Structure-function dynamics and modeling analysis of the micro-environment of activated sludge floc

2003 ◽  
Vol 47 (11) ◽  
pp. 267-273 ◽  
Author(s):  
B. Li ◽  
P. Bishop
Keyword(s):  
Dissolved Oxygen ◽  
Activated Sludge ◽  
Outer Layer ◽  
Substrate Concentration ◽  
Model Simulation ◽  
Redox Status ◽  
Pollutant Removal ◽  
Concentration Increase ◽  
Transfer Resistance ◽  
Oxygen Concentrations

Biodegradation by microorganisms and mass transfer resistance in the micro-environment of activated sludge floc can cause changes in substrate and dissolved oxygen concentrations within the floc and can contribute to stratification of microbial processes inside the flocs. In this study, an integrated model of the microenvironment of the activated sludge floc was developed for floc from wastewaters from several sources and of varying strengths for dynamic simulation of the combined biological processes of COD and nitrogen removal. The model simulation results and measured profiles show the heterogeneous and gradient-governed microenvironment of activated sludge floc under different substrate and bulk oxygen concentrations. The substrate concentration increase zones inside the floc were present in all activated sludge floc from the Miller Brewing Co. wastewater treatment facility (high pollutant strength), with an oxygen penetration depth of only 0.15 mm into the outer layer. The anoxic and substrate concentration increase zones also dominated in the activated sludge floc from the Mill Creek Plant influent (medium pollutant strength), with the outer layer (0.20 mm) participating in the metabolism of the pollutants. The radius of the substrate concentration increase zone inside the sludge floc decreased with pollutant removal along the length of the tank. When the pollutant concentration in the bulk wastewater was low (Muddy Creek Plant), the substrate concentration increase zone disappeared; the whole floc was aerobic and in a high redox status. Our experiments and model analyses demonstrate that the microorganisms' structure-functions inside activated sludge floc change with the bulk substrate concentration and dissolved oxygen concentration.

Nitrogen removal from wastewater and bacterial diversity in activated sludge at different COD/N ratios and dissolved oxygen concentrations

2012 ◽  
Vol 24 (6) ◽  
pp. 990-998 ◽  
Author(s):  
Magdalena Zielinska ◽  
Katarzyna Bernat ◽  
Agnieszka Cydzik-Kwiatkowska ◽  
Joanna Sobolewska ◽  
Irena Wojnowska-Baryla
Keyword(s):  
Dissolved Oxygen ◽  
Activated Sludge ◽  
Bacterial Diversity ◽  
Nitrogen Removal ◽  
Oxygen Concentrations

scholarly journals Relation Between Redox Potential and Oxygen Levels in Activated-Sludge Reactors

1989 ◽  
Vol 21 (8-9) ◽  
pp. 947-956 ◽  
Author(s):  
Alain Heduit ◽  
Daniel R. Thevenot
Keyword(s):  
Dissolved Oxygen ◽  
Activated Sludge ◽  
Electrode Potential ◽  
Platinum Electrode ◽  
Plug Flow ◽  
Metal Electrode ◽  
Factor B ◽  
Electrode Potentials ◽  
Oxygen Concentrations ◽  
Sludge Concentration

