Modeling the activated sludge floc microenvironment

1998 ◽  
Vol 37 (4-5) ◽  
pp. 243-250 ◽  
Author(s):  
Sean Scuras ◽  
Glen T. Daigger ◽  
C. P. Leslie Grady
Keyword(s):  
Activated Sludge ◽  
Rapid Progression ◽  
Structural Development ◽  
Sludge Flocs ◽  
Porosity Variation ◽  
Daughter Cells ◽  
Slow Expansion ◽  
The Difference ◽  
The Relationship ◽  
Activated Sludge Systems

Integrated modeling of activated sludge systems will only be complete when settling characteristics can be determined within the model. These characteristics are fundamentally related to the size, shape and porosity of both the sludge flocs and their component microcolonies. Microcolony porosity is of particular interest since it may both influence, and be influenced by, the substrate and electron acceptor gradients that establish competitive microenvironments. A model was developed to explore the relationship between biomass growth, death, and hydrolysis; soluble component diffusion and microcolony porosity. A key element of the model is the assumed distribution of daughter cells following replication. Preliminary results indicate rapid progression toward minimum porosity with relatively slow expansion of the microcolony surface. Although little is documented on porosity variation within flocs, these results contrast with observations for biofilms and may emphasize the difference between the mechanisms involved in the structural development of microcolonies and larger scale aggregates.

Study of factors affecting simultaneous nitrification and denitrification (SND)

1999 ◽  
Vol 39 (6) ◽  
pp. 61-68 ◽  
Author(s):  
Klangduen Pochana ◽  
Jürg Keller
Keyword(s):  
Carbon Source ◽  
Activated Sludge ◽  
Physical Phenomenon ◽  
Treatment Plant ◽  
Batch Reactors ◽  
Sequencing Batch Reactors ◽  
Factors Affecting ◽  
Floc Size ◽  
Sludge Flocs ◽  
Activated Sludge Systems

Experiments have been performed to gain an understanding of the conditions and processes governing the occurrence of SND in activated sludge systems. Sequencing batch reactors (SBRs) have been operated under controlled conditions using the wastewater from the first anaerobic pond in an abattoir wastewater treatment plant. Under specific circumstances, up to 95% of total nitrogen removal through SND has been found in the system. Carbon source and oxygen concentrations were found to be important process parameters. The addition of acetate as an external carbon source resulted in a significant increase of SND activity in the system. Stepwise change of DO concentration has also been observed in this study. Experiments to determine the effect of the floc size on SND have been performed in order to test the hypothesis that SND is a physical phenomenon, governed by the diffusion of oxygen into the activated sludge flocs. Initial results support this hypothesis but further experimental confirmation is still required.

The effect of low sludge age on wastewater fractionation (SS, SI)

2003 ◽  
Vol 47 (11) ◽  
pp. 203-209 ◽  
Author(s):  
S. Haider ◽  
K. Svardal ◽  
P.A. Vanrolleghem ◽  
H. Kroiss
Keyword(s):  
Activated Sludge ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
The Other ◽  
Second Stage ◽  
Lower Maximum ◽  
The Difference ◽  
Selection Of ◽  
Activated Sludge Systems ◽  
Raw Wastewater

In lab-scale experiments at the 2-stage activated sludge pilot plant of Vienna's central WWTP it is shown that the wastewater soluble COD concentration, which is inert to a sludge with SRT < 1 d (SIA) is about double compared to the SI concentration in sludge with SRT > 10 d (SIB). Unexpectedly the ratio of SIA/SIB is independent of the sludge age between SRTs of 0.4 and 1.0 days. The difference between the two SI fractions is soluble COD that is readily biodegradable by the sludge with SRT > 10 d. However, it is degraded at a lower maximum growth rate. These results comply with earlier results gained with different methods and at different WWTPs. It is hypothesised that very low sludge ages result in a selection of fast growing bacteria, which can utilise only part of the SS in the raw wastewater. The other part of SS therefore remains in the wastewater and can thus be utilised for enhanced denitrification in the second stage. It is still unknown beyond which sludge age the soluble inert COD SIA starts to decrease, finally reaching the value SIB for low loaded systems (SRT > 5 days). From this point on SI and SS are assumed only to depend on the wastewater composition and not on the sludge age. The assumption of the Activated Sludge Model No.1 that the biodegradable fractions can be modelled as a single substrate and by a single removal kinetic (one Monod term) appears not to be applicable for low sludge ages. Some suggestions for mathematical modelling, design and operation of 2-stage activated sludge systems are given.

Influence of the enhanced biological phosphorus removal on the waste activated sludge production

1996 ◽  
Vol 34 (1-2) ◽  
pp. 17-23 ◽  
Author(s):  
Norbert Jardin ◽  
H. Johannes Pöpel
Keyword(s):  
Activated Sludge ◽  
Phosphorus Removal ◽  
Waste Activated Sludge ◽  
Biological Phosphorus Removal ◽  
Significant Difference ◽  
The Difference ◽  
Biological Phosphorus ◽  
Phosphorus Storage ◽  
Activated Sludge Systems ◽  
Sludge Production

The effect of the enhanced phosphorus removal process (EBPR) on the waste activated sludge production and the type of phosphorus storage were investigated in two continuous flow activated sludge systems on semi-technical scale. One of the plants (plant II) was operated with the A/O process, whereas the other plant (plant I) was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated sludge solids in plant II it was proved that a major part of the enhanced phosphorus removal was due to a storage as polyphosphate (poly-P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass which was determined as 3.05 g SS/g P using the results of the measurements of the non volatile solid fraction. This value was also experimentally confirmed by the measurement of the difference between the WAS production of plant I and plant II. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated sludge solids of plant II.

