A Critical Review of the Factors Affecting Modeling Oxygen Transfer by Fine‐Pore Diffusers in Activated Sludge

Abstract

In this review, the factors affecting the transfer of oxygen in activated sludge processes using fine-pore diffusers for water resource recovery are critically discussed. In water resource recovery facilities, the energy required for aeration constitutes 50% to 80% of the total energy consumed by the plant. This critical review highlights the use of fine-pore diffuser aeration and emphasizes the significance of accounting for the following factors: diffuser aging and fouling, diffuser layout, diffuser type, selector benefits, local environmental conditions (temperature and atmospheric pressure), influent wastewater variability, dissolved oxygen control systems, and airflow rates. In our review, we were unable to find mathematical models that could be used to develop dynamic α-factor predictions and diffuser fouling predictions. Although the development of a model that considers all the factors that affect oxygen transfer efficiency (OTE) in activated sludge systems would be extremely valuable, the creation of such a model is outside the scope of this review.

The Changing and Distribution Laws of Oxygen Transfer Efficiency in the Full-Scale IFAS Process

“…However, to keep the carriers suspended, the IFAS process requires stronger turbulence [6], which leads to the IFAS process requiring much more aeration than the CAS process; therefore, the IFAS process has the disadvantage of poor aeration energy efficiency [7]. The energy required for the electromechanical equipment used in aeration represents 50-80% of the total energy costs of WWTPs [8]. Therefore, improving the oxygen transfer efficiency (αOTE) of the aeration system can produce significant economic effects for the IFAS process.…”

“…Many factors affect the OTE of aeration systems, such as the airflow rate [9,10], diffuser density [11,12], contaminant concentration [13][14][15], and sludge characteristics [16,17]. However, the influence of these factors is not the same [8]. The aeration type and carrier filling ratio (CFR) are two significant impact factors among these factors due to the existence of carriers [18].…”

Evaluating the performance of fine bubble diffused aeration systems in cylindrical aeration tanks by fuzzy c-means algorithm

“…In the past, simple calculation of overall mass transfer effect was used to evaluate the performance of aeration system. Kim & Ra (2005), Anjali & Rubina (2015) and Sun et al (2016) calculated the total volumetric oxygen transfer coefficient (K L a) of fine bubble diffused aeration systems in different aeration tanks, Capela (1999), Gillot et al (2000) and Andrés et al (2018) study the specific standard oxygen transfer efficiency (SSOTE) of fine-pore diffusers in activated sludge reactors, and Capela et al (2001) and Gillot et al (2005) defined a transfer number N T of fine bubble diffused aeration systems. Although these methods are more direct and simple for evaluating the performance of fine bubble diffused aeration systems, they tend to focus on overall efficiency of oxygen mass transfer and fail to take account of distribution uniformity of dissolved oxygen(DO) concentration in aeration tanks (Kim & Ra 2005;Pittoors et al 2014;Anjali & Rubina 2015;Sun et al 2016).…”

“…Although these methods are more direct and simple for evaluating the performance of fine bubble diffused aeration systems, they tend to focus on overall efficiency of oxygen mass transfer and fail to take account of distribution uniformity of dissolved oxygen(DO) concentration in aeration tanks (Kim & Ra 2005;Pittoors et al 2014;Anjali & Rubina 2015;Sun et al 2016). The nonuniform distribution of DO concentration in aeration tanks often lead to the inconsistency of the biological treatment status of sewage in the different position of cylindrical aeration tanks and then affect the biological treatment efficiency of them (Temmerman et al 2015;Wang & Zhang 2017;Andrés et al 2018). Therefore it is necessary to study a new means for performance evaluation of fine bubble diffused aeration systems, which takes both overall efficiency of oxygen mass transfer and distribution uniformity of DO concentration in cylindrical aeration tanks into consideration.…”

Impact of scaling on aeration performance of fine-pore membrane diffusers based on a pilot-scale study

“…Biological processes are the core components in wastewater treatment plants (WWTPs). Supplying air to biomass requires the highest energy use 1 , accounting for more than 50% of the net power demand 2 , which represents a significant fraction of total operating costs, ranging from 50% to 80% 3,4 . Since fine-pore diffusers have better performance in terms of specific energy consumption than coarse bubble diffusers 5 , they are extensively used for supplying oxygen to biomass in municipal WWTPs.…”