Anaerobic Selector Research Articles

Full-Scale Demonstration of Improvement in Aeration Efficiency

This paper describes the results of side-by-side full-scale aeration testing of a plug-flow process and a modified contact stabilization process incorporating an anaerobic selector at the wastewater treatment facility in Fredonia, N.Y. Over 40 tests were completed utilizing the off-gas technique during the 2-month investigation period (summer of 1995). Compared to the plug-flow process, the modified contact stabilization process with internal sludge recycle was shown to have higher α values and to require less blower energy consumption when the selector operation was properly controlled. Dissolved oxygen concentration, selector COD concentration, and internal recycle sludge levels were found to be critical parameters in the successful operation of the modified process. Higher internal recycle sludge levels allowed the plant to run at more stable operating conditions in terms of the oxygen transfer efficiency, α, and sludge volume index.

The Effect of Anaerobic Selectors on Nocardioform Organism Growth in Activated Sludge

Laboratory‐ and full‐scale experiments were conducted to investigate the use of anaerobic selectors for control of nocardioform organisms in activated sludge. The laboratory‐scale, anaerobic‐selector, activated‐sludge system, which exhibited enhanced biological phosphorus removal (EBPR) at a 2.4‐day total mean cell retention time (MCRT) with a pH of 6.3, a temperature of 20 °C, and an anaerobic selector hydraulic retention time (HRT) of 50 minutes, controlled nocardioforms to below detectable levels whereas nocardioforms were present in a completely mixed control. The full‐scale, anaerobic‐selector, activated‐sludge system performing EBPR at a 3.5‐day average MCRT, average temperature of 20 °C, and anaerobic selector HRT of 17 to 24 minutes reduced nocardioform organism levels below those achieved when the full‐scale plant was operated at conditions that did not permit EBPR (i.e., MCRT of 1.7 days and anaerobic selector HRT of less than 19 minutes). In the full‐scale plant, the lowest nocardioform organism levels and effluent dissolved orthophosphate concentrations were associated with the highest MCRT tested (4.6 days).

Treatment of a milkpowder/butter wastewater using the AAO activated sludge configuration

A laboratory-scale nutrient removal activated sludge system, based on the AAO configuration, was used to treat a synthetic wastewater from a milkpowder/butter factory. In this system, substrate is fed to anaerobic and anoxic selectors in series with an aerobic reactor. Sludge is returned to the anaerobic selector, and mixed liquor from the aerobic reactor is recycled to the anoxic selector. The overall system is operated at an HRT of 7 days and a nominal sludge age of 20 days. This system was prone to prolonged bulking periods, with filamentous bacteria Sphaerotilus natans, Type 0411 and Haliscomenobacter hydrossis being identified in the mixed liquors, although effective clarifier operation prevented loss of suspended solids. Theory suggests that selectors may be used to circumvent low F:M bulking, and to bring about enhanced biological nutrient removal. An investigation of the initial design revealed that relatively high nitrite levels were present in the system, and a larger anoxic selector with an HRT of 820 minutes was substituted for the original one with an HRT of 48 minutes. This resulted in a decrease in nitrite and a equivalent increase in nitrate in the system. Overall nitrogen removal remained unchanged at 66%, and SVI levels did not improve. On resetting the anoxic selector to its original size, the effect was not reversed. Phosphorus removal efficiency was detrimentally affected by the anoxic sizing experiment (49% to 20%), and this may be linked to the raised level of nitrate in the system. COD removal efficiency remained excellent throughout the trial at over 90% removal.

Treatment of a milkpowder/butter wastewater using the AAO activated sludge configuration

A laboratory-scale nutrient removal activated sludge system, based on the AAO configuration, was used to treat a synthetic wastewater from a milkpowder/butter factory. In this system, substrate is fed to anaerobic and anoxic selectors in series with an aerobic reactor. Sludge is returned to the anaerobic selector, and mixed liquor from the aerobic reactor is recycled to the anoxic selector. The overall system is operated at an HRT of 7 days and a nominal sludge age of 20 days. This system was prone to prolonged bulking periods, with filamentous bacteria Sphaerotilus natans, Type 0411 and Haliscomenobacter hydrossis being identified in the mixed liquors, although effective clarifier operation prevented loss of suspended solids. Theory suggests that selectors may be used to circumvent low F:M bulking, and to bring about enhanced biological nutrient removal. An investigation of the initial design revealed that relatively high nitrite levels were present in the system, and a larger anoxic selector with an HRT of 820 minutes was substituted for the original one with an HRT of 48 minutes. This resulted in a decrease in nitrite and a equivalent increase in nitrate in the system. Overall nitrogen removal remained unchanged at 66%, and SVI levels did not improve. On resetting the anoxic selector to its original size, the effect was not reversed. Phosphorus removal efficiency was detrimentally affected by the anoxic sizing experiment (49% to 20%), and this may be linked to the raised level of nitrate in the system. COD removal efficiency remained excellent throughout the trial at over 90% removal.