The relationship between the structure of activated sludge flocs and the sorption of hydrophobic pollutants

1998 ◽  
Vol 37 (4-5) ◽  
pp. 353-357 ◽  
Author(s):  
J. C. Finlayson ◽  
B. Liao ◽  
I. G. Droppo ◽  
G. G. Leppard ◽  
S. N. Liss
Keyword(s):  
Activated Sludge ◽  
Organic Contaminants ◽  
Ruthenium Red ◽  
Halogenated Hydrocarbons ◽  
Sludge Flocs ◽  
Floc Structure ◽  
Low Concentrations ◽  
Polycyclic Aromatic ◽  
Hydrophobic Pollutants ◽  
The Relationship

The relationships between the structure of minimally perturbed activated sludge flocs and the sorption of organic contaminants were studied. Sorption, settling velocity, size distributions, floc structure and EPS composition were all examined. The results show significant removal of selected halogenated hydrocarbons and polycyclic aromatic hydrocarbons by biosorption to activated sludge flocs. However, statistically significant effects on the settling or size of the flocs caused by this sorption were not observed. The addition of chromium (Cr(III)) metal ions to the biomass caused observable changes in the floc structure and decreased ruthenium red binding to the acidic polysaccharides of the floc matrix. At low concentrations (0.6 mg/l), chromium caused an increase in the sorption of organic compounds to flocs, suggesting that changes in the floc structure can be induced, which can have an impact on the sorption of pollutants to the flocs.

Adsorption and biodegradation of azo dye in biofilm processes

2004 ◽  
Vol 49 (11-12) ◽  
pp. 237-245 ◽  
Author(s):  
J. Li ◽  
P.L. Bishop
Keyword(s):  
Activated Sludge ◽  
Azo Dye ◽  
Operating Conditions ◽  
Acid Orange 7 ◽  
Sludge Flocs ◽  
Treatment Processes ◽  
Adsorption Capacities ◽  
Significant Difference ◽  
Aerobic Nitrification ◽  
Activated Sludge Systems

The removal of a common azo dye, acid orange 7 (AO7), in biofilm systems was investigated in this study. The abiotic and biotic fate of AO7 was examined under a variety of operating conditions: aerobic nitrification, anoxic denitrification and anaerobic digestion. A comparison of the performance between biofilm and activated sludge treatment processes was made. The adsorption of AO7 onto biofilm matrix and activated sludge flocs was found to fit the Langmuir equation. However, there is a significant difference in the adsorption capacities between biofilm and activated sludge. AO7 was recalcitrant in both biofilm and activated sludge systems under aerobic conditions. Under anaerobic conditions, AO7 was readily decolorized. AO7 decolorization was also observed under anoxic conditions. However, the presence of nitrate inhibited AO7 decolorization.

Phosphate and Nitrogen Removal Programme in The Netherlands

1993 ◽  
Vol 27 (5-6) ◽  
pp. 307-316
Author(s):  
Rob den Engelse
Keyword(s):  
Drinking Water ◽  
The Netherlands ◽  
Activated Sludge ◽  
Nitrogen Removal ◽  
Phosphate Removal ◽  
Market Situation ◽  
Nitrogen And Phosphate Removal ◽  
The Relationship ◽  
Initial Results ◽  
Activated Sludge Systems

A programme of research is being conducted in the Netherlands in the period 1990-1992 to find answers to the questions and solutions to the difficulties involved in the introduction of extensive nitrogen and phosphate removal. The purpose, organisation and implementation of the programme are considered. The most important initial results are set out relating to the clogging of aeration elements on simultaneous phosphate removal in activated sludge systems, to a guide to biological phosphate removal, phosphate stripping, the relationship between softening drinking water and phosphate removal and the market situation for chemicals for phosphate removal.

Comparison of In-the-Ear and Over-the-Ear Hearing Aid Fittings

1986 ◽  
Vol 51 (4) ◽  
pp. 362-369 ◽  
Author(s):  
Donna M. Risberg ◽  
Robyn M. Cox
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Comparative Evaluation ◽  
Speech Intelligibility ◽  
Hearing Aid ◽  
Hearing Aid Fitting ◽  
The Difference ◽  
Functional Gain ◽  
The Relationship

A custom in-the-ear (ITE) hearing aid fitting was compared to two over-the-ear (OTE) hearing aid fittings for each of 9 subjects with mild to moderately severe hearing losses. Speech intelligibility via the three instruments was compared using the Speech Intelligibility Rating (SIR) test. The relationship between functional gain and coupler gain was compared for the ITE and the higher rated OTE instruments. The difference in input received at the microphone locations of the two types of hearing aids was measured for 10 different subjects and compared to the functional gain data. It was concluded that (a) for persons with mild to moderately severe hearing losses, appropriately adjusted custom ITE fittings typically yield speech intelligibility that is equal to the better OTE fitting identified in a comparative evaluation; and (b) gain prescriptions for ITE hearing aids should be adjusted to account for the high-frequency emphasis associated with in-the-concha microphone placement.

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