The importance of dissolved oxygen level in determining the platinum electrode potential in activated sludge has been clearly demonstrated by current-potential curves plotted at different oxygen concentrations. Tests have been carried out, in the laboratory and in full scale treatment plants,to define the relationship between the platinum electrode potential at equilibrium (Eh) and the dissolved oxygen [O2] concentration in the activated sludge. These two parameters obey a law of the form Eh = a + b log [O2]. The measured values of coefficents a and b differ widely to those found from the oxygen reduction reaction in water (a = 0.8 V at pH 7 and b = 15 mV per decade). Factors a and b mainly depend on the sludge loading, the aeration conditions and the sludge concentration. Using non–polished stationary platinum ring electrodes, the following values of a. were obtained (at pH between 7 and 7.6) : + 410 mV/NHE for sludge aerated for several hours without feeding, + 265 mV/NHE for over-aerated/low-loaded sludge (Cm = 0.2 kg BOD.kg MLVSS−1. day−1) and + 180 mV/NHE for high-loaded activated sludge in plug-flow system (Cm = 1 kg BOD.kg MLVSS−1.day −1). Factor b would seem to lie between 55 and 65 mV when the sludge is continuously aerated without feeding.At low loads with excess aeration, it lies between 70 and 90 mV. When the medium is slightly septic at low dissolved oxygen concentrations (insufficient daily aeration time, high sludge concentration or aerators shut down for too long periods), factor b increases and can reach 200 mV. In the same way, at high loads, factor b can become 150 mV. These results demonstrate the importance of dissolved oxygen concentration in the mechanisms which determine the metal electrode potentials in activated sludge. They also illustrate the role that other electroactive species play in the process. The type and concentration of these species depend on parameters such as the sludge loading, the overall oxygen supply, the aeration sequence and the sludge concentration.

Nitrification studies on fertilizer wastewaters in activated sludge and biofilm reactors

1995 ◽  
Vol 32 (12) ◽  
pp. 141-148 ◽  
Author(s):  
Ferhan Çeçen ◽  
Elvan Orak ◽  
Pinar Gökçin
Keyword(s):  
Dissolved Oxygen ◽  
Activated Sludge ◽  
Continuous Flow ◽  
Removal Rate ◽  
Ammonia Concentration ◽  
Biofilm Reactor ◽  
Operating Conditions ◽  
Nitrite Accumulation ◽  
Operational Conditions ◽  
Oxygen Concentrations

Nitrification characteristics of a high-strength fertilizer wastewater were studied in a batch activated sludge and a continuous-flow biofilm reactor. In a batch activated sludge system one of the most decisive factors was the pH control. The results in terms of ammonium decrease and nitrite build-up were fitted to kinetic models and it was shown that in the absence of inhibitory factors like high free ammonia or nitrous acid build-up the behaviour was similar to that in the case of low-strength wastes. Continuous-flow studies in the biofilm reactor at different loading rates and dissolved oxygen concentrations indicated that such a biofilm reactor could be employed in the treatment of highly nitrogenous fertilizer wastes. Depending on operating conditions such as dissolved oxygen concentration and loading rate an effluent ammonia concentration as low as 4 mg NH4−N/L could be achieved. In the dissolved oxygen ranges of 3.2 mg/L–3.5 mg/L the system reached the maximum removal rate of 0.17 kg NH4−N/m3.d. When the dissolved oxygen was increased to 4.9 mg/L, removal rates as high as 0.41 kg NH4−N/m3.d could be obtained. Also in continuous-flow operation nitrite accumulation reached in some cases a considerable degree depending on the bulk nitrogen and dissolved oxygen concentrations. The nitrite accumulation in the effluent stream varied from 4–180 mg NO2−N/L depending on operational conditions.

A New Life for the St. Croix River

1988 ◽  
Vol 23 (4) ◽  
pp. 568-577
Author(s):  
Harold S. Bailey
Keyword(s):  
Water Quality ◽  
Dissolved Oxygen ◽  
Discharge Rate ◽  
Paper Mill ◽  
Regulated River ◽  
Secondary Treatment ◽  
Pulp And Paper Mill ◽  
Oxygen Regime ◽  
Oxygen Concentrations

Abstract The water quality of the upper 110 kilometres of the St. Croix River is considered to be pristine. A major industrial discharge renders the lower 14 kilometres of the river a water quality limited segment. Prior to 1970 the Georgia-Pacific Pulp and Paper Mill at Woodland, Maine, discharged untreated effluent directly into the river causing dissolved oxygen concentrations to drop well below 5 mg/L, the objective chosen in the interest of restoring endemic fish populations. Since 1972, the Mill has installed primary and secondary treatment, regulated river discharge rate and effluent composition which has greatly improved the summer dissolved oxygen regime. By 1980, dissolved oxygen concentrations were generally above 5.0 mg/L and restocking the river with Atlantic Salmon (Salmo salar) was initiated.

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