Effects of an anaerobic zone in a textile wastewater treatment plant

High concentration of textile industries represents a serious environmental problem in the Como area in Northern Italy. The Seveso treatment plant was formerly performing biological removal of nitrogen by means of a modified Ludzack-Ettinger configuration. Being the plant overloaded, nitrification was not achieved. Therefore the plant flow sheet has been modified. The former predenitrification tank has been changed in an anaerobic compartment, since the internal recycle was stopped. The efficiency of the anaerobic reactor for COD removal, the selective pressure on the microbial community and the enhanced biological phosphorus removal were evaluated. In the anaerobic tank 40% of the influent COD was removed with a reaction time of only 45 minutes. The activated sludge showed a very high presence of Poly-P bacteria; anaerobic P release was noticed during the anaerobic phase. Sludge settleability was always good (contrary to a similar activated sludge treatment plant, also treating textile wastewater but without an anaerobic selector, that suffers heavy filamentous bulking and Nocardia foaming). The final effluent PO4-P concentration was always lower than 1 mg L−1.

Effects of an anaerobic zone in a textile wastewater treatment plant

High concentration of textile industries represents a serious environmental problem in the Como area in Northern Italy. The Seveso treatment plant was formerly performing biological removal of nitrogen by means of a modified Ludzack-Ettinger configuration. Being the plant overloaded, nitrification was not achieved. Therefore the plant flow sheet has been modified. The former predenitrification tank has been changed in an anaerobic compartment, since the internal recycle was stopped.The efficiency of the anaerobic reactor for COD removal, the selective pressure on the microbial community and the enhanced biological phosphorus removal were evaluated.In the anaerobic tank 40% of the influent COD was removed with a reaction time of only 45 minutes. The activated sludge showed a very high presence of Poly-P bacteria; anaerobic P release was noticed during the anaerobic phase. Sludge settleability was always good (contrary to a similar activated sludge treatment plant, also treating textile wastewater but without an anaerobic selector, that suffers heavy filamentous bulking and Nocardia foaming). The final effluent PO4-P concentration was always lower than 1 mg L−1.

Boston Harbor Clean-Up: Comparison of Conventional Oxygen Activated Sludge with and without Anaerobic Selectors

To determine secondary treatment design parameters for the Massachusetts Water Resources Authority Deer Island Treatment Facility, a pilot study was conducted. Due to the constricted site, oxygen activated sludge processes were considered. A pilot-scale conventional oxygen activated sludge (COAS) and COAS preceded by an anaerobic selector process (ASP) were compared. Both processes achieved comparable levels of total and soluble BOD, total and soluble COD, total nitrogen, ammonia nitrogen, and phosphorus removal. Higher percent removals occurred during the spring and summer flow periods. Neither process appeared more stable than the other with respect to changing influent loading and hydraulic stress. Differences in the process were the sludge settleability and sludge yield. The ASP had a slightly higher sludge yield than COAS, but the solids settled faster.

The Influence of Operating Experience on Wastewater Treatment Plant Design in San Francisco, California, USA

Three main areas will be covered regarding the design and operation of a pure oxygen activated sludge plant. Air entrainment occurred in RAS and influent lines and gas entrainment occurred at the sixth stage effluent weirs in an enclosed pure oxygen aeration basin. This caused the oxygen feed to be shut off due to overpressurization and resulted in a combination of high apparent O2 usage and high vent gas purities. The use of an anaerobic selector for Nocardia control is discussed. Anaerobic digester operation has been adversely affected by Nocardia-dominated waste activated sludge. The effect of thick anaerobic digester foams on the ability to pump digested sludge is discussed.

Upgrading Wastewater Treatment Plants with Anaerobic Selectors

The anaerobic selector of the A/0™ process offers many advantages over conventional activated sludge processes with respect to process performance and operational stability. This high-rate, single-sludge process has been successfully demonstrated in full-scale operations for biological phosphorus removal and total nitrogen control in addition to BOD and TSS removal. This process can be easily utilized in upgrading existing treatment plants to meet stringent discharge limitations and to provide capacity expansion. Upgrades of two full-scale installations are described and performance data from the two facilities are presented.