Abstract
The integrated fixed-film activated sludge (IFAS) process has been widely used in the upgrading of wastewater treatment plants (WWTPs). The oxygen transfer efficiency (αOTE) is of great significance to the design and operation of the IFAS process. The carrier filling ratio (CFR) and aeration type are two critical factors affecting αOTE and standard oxygen transfer efficiency (αSOTE). However, the distribution and changing laws of αOTE and αSOTE in the full-scale IFAS process areunclear. To optimize the operation of a WWTP and to improve the αOTE of the aeration systems, several off-gas tests were conducted under different aeration types and different CFRs. The results show that for the aerobic tank investigated (the ratio of length and width was 8:1), the αOTE and the αSOTE of the middle of the aeration systems were higher than those of the other two sides. However, the reason for the low αOTE at the beginning and the end of the tank may be different. Coarse-bubble aeration systems had a lower αOTE and almost the same oxygenation capacity (αSOTE) as the fine-bubble aeration systems under constant CFR (43%). The average αSOTE (18.7–28.9%) of the hybrid aeration systems increased with increasing CFR (7.7–57.7%), and different locations exhibited different degrees of change. The results reveal the distribution and changing law of the αOTE of aeration systems in the IFAS process, and attention should be paid to the improvement of the OTE of the plug-flow IFAS process.
Highlights
The integrated fixed-film activated sludge (IFAS) process is a hybrid activated sludge/biofilm process [1]
This study investigated the effects of the carrier filling ratio (CFR) and aeration type on the αOTE and αOTE and standard oxygen transfer efficiency (αSOTE) of aeration systems and determined the distribution and changing law of αOTE and αSOTE of the aeration systems in the full-scale IFAS process
Effects of Aeration Type on αOTE of the IFAS Process The tests were conducted under the coarse-bubble aeration systems and fine-bubble aeration systems with the constant CFR (43%), respectively
Summary
The integrated fixed-film activated sludge (IFAS) process is a hybrid activated sludge/biofilm process [1]. The biomass attached to carrier elements moves freely along with the water in the reactor. The carriers are kept in the reactor by screens [2,3]; the biomass of the IFAS process is much higher than that of the conventional activated sludge (CAS) process. The IFAS process has strong nitrogen and phosphorus removal capacity and requires little space [4]; the IFAS process is widely used in the upgrading of wastewater treatment plants (WWTPs) [5]. The energy required for the electromechanical equipment used in aeration represents 50–80% of the total energy costs of WWTPs [8]. Improving the oxygen transfer efficiency (αOTE) of the aeration system can produce significant economic effects for the IFAS process
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