection of proteins, carbohydrates, humic compounds and DNA. Four fractions of polysaccharides were found, of which only one was responsible for the decrease in the carbohydrate content observed with storage time. The fraction was presumably of low molecular mass. Humic compounds and volatile fatty acids (acetate and propionate) were released to the bulk water from the flocs during the storage. A possible mechanism to explain the reduced dewaterability developed during anaerobic storage, partly because of the observed changes in EPS, is discussed.

Anaerobiosis↗

PubMed1979

N-acylglycines: gas chromatographic mass spectrometric identification and determination in urine by selected ion monitoring.

Eleven biologically interesting N-acylglycines have been synthesized and the gas chromatographic and mass spectrometric properties of their trimethylsilyl derivatives studied, A sharp and reproducible gas chromatographic peak could be obtained for each N-acylglycine as the N, O-bis-(trimethylsilyl)-N-acylglycine. By the use of these derivatives a sensitive and specific selected ion monitoring method for the determination of N-acylglycines in human urine has been developed.

Gas Chromatography-Mass Spectrometry↗