Assessment of Aeration System Performance Efficiency: Frequent Sampling for Damage Detection

Although feedback systems that control the air supply to aeration tanks inherently incorporate some assumption about oxygen transfer response to changes in airflow, it is rare to measure this relationship under process conditions. This paper reports measurements of oxygen mass-transfer curves (MTCs) for a tank at the Tillman Water Reclamation Plant in Los Angeles, California. The curves were obtained by measuring the oxygen transfer efficiency (OTE) at selected points for several set values of airflow while the plant was operating. They approximate inverted parabolas because increasing the airflow increases the amount of oxygen supplied by the blowers, but decreases the OTE, which is the fraction of the supplied oxygen that actually enters the water. Data were recorded from both recently cleaned diffusers and ones that were moderately to severely fouled.The peaks in the curves from the fouled diffusers are at or below the midpoints of the observed ranges of airflows. Hence, there is only a narrow range of usable airflows between the lower limit, determined by the manufacturer of the diffusers, and the peak of the MTC, which is the maximum amount of oxygen that can be supplied. The peaks for the cleaned diffusers are higher, which allows more ability to adjust to changing biological loads.These results show that existing dissolved oxygen control systems may not be adequate and that fouling may reduce not only the overall efficiency of an aeration system but its ability to respond to changes in the biological load. The measurements also provide some insight to the limitations of using sparsely distributed dissolved oxygen sensors to control the aeration process and the excess costs that are incurred by the consequent need to compensate for uncertainty with extra air. However, additional testing is needed to determine whether the present results are aberrant or typical of tanks with fouled or cleaned diffusers. Water Environ. Res., 73, 266 (2001).

Section: Observations and Analysissupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Relationship Between Oxygen Transfer Rate and Airflow for Fine‐Pore Aeration Under Process Conditions

Iranpour¹,

Stenstrom²

2001

“…With fine‐pore diffusers, the efficiency is also affected by the condition and age of the diffusers ( Iranpour et al, 2000a and b , 2001 , 2002 ). Membrane diffusers can harden or soften after use, resulting in increased pressure loss or increased bubble diameter.…”

Section: Introductionmentioning

confidence: 99%

Fifteen Years of Offgas Transfer Efficiency Measurements on Fine‐Pore Aerators: Key Role of Sludge Age and Normalized Air Flux

Rosso¹,

Iranpour²,

Mk³

2005

Self Cite

Fine‐pore diffusers, often called fine‐bubble diffusers, have nearly replaced coarse bubble diffusers in municipal wastewater treatment over the past 20 years. The rapid increases in energy costs, which began in the 1970s, created financial incentives to upgrade to this more expensive and maintenance‐intensive method of aeration. Fine‐pore diffusers have the added benefit of reducing volatile organic compound stripping and reduced aeration heat loss. This paper summarizes 15 years of oxygen transfer efficiency measurements using the offgas technique. Efficiencies are shown for different types of diffusers at various tank geometries (depth, diffuser size, and number), airflow rates, and mean cell retention times (MCRT or sludge age). By normalizing the airflow rates per unit of depth and diffusing area, efficiencies measured in different plants can be compared. The results show that aeration efficiencies are logarithmically related to the ratio between MCRT and the normalized air flux, with transfer rates suppressed by low MCRT or high normalized air flux systems. There is no evidence for different α factors among the different types of fine‐bubble diffuser types.

“…This confirmed the positive effect of the anoxic selector on oxygen transfer due to the reduction of readily biodegradable COD required for denitrification. (Iranpour et al., 2000; Rosso & Stenstrom, 2007). Hence, the negative impact of surfactants on oxygen transfer was reduced and comparable loading conditions between the screened and nonscreened line in the second aerobic zones were assessed, as confirmed by the soluble COD concentration which was reduced by 40% on average after the anoxic section, for the line without primary treatment.…”

Section: Resultsmentioning

confidence: 99%

Oxygen transfer and plant‐wide energy assessment of primary screening in WRRFs

Pasini

Garrido-Baserba

Ahmed

et al. 2020

Primary screening is gaining interest as a method to achieve removal performances comparable to primary clarification while reducing the footprint and increasing operational elasticity. Aeration efficiency indicators in a pilot sequential batch reactor (SBR) and a full scale water resource recovery facility (WRRF) were investigated after the implementation of rotating belt filters/screens (RBF). To compare the impact between screened (350 μm) and nonscreened primary influent, two identical treatment lines were monitored using off‐gas and respirometric measurements. The study provides the first result on improved oxygen transfer efficiency due to primary screening. Consistent aeration efficiency improvements of 27% and 20% between screened and nonscreened were obtained at pilot and full scale, respectively. Changes in aeration efficiency and carbon redirection were integrated into a set of models to investigate the primary screening impact on the WRRF energy balance. While the plant‐wide assessment for different scenarios improved the energy balance up to 15%, a detailed comparative analysis between various treatment schemes gained insight into the advantages and limitations of the energetic sustainability of primary screening. Practitioner points Aeration efficiency improved 27% at pilot scale Aeration efficiency improved 20% at full scale. Use of primary screening can improve the energy balance up to 15 Assessment of advantages and limitations of primary screening.